JP2547974B2 - Smectic liquid crystal device and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal display device and a liquid crystal display.
The present invention relates to a ferroelectric smectic liquid crystal device used in an optical shutter or the like and a manufacturing method thereof, and more particularly to a smectic liquid crystal device having improved display characteristics by improving the initial alignment state of liquid crystal molecules and a manufacturing method thereof.

[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. (Unexamined-Japanese-Patent No. 56-107216, US Patent No. 436792.
No. 4, etc.). This ferroelectric liquid crystal generally has a chiral smectic C phase (Sm) in a specific temperature range.
C ^* ) or H phase (SmH ^* ), in this state,
A first optically stable state and a second optical stable state in response to an applied electric field;
Has an optical stable state and maintains the state when no electric field is applied, that is, has bistability, and has a quick response to a change in the electric field.
Wide use as a high-speed and memory type display device is expected. However, in order for the optical modulation element using the liquid crystal having the bistability to exhibit a predetermined drivability, the liquid crystal disposed between the pair of parallel substrates is irrespective of the electric field application state as described above. It is necessary that the molecular arrangement state is such that the conversion between the two stable states occurs effectively. For example, for a ferroelectric liquid crystal having SmC ^* or SmH ^* phase, SmC ^* or SmH ^* phase vertical liquid crystal molecules phase to the substrate surface having the thus liquid crystal molecular axis is aligned substantially parallel to the substrate surface area (Mono domain)
Need to be formed.

As a method for orienting such a ferroelectric liquid crystal, as in the conventional TN type liquid crystal display device, first, a physical flaw is formed on the substrate surface in the liquid crystal cell by a rubbing method or oblique vapor deposition. An organic thin film, an inorganic vapor deposition film, and an organic thin film with a mark were formed to give the orientation of the molecules. For example, in the rubbing method, as shown in FIG.
This is a method in which after forming the transparent electrode 12 on the glass substrate 11, an organic molecular film 13 is formed and rubbed in one direction with a cloth such as velvet, and liquid crystal molecules are aligned by fine scratches on the film surface. Moreover, the oblique vapor deposition method is shown in FIG.
As shown in (1), a film 14 of an inorganic material such as SiO is formed by tilting the substrate instead of the organic molecular film, that is, by oblique evaporation.

The ferroelectric liquid crystal original alignment method includes a method in which glass substrates are rubbed up and down to arrange liquid crystal molecules, and a polyethylene terephthalate sheet is used as a spacer to form a cell gap and the directionality of the edge thereof. There are things that use.

However, in the conventional liquid crystal device using the liquid crystal having bistability, the alignment state of the liquid crystal having such a monodomain structure is not always formed satisfactorily, so that sufficient characteristics cannot be obtained. Is the reality.

[Object of the Invention] An object of the present invention is to provide a smectic liquid crystal device having improved display and drive characteristics by realizing a uniform initial alignment state of a monodomain in a liquid crystal device using a ferroelectric liquid crystal. It is to provide the manufacturing method.

SUMMARY OF THE INVENTION The present invention is firstly characterized in that each carries an electrode structure, at least one wall of which is housed between two cell walls which have been treated to orient liquid crystal molecules. A liquid crystal device comprising a layer of chiral smectic liquid crystal material, a first linear polarizer and a second polarizer, the liquid crystal material comprising: (a) a plurality of switching states at normal device operating temperatures. A chiral smectic C phase and a smectic A phase and a cholesteric phase at a temperature higher than the ambient temperature, and (b) a cholesteric pitch of 0.5 times or more the layer thickness at a temperature intermediate between the temperature ranges of the cholesteric phase. And (c) a cholesteric pitch that becomes longer toward a lower temperature in the temperature range of the cholesteric phase, and (d) a thickness equal to or larger than the thickness of the layer. Larsmectic C pitch, (e) Ferroelectric property coefficient, (f) Material component having at least one left-handed cholesteric twist direction, (g) Material component having at least one right-handed cholesteric twist direction, Where (h) the levorotatory and dextrorotatory material components have a combined cholesteric pitch, and (i) the levorotatory and dextrorotatory material components are additive. A liquid crystal device having a sexual characteristic has a first feature, and a second aspect of the present invention is a method for manufacturing a liquid crystal device, wherein an electrode structure is formed on an inner surface, and at least one of Of two cell walls whose wall surfaces have been treated to obtain liquid crystal orientation, spaced apart to accommodate a layer of liquid crystal material therein and isotropic with the chiral smectic C phase. And a cholesteric phase having a cholesteric pitch of 0.5 times or more the layer thickness at a temperature in the middle of the temperature range of the cholesteric phase, A chiral smectic liquid crystal material having a cholesteric pitch that becomes longer toward a lower temperature in a temperature range of, a ferroelectric characteristic coefficient in a chiral smectic C phase, and a pitch in the chiral smectic C phase being equal to or larger than a layer thickness. A method of manufacturing, comprising: providing, sealing a liquid crystal material by introducing a liquid crystal material into a space between the walls, and cooling the liquid crystal material from a cholesteric phase and a smectic A layer to a chiral smectic C layer. In addition, it has features.

