JPH01138536A - Liquid crystal display element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid crystal display element suitable for high-density display. [Conventional technology] Conventionally, by increasing the twist angle of liquid crystal molecules between both electrodes,
A super twist element (T
, J., 5chefferand J., Nehr.
ing, Appl, Phys, Lett,
45+1011021-1023 (19841) was known. However, in this method, the value of the product Δn-d of the birefringence Δn of the liquid crystal of the liquid crystal display element used and the thickness d of the liquid crystal layer is substantially between [1.13 and 1.2 μm (JP-A 1986-
No. 10720), good contrast was obtained only with specific combinations of hues, such as yellow-green and dark blue, bluish-violet and pale yellow, as display colors. As described above, since this liquid crystal display element could not perform black and white display, it had the disadvantage that it could not perform multicolor or full color display when combined with a microcolor filter. On the other hand, a method has been proposed that uses a similar method and sets the product Δn-d of the liquid crystal's birefringence and thickness to a small value of around 0.6 μm, thereby providing a display that is close to white and black. There is. (M, 5chadteL al', Ap
pl, Phys, LetL, 50(5),
+987°9.236) However, when this method is used, the display is dark, the maximum contrast is not very high, and the display is bluish, resulting in a lack of clarity. [9! [Problems to be Solved by Light] The purpose of the present invention is to eliminate the disadvantage of the above-mentioned characteristic color that the prior art had, to realize a display close to black and white, and, in particular, to achieve an excellent viewing angle characteristic. The object of this invention is to obtain a liquid crystal display element that is bright and has a high contrast ratio. Furthermore, attempts are being made to form a fine color filter inside or outside the cell to realize mono-color, multi-color, or full-color display, as previously achieved with a normal 90@twist twisted nematic (TN) element. 6 [Means for Solving the Problems 1] The present invention has been made to solve the above-mentioned problems. means for applying a voltage between a first liquid crystal layer made of a nematic liquid crystal having a positive dielectric anisotropy and containing an optically active substance, and transparent electrodes of upper and lower substrates sandwiching the first liquid crystal layer; Separately from the first liquid crystal layer, there is a second liquid crystal layer made of nematic liquid crystal containing an optically active substance, which is sandwiched between a pair of substrates having an alignment control film, and a pair of polarized light is provided on the outside of these liquid crystal layers. In the liquid crystal display element in which the plate is installed, the first liquid crystal layer is installed in front of the viewer, and the refractive index anisotropy Δn of the liquid crystal in the first liquid crystal layer and the thickness d of the liquid crystal layer are
The product Δn1·dI of the first liquid crystal layer and the second liquid crystal layer is 0.7 to 2.0 μm, and the long axis direction of the liquid crystal molecules adjacent to the second liquid crystal layer of the first liquid crystal layer and the first liquid crystal layer of the second liquid crystal layer The long axis direction of the liquid crystal molecules adjacent to the first liquid crystal layer is almost perpendicular to the long axis direction, and the twist angle of the liquid crystal molecules between the substrates sandwiching the liquid crystal layer is 200 to 30 in the first liquid crystal layer.
0°, and the second liquid crystal layer has a twist angle that is opposite to that of the first liquid crystal layer and is approximately the same, and the polarizing axes of a pair of polarizing plates placed outside these two liquid crystal layers. The direction of the polarization axis of the polarizing plate, which is arranged so that the intersection angle is 60 to +20 degrees, and which is placed in front of the viewer, is relative to the long axis direction of the liquid crystal molecules closest to the viewer. 1st
If the helical direction of the first liquid crystal layer is left helix, shift it clockwise, and if the first liquid crystal layer has a right helix, shift it by 30 to 6 [1"] counterclockwise. The present invention provides a liquid crystal display element characterized in that the liquid crystal layer is arranged in two layers.
The liquid crystal cell has the same structure as the liquid crystal cell of the conventional super twist liquid crystal display element, and has electrode groups facing each other, so that it is possible to control on/off for each dot. The twist angle of this first liquid crystal layer is approximately 200 to 300
It is said to be ゛. Specifically, a nematic liquid crystal with positive dielectric anisotropy containing an optically active substance is sandwiched between a pair of transparent electrode substrates arranged approximately parallel to each other, and the twist angle of the liquid crystal molecules between the two electrodes is set to 2.
It should be 00~300@. In the present invention, a second liquid crystal layer is laminated adjacent to the first liquid crystal layer. This second liquid crystal layer may be a nematic liquid crystal layer having approximately the same twist angle as the first liquid crystal layer and the opposite helical direction.The substrates on both sides of this second liquid crystal layer include: An electrode may or may not be formed. Here, the first liquid crystal layer is placed in front of the viewer. This means that the first liquid crystal layer is placed on the viewer's side, and the second liquid crystal layer is placed on the viewer's side.
There is no difference when viewed from the front compared to when the display is placed under the liquid crystal layer, but when viewed from a low viewing angle, the contrast ratio decreases less and the display has excellent viewing angle characteristics. This is because it can be obtained. Further, the long axes of adjacent liquid crystal molecules in one liquid crystal layer are arranged to be substantially perpendicular to each other. That is, the long axis direction of liquid crystal molecules in the first liquid crystal layer adjacent to the second liquid crystal layer and the long axis direction of liquid crystal molecules in the second liquid crystal layer adjacent to the first liquid crystal layer are approximately perpendicular to each other. Specifically, when configuring a two-layer liquid crystal layer with three substrates, the orientation treatment direction of the central substrate may be orthogonal on both surfaces; In the case of using a single substrate, the orientation processing directions of the two intermediate substrates to be stacked may be orthogonal to each other. The nematic liquid crystal used for this second liquid crystal layer is
When electrodes are not provided on the substrates that sandwich the liquid crystal layer, there is no need to electrically control the direction of molecular alignment, so the liquid crystal can be used even if the dielectric anisotropy is not positive. Also,
When using a liquid crystal display element by applying a voltage to the electrodes of the substrates sandwiching this second liquid crystal layer, the liquid crystal of the second liquid crystal layer is also a nematic liquid crystal whose dielectric anisotropy is positive. use. In the present invention, the product Δn-d of the refractive index anisotropy (Δn) of the liquid crystals of the first liquid crystal layer and the second liquid crystal layer and the thickness (d) of the liquid crystal layer is determined as follows. In the first liquid crystal layer, Δnl 6 d+ = 0.7 to 2.0
It is assumed to be μm. This is because if the thickness is less than 0.7 μm, it is not possible to obtain a sufficient viewing angle range and transmittance in which one display of negative/positive is not reversed. Also, if it exceeds 2.0μm,
This is because even if the arrangement of the polarizing plates is adjusted, a slight yellowish tinge remains in the background color, and sufficient transmittance cannot be obtained. In particular, in applications where wide viewing angles and achromatic display colors are strictly required, Δn1·dl of the first liquid crystal layer should be 0.8 to 0.8.
