JPH06186568A - Ferroelectric liquid crystal device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a ferroelectric liquid crystal device having no unevenness in the panel plane. [Structure] The ferroelectric liquid crystal and the ferroelectric liquid crystal are opposed to each other with the ferroelectric liquid crystal held therebetween, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposed surfaces, respectively. In a liquid crystal element that has a pair of substrates that have been subjected to a uniaxial orientation process for orientation, and the apparent tilt angle by the process of applying an alternating current is larger than that when no alternating current is applied, at the interface between the liquid crystal and the substrate. A ferroelectric liquid crystal device having a pretilt angle of less than 5 ° and a spontaneous polarization of the ferroelectric liquid crystal of 25 nC / cm ² or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element used in a liquid crystal display element, a liquid crystal shutter or the like, particularly a ferroelectric liquid crystal element. More specifically, it improves display characteristics by improving the alignment state of liquid crystal molecules. The present invention relates to a liquid crystal element.

[0002]

2. Description of the Related Art A display device of a type in which transmitted light rays are controlled by utilizing a refractive index anisotropy of ferroelectric liquid crystal molecules in combination with a polarizing element has been proposed by Clark and Lagerwall. (JP-A-56-107216, U.S. Pat. No. 43679)
No. 24, etc.). This ferroelectric liquid crystal generally has a non-helical chiral smectic C phase (Sm ^* C) or H phase (Sm ^* H) 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 maintains the state when no electric field is applied, that is, has bistability, and is resistant to changes in the electric field. It has a quick response and is expected to be widely used for high-speed and memory type display devices. In particular, its function is expected to be applied to a large-screen, high-definition display.

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 conversion between the two stable states occurs efficiently.

Further, in the case of a liquid crystal element utilizing the birefringence of liquid crystal, the transmittance under a crossed Nicols is I / I ₀ = sin
It is represented by ^{2 4} θsin ² (Δn · dπ / λ).

(In the formula: 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 twisted liquid crystal molecules in the first and second alignment states. According to the above equation, the tilt angle θ is 2
The maximum transmittance is obtained when the angle is 2.5 °, and it is necessary that the tilt angle in the non-helical structure that realizes the bistability is as close as possible to 22.5 °.

As a method for obtaining the above ferroelectric liquid crystal element, a liquid crystal element in which an orientation is changed by applying an alternating current has been proposed (Japanese Patent Laid-Open No. 62-161123). The tilt angle θ in the non-helical structure can be increased by this technique, and the alignment of the liquid crystal can be changed from the twist alignment between the upper and lower substrates to the parallel alignment (uniform alignment) having substantially the same C-director. The transmittance of the state can be reduced. This provides high contrast.

[0007]

When an alternating current is applied to make the alignment uniform, the presence of zigzag alignment defects in the Sm ^* C phase at the time of realignment makes the alignment state non-uniform. As a result, the distribution of zigzag alignment defects within the panel becomes uneven in the threshold value. In both black and white binary and gradation elements, unevenness in this plane reduces the driving margin of the entire panel, and especially in gradation elements, this unevenness becomes a serious problem.

In order to perform gradation display, it is not preferable that the threshold characteristic rises too rapidly with respect to the voltage and the pulse width. For example, when the voltage at which domain inversion starts due to the electric field is V _th and the voltage at which the domain inversion is completed is V _sat , V _sat / V _{th is set} to γ, and when this value is close to 1, the threshold characteristic rises too rapidly. And gradation display becomes difficult.

In order to realize a switching element with high brightness and high speed, it is necessary to use a ferroelectric liquid crystal having a large spontaneous polarization. However, in the orientation having the chevron structure, the switching characteristics are easily impaired due to the influence of the reverse electric field generated by the spontaneous polarization, and the display element does not function. Further, the smaller the electric capacity of the layer between the liquid crystal such as the alignment film and the electrode and the higher the electric resistance, the more easily the switching characteristics are deteriorated due to the influence of the reverse electric field generated by the spontaneous polarization.

The applied voltage in the alternating current application process that has been performed so far is usually ± 20 to 30 V / μm, and a high voltage is required. Therefore, it is difficult to perform the AC application process using the drive waveform generating circuit. If the AC application process can be performed in the vicinity of ± 10 V, the information signal generating circuit can be used and the AC application process can be easily performed.