[0008]

EXAMPLES When an attempt is made to align a ferroelectric liquid crystal using the above-mentioned alignment treatment method, the alignment state greatly differs due to the difference in the physical properties of the ferroelectric liquid crystal. An example of such a difference in physical properties is a difference in phase series. The following four patterns are known as the phase series in the ferroelectric liquid crystal.

[0009] (Iso; isotropic phase, Ch; cholesteric phase, SmA;
Smectic A phase)

The present inventors have studied the quality of the orientation of the above-mentioned phase series and SmC ^* , and as a result, the liquid crystal material having the above-mentioned (i) phase series is relatively aligned as compared with those having other phase series. I found that it has high quality.

More specifically, for example, in an experiment using a rubbing method as a uniaxial orientation treatment method, one belonging to the phase series of (ii), for example, DOBAMBC (P-decyloxybenzylidene-P'-amino-2). -Methylbutyl cinnamate), those belonging to the phase series of (iii), such as 80B described below, or those belonging to the phase series of (iv), such as MORA-8, are perfect no matter how the rubbing conditions are selected. While it was difficult to obtain such an alignment state, it was found that a suitable mixed liquid crystal belonging to the phase series (i) can obtain a much better alignment state than those belonging to the other series. The reason why such a condition is given to the phase series is that in the series of phase transitions from the isotropic phase to the SmC ^* or SmH ^* phase having a chiral layer structure, the phase series of (i) It can be considered that a relatively unreasonable smectic-phase molecular arrangement is realized when the symmetry gradually decreases. However,
According to the research conducted by the present inventors, as described in detail below (i)
It was found that not all of those having the phase sequence of (i) are easy to orient, and at least having the phase sequence of (i) is not a sufficient condition for obtaining good orientation.

Furthermore, as a result of a detailed study of the relationship between the phase sequence of (i) and the orientation, the present inventors have found that even a liquid crystal material belonging to the same phase sequence of (i) has a Ch phase. It has been found that the orientation is particularly improved when the temperature ranges of the SmA phase and the SmA phase are both wide, and preferably both have a temperature range of 5 ° C. or higher.

On the basis of such knowledge, the present inventors have decided to change to the Ch phase, which is considered to have an action of alleviating a sudden change in the molecular arrangement, as an intermediate state from the isotropic phase to the layer structure to the (SmA phase). As a result of paying attention to the relationship between the characteristics of the Ch phase and the orientation of the chiramesmectic phase in detail, the orientation of the chiral smectic phase was found to be the absolute value of the helical pitch of the Ch phase and the helical pitch of the Ch phase and the liquid crystal. It was found that it was governed by the relationship with the layer thickness. More specifically, C
The helical pitch of the h phase is 0.8 μm or more, and the ratio (P / d) of the helical pitch (P; μm) of the cholesteric phase and the distance between the pair of substrates [thickness of liquid crystal layer] (d; μm). It has been found that the orientation is remarkably improved even under the condition of 0.5 to 10 or less.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic perspective view of an example of a liquid crystal cell used for carrying out the present invention. This cell is a liquid crystal cell formed by a simple dot matrix method, and has stripe-shaped transparent electrode patterns 22a and 22b (for example, indium) that are in a relationship substantially orthogonal to each other on a pair of parallel glass substrates 21a and 21b. (In) -thein (Sn) -oxide film or the like),
A coating made of an insulating material, for example, an organic polymer film such as polyimide, polyvinyl alcohol, or polyamide is applied to the surface of the substrate, and the surface is subjected to rubbing treatment as uniaxial alignment treatment, so that both sides of the substrates 21a and 21b are covered. A crossed Nicol polarizer (not shown) is arranged.

