JP3277178B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism plate for efficiently emitting a light beam incident over a wide angle range within a certain angle range, and a liquid crystal display used for information display in an information processing apparatus such as a personal computer or a word processor. The present invention relates to an information display device such as a device.

[0002]

2. Description of the Related Art With the progress of the information-oriented society, portable information processing apparatuses such as personal computers and word processors are desired. The performance required for a portable information processing device is to be small and lightweight and to have low power consumption in order to enable long-time use with a small-capacity power supply. In particular, an information display unit in a portable information processing device determines a schematic shape of the device and constantly consumes power. Therefore, a thin and low power consumption one is desirable.
An example of such an information display device is disclosed in JP-A-4-67.
No. 016 discloses a backlight type liquid crystal display device. As shown in FIGS. 1 and 2 of JP-A-4-67016, light emitted from the light sources 23 and 24 and light reflected by the reflection plate 25 are scattered by the scattering plate 26 and the incident side is flat. At 28, the emission side passes through optical means 27 such as a prism plate on the prism surface 29 and enters the liquid crystal display element 12. In the embodiment of JP-A-4-67016, the optical means 26 such as a prism plate is formed of polycarbonate resin or the like, and the apex angle formed by the two surfaces of the prism on the prism surface 29 is, for example, 90 degrees (half apex angle). Is 45
Degree). Optical means 27 such as this prism plate
Is arranged on the scattering plate 26, the light emitted from the scattering plate 26 scattered over a wide angle range can be collected in the normal direction of the optical unit 27, and the luminance within the effective viewing angle range is improved. be able to.

[0003]

However, when a prism plate formed of a polycarbonate resin having a vertex angle of about 90 degrees (a half vertex angle of about 45 degrees) as shown in the above-described conventional example is used, There are the following problems. FIG. 6 is an enlarged cross-sectional view of a conventional prism plate, where 60 indicates a prism plate, and 61 indicates a light beam. The vertical angle 2θ formed by the prism surfaces 62 and 63 is 90 degrees (half-vertical angle θ = 45).
Degree), the refractive index n is 1.585, and the viewing angle characteristics of the light emitted from the prism plate 60 obtained by the ray tracing calculation are:
This is indicated by a solid line 70 in FIG. A broken line 71 indicates the angle dependence of the light intensity of the light beam 61 incident on the prism plate 60, and corresponds to a viewing angle characteristic when the prism plate 60 is not provided. As shown by the solid line 70 in FIG. 7, there is an effect of improving the luminance by a factor of 1.4 or more over the effective viewing angle range of −35 ° to 35 °, but the viewing angle is −80 ° to −60 ° and the viewing angle is 60 ° to 80 °. There is a problem that light is radiated in an invalid viewing angle range and power is wasted. Further, when viewed from this direction, there is a problem that the information display device appears to be unnecessarily shining. This is because, as shown in FIG. 6, the light beam 61 incident on the prism plate 60 is totally reflected on the prism surface 62 and exits from the prism surface 63.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, prevent the emission of light to an invalid viewing angle range, improve the intensity of light emitted within an effective viewing angle range, and provide portable information processing. An object of the present invention is to provide a thin and low power consumption information display device suitable for the device.

[0005]

In order to achieve the above object, according to a first aspect of the present invention, a prism plate having a large number of prism-like projection structures formed on one surface has two planes of the prism-like projection structure. The vertex angle 2θ is defined as 2θ> 2/3 * (π / 2 + 2 * arcsin (1 / n)) where n is the refractive index of the prism plate medium.

According to a second aspect of the present invention, in an information display apparatus having a light source, a scattering plate for scattering light from the light source, and a display plate to which the scattered light from the scattering plate is irradiated, one of the two displays is provided between the scattering plate and the display plate. A prism plate having a large number of prism-shaped protrusion structures formed on the surface thereof is disposed with the prism-shaped protrusion structures facing the scattering plate side, and the apex angle 2θ formed by the two planes of the prism-shaped protrusion structure is determined by the refraction of the prism plate medium. Assuming that the ratio is n, 2θ> 2/3 * (π / 2 + 2 * arcsin (1 / n)).