The thickness is preferably 1.5 μm. Note that this range of Δn2·dt is preferably satisfied within the operating temperature range of the liquid crystal display element, and a beautiful display can be obtained within the operating temperature range. Due to extreme performance requirements, only in a portion of the operating temperature range,
It is possible that this relationship may be satisfied. In this case, in a temperature range in which the range of Δn1·dn deviates from the above range, the display becomes colored and the viewing angle characteristics deteriorate. In the second liquid crystal layer, Δn8・da is the average tilt angle θ of the liquid crystal molecules with respect to the plane parallel to the liquid crystal layer when a non-selection voltage or selection voltage during time-division driving is applied to the first liquid crystal layer. The square of the cosine of the average θXI in the thickness direction (cos2(
Product Δn1 of θx, )) and Δn,・dn of the first liquid crystal layer
・d+-cos2(θx2) and the average θs in the thickness direction of the liquid crystal layer of the tilt angle θ3 of the liquid crystal molecules of the second liquid crystal layer with respect to the plane parallel to the liquid crystal layer during use, the square of the cosine (
cos” (θXo)) and Δn8・d of the second liquid crystal layer
2 and the product Δn2·d2·cos2(θx2) are made approximately equal. That is, the following is satisfied. That is, if the non-selective voltages applied during time-division driving to the first liquid crystal layer are made almost equal, the average tilt angle in the thickness direction of the first liquid crystal layer in this state is θ. , and is made to satisfy . In this state, the liquid crystal display element exhibits a so-called negative display in which the portion of the first liquid crystal layer to which the selective voltage is applied is white and light passes through it, and the other portions are black. Furthermore, if the selection voltages for time-division driving are applied to the first liquid crystal layer to be approximately equal, the average tilt angle in the thickness direction of the first liquid crystal layer in this state is θ81. Yes, and will be made to satisfy. In this state, in this liquid crystal display element, the portion of the first liquid crystal layer to which the selective voltage is applied becomes black, and the other portions are white and light passes through, resulting in a so-called positive display. Here, in the case of a type in which no voltage is applied to the second liquid crystal layer during use, the liquid crystal molecules in the second liquid crystal layer lie almost horizontally, so Δn1·d3 of the second liquid crystal layer is Δn1−d1・cos” (θXI) of the first liquid crystal layer
It suffices if it is made to be approximately equal to . That is, in the case of negative display, Δn1·d of the second liquid crystal layer
s is Δn1-dl-CO83(θII
) may be made to be approximately equal to. Specifically, when Δn,·dl is in the range of 0.7 to 2.0 μm, when the first liquid crystal layer is driven at a duty of 17600 or less, the Δn2·d of the second liquid crystal layer is equal to the first It is preferable to make it 1 to 20% smaller than Δn1·dt of the liquid crystal layer because a display element with good display quality can be obtained.
In particular, Δn2・d2 of the second liquid crystal layer is set to Δn2·d2 of the first liquid crystal layer.
It is preferable to make it 3 to 15% smaller than n1-dn. Conversely, in the case of positive display, Δna”d of the second liquid crystal layer
a is Δn1・dl-CO82(θ1) of the first liquid crystal layer
It suffices if it is made to be approximately equal to . Specifically, when the first liquid crystal layer is driven at a duty of 17,600 or less, the range T of Δn2・dn is 0.7 to 2.0 μm, and the second liquid crystal layer Δn,・d3 is the first liquid crystal layer. It is preferable to make Δn3·d2 of the second liquid crystal layer 25 to 90% smaller than dn of the first liquid crystal layer because a display element with good display quality can be obtained. It is preferable to make it 30 to 75% smaller than Δn+−d+. Further, it is also possible to use the second liquid crystal layer by applying a voltage during use. In this type of case, the dielectric anisotropy of the nematic liquid crystal used in the second liquid crystal layer is positive. Furthermore, Δns of the second liquid crystal layer when no voltage is applied. 'da is ΔrL+-dx of the first liquid crystal layer' cos2
(θx+). In order to apply a voltage to the second liquid crystal layer, transparent electrodes are formed on the surfaces close to the liquid crystal layer of the upper and lower substrates that sandwich the second liquid crystal layer, and a means for applying a voltage between these transparent electrodes is provided. establish. By applying a voltage between the transparent electrodes on both sides of the second liquid crystal layer, the liquid crystal molecules in the second liquid crystal layer are allowed to evaporate to some extent. This applied voltage is usually a non-selection voltage or a selection voltage driven in a time-division manner. This is because the non-selective voltage or selective voltage used to drive the first liquid crystal layer can be easily obtained and can be used for other purposes. The voltage may be as follows. As a result, the liquid crystal molecules of the second liquid crystal layer rise considerably, creating an inclination angle θ3 with respect to a plane parallel to the liquid crystal layer. In order to perform positive display, the product Δn,・dn・cos2(
θxi2 is Δn+ when the selection voltage is applied to the first liquid crystal layer
