JPH0836179A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To widen a display visual field angle in a direction that the wide visual field angle is required and to obtain a bright display screen by specifying the condensing property of a prism sheet constituted so that the groove direction of a fine prism is orthogonally crossed to the direction that the wide visual field angle is required. CONSTITUTION:This device is constituted of a back light 5 arranged under a liquid crystal display element, a cold cathode fluorescent lamp 36, a diffusion plate 39 and the first prism sheet 2 and the second prism sheet 3 arranged between the diffusion plate 39 of the light 5 and the liquid crystal display element. When two prism sheets 2 and 3 are used by being orthogonally crossed so that the groove direction of one sheet is aligned in the upper and lower direction and the groove direction of the other sheet is aligned in the left and right directions with respect to the display screen, the prism sheet whose condensing property is low is used as the prism sheet condensing light in the direction that the wide visual field angle is required and the prism sheet whose condensing property is high is used as the prism sheet condensing the light in the direction that the wide visual field angel is not required. Thus, the visual field angle is widened and high luminance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having improved display quality, and more particularly to a technique effective when applied to a backlight of a liquid crystal display device.

[0002]

2. Description of the Related Art In a conventional liquid crystal display device, a backlight is used to irradiate a liquid crystal display element with light.

As a backlight used in a conventional liquid crystal display device, a type in which cold cathode fluorescent lamps are arranged in proximity along a side surface of a light guide body made of a transparent synthetic resin plate for guiding light There are two known types, in which a plurality of cold cathode fluorescent lamps are arranged in parallel directly below a liquid crystal display element.

In the former type, the light is diffused between the light guide and the liquid crystal display element, and in the latter type, the light is diffused between a plurality of cold cathode fluorescent lamps and the liquid crystal display element to be uniform on the liquid crystal display element. A diffusing plate is arranged for irradiating light on.

FIG. 4 is an exploded perspective view of a backlight of a conventional liquid crystal display device, and FIG. 5 is a cross section of the liquid crystal display element and the backlight shown in FIG. 4 taken along the line AA ′. It is a figure.

The backlight shown in FIG. 4 is of a type in which cold cathode fluorescent lamps are arranged close to each other along the side surface of a light guide body made of a transparent synthetic resin plate for guiding light.

In FIGS. 4 and 5, reference numeral 62 is a liquid crystal display element, 5 is a backlight arranged under the liquid crystal display element 62, 36 is a cold cathode fluorescent lamp, 37 is a light guide, 39 is a diffusion plate, and 38. Is a reflector, 42 is a cold cathode fluorescent lamp 36, and a light guide 3
7, a frame-shaped body that holds the diffusion plate 39 and the reflection plate 38 and is formed by molding, and 2 and 3 are first prism sheets arranged between the diffusion plate 39 of the backlight 5 and the liquid crystal display element 62. And the second prism sheet.

Here, the reflecting plate 38, the light guide plate 37, the diffusing plate 39, the first prism sheet 2 and the second prism sheet 3 do not have a gap between them, that is,
They are in direct contact with each other and are held in the recesses provided in the frame-shaped body 42.

FIG. 6 is a diagram showing an arrangement relationship between the first prism sheet 2 and the second prism sheet 3 in FIGS. 4 and 5, and FIG. 7 is a first diagram in FIGS.
9 is a perspective view showing the prism sheet 2 and the second prism sheet 3, and FIG. 8 is a sectional view thereof.

As shown in FIG. 8, the first prism sheet 2 and the second prism sheet 3 have a fine prism surface on the upper surface and a smooth surface on the lower surface. It is configured.

Further, as shown in FIG. 7, a large number of V-shaped grooves are formed in parallel on the fine prism surfaces of the first prism sheet 2 and the second prism sheet 3, respectively. .

Further, as shown in FIG. 6, the first prism sheet 2 and the second prism sheet 3 are arranged so that the groove directions of the fine prism surfaces are orthogonal to each other, and the grooves of the fine prism surfaces are arranged. The pitch P3 and the apex angle θ3 are made equal.

