JPH03252624A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To display high-contrast images without generating after-images by forming a ferroelectric liquid crystal so as to have a specific orientation state. CONSTITUTION:This element has a pair of substrates 11a, 11b subjected to a uniaxial orientation treatment in the same direction. The four states having further a chevron structure in the C1 orientation states exist if the ferroelectric liquid crystal 15 is so formed as to have the orientation state expressed by theta<alpha+delta where the pretilt angle of the ferroelectric liquid crystal 15 is designated as alpha, the tilt angle as theta, and the angle of inclination of the Sm*C layer as delta. Of these four C1 states, the two states form a bistable state and the uniform state of the C1 orientation is higher in contrast than the bistable state in the C2 orientation. The large tilt angle theta is, therefore, generated by driving the liquid crystal in this uniform state. The high-contrast images are displayed in this way and the generation of the after-images is obviated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal element, particularly a ferroelectric liquid crystal element, used in a liquid crystal display element, a liquid crystal optical shutter, etc.
The present invention relates to a liquid crystal element with improved display characteristics by improving the alignment state of liquid crystal molecules.

[Prior Art] A type of display element that uses the refractive index anisotropy of ferroelectric liquid crystal molecules to control transmitted light in combination with a polarizing element has been developed by Clark and Lager.
wal 1) 5 6 (Japanese Unexamined Patent Publication No. 56-107216, US Pat. No. 4,367,924, etc.). This ferroelectric liquid crystal generally has a non-helical chiral smectic C phase (SmC'') or H phase (SmH'') in a specific temperature range, and in this state, it responds to an applied electric field to It has the property of being in one of the optically stable state and the second optically stable state and maintaining that state when no electric field is applied, that is, it has bistability, and it also responds rapidly to changes in the electric field. It is expected that it will be widely used as a high-speed and memory-type display element, and in particular, it is expected to be applied to large-screen, high-definition displays due to its functions.

In order for an optical modulation element using this bistable liquid crystal to exhibit predetermined driving characteristics, the liquid crystal disposed between a pair of parallel substrates must be
It is necessary that the molecules be in such a state that conversion between two stable states can occur effectively.

Furthermore, in the case of a liquid crystal element that utilizes the birefringence of liquid crystal, the transmittance under crossed Nicols is expressed as: 1/Io=5in24θs in 2minyrλ. Tilt angle θ in the non-helical structure mentioned above
is expressed as an angle between the average molecular axes of the liquid crystal molecules arranged in a heply manner in the first and second alignment states. According to the above formula, when the tilt angle θ is 22.5°, the transmittance is the highest, and the tilt angle θ in a non-helical structure that achieves bistability is as close as possible to 22.5°. It is necessary.

By the way, as a method for aligning a strong electroconductive liquid crystal, a molecular layer organized by a plurality of molecules forming a smectic liquid crystal can be uniaxially aligned along its normal line over a large area. Furthermore, it is desirable that the manufacturing process be realized by a simple rubbing process.

As an alignment method for ferroelectric liquid crystals, especially chiral smectic liquid crystals with a non-helical structure, for example, US Pat.
The one described in Japanese Patent No. 561726 is known.

[Problems to be Solved by the Invention] However, the orientation methods that have been used so far, especially the orientation method using a rubbed polyimide film, cannot be improved by the strong non-helical structure that exhibits bistability, as announced by Clark and Lagerwal. When applied to dielectric liquid crystals, it has the following problems.

In other words, the experiment conducted by the inventors revealed that the apparent tilt angle θ (between the molecular axes in the two stable states) of a ferroelectric liquid crystal with a non-helical structure obtained by aligning with a conventional rubbed polyimide film 1/2 of the angle formed) is smaller than the tilt angle of the ferroelectric liquid crystal with a helical structure (angle θ, which is 1/2 of the apex angle of the triangular pyramid shown in Fig. 4 (A) described later). It turned out that there was. In particular, the tilt angle θ of a ferroelectric liquid crystal with a non-helical structure obtained by aligning with a conventional rubbed polyimide film is generally about 3° to 8°, and the transmittance at that time is about 3 to 5% at most. Met.

In this way, according to Clark and Lagerwal, the tilt angle in a ferroelectric liquid crystal with a non-helical structure that achieves bistability should be the same as the tilt angle in a ferroelectric liquid crystal with a helical structure. However, in reality, the tilt angle θ in the non-helical structure is smaller than the tilt angle e in the helical structure. Moreover, it has been found that the reason why the tilt angle θ in the non-helical structure is smaller than the tilt angle θ in the helical structure is due to the twisted arrangement of the liquid crystal molecules in the non-helical structure. In other words, in a ferroelectric liquid crystal with a non-helical structure, the liquid crystal molecules are continuously twisted from the axis of the liquid crystal molecules adjacent to the upper substrate to the axis of the liquid crystal molecules adjacent to the lower substrate with respect to the normal to the substrate. This is the reason why the tilt angle θ of the non-helical structure is smaller than the tilt angle θ of the helical structure.90

Furthermore, the alignment state of the chiral smectic liquid crystal produced by the conventional rubbed polyimide alignment film is in the first optically stable state (e.g. When a one-polar voltage is applied to switch from a white display state to a second optically stable state (e.g., a black display state), after the one-polar voltage is removed, the ferroelectric liquid crystal A reverse electric field V rev of the other polarity is generated in the layer, and this reverse electric field V raV causes an afterimage during display.

This reverse electric field generation phenomenon can be explained, for example, in “Akio Yoshida, 1986.
This was clarified in October 2007, "Switching Characteristics of rS SF LC, Proceedings of the Liquid Crystal Conference JP, 142-143."

Meanwhile, one of the present inventors previously discovered the following phenomenon regarding the alignment state of ferroelectric liquid crystal.