It is sufficient if it is made approximately equal to "d+·cos" (θ8.). As a result, when a selection voltage is applied to the first liquid crystal layer, the linearly polarized light incident perpendicularly to the liquid crystal display element becomes almost completely linearly polarized light regardless of the wavelength even after passing through the two liquid crystal layers. By placing the polarizing plate on the observer side substantially perpendicular to the polarization direction of the transmitted light, the transmittance of that light can be made almost zero. On the other hand, when a non-selective voltage is applied to the first liquid crystal layer, the above-mentioned relationship regarding Δr++・d+−cos2(θx,) is broken, so the polarization state of the transmitted light is an ellipse whose principal axis direction differs depending on the wavelength. The light becomes polarized and the transmitted light is observed. In this way, the transmittance can be made close to 0 when selecting,
Since light passes through when not selected, a positive liquid crystal display element with a high contrast ratio can be obtained. moreover,
The above relationship is satisfied if the polarization axes of the pair of polarizing plates are substantially orthogonal, so the transmission when a non-selective voltage is applied to the first liquid crystal layer with the polarization axes of the pair of polarizing plates substantially orthogonal By setting the polarization axes of the pair of polarizing plates in the direction where the light is more effectively achromatic, a nearly black and white display can be obtained. Similarly, when performing a negative display, the square of the cosine of the average Ox+t in the thickness direction of the liquid crystal layer (cos2(
Product Δns of θx2)) and Δn8・dn of the second liquid crystal layer
” dm'cos2(θxs) may be made approximately equal to Δn1·d+−cos2(θ)l) when a non-selective voltage is applied to the first liquid crystal layer. The twist angle is said to be approximately 200 to 300 degrees. This is because if it is less than 200 degrees, there will be little improvement in contrast when time-division driving is performed at high duty;
This is because domains are likely to occur if the temperature exceeds °. The twist angle of the second liquid crystal layer is approximately equal and opposite to the twist angle of the first liquid crystal layer. If the difference is about ±20°, there is no need to make any special changes.
You can get the same effect as Habo. Note that in the case where a difference is made between the twist angle of the first liquid crystal layer and the twist angle of the second liquid crystal layer. By adjusting the intersecting angle of the alignment directions of both sides of the substrate at the center of Δn-dn, the intersecting angle of the polarizing axes of the polarizing plate, etc., it is possible to obtain a display close to black and white. Specifically, when the twist angle of the second liquid crystal layer is made small, Δn3・
If d2 is made a little larger and the twist angle of the second liquid crystal layer is made larger, Δn2・dn of the second liquid crystal layer is made a little smaller, and the intersection angle of the alignment directions on both sides of the central substrate is made a little smaller. By optimizing the angle of intersection of the polarization axes of the polarizing plates by shifting them from orthogonality, a black-and-white display with a contrast similar to that of the present invention, although inferior to that of the present invention, can be achieved. Furthermore, by making the nematic-isotropic phase transition temperatures (T, I) of the liquid crystals in the first liquid crystal layer and the second liquid crystal layer approximately equal, the refractive index anisotropy (Δn) of both liquid crystals can be increased. It is possible to make the temperature dispersion of the images almost equal, and a black-and-white display with a high foot-last ratio can be obtained over a wide temperature range. These two liquid crystal layers may be sandwiched between substrates on each side, and four substrates may be used to form two liquid crystal cells, and these may be stacked and used, or three substrates may be used. Alternatively, two liquid crystal layers may be sandwiched between them. In the present invention, the second liquid crystal layer does not need to have an electrode, and even if it is formed, it can be a solid electrode, so problems such as alignment do not occur, so three substrates can be easily used. It is possible to sandwich two liquid crystal layers. In the present invention, a pair of polarizing plates is placed outside these two liquid crystal layers. The polarization axes of these pair of polarizing plates are arranged to be almost perpendicular to each other, but the optimum angle of attachment depends on the value of Δn-d of the I and second liquid crystal layers and the degree of alignment thereof. Therefore, in reality, the crossing angle of the polarization axes can be varied in the range of 60 to +20 degrees for optimization. Therefore, the difference between Δn-d and cos'' (θ If the product values are matched, it is preferable that the polarization axes of the pair of polarizing plates are arranged orthogonally, and a display that is closer to black and white and has a high contrast ratio can be obtained. If the direction of the polarization axis of the polarizing plate installed on the front side is left-handed with respect to the long axis direction of the liquid crystal molecules closest to the viewer, the helical direction of the first liquid crystal layer is left-handed. If the helical direction of the first liquid crystal layer is right-handed, the first liquid crystal layer is shifted counterclockwise by 30 to 60 degrees. In particular, it is preferably shifted by 35 to 55 degrees. For the polarizing plate, the intersection angle between the polarizing plate on the front side and the polarization axis is 60~
1201 is preferable. In particular, Δn-d and cos'' (θ
As mentioned above, it is preferable that the polarization axes of these polarizing plates are arranged to be substantially perpendicular to each other as long as the value of the product with X) matches. This may occur if the deviation of the polarization axis of the front polarizing plate from the long axis direction of the liquid crystal molecules is smaller than 30° or 60°.
