JPH0540265A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal element which has a high contrast in a bright state and a dark state, is extremely high in display contrast at the time of multiplexing driving in particular, provides a display of a high grade and does not generate after-images unsightly to the eyes. CONSTITUTION:This liquid crystal element is constituted by crimping a chiral smectic liquid crystal 15 between a pair of parallel substrates 11a and 11b formed with transparent electrodes 12a, 12b and having the oriented films 14a, 14b consisting of polyamide or polyamide on at least one of the substrates. The oriented films 14a, 14b mentioned above consist of the polyamide or polyimide which has <=35(dyne/cm) surface energy in a coated state and is increased in refractive index anisotropy (DELTAn) by a rubbing treatment.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a liquid crystal display device and a liquid crystal display.
The present invention relates to a liquid crystal element used in an optical shutter or the like, particularly a ferroelectric liquid crystal element, and more specifically to a liquid crystal element having improved display characteristics by improving the alignment state of liquid crystal molecules.

[0002]

2. Description of the Related Art A display device of a type in which transmitted light rays are controlled by using a refractive index anisotropy of ferroelectric liquid crystal molecules in combination with a polarizing device has been proposed by Clark and Lagerwall. (Unexamined-Japanese-Patent No. 56-107216, U.S. Patent No. 436792)
No. 4, 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. Has either a first optical stable state or a second optical stable state, and has the property of maintaining that state when no electric field is applied, that is, bistability, and is resistant to changes in the electric field. It has a quick response and is expected to be widely used as a high-speed and memory type display element, and in particular, due to its function, it is expected to be applied as a display with a large screen and high definition.

In order for the optical modulation element using the liquid crystal having the bistability to exhibit a predetermined driving characteristic, the liquid crystal arranged between the pair of parallel substrates is irrespective of the electric field application state. It is necessary that the molecular arrangement is such that the conversion between the two stable states occurs effectively.

Further, in the case of a liquid crystal element utilizing the birefringence of liquid crystal, the transmittance under orthogonal Nicols is

[0006]

[Equation 1]

(Wherein I _{0 is the} incident light intensity, I is the transmitted light intensity, θ is the tilt angle, Δn is the refractive index anisotropy, d is the thickness of the liquid crystal layer, and λ is the wavelength of the incident light. ). The tilt angle θ in the above-mentioned non-helical structure appears as an angle in the average molecular axis direction of the liquid crystal molecules in the first and second alignment states which are twisted and aligned. According to the above equation, the maximum transmittance is obtained when the tilt angle θ is 22.5 °,
The tilt angle θ of the non-helical structure that achieves bistability is 2
It should be as close as possible to 2.5 °.

By the way, as a method for orienting a ferroelectric liquid crystal, a liquid crystal molecular layer composed of a plurality of molecules forming a smectic liquid crystal is uniaxially oriented along its normal line over a large area. It is desirable that the manufacturing process can be realized by a simple rubbing treatment.

For example, US Pat. No. 4,561,726 is known as an alignment method for a ferroelectric liquid crystal, especially a chiral smectic liquid crystal having a non-helical structure.

However, the alignment method that has been used so far, particularly the alignment method using a rubbing-treated polyimide or polyamide film, is applied to the ferroelectric liquid crystal of the non-helical structure exhibiting the bistability disclosed by Clark and Ragawall. When applied to, the following problems were encountered.

That is, according to the experiments by the present inventors, a tilt angle θ in a non-helical ferroelectric liquid crystal obtained by aligning with a conventional rubbing-treated polyimide or polyamide film (see FIG. 3, which will be described later). It was found that the angle (shown) is smaller than the tilt angle H (angle shown in FIG. 2 described later) in the ferroelectric liquid crystal having a spiral structure. In particular, the tilt angle θ of a ferroelectric liquid crystal having a non-helical structure obtained by aligning with a conventional rubbing-treated polyimide or polyamide film is generally about 3 ° to 8 °, and the transmittance at that time is at most 3-5. It was about%.

