JP2003342572A - Chiral smectic liquid crystal composition and liquid crystal element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal element having excellent orientation uniformity in its display surface, having few defects and, when used for display device such as a flat panel display, showing a preferable display performance. <P>SOLUTION: The chiral smectic liquid crystal composition comprises a chiral smectic liquid crystal of Iso-Ch-SmC* or Iso-SmC* and has ≥0.992 d(Tc-5)/ d(Tc) ratio, wherein d(Tc) is a layer spacing at Tc and d(Tc-5) is a layer spacing at Tc-5°C, and the liquid crystal element is provided by using the composition. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device including a liquid crystal element used for a light valve used in a flat panel display, a projection display, a printer and the like, and a display device using the same.

[0002]

2. Description of the Related Art A typical liquid crystal mode of a nematic liquid crystal display element which has been widely used as a display element using an active element such as a TFT (Thin Film Transistor) is, for example, M. Schatt. And W. Helfrich A
18th Applied Physics Letters
The Twisted Nematic mode, shown in Vol. 4, No. 4, (Published February 15, 1971), pages 127 to 128, is widely used. On the other hand, recently, an in-plane switching mode using a lateral electric field and a vertical alignment (Verti
A liquid crystal display using the cal alignment mode has been announced, and the viewing angle characteristic, which was a drawback of the conventional liquid crystal display, has been improved. Thus, there are several liquid crystal modes for use in a TFT display device using nematic liquid crystal.
In any of the modes, the response speed of the liquid crystal is as slow as several tens of milliseconds or more, and further improvement in response speed is required.

In order to improve the response speed of such a conventional nematic liquid crystal device, a voltage is applied to the splay alignment obtained in a cell rubbed in the same direction to change the alignment to the bend alignment, thereby improving the response speed. An improved scheme was announced by Bos et al. In 1983 (π cell). In 1992, Uchida et al. Announced a study to improve viewing angle characteristics by performing phase compensation on such a bend-oriented cell (OCB cell). Furthermore, some liquid crystal modes using a liquid crystal exhibiting a chiral smectic phase have been proposed. For example, "short-pitch type ferroelectric liquid crystal", "polymer stable ferroelectric liquid crystal", "threshold antiferroelectric liquid crystal", etc. have been proposed, but they have not yet been put to practical use. It has been reported that a high-speed response of sub-millisecond or less can be realized.

On the other hand, we have invented and proposed the element described in Japanese Patent Laid-Open No. 2000-338464 (hereinafter referred to as "prior application 1"). In the present invention, for example, focusing on the material of the phase series showing the isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) from the high temperature side, the position inside the edge of the virtual cone I am trying to make it mono-stabilized. Then, for example, by applying a positive or negative DC voltage between the pair of substrates at the time of the Ch-SmC * phase transition, the layer direction is made uniform in one direction, which enables high-speed response and gradation control. Therefore, a high-brightness liquid crystal element excellent in moving image quality can be realized with high mass productivity. The element of the prior application can reduce the spontaneous polarization value as compared with the above-mentioned various smectic liquid crystal modes, and therefore, is an element that is well matched with an active element such as a TFT.

Similarly, we have invented and proposed the element described in Japanese Patent Laid-Open No. 2000-010076 (hereinafter referred to as "Prior Application 2"). In the present invention, for example, focusing on a material of a phase series showing an isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) from the high temperature side, a simple cone is formed at the position of the virtual cone edge. I try to stabilize it. Then, for example, by applying a positive or negative DC voltage between the pair of substrates at the time of the Ch-SmC * phase transition, the layer direction is made uniform in one direction, which enables high-speed response and gradation control. Therefore, a high-brightness liquid crystal element excellent in moving image quality can be realized with high mass productivity. The element of the prior application 2 has small hysteresis and can realize stable halftone display.
Moreover, since the spontaneous polarization value can be made smaller than the other various smectic liquid crystal modes described above, it is an element that is well matched with an active element such as a TFT.

As described above, in the sense that the problems relating to the response speed, which the conventional TFT liquid crystal display using the nematic liquid crystal has, can be solved, a novel liquid crystal element, particularly the liquid crystal elements of the prior applications 1 and 2 are used. Realization of a liquid crystal display device using is expected.

[0007]

As described above, the smectic liquid crystal device of the prior application having the gradation display capability is expected in the next-generation displays and the like which are required to have high-speed response performance. On the other hand, when these smectic liquid crystal elements are used in a display device such as a flat panel display, it is essential in terms of display quality to realize uniform alignment in the display surface.

The present invention has been made in view of the above problems, and its problem is that it is excellent in uniform alignment in the display surface, particularly high in contrast, and is used in a display device such as a flat panel display. Another object of the present invention is to provide a liquid crystal element having suitable display performance, and a liquid crystal device using the element.

[0009]

The problems of the present invention are solved by the following inventions.

That is, the first aspect of the present invention is that the phase transition sequence of the chiral smectic liquid crystal is changed from the high temperature side to the isotropic liquid phase.
(Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) or isotropic liquid phase (Iso) -chiral smectic C phase (SmC *), wherein the chiral smectic liquid crystal is a chiral smectic C phase. When the transition temperature from the higher temperature phase to the chiral smectic C phase is Tc, the layer spacing d (Tc) of the smectic layer at Tc ° C and the layer spacing d (Tc-5) of the smectic layer at Tc-5 ° C. A chiral smectic liquid crystal composition having a ratio d (Tc-5) / d (Tc) of 0.992 or more.

