JPH10104611A - Liquid crystal image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display an image which has a high contrast and no visual angle dependency on the liquid crystal image display device. SOLUTION: Nearly parallel light from a light emitting means 30 is polarized by a polarizing plate 22a, and passed through a phase difference film 21a and then made incident on a liquid crystal cell part 10, the light transmissivity of the liquid crystal cell part 10 is varied by adjusting a voltage applied to the liquid crystal cell part 10 to compensate a phase difference generated when the light is transmitted through the liquid crystal cell part 10 by a phase difference film 21b after the light is passed through the liquid crystal cell part 10, and the light is further polarized by a polarizing plate 22b and diffused by a light diffusion layer 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal image display device, and more particularly to a liquid crystal image display device having improved viewing angle dependency and contrast.

[0002]

2. Description of the Related Art At present, many liquid crystal displays (liquid crystal image display devices) are used as displays for notebook computers, electronic organizers, car navigation systems and the like.

A basic configuration of a TN (Twisted Nematic) mode, which is generally widely used in a liquid crystal display, is that a liquid crystal cell is sealed in a state where liquid crystal molecules are twisted by 90 degrees between two glass substrates having transparent electrodes. In this configuration, two polarizing plates are orthogonally arranged outside the glass substrate. Image display is performed by changing the orientation of liquid crystal molecules by adjusting the voltage applied between the two substrates to change the output of light passing through the liquid crystal. That is, when the applied voltage is lower than the threshold voltage, the direction of polarization of the linearly polarized light that has passed through the polarizing plate on the incident side is rotated (rotated) by 90 degrees along the twist of the liquid crystal molecules. A bright state is displayed by passing through the polarizing plate on the emission side that is orthogonal to the plate. On the other hand, when the applied voltage becomes higher than the threshold voltage, the long axis of the liquid crystal molecule starts to rise from the central portion between the electrodes,
Optical rotation begins to decrease. When the applied voltage is further increased, the optical rotatory power finally disappears, and the linearly polarized light that has passed through the incident-side polarizing plate reaches the emitting-side polarizing plate without optical rotation, so that it cannot be emitted, and a dark state is displayed.

Generally, a liquid crystal image display (LCD) is
The matrix is classified into a simple matrix and an active matrix according to a method of applying a voltage to a pixel. Currently, the most widely used simple matrix STN (Super Twisted
Nematic) and active matrix TFT (Thin Film)
Transistor-LCD), but various other modes are known.

[0005] The conventional liquid crystal image display device has a problem that the gradation characteristic of the image changes depending on the viewing angle with respect to the liquid crystal screen, and a problem that the contrast is low. As a method for solving these problems, a liquid crystal display device (Japanese Patent Laid-Open No. 58-95378) in which a display cell is provided with a light guide layer and a light diffusion layer to increase the viewing angle, and a parallel light irradiating a parallel light. A liquid crystal display device or the like has been proposed in which an irradiating section is provided to achieve a wide viewing angle and a high contrast.

[0006]

However, it is extremely difficult to completely collimate light. In practice, the light often includes light in multiple directions, and an image formed by light having oblique components is superimposed on an image formed by vertical components. Therefore, there is a problem that the contrast is reduced.

Further, as another method, a method has been proposed in which a phase difference film is added to liquid crystal to reduce a change in visual gradation. However, even with this method, there is a problem that the viewing angle dependency cannot be completely eliminated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a liquid crystal image display device capable of displaying an image having a high contrast without a viewing angle dependency. .

[0009]

The liquid crystal image display device of the present invention irradiates substantially parallel light from one substrate side of a liquid crystal cell portion having a liquid crystal sandwiched between two transparent electrode substrates, and the other side. In a transmission type liquid crystal image display device for observing an image from the substrate side, optical compensation means is provided on both the one substrate side and the other substrate side of the liquid crystal cell portion, and the other substrate side of the liquid crystal cell portion is provided. In which a light diffusion layer is provided.

Here, the "one substrate side" refers to a surface side on which light enters the liquid crystal cell portion, that is, a light incident surface side of the liquid crystal cell portion, and the "other substrate side" refers to a liquid crystal cell portion. It refers to the surface from which light transmitted through the cell unit is emitted, that is, the light emission surface of the liquid crystal cell unit. Further, “substantially parallel light” refers to light that has been converted into parallel light and includes light of a component that is slightly shifted.

That is, in the liquid crystal image display device of the present invention, substantially parallel light containing a component slightly shifted is compensated by the optical compensation means provided on the light incident surface side and the light emission surface side of the liquid crystal cell portion. The optical characteristics for light at an angle slightly deviated from parallel can be made almost the same as that of parallel light, and by providing a light diffusion layer on the light exit surface side, the contrast is high and the viewing angle dependency is eliminated. This makes it possible to display the resulting image.

As the liquid crystal, for example, various liquid crystals such as a twisted nematic liquid crystal can be used.