The space d between the pair of substrates is held by a spacer (not shown) arranged on the surface of the substrates. In such a liquid crystal cell, in the phase sequence (i)
After enclosing several kinds of chiral smectic liquid crystals belonging to the phase series, the cell temperature was raised to make an isotropic phase once, and then gradually cooled (for example, 0.5 ° C./hour), Ch phase, SmA were sequentially added.
The orientation state in the chiral smectic layer when the phase and the phase transition to the SmC ^* (or SmH ^* phase) were performed was examined. At this time, as the chiral smectic liquid crystal, chiral smectic C phase, H phase, I phase, G phase or F phase can be used.

The results will be described in detail below.

Specific examples of the liquid crystal used in this embodiment are shown in Table 1 below.

[0019]

[Table 1] Etc., and all of them belong to the phase series of (i) above. In addition, LC-1 and 80B in the table are different from each other in the helical direction in the cholesteric phase. As can be seen from Table 1, the liquid crystal having the right-handed helical direction in the cholesteric phase and the left-handed helical direction in the cholesteric phase. It is possible to increase the value of the helical pitch (P) in the cholesteric phase by mixing the liquid crystals having the above with each other.

"LC-1", "80B" and "80SI ^* " in Table 1 are compounds of the following structural formulas, and MIX
-1 is a liquid crystal having the following composition, and the subscripts in the table each represent a weight ratio.

[0021]

[Outside 1] MIX-1 P-n-octyloxybenzoic acid-P '-(2-methylbutyloxy) phenyl ester and Pn-nonyloxybenzoic acid-P'-(2-methylbutyloxy) phenyl ester as main components Liquid crystal composition.

FIG. 2 shows the values of the helical pitch (P) in the Ch phase of each liquid crystal listed in Table 1 and the distance (d) between the pair of substrates when the spacer thickness is changed. This shows the result of orientation. In the figure, ◯ represents a good alignment state, Δ represents a slightly poor alignment state, and X represents a poor alignment state.

The spiral pitch of the Ch phase is the Oxford University Press Elay House, London by P. G. de Genenes.
Press Ely House, London) 19
Published in 1974, "The Physics of Liquid Crystals"("The Physics of Li
(Guid Crystals "), page 265, Grange yarn-Cano.
It measured according to the method. That is, using a wedge-shaped cell in which the inclination angle φ was obtained in advance, the fringe spacing l (μ) corresponding to the helical pitch appearing in the Ch phase from the micrograph at that time was used.
By measuring m), the pitch P (μm) = ta
The helical pitch of the Ch phase was measured by the formula of nθ × l × 2.

The wedge cell used at this time has an inclination angle of
Each of them is tan θ = (1.34 × ± 0.07) × 10 ⁻³ , and the inclination angle is obtained by using monochromatic light (D line of sodium) and utilizing the interference of light on the glass surface of the wedge-shaped cell. Measured.

Further, the helical pitch of the Ch phase generally depends on the temperature. For example, in the case of the (LC-1) ₆₀ / (80B) ₄₀ composition, it changes according to the temperature change as shown in FIG. In the present invention, it means the value of the helical pitch measured at the temperature at the midpoint of the temperature region showing the Ch phase in each liquid crystal. The value of the helical pitch of the Ch phase measured by this method is shown in Table 1.