Further, the chiral smectic liquid crystal,
A pair of electrodes for applying a voltage to the liquid crystal, a pair of substrates facing each other with the liquid crystal sandwiched therebetween, and subjected to a uniaxial alignment treatment for aligning the liquid crystal, and a polarizing plate on at least one of the substrates. It is a liquid crystal element provided with. Further, at least one of the substrates used for the liquid crystal element has a chiral smectic liquid crystal element characterized by having an active element connected to an electrode corresponding to each pixel. Also,
The liquid crystal element shows a first state in which the average molecular axis of the liquid crystal is mono-stabilized when no voltage is applied, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal shows the magnitude of the applied voltage. When tilted to one side from the mono-stabilized position at an angle according to, and a voltage of a second polarity opposite to the first polarity is applied, the average molecular axis of the liquid crystal is mono-stabilized. Is a liquid crystal element that tilts to the opposite side to that when a voltage of the first polarity is applied from the position where the voltage of the first polarity is applied and the average molecular axis of the liquid crystal when a voltage of the second polarity is applied. When the tilt angles in the maximum tilt state with respect to the mono-stabilized position in the first state are β1 and β2, respectively,
In the liquid crystal element satisfying 1> β2, it is more preferable that the relation between β1 and β2 is β1 ≧ 5 × β2.

Alternatively, β2 is preferably substantially zero.

(Operation) In the smectic C phase, liquid crystal molecules have a layered structure. The layered structure has a bookshelf structure in which the layer direction is formed perpendicular to the upper and lower substrate surfaces, and has a certain inclination. It is known that a chevron structure that bends in a V shape, an oblique bookshelf structure that similarly tilts in one direction with a certain inclination, or an asymmetric chevron structure in which a part of the oblique bookshelf bends to the opposite side is formed.

Among them, it is known that the bookshelf structure is stably exhibited in a limited material system such as a naphthalene type liquid crystal and a polyfluorine type liquid crystal, and many smectic C liquid crystals have a chevron structure in which layers are inclined and an oblique direction. It has a bookshelf structure or an asymmetric chevron structure. In particular, the uniaxial orientation treatment directions are parallel, and in parallel rubbing cells made in the same direction, a chevron structure is generally taken, while the uniaxial orientation treatment directions are parallel,
In addition, an anti-parallel rubbing cell in the reverse direction often has an oblique bookshelf structure or an asymmetric chevron structure.

Further, it is generally known that various physical property values such as tilt angle, spontaneous polarization and liquid crystal layer spacing have temperature characteristics as characteristics of the chiral smectic liquid crystal itself. In particular, changes in the tilt angle and the layer spacing are greatly involved in the layer structure that greatly affects the in-plane uniformity of a liquid crystal device.

In many chiral smectic liquid crystals, the tilt angle gradually increases and the layer spacing decreases from the upper limit temperature of the chiral smectic C phase to a certain temperature as the temperature decreases. The layer inclination angle in the layer changes in order to compensate for the decrease in the layer interval. At this time, in the symmetrical chevron structure in which the square-shaped kink portion exists in the center of the upper and lower substrates, the upper and lower interfaces can be fixed and the change in the layer inclination angle can be absorbed without moving the horizontal position of the kink. On the other hand, in the slanted bookshelf structure, the interface molecules are inevitably moved in response to the change in the layer inclination angle. Further, even in the asymmetric chevron structure, the change in the layer inclination angle is accompanied by the movement of the kink position in the in-layer direction.

That is, it is conceivable that it is difficult to absorb the change in the layer inclination angle in the antiparallel rubbing cell in which the diagonal bookshelf structure or the asymmetric chevron structure is dominant. As a result, it is considered that the uniformity of orientation is deteriorated and defects are generated.

Based on the above consideration, we arrived at the present invention. That is, as shown in the present invention, when Tc is the temperature at which the phase higher than the chiral smectic C phase transitions to the chiral smectic C phase,
The layer spacing d (Tc) and Tc-5 of the smectic layer at c ° C
Ratio of the smectic layer to the interlayer spacing d (Tc-5) at ℃ d (T
The inventors have found that by using a chiral smectic liquid crystal material having a c-5) / d (Tc) of 0.992 or more, a high-contrast alignment state can be generated even in an antiparallel rubbing cell.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The chiral smectic liquid crystal used in the present invention has a phase transition sequence of an isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) from the high temperature side. Those are preferable. That is, the liquid crystal of the present embodiment has a differential scanning calorimeter (DSC; D) during the phase transition from the high temperature phase to the chiral smectic C phase (SmC *).
The presence of smectic A phase (SmA) was not confirmed by ifferential scanning calorimeter).

Specific examples of preferable compounds constituting the liquid crystal composition used in the present invention are shown below in (1) to (4).

[Outer 1]

R ₁ , R ₂ : linear or branched alkyl group having 1 to 20 carbon atoms and optionally having a substituent X ₁ , X ₂ : single bond, O, COO, OOC Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F n: 0 or 1

[Outside 2]

R ₁ , R ₂ : a linear or branched alkyl group having 1 to 20 carbon atoms and optionally having a substituent X ₁ , X ₂ : a single bond, O, COO, OOC Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F

[Outside 3]

R ₁ , R ₂ : a linear or branched alkyl group having 1 to 20 carbon atoms and optionally having a substituent X ₁ , X ₂ : a single bond, O, COO, OOC Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F

[Outside 4]

R ₁ , R ₂ : a linear or branched alkyl group having 1 to 20 carbon atoms and optionally having a substituent X ₁ , X ₂ : a single bond, O, COO, OOC Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F In particular, in the present invention, at least one of a plurality of compounds constituting the liquid crystal composition is provided with a smectic A phase in the phase transition series as a single compound. Compounds that do not have, for example, compounds in which the phase transition sequence is isotropic phase-nematic phase (or cholesteric phase) -smectic C phase (or chiral smectic C phase) or isotropic phase-smectic C phase (or chiral smectic C phase) It is preferable to use.

