JPS60140322A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a uniform brightness having a high contrast by placing an optical diffusion plate and a light control film between a light source for illuminating a transmission type liquid crystal display plate and the display plate, and irradiating a light of a good visual angle direction. CONSTITUTION:Three fluorescent lamps 2 are placed on the back of a twist nematic type liquid crystal display plate 1 of a time division driving, and an optical diffusion plate 4 is placed in front of the display plate 1. A light control film 5 and an optical diffusion plate 6 are placed between the display plate 1 and the fluorescent lamp 2. As for the light control film 5, its passing layer 5a and an absorbing layer 5b of a light are laminated by a smaller pitch than a pitch of a dot of a matrix, only a light between prescribed incident angles (phi1- phi2) is made to pass through, and its direction is made to coincide with a good visual angle direction. A light of the fluorescent lamp 2 is distributed uniformly by the diffusion plate 6, and only a light of a good visual angle direction in said light passes through the film 5, transmits through the display plate 1, and is diffused by the diffusion plate 4. In this way, a device which is thin and high in its contrast is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention particularly relates to a TN (Twist) that performs time-division driving.
The present invention relates to a liquid crystal display device suitable for a dNelatio type liquid crystal display device.

[Technical background of the invention and its problems] Conventionally, TN type liquid crystal display devices have been widely used as reflective liquid crystal display devices that perform display by reflecting external light.

However, reflective LCD displays have the disadvantage that the display is difficult to see in dark surroundings, so if you often use them indoors or need to be visible to many people, you may need to install a lighting device behind them. It is increasingly being used as a transmissive liquid crystal display device that provides a bright display using background illumination.

FIG. 1 is a sectional view schematically showing the structure of such a conventional liquid crystal display device. In the figure, reference numeral 1 indicates a so-called negative display type liquid crystal display which is dark when no voltage is applied and becomes bright when a voltage is applied.

The liquid crystal display 1 performs a dot matrix display of characters and graphics by selectively lighting up a large number of dots in response to control signals from a control section (not shown).

Behind the liquid crystal display 1 is a fluorescent lamp 2 that illuminates it.
A cylindrical lens 3 is arranged between the fluorescent lamp 2 and the liquid crystal display 1 to convert the light from the fluorescent lamp 2 into parallel light. Reference numeral 4 denotes a light diffusing plate placed in front of the liquid crystal display 1 and serving to diffuse transmitted light.

However, in such a conventional dot matrix liquid crystal display device, since time-division driving is performed, a constant 0-Stokes voltage is applied even to non-selected segments that are not originally desired to be displayed. In addition to the light that passes through the selected segment shown in Figure B, the light that passes through the non-selected segment that is oblique to the normal direction of the display device is also displayed, causing the image to appear double. , the contrast between selected and non-selected segments decreases,
There was a problem that the display became difficult to see.

Furthermore, although the light is incident in the normal direction of the liquid crystal display, generally when the liquid crystal display is time-divisionally driven,
As shown in , the angular distribution of transmittance of the selected segment is
The transmittance is higher in a direction slightly oblique to the normal direction, and the transmittance of non-selected segments is also higher in a specific direction, as already indicated by the reference numeral in the figure. On the other hand, the cylindrical lens mentioned above converts the incident light into parallel light only in the case of an ideal linear light source, and since an actual fluorescent lamp has a fixed diameter, it is not possible to convert the incident light into perfectly parallel light. 1
Light B that is oblique to the normal line in the figure remains.

Therefore, in such a dot matrix liquid crystal display device, there is a problem that the contrast is lowered and the angle range Φ1 to Φ2 is narrowed.

In addition, it is generally difficult to shorten the focal length (L in Fig. 1) of the cylindrical lens described above (
The shortest distance is 40 mm>, and there was also the drawback that it was not possible to reduce the thickness of the entire liquid crystal display.

Furthermore, since the above-mentioned fluorescent lamp is not a linear light source, it also has the disadvantage that the entire display surface does not have uniform brightness. Such unevenness in brightness can be improved by installing a light diffusion plate in front of the fluorescent lamp, but in this case, the light source is no longer a linear light source (as a result, the illumination light is no longer parallel light, and the liquid crystal display It was not possible to provide a light diffusing plate because the transmitted light would be significantly reduced.