As described above, in the backlight 5 of the conventional liquid crystal display device, between the liquid crystal display element 62 and the diffusion plate 39, the groove pitch P3 of the fine prism surface and the apex angle θ3 are equal to each other. The prism sheet 2 and the second prism sheet 3 are arranged so that the brightness is increased and a bright liquid crystal display screen is obtained.

[0014]

However, in the backlight 5 shown in FIGS. 4 and 5, if prism sheets having a high light converging property are used as the first prism sheet 2 and the second prism sheet 3, Although high brightness is obtained, the viewing angle is narrowed, and the first prism sheet 2
When a prism sheet having a low light collecting property is used as the second prism sheet 3, the viewing angle becomes wide, but the luminance becomes low.

That is, there is a problem that high brightness and wide viewing angle cannot be achieved at the same time.

Further, due to the interference between the first prism sheet 2 and the second prism sheet 3 and the dots of the liquid crystal display element 62, moire fringes are generated, and through the liquid crystal display element 62, as shown in FIG. Moire stripes on the screen 10
There was a problem that you could see.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a liquid crystal display device having a wide viewing angle with respect to a predetermined direction.
In addition, it is to provide a technique capable of obtaining a bright display screen.

Another object of the present invention is to provide a technique capable of obtaining a uniform display screen in a liquid crystal display device without causing moire fringes due to the interference between the prism sheet and the liquid crystal display element.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0020]

Of the inventions disclosed in the present application, a representative one will be briefly described below.
It is as follows.

(1) A liquid crystal display element and a backlight for illuminating the liquid crystal display element are provided, and the backlight is disposed between the diffusion plate and the diffusion plate and the liquid crystal display element. In a liquid crystal display device having at least two prism sheets each having an upper surface made up of a large number of fine prisms, a group of prism sheets in which a groove direction of the fine prisms is orthogonal to a direction in which a wide viewing angle is required. It is characterized in that the light property is lower than that of other prism sheets.

(2) A liquid crystal display element having different dot pitches in the vertical direction and the horizontal direction, and a backlight for illuminating the liquid crystal display element are provided, and the backlight is a diffusion plate and the diffusion plate. And a liquid crystal display element, the upper surface of which is composed of many fine prisms 2
In a liquid crystal display device having at least one prism sheet, the groove pitch of the fine prisms of the prism sheet, which is arranged on the side closer to the liquid crystal display element,
The dot pitch is smaller than the dot pitch of the liquid crystal display element, which coincides with the groove pitch direction of the prism sheet.

(3) A liquid crystal display element having different dot pitches in the vertical direction and the horizontal direction, and a backlight for illuminating the liquid crystal display element are provided, and the backlight is a diffusion plate and the diffusion plate. And a liquid crystal display element, the upper surface of which is composed of many fine prisms 2
In a liquid crystal display device having at least one prism sheet, the groove pitch of the fine prisms of the prism sheet, which is arranged on the side closer to the liquid crystal display element,
It is characterized in that an integer multiple of the groove pitch and the dot pitch of the liquid crystal display element do not match.

[0024]

According to the means of the above item 1, in the backlight of the liquid crystal display device, in the two prism sheets arranged between the diffusion plate and the liquid crystal display element, the groove direction of the fine prism is The prism sheet's light-collecting property, which is orthogonal to the direction that requires a wide viewing angle, is different from other prism sheets by making the prism sheet material, fine prism groove pitch, or apex angle different from other prism sheets. Since it is made lower than the light-condensing property of the prism sheet, it is possible to widen the display viewing angle in the direction where a wide viewing angle is required and obtain a bright display screen.

According to the means of the above item 2, in the backlight of the liquid crystal display device, among the two prism sheets arranged between the diffusion plate and the liquid crystal display element, the prism sheet on the side closer to the liquid crystal display element is provided. Since the groove pitch of the fine prisms of the prism sheet to be arranged is made smaller than the dot pitch of the liquid crystal display element that coincides with the groove pitch direction of the prism sheet, the prism sheet and the liquid crystal display element are arranged. It is possible to obtain a uniform display screen free from moire fringes due to the interference with.