A specific embodiment of the liquid crystal device of the present invention will be described below with reference to FIG.

In the liquid crystal element shown in the figure, a pair of glass,
Substrates 11a, 11 made of highly transparent material such as plastic
A cell in which a liquid crystal 15, preferably a liquid crystal exhibiting a chiral smectic phase is sandwiched between b is sandwiched between a pair of polarizing plates (not shown) whose polarization axes are orthogonal to each other.

On the substrates 11a and 11b, electrodes 12 made of a material such as In ₂ O ₃ or ITO for applying a voltage to the liquid crystal 15 are provided.
a and 12b are provided, for example, as described later, dot-shaped transparent electrodes are arranged in a matrix on one substrate, and a TFT or MIM (Metal-Insulator-Meta) is arranged on each transparent electrode.
l) and other switching elements are connected to each other, and one surface of the other substrate or a counter electrode having a predetermined pattern is provided to form an active matrix structure.

The electrodes 12a, On 12b, SiO _2, TiO ₂ having a function such as to prevent these short as necessary,
Insulating films 13a and 13b made of a material such as Ta ₂ O ₅ are provided respectively.

Further, on the insulating films 13a and 13b, an alignment control film which is in contact with the liquid crystal 15 and functions to control the alignment state thereof.
14a and 14b are provided. Such an orientation control film 14a,
At least one of 14b is uniaxially oriented. As such a film, for example, an organic material such as polyimide, polyimideamide, polyamide, or polyvinyl alcohol, which is solution-coated, is subjected to a rubbing treatment on the surface of the film, or an oxide such as SiO or a nitride is obliquely applied to the substrate. An oblique vapor deposition film of an inorganic material vapor-deposited at a predetermined angle from the direction can be used.

Regarding the orientation control films 14a and 14b, the pretilt angle of the molecules of the liquid crystal 15 (the film surface near the interface of the orientation control film of the liquid crystal molecules) depends on the selection of the material and the conditions of the treatment (uniaxial orientation treatment etc.). The angle with respect to) is adjusted.

When the orientation control films 14a and 14b are both uniaxially oriented films, the uniaxial orientation treatment directions (especially rubbing directions) of the respective films are antiparallel or parallel depending on the liquid crystal material used. , Or cross rubbing, or rubbing on only one side can be set.

The substrates 11a and 11b face each other with a spacer 16 in between. The spacer 16 is formed on the substrates 11a, 11
determines the distance (cell gap) between b,
Silica beads and the like are used. Regarding the cell gap determined here, the optimum range and the upper limit differ depending on the liquid crystal material, but uniform uniaxial orientation, and when the voltage is not applied, the average molecular axis of the liquid crystal molecules is almost the same as the average orientation axis. In order to develop an alignment state that is substantially the same as the axis, it is preferably set in the range of 0.3 to 10 μm.

In addition to the spacer 16, the substrates 11a and 1a
Adhesive particles made of a resin material such as an epoxy resin may be dispersed and arranged in order to improve the adhesiveness between the 1b and the impact resistance of the liquid crystal exhibiting the chiral smectic phase (not shown).

In the liquid crystal device having the above structure, when a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal 15, the composition of the material is adjusted, and further, the treatment of the liquid crystal material and the device configuration, for example, the alignment control films 14a and 14b. By appropriately setting the materials, processing conditions, etc., when no voltage is applied,
The average molecular axis (liquid crystal molecule) of the liquid crystal shows an alignment state in which it is mono-stabilized, and one polarity (first polarity) when driven.
When the voltage is applied, the tilt angle based on the position where the average molecular axis is monostabilized changes continuously according to the magnitude of the applied voltage, and when the voltage of the other polarity (second polarity) is applied, The average molecular axis is made to exhibit a characteristic of tilting at an angle according to the magnitude of the applied voltage. At this time, the characteristic may be such that the maximum tilt angle due to the voltage application of the first polarity is larger than the maximum tilt angle due to the voltage application of the second polarity. Alternatively, when the voltage of the second polarity is applied, the average molecular axis may not tilt regardless of the magnitude of the applied voltage.

The liquid crystal material 15 exhibiting the chiral smectic phase has various characteristics (conical property value cone angle Θ peculiar to the liquid crystal material, layer spacing d of the smectic layer, inclination angle δ).
, Etc.) are selected appropriately as the hydrocarbon liquid crystal material having a biphenyl skeleton, a phenylcyclohexane ester skeleton, a phenylpyrimidine skeleton, a naphthalene liquid crystal material, and a polyfluorine liquid crystal material. The composition thus prepared is used.

In the liquid crystal element, at least one of R, G and B color filters is provided on one of the substrates 11a and 11b,
It can also be a color liquid crystal element. Alternatively, a method of performing full-color display by utilizing color mixing by time division can be used by sequentially switching the R, G, and B light sources as light sources.

The liquid crystal element is a transmissive liquid crystal element in which a pair of polarizing plates are provided on both substrates 11a and 11b.
That is, both the substrates 11a and 11b are translucent substrates,
Incident light from one substrate side (for example, light from an external light source)
Of the type which modulates the light and outputs it to the other side, or a reflective liquid crystal element in which a polarizing plate is provided on at least one substrate, that is, a reflector is provided on either one of the substrates 11a and 11b, or one of the substrates is provided. The present invention can be applied to any type of element that modulates incident light and reflected light by using a reflective material as itself or as a member provided on the substrate and emits light to the same side as the incident side.

