JPH03111823A - Two-layer type stn liquid crystal display element - Google Patents

Abstract

PURPOSE:To make an excellent color display against wide-range temperature variation by using a liquid crystal material which is small in temperature dependency of refrac tive index anisotropy as the liquid crystal of a liquid crystal cell for color compensa tion and setting the product of the refractive index anisotropy of the liquid crystal and the liqiuid crystal layer thickness within a specific range. CONSTITUTION:The two-layer type STN liquid crystal display element which has the liquid crystal cell 2 for color compensation arranged on the light projection side of a liquid crystal cell 1 for display uses the liquid crystal material which is small in the temperature dependency of refractive index anisotropy DELTAn as the liquid crystal of the liquid crystal cell for color compensation and the value of the product DELTAn.d of the thickness (d) of the liquid crystal of the liquid crystal 1 for color compensation and the refractive index anisotropy DELTAn of the liquid crystal is made nearly constant irrelevantly to temperature variation. Consequently, even if the value DELTAn.d of the display liquid crystal cell varies with temperature, an excellent white display which is free from coloring is obtained. Further, the value DELTAn.d of the liquid crystal cell for color compensation and display liquid crystal cell 1 is set within the specific range to obtain an excellent black display.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a two-layer STN liquid crystal display in which an STN color compensation liquid crystal cell is disposed on the light incidence side or the light emission side of an STN display liquid crystal cell. It is related to the element.

[Conventional technology]

Recently, the number of display pixels of dot matrix liquid crystal display elements that display television images, etc. has become extremely large due to larger screens and higher resolutions. TN, which is required but has been widely used
When high-duty multiplex drive is applied to LCD-type LCD elements, the operating margin decreases, which reduces display contrast and worsens viewing angle characteristics.Recently, in order to improve multiplex drive characteristics, LCD An STN type liquid crystal display element has been developed in which the molecules are arranged in a twisted manner at a larger twist angle (180' to 270'') than a normal TN type liquid crystal display element.

However, in this STN type liquid crystal display element, the direction of the polarization axis (transmission axis or absorption axis) of the polarizing plate on the negative side is at a certain deviation angle (35 '~50＠), linearly polarized light incident through the input side polarizing plate is converted into elliptically polarized light by the birefringence of the liquid crystal layer, and the transmission of light is controlled by the other output side polarizing plate. The liquid crystal layer has a different refractive index anisotropy for light of each wavelength, so the transmittance of light in a specific wavelength range increases, causing coloring on the display screen. .

For this reason, a two-layer STN liquid crystal display element has been considered in the past, in which an STN color compensation liquid crystal cell is disposed on the light incidence side or the light emission side of an STN display liquid crystal cell.

This two-layer STN liquid crystal display element uses a color compensation liquid crystal cell to eliminate the coloring of the display that occurs in the above-mentioned STN type liquid crystal display element in its display liquid crystal cell. , except that there is no display electrode, the other configuration is the same as the display liquid crystal cell, and the liquid crystal molecules of this color compensation liquid crystal cell have the same twist angle in the opposite direction to the twist direction of the liquid crystal molecules of the display liquid crystal cell. It is arranged in a twisted manner. Conventionally, the same liquid crystal material as the liquid crystal of the display liquid crystal cell has been used as the liquid crystal of the color compensation liquid crystal cell, and the liquid crystal of one of the display liquid crystal cell and color compensation liquid crystal cell is made of this material. A levorotatory optically active substance (
The liquid crystal of the other cell is twisted clockwise by mixing a dextrorotating optically active substance therein, and the liquid crystal of the other cell is twisted clockwise by mixing a dextrorotating optically active substance therein. Further, the alignment directions of liquid crystal molecules on the adjacent substrate surfaces of the display liquid crystal cell and the color compensation liquid crystal cell are substantially perpendicular to each other.

According to this two-layer STN liquid crystal display element, the axes of the ellipse of the elliptically polarized light for each wavelength, which is caused by the optical rotation dispersion phenomenon of the liquid crystal layer of the display liquid crystal cell and the color compensation liquid crystal cell, almost coincide, so that a specific It is possible to eliminate discoloration of the display due to leakage of light in the wavelength range.

