JPS63301021A - Color liquid crystal display element - Google Patents

Abstract

PURPOSE:To enable bright display by adding a dichromatic dye to a specific liquid crystal compsn. and disposing color filters or coloring light sources. CONSTITUTION:This display device is constituted of a liquid crystal cell having a liquid crystal compsn. layer 16 which is sandwiched between a pair of oriented substrates 11 and 11' having electrodes 13, 13' for display, is oriented approximately horizontally with the substrates 11, 11' at the time of absence of electric field impression and oriented with the liquid crystal molecules so as to have the helix angle in the range of over 90 deg. and below 270 deg. between the substrates 11 and 11' as well as the color filters 15. A polarizing plate 12 is disposed on the outside of this liquid crystal cell at need. The brought display is thereby enabled.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a so-called 5TN liquid crystal composition layer arranged between substrates in which liquid crystal molecules in a liquid crystal composition layer have a twist angle in a range of more than 90° and less than 270°. This invention relates to a (super nematic) color liquid crystal display element.

[Prior art]

The liquid crystal display method that has been mainly used in the past is called the TN (twisted nematic) type, in which a liquid crystal layer made of nematic liquid crystal or a mixture of nematic liquid crystal and cholesteric liquid crystal is arranged between a pair of substrates having display electrodes. Although this display method was sufficient for low time division driving such as watches and calculators, when high time division driving was used to increase the display capacity, the contrast deteriorated and the viewing angle became narrower. There was a drawback. This is because with high time division driving, the ratio of voltages applied to selected points and non-selected points approaches 1, and in order to obtain a display element with high contrast and a wide viewing angle, the relative transmittance of the element must be 50%. The pressure VSO changes and the voltage V changes 10%. Which ratio (VS./V
,. ) is required to be as small as possible. Furthermore, in the above display method, a color liquid crystal display element that uses a liquid crystal cell as a shutter and displays color by adjusting the transmitted light intensity of colored light through a color filter etc. has also been put into practical use, but the spectral transmission of the liquid crystal cell Since the characteristics are not flat, the color purity is reduced and the color changes depending on the viewing angle. On the other hand, G/i
Color liquid crystal display elements using a T-type (guest-host type) display mode are also known. Although this device has few of the above-mentioned drawbacks, it has the disadvantage that time-division driving is not possible due to poor steepness, and it is generally used as a display element with a small display capacity. Each element must be formed.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to provide a wide-angle viewing color liquid crystal display element that improves the drawbacks of the TN system and G/H system and is capable of displaying a large capacity using simple matrix driving.

〔composition〕

According to the present invention, a pair of alignment-treated substrates having display electrodes are sandwiched between the substrates, the liquid crystal molecules are oriented substantially horizontally to the substrates when no electric field is applied, and the liquid crystal molecules are arranged at 90 degrees centigrade between the substrates.
In a liquid crystal display element having a liquid crystal composition layer oriented to have a twist angle in a range of more than 270 degrees, a dichroic dye is added to the liquid crystal composition, and
A color liquid crystal display element is provided, which is characterized by disposing a color filter or a colored light source.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing a conventional liquid crystal display element and FIG. 2 is a sectional view showing an example of the structure of a liquid crystal display element according to the present invention. In the figure, 1.1', 11°11'
is the substrate, 2.2', 12 is the polarizer, 3.3', 13
．． 13' is a transparent electrode, 4.4' and 14.14' are alignment films, and 5. ■5 is a color filter, 6 and 16 are liquid crystals, 7
, 17 indicate sealants, respectively.

In the liquid crystal display element of the present invention, a first substrate 11 having a transparent electrode 13 on which an alignment film 14 is formed and which has been subjected to an alignment treatment, and a similar second substrate 11' are spaced apart and arranged facing each other. A liquid crystal cell is formed by sealing a liquid crystal 16 therebetween. Further, a color filter 15 is arranged in this liquid crystal cell, and a polarizing plate 12 is arranged outside the liquid crystal cell as required. Note that the display element of the present invention can perform display without essentially requiring a polarizer, and therefore can provide bright display. Contrast can be further improved using a polarizer.

The first substrate 11 and the second substrate 11' are subjected to alignment treatment so that the liquid crystal molecules are aligned substantially horizontally, and the liquid crystal molecules are preferentially aligned along the direction of the alignment treatment.

In this case, the nearly horizontal alignment of the liquid crystal molecules means that the tilt angle of the liquid crystal molecules with respect to the substrate is approximately 0 to 30 degrees.
say that it is within the range of The angle ω between the preferential alignment direction of liquid crystal molecules on the first substrate 11 and the preferential alignment direction of liquid crystal molecules on the second substrate 11' is in the range of 90<ω≦270°, preferably 160≦ω≦ 270°, and the liquid crystal molecules have a helical structure twisted at this angle between the peripheral substrates 11 and 11'. In this way, ω is the twist angle determined by the orientation treatment, and this orientation control can be performed by conventionally known oblique vapor deposition or by rubbing with a cotton cloth after forming an inorganic or organic film. Note that in order to prevent reverse rotation twist, it is preferable to add cholesteric liquid crystal or chiral nematic liquid crystal to the nematic liquid crystal. When the twist angle ω exceeds the above range, scattering structures are likely to occur when an electric field is applied, and when the twist angle ω is below the above range, the steepness decreases and the time-division drive characteristics deteriorate.

