JPH03200929A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain good display characteristics without allowing moire fringes to be confirmed by providing a linear Fresnel prism plate which forms the patterns of an incident surface and a reflecting surface at a pitch of 2+ or -0.4 times picture element pitch. CONSTITUTION:The conditions under which the moire fringes are not confirmed merely necessitate the increasing of the number of the moire fringes per unit length. The formation of the linear Fresnel prism plate to the pitch PPR finer than PLCD is difficult and the PPR is so determined that the min. value of the number of the moire fringes is largest while PPR>PLCD is attained. Namely, PPR 2PLCD is the conditions of the PPR under which the degradation in image quality by the moire fringes is little. The number of the moire fringes is increased if the PPR is set at (2+ or -0.4)XPLCD. The moire fringes are hardly confirmed in this way and the good display characteristics are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device whose backlight is an edge-light illumination device using a linear Fresnel prism plate.

[Conventional technology]

A liquid crystal display device is a passive display device that does not emit light by itself, and by controlling the transmittance or reflectance of light, it modulates the illumination light such as natural light or the illumination light of the internal backlight, and displays patterns. This is what we do. In particular, in the case of color liquid crystal display devices that use color filters, the amount of light decreases, so it is essential to install a backlight. The method is valid.

FIG. 4 is a side view of a liquid crystal display device using a conventional edge-light backlight disclosed in, for example, Japanese Unexamined Patent Publication No. 61-158367. It is a linear Fresnel prism plate having a pitch pattern, 2a is an entrance surface, 2b is a reflection surface, and 2C is an exit surface. 5 is a tubular light source, and 6 is a plane mirror.

In the above configuration, the light from the tubular light source 5 enters the incident surface 2a of the prism plate 2 either directly or after being reflected by the plane mirror 6, is reflected by the reflective surface 2b, and is emitted substantially perpendicularly from the output surface 2C. In a conventional liquid crystal display device in which this light is recorded on a liquid crystal display, the linear Fresnel prism plate 2 is
A and reflective surfaces 2b are formed in large numbers at a constant pitch,
When viewed from the exit surface 2C, it is recognized as a pattern with a constant pitch as shown in FIG. 5(a). On the other hand, the liquid crystal panel 1 also has a pixel arrangement or pattern with a constant pitch, as shown in FIG. 5(b) 1ζ. Therefore, when the liquid crystal panel 1 is disposed on the output surface 2c of the display 1, brightness and darkness, that is, moiré fringes, appear in the display due to the two patterns alone or due to their interaction, resulting in deterioration of the image quality.

Here, liquid crystal panel 1. If the pixel pitch of is Ptco, and the pattern pitch of the linear Fresnel prism plate 2 is PPR, then the number of lines per unit length of the moiré fringe is expressed by the following formula % () (m * n = Oe ± 1, where m = n = Exclude o.

) At this time, if the values of P t, co and PPR are close, voice = l
1/PLCD-1/Pptt I (DMo 1'!
:su'), %7 The stripes become so rough that the moiré stripes become clearly visible even when viewed from a distance, resulting in a fatal defect in the display. As a countermeasure to this problem, an attempt was made to make the pattern less noticeable by subjecting the linear Fresnel prism plate 2 to a diffusion process, but it was not possible to completely eliminate the moire fringes.

This invention was made to solve the above problems, and has good display characteristics without moire fringes caused by this interaction between the pattern of the liquid crystal panel and the pattern of the linear Fresnel prism plate. The purpose is to improve liquid crystal display devices.

[Means to solve the problem]

The liquid crystal display device according to the present invention includes a liquid crystal panel in which adjacent pixels or pixels representing the same color are formed at a constant pitch, and the liquid crystal panel is arranged opposite to the back surface of the liquid crystal panel, and is arranged opposite to the liquid crystal panel. The above pixel pitch is 2±0.
A linear Fresnel prism plate having a pattern of an incident surface and a reflective surface formed at a pitch of 4 times, and a light emitting surface, the light emitting surface being arranged opposite to the pattern forming surface side of the linear Fresnel prism plate. It is provided with a light guide plate and a tubular light source arranged on the end face of the light guide plate.

Further, a light diffusing plate is provided on the back surface of the liquid crystal panel, and a linear Fresnel prism plate is arranged at a distance of 0.5 to 5 fi from the light diffusing plate.

[For production]

By setting the pattern pitch of the linear Fresnel prism plate in this invention to 2±0.4 times the pixel pitch of the liquid crystal spring Iv, the number of moire fringes becomes large 72, the pitch becomes fine, and the moire fringes become less noticeable. Also, by separating the light diffusing plate from the linear Fresnel prism plate by 0.5 to 5 fl, the pattern of the prism plate is flattened,
Similarly, moiré stripes disappear.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIGS. 1(a) and 1(b) show a side view and a perspective view of a liquid crystal display device using an edge-light type backlight.