[Problem to be solved by the invention]

However, the conventional two-layer STN liquid crystal display element described above has a problem in that the displayed color in the white display state changes depending on the temperature. In other words, FIG. 5 shows that the twist angle of the liquid crystal molecular alignment of the display liquid crystal cell and the color compensation liquid crystal cell is 240'', and the Δnod of both cells at 25°C is
A chromaticity diagram showing changes in chromaticity with respect to temperature changes in a conventional two-layer STN liquid crystal display element whose value (product of refractive index anisotropy Δn of liquid crystal and layer thickness d of the liquid crystal layer) is 0.82. In the conventional two-layer STN liquid crystal display element, when the temperature is 25°C, the displayed color is near the white point (achromatic color point) C.
When the temperature is as low as 0° C., the displayed color becomes yellowish, and when the temperature is as high as 40° C., the displayed color becomes blueish.

This is because the refractive index anisotropy Δn of the liquid crystal changes depending on the temperature, and in conventional two-layer STN liquid crystal display elements, the same liquid crystal material as the liquid crystal of the display liquid crystal cell is used as the liquid crystal of the color compensation liquid crystal cell. Therefore, the Δn-d of both cells changes at the same rate at both high and low temperatures, but since the refractive index anisotropy Δn of the liquid crystal changes when the temperature changes, the refractive index anisotropy Δn of this liquid crystal Δn−d of both cells due to the change in
The value changes, and the display color changes accordingly. Figure 6 shows a two-layer STN liquid crystal display element in which the twist angle of the liquid crystal molecular alignment of the display liquid crystal cell and color compensation liquid crystal cell is 240@, and the value of Δnφd of both cells is 0.78 to 0.87.
This is a chromaticity diagram showing the results of examining changes in chromaticity in a white display state by varying the range of chromaticity.
The display color of the TN liquid crystal display element changes depending on the value of Δn−d of both cells.

The value of Δn-d for both cells is determined by the refractive index anisotropy Δn of the liquid crystals of both cells and the liquid crystal layer thickness d, so if the refractive index anisotropy Δn of the liquid crystals of both cells changes with temperature, This changes the value of Δna d in both cells, and this Δ
The display color changes depending on the value of nd.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide liquid crystal molecules of the STN type display liquid crystal cell on the light incident side or the light output side of the display liquid crystal cell. As a two-layer STN liquid crystal display element equipped with an STN color compensation liquid crystal cell in which liquid crystal molecules are twisted in a direction opposite to the twist direction, it can display a good white color without coloration even under a wide range of temperature changes. It's about giving what you can get.

[Means to solve the problem]

In order to achieve the above object, the two-layer STN liquid crystal display element of the present invention uses a liquid crystal material whose refractive index anisotropy has small temperature dependence as the liquid crystal of the color compensation liquid crystal cell, and the color compensation The value of the product Δn2・d2 of the refractive index anisotropy Δn2 of the liquid crystal and the liquid crystal layer thickness d2 in the liquid crystal cell for display, and the refractive index anisotropy Δn1 of the liquid crystal and the liquid crystal layer thickness d in the liquid crystal cell for display.
The value of the product Δn1・d with 1, Δn2・d2≦Δn +ed +≦Δn 2ad 2x
t, t.

The range is as follows.

[Effect]

That is, the two-layer STN liquid crystal display element of the present invention uses a liquid crystal material whose refractive index anisotropy has small temperature dependence as the liquid crystal of the color compensation liquid crystal cell. The value of Δn−d of the color compensation liquid crystal cell is set to be almost constant regardless of temperature changes.
If the value of is constant, the display color will not change even if the value of Δn-d of the display liquid crystal cell changes depending on the temperature, and a good white display without coloring can be obtained even under a wide range of temperature changes. Δn2ad2 of the liquid crystal cell for color compensation
and the value of Δn1・d of the display liquid crystal cell, Δn2・d2≦Δn, ad, ≦Δn z'd 2X
If the value is within the range of 1.10, good black display can be obtained.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 is a cross-sectional view of a two-layer STN liquid crystal display element of this embodiment, in which a color compensation liquid crystal cell is arranged on the light output side of a display liquid crystal cell.