In the present invention, a drive circuit for supplying a gradation signal to the above-mentioned liquid crystal element is provided, and a continuous tilt angle from the monostable position of the average molecular axis of the liquid crystal is provided by applying the voltage as described above. It is possible to configure a liquid crystal display element that performs gradation display by utilizing the characteristics of the change and the amount of light emitted from the element that continuously changes. For example, by using an active matrix substrate having the above-mentioned TFT or the like as one substrate of the liquid crystal element, and performing active matrix driving by amplitude modulation in the drive circuit, analog gray scale display is possible.

An example using such an active matrix substrate in the liquid crystal element of the present invention will be described with reference to FIGS.

FIG. 2 is a diagram schematically showing the element with a driving means, focusing on the structure of one substrate (active matrix substrate).

In the configuration shown in FIG. 2, in the panel portion corresponding to the liquid crystal element, the scanning signal driver 21 which is the driving means.
Gate lines in the horizontal direction on the drawing that correspond to the scanning lines connected to
, And a source line S1 in the vertical direction on the drawing, which corresponds to the information signal line connected to the information signal driver 22 which is the driving means,
S2 ... Are provided so as to be orthogonal to each other while being insulated from each other, and a thin film transistor (TFT) 24 corresponding to a switching element and a pixel electrode 25 corresponding to a pixel at each intersection thereof.
Is provided (only 5x5 pixel area is shown in the figure for simplification). As the switching element, a MIM element can be used instead of the TFT. Gate line G1, G2
... are connected to the gate electrode (not shown) of the TFT24, the source lines S1, S2 ... Are connected to the source electrode (not shown) of the TFT24, and the pixel electrode 25 is the drain electrode (not shown) of the TFT24.
It is connected to the. In such a configuration, the gate lines G1, G2, ... Are scan-selected, for example, in a line-sequential manner by the scan signal driver 21, and a gate voltage is supplied, and the information signal driver 22 writes in each pixel in synchronization with the scan selection of the gate line. Information signal voltage corresponding to information is supplied to the source lines S1, S2 ... And applied to each pixel electrode via the TFT 24.

FIG. 3 shows an example of a sectional structure of each pixel portion (for one bit) in the panel structure as shown in FIG. In the structure shown in the figure, a liquid crystal layer 59 having spontaneous polarization is sandwiched between an active matrix substrate 30 having a TFT 24 and a pixel electrode 25 and a counter substrate 50 having a common electrode 52.
A liquid crystal capacitor (Clc) 41 is configured.

Regarding the active matrix substrate 30,
An example using an amorphous Si TFT as the TFT 24 is shown. The TFT 24 is formed on the substrate 31 made of glass or the like,
An a-Si layer 34 is provided on a gate electrode 32 connected to the gate lines G1, G2 ... Shown in FIG. 2 via an insulating film (gate insulating film) 33 made of a material such as silicon nitride (SiNx), On the a-Si layer 34, a source electrode 37 and a drain electrode 38 are provided separately from each other via n ⁺ a-Si layers 35 and 36, respectively. The source electrode 37 is the source lines S1 and S2 shown in FIG.
, And the drain electrode 38 is connected to the pixel electrode 25 made of a transparent conductive film such as an ITO film. The channel protective film 39 covers the a-Si layer 34 of the TFT 24. this
The TFT 24 is turned on by applying a gate pulse to the gate electrode 32 during a period in which the corresponding gate line is scanned and selected.

Further, in the active matrix substrate 30, the insulating film 33 (continuously provided with the insulating film on the gate electrode 32 by the pixel electrode 25 and the storage capacitor electrode 40 provided on the glass substrate side of the electrode). A storage capacitor (CS) 42 is provided in parallel with the liquid crystal layer 41 by a structure in which a film is sandwiched. When the area of the storage capacitor electrode is large, the aperture ratio is lowered, and thus the storage capacitor electrode is formed of a transparent conductive film such as an ITO film.

On the TFT 24 and the pixel electrode 25 of the active matrix substrate 30, an alignment control film 53 which is subjected to a uniaxial alignment process such as a rubbing process for controlling the alignment state of liquid crystal.
a is provided.

On the other hand, in the counter substrate 50, the common electrode 52 and the alignment control film 53b for controlling the alignment state of the liquid crystal are laminated on the glass substrate 51 with the same thickness as the entire surface.

The cell structure is sandwiched between a pair of polarizing plates whose polarization axes are orthogonal to each other (not shown).

In the pixel portion of the panel having the above structure, a liquid crystal having spontaneous polarization, for example, a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal layer 59.

In the panel structure as shown in FIGS. 2 and 3, polycrystalline Si (p
A substrate with -Si) TFT can be used.

An equivalent circuit of the pixel portion of the panel shown in FIG. 3 is shown in FIG.

Active matrix driving utilizing the characteristics of the liquid crystal element having the above structure will be described with reference to FIGS. In active matrix driving in the liquid crystal element of the present invention, for example, a period (one frame) for displaying certain information in one pixel is divided into a plurality of fields (for example, 1F and 2F shown in FIG. 5), and an average is calculated in these two fields. The amount of emitted light corresponding to predetermined information is obtained. In the following, an example in which the liquid crystal layer 59 is divided into two fields in the case where the liquid crystal layer 59 has a characteristic that the transmitted light intensity is sufficient when a voltage of one polarity is applied and the transmitted light intensity is smaller when the polarity is opposite is described.