An alignment film such as LP64 (manufactured by Toshiku Co., Ltd.), which has a relatively low pre-tilt, is coated on the substrate and rubbed, and then the upper and lower sheets are bonded together with the same rubbing direction and a gap of approximately 1.5 μm to form a cell. and add C31014 (
When a ferroelectric liquid crystal (manufactured by Chisso Corporation) or the like is injected and the temperature is lowered, the process shown in Fig. 2<8) to (e) follows.

In other words, the same figure immediately after the transition from the high temperature phase to the Sc'' phase (
In the state shown in a), orientation states 21 and 22 with low contrast (C1 orientation state) are taken, and when the temperature is lowered and reaches a certain temperature range, a zigzag-shaped defect 23 occurs as shown in FIG. , high-contrast alignment states (C2 alignment states) 24 and 25 appear with the defect as a boundary.

As the temperature further decreases, the 02 orientation state spreads (Figures (C) and (d)), and finally the entire structure becomes the C2 orientation state (Figure (e)).

The orientation states of the 2fffi types of C1 and C2 are explained by the difference in the chevron structure of the smectic layer as shown in FIG. In Figure 3, 31 is a smectic layer, 32
33 represents a C1-oriented region, and 33 represents a C2-oriented region.

Smectic liquid crystals generally have a layered structure, ranging from SA phase to S phase.
c phase or S. ’ phase, the interlayer spacing decreases, so the third
As shown in the figure, the layers are bent at the center of the upper and lower substrates (a chevron structure). There are two possible bending directions, 01 and 02, as shown in the figure, but as is well known, due to rubbing, the liquid crystal molecules at the substrate interface are tilted at no angle to the substrate (pre-tilt), and the direction is toward the rubbing direction. The orientation is such that the liquid crystal molecules raise their heads (the tips appear floating). Because of this pretilt, C1 orientation and C
The two orientations are not equivalent in terms of elastic energy, and a transition occurs at a certain temperature as described above. Rolling may also occur due to mechanical strain.

When the layer structure in Fig. 3 is viewed in plan, the boundary 34 when changing from the C1 orientation to the C2 orientation in the rubbing direction has a zigzag lightning shape and is called a lightning defect, and the boundary 34 when changing from the C2 orientation to the C1 orientation The boundary 35 is a wide gentle curve and is called a hairpin defect. Conventionally, the C1 and C
2 orientation, a liquid crystal element using the C2 orientation state was provided from the viewpoint of contrast. but,
The present invention provides a liquid crystal element with even higher contrast.

Therefore, an object of the present invention is to solve the above-mentioned problems and provide a ferroelectric liquid crystal element with further high contrast.
In particular, the object of the present invention is to provide a ferroelectric liquid crystal element that can produce a large tilt angle θ in a non-helical structure of chiral methacrylic liquid crystal, display a high-contrast image, and achieve a display that does not produce an afterimage.

[Means for Solving the Problems] Accordingly, the present invention provides a ferroelectric liquid crystal element that includes a ferroelectric liquid crystal,
The ferroelectric liquid crystals are held in between and face each other, and electrodes for applying voltage to the ferroelectric liquid crystals are formed on the opposing surfaces of the ferroelectric liquid crystals. 3 4 ■ The pretilt angle of the ferroelectric liquid crystal is α, the tilt angle is Θ,
If the tilt angle of the Sm*C layer is δ, then the ferroelectric liquid crystal has an alignment state expressed by θ〈α + δ, or ■ The ferroelectric liquid crystal has an orientation state expressed by θ<α + δ. By applying strain to the substrate, an alignment state surrounded by hairpin defects and lightning defects is produced, and this alignment state is caused by the pretilt in the order of lightning defects and asbin defects with respect to the direction in which the liquid crystal molecules are floating from the alignment surface. Is this caused by the occurrence of these defects? ■ The ferroelectric liquid crystal is in an alignment state surrounded by hairpin defects and lightning defects due to foreign objects such as spacers between the substrates or by applying distortion to the substrates. Also, this orientation state is caused by the occurrence of these defects in the order of lightning defects and hairpin defects in the rubbing direction, or.
There is no alignment change accompanied by defects during the process of cooling to m*C, and ■ The ferroelectric liquid crystal in the alignment state exhibits at least two stable states, and the angle formed by their optical axes is 1/2
θa and the tilt angle e of the ferroelectric liquid crystal, O〉Θ, )e/2, Align the absorption axis of one polarizing plate to the position that bisects the angle formed by the angle, and align the absorption axis of the other polarizing plate perpendicularly thereto, then rotate only one polarizing plate by 3° to 30° clockwise. Is the color exhibited by the first stable state when rotated counterclockwise the same as the color exhibited by the second stable state when rotated by the same angle counterclockwise?
The ferroelectric liquid crystal in the alignment state is under crossed nicols,
The ferroelectric liquid crystal has a total of 3 or 4 states: two stable states with low transmittance at the extinction value and one or two stable states with high transmittance at the extinction value under crossed nicols, or ■ the ferroelectric liquid crystal is in a crossed nicol state Below, two stable states, first and second, with low transmittance at the extinction position, and under crossed Nicols,
4 of two stable states, 3rd and 4th, with high transmittance at extinction position
The absorption axis of one polarizing plate is aligned at a position that bisects the angle formed by these optical axes, and the absorption axis of the other polarizing plate is aligned perpendicularly thereto. The first result when rotated 3° to 30° clockwise.
The color exhibited by the stable state is the same as the color exhibited by the second stable state when rotated counterclockwise by the same angle, and when only one polarizing plate is rotated 3° to 30° clockwise. To provide a strong electrostatic liquid crystal element characterized in that the color exhibited by the third stable state is different from the color exhibited by the fourth stable state when rotated by the same angle in the counterclockwise direction.

The orientation state changes from (Tl s)t to (Tl
It is preferably present over the entire temperature range from (10 to 40))*C.

Further, it is preferable that the relationship between the pretilt angle α and the inclination angle δ of the Sm*C layer has an orientation state represented by δ and α.