According to the means of the above item 3, in the backlight of the liquid crystal display device, the two prism sheets arranged between the diffusion plate and the liquid crystal display element are arranged on the side closer to the liquid crystal display element. Since the groove pitch of the fine prisms of the prism sheet is set such that an integer multiple of the groove pitch does not match the dot pitch of the liquid crystal display element, moire fringes due to interference between the prism sheet and the liquid crystal display element. It is possible to obtain a uniform display screen without

[0027]

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

In all the drawings for explaining the embodiments, parts having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted.

FIG. 1 is an exploded perspective view of a backlight of a liquid crystal display device which is an embodiment of the present invention.

In FIG. 1, 5 is a backlight arranged under the liquid crystal display element, 36 is a cold cathode fluorescent lamp, 39 is a diffusion plate, and 2 and 3 are a diffusion plate 39 of the backlight 5 and the liquid crystal display element. A first prism sheet and a second prism sheet arranged between them. Since the structure of the backlight shown in FIG. 1 is the same as that of the backlight shown in FIG. 5, the detailed description thereof will be omitted.

FIG. 2 is a sectional view of the first prism sheet 2 and the second prism sheet 3 in the backlight 5 of the liquid crystal display device which is an embodiment of the present invention.

The lower surfaces of the first prism sheet 2 and the second prism sheet 3 are smooth surfaces (2b, 3b), and a large number of V-shaped grooves (2c, 3c) are formed on the upper surface thereof. Each of them is arranged in parallel and has a fine prism surface (2
a, 3a) is formed.

The prism surfaces (2a, 3a) mainly direct the light emitted from the diffusion plate 39 to the prism surfaces (2a, 3a).
Focus in the direction perpendicular to the V-shaped groove (2c, 3c) of
The light is emitted toward the upper surface of the prism surface (2a, 3a).

Therefore, the viewing angle in the V-shaped groove (2c, 3c) direction of the prism surface (2a, 3a) is widened, and the viewing angle in the direction perpendicular to the V-shaped groove (2c, 3c) is narrowed. It has a property.

Further, the light-collecting ability of the prism sheet (2, 3) depends mainly on the apex angles (θ1, θ2) of the prism surface (2a, 3a) and the material of the prism sheet (2, 3). It is determined.

Therefore, in the case of prism sheets (2, 3) made of the same material, the ability to collect light in the upper surface direction of the prism surfaces (2a, 3a) differs depending on the sizes of the apex angles θ1 and θ2. .

If the light-collecting ability is strong, the viewing angle in the direction perpendicular to the V-shaped grooves (2c, 3c) of the prism surfaces (2a, 3a) is narrowed, but the brightness is increased and the light is collected. If the light power is weak, the viewing angle in the direction orthogonal to the V-shaped grooves (2c, 3c) of the prism surface (2a, 3a) becomes wide, but the brightness becomes low.

Therefore, when two prism sheets having a strong light-collecting ability are orthogonally arranged and overlapped with each other, the luminance is greatly improved, but the viewing angle becomes extremely narrow.

However, as described above, by changing the light collecting ability of the prism sheets (2, 3),
Since it is possible to change the viewing angle and brightness, the two prism sheets (2, 3) are orthogonal to each other, one in the vertical direction with respect to the display screen and the other in the horizontal direction with the groove direction aligned. When used as a prism sheet, a prism sheet with a low light-collecting property is used as a prism sheet that collects light in a direction that requires a wide viewing angle, and a prism sheet that collects light in a direction that may have a narrow viewing angle. By using the prism sheet having high light property, the viewing angle can be widened and high brightness can be obtained.

Therefore, in this embodiment, for example, a polycarbonate film having a thickness of 0.23 mm is used, and the apex angle θ1 is 90 degrees and the apex angle θ2 is 100 degrees.
Using the first prism sheet 2 and the second prism sheet 3, the light diffused from the diffuser plate 39 at a large angle is strongly condensed in the vertical direction of the display screen by the prism surface 2a of the first prism sheet 2. Then, the second prism sheet 3
The prism surface 3a of (1) is designed to weakly collect light in the horizontal direction of the display screen.

