JPH075461A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device realizing color display with a correct color tone. CONSTITUTION:This color light source type liquid crystal display device 1 realizes the color display by alternately irradiating the back surface of a liquid crystal display panel 2 with red, green and blue lights; and it is provided with a light transmission plate 3 arranged on the back surface of the panel 2, a 1st light irradiation means 4 radiating the green and blue lights at the end position of the side in the longitudinal direction of the plate 3, and a 2nd light irradiation means 5 radiating the red light at the end position of the side in the lateral direction of the plate 3.

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,
In particular, it relates to a liquid crystal display device that performs color display using a ferroelectric liquid crystal.

BACKGROUND OF THE INVENTION In general, a substance that is polarized only when an electric field is applied from the outside is called a "dielectric". In particular, there is a polarization even when there is no external electric field (this polarization is spontaneous polarization). Is referred to as "ferroelectric". The ferroelectric substance has a characteristic that the direction of spontaneous polarization can be reversed depending on the direction of an applied electric field, and the spontaneous polarization can be aligned in one direction.

Some types of liquid crystals have such spontaneous polarization, and such liquid crystals are called "ferroelectric liquid crystals (F
LC: Ferroelectric liquid crystal) ". A liquid crystal exhibiting ferroelectricity is a smectic liquid crystal having an asymmetric carbon atom in its molecular structure, and smectic C in which liquid crystal molecules are inclined at a certain angle with respect to each layer is known. Since it has an asymmetric carbon atom, it is also called chiral smectic C, and the liquid crystal molecule has a helical structure like the chiral nematic liquid crystal (cholesteric liquid crystal).

However, the molecular arrangement is completely different from that of the cholesteric liquid crystal, and the long axes of the liquid crystal molecules are arranged so as to be inclined at a certain angle from the direction perpendicular to each layer. They are arranged so that they gradually shift to, and have a spiral structure. The dipole moment also rotates with the spiral.

The pitch of the spiral of the ferroelectric liquid crystal is usually on the order of several microns, but when the thickness of the liquid crystal layer becomes thinner than this spiral pitch, the spiral structure is dissolved and the liquid crystal molecules become aligned in one direction. . When a DC voltage is applied to the liquid crystal in such a state, the dipole direction, that is, the liquid crystal molecule direction can be switched by the positive or negative polarity of the voltage. The time required for this switching is much faster than the time required for the molecular arrangement in a nematic liquid crystal device or the like, and a response time shorter than one millionth of a second has been reported.

In the ferroelectric liquid crystal, in addition to such a high speed response, TN (twisted nematic) and STN (super t
wisted nematic), which has a bistability that results in two different optical stable states for two different types of electric field vectors. However, having a memory function to maintain a stable state of either, suitable for large-capacity display, wide viewing angle, etc.
In recent years, liquid crystal display devices using surface-stabilized ferroelectric liquid crystals, which display by utilizing the spontaneous polarization of the ferroelectric liquid crystals, have attracted attention because they have extremely excellent properties compared to conventional liquid crystals. ing.

The surface-stabilized ferroelectric liquid crystal is displayed by utilizing the spontaneous polarization of the ferroelectric liquid crystal, and the transition time to the above-mentioned two optically stable states is 100 μs or less, which is a normal liquid crystal. Very fast compared to
Since it is possible to obtain high contrast, it is expected as a flat panel display for OA.

However, the property of bistability, which is a characteristic of ferroelectric liquid crystals, becomes an obstacle to colorization (multi-gradation),
It is difficult to display halftones.

Therefore, there is a demand for a color liquid crystal display that makes use of the excellent characteristics of the ferroelectric liquid crystal.

[0010]

2. Description of the Related Art Conventionally, color display devices using ferroelectric liquid crystals are roughly classified into color filter type LCDs (Li
A quid crystal display) and a color light source type LCD are under study.

The color filter type LCD is a birefringence type, dichroic type, or light scattering type transmission type ferroelectric LC.
D is used as a high speed black and white (B / W) optical shutter,
RGB micro color filters are built in this LCD. Then, a white backlight is added to the back surface of the LCD and is generally applied as a direct-view LCD. Incidentally, as a typical driving method of a color filter type ferroelectric liquid crystal, as shown in [Table 1],
There are driving methods such as a two-field method, a multiple line simultaneous erasing method, and a four-pulse method. Table 1 shows various driving methods and multiplex driving characteristics.

[0012]

[Table 1] An example of a ferroelectric color LCD with a built-in RGB micro color filter is a diagonal of 12 inches, a panel size of 260 × 200 mm ² , and a pixel number of 639 × 40.
Those with 0 and a cell gap of 2 μm are provided on the market.