[0011]

In order to improve the above-mentioned various problems, in particular, uniform alignment, the present invention is directed to a ferroelectric liquid crystal and a ferroelectric liquid crystal which are opposed to each other with the ferroelectric liquid crystal held therebetween. Each of them has a pair of substrates on which electrodes for applying a voltage to the ferroelectric liquid crystal are formed and which is subjected to a uniaxial alignment treatment for aligning the ferroelectric liquid crystal. In a liquid crystal device in which the tilt angle is made larger than that when no alternating current is applied, the pretilt angle is less than 5 ° in the direction in which the liquid crystal and the substrate interface are tilted in the opposite direction between the upper and lower substrates. Is a ferroelectric liquid crystal element having a spontaneous polarization of 25 nC / cm ² or more.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 schematically shows an example of the ferroelectric liquid crystal cell of the present invention.

Reference numerals 11a and 11b denote substrates (glass plates) covered with transparent electrodes 12a and 12b such as In ₂ O ₃ and ITO (Indium Tin Oxide), respectively, on which alignment control films 13a and 13b are laminated. Has been done. The orientation control films 13a and 13b are subjected to uniaxial orientation treatment such as rubbing.

A low resistance short-circuit prevention layer may be laminated between the transparent electrode 12 and the orientation control film 13. Substrates 11a and 1
The ferroelectric liquid crystal 14 is arranged between the substrate 1 and
The space between a and 11b is held by the bead spacer 15. Reference numerals 16a and 16b are deflection plates.

In such a structure, the tilt direction at the interface between the liquid crystal and the substrate is opposite between the upper and lower substrates, the pretilt is less than 5 °, preferably 0 to 3 °, and the spontaneous polarization of the ferroelectric liquid crystal is 25 nC. / Cm ² or more, preferably 50n
By setting the ratio to C / cm ² or more, it is possible to obtain a high-speed and high-contrast ferroelectric liquid crystal element without unevenness in the panel surface. In the present invention, "the tilt directions of the liquid crystal and the substrate interface are opposite between the upper and lower substrates" means that the heads of the liquid crystal molecules at the upper and lower substrate interfaces are held in the state shown in FIG. As shown by an arrow A in FIG. 1, the substrates 11a and 1a are arranged so that the uniaxial alignment treatment directions are parallel and in the same direction.
It is necessary to attach 1b.

The thickness of the orientation control film 13 is preferably 5 nm or less in consideration of the further improvement of the switching characteristics.
When the low resistance orientation control film is used, the film thickness may be 5 nm or more.

The chiral smectic C phase of the ferroelectric liquid crystal used in the present invention has a spiral pitch of 1 μm.
The following is preferable because the gradation can be further improved.

Furthermore, the ferroelectric liquid crystal alignment state has two layers having different layer normals, and the layers are regularly and alternately arranged in stripes, which means that the thresholds between the stripes are different, and It is preferable in that the tonality can be further improved.

The change in orientation and the change in layer structure due to the alternating current application treatment in the present invention will be described.

FIG. 3 shows an alignment state (1) of the above liquid crystal material (FLC3) alignment film, Semicofine Lp64 (3 nm) manufactured by Toray Industries, Inc. before AC application. Fig. 4 shows the orientation state (2) after applying ± 10 V AC and 10 Hz to it.
Is. The tilt angle θ in the non-helical structure in the alignment state (1) was 8 °, but the tilt angle θ in the non-helical structure in the alignment state (2) was 26 °. Further, the results of measuring the change in the layer structure by X-ray bending are shown in FIG. 5 {alignment state (1)} and FIG. 6 {alignment state (2)}. It can be seen from FIG. 5 that the alignment state (1) is an alignment having one or more bends between the upper and lower substrates. It can be seen from the results in FIG. 6 that the orientation state is a pseudo bookshelf structure due to the application of alternating current.

[0022]

EXAMPLES The present invention will be described below with reference to examples. The measuring method in this example is as follows.

[Measurement of Apparent Tilt Angle] After applying a single pulse equal to or more than the threshold value of the liquid crystal, the ferroelectric liquid crystal element placed between them under no electric field and under crossed Nicols is placed horizontally with the deflection plate. After rotating, the first extinction position is searched, and after applying a pulse having a polarity opposite to that of a single vapor pulse, the second extinction position is searched under no electric field. The half of the angle to the first extinction position at this time was defined as θa.

[Measurement of Pretilt Angle α] Jpn. J. A
ppl. Phys. Vo. 119 (1980) NO. 1
0, according to the method (crystal rotation method) described in Short Notes 2013.

The examples in the present invention were obtained with a liquid crystal material having the following physical properties at room temperature.