In the present invention, the liquid crystal 16 is doped with a dual dye having different light absorption coefficients in the long axis direction and the short axis direction of the molecule. In the present invention, it is preferable to use a dye having a large absorption coefficient in the direction of the long axis of the molecule, and when a voltage is applied, the color of the dye disappears and the color of the color filter 15 is displayed. The amount of the dye added is preferably selected so that the absorbance of the cell upon coloring is 0.5 to 3.

Most preferably, the maximum absorption wavelength of the added dye substantially matches the wavelength at which the intensity of the colored light passing through the filter is maximum. Further, when a plurality of filters are formed in the same cell to perform full color display, several types of dyes can be mixed to produce black. In the example shown in FIG. 2, the color filter is formed on the transparent electrode 13' inside the cell, but it may be formed between the substrate and the transparent electrode or on the outside of the substrate. Alternatively, a colored light source such as a light emitting diode or a fluorescent lamp may be placed outside the cell without using a filter.

The color filter can be formed by conventionally known dyeing methods, printing methods, vapor deposition methods, and the like.

As the dichroic dye in the present invention, conventionally known dichroic dyes, such as azo, anthraquinone, quinophthalone, naphthoquinone, and tetrazine dyes, can be used. These dyes can be added to the liquid crystal alone or as a mixture. In addition, the substrate may be anything that has translucency, such as glass or plastic.
Further, a thin film transistor or a nonlinear element may be formed on the substrate. In particular, when using an optically anisotropic substrate, a polarizing plate may not be used, or only one polarizing plate may be used, eliminating the need for complicated operations to reduce birefringence of the substrate, such as aligning the optical axis of the substrate. The degree of freedom in design can be increased.

〔effect〕

The liquid crystal cell of the present invention constructed as described above exhibits a steepness γ of 1.135, for example, when ω=zoo', and is capable of time-division driving with a duty of about 1764. This steepness is almost the same as the TN type, but the conventional G/
This is a significant improvement compared to the steepness of γ=1.7 in an H-type (twist 0°) color display liquid crystal element. Also,
Unlike the TN type, the spectral transmission characteristics do not depend on voltage, temperature, viewing angle, etc., so high-quality color display is possible.

Furthermore, since the liquid crystal display element of the present invention uses only one polarizing plate or does not require one, bright display is possible and the cost is low.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 As a liquid crystal composition, a nematic liquid crystal, a chiral nematic liquid crystal (manufactured by Merck & Co., Ltd., sgtt), and a mixed dye of anthraquinone and azo dichroic dyes were added at 0.00%, respectively.
Using 5% and 1.5% additives, the liquid crystal layer thickness was 9 μm.
A liquid crystal cell as shown in FIG. 2 was prepared. The alignment treatment was performed by rubbing the polyimide coated on the glass substrate so that the twist angle ω was 2006. 2 of this example
The color pigment is black when no voltage is applied. Note that color filters of three colors, red, green, and blue, were formed on the outside of the substrate by a printing method. The liquid crystal display element thus formed becomes black when a non-selection voltage is applied, and the color of the filter cannot be seen, but becomes transparent when a selection voltage is applied, and is capable of color display. Further, the color tone has little dependence on viewing angle, voltage, and temperature, and high time division driving of 1/64 to 1/100 duty was possible.

Comparative Example The same liquid crystal as shown in Example was used, the amount of chiral nematic liquid crystal added was 0.01%, and the twist angle was 90.
A liquid crystal cell with a color filter was manufactured in the following manner. This cell showed good shutter characteristics for non-selective blue and green light, but there was some red light leakage. By changing the cell thickness, the spectral transmission characteristics changed, but a perfect shutter effect could not be obtained. Additionally, the color tone changed depending on the viewing angle, voltage, and temperature.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example of the configuration of a conventional liquid crystal display element. FIG. 2 shows a cross-sectional view of the liquid crystal display element of the present invention. 1.1', 11.11'...substrate, 2.2', 12.
...Polarizer, 3.3'. 13.13'...transparent electrode, 4.4', 14.14'
...Alignment film, 5.15...Color filter, 6,
16...Liquid crystal, 7,17...Sealing agent.

Claims (1)

[Claims] (1) A pair of alignment-treated substrates having display electrodes, which are sandwiched between the substrates, are oriented substantially horizontally to the substrates when no electric field is applied, and liquid crystal molecules are arranged at an angle exceeding 90° between the substrates.
A color liquid crystal comprising a liquid crystal cell having a liquid crystal composition layer containing a dichroic dye oriented to have a twist angle in a range of 70° or less, and a color filter or a colored light source. display element.