The alignment film of this panel has a target PI / PI.
A rubbing film is used and a hot cathode tube is used as a backlight.

FIG. 7 is a sectional view of a ferroelectric multi-color LCD. In FIG. 7, 101 is a polarizing plate, 102 is a glass substrate, 103R is a red color filter, 103G is a green color filter,
Reference numeral 03B is a blue color filter, 103M is a black matrix, 104 is a transparent electrode, 105 is an insulating film, 106 is an alignment film, 107 is a ferroelectric liquid crystal, and 108 is a sealing agent.

A plurality of driving methods for this color LCD (8
The line) simultaneous erasing method is adopted.

However, in the color filter type LCD, since the color filter is provided on the surface of the liquid crystal display panel, the utilization efficiency of the light from the backlight is extremely deteriorated. Also,
Since the color display pixel is configured by using three pixels of R, G and B as one unit, there is a problem that the resolution is lowered.

On the other hand, the color light source type LCD is roughly classified into a direct view type in which an image displayed on the LCD panel is directly viewed and a projection type in which the image is enlarged and projected on a screen.

As a color light source of a color generation source used in combination with a ferroelectric LCD which is a high-speed black and white (B / W) light shutter, in the case of a direct-view type, as shown in FIG. In general, the projection type uses an RGB color light source in which high-intensity white light is separated by a dichroic mirror or the like.

FIG. 8 is a schematic view of the essential parts of a direct-viewing type color light source LCD. In FIG. 8, 201 is a liquid crystal display panel, 202 is a fluorescent lamp, 203 is a light source cell, and 204 is a light source cell.
R is a red color filter, 204G is a green color filter, 204B is a blue color filter, and 205 is a light guide plate having a diffusion plate formed on its surface.

With the above arrangement, sequential color illumination (color se
quential lighting) method is explained.

FIG. 9 shows the color display principle of the sequential color illumination system.

In sequential color illumination, one frame period is divided into three primary color R, G, and B subframes, and an image of a specific color is written and a light source of a specific color is turned on during each subframe period. By performing and, color display is performed.

Here, the written image of the specific color needs to be stored in the memory during the lighting period of the light source of the specific color that follows.

That is, in the color light source type LCD, since one frame period is divided into three sub-frames for use, the LCD is required to have a high response speed.

That is, in the color display LCD based on the sequential color illumination system, the response speed of the LCD is required to be three times higher than that of the RGB color system described above, but the light utilization efficiency is high. A bright display screen (at least 2 times or more) can be obtained, and since a color display pixel can be configured with one pixel, high resolution display of 3 times is possible.

Therefore, for an LCD using a ferroelectric liquid crystal, which excels in high-speed response, a color display method in combination with a monochrome (B / W) optical shutter is effective.

[0027]

However, in the above-mentioned color light source type LCD, as shown in FIG.
Each of the color filters 204 (204R, 204G, 2) is arranged in parallel to the end of the side in the lateral direction of the liquid crystal display panel 201.
04B) is provided, there is a problem as described below.

That is, from the fluorescent lamp 202 to the diffusion plate 2
The surface brightness of the diffusion plate 205 due to the light irradiated on
Generally, as shown in FIG. 10, the color filter 204 becomes lower as it goes from the end to the center of the light guide plate 205.
The wavelengths of the respective color lights (red, green, blue) that have passed through (204R, 204G, 204B) are different, so the amount of light transmitted to the light guide plate 205 is also different.

Specifically, the red color filter 204R
The wavelength of the red light transmitted through is about 620 nm, and the wavelength of the green light transmitted through the green color filter 204G is about 550 n.
m, the wavelength of blue light transmitted through the blue color filter 204B is about 440 nm, and the longer the wavelength of light, the greater the amount of transmission. That is, in this case, the ratio of the transmission amounts of red light, green light, and blue light is about 9: 7: 6, and the transmission amount of red light is higher than that of green light and blue light.

Therefore, as shown in FIG. 8, if the respective colored lights are arranged at the same position, only the red light is emphasized, and the color display cannot be performed in the correct color tone. .

[Object] In view of the above problems, it is an object of the present invention to provide a liquid crystal display device that performs color display with a correct color tone.

[0032]

The invention according to claim 1 is
As shown in FIG. 1, red from the back of the liquid crystal display panel 2,
In a color light source type liquid crystal display device 1 that performs color display by alternately irradiating green and blue light, a light guide plate 3 arranged on the back surface of the liquid crystal display panel 2, and a side in the longitudinal direction of the light guide plate 3. First light irradiating means 4 for irradiating green and blue light to the end positions of the two, and second light irradiating means 5 for irradiating red light to the end positions of the sides of the light guide plate 3 in the lateral direction.
By including the above, the above-mentioned object is achieved.