This is because if the value exceeds 1, the transmittance of the segment to which the non-selective voltage is applied will not be sufficiently obtained, resulting in a dark display as a whole. Further, in such a case, there arises a problem that the hue of the display becomes more yellowish or bluish, making it impossible to obtain an achromatic color. Therefore, the direction of the polarization axis of the polarizing plate placed in front of the viewer is a left-handed helical direction of the first liquid crystal layer with respect to the long axis direction of the liquid crystal molecules closest to the viewer. If the helical direction of the first liquid crystal layer is right-handed, the first liquid crystal layer is shifted by 30 to 60 degrees counterclockwise. Here, even when the pair of polarizing plates are rotated by 90 degrees and the direction of deviation of the polarization axis with respect to the liquid crystal molecules is set in the opposite direction, no optical difference is observed when observed from the normal direction. However, in this case, there is a disadvantage in terms of viewing angle characteristics, so the above-mentioned configuration is preferable in order to obtain a monochrome display with excellent viewing angle characteristics. The relative positions of the long axes of the liquid crystal molecules and the polarization axes of the polarizing plates in the liquid crystal display element of the present invention when no voltage is applied are shown in FIGS. 1 and 2. FIG. 1 is a perspective view schematically showing a liquid crystal display element according to the present invention, and FIGS. 2(A) and 2(B) respectively show the first liquid crystal cell on the upper side of FIG. It is a plan view showing the relative positions of the length of the liquid crystal molecules in the lower second liquid crystal cell in the +i+h direction and the polarizing axes of the adjacent polarizing plates. The first liquid crystal cell 4, which specifically displays characters, etc. by applying a voltage, is a second liquid crystal cell in which no voltage is applied, or a solid electrode is provided, and a voltage is applied to the whole. The polarizing axis of the polarizing plate 1, 6 the polarizing axis of the lower polarizing plate 2, 7 the long axis direction of the liquid crystal molecules on the upper side of the first liquid crystal cell, and 8 the longitudinal direction of the liquid crystal molecules on the lower side of the first liquid crystal cell. In the long axis direction, 9 indicates the long axis direction of the liquid crystal molecules on the upper side of the second liquid crystal cell, and 10 indicates the long axis direction of the liquid crystal molecules on the lower side of the second liquid crystal cell. The long axes of adjacent liquid crystal molecules in the layer are approximately orthogonal, that is, the long axis direction 8 of the liquid crystal molecules on the lower side of the first liquid crystal cell and the long axis direction 9 of the liquid crystal molecules on the upper side of the second liquid crystal cell are substantially perpendicular to each other. The angle ψ formed is approximately 90@. Also, as in this example, it is preferable that the polarization axes 5.5 of the pair of polarizing plates are approximately perpendicular to each other.Furthermore, in this case, the upper The polarization axis 5 of the polarizing plate l is α in the counterclockwise direction with respect to the long axis direction of the liquid crystal molecules closest to the observer, that is, the long axis direction 7 of the upper liquid crystal molecules in the upper first liquid crystal cell 3. = are arranged in a direction that makes an angle of approximately 50°,
The polarizing axis 6 of the lower polarizing plate 2 is arranged in a direction substantially perpendicular to the polarizing axis 5 of the upper polarizing plate l. That is, the polarization axis 6 of the lower polarizing plate 2 is similarly rotated counterclockwise with respect to the long axis direction lO of the liquid crystal molecules furthest from the observer.
In the present invention, this angle α is arranged in a direction shifted by 0°. and α2 is 30 to 60°. In the present invention, the first liquid crystal layer and the second liquid crystal layer are made to satisfy the above formula ( ). As a result, this liquid crystal display element is capable of black and white display with excellent viewing angle characteristics and a high contrast ratio. Further, in the above example, the first liquid crystal layer disposed on top is a right-handed spiral, and the second liquid crystal layer disposed below is a left-handed spiral, but the combination of upper and lower spirals may be reversed. FIGS. 3 and 4 show cross-sectional views of specific examples of the present invention. FIG. 3 shows an example in which the second liquid crystal layer is not provided with electrodes. In FIG. 3, 21 is a first liquid crystal cell of 200 to 300@twist that performs a concrete display by applying a voltage;
2 shows a second liquid crystal cell with reverse twist for correcting elliptical polarization. 23a, 23b are substrates made of plastic, glass, etc. that constitute the first liquid crystal cell; 24a, 24b are ITO (Inm0*-SnOm) formed on the inner surface;
Transparent electrodes such as SnOm, 25a, 25b are alignment control films formed by rubbing polyimide, polyamide, etc. films, or obliquely depositing %SiO, etc., 26a, 26
b is Ti0m, 5ins, Ale, which is provided between the transparent electrode and the alignment controlling a film as necessary to prevent short circuit between the substrates.
's etc. insulating film, 27a is these two substrates 24a,
A sealing material for sealing the periphery of 24b, 28a indicates a nematic liquid crystal with positive dielectric anisotropy sealed therebetween, and the alignment treatment direction of the alignment control films 25a and 25b and the pitch of the liquid crystal are 200 to 300. °It is designed to be twisted. 23c and 23d are substrates constituting the second liquid crystal cell;
5c, 25d are alignment control films, 27b is a sealing material, 28
b shows the nematic liquid crystal sealed between them,
The alignment treatment direction of the alignment control films 25c and 25d and the pitch of the liquid crystal are twisted in the opposite direction to that of the first liquid crystal layer, so that the twist angle is substantially the same. In this example,
Since no voltage is applied to the second liquid crystal cell, there is no need to sharpen the threshold characteristics of the liquid crystal, and there is no need for a high tilt angle as required for normal super twist liquid crystal display elements. The long axis direction of the liquid crystal molecules on the second liquid crystal cell side of the first liquid crystal cell and the long axis direction of the liquid crystal molecules on the first liquid crystal cell side of the second liquid crystal cell are respectively arranged so that they are substantially perpendicular to each other. Oriented. A pair of polarizing plates 29a are provided outside these two liquid crystal layers,
29b is arranged, and the intersection angle of their polarization axes is set to 60~+
20@, preferably arranged substantially orthogonally. In particular, the direction of the polarization axis of the polarizing plate 29a installed on the front side with respect to the viewer, that is, installed on the upper side in this figure, is the long axis direction of the liquid crystal molecules of the alignment control film 25a closest to the viewer. 30 to 60' clockwise when the first liquid crystal layer has a left-handed spiral, and 30 to 60' counterclockwise when the first liquid crystal layer has a right-handed spiral. It is arranged so that it is installed offset by a certain amount. In this case, by making the polarization axes of the pair of polarizing plates almost orthogonal, the polarizing plate 2 on the back side
The orientation control film 25 whose polarization axis direction 9b is farthest from the observer
It will also be placed offset by 30 to 60 degrees clockwise or counterclockwise with respect to the long axis direction of the liquid crystal molecules of d. 30 is a drive circuit which is means for applying voltage to the first liquid crystal cell, and 31 is a light source. In this example, since no voltage is applied to the second liquid crystal cell, no transparent electrode or insulating film is formed, and no drive circuit is provided. In this case, since no voltage is applied to the second liquid crystal layer during use, the second liquid crystal layer 6, d. is Δn1・dn・c of Σ when a non-selective voltage is applied to the first liquid crystal layer (negative display) or when a selective voltage is applied (positive display).