FIG. 5A shows a voltage applied to one gate line which is a scanning line connected to the pixel when one pixel is focused on. In the liquid crystal device having the above structure, the gate lines G1, G2, ... Are selected line by line, for example, in each field, a predetermined gate voltage Vg is applied to one gate line in the selection period Ton, and the voltage Vg is applied to the gate electrode 32. The TFT24 is turned on. During a non-selection period Toff corresponding to a period when another gate line is selected, the TFT 24 is in a high resistance state (off state) without applying a voltage to the gate electrode 32, and a predetermined same gate line is selected for each Toff. The gate voltage Vg is applied to the gate electrode 32.

FIG. 5B shows the voltage Vs applied to the information signal line (source line) of the pixel. As shown in FIG. 5A, when a gate voltage is applied to the gate electrode 32 in the selection period Ton in each field, the source lines S1, S2 ... Electrode 37
A predetermined source voltage (information signal voltage) Vs (the reference potential is the potential Vc of the common electrode 52) is applied to.

Here, in the first field (1F) that constitutes one frame, the optics to be obtained in the pixel based on the information written in the pixel, for example, the voltage-transmittance characteristic according to the liquid crystal used. A positive source voltage (information signal voltage) of level Vx corresponding to the state or display information (transmittance) (the reference potential is the potential Vc of the common electrode 52) is applied. At this time, since the TFT 24 is on, the source electrode 37
The voltage Vx applied to the pixel electrode (25) is applied via the drain electrode 38 to the liquid crystal capacitance (Clc) 41 and the storage capacitance 42.
(Cs) is charged and the potential of the pixel electrode is the information signal voltage
Become Vx. Subsequently, since the TFT 24 has a high resistance (off state) in the non-selection period Toff of the gate line to which the pixel belongs, the liquid crystal cell (liquid crystal capacitance Clc) 41 is generated in this non-selection period.
The storage capacitor (Cs) 42 maintains the state in which the charge charged in the selection period Ton is stored and holds the voltage Vx. Then, the first field 1F is formed on the liquid crystal layer 59 in the pixel.
The voltage Vx is applied during the period of, and an optical state (amount of transmitted light) corresponding to this voltage value is obtained in the liquid crystal portion of the pixel. At this time, if the response speed of the liquid crystal is slower than the gate-on period, the liquid crystal cell (liquid crystal capacitance Clc) 41 and the storage capacitance (Cs) 4
Switching is started during the non-selected period when the charging is completed to 2 and the gate is turned off. In such a case, the charges charged by the reversal of the spontaneous polarization are offset, and the voltage applied to the liquid crystal layer takes a value Vx 'smaller than Vx as shown in FIG. 5C.

Next, in the selection period Ton of the second field (2F), the source voltage (-Vx) having a polarity opposite to that of the first field 1F and having substantially the same voltage value Vx is the source electrode 37. Applied to. At this time, the TFT 24 is in the ON state, the voltage −Vx is applied to the pixel electrode 25, the liquid crystal capacitance (Clc) 41 and the storage capacitance (Cs) 42 are charged, and the potential of the pixel electrode is changed to the information signal voltage −Vx. become. Subsequently, since the TFT 24 has a high resistance (off state) in the non-selection period Toff, the liquid crystal cell (liquid crystal capacitance Clc) 41 is in the non-selection period Toff.
The storage capacitor (Cs) 42 maintains the state in which the charge charged in the selection period Ton is stored, and holds the voltage -Vx.
Then, the voltage -Vx is applied to the liquid crystal layer 59 in the pixel through the second field 2F period, and in the pixel, an optical state (amount of emitted light) corresponding to the voltage value is obtained. At this time as well, when the response speed of the liquid crystal is slower than the gate-on period, the liquid crystal cell (liquid crystal capacitance Clc) 41 and the storage capacitance (C
s) Charging is completed at 42 and switching is started during the non-selection period when the gate is turned off. In such a case, the charged charges are canceled by the inversion of the spontaneous polarization, and the voltage applied to the liquid crystal layer takes a value of −Vx ′ smaller than −Vx as shown in FIG. 5C. FIG. 5C shows the voltage value Vpix that is actually held in the liquid crystal capacity and the holding capacity of the pixel as described above and is applied to the liquid crystal layer 59. FIG. 5D shows the actual value of the liquid crystal in the pixel. The optical response (optical response when a transmissive liquid crystal element is used) is schematically shown. As shown in (c),
The applied voltages are at the same level (absolute value) Vx 'only with their polarities inverted with respect to each other through the two fields 1F and 2F.
On the other hand, in the first field 1F as shown in (d), V
A gradation display state (amount of emitted light) corresponding to x'is obtained, and a gradation display state corresponding to -Vx 'is obtained in the second field 2F, but only a slight change in the amount of transmitted light is actually obtained. , The transmitted light amount is smaller than Tx and becomes Ty close to 0 level.

In the active matrix driving as described above, when a liquid crystal exhibiting a chiral smectic phase is used, gradation display based on good high-speed response is possible, and at the same time gradation display of a level of one pixel is performed. Since the first field that obtains a high transmitted light amount and the second field that obtains a low transmitted light amount are divided and continuously performed, the time aperture ratio is 50
% Or less, the moving image high-speed response characteristics that human eyes perceive will be good. Further, in the second field, the amount of transmitted light does not completely become zero due to a slight switching operation of the liquid crystal molecules, so that the brightness perceived by human eyes in the entire frame period is secured.