As a result, in this embodiment, it is possible to improve the brightness of the entire backlight 5 and keep the viewing angle in the left-right direction wide.

The apex angles θ1 and θ2 do not necessarily have to be 90 degrees and 100 degrees, and values in the vicinity thereof, for example, 80 degrees ≦ θ1 ≦ 100 degrees, 90 degrees ≦ θ.
If the value is 2 ≦ 110 degrees, the brightness of the entire backlight 5 can be improved and the horizontal viewing angle can be kept wide.

FIG. 3 is a diagram showing the relationship between the color filter of the liquid crystal display element 62 and two prism sheets whose groove directions are orthogonal to each other and overlap each other.

The two prism sheets (2, 3) have straight V-shaped grooves (2) in the directions indicated by 2d and 3d in FIG.
c, 3c) are engraved.

When the line of the V-shaped groove (2c, 3c) and the matrix line of the color filter 40 of the liquid crystal display element 62 are deviated by a slight angle, the moire fringes 10 are generated as shown in FIG.

However, the pitch of the moire stripes 10 is
If the pitch is so fine that human eyes cannot recognize it, even if moire fringes 10 occur, they will not be visible to human eyes.

The pitch of the moire fringes 10 is determined by the groove pitch of the V-shaped grooves (2c, 3c) of the prism sheet (2, 3) V.

As shown in FIG. 2, the prism sheet (2,
V-shaped grooves (2c, 3c) are carved in 3),
The finer the groove pitch (P1, P2), the more moire stripes 1
The 0 pitch also becomes finer.

Further, in general, the dot pitch of the color filter 40 is long in the vertical direction of the screen and short in the horizontal direction.

Therefore, in a backlight of a liquid crystal display device, when two prism sheets are used so that one prism sheet is vertically aligned with the display screen and the other is horizontally aligned with the groove direction, the The V-shaped groove pitch of the prism sheet arranged close to the filter 40 needs to be sufficiently fine with respect to the dot pitch of the color filter 40 that matches the direction of the V-shaped groove of the prism sheet. is there.

Therefore, in the present embodiment, the groove pitch P2 of the V-shaped grooves 3c of the prism sheet 3 is set to be sufficiently smaller than the dot pitch of the color filter 40 in the left-right direction.

In this case, as a sufficiently fine pitch, the dot pitch in the horizontal direction of the color filter 40 is P
When it is set to 5, it is necessary that P2 ≦ P5 / 2.

When the prism sheet 2 is arranged close to the color filter 40, the prism sheet 2
It is necessary to make the groove pitch P1 of the straight V-shaped grooves 2c that is sufficiently smaller than the dot pitch in the vertical direction of the color filter 40.

In this case, as the sufficiently fine pitch, the dot pitch P4 in the vertical direction of the color filter 40 is used.
Then, P1 ≦ P4 / 2 needs to be satisfied.

Further, as a method of preventing the moire fringes 10, the dot pitch in the horizontal or vertical direction of the color filter 40 and the groove pitch (P1) of the V-shaped grooves (2c, 3c) of the prism sheet (2, 3). , P2) pitch is
There is a method to prevent the relationship of integral multiples.

In general, moire fringes appear when the lattice spacings of two lattices which are tilted by a small angle and overlap each other are equal, or when an integral multiple of the lattice spacing of one is equal to the lattice spacing of another.

In the backlight 5, the color filter 40
When the prism sheet (2, 3) is arranged substantially parallel to the dots in the left-right direction or the up-down direction, the groove pitch (P1, P2) of the prism sheet (2, 3) with a slight angle deviation is
Moire fringes 10 appear when the above conditions are satisfied.

Therefore, for example, when the dot pitch of the color filter is 300 μm, and when the groove pitch (P1, P2) of the prism sheet (2, 3) is 31 μm,
Moire fringe 10 does not occur.

The results of measuring and comparing the brightness of the backlight 5 of the liquid crystal display device of this embodiment and the backlight 5 of the conventional liquid crystal display device will be described below.