In the figure, 1 is a liquid crystal panel made of Pt or Co, and 3 is a light diffusion plate made of acrylic resin that diffuses light, which is pasted or closely attached to the back surface of the liquid crystal panel 1.

If the light diffusing degree of the light diffusing plate 3 is too high, the backlight brightness will decrease, and if it is too low, the moire fringes will not be completely erased, both of which will lead to a deterioration of the image quality of the liquid crystal display device. Therefore, a front transmittance of about 80% is optimal. 7 is the distance fi from the light diffusing plate 3
d # S1. The distance d is set within the range of 0.5 to 5 fi. The linear Fresnel prism plate 7 is made of, for example, acrylic resin without being subjected to light diffusion treatment, and has an output surface 7C formed directly on the light diffusion plate 3 side, and an input/reflection surface 7a on the opposite surface.

A pattern consisting of pixels is formed at a constant pitch PPR, and the pin f PPR is the pixel pitch y-PLCD of the liquid crystal panel l.
(2±O-4) Ptco tζ is set for. Reference numeral 4 denotes a light guide plate made of acrylic resin and having a light emitting surface 4a formed on one surface, and is arranged so that the light emitting surface 4a overlaps the pattern forming side of the linear Fresnel prism plate 7.

5a and 5b are tubular light sources disposed facing the end surfaces 4b and 4C of the light guide plate 4.

In the above configuration tζ, the light from the tubular light sources 5ae and 5b enters the light guide plate 4 from the ends ([4b, 4c), is condensed, and exits from the light exit surface 4a. After entering the incident reflection surface 7a of the reprism plate 7, it is reflected by the incident reflection surface 7b, and on the other hand, the incident reflection surface 7b
After entering the beam, it is reflected by the incident reflection surface 7a, and is emitted from the output surface 7c in a substantially perpendicular direction 11. This light is diffused by a light diffusing plate 3,
The pattern is displayed by modulating it on the liquid crystal panel l.

Here, considering the conditions under which moire fringes are not recognized, it is necessary to increase the value of the number μ of moire fringes per unit length, that is, to make the pitch of the moire fringes finer, so that they are difficult to recognize, or to change the pattern of the near Fresne I reprism plate 7. It can be seen that it is better to flatten the .

From the former condition, consider the conditions for the pattern pin fPPR of the linear Fresnel prism plate 7. However, since the pixel pitches Pt and co of the liquid crystal spring IL/1 are usually already determined, they are considered to be fixed values. The PPR of the linear Fresnel prism plate 7 is Pt, c due to precision issues during manufacturing.

It is difficult to achieve the following fine pitch, and PPR>P
It becomes an LCD. On the other hand, the number of moiré fringes can be determined from the equation (1), and the PPR may be determined so that the minimum value μml of the voice is the thickest. In formula (1), m.

Substituting -1, 0, 1 for n gives μml. is l/Ptc
o -1/PPR or 1/PPR. The former is μml.

This occurs when PPR≦2 PLCD, and the latter becomes μml when PPR≧2 PLCD, so the glaze ultimately becomes the maximum value 1/2 PLCD when PPR=2 Pi and CD. That is, PPRe” 2 PLC
D is a PPR condition in which there is little deterioration in image quality due to moiré fringes. In this example, PPR is (2±0.4')
Since Pt and co are used, the conditions of PpRv42P LCD are satisfied, and the number of moire fringes can be made louder. For this reason, the pitch of the moire fringes becomes finer,
Difficulty recognizing light and darkness.

Next, fζ when the light diffusing plate 3 is installed apart from the linear Fresnel prism plate 7 will be explained.

Since the linear Fresnel prism plate 7 has a pattern, the light wind incident on the light diffusing plate 3 has a pattern pitch PP.
A distribution equal to R results.

Here, the flatness r of the forward distribution is defined as shown in the following equation.

In this formula (2), 1 mtlIL and -ml. are the maximum and minimum values of light wind, respectively. FIG. 3 shows the relationship between the distance d from the exit surface 7C of the linear Fresnel prism plate 7 and the degree of flatness γ. In the figure, d is 0.5wI
If it is II or more, T will be 955% or more, so if the light diffusing plate 3 is placed at this position, the light transmission distribution can be more effectively flattened. Even without special measures, it becomes difficult to recognize brightness and darkness.

Note that if the light diffusing plate 3 is separated by 5 mm or more, the display brightness will decrease because the light and air can be used effectively, and the feature of thinness will be lost due to the increase in the number of military personnel in the display system. This will result in something unsatisfactory.

In addition, in the above-mentioned Example 1ζ, in the case of a liquid crystal display device for an OA terminal in which the pixel pitch Ptco is 1300 μm, the pattern pitch Ppta of the prism plate 7 is set to 50 μm.
It was appropriate to set it to 0±50 μm. Also, Figure 2 (a
) to (e) show examples of each pixel arrangement of a liquid crystal panel 1 in the case of a color liquid crystal display device, where R indicates a red pixel, G indicates a green pixel, and B indicates a blue pixel. In the above example #J
While the prime pitch PLCD is the pitch between adjacent pixels, in these examples, the pitch between pixels representing the same color, such as the green pixel G, is taken as the pitch ';'f'tco'; It is not necessary to set the pitch between the pixels Pt and co, and the same effect can be obtained by setting the pattern pitch PPR of the prism plate 7 so as to satisfy the certain conditions as described above.

Further, in the above embodiment, the pattern of the prism plate 7 is vertical, but it may be horizontal. In this case, the above-mentioned conditions must be satisfied for the vertical pixel pitch of the Hlis spring IL/l. In short, it is sufficient to satisfy the condition that the pixel pitch of the liquid crystal panel 1 in the direction matching the pattern pitch direction of the prism plate 7 is one foot between this.

〔Effect of the invention〕

As described above, according to the present invention, the pattern pitch of the linear Frenet prism plate is set with respect to one white pixel pitch of the liquid crystal panel so that the number of moire fringes generated per unit length is increased. This has the effect that stripes become difficult to recognize and a liquid crystal display device with good display characteristics can be obtained. Further, the light diffusing plate was placed a predetermined distance in front of the linear Fresnel prism plate. Therefore, it is possible to make moire fringes difficult to see without applying special measures such as diffusion treatment to the cough prism plate, and furthermore, to provide a liquid crystal display device having even better display characteristics by combining these features. I can do it.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are a side view and a perspective view of a liquid crystal display device according to the present invention 1ζ, and FIGS. 2(a) to (e) are respective views of a color liquid crystal panel according to another embodiment 1ζ of the present invention. A schematic diagram showing an example of a pixel arrangement, Fig. 3 is a characteristic diagram showing the relationship between the light intensity on the light diffusing plate and the distance from the output surface of the linear Frene I Sibrism plate, and Fig. 4 is a side view of a conventional liquid crystal display device. Figures 5(a) and 5(b) are a pattern diagram of a linear Frenet fres prism board and a pixel pattern diagram of a liquid crystal panel in a conventional liquid crystal display. 1...Liquid crystal panel, 3...Light diffusion plate, 4...Light guide plate. 4a...Light exit surface, +b* 4c...End surface, sa,
sb...Tubular light source, 7...Linear Fresnet r prism plate, ? a m 7 b...Incoming reflection surface, 7C...
Out! ) Page 1. In addition, in the figure, the same symbol indicates the same or equivalent part. Figure 1

Claims (3)

[Claims] (1) A liquid crystal panel in which adjacent pixels or pixels representing the same color are formed at a constant pitch, and the pixels are arranged opposite to each other on the back surface of this liquid crystal panel, and the pixels are arranged on the opposite side of the liquid crystal panel. A linear Fresnel prism plate has a pattern of an incident surface and a reflective surface formed at a pitch of 2±0.4 times the pitch, and a light exit surface, and this light exit surface is the pattern forming surface of the linear Fresnel prism board. 1. A liquid crystal display device comprising: a light guide plate disposed opposite to each other; and a tubular light source disposed on an end face of the light guide plate. (2) A liquid crystal panel in which adjacent pixels or pixels representing the same color are formed at a constant pitch, a light diffusion plate placed on the back side of this liquid crystal panel to perform light diffusion processing, and an incident surface. It has a reflective surface pattern, and has a reflection surface pattern of 0.5 from the light diffusing plate.
A linear Fresnel prism plate facing each other with a distance of ~5 mm, a light guide plate having a light exit surface, the light exit surface facing the pattern forming surface side of the linear Fresnel prism board, and an end face of the light guide plate. A liquid crystal display device comprising: a tubular light source disposed in a tubular light source; (3) a liquid crystal panel in which adjacent pixels or pixels representing the same color are formed at a constant pitch, and a light diffusion plate disposed opposite to the back surface of the liquid crystal panel to perform light diffusion processing; The pixel pitch is 2± of the pixel pitch on the opposite side of the light diffusing plate, and is arranged facing away from the light diffusing plate at a distance of 0.5 to 5 mm.
A linear Fresnel prism plate having a pattern of an incident surface and a reflective surface formed at a pitch of 0.4 times, and a light exit surface, and this light exit surface is arranged opposite to the pattern forming surface side of the linear Fresnel prism board. What is claimed is: 1. A liquid crystal display device comprising: a light guide plate having a cylindrical shape, and a tubular light source disposed on an end surface of the light guide plate.