Further, the voltages of the same level in the first and second fields are reversed in polarity and applied to the liquid crystal layer 59.
The voltage actually applied to the liquid crystal layer 59 is converted into an alternating voltage to prevent deterioration of the liquid crystal.

In the above active matrix driving, 2
In the entire one frame composed of fields, the transmitted light amount obtained by averaging Tx and Ty can be obtained. Therefore, for the information signal voltage Vs, a voltage value that can obtain a large amount of transmitted light by a predetermined level is selected in accordance with the image information (gradation information) actually obtained by the pixel in the frame. It is also preferable to display the gradation state with a level transmitted light amount higher than the desired gradation state in the first field 1F by applying the voltage.

Although not described in detail here, it is also possible to apply the above-mentioned driving method and use a method in which full color display is performed by utilizing color mixture by time division by combining with RGB light sources.

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

(Example 1) (Preparation of liquid crystal composition) The following liquid crystal compounds were mixed to prepare a liquid crystal composition LC-1. The numerical values given in the structural formulas are weight ratios upon mixing.

[Outside 5]

The physical property parameters of the above liquid crystal composition LC-1 are shown below. Phase transition temperature (℃)

[Outside 6]

The phase transition temperature was measured under the following conditions. Measuring device Perkin Elmer DSC Pyris1 Measurement conditions After holding at 100 ° C for 1 minute, lower the temperature to -30 ° C at 5 ° C / min, then hold at -30 ° C for 5 minutes, and then at 1 ° C at 5 ° C / min.
Measure up to 00 ℃

[Outside 7]

(Production of Liquid Crystal Cell) An active matrix substrate having an a-Si TFT having a pixel structure described in the specification as one substrate and a silicon nitride film as a gate insulating film, and an RGB substrate as an opposing substrate. A pair of substrates having a color filter and a transparent electrode having a thickness of 1.1 mm were prepared. Screen size 10.4 inches, pixel number 800 × 600
And On the transparent electrode of the substrate, a commercially available alignment film for TFT SE
7992 (Nissan Chemical Co., Ltd.) is applied by spin coating,
Then, after pre-drying at 80 ° C. for 5 minutes, heating and baking was performed at 200 ° C. for 1 hour to obtain a polyimide film having a film thickness of 500 Å.

Subsequently, the polyimide film on the substrate was rubbed with a nylon cloth as a uniaxial orientation process. The rubbing condition is a rubbing roll in which nylon (NF-77 / made by Teijin) is bonded to a roll with a diameter of 10 cm. Pushing amount 0.3 mm, feed speed 10 cm / sec, rotation speed 100
It was set to 0 rpm and the number of feeds was 4.

Subsequently, silica beads having an average particle size of 1.5 μm are dispersed as spacers on one substrate, and the rubbing directions of the substrates are antiparallel to each other (antiparallel).
So as to face each other to obtain a cell (active matrix panel) having a uniform cell gap.

The liquid crystal composition LC-1 was injected into the cell manufactured by the above process at the temperature of the Ch phase, and the liquid crystal was cooled to a temperature showing the chiral smectic liquid crystal phase.
Before and after the −SmC ^* phase transition, an element sample A was manufactured by applying a −3V offset voltage (DC voltage) to perform cooling. The following evaluations were performed on such samples.

1. Alignment State The alignment state of the liquid crystal of the element sample A was observed with a polarizing microscope.

As a result, at room temperature (30 ° C.), it was observed that the darkest axis was slightly deviated from the rubbing direction with no voltage applied, and the layer normal direction was only one direction in the entire cell. . In addition, although a slight light leakage was observed around the beads in the plane, no defect causing light leakage was observed in other portions, and a uniform alignment state without unevenness in alignment was obtained. An orientation photograph is shown in Fig. 6 (the photograph is of an ITO single bit cell prepared by the same process).

2. Optical response In order to measure the electro-optical response of the liquid crystal element, the cell of the element sample A was placed in a polarizing microscope with a photomultiplier so that a dark field was obtained under no voltage applied under crossed Nicols. did.

Observing the optical response when a triangular wave of ± 5 V and 0.2 Hz was applied to this at 30 ° C., the amount of transmitted light (transmitted light) gradually increased in accordance with the magnitude of the applied voltage when a positive voltage was applied. Rate) has increased. On the other hand, the state of the optical response when a negative voltage is applied shows that although the transmitted light amount changes with respect to the voltage level, the maximum light amount is 1 when compared with the maximum transmittance when a positive voltage is applied. It was about / 10.

3. Rectangular Wave Response Device Sample A was applied with a rectangular wave voltage of 60 Hz (± 5 V) using the same device as the triangular wave response to measure the optical level while changing the voltage.

As a result, it was confirmed that a sufficient positive optical response was made to the positive voltage, and a stable halftone state was obtained without depending on the previous state of the optical response. In addition, an optical response of about 1/10 of the case of applying a positive polarity voltage of the same voltage absolute value to a negative polarity voltage was confirmed, and the average value of the optical response to positive and negative voltages does not depend on the previous state. It was confirmed that a stable halftone was obtained. 4. Measurement of Layer Interval An X-ray diffractometer manufactured by MAC Science Co., Ltd. of a rotating anticathode method was used as a measurement device, and copper Kα ray was used as an analysis line. To measure the liquid crystal layer spacing, apply liquid crystal composition LC-1 to a glass substrate with a thickness of 80 μm.
Apply so that the surface is smooth at mm square, and perform 2θ / θ scan in the same manner as usual powder X-ray diffraction.
The layer spacing d was found by applying the agg diffraction condition.