First, in the backlight 5 of the present embodiment, which includes the cold cathode fluorescent lamp 36, the light guide 37, the diffusion plate 39, the first prism sheet 2, the second prism sheet 3, and the reflection plate 38, The brightness was 1960 cd / m ² .

The first prism sheet 2 having a high light collecting property
The brightness was improved by 13% when one sheet and the groove directions were overlapped with each other, but the viewing angle was 26 degrees in the case of the backlight in the present embodiment, while the luminance was 2 degrees in the first prism sheet 2. In the case of one sheet, it was 21 degrees.

The difference between the two is only 5 degrees, but when the viewing angle is 21 degrees, it is so narrow that the screen can be seen only directly in front of the backlight, which is 5 minutes of the viewing angle of the backlight in this embodiment. It will be 4.

Further, when the backlight is viewed while moving from the front of the backlight to the right or left, the brightness decreases sharply when the number of the first prism sheets 2 is two. Since the backlight in the case of the embodiment is smoothly reduced, it seems wider than the actually measured viewing angle.

Regarding the moire fringes 10, when the short dot pitch of the color filter 40 is 100 μm and the long dot pitch is 300 μm, a prism sheet with a groove pitch of 50 μm and a groove direction of the color filter is used. Moire fringes 10 are generated when the liquid crystal display device is arranged adjacent to the liquid crystal display device so as to be parallel to the matrix, that is, the groove direction is the vertical direction or the horizontal direction with respect to the screen.

However, the groove pitch of the liquid crystal display device is 50 μm.
Moire fringes 10 could be eliminated by disposing a prism sheet having a groove pitch of 31 μm between them.

In this embodiment, various materials, thicknesses, configurations, etc. can be used for the diffusion plate 39, the first prism sheet 2 and the second prism sheet 3.

The cross-sectional shapes of the first prism sheet 2 and the second prism sheet 3 are not limited to those shown in FIG. 2, and for example, in the case where the peaks of the prism surfaces (2a, 3a) are sharp. No, it may be rounded,
Various angles and pitches of the V-shaped peaks and valleys of the V-shaped stripe groove can be used in consideration of the refractive index of the material.

The angles and pitches of the prism grooves may not be uniform over the entire prism sheet 2.

Further, the prism surfaces 2a and 3a are not limited to the stripe shape, but may be a cone shape, a pyramid shape or the like, and such prism sheets may be overlapped or combined with a stripe-shaped lens film.

Further, the second prism sheet 3 and the diffusion plate 3
9 may be integrated with each other. For example, the lower surface side may be integrally formed with a transparent resin material mixed with diffusing particles to form a diffusion layer and the upper surface side to form a prism surface.

The smooth surfaces 2b and 3b of the first prism sheet 2 and the second prism sheet 3 may be slightly concave or convex.

As the diffusion plate 39, various known diffusion plates can be used.

Further, in the present embodiment, the case where the present invention is applied to the backlight 5 of the type including the light guide 37 and the cold cathode fluorescent lamp 36 arranged close to each other along the side surface thereof has been described. , A plurality of cold cathode (or hot cathode) fluorescent lamps are arranged under the liquid crystal display element 62, a diffusion plate is arranged between these fluorescent lamps and the liquid crystal display element 62, and a reflector plate is provided under the fluorescent lamp. It goes without saying that the present invention can also be applied to a backlight in which is arranged.

Further, the liquid crystal display device may be a simple matrix type liquid crystal display device or an active matrix type liquid crystal display device.

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention. .

[0076]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) In the backlight of the liquid crystal display device, in the two prism sheets arranged between the diffusion plate and the liquid crystal display element, the groove direction of the fine prism is required to have a wide viewing angle. The prism sheet, which is orthogonal to the vertical direction, is made to have a light-collecting property lower than that of other prism sheets, so the display viewing angle in the direction where a wide viewing angle is required is widened and a bright display screen is displayed. Can be obtained.