This two-layer STN liquid crystal display element has two STN liquid crystal cells 1 and 2 stacked together, and polarizing plates 3 and 4 are provided on both sides of this cell stack, respectively. Among the cells 1゜2, the lower side (light incident side) in the figure is the liquid crystal cell 1 used for display, and the upper side (light output side) is used for display purposes.
The liquid crystal cell 2 is used for color compensation. Hereinafter, the liquid crystal cell 1 for display will be referred to as a display cell, and the liquid crystal cell 2 for color compensation will be referred to as a compensation cell.

The display cell 1 has a liquid crystal 13 sealed between a pair of transparent substrates 11 and 12 that are polymerized and bonded via a frame-shaped sealing material 10, and on the opposing surfaces of the side substrates 11 and 12, although not shown, Transparent electrodes for display (for example, scanning electrodes and signal electrodes in the case of a simple matrix type liquid crystal cell) are formed, and an alignment process is performed thereon. In addition, the compensation cell 2
, a liquid crystal 23 is sealed between a pair of transparent substrates 21 and 22 that are polymerized and bonded via a frame-shaped sealing material 20, and there are no display electrodes on the opposing surfaces of the side substrates 21 and 22, and no alignment treatment is performed. only. The alignment treatment of the side substrates 11.12 and 21.22 of the display cell 1 and compensation cell 2 is performed by rubbing the surface of a horizontal alignment film made of polyimide or the like.

FIG. 2 shows the orientation direction of liquid crystal molecules in the display cell 1 and the compensation cell 2 and the direction of the polarization axes of the polarizing plates 3 and 4.
In the figure, lla and 12a are the lower substrate 1 of the display cell 1.
The direction of alignment treatment on the first surface and the 12th surface of the upper substrate, TI indicates the twist direction of liquid crystal molecule alignment. The liquid crystal 13 of the display cell 1 is a nematic liquid crystal that has been given counterclockwise optical rotation by mixing a levorotatory optically active substance (chiral liquid crystal, etc.), and the molecules of this liquid crystal 13 are distributed between the side substrates 11° and 12°. , they are twisted counterclockwise when viewed from the traveling direction of the transmitted light (when viewed from the lower substrate 12 side) at a twist angle (240' in the figure) corresponding to the deviation angle of the alignment treatment directions 11a and 12a. . In addition, in FIG. 2, 21a
and 22. a indicates the alignment treatment direction of the lower substrate 21 surface and the upper substrate 22 surface of the compensation cell 1, and T2 indicates the twist direction of liquid crystal molecule alignment, and the alignment treatment direction 21a of the lower substrate 21 surface of the compensation cell 2 is indicated above. It is substantially perpendicular to the orientation treatment direction 12a of the upper substrate 12 surface of the cell 1. The liquid crystal 23 of this compensation cell 2 is a nematic liquid crystal that has been given clockwise optical rotation by mixing a dextrorotatory optically active substance (chiral liquid crystal, etc.), and the molecules of this liquid crystal 23 are distributed between both substrates 21 and 2.
2, they are twisted clockwise as viewed from the traveling direction of transmitted light at the same angle (24G@) as the twist angle of the liquid crystal molecular arrangement in the display cell 1. On the other hand, in FIG. 2, 3a and 4a are the polarization axis directions of a pair of polarizing plates 3 and 4, and the polarization axis direction 4a of the upper polarizing plate 4 is the direction of the polarization axis of the liquid crystal cell (compensation cell) 2 on the side of the upper polarizing plate 4. With respect to the alignment direction 22a of the upper substrate 22 surface, it is shifted clockwise by 35° to 50'' when viewed from the traveling direction of the transmitted light, and the polarization axis direction 3a of the lower polarizing plate 3 is the same as the polarization axis of the upper polarizing plate 4. It is substantially orthogonal to direction 4a.

Further, as the nematic liquid crystal 13 of the display cell 1, a liquid crystal material for an STN liquid crystal element, which is used for the display cell and the compensation cell in a conventional two-layer STN liquid crystal display element, is used. As the material, a liquid crystal material whose refractive index anisotropy Δn has small temperature dependence is used.