og"(θx'+). In FIG. 4, electrodes are also provided on the second liquid crystal layer, and a certain voltage is applied during use. An example is shown. In Fig. 4, 41 is a first liquid crystal cell with a twist of 200 to 300°, which performs a concrete display by applying a voltage;
2 shows a second liquid crystal cell with reverse twist for correcting elliptical polarization. 43a and 43b are plastic, glass, etc. substrates constituting the first liquid crystal cell; 44a and 44b are ITO (10101-Sn01) formed on the inner surfaces thereof;
Transparent electrodes such as 5n01, 45a, 45b are alignment control films 46a, 46b formed by rubbing a film of polyimide, polyamide, etc., or diagonally depositing Si ports, etc.
TiO□, Sio, ^18o1 are provided between the transparent electrode and the alignment control film as necessary to prevent short circuit between the substrates.
The insulating films 47a are these two substrates 44a, 44.
A sealing material 48a for sealing the periphery of b indicates a nematic liquid crystal with positive dielectric anisotropy sealed therebetween, and the alignment treatment direction of the alignment control films 45a and 45b and the pitch of the liquid crystal are 200 to 300. 43c and 43d are substrates constituting the second liquid crystal cell;
4c, 44d are solid transparent electrodes, 45c, 45
d is an alignment control film; 46c and 46d are insulating films provided as needed; 47b is a sealing material; 48b is a nematic liquid crystal with positive dielectric anisotropy sealed therebetween; The orientation process direction of 45d and the pitch of the liquid crystal are twisted in the opposite direction to that of the first liquid crystal layer so that the twist angle is approximately the same. In this example, voltage is applied to the second liquid crystal cell, but since it does not turn on and off finely, if the liquid crystal has a sharp threshold characteristic, Δn8・d2・cos” (θx, l
Since the voltage margin for adjusting the voltage is small, a high tilt angle as required for a normal supertwist liquid crystal display element is not necessarily required. The long axis direction of the liquid crystal molecules on the second liquid crystal cell side of this first liquid crystal cell is aligned in the same direction as the first direction of the second liquid crystal cell. A pair of polarizing plates 49a are provided outside these two liquid crystal layers,
49b is arranged, and the crossing angle of their polarization axes is set to 60~1
20 degrees, preferably substantially orthogonal. In this example as well, the direction of the polarization axis of the polarizing plate 49a, which is installed on the front side with respect to the viewer, that is, on the upper side in this figure, is the closest to the viewer. If the helical direction of the first liquid crystal layer is left helical with respect to the long axis direction, clockwise, and if the first liquid crystal layer has a right helical helical direction, counterclockwise. They are installed offset by 3a to 60°. In this case, by making the polarizing axes of the pair of polarizing plates almost orthogonal, the polarizing plate 4 on the back side
The orientation control film 45 whose polarization axis direction 9b is farthest from the observer
It will also be installed to be shifted clockwise or counterclockwise by 3D to 50 degrees with respect to the long axis direction of the liquid crystal molecules of d. 50a and 50b are drive circuits which are means for applying voltage to the first liquid crystal cell and the second liquid crystal cell, respectively; and 51 is a light source. In this case, since a voltage is applied to the second liquid crystal layer during use, Δn,・dn・
cos” (If θxs2 is a positive display, Δn,・dl・cos” of the first liquid crystal layer when the selection voltage is applied)
θ31), and in the case of negative display, Δn1・dl−cog2 of the first liquid crystal layer when a non-selected voltage is applied.
(θ3.). The voltage applied to this second liquid crystal is 80·d and cot
It is sufficient if the voltage makes the product of (θ The substrate constituting the first liquid crystal cell may be any optically isotropic transparent substrate, and glass, plastic, etc. may be used. The electrodes are formed, and display is performed by turning on and off the liquid crystal by applying a voltage between the desired electrodes.These electrodes are usually transparent electrodes such as ITO, SnO, etc., and as necessary. AI combined with
Low resistance leads such as Cr and Ti can be used and desired patterning can be achieved. A typical example of this is a dot matrix liquid crystal display device in which a large number of electrodes are formed in rows and columns, with 640 stripe-like electrodes formed on one substrate and stripes perpendicular to these electrodes on the other substrate. 400 strip-shaped electrodes are formed, 640 x 400
A dot-like display will appear. As a treatment for aligning liquid crystal molecules, known rubbing methods, oblique evaporation methods, etc. can be used, and if necessary, S is applied on the electrodes.