The measurement temperature is the temperature at which the liquid crystal composition LC-1 is in the cholesteric phase state (T to increase the smoothness of the diffraction surface).
c + 10 ℃), then Tc (55.7 ℃) and Tc-5 ℃ (50.7 ℃)
The measurement was carried out while descending at a rate of 2 ° C. per minute. The automatic temperature controller used in the experiment was about ± 0 at each temperature.
The control accuracy of 3 ℃ was shown.

As a result, the layer spacing (d_Tc) at Tc is 28.19.
Å, the layer spacing (d_Tc-5) at Tc-5 ℃ was 28.00Å, and the ratio (d_Tc-5 / d_Tc) was 0.993.

Comparative Example 1 (Preparation of Liquid Crystal Composition) The following liquid crystal compounds were mixed to prepare a liquid crystal composition LC-2. The numerical values given in the structural formulas are weight ratios upon mixing.

[Outside 8]

The physical property parameters of the above liquid crystal composition LC-2 are shown below. Phase transition temperature (℃)

[Outside 9]

The phase transition temperature was measured under the following conditions. Measuring device Perkin Elmer DSC Pyris1 Measurement conditions After holding at 100 ° C for 1 minute, lower the temperature to -30 ° C at 5 ° C / min, then hold at -30 ° C for 5 minutes, and then at 1 ° C at 5 ° C / min.
Measure up to 00 ℃

[Outside 10]

(Preparation of Liquid Crystal Cell) The liquid crystal composition LC-2 was injected into a cell prepared by the same process as in Example 1 at the temperature of the Ch phase, and the liquid crystal was cooled to the temperature showing the chiral smectic liquid crystal phase. At the time of cooling, before and after the Ch—SmC ^* phase transition, an offset voltage (DC voltage) of −3 V was applied to perform cooling, and an element sample B was produced. The following evaluations were performed on such samples.

1. Alignment State The alignment state of the liquid crystal of the device sample B was observed with a polarizing microscope.

As a result, at room temperature (30 ° C.), it was observed that the darkest axis was slightly displaced from the rubbing direction with no voltage applied, and the layer normal direction was only one direction in the entire cell. . However, many defects are generated in the plane, which causes light leakage in the state where no voltage is applied. The orientation photograph is shown in Fig. 7 (The photograph shows ITO made by the same process.
Single bit cells).

2. Optical response In order to measure the electro-optical response of the liquid crystal element, the cell of the element sample B was placed in a polarizing microscope with a photomultiplier so as to form a dark field in the absence of applied voltage under crossed Nicols. did.

Observing the optical response when a triangular wave of ± 5 V and 0.2 Hz was applied to this at 30 ° C., when the voltage of positive polarity was applied, the amount of transmitted light (transmission) gradually increased depending on the magnitude of the applied voltage. Rate) has increased. On the other hand, the state of the optical response when a negative voltage is applied shows that although the transmitted light amount changes with respect to the voltage level, the maximum light amount is 1 when compared with the maximum transmittance when a positive voltage is applied. It was about / 10.

3. Rectangular Wave Response Element Sample B was applied with a rectangular wave voltage of 60 Hz (± 5 V) using the same device as the triangular wave response, and the optical level was measured while changing the voltage.

As a result, it was confirmed that a sufficient positive optical response was made to the positive voltage, and the stable optical halftone state was obtained without depending on the previous state of the optical response. Also, for negative voltage, an optical response of about 1/10 of the case of applying positive voltage of the same voltage absolute value was confirmed, and the average optical response for positive and negative voltages does not depend on the previous state. It was confirmed that a stable halftone was obtained. 4. Measurement of Layer Interval The rotating apparatus was a rotating anticathode X-ray diffractometer manufactured by MAC Science Co., Ltd., and the copper Kα ray was used as the analysis line. To measure the liquid crystal layer spacing, apply liquid crystal composition LC-1 to a glass substrate with a thickness of 80 μm.
Apply so that the surface is smooth at mm square, and perform 2θ / θ scan in the same manner as usual powder X-ray diffraction.
The layer spacing d was found by applying the agg diffraction condition.

The measurement temperature is the temperature at which the liquid crystal composition LC-1 is in the cholesteric phase state (T to increase the smoothness of the diffraction surface).
c + 10 ℃), then Tc (60.7 ℃) and Tc-5 ℃ (55.7 ℃)
The measurement was carried out while descending at a rate of 2 ° C. per minute. The automatic temperature controller used in the experiment was about ± 0 at each temperature.
The control accuracy of 3 ℃ was shown.

As a result, the layer spacing (d_Tc) at Tc is 28.18.
Å, the layer spacing (d_Tc-5) at Tc-5 ℃ was 27.88Å, and the ratio (d_Tc-5 / d_Tc) was 0.989.

[0088]

As described in detail above, it can be seen that the use of a liquid crystal composition having a small change in the layer spacing from immediately below Tc can suppress the generation of defects that cause light leakage in the absence of applied voltage. . That is, according to the present invention,
The phase transition sequence of the chiral smectic liquid crystal is an isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) or an isotropic liquid phase from the high temperature side.
(Iso) -Chiral smectic C phase (SmC *),
When the transition temperature of the chiral smectic liquid crystal from the phase higher than the chiral smectic C phase to the chiral smectic C phase is Tc, the layer spacing d (Tc) of the smectic layer at Tc ° C and the smectic at Tc-5 ° C. Ratio of layer spacing d (Tc-5) d (Tc-5) / d (Tc)
Is 0.992 or more, and a liquid crystal element having few defects is provided by using the chiral smectic liquid crystal composition.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the basic configuration of a liquid crystal element of the present invention.