21 and 22 in FIG. 2 are P = 10d, respectively.
And a straight line indicated by P = 0.5d, and as can be seen from the figure, the liquid crystal cell in the region of P> 0.5d, preferably the region sandwiched by the straight lines 21 and 22, has a smectic phase monodomain. In terms of formability, it is superior to the liquid crystal cells in other regions, but the straight line 23 indicated by P = 4d
The liquid crystal cell in the region sandwiched by the line 22 and 22 can obtain an alignment state with better reproducibility. Specifically, according to FIG. 2, the above-mentioned MIX-7 in which the helical pitch of the Ch phase is 4 μm.
In contrast, it is possible to form a smectic phase of a monodomain having a good bistability with a liquid crystal cell having a substrate spacing d of 1 μm and 2 μm, while a substrate spacing d of 0.
In the case of a liquid crystal cell having a thickness of 25 μm, it is shown that the alignment state showing sufficient bistability necessary for switching is not formed. Other liquid crystals, eg (LC-1) ₉₀ /
It is easily understood from FIG. 2 that the same tendency is obtained even when (80B) ₁₀ or (LC-1) ₇₀ / (80B) ₃₀ is used.

As described above, according to the present invention, the ratio (P / P) of the helical pitch (P; μm) of the Ch phase to the substrate interval (d; μm).
d) is 0.5 or more and 10 or less, more preferably (P
When a liquid crystal cell in which / d) exists in a region of 0.5 or more and 4 or less, a remarkably good alignment state can be obtained.

The following may be considered as the reason why the above-mentioned conditions for the orientation of the smectic phase are given. Since the direction of the helical axis in the Ch phase is considered to be substantially parallel to the thickness direction of the liquid crystal layer, the ratio of the helical pitch of the Ch phase to the substrate spacing (thickness of the liquid crystal layer) is It can be considered as a parameter indicating the number of turns. That is, when the number of helical turns of the Ch phase satisfies the above-mentioned conditions, the phase transition from the Ch phase to the SmA phase is smoothly performed under the temperature decrease, and as a result, a good orientation state is obtained in the chiral smectic phase. I think it will be done.

Further, from the experiments conducted by the present inventors, when a smectic liquid crystal in which the helical pitch of the Ch phase does not reach 0.8 μm is used, switching is not performed under extremely good alignment treatment conditions. It has been found that the necessary and sufficient alignment state may not be obtained in some cases. The cause is
In the case of a liquid crystal cell using a smectic liquid crystal in which the helical pitch in the Ch phase does not reach 0.8 μm,
Since a liquid crystal having a very short helical pitch has an extremely strong spiral winding in the Ch phase, controlling the thickness of the liquid crystal layer is no longer sufficient in the process of the phase transition to the SmA phase. It can be considered that it is difficult to uniformly form the layer structure of the SmA phase because the helical pitch in the phase cannot be uniformly unwound. Therefore, use of a smectic liquid crystal having a helical pitch of 0.8 μm in the Ch phase, that is, P = 0.
The liquid crystal cell in the region surrounded by the straight line 24 and the straight lines 21 and 22 indicated by 8 μm, preferably the straight lines 24, 23 and 22
The liquid crystal cell in the region surrounded by can obtain a uniform monodomain alignment state of the smectic phase.

Further, in applying a ferroelectric liquid crystal as an optical switching element represented by a display or a linear shutter array, Clark and Lagerwall, "Applied Physics", Jun. 1, 1980.・ Letters ”(“ Appli
ed Physics Letters ") Volume 36,
No. 11, pp. 899 to 901, "Sub-microsecond bistable electro-optical switching in liquid crystal"("Submi
crossbible bistable electr
optics switching in liquid
The surface-stable memory cell announced in "Crystals") has a layer structure of a chiral smectic phase in which a spiral structure is unwound even when there is no electric field, and the layer structure is formed perpendicular to the substrate. It is considered to be the most effective because it becomes parallel to the substrate surface and has bistability.

According to the experiments conducted by the present inventors, it was found that it is necessary to set the substrate distance d (thickness of the liquid crystal layer) to 3 μm or less in order to prepare the above-mentioned surface-stabilized memory cell. There is. Therefore, particularly in forming the above-mentioned surface-stable memory cell, the three straight lines 22, 24 in FIG.
25 (the straight line 25 represents d = 3 μm), preferably the four straight lines 21, 2 in FIG.
A region surrounded by 2, 24 and 25 (the straight line 25 represents d = 3 μm) (a region shown by a hatched portion in the drawing), preferably surrounded by four straight lines 23, 22, 24 and 25. When a liquid crystal cell in a region is used, a liquid crystal element having extremely high orientation and bistability can be obtained.