The orientation treatment may be performed after forming an insulating film of an inorganic material such as iO□, Tin, or A11as to prevent short circuits and/or a film of an organic material such as polyimide or polyamide. Note that in the present invention, since a display close to black and white can be obtained, a colorful display can be achieved by using a color filter in combination. In particular, it is possible to achieve a high contrast ratio even with high duty driving. Full-color gradation display is also possible, and it can also be used on LCD televisions. By forming this color filter on the inner surface of the cell, more precise color display is possible without causing deviation due to viewing angle. Specifically, it may be formed below the electrode or above the electrode. In particular, since the present invention enables bright display, it can be applied to either a transmissive type or a reflective type, and has a wide range of applications. In the above description, four substrates were used to constitute the two liquid crystal layers, but it is clear that one substrate may be used instead of the two intermediate substrates. Furthermore, if it is necessary to completely convert the color to black and white, a color filter for correcting one color may be used in combination, or illumination having a specific wavelength distribution may be used. When performing positive display, the liquid crystal display element of the present invention is often used as a 5-reflection type because it displays black on a white background, but it can also be used as a transmission type. Conversely, when performing negative display, the display is white on a black background, so a transmissive type is often used, but a reflective type can also be used. When used as a transmissive type, the contrast ratio of the display can be increased by covering the background portion other than the pixels with a light-shielding film formed by printing or the like. Furthermore, in addition to using a light-shielding film, it is also possible to perform reverse driving so as to apply a selection voltage to a portion that is not desired to be displayed. In addition to this, the present invention includes, within the scope that does not impair the effects of the present invention,
Various techniques used in ordinary liquid crystal display elements can be applied. [Operation 1] Although the principle of operation of the present invention is not necessarily clear, it can be estimated as follows. That is, when a selective voltage is applied to the first liquid crystal layer, when light that is almost completely linearly polarized through the polarizing plate is transmitted through the first liquid crystal layer, it becomes elliptical polarized light. However, by transmitting this elliptical polarized light through the first liquid crystal layer, the state of the elliptical polarized light can be approximated to that of linearly polarized light before entering the second liquid crystal layer. In this case, the first liquid crystal layer and the second liquid crystal layer are in opposite directions and have approximately the same twist angle, and in the second liquid crystal layer, Δn−d3 is time-divisionally driven to the first liquid crystal layer. Δn+−dt' cos2(θs,
) and Δn3・d3・of the second liquid crystal layer during use.
By making cos2(θxs) almost equal, the light is almost completely returned to linear polarization. Such an effect when using a two-layer liquid crystal layer as shown in the present invention can be achieved by laminating media such as thin layers having optical uniaxial anisotropy so that their front axes are perpendicular to each other. This is based on the fact that the apparent anisotropy is lost if the By arranging the polarization axis of the output side polarizing plate in a direction perpendicular to the polarization axis of the input side polarizing plate for the output light that has been returned to almost linearly polarized light in this way, the transmitted light is absorbed.
Turns black. On the other hand, in a state where a non-selective voltage is applied to the first liquid crystal layer or a state where no background voltage is applied, the first
The alignment of the liquid crystal molecules in the liquid crystal layer changes, and the light that has passed through both liquid crystal layers passes through the polarizing plate placed on the output side. part) or the background part becomes white, resulting in a positive type display with display colors of white and black. Also, based on the same principle, Δn□・dn of the second liquid crystal layer
・cos” (θxt) is Δn+ ”d+・co when a non-selective voltage is applied during time-division driving of the first liquid crystal layer
s” (θ, 1) and Δ of the second liquid crystal layer during use.
A black and white negative display can be obtained by making n2·dn·cos2(θxt) approximately equal. Furthermore, in the present invention, Δn of the liquid crystal in the first liquid crystal layer
By setting 1·d+ to 0.7 to 2.0 μm, a display with excellent viewing angle characteristics can be obtained. As a result, while conventional super-twist liquid crystal display elements showed good contrast only in specific combinations of hues such as yellow-green and dark blue, bluish-purple and light yellow, the present invention provides bright and clear black and white display. Furthermore, display with a high contrast ratio and excellent viewing angle characteristics is possible. In the present invention, the time division characteristics are on the same level as those of super twist liquid crystal display elements, and as mentioned above, bright and clear black and white display is possible. Therefore, fine color filters of the three primary colors of red, green, and blue are installed on the inner surface of the cell, etc. By arranging them, it is possible to obtain a high-density multicolor liquid crystal display element. The liquid crystal display element of the present invention can be used for personal computers,
It is suitable as a display element for word processors, workstations, etc., but it is also suitable for external liquid level TVs, fish finders, etc.
It can be used for a variety of purposes, including radars, oscilloscopes, and various consumer dot matrix display devices, regardless of black and white display or color display.

[Example]

Next, embodiments of the present invention will be described in detail using the drawings. Example 1 TTO provided on a glass substrate as the first substrate
A substrate was used in which a transparent electrode was patterned into stripes, a 5-ins insulating film for short circuit prevention was formed by vapor deposition, a polyimide overcoat was spin-coded, and an alignment control film was formed by rubbing this. . As a second substrate, the ITO transparent electrodes provided on the first substrate and the glass substrate were patterned into stripes so as to be orthogonal to the first substrate, and a 5-ins insulating film was formed. Apply a polyimide overcoat and add this to 1.
An alignment control film is formed by rubbing at an angle of 60° with the rubbing direction of the second substrate, and a polyimide overcoat is applied to the back side where no electrodes are formed, and this is applied in the rubbing direction on the front side. A substrate on which an alignment control film was formed by rubbing in a direction perpendicular to that was used. As the third substrate, we used a simple glass substrate with no electrodes formed on it, and overcoated it with polyimide.
A substrate on which an alignment control film was formed by rubbing this was used. The peripheries of these three substrates were sealed with a sealant to form two layers into which liquid crystal was injected. Nematic liquid crystals with positive dielectric anisotropy and opposite twists are injected into the first liquid crystal layer where the ITo electrodes patterned in stripes face each other and the second liquid crystal layer where no opposing electrodes are formed. The injection port was sealed. At this time, the first liquid crystal layer was a right-handed spiral with a 240° twist, and the second liquid crystal layer was a left-handed spiral with a 240° twist. That Δ
n-d is Δn,・dn=0.80μ in the first liquid crystal layer
m, and in the second liquid crystal layer Δnx-d*=0.75.