FIG. 2 is a plan view schematically showing a form in which a drive circuit is provided on an active matrix substrate of an active matrix liquid crystal element which is a preferable mode of the liquid crystal element of the present invention.

3 is a schematic sectional view of one pixel in the panel configuration shown in FIG.

4 is an equivalent circuit of the pixel of FIG.

FIG. 5 is a timing chart of an example of a driving method of the liquid crystal element having the configuration shown in FIGS.

FIG. 6 shows the measurement results of the liquid crystal composition LC-1 by X-ray diffractometry.

FIG. 7: Measurement results of liquid crystal composition LC-2 by X-ray diffraction method

[Explanation of symbols]

11a, 11b Substrates 12a, 12b Electrodes 13a, 13b Insulation films 14a, 14b Alignment control film 15 Liquid crystal 16 Spacer 20 Panel 21 Inspection signal driver 22 Information signal driver 23 Information signal line (source line) 24 TFT 25 Pixel electrode 26 Scanning signal Line (gate line) 30 active matrix substrate 31 substrate 32 gate electrode 33 gate insulating film 34 a-Si layers 35, 36 n ⁺ a-Si layer 37 source electrode 38 drain electrode 39 channel protective film 40 storage capacitor electrode 41 liquid crystal capacitor 42 Storage capacitor 50 Counter substrate 51 Substrate 52 Common electrodes 53a and 53b Alignment control film 59 Liquid crystal

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H088 EA03 EA13 EA33 FA20 JA19                       KA13 KA15 MA10                 2H093 NA16 NA32 NA43 NA61 ND32                       NF19 NG02 NH18                 4H027 BA06 BC04 BD08 BD12 BD16                       BD18 BD20 BE02 DE01 DE03                       DE09 DF01 DJ01

Claims (9)

[Claims] 1. A phase transition sequence of a chiral smectic liquid crystal is an isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) or an isotropic liquid phase (Iso) from the high temperature side. -Chiral smectic C phase (Sm
C *), where the temperature at which the chiral smectic liquid crystal transitions from a phase on the higher temperature side than the chiral smectic C phase to the chiral smectic C phase is Tc, the layer spacing d (Tc) of the smectic layers at Tc ° C. A chiral smectic liquid crystal composition having a ratio d (Tc-5) / d (Tc) of not less than 0.92 to the layer spacing d (Tc-5) of the smectic layer at Tc-5 ° C. 2. A pair of substrates, which face each other with a chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal sandwiching the liquid crystal, and which have been subjected to a uniaxial alignment treatment for aligning the liquid crystal. And a liquid crystal device including a polarizing plate on at least one of the substrates, wherein the phase transition sequence of the chiral smectic liquid crystal is an isotropic liquid phase (Is
o) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) or isotropic liquid phase (Iso) -chiral smectic C phase (SmC *), wherein the chiral smectic liquid crystal is better than the chiral smectic C phase. Also, when the temperature at which the phase on the high temperature side transitions to the chiral smectic C phase is Tc, the layer spacing d (Tc) of the smectic layer at Tc ° C. and the layer spacing d (Tc-5) of the smectic layer at Tc-5 ° C. Ratio of d (Tc-5) / d (Tc)
Is 0.992 or more, a chiral smectic liquid crystal device using a chiral smectic liquid crystal composition. 3. When no voltage is applied, the average molecular axis of the liquid crystal exhibits a first state in which it is mono-stabilized, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal shows a large applied voltage. The average molecular axis of the liquid crystal is tilted to one side from the monostable position at an angle according to the height, and the average molecular axis of the liquid crystal is monostable when a voltage having a second polarity opposite to the first polarity is applied. In a liquid crystal element that tilts to the opposite side from when the voltage of the first polarity is applied from the changed position, the average molecular axis of the liquid crystal when the voltage of the first polarity and the voltage of the second polarity are applied. 3. The liquid crystal device according to claim 2, wherein β1> β2, where β1 and β2 are tilt angles in the maximum tilt state based on the mono-stabilized position in the first state. 4. The tilt in the maximum tilt state with reference to the mono-stabilized position of the average molecular axis of the liquid crystal when the voltage of the first polarity is applied and when the voltage of the second polarity is applied. 4. The liquid crystal element according to claim 3, wherein β1 ≧ 5 × β2 when the angles of β1 and β2 are respectively set. 5. When no voltage is applied, the average molecular axis of the liquid crystal exhibits a first state in which it is mono-stabilized, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal shows a large applied voltage. The average molecular axis of the liquid crystal is tilted to one side from the monostable position at an angle according to the height, and the average molecular axis of the liquid crystal is monostable when a voltage having a second polarity opposite to the first polarity is applied. 3. The liquid crystal element according to claim 2, which is a liquid crystal element that does not substantially change from the changed position. 6. A substrate having a plurality of pixels, one of the pair of substrates having an active element connected to an electrode corresponding to each pixel, comprising a drive circuit for performing active matrix driving, and an analog floor. 6. The liquid crystal device according to claim 2, wherein the liquid crystal device performs gray scale display. 7. The liquid crystal device according to claim 2, wherein the helical pitch of the chiral smectic liquid crystal in the bulk state is longer than twice the cell thickness. 8. The liquid crystal device according to claim 2, which is a transmissive liquid crystal device. 9. The liquid crystal device according to claim 2, which is a reflective liquid crystal device.