[0032]

According to the present invention, in producing a liquid crystal cell, it is particularly preferable to control the thickness (d) of the liquid crystal layer and the helical pitch (P) in the Ch layer in the region shown by the inclined portion in FIG. By selecting it, it becomes possible to realize a uniform initial alignment state of a monodomain and bistability, and it is possible to obtain a ferroelectric liquid crystal element having excellent display and driving characteristics.

[Brief description of drawings]

FIG. 1 is a perspective view of a device of the present invention.

FIG. 2 is an explanatory diagram showing the relationship between the thickness (d) of the liquid crystal layer, the helical pitch (p) in the Ch phase, and the orientation.

FIG. 3 is an explanatory diagram showing the relationship between the helical pitch (p) of the Ch phase and the temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichiro Kannabe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-61-250087 (JP, A)

Claims (9)

(57) [Claims] 1. A layer of chiral smectic liquid crystal material, each carrying an electrode structure, at least one wall of which is housed between two cell walls treated to orient liquid crystal molecules. A liquid crystal device comprising a linear polarizer of 1. and a second polarizer, the liquid crystal material comprising: (a) a chiral smectic C phase that produces a plurality of switching states at a normal device operating temperature and a higher ambient. A smectic A phase and a cholesteric phase at a temperature equal to or higher than a temperature, and (b) a cholesteric pitch of 0.5 times or more the layer thickness at a temperature intermediate between the temperature ranges of the cholesteric phase and (c) a temperature range of the cholesteric phase. A cholesteric pitch that becomes longer toward a lower temperature, and a chiral smectic C pitch that is (d) the layer thickness or more, ) A ferroelectric characteristic coefficient, (f) a material component having at least one left-handed cholesteric twist direction, and (g) a material component having at least one right-handed cholesteric twist direction, wherein (h) ) The levorotatory and dextrorotatory material components have a combined cholesteric pitch, and (i) the levorotatory and dextrorotatory material components have additive ferroelectric properties. Liquid crystal device. 2. The liquid crystal device according to claim 1, wherein the electrodes are formed as strip electrodes arranged in a matrix form. 3. The liquid crystal device according to claim 1, wherein the thickness of the liquid crystal layer is 3 μm or less. 4. The liquid crystal device according to claim 1, wherein the optical axis of one of the polarizers is arranged so as to intersect the optical axis of the other polarizer. 5. The liquid crystal device according to claim 1, further comprising means for switching the liquid crystal material between its two different states by applying different electric fields to the electrode structure. 6. A method of manufacturing a liquid crystal device, comprising two cell walls, each of which has an electrode structure formed on an inner surface thereof and at least one wall surface of which has been treated so as to obtain liquid crystal alignment. Between the chiral smectic C phase and the isotropic phase, which have a smectic A phase and a cholesteric phase between the chiral smectic C phase and the isotropic phase. It has a cholesteric pitch of 0.5 times or more the layer thickness at a temperature in the middle of the temperature range, has a cholesteric pitch that becomes longer toward a lower temperature in the temperature range of the cholesteric phase, and has a ferroelectricity in the chiral smectic C phase. A chiral smectic liquid crystal material having a property characteristic coefficient and having a pitch in the chiral smectic C phase equal to or larger than the layer thickness is prepared. Phase and the steps of sealing by introducing a liquid crystal material into the space between the walls, the manufacturing method comprising the steps of cooling the liquid crystal material from the cholesteric phase and smectic A layer to the chiral smectic C layer. 7. The liquid crystal material according to claim 6, wherein the liquid crystal material has at least one material component having a left-handed cholesteric twist direction and at least one material component having a right-handed cholesteric twist direction. Production method. 8. The manufacturing method according to claim 6, wherein the liquid crystal layer has a thickness of 3 μm or less. 9. The manufacturing method according to claim 6, wherein the optical axis of one of the polarizers is arranged so as to intersect with the optical axis of the other polarizer.