As described above, according to Clark and Ragawall, the tilt angle of the ferroelectric liquid crystal having a non-helical structure which realizes the bistability has the same angle as the tilt angle of the ferroelectric liquid crystal having the spiral structure. As expected, the tilt angle θ in the non-helical structure is actually smaller than the tilt angle H in the spiral 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 H in the helical structure is due to the twist alignment of the liquid crystal molecules in the non-helical structure. That is, in a ferroelectric liquid crystal having a non-helical structure, the liquid crystal molecules are continuous with respect to the normal line of the substrate in the axis of the liquid crystal molecules adjacent to the lower substrate (direction of twist alignment) than the axis of the liquid crystal molecules adjacent to the upper substrate. Are arranged with a twist angle δ, which causes the tilt angle θ in the non-helical structure to be smaller than the tilt angle H in the spiral structure.

In addition, the alignment state of the chiral smectic liquid crystal produced by the conventional rubbing-treated polyimide or polyamide alignment film is affected by the presence of the polyimide or polyamide alignment film as an insulating layer between the electrode and the liquid crystal layer. Optically stable state (for example, white display state)
From one to a second optically stable state (for example, a black display state), a unipolar voltage is applied,
After applying release of one polarity voltage, a reverse electric field V _rev of the other polarity to the ferroelectric liquid crystal layer is generated, the reverse electric field V _{re v} had caused an after-image during display. The above-mentioned reverse electric field generation phenomenon has been clarified, for example, by Akio Yoshida, "Switching Characteristics of SSFLC" on pages 142-143 of "Liquid Crystal Conference Proceedings", October 1987.

[0014]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a ferroelectric liquid crystal device which solves the above-mentioned problems of the prior art, and particularly to a large chiral smectic liquid crystal non-helical structure. It is an object of the present invention to provide a ferroelectric liquid crystal element that can achieve a display in which a tilt angle θ is generated, a high-contrast image is displayed, and an afterimage does not occur.

[0015]

That is, the present invention is a liquid crystal device having a chiral smectic liquid crystal sandwiched between a pair of parallel substrates on which transparent electrodes are formed, and a liquid crystal element having a polyimide or polyamide alignment film on at least one substrate, The alignment layer has a surface energy of 35 (d
and a refractive index anisotropy (Δn) increases by rubbing treatment.

The present invention will be described in detail below. FIG. 1 is a schematic view showing an example of a ferroelectric liquid crystal device of the present invention.

In FIG. 1, 11a and 11b are respectively I
n ₂ O ₃ and ITO (indium tin oxide; I
transparent electrode 12a such as ndium tin oxide)
And a substrate (glass substrate) covered with 12b, on which insulating films 13a and 13b having a thickness of 200Å to 1500Å are formed.
50 (for example, SiO ₂ film, TiO ₂ film, Ta ₂ O ₅ film, etc.) and the polyimide or polyamide
Alignment films 14a and 14b each having a thickness of Å to 1000Å are laminated.

At this time, the alignment films 14a and 14b, which have been rubbed (in the arrow direction) so as to be parallel and in the same direction (direction A in FIG. 1), are arranged. Substrates 11a and 11
b between the ferroelectric chiral smectic liquid crystal 15 and
Are arranged, and the distance between the substrates 11a and 11b is sufficiently small to suppress the formation of the helical alignment structure of the ferroelectric chiral smectic liquid crystal 15 (for example, 0.
1 μm to 3 μm), and the ferroelectric chiral smectic liquid crystal 15 has a bistable alignment state. The sufficiently small ferroelectric chiral smectic liquid crystal 1 described above
The distance between the liquid crystals in which 5 is arranged is determined by the alignment films 14a and 14a.
bead spacer 16 (for example,
Silica beads, alumina beads, etc.). Further, 17a and 17b represent polarizing plates.

In the present invention, the polyimide or polyamide used for the alignment film is 35 (d
yne / cm) or less, preferably 32 (dyne / c)
m), which has a low surface energy and whose birefringence of the alignment film, that is, refractive index anisotropy (Δn) is increased to some extent by rubbing treatment, has good display characteristics with a large tilt angle. It has been found that it is suitable for obtaining a ferroelectric liquid crystal device. Regarding the degree of increase in the refractive index anisotropy, the smaller the change in increase is, the better the display characteristics can be obtained at the same surface energy level.