[0026]

[Table 1] (Example 1) 0.4% NM of polyamic acid LQ1802 manufactured by Hitachi Chemical Co., Ltd. was placed on a glass substrate having a transparent electrode.
A P / nBC = 1/1 solution was applied with a spinner, pre-dried at 80 ° C. for 5 minutes, and then baked at 270 ° C. for 1 hour. At this time, the orientation film thickness was 30Å. Next, push in this substrate 0.4 mm, rotation speed 1000 rpm, feed speed 40 m
It was rubbed with a nylon cloth at m / s × 2 times.

After this, keeping a gap of 1.5 μm,
A bonded cell was prepared so that the rubbing directions were parallel to each other. The pretilt angle of the cell was measured by injecting a liquid crystal into a cell in which substrates subjected to the same treatment were attached so that the rubbing directions were anti-parallel, and was measured by a crystal rotation method in the SmA state. there were. FL in the above cell
C2 was heated to 80 ° C. under reduced pressure and injected by capillarity. After cooling, the alignment was observed with a polarizing microscope at room temperature. As a result, there were almost no zigzag defects, and there were two states, pale white and black. ± 20V / μm in this state,
When a square wave of 10 Hz was applied for 5 minutes at 30 ° C. and the texture was changed, the apparent tilt angle θ _a changed from 8 ° to 19.5 °, and a uniform alignment state without defects was formed. Was done.

The switching characteristics of this orientation state were observed by changing the transmitted light by applying a pulse width of 40 μS bipolar pulse and 1.5 times the switching threshold between the white state and the black state. Was obtained, and 100% black and white reversal was confirmed.

(Example 2) On a glass substrate with a transparent electrode, polyamic acid Sanever SE manufactured by Nissan Chemical Industries, Ltd.
A 0.4% solution of 100, NMP / nBC = 1/1 was applied by a spinner and pre-dried at 80 ° C. for 5 minutes, and then 270
Calcination was performed for 1 hour. At this time, the orientation film thickness was 30Å. Next, this substrate was pushed by a roller of 0.40 (m
m), roller rotation number 1000 (rpm), roller feed speed 12 (mm / s) × 1 time, and rubbing with a nylon cloth.

Then, the cells were prepared by laminating the gaps of 1.5 μm so that the rubbing directions were parallel to each other. The pretilt angle α of the cell was 3 ° as measured by the crystal rotation method.

The above-mentioned FLCs 2 and 3 were placed in the cell under reduced pressure at 80
The temperature was raised to ° C and the mixture was injected by capillarity. After cooling, the alignment was observed at room temperature using a polarizing microscope.
C2 had almost no zigzag defects and had a pale white state and a black state. FLC3 had a pale black and white state in which the extinction position was slightly shifted. Therefore, FLC2 applies ± 20 V / μm at 30 ° C. and 10 Hz for 5 minutes to change the texture to obtain uniform orientation with an apparent tilt angle θ _a of 19.5 °, and FLC3 ± 70 V from 70 ° C. to 30 ° C.
/ Μm, while gradually cooling while applying an alternating electric field of 10 Hz, a uniform orientation with an apparent tilt angle θ _a of 26 ° was obtained. In the above uniform alignment state, a single pulse of 10 V / μm is applied to the pulse width Δ
T was changed and applied, and the process of changing from the black state to the white state was measured by the amount of transmitted light. At this time, FIG. 8 is a graph in which the transmitted light amount in the black state is 0% and the white state is 100%.
If the steepness of the threshold is γ = ΔT _sat / ΔT _th , then F
LC3 is γ≈2.04 and FLC2 is γ≈1.15, and it can be seen that the gradation is more advantageous for FLC3 having a short spiral pitch. Here, ΔT _sat is a transmitted light amount of 10
The pulse width when 0% is reached, and ΔT _th is the pulse width when the amount of transmitted light rises from 0%.

Example 3 On a glass substrate having a transparent electrode, a polyamic acid sun ever SE10 manufactured by Nissan Chemical Co., Ltd.
0.4% NMP / nBC = 2/1 solution of 0 was spin-coated, pre-dried at 90 ° C. for 5 minutes, and then baked at 200 ° C. for 1 hour. At this time, the orientation film thickness was 30Å. next,
Push in this substrate 0.4 (mm), rotation speed 1000 (r
pm) and a feed rate of 12 (mm / s) × 1 time, and rubbing with a nylon cloth.

Thereafter, a cell was prepared by laminating the gaps of 1.5 μm so that the rubbing directions were parallel to each other. The pretilt angle of the cell was 1.3 ° as measured by the crystal rotation method. FLC1 to the cell
4 is injected and a square wave of ± 7 V / μm, 10 Hz is applied at 30 ° C.
When applied for 5 minutes, the FLC1 showed a slight scratch-like orientation and had unevenness of θa = 8 to 17 °. FLC
No. 2 has a haze-like orientation and a stripe-like orientation, and θa
= 17 to 19 °, and FLC3 and FLC4 had a stripe-like orientation and θa = 25.5 ° and 26 °, respectively.
Therefore, the larger Ps is, the more θ
It can be seen that a is likely to be Θ.