[0007]

First, the principle of the present invention will be described with reference to FIG. FIG. 4 is a ray tracing diagram of the prism plate.
Is that the vertex angle between the prism surface 42 and the prism surface 43 is 2θ
(Half apex angle is θ) and refractive index n is a prism plate, 41
Denotes a light ray having an incident angle α (the direction indicated by the arrow in the drawing is negative). The angle of refraction α ′ on the plane 44 (the direction indicated by the arrow in the drawing is negative) and the angle of incidence β on the prism surface 42 (the direction indicated by the arrow in the drawing is negative) are α ′ = arcsin (1 / N * sinα) β = α ′ + θ−π / 2. Light rays satisfying n * sin β <−1 are prism surfaces 42
, And is incident on the prism surface 43. Prism surface 4
The incident angle δ at 3 is δ = −β−2θ. If n * sin δ <−1 holds when α is −1, all rays incident on the prism surface 43 are totally reflected, emitted from the plane 44 side of the prism plate 40 and scattered by a scattering plate or the like, It becomes a light beam that enters the prism plate 40 again. Rewriting this inequality, δ <arcsin (−1 / n), and using the above relational expression, β> −2θ + arcsin (1 / n) θ >＞ * (π / 2 + arcsin (1 / n) − α '). Further, from α = −1, α ′ = − arcsin (1 /
n), 2θ> 2/3 * (π / 2 + 2 * arcsin (1 / n)) (1) Therefore, if a prism plate whose prism apex angle 2θ satisfies the expression (1) is used, it is possible to prevent the emission of light to an invalid viewing angle range which is a problem in the conventional example, and
Since the light emitted to the invalid viewing angle range in the conventional example can be reused as the incident light to the prism plate, the light intensity within the effective viewing angle range can be further improved as compared with the conventional example.

[0008]

1 is a sectional view of a sidelight type liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view thereof. 1 is a cold cathode ray tube, 2 is a reflection plate, 3 is a light guide plate of acrylic resin or the like, and a reflection member 4 such as white paint is applied on the lower surface. Reference numeral 5 denotes a thin scattering plate having fine irregularities on the surface, and is disposed on the upper surface of the light guide plate 3. 6 is a prism plate according to the present invention, the lower surface is a flat surface, and the upper surface is formed with a prism. 7 is a liquid crystal display element.

Next, the operation of the liquid crystal display device of this embodiment will be described. The light emitted from the cold cathode ray tube 1 is directly or after being reflected by the reflector 2, enters the light guide 3 from the side surface of the light guide 3, and is reflected by the reflection member 4 applied to the lower surface of the light guide 3. The light exits from the upper surface of the light guide plate 3. Light guide plate 3
Is emitted into the prism plate 6 with a uniform light intensity distribution over a wide angle range by the scattering plate 5. The prism plate 6 emits light only within an effective viewing angle range, and displays information through the liquid crystal display element 7.

FIG. 3 is an enlarged sectional view of the prism plate 6. In this embodiment, the prism plate 6 is formed of an acrylic resin, and has a refractive index n of 1.585. Substituting the refractive index n = 1.585 of the prism plate 6 into the right side of the expression (1), 2/3 * (π / 2 + 2 * arcsin (1 / n)) = 112.
Since it is 2 degrees, the expression (1) is 2θ> 112.2 degrees. Therefore, the vertex angle 2θ of the prism formed on the upper surface
Is set to an angle greater than 112.2 degrees. For example, 1
20 degrees (half angle θ is 60 degrees) is preferable. The interval P between the prisms is, for example, 50 μm. 1 to 3, the shape of the prism is exaggerated with respect to the thickness of the prism plate, but the thickness of the prism plate is, for example, 1 mm.