The surface energy is a value measured by a droplet method using a contact angle meter. A high-sensitivity automatic birefringence measuring apparatus using a photoelastic modulator was used for evaluating the refractive index anisotropy of the alignment film.

The alignment film in the present invention is not particularly limited in structure as long as it satisfies the above conditions, and examples thereof include the followings.

Examples of the tetracarboxylic acid component constituting the polyimide include pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride and the like.

Examples of the dicarboxylic acid component constituting the polyamide include terephthalic acid, 4,4'-biphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid and the like.

Further, as the diamine component constituting the polyimide or polyamide, for example, a bis [4- (aminophenoxy) phenyl] compound represented by the following general formula (I) can be used.

[0025]

[Chemical 1]

(In the formula, R ₁ and R ₂ are CF ₃ (CF ₂ ) _m (CH ₂ ) _L-
Represents a fluoroalkyl chain (where L ≧ 0, m ≧ 0), and R ₁ and R ₂ may be the same or different. )
When the polyimide or polyamide film used in the present invention is provided on the substrate, the polyamic acid or polyamide itself, which is a precursor of the polyimide, may be used as dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, or the like. Dissolved in a solvent 0.01 ~
As a 40 wt% solution, the solution is applied on a substrate by a spinner coating method, a spray coating method, a roll coating method, or the like, and then 100 to 350 ° C., preferably 200 to 300 ° C.
In the case of polyimide, dehydration ring closure is performed to form a polyimide film, and in the case of polyamide, the solvent is evaporated to form a polyamide film. This polyimide or polyamide film is then rubbed with a cloth or the like. The polyimide or polyamide film used in the present invention is about 30Å to 1 μm, preferably 20
The film thickness is set to 0Å to 2000Å. At this time, the use of the insulating films 13a and 13b shown in FIG. 1 can be omitted. Further, in the present invention, when the polyimide or polyamide film is provided on the insulating films 13a and 13b, the thickness of the polyimide or polyamide film can be set to 500 Å or less, preferably 300 Å or less.

The liquid crystal substance used in the present invention is preferably a liquid crystal which produces a chiral smectic C phase through an isotropic phase, a cholesteric phase and a smectic A phase in the temperature lowering process. In particular, it is preferable that the pitch in the cholesteric phase is 0.8 μm or more (however, the pitch in the cholesteric phase is measured at the center point in the temperature range of the cholesteric phase). As a concrete liquid crystal substance thereof, for example, a liquid crystal substance “LC-
1 "," 80B "and" 80SI ^* "are preferably used in the liquid crystal composition.

[0028]

[Chemical 2]

Liquid crystal (1) (LC-1) ₉₀ / (80B) ₁₀ (2) (LC-1) ₈₀ / (80B) ₂₀ (3) (LC-1) ₇₀ / (80B) ₃₀ (4) (LC-1) ₆₀ / (80B) ₄₀ (5) 80SI ^* (The above compounding ratios represent weight ratios.)

FIG. 2 is a schematic drawing of an example of a cell for explaining the operation of the ferroelectric liquid crystal. 21a and 2
1b is a substrate (glass plate) covered with a transparent electrode composed of a thin film of In ₂ O ₃ , SnO ₂ or ITO, and SmC ^{* in} which the liquid crystal molecular layer 22 is oriented perpendicular to the glass substrate surface ^. Liquid crystal of (chiral smectic C) phase or SmH ^* (chiral smectic H) phase is enclosed. A thick line 23 represents a liquid crystal molecule, and the liquid crystal molecule 23 has a dipole moment (P⊥) 24 in a direction orthogonal to the molecule. At this time, the tilt angle H in the chiral smectic phase of the helical structure that the angle forming the apex angle of the triangular pyramid is applied is shown. Board 2
When a voltage above a certain threshold is applied between the electrodes on 1a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the dipole moment (P⊥) 24 is oriented in the electric field direction. Can be changed. The liquid crystal molecules 23 have an elongated shape, and exhibit refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass substrate surface, a voltage application It is easy to understand that the liquid crystal optical modulator has optical characteristics that change depending on the polarity.

The surface-stabilized ferroelectric liquid crystal cell in the bistable alignment state used in the liquid crystal device of the present invention can be made sufficiently thin (for example, 0.1 to 3 μm). As the liquid crystal layer becomes thinner in this way, as shown in FIG. 3, the helical structure of the liquid crystal molecules is unwound and becomes a non-helical structure even when no electric field is applied, and the dipole moment Pa or Pb of the liquid crystal molecule is directed upward (34a). ) Or downward (34
Take one of the states of b).

When an electric field Ea or Eb having a polarity different from a certain threshold value is applied to such a cell by the voltage applying means 31a and 31b as shown in FIG. 3, the dipole moment becomes the electric field vector of the electric field Ea or Eb. Correspondingly, the direction is changed to the upward direction 34a or the downward direction 34b, and the liquid crystal molecules are aligned to either the first stable state 33a or the second stable state 33b accordingly. First and second at this time
1/2 of the angle formed by the stable state of 1 corresponds to the tilt angle θ.

The effects obtained by this ferroelectric liquid crystal cell are, firstly, that the response speed is extremely fast, and secondly that the orientation of the liquid crystal molecules is bistable. The second point will be further explained with reference to FIG. 3, for example.
When a is applied, the liquid crystal molecules are aligned in the first stable state 33a, but this state is stable even when the electric field is cut off. When a reverse electric field Eb is applied, the liquid crystal molecules are oriented in the second stable state 33b and change their orientation, but they remain in this state even when the electric field is turned off. Further, as long as the applied electric field Ea does not exceed a certain threshold value, the respective alignment states are still maintained.

Next, FIG. 4 is a sectional view schematically showing an alignment state of liquid crystal molecules aligned by an alignment method using a polyimide or polyamide alignment film in the liquid crystal element of the present invention,
FIG. 5 is a diagram showing the C-director.

Reference numerals 51a and 51b shown in FIG. 4 represent an upper substrate and a lower substrate, respectively. 50 is a liquid crystal molecule 52
In the liquid crystal molecule layer organized by, the liquid crystal molecules 52 are arranged at different positions along the bottom surface 54 (circle) of the cone 53.

FIG. 5 is a diagram showing a C-director.
In FIG. 5, U ₁ is the C-director 81 in one stable orientation state, and U ₂ is the C-director 81 in the other stable orientation state. The C-director 81 is a projection of the molecular long axis on a virtual plane perpendicular to the normal line of the liquid crystal molecular layer 50 shown in FIG.

On the other hand, the alignment state produced by the conventional rubbing-treated polyimide or polyamide film is shown by the C-director diagram of FIG. In the orientation state shown in FIG. 6, the tilt angle θ is small because the twist of the molecular axis is large from the upper substrate 51a to the lower substrate 51b.

Next, FIG. 7A shows a C-director 81.
Is an explanatory view showing the tilt angle θ in the state of FIG. 5 (referred to as a uniform orientation state), and FIG. 7B shows the tilt angle θ when the C-director 81 is in the state of FIG. 6 (referred to as a splay orientation state). FIG. In the figure, 60 represents a rubbing treatment axis applied to the above-described specific polyimide or polyamide film of the present invention, 61a is an average molecular axis in an alignment state U ₁ , 61b is an average molecular axis in an alignment state U ₂ , 62a Is the average molecular axis in the oriented state S ₁ , and 62b is the average molecular axis in the oriented state S ₂ . The average molecular axes 61a and 61b are
It is possible to perform conversion by applying voltages of opposite polarities which exceed each other's threshold voltage. The same applies to the average molecular axes 62a and 6
It also occurs with 2b.

Next, the usefulness of the uniform orientation state with respect to the delay (afterimage) of the optical response due to the reverse electric field V _rev will be described.

The capacitance C _i of the insulating layer (alignment film) of the liquid crystal cell,
When the capacitance of the liquid crystal layer is C _LC and the spontaneous polarization of the liquid crystal is Ps, V _rev that causes an afterimage is represented by the following equation.

[0041]

[Equation 2]

FIG. 8 is a sectional view schematically showing the distribution of charges in the liquid crystal cell, the direction of spontaneous polarization Ps, and the direction of the reverse electric field V _rev . FIG. 8A shows the distribution state of + and-charges under the memory state before the application of the pulse electric field, and the direction of the spontaneous polarization Ps at this time is from the + charge to the-charge.
FIG. 8B shows that the direction of the spontaneous polarization Ps immediately after the release of the pulse electric field is opposite to that in the case of FIG. 8A (therefore, the liquid crystal molecules are changed from one stable alignment state to the other stable alignment state). However, since the distribution state of + and − charges is the same as that in the case of FIG. 8A, the reverse electric field V _rev is generated in the liquid crystal in the arrow B direction. This reverse electric field V _rev disappears after a while, and the distribution state of + and − charges changes as shown in FIG. 8C.

FIG. 9 is an explanatory view showing a change in optical response in a splay alignment state caused by a conventional polyimide or polyamide alignment film in place of a change in tilt angle θ. As shown in FIG. 9, when the pulse electric field is applied, the arrow X ₁
Along the direction of the mean molecular axis S under splay orientation
From (A) to the average molecular axis U _{2 in} the uniform orientation state near the maximum tilt angle H, the reverse electric field V _rev shown in FIG.
And the tilt angle θ decreases along the direction of arrow X ₂ to the average molecular axis S (B) in the splay alignment state,
Then, due to the action of the attenuation of the reverse electric field V _rev shown in FIG. 8C, a stable alignment state in which the tilt angle θ is slightly increased along the direction of the arrow X ₃ to the average molecular axis S (C) under the splay alignment state is obtained. can get. FIG. 10 is a graph showing the state of optical response at this time.

According to the present invention, as described above, the orientation film has a low surface energy of 35 (dyne / cm) or less in the coating film state, and the refractive index anisotropy (Δn) is increased by the rubbing treatment. In this alignment state, the average molecular axes S (A), S (B) and S (C) in the splay state shown in FIG. It can be arranged on the average molecular axis that produces a tilt angle θ close to the tilt angle H. Figure 1
1 is a graph showing the state of the optical response of the present invention at this time. According to FIG. 11, it can be seen that the optical response is not delayed due to the afterimage and that the high contrast in the memory state is caused.

The liquid crystal device of the present invention exhibits a large optical contrast in a bright state and a dark state by using an alignment method using a specific rubbing-treated polyimide or polyamide alignment film, and particularly US Pat. No. 4,655. 5
A large contrast is generated with respect to non-selected pixels at the time of multiplexing driving disclosed in Japanese Patent No. 61
Furthermore, an alignment state was achieved in which the optical response at the time of switching (at the time of multiplexing driving), which causes the afterimage at the time of display, did not occur.

[0046]

EXAMPLES The present invention will be described more concretely with reference to the following examples. Example 1 Two 1.1 mm-thick glass plates provided with a 1000 Å-thick ITO film were prepared, and N-methyl-polyamic acid represented by the following structural formula (II) was formed on each glass plate.
2. Pyrrolidone / n-butyl cellosolve = 5/1 3.
Approximately 1 hour after spin-coating a 0 wt% solution for 2 hours
It was heated and baked at 50 ° C. The film thickness at this time is 226
It was Å.

[0047]

[Chemical 3]

Measurement of the contact angle of this coating film by the droplet method (using a contact angle meter manufactured by Kyowa Interface Science Co., Ltd.)
The surface energy γ _s (= γ ^d + γ ^p + γ ^h , where γ ^{d is a} dispersion component, γ ^{p is a} polar component, and γ ^h is a hydrogen bond component) is 31.
It was 4 dyne / cm.

When the refractive index anisotropy Δn of this coating film was measured (manufactured by Oak Manufacturing Co., Ltd., high-sensitivity automatic birefringence measuring device), Δn = 0.066.

Next, the coating film thus formed is
One-way rubbing treatment with a nylon blanket was performed.
The refractive index anisotropy at this time is Δn = 0.0221,
The change in Δn due to the rubbing treatment was 0.0155.

After that, alumina beads having an average particle diameter of about 1.5 μm are dispersed on one of the substrates, and two glass substrates are stacked so that the rubbing treatment axes are parallel to each other and in the same treatment direction. A cell was also prepared.

In this cell, "CS-1014" (trade name), which is a ferroelectric smectic liquid crystal manufactured by Chisso Co., Ltd.
After vacuum injection under isotropic phase, 0.5
Orientation could be achieved by slow cooling to 30 ° C. for h. The phase change in the cell of this example using this ferroelectric liquid crystal "CS-1014" was as follows.

[0053]

[Equation 3]

(Iso. = Isotropic phase, Ch = cholesteric phase, SmA = smectic A phase, SmC ^* = chiral smectic C phase) The above liquid crystal cell is sandwiched between a pair of 90 ° crossed Nicol polarizers. , 50μsec of 30V pulse is applied, then 90 ° crossed Nicol is set to the extinction position (darkest state), the transmittance at this time is measured by a photomultiplier, and then 50μsec of -30V pulse is applied. When the transmittance (bright state) at this time was measured by the same method, the tilt angle θ was 15 °, the transmittance in the darkest state was 1%, and the transmittance in the bright state was 28%. Yes, so the contrast ratio was 28: 1.

Further, the delay of the optical response which causes the afterimage was 0.2 seconds or less.

Further, when this liquid crystal cell was displayed by multiplexing driving using the driving waveform shown in FIG. 12, a high-contrast and high-quality display was obtained, and after the image was displayed by inputting a predetermined character, the entire screen was displayed. When the image was erased to a white state, the afterimage could not be read.
Note that S _N , S _{N + 1} , and S _{N + 2} in FIG. 12 represent voltage waveforms applied to scanning lines, and I represents voltage waveforms applied to typical information lines. (I-S _N ) is the information line I
Is a combined waveform applied to the intersection of the scanning line S _N and the scanning line S _N.
Further, in this embodiment, V ₀ = 5 to 8 V, ΔT = 20 to 70
It was performed in μsec.

Example 2 A cell was prepared in the same manner as in Example 1 except that a polyimide alignment film obtained from a polyamic acid represented by the following structural formula (III) was used.

[0058]

[Chemical 4]

The same test as in Example 1 was conducted, and the surface energy of the coating film γ _s = 31.1 dyne / cm,
The refractive index anisotropy Δn of the coating film was 0.0154, the refractive index anisotropy after the rubbing treatment was Δn = 0.0241, and the change in Δn due to the rubbing treatment was 0.00877.

At this time, the result was that the contrast ratio was 35: 1 and the optical response time was 0.1 second.

Further, when a display was performed by the same multiplexing driving as in Example 1, good results similar to those in Example 1 were obtained in terms of contrast and afterimage.

Example 3 A cell was prepared in the same manner as in Example 1 except that a polyimide alignment film obtained from a polyamic acid represented by the following structural formula (IV) was used.

[0063]

[Chemical 5]

The same test as in Example 1 was conducted, and the surface energy of the coating film γ _s = 30.5 dyne / cm,
The refractive index anisotropy Δn of the coating film was 0.0122, the refractive index anisotropy after the rubbing treatment was Δn = 0.0454, and the change in Δn due to the rubbing treatment was 0.0332.

At this time, the result was that the contrast ratio = 32: 1 and the optical response time was 0.1 second.

Further, when a display was performed by the same multiplexing driving as in Example 1, good results similar to those in Example 1 were obtained in terms of contrast and afterimage.

Example 4 A cell was produced in the same manner as in Example 1 except that the polyamide alignment film represented by the following structural formula (V) was used.