(Comparative Example 1) A lot of zigzag defects were observed by observing the alignment state of the element which was subjected to the same treatment as that of Example 1 except that the rubbing directions were bonded in antiparallel to each other before the application of an alternating electric field. ± 20 V / μm in this state, 10
When an alternating electric field of Hz was applied for 5 minutes at 30 ° C. and the texture was changed, the apparent tilt angle θ _a was 8 ° to 1
Although it was spread over 9 °, a triangular texture remained at the place where the zigzag defect was present, and uniform alignment was not obtained.

[0035]

As described above, according to the present invention, it is possible to obtain a ferroelectric liquid crystal element having no unevenness in the panel surface, excellent gradation, and preventing switching failure.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a tilt direction at a liquid crystal / substrate interface.

FIG. 3 is a diagram showing an alignment state (1) of the liquid crystal device of the present invention before application of an alternating current.

FIG. 4 is a diagram showing an alignment state (2) of the liquid crystal element of the present invention after application of an alternating current.

5 is a diagram showing an X-ray profile in the orientation state of FIG.

6 is a diagram showing an X-ray profile in the orientation state of FIG.

FIG. 7 is a diagram showing transmitted light characteristics of the liquid crystal element of the present invention.

FIG. 8 is a graph showing T-ΔT characteristics of FLC2 and FLC3.

[Explanation of symbols]

 11 substrate 12 transparent electrode 13 alignment control film 14 ferroelectric liquid crystal 15 bead spacer 16 polarizing plate A uniaxial alignment treatment direction

Claims (9)

[Claims] 1. A ferroelectric liquid crystal and a ferroelectric liquid crystal which face each other with the ferroelectric liquid crystal held therebetween, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposing surfaces, respectively. In a liquid crystal element, which comprises a pair of substrates that have been subjected to a uniaxial alignment treatment for aligning the liquid crystal, and the apparent tilt angle by the treatment of applying an alternating current is larger than that when no alternating current is applied, the liquid crystal and the substrate The tilt direction at the interface is opposite between the upper and lower substrates, the pretilt angle is less than 5 °, and the spontaneous polarization of the ferroelectric liquid crystal is 25 nC / cm.
^A ferroelectric liquid crystal device characterized by being ² or more. 2. The ferroelectric liquid crystal element according to claim 1, wherein the thickness of the alignment control film for the uniaxial alignment treatment is 5 nm or less. 3. The ferroelectric liquid crystal device according to claim 1, wherein the spiral pitch of the chiral smectic C phase of the ferroelectric liquid crystal is 1 μm or less. 4. The spontaneous polarization of the ferroelectric liquid crystal is 50 nC.
/ Cm ² or more, the ferroelectric liquid crystal element according to claim 1. 5. The ferroelectric liquid crystal and the ferroelectric liquid crystal are opposed to each other with the ferroelectric liquid crystal held therebetween, and electrodes for applying a voltage to the ferroelectric liquid crystal are formed on the opposed surfaces, respectively. A uniaxial alignment in a liquid crystal element that has a pair of substrates that have been subjected to a uniaxial alignment treatment for aligning liquid crystals and has a larger apparent tilt angle due to the treatment of applying an alternating current than that when no alternating current is applied. The rubbing as a treatment is parallel between the upper and lower substrates, the pretilt angle is less than 5 ° in the same direction, and the spontaneous polarization of the ferroelectric liquid crystal is 2
A ferroelectric liquid crystal device characterized by having 5 nC / cm ² or more. 6. The ferroelectric liquid crystal device according to claim 5, wherein the thickness of the alignment control film for the uniaxial alignment treatment is 5 nm or less. 7. The ferroelectric liquid crystal device according to claim 5, wherein the spiral pitch of the chiral smectic C phase of the ferroelectric liquid crystal is 1 μm or less. 8. The spontaneous polarization of the ferroelectric liquid crystal is 50 nC.
6. The ferroelectric liquid crystal element according to claim 5, wherein the ferroelectric liquid crystal element has a density of / cm ² or more. 9. The ferroelectric liquid crystal structure according to claim 1, wherein the ferroelectric liquid crystal alignment state has two different layers having different layer normals, and the layers are arranged regularly and alternately in a stripe pattern. Liquid crystal element.