A solid line 50 in FIG. 5 shows the viewing angle characteristic of the light emitted from the prism plate 6 obtained by the ray tracing calculation as in FIG. A broken line 71 corresponds to the viewing angle characteristic of the scattering plate 5 without the prism plate 6 as in the description of FIG. 7, and has a uniform light intensity distribution over a wide angle range of about ± 80 degrees. As shown by the solid line 50 in FIG.
Since there is no light emission in an invalid viewing angle range of a viewing angle of −60 degrees or less and 60 degrees or more, there is no problem of wasting power, and an information display device is unnecessary when viewed from this direction. There is no problem of shining. Furthermore, the effective viewing angle range ± indicated by a solid line 70 in FIG.
Compared with 35 degrees, the effective viewing angle range is wider ± 45 degrees, and there is an effect of improving the brightness by 1.4 times or more.

The present invention is not limited to the above embodiment, but any prism plate may be used as long as it has a refractive index and an apex angle satisfying the expression (1). Further, the prism plate is not limited to the prism plate having a prism shape in only one direction shown in FIGS. 1 and 2, and may be a prism plate having a quadrangular pyramid or a cone shape having a prism shape in two directions. FIG.
Further, the positions of the prism plate and the liquid crystal display element may be interchanged without being limited to the configuration of FIG. Also,
Needless to say, the present invention can be used for a backlight type liquid crystal display device as shown in FIGS. 1 and 2 of JP-A-4-67016.

[0013]

According to the present invention, the emission of light to an invalid viewing angle range is prevented, the intensity of light emitted within an effective viewing angle range is improved, and the present invention is suitable for a portable information processing apparatus. An object of the present invention is to provide a thin and low power consumption information display device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device using the present invention.

FIG. 2 is an exploded perspective view of a liquid crystal display device using the present invention.

FIG. 3 is an enlarged sectional view of a prism plate using the present invention.

FIG. 4 is a ray tracing diagram of a prism plate.

FIG. 5 is a view angle characteristic of the prism plate of the present invention.

FIG. 6 is an enlarged sectional view of a conventional prism plate.

FIG. 7 is a view angle characteristic of a conventional prism plate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cold cathode ray tube, 3 ... Light guide plate, 5 ... Scattering plate, 6, 40 ...
Prism plate, 7: liquid crystal display element, 42, 43: prism slope.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuhiko Shibata 3300 Hayano, Mobara City, Chiba Prefecture, Hitachi, Ltd. Display Group (56) References JP-A-4-67016 (JP, A) JP-A-2- 13925 (JP, A) JP-A-3-238490 (JP, A) JP-A-2-33028 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/13357 G02B 5 / 02 G09F 9/00 324 G09F 9/00 336

Claims (1)

(57) [Claims] A liquid crystal display element; a light guide plate disposed below the liquid crystal display element; a cold cathode ray tube disposed to face a side surface of the light guide plate; comprising a scattering plate disposed between the light plate, a prism plate forming a prismatic protrusion structure disposed and the surface of the liquid crystal display element side between the scattering plate and the liquid crystal display device, the prism The projections correspond to the lower surface of the prism plate.
First prism tilted and extending along the cold cathode ray tube
Surface and the second prism surface are provided alternately, and the first prism
The vertex angle 2θ formed by the rhythm surface and the second prism surface is
For the refractive index n of the medium of the prism plate, the relationship 2θ> ２ * (π / 2 + 2 * arcsin (1 / n)) is satisfied, and the first prism surface and the top surface
All the light reflected on one side of the angled second prism surface
The first prism surface and the second prism forming the apex angle with the first prism surface
The other surface is formed so as to reflect toward the light guide plate, the scattering plate has an uneven shape on the surface, and a reflection member is applied to a surface of the light guide plate on the opposite side where the scattering plate is arranged. A liquid crystal display device characterized in that: