JPH07281191A - Ferroelectric liquid crystal panel - Google Patents

Abstract

PURPOSE:To attain perfectly uniform orientation by controlling a (c) director pretilt and to obtain a high-contrast ferroelectric liquid crystal panel by clamping ferroelectric liquid crystals between a pair of substrates provided with orientation control films on transparent electrodes and using an orientation control film having chirality for one of the orientation control films. CONSTITUTION:The orientation control films are so formed that at least one thereof have the chirality. If the functional groups R2 of the orientation control film All and the orientation control film B21 and the liquid crystal molecules 2 are assumed to have the nature to attract each other, the liquid crystal molecules 2 on the orientation control film All incline in an R2 direction, i.e., in a left direction and the (c) director pretilt A17 is obtd. (c). The liquid crystal molecules 2 on the orientation control film B21 incline in the R2 direction as well but the direction where the molecules incline is rightward and the (c) director pretilt B27 is obtd. (f). A pair of the orientation control films which are optical euantiomers with each other impart the characteristics reverse with respect to the directions where the (c) directors incline to the molecules in such a manner. As a result, the easy control of the direction where the (c) directors incline is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal panel such as a liquid crystal display device and a liquid crystal optical shutter array.
In particular, the present invention relates to a ferroelectric liquid crystal optical device using a ferroelectric liquid crystal having a layer structure and a molecular arrangement.

[0002]

2. Description of the Related Art A panel using a ferroelectric liquid crystal utilizes the spontaneous polarization of liquid crystal molecules as shown by Clark et al. Ferroelectric liquid crystal has spontaneous polarization due to the structure of the molecule. In other words, in a structure that is a racemate having an asymmetric carbon in the molecule and has a dipole moment perpendicular to the long axis of the molecule, the long axes of the liquid crystal molecules are aligned and rotation around the long axis is obstructed. Sm
In the C ^* phase, the directions of dipole moments are also aligned, and spontaneous polarization appears there. By controlling the direction of this spontaneous polarization by the direction of the externally applied electric field, two stable molecular configurations are obtained, so these two states are called bistable states, and under crossed nicols, either By setting the absorption axis of the polarizing plate to display black (minimum transmitted light), white can be displayed in the other state. Further, since these stable states are retained even after the electric field is removed, they also have a memory property. Furthermore, the response speed is fast due to the response that is first-order coupled with the electric field, and attention has been paid to the fact that it changes to a paraelectric liquid crystal, and many attempts have been made for its practical use.

However, since it is a system having an asymmetric carbon and has a spiral property, and the SmC ^* phase forms a layered structure, it is difficult to control the direction of spontaneous polarization, which was shown by Clark et al. It was difficult to make a ferroelectric liquid crystal panel having bistability and memory property. Above all, the layer structure is complicated, and in addition to the bookshelf structure originally proposed, twist structures, chevron structures, etc. have become known, and it is clear that the layer structure is involved in various characteristics of the ferroelectric liquid crystal panel. Has become.

While molecular orientation including the layered structure has been studied in this way, Kamibe et al. Found that the c-director was tilted from the substrate interface in the vicinity of both substrates (the tilt of this c-director will be referred to as c in the text below). This c-director is a line-symmetrical arrangement having a central axis in the center of both substrates, and a ferroelectric liquid crystal panel exhibiting a chevron type layer structure and a splay alignment was announced. (199
(2nd year, published by CMC, "Next Generation Liquid Crystal Displays and Liquid Crystal Materials", Patent Disclosure Bulletin Sho 63-124030, etc.)

In order to create a layered structure and a molecular arrangement having such a constitution, conventionally, an organic polymer film typified by polyimide was used as an alignment control film, and the rubbing treatment was performed to control the alignment. This method has been generally used for liquid crystal panels using paraelectric liquid crystals, and has also been used for panels using ferroelectric liquid crystals.

FIG. 2 is a schematic diagram showing the relationship between the rubbing direction and the pretilt in the paraelectric liquid crystal. The rubbing direction on the substrate is the z axis, the direction perpendicular to the substrate is the y axis, and the axis orthogonal to them is the x axis. Further, FIG. 3 is a schematic diagram showing the relationship between the rubbing direction and the pretilt in the ferroelectric liquid crystal. Similar to FIG. 2, the rubbing direction is the z axis, the direction perpendicular to the substrate is the y axis, and the axis orthogonal to them is the x axis. Here, the pretilt is a unit vector (n
(Definition as director) and the xz plane are defined as an angle, the pretilt 5 of the liquid crystal molecule 1 exists in the yz plane in the paraelectric liquid crystal as shown in FIG. On the other hand, in the ferroelectric liquid crystal, since the liquid crystal molecules 2 are inclined at a constant angle with respect to the plane of the layer, if the plane of the layer is a conical lower surface, as shown in FIG. It can be assumed that it exists on the ridge of a cone with one end of as the apex. At this time, the projection unit vector of the liquid crystal molecule 2 on the layer plane is c director 3, the vector perpendicular to the layer plane is a director 4, and the angle formed by the liquid crystal molecule 2 and the xz plane (substrate surface) is pretilt 6. The inclination from the projection line of the y-axis on the layer plane of the c-director is determined by the c-director pretilt 7
And Pretilt except when the sum of the tilt angle of the liquid crystal molecules 2 from the layer normal (hereinafter referred to as cone angle) and the tilt angle of the layer plane from the y axis (hereinafter referred to as layer tilt angle) matches the pretilt 6. 6 cannot exist in the yz plane and will have a c-director pretilt 7.

Actually, it is reported that the cone angle is about 15 to 30 degrees, although it depends on the liquid crystal material, and the layer tilt angle is about 3 to 18 degrees based on the result of x-ray diffraction. On the other hand, the pretilt is reported to be about 0 to 15 degrees, and the pretilt is y in most cases.
It can be said that it does not exist in the z plane.

At this time, the tilting direction of the c-director is determined by the combination of the alignment control film and the liquid crystal material (especially the spiralness and polarization direction of the liquid crystal material) and the rubbing condition.
After rubbing the same kind of alignment control film under the same conditions and sandwiching the liquid crystal facing each other, the c-directors on the two substrate surfaces are line-symmetrical with the symmetry axis in the center of both substrates. Become. However, in a line-symmetrical c-director arrangement, the c-directors are not aligned in the same direction from one substrate side to the other substrate side, and so-called splay orientation is likely to occur, and the c-director direction is the same between substrates. It was difficult to obtain high contrast as compared with uniform uniform orientation.

Therefore, even if an attempt is made to obtain a plane-symmetrical c-director arrangement instead of a line-symmetrical c-director arrangement in order to obtain a perfect uniform orientation, the direction in which the c-director is inclined shows that the liquid crystal material is spiral. It was very difficult to obtain a plane-symmetric c-director arrangement because it depends on the polarization direction.

[0010]

As described above, in the line-symmetrical c-director arrangement, a perfect uniform orientation cannot be obtained, which makes it very difficult to obtain a ferroelectric LCD panel with high contrast. . Therefore, the present invention achieves perfect uniform orientation by controlling the c-director pretilt and easily realizing a plane-symmetrical c-director arrangement instead of a line-symmetrical c-director arrangement, resulting in high contrast ferroelectricity. A liquid crystal panel is provided.

[0011]

In order to solve the above-mentioned problems, a ferroelectric liquid crystal panel of the present invention comprises a pair of substrates having an alignment control film on a transparent electrode and sandwiching a ferroelectric liquid crystal. The orientation control film having chirality is used in at least one of the orientation control films.

Further, an orientation control film having spiral properties opposite to each other is used on the pair of substrates.

An achiral organic polymer material added with a chiral material is used for the orientation control film.

Alternatively, an organic polymer material having chirality is used for the orientation control film.

[0015]

The structure of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram of an orientation control film having chirality and ferroelectric liquid crystal molecules on the orientation control film. Figure 1 (a)
In the above, as a model showing the chirality of the orientation control film A11, it is assumed that a chiral material is present on the surface of the orientation control film, and four functional groups around the asymmetric carbon C ^* of the chiral material are R1, R2, R3 and R4, respectively. far. Also, FIG.
In (d), the alignment control film B21 is an enantiomer with the alignment control film A11, and the four functional groups R1, R2, R3 and R4 around the chiral asymmetric carbon C ^* are mirror symmetric with the alignment control film A11. It is assumed that they are placed in different positions. At this time, the rubbing direction is from R1 to R3. Figure 1
FIGS. 1B and 1E show the conical model of the ferroelectric liquid crystal as described in the description of FIG. The liquid crystal molecule 2 is located on the ridgeline of the cone, and the projection vector of the liquid crystal molecule 2 onto the cone bottom surface, that is, the layer plane is the c-director 3.

Assuming that the functional groups R2 of the alignment control film A11 and the alignment control film B21 and the liquid crystal molecules 2 are attracted to each other, the liquid crystal molecules on the alignment control film A11 are as shown in FIG. 1C. 2 tilts in the R2 direction, that is, to the left, and obtains the c-director pretilt A17. See also FIG.
As shown in (f), the liquid crystal molecules 2 on the alignment control film B21 also tilt in the R2 direction. In this case, the position of R2 is the alignment control film A.
Since 11 exists at a mirror-symmetrical position, the tilt direction is the right direction, and the c-director pretilt B27 is obtained.

As described above, the pair of orientation control films, which are mirror images of each other, give opposite characteristics in the direction in which the c-director is tilted. The principle at this time follows the model described above, but it is qualitatively due to the chirality based on the chirality of the alignment control film, and the alignment control film having a left-handed spiral property and the alignment having a right-handed spiral property. With the control film, the opposite characteristics are given to the direction in which the c-director is tilted. By utilizing this property and using a material with chirality as an orientation control film, the direction in which the c-director tilts can be easily controlled, and perfect uniform orientation can be obtained, resulting in high contrast. It is possible to obtain an excellent ferroelectric liquid crystal panel.

Next, a method for confirming the actual orientation of the ferroelectric liquid crystal panel produced according to the present invention will be described. Although X-ray diffraction and measurement of electro-optical characteristics are generally known methods for confirming the orientation, the ATR method that can know more detailed orientation will be described. ATR (Att
enumerated Total Reflection =
For details of the attenuated total reflection method, see Samles et al.
mbles; Liquid Crystals, 199
3, Vol. 13, No. 1, 1-11, etc.), but the outline is as follows.

The liquid crystal panel used for the measurement has a structure in which a film exhibiting optical absorption (usually a metal vapor deposition film of gold or silver having a thickness of 30 to 50 nm) is provided in place of the transparent electrode, and the alignment control film and The liquid crystal is created as usual. P-polarized light (having an electric field vector in the incident plane) is incident on this panel at different incident angles, and the incident angle dependence of the reflected light intensity is considered. Light is mostly reflected by the metal film up to a certain incident angle, but induces a phenomenon (excitation of surface plasmon polaritons) in which light energy is transferred between the metal film and the total reflection angle defined by the dielectric tensor. However, it shows a specific reflected light intensity profile such as attenuation of reflected light. The reflected light intensity profile with respect to this incident angle is determined by the alignment state of the metal film, the alignment control film and the liquid crystal.

In particular, this reflected light intensity profile is sensitive to the properties of the substance in the vicinity of the metal film (the layer structure and molecular arrangement of the liquid crystal), and the relationship between the absolute value of the reflected light intensity and the incident angle that gives that intensity (hereinafter referred to as ATR). It is possible to discuss the layer structure and molecular arrangement in the vicinity of the substrate interface of the liquid crystal panel in detail and sufficiently from the curve). Actually, the reflected light intensity profile (= ATR curve) measured by changing the incident angle is matched with the optical behavior estimated by calculation to determine the arrangement and layer structure of the c-director.

Next, a method of estimating the optical behavior by calculation will be described. The c and a directors are used to describe the layer structure and molecular arrangement. The positional relationship between them is shown in FIG. The free energy density F of the liquid crystal in consideration of elastic deformation of the c-director 3 and the a-director 4 is represented by the following formula (Nakagawa; Liqu).
id Crystals 1990, Vol. 8, N
o. 5,651-675).

[0022]

[Equation 1]

In equation (1), capital letters A, B, C,
D and L are elastic constants that represent the deformation of the layers and the molecular arrangement.
Further, Ps is the spontaneous polarization, and φ is the scalar potential of the electric field. In the formula, the symbol-indicates the inner product of vectors and the symbol x indicates the outer product of vectors. The relational expressions (2) to (6) below hold for the other parameters.

[0024]

[Equation 2]

Here, d _A represents the layer thickness in the smectic A phase, and d _C represents the layer thickness in the smectic C ^* phase. ν is a unit vector in the layer normal direction, p is a polarization vector,
The a and c directors have an orthogonal relationship as shown in FIG.

In an actual liquid crystal panel, a value obtained by integrating the energy density represented by the equation (1) over the bulk and surface anchoring energy Fs (lower substrate side F _s0 , upper substrate side F) indicating the regulation from the interface. _sd ) is considered to have an energetically stable layer structure and molecular arrangement in a balanced state. In Equations (7) and (8) shown in the following Equation 3, g and σ are coefficients that define anchoring of the interface, Φ ₀
Is the c-director pretilt on the lower substrate side (y = 0 in the coordinate system of FIG. 3), Φ is the tilt angle of the c-director adjacent to the bulk side, and Φ _d is the upper substrate side of the c-director pretilt (Fig. In the coordinate system of 3, y = panel thickness).

[0027]

[Equation 3]

Based on the formulas (1), (7) and (8), the Euler-Lag is used so that the total energy amount of the liquid crystal panel is minimized.
The range equation is calculated, the liquid crystal panel is divided into about 100 layers in parallel with the xz plane, and the layer tilt angle and the c-director arrangement in each layer are calculated. The dielectric tensor in each layer is calculated based on the obtained c-director arrangement, these layers are regarded as a laminated film, and the ATR curve is calculated based on Snell's law. ATR curve obtained by experiment and ATR by calculation
It is estimated that the elastic constants, coefficients, parameters, etc. are changed so that the curves coincide with each other, and that the sufficiently fitted portions are the actual layer structure and molecular arrangement.

[0029]

【Example】

(Example 1) A substrate obtained by coating a transparent electrode film on glass with 1% of a Chiral CM14 manufactured by Chisso having a left-handed spiral as Polix008 manufactured by Hoechst as an orientation control film, and A rubbing treatment was performed on a transparent electrode film on glass, which was subjected to rubbing treatment on a substrate coated with Hoxist's Polix008 as an orientation control film to which 1% of a right-handed spiral Merck's chiral material CB15 was added. Opposing so that the directions are the same, 1.7μ
Fellow liquid crystal material Fel made by Hoechst Co., Ltd.
ix-T252 was injected to prepare a ferroelectric liquid crystal panel.

When the alignment state of the produced liquid crystal panel was measured by using the above-mentioned ATR method, it was confirmed that the tilt direction of the c-director in the vicinity of the substrates was symmetrically arranged between the two substrates. It was Next, in order to measure the contrast, align the white light source, the polarizer, the liquid crystal panel, the analyzer, and the photodetector in that order, and align the absorption axis of the polarizer so that it matches the cone angle on the c-director side. The absorption axis was arranged so as to be orthogonal to the absorption axis of the polarizer. Then, a rectangular wave is applied to the liquid crystal panel and the amount of transmitted light is measured. The amount of transmitted light becomes the minimum on the side where the molecular arrangement coincides with the absorption axis of the polarizer, indicating a dark state, and the other arrangement indicates a bright state. When the ratio of the amount of transmitted light between these two states is obtained as the contrast, the amount of transmitted light in the dark state is lower than that in a liquid crystal panel using the same alignment control film on both substrates, and high contrast can be obtained. It could be confirmed.