In this case, in order to perform the color display with the correct color tone which is the above-mentioned object, for example, as described in claim 2, the first light irradiation means 4 and the second light irradiation means 5 are: A fluorescent lamp 6 serving as a light source, and an optical shutter means 7 for selectively transmitting light emitted from the fluorescent lamp 6.
And a color filter 8 for transmitting light of a specific wavelength in the light transmitted through the optical shutter means 7, and the first light irradiation means 4 as described in claim 3.
And the second light irradiation means 5 is a fluorescent lamp 6 serving as a light source.
A color filter 8 that transmits light of a specific wavelength in the light emitted from the fluorescent lamp 6, and the color filter 8
It is preferable to have an optical shutter unit 7 that selectively transmits light emitted through the optical shutter unit.

Further, in this case, as described in claim 4, it is effective that the optical shutter means 7 is an optical shutter using a ferroelectric liquid crystal cell.

[0035]

According to the first aspect of the invention, the second light irradiating means for irradiating the red light, which has a higher light transmission amount than the green light and the blue light, emits the green light and the blue light. Since it is arranged at a position where the optical path distance is longer in the light guide plate as compared with the means, the color tone of the light is properly maintained by the attenuation of the transmitted light.

In this case, as described in claim 2 or claim 3, the fluorescent lamp, the optical shutter means, and the color filter are arranged to irradiate the light guide plate with desired color light.

Further, as the optical shutter means in this case, a ferroelectric liquid crystal cell is used, so that a high-speed optical shutter is realized in the color light source type liquid crystal display device. .

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to FIGS.
Will be described with reference to. In addition, in FIGS.
The same reference numerals are given to the same portions as.

First, the structure of this embodiment will be described.

FIG. 2 is a perspective view showing the structure of the main part of this embodiment. In FIG. 2, the liquid crystal display device 1 includes a liquid crystal display panel 2, a light guide plate 3, a first light irradiating means 4, and a second light irradiating means 5, and in particular, the first light irradiating means 4 includes a fluorescent lamp 6 and a light source. The shutter means 7, a green color filter 8G, and a blue color filter 8B are included, and the second light irradiation means 5 includes a fluorescent lamp 6, an optical shutter means 7, and a red color filter 8R.

FIG. 3 is a sectional view of the liquid crystal display panel 2.

The liquid crystal display panel 2 is, as shown in FIG.
Glass substrates 11 and 12, polarizing plates 13 and 14, transparent electrode 1
5, 16, alignment films 17, 18, spacer 19, liquid crystal layer 2
It consists of zero.

Polarizing plates 13 and 14 are formed on the outer surfaces of the glass substrates 11 and 12, respectively.
Transparent electrodes 15 and 16 are formed on the opposing surfaces of 1 and 12, respectively, and alignment films 17 and 18 are further formed on the surfaces of the transparent electrodes 15 and 16.

The alignment films 17 and 18 are organic polymer films that are subjected to a treatment such as rubbing to align the liquid crystal molecules, and are polyvinyl alcohol (PVA: Poly Vinyle Alcohol).
Alternatively, a polyimide resin is used.

The spacer 19 is for ensuring the uniformity of the gap between the glasses of the liquid crystal cell and has a diameter of 10 μm.
It has a spherical shape of m.

The liquid crystal layer 20 comprises two transparent glass substrates 1
The nematic liquid crystal sandwiched between 1 and 12 is used for the glass substrate 11
It is so-called TN (Twisted Nematic) in which the molecular axis is twisted by about 90 degrees between the side and the glass substrate 12.

The light guide plate 3 is made of a transparent acrylic plate, and guides the light entering from the end face to the back surface of the liquid crystal display panel 2, and the light guided by the light guide plate 3 is on the front surface of the liquid crystal. When the display panel 2 is irradiated, a diffusion plate (not shown) is formed to diffuse the light and balance the brightness.
In addition, a dot pattern is printed on the back surface, and a reflection plate (not shown) is formed so that the light entering the light guide plate 3 does not pass through the back surface of the light guide plate 3 and go out. ing.

As described above, the first light irradiation means 4 has the fluorescent lamp 6, the optical shutter means 7, and the green color filter 8.
G, blue color filter 8B.

The fluorescent lamp 6 comprises a cold cathode FL lamp arranged at the end of the light guide plate 3, and emits light to the end face position of the light guide plate 3 via the optical shutter means 7 and the color filters 8 (8G, 8B). It is to irradiate.