Note that the layer thicknesses (cell gaps) d+ and d2 of the liquid crystal layers of the display cell 1 and the compensation cell 2 are approximately the same, or the compensation cell 2 is slightly smaller.

The nematic liquid crystal 23 of the compensation cell 2, that is, the liquid crystal material whose refractive index anisotropy Δn has small temperature dependence, is C
A liquid crystal material with a wide temperature range that exhibits a nematic phase with -N point of 125°C or higher and N-1 point of 100°C or higher is suitable;
For example, a phenylcyclohexane liquid crystal. R3 is an alkyl group R2 is an alkyl group having 2 to 5 carbon atoms or an alkoxy group. A liquid crystal with a positive dielectric anisotropy Δ ε. For example, a phenylcyclohexane liquid crystal. 3 is carbon. An alkyl group having 2 to 5 carbon atoms, or a biphenyl liquid crystal, or 4R is an alkyl group having 2 to 5 carbon atoms.■ High temperature liquid crystal (liquid crystal with a high N-1 point) For example, a biphenyl liquid crystal, or Rh , Ry, Rs, and Rh can be obtained as a liquid crystal composition by mixing various liquid crystal compounds such as alkyl groups having 2 to 5 carbon atoms in appropriate proportions. Note that the compensation cell 2 does not have a driving voltage applied to its liquid crystal layer, and therefore the liquid crystal 23 of the compensation cell 2 is always in a twisted alignment state, so the liquid crystal 23 of the compensation cell 2 is an STN liquid crystal element. It is not limited to liquid crystal materials for use in other applications, but as long as it exhibits a nematic phase over a wide temperature range, it is possible to use liquid crystals with a wide temperature range, such as those used in TN liquid crystal display elements for automobiles (in this case, (The amount of optically active substance such as chiral liquid crystal mixed into the liquid crystal should be appropriately selected.)

Further, the value of the product Δn2·d2 of the refractive index anisotropy Δn2 of the liquid crystal 23 in the compensation cell 2 and the liquid crystal layer thickness d2, and the value of the product Δn2·d2 of the refractive index anisotropy Δnl of the liquid crystal 13 in the display cell 1 and the liquid crystal layer thickness d1. The value of the product Δn,・dl is Δn2・d2≦Δn , −d , ≦Δn2@d 2X
It is set in the range of 1.10.

This two-layer STN liquid crystal display element is driven for display by multiplex driving the display cell 1 at high duty, and coloring of the display in the display cell 1 is prevented by the compensation cell 2.

Figure 3 shows the change in light transmittance with respect to the drive voltage when the two-layer STN liquid crystal display element is multiplex driven at high duty. In the non-selected state, the display is black with light transmittance close to 0%, and in the selected state, the display is white with high light transmittance.

Therefore, in the two-layer STN liquid crystal display element of the above embodiment, the liquid crystal of the compensation cell 2 has a refractive index anisotropy Δ
Since a liquid crystal material with small temperature dependence of n is used, the value of Δn2ed2 of the compensation cell 2 is almost constant regardless of temperature changes.If the value of Δn2・d2 of the compensation cell 2 is constant, the display cell Even if the value of Δn,·dl of 1 changes with temperature, the displayed color does not change, and a good white display without coloration can be obtained even under a wide range of temperature changes.

That is, FIG. 4 shows that the value of Δn1·dl of display cell 1 is 0 for the two-layer STN liquid crystal display element of the above example.
．． This is a chromaticity diagram showing the results of examining changes in chromaticity in a white display state when changing from 78 to 0.87. Here, the twist angle of the liquid crystal molecular arrangement of display cell 1 and compensation cell 2 is 240" value of Δn2·d2 of compensation cell 2 is set to 0.
82 shows the chromaticity change of a two-layer STN liquid crystal display element.

As shown in this chromaticity diagram, if the value of Δn2·d2 of compensation cell 2 is constant, Δn, ad of display cell 1.

No matter how the value of C changes, the displayed color is always near the white point (achromatic color point) C. This means that the refractive index anisotropy Δn1 of the liquid crystal 13 of the display cell 1 changes due to temperature change,
This shows that even if the value of Δn1 dl of display cell 1 changes, the display color of the two-layer STN liquid crystal display element hardly changes. Therefore, the two-layer STN liquid crystal display element of the above example Accordingly, it is possible to obtain a good white display without coloration even under a wide range of temperature changes.