Furthermore, in the cases of (1) and (2) above, it is preferable that the alignment state has three or four different stable states that are not mediated by lightning defects and hairpin defects.

[Detailed Description of Aspects of the Invention] FIG. 1 schematically depicts one example of a ferroelectric liquid crystal cell of the present invention.

11a and flb are r n203 and ITO (I
Transparent electrode 12a such as ndium Tin Oxide)
12b is a substrate (glass plate) coated with insulating films 13a and 13b (
Si20 film, TiO2 film, Ta205 film, etc.),
The alignment control films 14a and 14b made of polyimide and having a thickness of 50 to 1000 layers are laminated, respectively. The alignment control films 14a and 14b are subjected to rubbing treatment (in the direction of the arrow) so that their alignment directions are parallel and in the same direction (direction A in FIG. 1). A ferroelectric smectic liquid crystal 15 is disposed between the substrates 11a and 11b, and the distance between the substrates 11a and 11b is sufficient to suppress the formation of a helical alignment structure of the ferroelectric smectic liquid crystal 15. Small distance! (for example, 0.1 to 3 μm), and the ferroelectric smectic liquid crystal 15 is in a bistable alignment state. The above-mentioned sufficiently small distance is the distance between the substrate 11a
and fib by bead spacers 16 (silica beads, alumina beads). 17a
, 17b are polarizing plates.

In such a configuration, the present inventors have found that if a specific alignment film and liquid crystal combination is used, (1) the above C1-C2 transition is less likely to occur, and depending on the liquid crystal material, the total<C2 configuration state does not occur; ■Low contrast 2 previously found in C1 orientation
In addition to this stable state, we newly discovered that two other stable states with high contrast appear.

Therefore, if the entire screen as a display element is unified to the 01 orientation state and the two high contrast states in the C1 area are used as the two states of black and white display, it is expected that a display with higher quality than before can be achieved.

In other words, the present inventors placed a ferroelectric liquid crystal element facing a ferroelectric liquid crystal with the ferroelectric liquid crystal held between them, and applied a voltage to each of the ferroelectric liquid crystals on the opposing surfaces. a pair of substrates on which electrodes are formed and uniaxially aligned in the same direction and substantially parallel to each other for aligning the ferroelectric liquid crystal, and the pretilt angle of the ferroelectric liquid crystal is α, The angle (1/2 of the cone angle) is Θ, Sm”0
It was confirmed that if the ferroelectric liquid crystal has an orientation state expressed by α+δ, where the tilt angle of the layer is δ, there are four states having a chevron structure in the C1 orientation state. These four 01 states are different from the conventional 01 states, and two of the four 01 states are bistable states (uniform states).
is formed. This uniform state of C1 orientation is
The contrast is higher than the conventionally used bistable state in the C2 orientation, and therefore, by driving the liquid crystal in this uniform state, a large tilt angle e is generated and a high contrast image is displayed.
Moreover, no afterimage occurs.

Below, the above item (2) will be explained in detail.

Regarding point (2), as shown in Table 1, the likelihood of C1→C2 transition S occurring depends on the angle that the liquid crystal molecules near the substrate interface form with the substrate (pretilt angle), the tilt angle of the layer, and the liquid crystal It depends on the tilt angle.

Table 1 Table 1 shows three types of alignment films A-C with different pretilt angles.
These are the results of injecting three types of liquid crystals a''-e with different tilt angles into a cell and observing the alignment state. However, the alignment is 11!
A is LP64 (manufactured by Toshiku Co., Ltd.), alignment film B is 5E61
0 (manufactured by Nissan Chemical Co., Ltd.) and orientation 1IIC are polyimides obtained by firing polyamic acid having the structural formula shown in FIG. Ta.

From Table 1, it can be seen that the C1 orientation is maintained when the pretilt angle is large and the tilt angle is small. This result can be understood if considered as follows.

Since the directors near the substrate in the C1 orientation and the C2 orientation are on the cones 41 in FIGS. 4A and 4B, respectively, the tilt angle e, the pretilt angle α, and the forward tilt angle δ are
The following relationship must hold between e+δ>α for C1 orientation (2) and θ−δ>α for C2 orientation (3). Since the forward tilt angle δ has a value slightly smaller than the tilt angle e, for liquid crystals with a small tilt angle e, e−δ is also small, and when the pretilt angle α is large, the relationship in equation (3) is no longer satisfied, and C2 Orientation does not appear. Therefore, the conditions for producing C1 orientation without producing C2 orientation in the present invention are e−δ α (4
) is required.

Since the tilt angle and forward tilt angle depend on the temperature of the liquid crystal, even if equation (4) holds true at a certain temperature, this condition may be broken at even lower temperatures and a C2 orientation may appear. The condition of equation (4) needs to hold true over the entire temperature range in which the liquid crystal is used as a display device.

In the present invention, the pretilt angle α is preferably 6° × α × 30°, more preferably 8° × α × 30°, even more preferably 10° < α × 30°, and the tilt angle e is 7°.
'<8<27°, and δ preferably represents 0°<δ<25''.

FIG. 4(B) shows how the tilt angle θ of a typical liquid crystal and the layer inclination angle δ change with temperature. e and δ are 5A-3c''
It shows a sudden change just below the phase transition point TAc, and increases as it moves away from the transition point, but the temperature change becomes gradual.

As shown in Figure 4(B), the difference between e and 6 is T
It is 0 at AC, and increases as the temperature decreases.

Therefore, formula (4) holds true in the range from the phase transition point to a certain temperature determined by the liquid crystal and the alignment film, and does not hold below that temperature. If used as a display element within this temperature range, C
Since it is possible to maintain one orientation, it is desirable to have as wide a temperature range as possible, but in practical terms
It is sufficient if a temperature range of ~35 deg can be secured.

On the other hand, if the temperature is too close to the phase transition point, e becomes too small to be of practical use, so in reality, it is often used at a temperature about 5 degrees away from the phase transition point. Therefore, assuming that the phase transition point is TAc℃, equation (4) is at least (TAo-5)
It is necessary that the temperature is satisfied in the range from .degree. C. to (TAClO).degree. C., preferably in the range from (TAC5)t to (TAC40).degree.

Next, point (■) will be explained. In the conventional low pretilt alignment film, only two states with relatively low contrast could stably exist in the C1 alignment. However,
In a high pretilt alignment film such as alignment film C shown in Table 1, there are four states in the C1 orientation, two of which are the same low contrast two states (under the field of view of a polarizing microscope) as before. In this case, there is no extinction level and it appears blue, so the liquid crystal director is twisted between the upper and lower substrates (hereinafter referred to as a splay state), and the other two have extremely high contrast and a large apparent tilt angle. state (there is an extinction position under a polarizing microscope. Hereafter referred to as uniform state)
It is. The contrast and transmittance of the newly discovered 22-frame state are higher than those in the C2 orientation.
The uniform state of C1 is compared to the spray state of C1, under crossed nicols, and the transmittance at the extinction position is low, and the spray state of C1 is indistinguishable between the two states.
In some cases, only a total of three states, the 1st state and the 1st spray state, are observed.

Table 2 shows the apparent tilt l-angle θ 5play in the absence of an electric field in the spray state of some liquid crystals a to d, and the apparent tilt angle θ unlf in the uniform state.

rm and del1-angle θ are shown. Table 2 also shows the ratio of θ 5play and θ uniform to e. As can be seen from this table, even with the same liquid crystal material, the apparent tilt angle is small in the spray state and large in the uniform state. Looking at the ratio to e, θ@pla)'/9≦0.4 in the spray state, and θunlform/6≧0.5 in the uniform state. Here, in the present invention, among the four states in the C1 state, a state exhibiting a relationship of e>Θ and >e/2 is referred to as a uniform state.

Table 2 Therefore, in the present invention, a ferroelectric liquid crystal is held facing a ferroelectric liquid crystal with the ferroelectric liquid crystal held between them, and a voltage is applied to each of the ferroelectric liquid crystals on the opposing surfaces. a pair of substrates on which electrodes are formed to align the ferroelectric liquid crystal, and a pair of substrates are uniaxially aligned in the same direction and approximately parallel to each other for aligning the ferroelectric liquid crystal, and the pretilt angle of the ferroelectric liquid crystal is
, the tilt angle (1/2 of the cone angle) is Θ, and the inclination angle of the Sm*C layer is 6, then the ferroelectric liquid crystal has an orientation state expressed by e α + δ, and in this orientation state, The ferroelectric liquid crystal exhibits at least two stable states, and the relationship between C8, which is 1/2 of the angle formed by their optical axes, and the tilt angle e of the ferroelectric liquid crystal is e〉Θ, >0/2. The purpose is to utilize the uniform state in the C1 orientation that satisfies this requirement for display.

In addition, the C1 state referred to in the present invention is an alignment state surrounded by hairpin defects and lightning defects caused by foreign substances such as spacers between the substrates or by applying distortion to the substrates, and the alignment state of the parentheses is caused by pretilting of liquid crystal molecules. This is a state that occurs when these defects occur in the order of anti-site defects, lightning defects, and asbin defects in the direction in which the surface is floating from the oriented surface or in the rubbing direction. Alternatively, it can be said that there is no orientation change accompanied by defects in the process of lowering the temperature from a high temperature such as smectic A (SmA) to smectic c (Sm''c).

The difference between the spray state and the uniform state in the C1 orientation of the present invention is not only the difference in the above-mentioned apparent tilt angle but also the difference in contrast. As mentioned above, in the splay orientation, even in the dark state, a perfect extinction position cannot be obtained under crossed nicols, and it becomes darker when the polarizing plate is arranged at a position twisted several degrees from crossed nicols. On the other hand, the uniform orientation has an almost complete extinction position under crossed nicols, and therefore exhibits a high contrast ratio. This difference becomes even clearer when the following measurements are performed.

First, align the absorption axis of one polarizing plate to the position where the contrast between the up and down two states disappears under crossed Nicol conditions, that is, the direction that bisects the angle formed by the optical axes of the two states (smectic layer direction). Align the absorption axis of the other polarizing plate perpendicular to .

If only the analyzer (polarizing plate on the observer's side) is rotated clockwise by an appropriate angle of 3° to 30° from this position, a difference is created between the transmitted light states in the up and down states, creating a contrast. In many cases, the color appears darker when viewed up, and the color appears lighter when viewed down. Conversely, if you rotate the analyzer counterclockwise by the same angle, you will see the opposite coloration. That is, the color becomes lighter in the up state, and the color becomes darker in the down state.

Therefore, focusing on the appearance of coloration with respect to the rotation of the analyzer, we find that for cells with a gap of 1.0 μm) and 2.0 μm, (1) For two states of up and down spray orientation, rotation clockwise. The color of the up view when rotated is brownish to reddish-purple, while the color of the down view when rotated counterclockwise is blue to indigo, and these two colors are different. On the other hand, regarding (2) the two states of up and down uniform orientation,
Both are the same color, ranging from brownish to reddish-purple.

This difference is thought to be based on whether or not the director is twisted between the upper and lower substrates as described below, but in any case, the splayed orientation and the uniform orientation can be qualitatively distinguished from this measurement.

Furthermore, the four states of C1 orientation in the present invention transition to each other when an electric field is applied. Applying a weak positive and negative pulsed electric field causes a transition between two spray states, and applying a strong positive and negative pulsed electric field causes a transition between two uniform states. By using the uniform 2 state, a display element that is brighter and has higher contrast than the conventional one can be realized.

Incidentally, depending on how the liquid crystal is selected, there is a difference in the ease with which the uniform state occurs. Table 3 shows the results of examining the presence or absence of a uniform state in several liquid crystals using the alignment film C shown in Table 1. It can be seen that liquid crystals with small tilt angles tend to take a uniform state. Although the cause of this is not necessarily clear, the following is presumed.

In the uniform state shown in Table 3, it is considered that the director is not twisted between the upper and lower substrates in view of its optical properties. FIG. 5A is a schematic diagram showing the arrangement of the director at each position between the substrates in each state of C1 orientation. In the figure,
51 to 54 show the director projected onto the bottom surface of the cone in each state, as viewed from the bottom direction,
51 and 52 are director arrangements considered to be in a spray state, and 53 and 54 to be considered to be in a uniform state. As can be seen from the same figure, the two states of the uniform 53 and 54
In this case, the position of the liquid crystal molecules at either the upper or lower substrate interface is replaced with the position in the spray state. Fifth (B)
The figure shows the C2 orientation, with no interfacial switching and two states due to internal switching. FIG. 6 shows the state of the director near the boundary between two regions with different interfacial molecular positions. Since the position of the interfacial molecules is considered to shift from one side to the other through the apex 60 of the cone as shown in the figure, the smaller the tilt angle, the easier the shift.

For this reason, a uniform state can be achieved using liquid crystals with a small tilt angle.

The direction of the torque that a molecule at the interface experiences as it is moved from one location to another by an electric field depends on where the molecule is on the cone. That is, if the pretilt is at a higher position than the cone ends 61 and 62 in FIG. 6, the torque will be applied in the direction passing through the apex 60 of the cone; Receives torque in the direction of being pushed. Therefore, switching is more likely to occur in the former position. The condition for the pretilt to be higher than the cone ends 61 and 62 is 5ina>sin δ cos θ (5) based on simple geometric considerations, and when the pretilt angle α, forward inclination angle δ, and tilt angle e are small, this condition is satisfied. Approximately, the condition is α>δ (6). It is interpreted that the experimental results shown in Table 3 were obtained because the forward tilt angle δ has a value close to the tilt angle θ.

Therefore, in order to more stably form a uniform state in the C1 orientation, it is effective to roughly satisfy the relationship α>δ.

Further, in order to stably form a uniform state, cross rubbing is also possible in which the rubbing directions of the upper and lower substrates are shifted within a range of 0 to 20''.

In addition, in the above experiment, the tilt angle Θ, the layer tilt angle δ, the pretilt angle α, and the apparent tilt angle θa
was measured as follows.

Measurement of tilt angle θ While applying 10V to 30V DC between the upper and lower substrates of the FLC element, the FL placed between them is
Rotate the C element horizontally with the polarizing plate to find the first extinction position (the position where the transmittance is lowest), then rotate the D element with the opposite polarity to the above.
While applying C, search for the second extinction position. 1/2 of the angle from the first extinction position to the second extinction position at this time was defined as the tilt angle e.

Measurement of apparent tilt angle θa After applying a single pulse of the threshold value of the liquid crystal, under no electric field,
Then, under orthogonal crossed nicols, the FLC element placed between them was rotated horizontally with the polarizing plate to find the first extinction position, and then, after applying a pulse with the opposite polarity to the above single pulse, the first extinction position was applied under no electric field. Find the extinction position of 2. At this time, 1/2 of the angle from the first extinction position to the second extinction position was set as 08.

Layer inclination angle δ measuring X-ray analyzer RAD-11B (45KV, 30mA)
6 was measured using X-ray analysis method.

Measurement of pretilt angle α Jpn, J, 8pp1. Phys, vol19 (19
80) NO,10,5 It was determined according to the method described in hortNotes 2013 (crystal rotation method).

That is, a cell with a cell thickness of 20 μm was created by bonding substrates rubbed in parallel and opposite directions, and a liquid crystal (A) having an SmA phase was filled in the cell at a temperature of 0° C. to 60° C., and measurements were performed.

While rotating the liquid crystal cell in a plane perpendicular to the upper and lower substrates and including the alignment axis, a helium-neon laser beam with a polarization plane making an angle of 45° with the rotation axis is irradiated from a direction perpendicular to the rotation axis, and the opposite side is The intensity of transmitted light was measured using a photodiode through a polarizing plate with a transmission axis parallel to the incident polarization plane.

The angle between the central corner of the hyperbolic group of transmitted light intensity created by interference and a line perpendicular to the liquid crystal cell was defined as φo, and the pretilt angle α0 was determined by substituting it into the following formula.

no: ordinary light refractive index n8: extraordinary light refractive index [Example] Hereinafter, an example in which a liquid crystal element according to the present invention was created will be described.

1. A thin film of tantalum oxide was formed by sputtering on a glass substrate with a transparent electrode, and a 1% NMP solution of polyamic acid LQ1802 (manufactured by Hitachi Chemical Co., Ltd.) was applied using a spinner, and the film was heated at 270°C. Baked for 1 hour. Next, this substrate was rubbed and bonded to another similarly treated substrate with a gap of 15 μm maintained so that the rubbing direction was parallel and in the same direction to create a cell. The pretilt angle of the cell is 14° by the crystal rotation method.

A mixed liquid crystal containing phenylpyrimidine as a main component, a ferroelectric liquid crystal having a tilt angle of 12° at room temperature and an oblique angle of 10° at room temperature, was injected into the cell.

The phase transition temperature was as follows.

-20℃ 45℃ 70℃ 78℃ Crysta14-3♂←5A4-Ch←■s.

FIG. 7 shows the change in the tilt angle of this liquid crystal with temperature.

After aging the cell injected with liquid crystal at 100°C for 1 hour, we observed it while lowering the temperature within the Sc'' phase range, and found that the C1 orientation was maintained over the entire temperature range, and four-state transition was possible using an electric field. Figure 8 is a polarizing microscope observation sketch of a cell in which these four states are mixed, 81 and 82 are in the splay state, and 83 and 84 are in the uniform state.The apparent tilt angle is 5'' between the two splay states. , 10° between the two uniform states, and when a rectangular pulse with a peak value of 24 V was applied, switching between the spray states occurred with a pulse width of 20 μs, and switching between the uniform states occurred with a pulse width of 60 μs 7 8 .

Next, display characteristics in the uniform state are evaluated.

After sandwiching the above-mentioned liquid crystal cell between a pair of 90° crossed Nicol polarizers, 30 pulses of 50 μsec are applied to set the 90° crossed Nicols at the extinction position (darkest state), and the transmittance at this time is determined. was measured using a photomultibler, then a 30V pulse of 50μSee was applied, and the transmittance (bright state) was measured in the same manner.The transmittance in the dark state was 0.5%. Transmission in the bright state was 10%, so the contrast ratio was 50:1.

Further, when the optical response time (change in amount of transmitted light from 0 to 97%) was measured, it was 0.1 sec (Fig. 10).

In other words, efficient switching is performed.

Furthermore, when we fabricated a matrix display panel with the same configuration as above, except that stripe-shaped electrodes were attached to the upper and lower substrates and pixels were formed at the intersections of these electrodes, and the driving waveform shown in Figure 9 was applied, it worked well. did. In Figure 9, SN, 5N
41 and the like are voltage waveforms applied to the scanning electrodes, ■ are voltage waveforms applied to the signal electrodes, and I-S are voltage waveforms applied to the pixels.

1 Tsuji: Another liquid crystal containing phenylpyrimidine as a main component (tilt angle of 21° and tilt angle of 17° at room temperature) was placed in a cell with the same alignment film as used in Example 1. Although a uniform state is shown in the C1 orientation, when a matrix driving waveform is applied, a splayed state often exists at room temperature. However, when used at 55°C or higher (tilt angle of 11° and inclination angle of 9° at 55°C), a uniform state stably existed. The phase transition temperature of this liquid crystal was as follows.

By using it at high temperature, the inclination angle can be reduced and the formula (5
) or satisfying the condition of equation (6), it can be optimally used not only for contrast but also for matrix drive.
A more stable uniform state can be formed.

LP64 manufactured by Toshiku Co., Ltd. as an alignment film with a low pre-tilt angle.
A liquid crystal cell was prepared in the same manner as in Example 1, except that the liquid crystal cell (tilt angle 17° and tilt angle 13.5
) was injected, resulting in a C2 orientation state.

The pretilt angle of the cell was 2.5° as measured by the crystal rotation method.

Transmittance in dark state is 1%, transmittance in bright state is 6%, contrast is 6:1, optical response time is 2.0se
c (Figure 10).

[Effects of the Invention] As explained above, the liquid crystal element of the present invention that utilizes the uniform state in the C1 orientation for display is a liquid crystal element that can achieve a display with high contrast images, good switching, and no afterimages.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a ferroelectric liquid crystal cell of the present invention, and FIGS. 2(a) to (e) show a ferroelectric liquid crystal injected into the liquid crystal cell of FIG. FIG. 3 is an explanatory diagram showing the difference between the two types of orientation states of C1 and C2; FIG. is an explanatory diagram showing the relationship between the tilt angle, pretilt angle, and point oblique angle in C1 and C2 orientations; FIG. 4(B) is a diagram showing temperature changes in the tilt angle e of the liquid crystal and the tilt angle δ of the layer; FIG. 5(A) is a schematic diagram showing the arrangement of directors at each position between substrates in each state of C1 orientation. FIG. 5(B) is a schematic diagram showing the arrangement of directors at each position between substrates in each state of C2 orientation. FIG. 6 is a schematic diagram showing the arrangement of the director at different positions. FIG. 7 is a schematic diagram showing the state of the director near the boundary between two regions with different interfacial molecular positions. A graph showing temperature changes in tilt angle, FIG. 8 is a schematic diagram sketching how four states coexist in the liquid crystal element, FIG. 9 is a timing chart showing a driving waveform applied to the liquid crystal element, and FIG. 10 is a graph comparing the measurement results of optical properties in the uniform orientation state of Example 1 and the measurement results of optical properties of Comparative Example, and FIG. 11 is a graph of the polyimide alignment film obtained by firing polyamic acid. The structural formula is 11a, 11b: Substrate, 12a, 12b: Transparent electrode, 1
3a, 13b: insulating film, 14a, 14b orientation control film, 1
5: Ferroelectric liquid crystal. ×100 xlOO Figure 2 (25°C) Figure 2 O

Claims (22)

[Claims] (1) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, respectively. It is equipped with a pair of substrates that are substantially parallel to each other and subjected to uniaxial alignment treatment in the same direction for alignment, and the pretilt angle of the ferroelectric liquid crystal is α, the tilt angle is Θ, and the tilt angle of the Sm^*C layer is set. is δ, the ferroelectric liquid crystal has an orientation state expressed by Θ<α+δ, and the ferroelectric liquid crystal in this orientation state exhibits at least two stable states, and the angle formed by their optical axes is θ_a which is 1/2 and the tilt angle Θ of the ferroelectric liquid crystal are Θ>θ_a>Θ/2 (2) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, and the ferroelectric liquid crystal is It is equipped with a pair of substrates that are substantially parallel to each other and subjected to uniaxial alignment treatment in the same direction for alignment, and the pretilt angle of the ferroelectric liquid crystal is α, the tilt angle is Θ, and the tilt angle of the Sm^xC layer is If δ, the ferroelectric liquid crystal has an alignment state expressed by Θ<α+δ, and the ferroelectric liquid crystal in the alignment state exhibits at least two stable states, and the angle formed by their optical axes is 2. Align the absorption axis of one polarizing plate at the equal dividing position, and align the absorption axis of the other polarizing plate perpendicularly thereto, then rotate only one polarizing plate clockwise by 3 degrees.
the color exhibited by the first stable state when rotated by 30°;
A ferroelectric liquid crystal element characterized in that a second stable state exhibits the same color when rotated counterclockwise by the same angle. (3) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on each of the opposing surfaces, and the ferroelectric liquid crystal is It is equipped with a pair of substrates that are substantially parallel to each other and subjected to uniaxial alignment treatment in the same direction for alignment, and the pretilt angle of the ferroelectric liquid crystal is α, the tilt angle is Θ, and the tilt angle of the Sm^*C layer is set. If δ is the ferroelectric liquid crystal, the ferroelectric liquid crystal has an orientation state expressed by Θ<α+δ, and the ferroelectric liquid crystal in this orientation state has two stable states with low transmittance: under crossed Nicols and at the extinction position. A ferroelectric liquid crystal element characterized by having a total of three or four states, including one or two stable states with high transmittance under crossed Nicols and extinction positions. (4) The ferroelectric liquid crystal has two stable states: the first and second stable states under crossed nicols, with low transmittance at the extinction position, and the third and fourth stable states under crossed nicols, with high transmittance at the extinction position. Four stable states are shown, and the absorption axis of one polarizing plate is aligned at a position that bisects the angle formed by their optical axes, and the absorption axis of the other polarizing plate is aligned perpendicularly thereto. The color that appears in the first stable state when only the polarizing plate is rotated clockwise by 3° to 30° is the same as the color that appears in the second stable state when the polarizing plate is rotated by the same angle counterclockwise. can be,
The color exhibited by the third stable state when only one polarizing plate is rotated clockwise by 3° to 30° is different from the color exhibited by the fourth stable state when rotated by the same angle counterclockwise. The ferroelectric liquid crystal device according to claim 3, characterized in that: (5) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces of the ferroelectric liquid crystal. The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is produced by a foreign substance such as a spacer between the substrates or by applying distortion to the substrates. An alignment state surrounded by hairpin defects and lightning defects is produced, and this alignment state is caused by the formation of these defects in the order of lightning defects and hairpin defects with respect to the direction in which the liquid crystal molecules are floating from the alignment surface due to pretilt. The ferroelectric liquid crystal in the alignment state exhibits at least two stable states, and θ_a, which is 1/2 of the angle formed by their optical axes, and the tilt angle Θ of the ferroelectric liquid crystal are Θ> A ferroelectric liquid crystal element characterized by having a relationship of θ_a>Θ/2. (6) The ferroelectric liquid crystal is held in between and faces each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, and the ferroelectric liquid crystal is The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is produced by a foreign substance such as a spacer between the substrates or by applying distortion to the substrates. An alignment state surrounded by hairpin defects and lightning defects is generated, and this alignment state is caused by the formation of these defects in the order of lightning defects and hairpin defects in the direction in which the liquid crystal molecules are floating from the alignment surface due to pretilt. The ferroelectric liquid crystal in the alignment state exhibits at least two stable states, and the angle formed by their optical axes is 2.
The absorption axis of one polarizing plate is aligned at the equal dividing position, and the absorption axis of the other polarizing plate is aligned perpendicularly to the position where the absorption axis of the other polarizing plate is aligned. A ferroelectric liquid crystal element characterized in that the color exhibited by a first stable state is the same as the color exhibited by a second stable state when rotated counterclockwise by the same angle. (7) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces of the ferroelectric liquid crystal. The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is produced by a foreign substance such as a spacer between the substrates or by applying distortion to the substrates. An alignment state surrounded by hairpin defects and lightning defects is produced, and this alignment state is caused by the formation of these defects in the order of lightning defects and hairpin defects with respect to the direction in which the liquid crystal molecules are floating from the alignment surface due to pretilt. and the ferroelectric liquid crystal in the alignment state has two stable states with low transmittance under crossed nicols and at the extinction position,
A ferroelectric liquid crystal element characterized by having a total of three or four states, one or two stable states with high transmittance at the extinction position under crossed Nicols. (8) The ferroelectric liquid crystal has two stable states under crossed Nicols, the first and second stable states with low transmittance at the extinction position, and two stable states under crossed Nicols and the third and fourth stable states with high transmittance at the extinction position. Four stable states are shown, and the absorption axis of one polarizing plate is aligned at a position that bisects the angle formed by their optical axes, and the absorption axis of the other polarizing plate is aligned perpendicularly thereto. The color that appears in the first stable state when only the polarizing plate is rotated clockwise by 3° to 30° is the same as the color that appears in the second stable state when the polarizing plate is rotated by the same angle counterclockwise. can be,
The color exhibited by the third stable state when only one polarizing plate is rotated clockwise by 3° to 30° is different from the color exhibited by the fourth stable state when rotated by the same angle counterclockwise. The ferroelectric liquid crystal device according to claim 7, characterized in that: (9) The ferroelectric liquid crystal is held in between and faces each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, and the ferroelectric liquid crystal is The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is produced by a foreign substance such as a spacer between the substrates or by applying distortion to the substrates. An oriented state surrounded by hairpin defects and lightning defects is produced, and this oriented state is caused by the occurrence of these defects in the order of the lightning defects and hairpin defects in the rubbing direction, and in the oriented state, The ferroelectric liquid crystal exhibits at least two stable states, and θ_a, which is 1/2 of the angle formed by their optical axes, and the tilt angle Θ of the ferroelectric liquid crystal have a relationship of Θ>θ_a>Θ/2. A ferroelectric liquid crystal element characterized by: (10) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces of the ferroelectric liquid crystal. The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is produced by a foreign substance such as a spacer between the substrates or by applying distortion to the substrates. An oriented state surrounded by hairpin defects and lightning defects is produced, and this oriented state is caused by the occurrence of these defects in the order of the lightning defects and hairpin defects in the rubbing direction, and in the oriented state, A ferroelectric liquid crystal exhibits at least two stable states, and the absorption axis of one polarizing plate is aligned at a position that bisects the angle formed by their optical axes, and the absorption axis of the other polarizing plate is aligned perpendicularly thereto. Turn only one polarizing plate 3° to 30° clockwise from the arrangement.
A ferroelectric liquid crystal element characterized in that the color exhibited in a first stable state when rotated is the same as the color exhibited in a second stable state when rotated counterclockwise by the same angle. (11) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, respectively. The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is produced by a foreign substance such as a spacer between the substrates or by applying distortion to the substrates. An oriented state surrounded by hairpin defects and lightning defects is produced, and this oriented state is caused by the occurrence of these defects in the order of the lightning defects and hairpin defects in the rubbing direction, and in the oriented state, The ferroelectric liquid crystal has two stable states, one under crossed Nicols, with low transmittance at the extinction position, and one under crossed Nicols, with high transmittance at the extinction position.
A ferroelectric liquid crystal element characterized by having three or four stable states, one or two stable states. (12) The ferroelectric liquid crystal has two stable states, first and second, under crossed Nicols, with low transmittance at the extinction position, and two stable states, third and fourth, under crossed Nicols, with high transmittance at the extinction position. Four stable states are shown, and the angles formed by their optical axes are 2
The absorption axis of one polarizing plate is aligned at the equal dividing position, and the absorption axis of the other polarizing plate is aligned perpendicularly to the position where the absorption axis of the other polarizing plate is aligned. The color exhibited by the first stable state is the same as the color exhibited by the second stable state when rotated counterclockwise by the same angle, and only one polarizing plate is rotated clockwise by 3° to 30°. 12. The ferroelectric liquid crystal element according to claim 11, wherein the color exhibited by the third stable state is different from the color exhibited by the fourth stable state when rotated by the same angle in a counterclockwise direction. (13) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on each of the opposing surfaces, and the ferroelectric liquid crystal is The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is aligned in the process of cooling from a high temperature such as SmA to Sm^*C. θ_a where there is no orientation change accompanied by defects, and where the ferroelectric liquid crystal in the orientation state exhibits at least two stable states, and which is 1/2 of the angle formed by their optical axes.
and a tilt angle Θ of the ferroelectric liquid crystal having a relationship of Θ>θ_a>Θ/2. (14) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, and the ferroelectric liquid crystal is The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is aligned in the process of cooling from a high temperature such as SmA to Sm^*C. ferroelectric liquid crystal exhibits at least two stable states in which there is no orientation change accompanied by defects, and in which the ferroelectric liquid crystal in the orientation state exhibits at least two stable states, and the absorption axis of one polarizing plate is aligned at a position that bisects the angle formed by their optical axes; The color that appears in the first stable state when only one polarizing plate is rotated 3° to 30° clockwise from the arrangement where the absorption axis of the other polarizing plate is aligned perpendicularly to that, and the same angle in the counterclockwise direction. 2nd when rotated
A ferroelectric liquid crystal element characterized in that the stable state of the ferroelectric liquid crystal element exhibits the same color. (15) A ferroelectric liquid crystal and a ferroelectric liquid crystal that are held in between and face each other, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on each of the opposing surfaces, and the ferroelectric liquid crystal is The ferroelectric liquid crystal is equipped with a pair of substrates that are uniaxially aligned in the same direction and almost parallel to each other for alignment, and the ferroelectric liquid crystal is aligned in the process of cooling from a high temperature such as SmA to Sm^*C. There is no alignment change accompanied by defects, and the ferroelectric liquid crystal in the alignment state has two stable states: under crossed Nicols, with low transmittance at the extinction position, and under crossed Nicols, one or two stable states with high transmittance at the extinction position. A ferroelectric liquid crystal element characterized by having three or four stable states in total. (16) The ferroelectric liquid crystal has two stable states, first and second, under crossed Nicols, with low transmittance at the extinction position, and two stable states, third and fourth, under crossed Nicols, with high transmittance at the extinction position. Four stable states are shown, and the angles formed by their optical axes are 2
The absorption axis of one polarizing plate is aligned at the equal dividing position, and the absorption axis of the other polarizing plate is aligned perpendicularly to the position where the absorption axis of the other polarizing plate is aligned. The color exhibited by the first stable state is the same as the color exhibited by the second stable state when rotated counterclockwise by the same angle, and only one polarizing plate is rotated clockwise by 3° to 30°. 16. The ferroelectric liquid crystal element according to claim 15, wherein the color exhibited by the third stable state is different from the color exhibited by the fourth stable state when rotated by the same angle in a counterclockwise direction. (17) Claims 1 to 3, 13 to 1, wherein the orientation state has three or four different stable states that do not involve lightning defects and hairpin defects.
5. The ferroelectric liquid crystal device according to any one of Item 5. (18) If the temperature at which the orientation state transitions from SmA to Sm^*C is T_1°C, the transition from (T_1-5)°C to (T
Claim 1 present in the entire temperature range up to _1-10)°C
17. The ferroelectric liquid crystal device according to any one of items 1 to 16. (19) If the temperature at which the orientation state transitions from SmA to Sm^*C is T_1°C, then it changes from (T_1-5)°C to (T
Claim 1 present in the entire temperature range up to _1-20)°C
17. The ferroelectric liquid crystal device according to any one of items 1 to 16. (20) If the temperature at which the orientation state transitions from SmA to Sm^*C is T_1°C, the transition from (T_1-5)°C to (T
Claim 1 present in the entire temperature range up to _1-30)°C
17. The ferroelectric liquid crystal device according to any one of items 1 to 16. (21) If the temperature at which the orientation state transitions from SmA to Sm^*C is T_1°C, the transition from (T_1-5)°C to (T
Claim 1 present over the entire temperature range from _1 to 40)°C
17. The ferroelectric liquid crystal device according to any one of items 1 to 16. (22) The ferroelectric liquid crystal device according to any one of claims 1 to 16, wherein the relationship between the pretilt angle α and the tilt angle δ of the Sm^*C layer is approximately δ<α.