The same test as in Example 1 was conducted, and the surface energy of the coating film γ _s = 33.4 dyne / c
m, refractive index anisotropy of coating film Δn = 0.033
3. Refractive index anisotropy after rubbing treatment Δn = 0.0600
The change in Δn due to the rubbing treatment was 0.0267.

At this time, the results were that the contrast ratio was 20: 1 and the optical response time was 0.5 seconds.

Further, when the display was performed by the same multiplexing driving as in Example 1, the same good results as in Example 1 were obtained in terms of contrast and afterimage.

Comparative Examples 1 to 3 A cell was prepared in the same manner as in Example 1 except that the polyamide alignment film (Comparative Example 1) shown in Table 1 and the polyimide alignment film obtained from polyamic acid were used.

Table 2 shows the surface energy γ _s value for the coating film, the refractive index anisotropy Δn of the coating film, the refractive index anisotropy Δn after the rubbing treatment, the contrast ratio for each cell, and the optical response time. It was shown to.

Further, when a display was performed by the same multiplexing driving as in Example 1, the contrast was smaller than that in Example 1 and an afterimage was generated.

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

As described above, according to the liquid crystal element of the present invention, the contrast in the bright state and the dark state is high, and particularly the display contrast during the multiplexing driving is very large and a high quality display can be obtained. In addition, an effect that a noticeable afterimage phenomenon does not occur can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a liquid crystal element of the present invention.

FIG. 2 is a perspective view showing an alignment state of a chiral smectic liquid crystal having a helical structure.

FIG. 3 is a perspective view showing an orientation state of a chiral smectic liquid crystal having a non-helical molecular arrangement.

FIG. 4 is a cross-sectional view showing an alignment state of a chiral smectic liquid crystal aligned by an alignment method using an alignment film according to the present invention.

5 is a C-director diagram of the chiral smectic liquid crystal of FIG. 4 in a uniform alignment state.

FIG. 6 is a C-director diagram in a splay alignment state.

7A is an explanatory diagram showing a tilt angle θ in a uniform alignment state, and FIG. 7B is an explanatory diagram showing a tilt angle θ in a splay alignment state.

FIG. 8 is a cross-sectional view showing a charge distribution in a ferroelectric liquid crystal, a direction of spontaneous polarization Ps, and a direction of a reverse electric field V _rev .

FIG. 9 is an explanatory diagram showing changes in tilt angle θ during and after application of an electric field.

FIG. 10 is a graph showing optical response characteristics of a liquid crystal element of a conventional example.

FIG. 11 is a graph showing optical response characteristics of the liquid crystal element of the present invention.

FIG. 12 is a waveform diagram of a drive voltage used in an example of the present invention.

[Explanation of symbols]

11a, 11b Glass substrate 12a, 12b Transparent electrode 13a, 13b Insulating film 14a, 14b Alignment film 15 Ferroelectric chiral smectic liquid crystal 16 Bead spacer 17a, 17b Polarizing plate 21a, 21b Substrate 22 Liquid crystal molecular layer 23 Liquid crystal molecule 24 Dipole moment 31a, 31b Voltage application means 32 Vertical layer 33a First stable state 33b Second stable state 34a Upward dipole moment 34b Downward dipole moment H Tilt angle in helical structure θ Tilt angle in non-helical structure Ea, Eb Electric field 50 liquid crystal molecule layer 51a upper substrate 51b lower substrate 52 liquid crystal molecules 53 cone 54 bottom surface 60 substrate pulling direction or rubbing treatment axis 61a average molecular axis in orientation state U ₁ 61b average molecular axis in orientation state U ₂ 62a orientation state S ₁ Average molecular axis at 62 The average molecular axes 81 C-director in the orientation state S ₂

Claims (1)

[Claims] 1. A liquid crystal device having a chiral smectic liquid crystal sandwiched between a pair of parallel substrates on which transparent electrodes are formed, and a polyimide or polyamide alignment film on at least one of the substrates, wherein the alignment film has a surface energy in a coating state. A liquid crystal element having a refractive index anisotropy (Δn) of 35 (dyne / cm) or less and having a refractive index anisotropy (Δn) increased by rubbing treatment.