In addition, in the two-layer STN liquid crystal display element of the above embodiment, the value of Δn2 of the compensation cell 2 and the value of Δn1 of the display cell 1 are
・The value of dl is Δn2ad2≦Δn1・dl≦Δn 2'd 2X 1
．． 05, black display is also good in the no-voltage state and in the non-selected state.Therefore, according to the two-layer STN liquid crystal display element of the above embodiment, the black and white display is always good regardless of temperature changes. can be realized.

In addition, in the above embodiment, the value of Δn2·d2 of compensation cell 2 and the value of Δn,·dl of display cell 1 are expressed as Δ n 2ad 2≦Δ n , *d ,≦
Δn fd 2X is in the range of 1.05, but the values of Δn2 d2 and Δn, *d are as follows: Δn2ad2≦Δn + d, ≦Δn 2'd 2X
The twist angle of the liquid crystal molecular alignment of display cell 1 and compensation cell 2 may also be within the range of 180' to 2.
Any twist angle may be used as long as it is within the range of 70@.

Further, in the above embodiment, the compensation cell 2 is provided on the light output side of the display cell 1, but the compensation cell 2 may be provided on the light incidence side of the display cell 1.

〔Effect of the invention〕

The two-layer STN liquid crystal display element of the present invention uses a liquid crystal material with small temperature dependence of refractive index anisotropy as the liquid crystal of the color compensation liquid crystal cell, so that coloring remains stable even under wide temperature changes. In addition, the value of Δn2・d2 of the liquid crystal cell for color compensation and the value of Δn1・dl of the liquid crystal cell for display are set as follows: Δn2*d2≦Δn, ad, ≦Δn2 “d 2X
Since the value is within the range of 1.10, good black display can be obtained.

[Brief explanation of drawings]

Figures 1 to 4 show an embodiment of the present invention. Figure 1 is a cross-sectional view of a two-layer STN liquid crystal display element, and Figure 2 is a cross-sectional view of a display liquid crystal cell and a color compensation liquid crystal cell. FIG. 3 is a plan view showing the orientation direction of liquid crystal molecules and the direction of the polarization axis of the polarizing plate; FIG. 3 is a diagram showing changes in light transmittance with respect to driving voltage when a two-layer STN liquid crystal display element is multiplex driven at high duty; FIG. 4 is a chromaticity diagram showing changes in display color due to changes in Δn,·d of a display liquid crystal cell. Figure 5 is a chromaticity diagram showing changes in display color with respect to temperature changes in a conventional two-layer STN liquid crystal display element, and Figure 6 is a chromaticity diagram showing changes in display color with respect to temperature changes in a conventional two-layer STN liquid crystal display element.
FIG. 2 is a chromaticity diagram showing changes in display color due to changes in Δnod of a display liquid crystal cell and a color compensation liquid crystal cell in a liquid crystal display element. 1... Liquid crystal cell for display, 2... Liquid crystal cell for color compensation, 3゜4... Polarizing plate.

Claims (1)

[Claims] On the light input side or output side of the STN type display liquid crystal cell,
In a two-layer STN liquid crystal display element in which an STN type color compensation liquid crystal cell is arranged in which liquid crystal molecules are twisted in a direction opposite to the twist direction of the liquid crystal molecules of the display liquid crystal cell, the color compensation liquid crystal cell is As the liquid crystal, a liquid crystal material whose refractive index anisotropy has small temperature dependence is used, and the value of the product Δn_2・d_2 of the refractive index anisotropy Δn_2 of the liquid crystal and the liquid crystal layer thickness d_2 in the color compensation liquid crystal cell. , the value of the product Δn_1・d_1 of the refractive index anisotropy Δn_1 of the liquid crystal and the liquid crystal layer thickness d_1 in the display liquid crystal cell is expressed as Δn_2・d_1.
_2≦Δn_1・d_1≦Δn_2・d_2×1.10
A two-layer STN liquid crystal display element characterized in that the range of .