It was um. A pair of polarizing plates were placed on both sides of this liquid crystal cell so that their polarization axes were perpendicular to each other. At this time, the polarization axis of the polarizing plate placed in front of the viewer was shifted by 45° counterclockwise with respect to the long axis direction of the liquid crystal molecules closest to the viewer. When this liquid crystal display element was driven at 1/200 duty and 1/15 bias with a backlight made of cold cathode discharge tube material placed on the back side, a clear black and white display with excellent viewing angle characteristics was obtained. At this time, the segment corresponding to the non-selection voltage was white, and the segment corresponding to the selection voltage was black, which was a so-called positive display, and the contrast ratio was about 30. Furthermore, when the voltage waveform applied to the first liquid crystal layer of this liquid crystal display element was set as a 1001 (z rectangular wave) and the voltage versus transmittance was measured, the transmittance in the state where the non-selective voltage was applied was 29%. This is considerably higher than 19%, which is the result measured for an OMI element that is capable of displaying relatively close to black and white, and it was found that the liquid crystal display element of the example of the present invention is capable of bright display. In addition, as a comparative example, a liquid crystal display element was created in the same manner as in Example 1, except that the first liquid crystal layer and the second liquid crystal layer were switched upside down and the pair of polarizing plates were rotated by 90 @ and arranged. However, when driven in the same manner, the contrast ratio was almost the same as that of the example!, but a display with slightly inferior viewing angle characteristics was obtained.In this way, by the present invention, the hue of one display was changed to an achromatic color. It was found that a black-and-white display with excellent viewing angle characteristics could be obtained.Example 2 In the liquid crystal display element of Example 1, transparent electrodes were also formed on both sides of the second liquid crystal layer. Δn−d was set to Δ1.−dn=0.80 μm in the first liquid crystal layer, and Δn8·dx”0.90 μm in the second liquid crystal layer. During use, a voltage is also applied to this second liquid crystal layer. Δn with the non-selective voltage applied to the first liquid crystal layer
I” dr ・cos2 (θ2.) and Δn3・d3・cow” (θl
11) Made it almost equal. As a result, a black and white display similar to that in Example 1 was obtained. In addition, the voltage applied to the second liquid crystal layer is increased, and Δn1・dn・cos with the selection voltage of the first liquid crystal layer applied.
” (θ, 8) and Δn,・dn・cos2(θ33) when voltage is applied to the second liquid crystal layer are made almost equal, and the negative/positive display is reversed, resulting in a wide field of view. A positive black and white display having angular characteristics was obtained. Example 3.4 A liquid crystal display was produced in the same manner as in Example 1 and Example 2, except that the twist angle in Example 1 and Example 2 was changed to 260°. When the device was manufactured and driven, a black and white display similar to that of Example 1 was obtained, except that the contrast ratio was slightly increased.Example 5.6 The liquid crystal layers of Example I and Example 2 were separated, respectively. Example 1 except that it was constructed using four substrates sandwiched between two substrates.
When a liquid crystal display element was prepared and driven in the same manner as in Example 2, a black and white display similar to that in Example 1 was obtained, except that the contrast ratio was slightly lowered. Example 7 Three color filters were formed in a stripe shape on the electric bridge of the liquid crystal display device of Example 1 and the device was driven. Full color gradation drive was possible. [Effects of the Invention] As explained above, the present invention enables black-and-white display with a better contrast ratio than conventional super-twist liquid crystal display elements, and enables clear and high-quality positive or negative type displays. Display is obtained. Furthermore, the time division display characteristics are also equivalent to those of conventional super twist liquid crystal display elements, and the device has effects such as superior viewing angle characteristics. In addition, since the display is close to black and white, by combining it with a color filter, a colorful display is possible.In particular, by arranging red, green, and -blue color filters for each pixel, multi-color and full-color displays are possible. It has also been recognized that it is effective in displaying images, opening up more diverse applications. In particular, the present invention allows a bright display even though it is capable of black-and-white display, and enables not only a transmissive type display but also a reflective type display, and has a wide range of applications. The present invention can be applied in various ways in the future without detracting from the effects of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing a liquid crystal display element according to the present invention. FIGS. 2A and 2B show the directions of the liquid crystal molecular axes of the first liquid crystal cell on the upper side and the second liquid crystal cell on the lower side of FIG. FIG. 3 is a plan view showing relative positions. 3 and 4 are cross-sectional views of examples of the liquid crystal display element of the present invention. 1.2 is a polarizing plate, 3 is a first liquid crystal cell to which a voltage is applied, 4 is a second liquid crystal cell to which no voltage is applied, 5 is a polarization axis of the upper polarizing plate l, 6 is a lower polarizing plate 2 polarization axis. 7 is the long axis direction of the liquid crystal molecules above the first liquid crystal cell, 8 is the long axis direction of the liquid crystal molecules below the first liquid crystal cell, and 9 is the long axis direction of the liquid crystal molecules above the second liquid crystal cell. direction, 10 is the longitudinal direction of the liquid crystal molecules at the bottom of the second liquid crystal cell.I Figure 2nd

Claims (17)

[Claims] (1) A first liquid crystal layer made of a nematic liquid crystal with positive dielectric anisotropy containing an optically active substance and sandwiched between a pair of substrates arranged substantially in parallel and having an alignment control film; and the first liquid crystal layer. means for applying a voltage between the transparent electrodes of the upper and lower substrates sandwiching the liquid crystal layer; In a liquid crystal display element having two liquid crystal layers and a pair of polarizing plates installed outside the liquid crystal layers,
A first liquid crystal layer is placed in front of the viewer, and a first
The product Δn_1・d_1 of the refractive index anisotropy Δn_1 of the liquid crystal in the liquid crystal layer and the thickness d_1 of the liquid crystal layer is 0.7 to 2.0 μm
The long axis direction of the liquid crystal molecules in the first liquid crystal layer adjacent to the second liquid crystal layer and the long axis direction of the liquid crystal molecules in the second liquid crystal layer adjacent to the first liquid crystal layer are substantially orthogonal, The twist angle of the liquid crystal molecules between the substrates sandwiching the liquid crystal layer is 2 in the first liquid crystal layer.