In order to further increase the brightness, it is possible to increase the number of fluorescent lamps or increase the diameter of the fluorescent lamps, but in either case, the incident light will significantly cease to be parallel light, so the brightness will be reduced. It was difficult to increase.

For this reason, in the case of a large liquid crystal display with a height of 1→), the angle of incidence H becomes large (and the light causes total reflection on the lens surface, so the height of the display must be increased to a certain extent). I couldn't do it.

[Object of the Invention] The present invention has been made to eliminate such conventional drawbacks, and provides a liquid crystal display device that has good contrast, can reduce the overall thickness of the liquid crystal display device, and can also increase the height of the liquid crystal display device. An object of the present invention is to provide a transmission type liquid crystal display device.

[Summary of the Invention J That is, the liquid crystal display device of the present invention is a liquid crystal display device having a transmissive liquid crystal display and a lighting device located behind the transmissive liquid crystal display and illuminating the transmissive liquid crystal display. , the lighting device is characterized in that a device that irradiates light in a direction with a good viewing angle of the liquid crystal display is used.

[Embodiment of the Invention] The details of the present invention will be described below with reference to an embodiment shown in the drawings.

FIG. 3 is a sectional view schematically showing an embodiment of the present invention. In this figure, parts common to those in FIG. 1 are designated by the same reference numerals.

In this embodiment, a time division driven TN type liquid crystal display 1
Three fluorescent lamps 2 are arranged on the back of the T'
A light diffusing plate 4 is arranged in front of the N-type liquid crystal display 1.

However, in this embodiment, a light control film 5 and a light diffusing plate 6 are arranged between the liquid crystal display 1 and the fluorescent lamp 2 in this order from the liquid crystal display 1 side.

As shown in FIG. 4, this light control film 5 includes a light transmitting layer 5a that transmits light and a light absorbing layer 5 that does not transmit light.
B and C are alternately laminated at a pitch finer than the pitch of the dots in the dot matrix, and have the property of allowing only light between a certain angle of incidence (φ1 to φ2 in the figure) to pass through. .

In the present invention, this light control film 5
As shown in Fig. 3, the incident angles φ1 and φ2 are designed to almost match the direction of good viewing angle when the liquid crystal display is selected, and the transmission direction when not selected is not included in φ1 to φ2. .

In the liquid crystal display device of the present invention configured as described above, the light control film blocks the transmitted light when no selection is made, so the contrast is good, and since no lenses are used, the number of fluorescent lamps can be increased. It is possible to increase the brightness and height of the liquid crystal display 1. Furthermore, since there is no restriction on the focal length, by making the entire t4m thinner, the liquid crystal display device of the present invention has a higher contrast and can obtain uniform brightness.

Further, it is possible to manufacture a liquid crystal display device that is thin and has a high height.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing the structure of a conventional transmissive liquid crystal display device, FIG. 2 is a graph showing the transmittance angle distribution of a conventional transmissive liquid crystal display device, and FIG. 3 is a graph showing the structure of a conventional transmissive liquid crystal display device. FIG. 4 is a cross-sectional view schematically showing an example, and FIG. 4 is an enlarged cross-sectional view showing a light control film used in this example. １・・・・・・・・・・・・Liquid crystal display ２・・・・・・
・・・・・・Fluorescent lamp 3・・・・・・・・・Cylindrical lens 4.6・・・・・・Light diffuser plate 5・・・・・・・・・Light Control film 5a......Light transmitting layer 5b......Light absorbing layer Patent attorney Sa Suyama - 1 Figure 2 Section 1 11 ψ Figure 3 Figure 4

Claims (3)

[Claims] (1) In a liquid crystal display device having a transmissive liquid crystal display and a lighting device located behind the transmissive liquid crystal display and illuminating the transmissive liquid crystal display, the lighting device may be a transmissive liquid crystal display. A liquid crystal display device characterized by using a device that irradiates light in a viewing angle direction. (2) The liquid crystal display device according to claim 1, wherein the illumination device comprises a light source and a transparent body placed in front of the light source that transmits light in a certain direction. (3) The liquid crystal display device according to claim 2, wherein a light diffusing plate is disposed between the light source and the transparent body that transmits only a certain amount of light.