FIG. 4 is a sectional view of a ferroelectric liquid crystal cell which constitutes the optical shutter means 7.

The optical shutter means 7, as shown in FIG.
Glass substrates 21 and 22, transparent electrodes 23 and 24, insulating film 2
5, 26, alignment films 27 and 28, spacers 29, and ferroelectric liquid crystal layer 30.

Transparent electrodes 23 and 24 are formed on the facing surfaces of the glass substrates 21 and 22, respectively, and insulating films 25 and 26 are formed on the facing surfaces of the transparent electrodes 23 and 24, respectively. , 26 have alignment films 27, 2 on their surfaces.
8 forming.

The alignment films 27 and 28 are organic polymer films for aligning liquid crystal molecules when subjected to a treatment such as rubbing, and are polyvinyl alcohol (PVA: Poly Vinyle Alcohol).
Alternatively, a polyimide resin is used.

The spacer 29 is for ensuring the uniformity of the gap between the glasses of the liquid crystal cell and has a diameter of 1.5.
It has a spherical shape of μm.

The ferroelectric liquid crystal layer 30 uses a ferroelectric liquid crystal composed of an ester-based mixed composition having good stability.

The color filter 8 (8G, 8B) is coated with a color resin solution in which a coloring material such as a dye or an organic pigment is uniformly dispersed in a transparent photosensitive resin or a transparent resin by a dispersion method, and then exposed or developed. Exposure through photoresist
It is developed to sequentially form a colored pattern in a predetermined shape. The color filter 8 in this case includes a green color filter 8G and a blue color filter 8B.

The second light irradiating means 5 is, as described above, the fluorescent lamp 6, the optical shutter means 7, and the red color filter 8.
It is composed of R.

The fluorescent lamp 6 and the optical shutter means 7 have the same structure as the above-mentioned first light irradiation means 4, and even in the color filter 8 (8R), the colored color of the color filter 8 (in this case, The forming method is the same except that the number of red color) and the number of color filters 8 (one in this case) are different.

Next, the operation (action) of this embodiment will be described.

FIG. 5 is a waveform diagram showing drive signals for the first light irradiation means 4 and the second light irradiation means 5 in this embodiment. In FIG. 5, PR is a red light irradiation timing pulse, PG is a green light irradiation timing pulse, PB is a blue light irradiation timing pulse, and CK is a basic clock pulse.

First, red display image data is prepared based on the timing of the reference clock pulse CK, the optical shutter means 7 corresponding to the red color filter 8R is turned on at a predetermined timing, and red writing is performed in the R sub-frame. Is done. At this time, the green color filter 8
The optical shutter means 7 corresponding to the G and blue color filters 8B is in the off state.

Next, green display image data is prepared,
The optical shutter means 7 corresponding to the green color filter 8G is turned on at a predetermined timing, and green writing is performed in the G sub-frame. Thereafter, similarly, blue display image data is prepared, the optical shutter unit 7 corresponding to the blue color filter 8B is turned on at a predetermined timing, and blue writing is performed in the B sub-frame.

That is, by continuously writing R, G, and B during a predetermined one frame period, one display pixel visually appears as if it was displayed in color.

In this case, the aspect ratio of the liquid crystal display panel 2 is
Generally, 2: 3 (480: 640) or 5: 8 (4
00: 640), the optical path length of the red light in the light guide plate 3 is 1.5 to 1.6 times longer than the optical path lengths of the green light and the blue light in the light guide plate 3. Become.

Therefore, the red light having a high transmission amount is attenuated to the same brightness as the green light and the blue light, and the balance of the color tone is adjusted.

As described above, in the present embodiment, it is possible to perform color display of high quality while maintaining the balance of color tone while making the most of the advantages of brightness and high resolution, which are the features of the liquid crystal display device of the color light source type. .

Another preferred embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to. In FIG. 6, the same parts as those in FIG. 2 are designated by the same reference numerals.

In the above-described embodiment, the light emitted from the fluorescent lamp 6 passes through the color filter 8 through the optical shutter means 7 and is applied to the end portion of the light guide plate 3, but in the present embodiment. The light emitted from the fluorescent lamp 6 first passes through the color filter 8 to become a predetermined colored light, and the colored light is controlled by the optical shutter means 7 to be transmitted / non-transmitted.

As described above, in this embodiment, the second light irradiating means 5 for irradiating the red light having a higher light transmission amount than the green light and the blue light irradiates the green light and the blue light. Since the light guide plate 3 is arranged at a position where the optical path distance is longer than that of the first light irradiation means 4, the color tone of the light can be properly maintained by the attenuation of the red transmitted light.

Although the invention made by the present inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, in the above embodiment, the liquid crystal display panel 2 was made of TN, but the liquid crystal display panel 2 was used.
Alternatively, a panel using a ferroelectric liquid crystal may be used.

In the above embodiment, the color filter 5 is used.
Although R, 5G, and 5B are formed by the dispersion method, the organic filter may be a filter such as a dyeing method, a printing method, or an electrodeposition method. In addition, an inorganic filter using an inorganic material or Alternatively, they may be formed by a composite filter formed by a combination of these.

Further, in the above-mentioned embodiment, the liquid crystal composed of the ester-based mixed composition is used as the ferroelectric liquid crystal material, but the invention is not limited to this, and for example, a cyanobiphenyl-based liquid crystal or a multiplex operation is used. A phenylpyrimidine-based material that can obtain high contrast may be used, and any material may be used as long as it has characteristics as a ferroelectric liquid crystal material.

[0074]

According to the present invention, in the invention according to claim 1, the second light irradiating means for irradiating the red light having a higher light transmission amount than the green light and the blue light is provided with the green light and the blue light. By arranging the light guide plate at a position where the optical path distance is longer than that of the first light irradiation means for irradiating light, the color tone of the light can be properly maintained by the attenuation of transmitted light.

In this case, by disposing the fluorescent lamp, the optical shutter means, and the color filter as described in claim 2 or 3, it is possible to irradiate the light guide plate with desired color light. By using a ferroelectric liquid crystal cell as the optical shutter means in this case, a high-speed optical shutter can be realized in a color light source type liquid crystal display device.

Therefore, in the color light source type liquid crystal display device, color display can be performed with a correct color tone.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of a liquid crystal display device according to the present invention.

FIG. 2 is a perspective view showing a main configuration of a liquid crystal display device according to the present embodiment.

FIG. 3 is a cross-sectional view of a liquid crystal display panel.

FIG. 4 is a cross-sectional view of a ferroelectric liquid crystal cell that constitutes an optical shutter means.

FIG. 5 is a waveform diagram showing drive signals for the first light irradiation means and the second light irradiation means.

FIG. 6 is a perspective view showing a main configuration of a liquid crystal display device according to another embodiment.

FIG. 7 is a sectional view of a ferroelectric multi-color LCD.

FIG. 8 is a configuration diagram of a main part of a direct-view color light source LCD.

FIG. 9 is a diagram showing a color display principle of a sequential color illumination system.

FIG. 10 is a diagram showing an amount of light transmitted through a light guide plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal display panel 3 Light guide plate 4 First light irradiation means 5 Second light irradiation means 6 Fluorescent lamp 7 Optical shutter means 8 Color filter 8R Red color filter 8G Green color filter 8B Blue color filter 11, 12 Glass substrate 13, 14 Polarizing plate 15, 16 Transparent electrode 17, 18 Alignment film 19 Spacer 20 Liquid crystal layer 21, 22 Glass substrate 23, 24 Polarizing plate 25, 26 Transparent electrode 27, 28 Alignment film 29 Spacer 30 Ferroelectric liquid crystal layer 101 Polarization Plate 102 Glass substrate 103R Red color filter 103G Green color filter 103B Blue color filter 103M Black matrix 104 Transparent electrode 105 Insulating film 106 Alignment film 107 Ferroelectric liquid crystal 108 Sealant 201 Liquid crystal display panel 202 Fluorescent lamp 203 Light source Cell 204R Red color filter 204G Green color filter 204B Blue color filter 205 Light guide plate

Claims (4)

[Claims] 1. A color light source type liquid crystal display device for performing color display by alternately irradiating red, green and blue lights from the back surface of the liquid crystal display panel, and a light guide plate disposed on the back surface of the liquid crystal display panel. First light irradiating means for irradiating green and blue light at end portions of longitudinal sides of the light guide plate, and red light for illuminating red light at end portions of lateral sides of the light guide plate A liquid crystal display device comprising: two-light irradiation means. 2. The first light irradiating means and the second light irradiating means, a fluorescent lamp as a light source, an optical shutter means for selectively transmitting light emitted from the fluorescent lamp, and the optical shutter means. The liquid crystal display device according to claim 1, further comprising: a color filter that transmits light having a specific wavelength in light transmitted through the color filter. 3. The first light irradiating means and the second light irradiating means, a fluorescent lamp as a light source, a color filter for transmitting light of a specific wavelength in the light emitted from the fluorescent lamp, The liquid crystal display device according to claim 1, further comprising: an optical shutter unit that selectively transmits light emitted through the color filter. 4. The liquid crystal display device according to claim 2, wherein the optical shutter means is an optical shutter using a ferroelectric liquid crystal cell.