(2) In the backlight of the liquid crystal display device, of the two prism sheets arranged between the diffusion plate and the liquid crystal display element, the prism sheet arranged on the side closer to the liquid crystal display element. Since the groove pitch of the fine prism is made smaller than the dot pitch of the liquid crystal display element, which coincides with the groove pitch direction of the prism sheet, the moire fringes due to the interference between the prism sheet and the liquid crystal display element It is possible to obtain a uniform display screen.

(3) In the backlight of the liquid crystal display device, of the two prism sheets arranged between the diffusion plate and the liquid crystal display element, the prism sheet arranged nearer the liquid crystal display element. Since the groove pitch of the fine prism is set so that the integral multiple of the groove pitch and the dot pitch of the liquid crystal display element do not match, a uniform display screen without moire fringes due to interference between the prism sheet and the liquid crystal display element It is possible to obtain

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a backlight of a liquid crystal display device that is an embodiment of the present invention.

FIG. 2 shows a first prism sheet and a second prism sheet in a backlight of a liquid crystal display device which is an embodiment of the present invention.
3 is a cross-sectional view of the prism sheet of FIG.

FIG. 3 is a diagram showing a relationship between a color filter of a liquid crystal display element and two prism sheets that overlap each other with their groove directions orthogonal to each other.

FIG. 4 is an exploded perspective view of a backlight of a conventional liquid crystal display device.

5 is a cross-sectional view of the liquid crystal display element and the backlight shown in FIG. 4 taken along the line AA ′.

FIG. 6 is a diagram showing a positional relationship between a first prism sheet 2 and a second prism sheet 3 in FIGS. 4 and 5;

7 is a perspective view of a first prism sheet 2 and a second prism sheet 3 in FIGS. 4 and 5. FIG.

FIG. 8 is a cross-sectional view of the first prism sheet 2 and the second prism sheet 3 in FIGS. 4 and 5.

FIG. 9 is a diagram showing moire fringes due to interference between the first prism sheet and the second prism sheet and the dots of the liquid crystal display element.

[Explanation of symbols]

2 ... 1st prism sheet, 3 ... 2nd prism sheet, 5 ... Backlight, 10 ... Moire fringes, 36 ... Cold cathode fluorescent lamp, 37 ... Light guide, 38 ... Reflector, 39 ... Diffuser,
40 ... Color filter, 42 ... Frame-shaped body, 62 ... Liquid crystal display element, P1, P2, P3 ... Fine prism surface groove pitch, θ1, θ2, θ3 ... Fine prism surface apex angle, 2
a, 3a ... Prism surface of prism sheet, 2b, 3b ...
Smooth surface of prism sheet, 2c, 3c ... V-shaped groove of prism sheet.

Claims (3)

[Claims] 1. A liquid crystal display device, and a backlight for illuminating the liquid crystal display device, wherein the backlight is disposed between the diffusion plate and the diffusion plate and the liquid crystal display device. , The upper surface consists of many fine prisms 2
In a liquid crystal display device having at least one prism sheet, the groove direction of the fine prism is orthogonal to the direction in which a wide viewing angle is required, and the converging property of another prism sheet is A liquid crystal display device characterized by being made lower. 2. A liquid crystal display device having different dot pitches in the up-down direction and the left-right direction, and a backlight for illuminating the liquid crystal display device, wherein the backlight includes a diffusion plate and the diffusion plate. A liquid crystal display device having at least two prism sheets each having an upper surface formed of a large number of fine prisms, the prism sheet being disposed between the liquid crystal display element and the liquid crystal display element. 2. The liquid crystal display device, wherein the groove pitch of the fine prism is smaller than the dot pitch of the liquid crystal display element, which coincides with the groove pitch direction of the prism sheet. 3. A liquid crystal display device having different dot pitches in the up-down direction and the left-right direction, and a backlight for illuminating the liquid crystal display device, wherein the backlight comprises a diffusion plate and the diffusion plate. A liquid crystal display device having at least two prism sheets each having an upper surface formed of a large number of fine prisms, the prism sheet being disposed between the liquid crystal display element and the liquid crystal display element. 2. The liquid crystal display device, wherein the groove pitch of the fine prism is set such that an integer multiple of the groove pitch does not match the dot pitch of the liquid crystal display element.