(Embodiment 2) Further, when a liquid crystal having a spiral direction opposite to that of the liquid crystal is injected into the cell of the embodiment, c
It was also confirmed that the director was in the opposite direction to the liquid crystal. In this liquid crystal panel as well, when the absorption axes of the analyzer and the polarizer were similarly set to the c-director side and the contrast was measured, a higher contrast was obtained as compared with a liquid crystal panel using the same alignment control film on both substrate sides. I was able to.

(Example 3) Next, a side chain type thermotropic liquid crystalline polymer material as a polymer having chirality,
For example, a film having a structure shown in the following chemical formula 1 is used as the orientation control film.

[0033]

[Chemical 1]

In this case, a rubbing treatment is performed after forming the orientation control film, but if the rubbing treatment is also performed on the transparent electrode before the formation of the orientation control film, the orientation property of the liquid crystalline polymer itself increases, and A good alignment state can be obtained. The liquid crystal polymer material in which the liquid crystal polymer materials in which the bonding arrangements of the four kinds of functional groups to the R asymmetric carbons of the orientation control film are mirror images of each other are opposed to each other as the orientation control film It was possible to obtain higher contrast than the liquid crystal panel facing as an alignment control film.

[0035]

As described above, in the ferroelectric liquid crystal panel using the alignment control film of the present invention, not only the standing angle of liquid crystal molecules (pretilt referred to as paraelectric liquid crystal) but also the direction in which the c director tilts. It is possible to control, and it is possible to easily realize not only a line-symmetric c-director arrangement between a pair of substrates but also a plane-symmetric c-director arrangement, so that a perfect uniform orientation can be achieved. did it. Therefore, by setting the absorption axis of the polarizer in the uniform orientation direction, the amount of transmitted light in the dark state is significantly reduced as compared with a liquid crystal panel with a line-symmetrical c-director arrangement, and the contrast, which is the ratio with the bright state, is reduced. It was possible to easily obtain a dramatically increased ferroelectric liquid crystal panel.

[Brief description of drawings]

FIG. 1 is a diagram showing a model of a stereoisomer structure of an alignment control film and a tilt direction of a C director in a ferroelectric liquid crystal panel of the present invention.

FIG. 2 is a diagram showing a model showing a relationship between liquid crystal molecules and pretilt in a paraelectric liquid crystal panel.

FIG. 3 is a diagram showing a model showing the relationship between liquid crystal molecules and pretilt in a ferroelectric liquid crystal panel.

FIG. 4 is a diagram showing a relationship between a polarization vector p and another vector parameter in a ferroelectric liquid crystal.

[Explanation of symbols]

 1 liquid crystal molecule (paraelectric liquid crystal) 2 liquid crystal molecule (ferroelectric liquid crystal) 3 c director 4 a director 5 pretilt (n director of paraelectric liquid crystal) 6 pretilt (n director of ferroelectric liquid crystal) 7 c director pretilt 11 alignment control film A 17 c director pretilt A 21 alignment control film B 27 c director pretilt B

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Suzutaro Takahashi 840 Takeno, Shimotomi, Tokorozawa, Saitama Prefecture Citizen Watch Co., Ltd.

Claims (4)

[Claims] 1. A ferroelectric liquid crystal panel in which a ferroelectric liquid crystal is sandwiched between a pair of substrates provided with an alignment control film on a transparent electrode, wherein at least one of the alignment control films has chirality. Ferroelectric liquid crystal panel characterized by having. 2. The ferroelectric liquid crystal panel according to claim 1, wherein the alignment control films having mutually opposite spiral properties are provided on a pair of substrates. 3. The ferroelectric liquid crystal panel according to claim 1, wherein the alignment control film is an achiral organic polymer material to which a chiral material is added. 4. The ferroelectric liquid crystal panel according to claim 1, wherein the alignment control film is an organic polymer material having chirality.