00 to 300°, and the second liquid crystal layer has a twist angle that is opposite to that of the first liquid crystal layer and is approximately the same, and is polarized by a pair of polarizing plates arranged outside these two liquid crystal layers. arranged so that the axes intersect at an angle of 60 to 120°,
Furthermore, the direction of the polarization axis of the polarizing plate placed in front of the viewer is such that the helical direction of the first liquid crystal layer is left-handed with respect to the long axis direction of the liquid crystal molecules closest to the viewer. A liquid crystal display element, characterized in that the liquid crystal display element is arranged clockwise in some cases, and counterclockwise in cases where the helical direction of the first liquid crystal layer is right-handed. (2) Transparent electrodes are provided on the entire surface of the pair of substrates that sandwich the second liquid crystal layer, corresponding to the display area of the first liquid crystal layer, and between the transparent electrodes of the upper and lower substrates that sandwich the second liquid crystal layer. 2. The liquid crystal display element according to claim 1, further comprising means for applying a voltage to the second liquid crystal layer, and the voltage is applied to the second liquid crystal layer when the liquid crystal display element is used. (3) The liquid crystal display element according to claim 1, wherein no voltage is applied to the second liquid crystal layer during use. (4) The product Δn_2・d_2 of the refractive index anisotropy of the second liquid crystal layer and the thickness of the liquid crystal layer is the liquid crystal layer of liquid crystal molecules when a non-selective voltage during time-division driving is applied to the first liquid crystal layer. The average tilt angle θ with respect to the plane parallel to the thickness direction of the liquid crystal layer θ_1
The square of the cosine of _1 (cos^2(θ_1_1)) and the first
The product of Δn_1·d_1 of the liquid crystal layer is Δn_1·d_1·
cos^2 (θ_1_1) and the tilt angle θ_ of the liquid crystal molecules of the second liquid crystal layer with respect to the plane parallel to the liquid crystal layer during use.
The square of the cosine (c
os^2(θx_2)) and Δn_2・d of the second liquid crystal layer
Product with _2 Δn_2・d_n・cos^2(θx_2)
4. The liquid crystal display element according to claim 3, wherein: (5) The product Δn_2・d_2 of the refractive index anisotropy of the second liquid crystal layer and the thickness of the liquid crystal layer is the change in the liquid crystal layer of liquid crystal molecules when the selection voltage during time-division driving is applied to the first liquid crystal layer. Average tilt angle θ with respect to parallel planes in the thickness direction of the liquid crystal layer θ_2_
Product Δn_1・d_1・c of the square of the cosine of 1 (cos^2(θ_2_1)) and Δn_1・d_1 of the first liquid crystal layer
os^2 (θ_2_1) and the tilt angle θ_2 of the liquid crystal molecules of the second liquid crystal layer with respect to the plane parallel to the liquid crystal layer during use.
The square of the cosine of the average θx_2 in the thickness direction of the liquid crystal layer (co
s^2(θx_2)) and Δn_2・d_ of the second liquid crystal layer
3. The liquid crystal display element according to claim 3, wherein the product Δn_2·d_2·cos^2(θx_2) of 2 is approximately equal. (6) Δn_2・d_2 of the second liquid crystal layer when no voltage is applied
is Δn_1・d_1・cos^2(θ
By applying a voltage between the transparent electrodes of the second liquid crystal layer during use, the tilt angle θ_2 of the liquid crystal molecules of the second liquid crystal layer with respect to the plane parallel to the liquid crystal layer is increased.
The square of the cosine of the average θx_2 in the thickness direction of the liquid crystal layer (co
s^2(θx_2)) and Δn_2・d_ of the second liquid crystal layer
The product Δn_2・d_2・cos^2(θx_2) with 2 is Δn when a non-selective voltage is applied to the first liquid crystal layer.
3. The liquid crystal display element according to claim 2, wherein _1·d_1·cos^2 (θ_1_1) are approximately equal. (7) Δn_2・d_2 of the second liquid crystal layer when no voltage is applied
is Δn_1・d_1・cos^2(θ
By applying a voltage between the transparent electrodes of the second liquid crystal layer during use, the tilt angle θ_2 of the liquid crystal molecules of the second liquid crystal layer with respect to the plane parallel to the liquid crystal layer is increased.
The square of the cosine of the average θx_2 in the thickness direction of the liquid crystal layer (co
s^2(θx_2)) and Δn_2・d_ of the second liquid crystal layer
2, the product Δn_2・d_2・cos^2(θx_2) is Δn_2 when the selection voltage is applied to the first liquid crystal layer.
The liquid crystal display element according to claim 2, wherein the liquid crystal display element is made to be approximately equal to 1·d_1·cos^2 (θ_2_1). (8) The liquid crystal display element according to claim 3, wherein Δn_2·d_2 of the second liquid crystal layer is 1 to 20% smaller than Δn_1·d_1 of the first liquid crystal layer. (9) The liquid crystal display element according to claim 8, wherein Δn_2·d_2 of the second liquid crystal layer is 3 to 15% smaller than Δn_1·d_1 of the first liquid crystal layer. (10) The liquid crystal display element according to claim 3, wherein Δn_2·d_2 of the second liquid crystal layer is 25 to 90% smaller than Δn_1·d_1 of the first liquid crystal layer. (11) The liquid crystal display element according to claim 10, wherein Δn_2·d_2 of the second liquid crystal layer is 30 to 75% smaller than Δn_1·d_1 of the first liquid crystal layer. (12) Δn_1・d_1 of the first liquid crystal layer is 0.8 to 1
．． The liquid crystal display element according to any one of claims 1 to 11, which has a thickness of 5 μm. (13) Claims 1 to 12, wherein the nematic-isotropic phase transition temperature of the first liquid crystal layer and the nematic-isotropic phase transition temperature of the second liquid crystal layer are approximately equal. The liquid crystal display element according to any one of the items. (14) Any one of claims 1 to 13, wherein the substrate provided between the first liquid crystal layer and the second liquid crystal layer is a single substrate with alignment control films formed on both sides. The liquid crystal display element according to item (1). (15) The liquid crystal display element according to any one of claims 1 to 14, wherein a color filter is formed corresponding to each electrode. (16) The liquid crystal display element according to claim 15, wherein the color filter is formed inside the cell. (17) The liquid crystal display element according to claim 15 or 16, wherein the color filter is a red, green, and blue color layer, and provides multicolor display.