[0013]

According to the liquid crystal image display device of the present invention, the optical compensating means is provided on both the light incident surface side and the light emitting surface side of the liquid crystal cell portion, so that the liquid crystal image display device can prevent light having an angle slightly shifted from parallel. Optical characteristics can be made almost the same as parallel light, and a liquid crystal image with high contrast can be displayed. Further, by providing the light diffusion layer on the light emission surface side of the liquid crystal cell, the viewing angle dependency can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the liquid crystal image display device of the present invention has a liquid crystal cell section 10 having liquid crystal sandwiched between two electrode substrates, and is disposed so as to sandwich the liquid crystal cell section 10. Retardation films 21a and 21b as optical compensating means, and a polarizing plate 22 further disposed so as to sandwich the retardation films 21a and 21b
a, 22b, a light diffusion layer 23 formed outside the one polarizing plate 22b, and a light irradiating means arranged on the other polarizing plate 22a side.
Consists of 30.

Although the details of the liquid crystal cell section 10 differ depending on the liquid crystal material and display method used, here, a TFT (Tin Film Transi) using a TN (twisted nematic) liquid crystal is used.
The ster) method will be described as an example.

FIG. 2 is a sectional view of one pixel of the liquid crystal cell section 10 of the TFT-LCD. The two electrode substrates described above include an amorphous silicon TFT 12 and a transparent electrode 13a.
Is formed on the light incident side glass substrate 11a, the black matrix 14, the color filters 15a, 15b, 15c and the transparent electrode 1.
3b is formed on the light emitting side glass substrate 11b, and the liquid crystal cell unit 10 is arranged such that the light incident side glass substrate 11a and the light emitting side glass substrate 11b face each other with the transparent electrodes 13a and 13b facing each other, In the meantime, the TN liquid crystal 16 is sealed.

The light irradiating means 30 comprises a point light source 31 such as an incandescent lamp or a fluorescent lamp for emitting light, and a microlouver 32. The microlouver 32 has a property of transmitting only parallel incident light among the light emitted from the point light source 31 and absorbing the other light, so that the angular distribution of transmitted light can be limited, and as a result, The liquid crystal cell unit 10 is irradiated with substantially parallel light.

Hereinafter, the operation of the liquid crystal image display device will be described.

The light emitted from the point light source 31 passes through the microlouver 32 and is converted into parallel light. The parallelized light (substantially parallel light) is polarized by the polarizing plate 22a and is converted by the phase difference film 21a. The phase difference is compensated and the light enters the liquid crystal cell unit 10. In the liquid crystal cell section 10, the transparent electrodes 13a, 13b
The light transmittance is adjusted by the voltage applied in between. That is,
The molecular arrangement of the TN liquid crystal changes according to the applied voltage, and the light transmittance is adjusted. The color filters 15a, 15b and 15c are R (red), G (green) and B (blue) filters, respectively. Light transmitted through the liquid crystal cell unit 10 exits from the exit surface,
The retardation film 21b compensates for a phase difference generated when light passes through the liquid crystal cell unit 10, is polarized by the polarizing plate 22b, is diffused in all directions by the light diffusion layer, is emitted, and is used for observation. You.

As described above, in the liquid crystal image display means of the present invention, the substantially parallel light emitted from the light source means is compensated for the phase difference by the phase difference films provided on both sides of the liquid crystal cell portion, and the liquid crystal cell is displayed. Since the light enters the unit 10 and exits through the light diffusion layer, the observer can observe a display image with high contrast and no dependence on viewing angle.

Incidentally, the parallel light irradiating means is not limited to the above-mentioned means. For example, as another embodiment, as shown in FIG. 3, light emitted from a point light source 31 is converted into parallel light by using a condenser lens 33 and a Fresnel lens 34, and the parallel light is reflected by a reflection mirror 35 so as to form a liquid crystal. A parallel light irradiating means or the like configured to make the light vertically enter the cell portion may be used. In the parallel light irradiating means 30 ', a reflector 35 is disposed behind the point light source 31 so as to increase the light source light use efficiency.

In addition to the TN liquid crystal, a liquid crystal of a vertical alignment nematic type using the ECB effect, a STN (super twisted nematic type), a ferroelectric type, an antiferroelectric type, or a polarizing plate may be used. Various liquid crystals such as a dispersion polymer type which does not need to be used can be used. Further, these driving methods are roughly classified into a simple matrix method and an active matrix method. In the above-described embodiment, the TFT method which is one form of the active matrix method has been described as an example. It is not limited to this.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of one pixel of a liquid crystal cell portion of a TFT-LCD.

FIG. 3 is a schematic cross-sectional view of a liquid crystal display device according to another embodiment of the present invention.

[Explanation of symbols]

 10 Liquid crystal cell section 11a, 11b Glass substrate 12 TFT 13a, 13b Transparent electrode 14 Black matrix 15a, 15b, 15c Color filter 16 Liquid crystal 21a, 21b Phase difference film 22a, 22b Polarizer 23 Light diffusion layer 30 Light irradiation part

Claims (2)

[Claims] 1. A transmissive liquid crystal image display in which substantially parallel light is emitted from one substrate side of a liquid crystal cell portion having a liquid crystal sandwiched between two transparent electrode substrates, and an image is observed from the other substrate side. A liquid crystal display, comprising: an optical compensator provided on both the one substrate side and the other substrate side of the liquid crystal cell unit; and a light diffusion layer provided on the other substrate side of the liquid crystal cell unit. Image display device. 2. The liquid crystal image display device according to claim 1, wherein a twisted nematic liquid crystal is used as said liquid crystal.