JPS61267736A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To improve monodomain formability or initial orientation and to decrease the generation rate of defects by specifying the length on the side of a projecting body along the direction perpendicular to the uniaxial orientation treatment direction at 0-20mum. CONSTITUTION:A spacer 307 to be used for this liquid crystal element is obtd. by providing an insulating coated film formed of a resin such as PVA, polyimide or polyparaxylene or inorg. insulating film of SiO, SiO2 or TiO2 on a substrate 302 formed thereon with an orientation control film 306, then etching the film to a prescribed shape by an ordinary photolithographic process. The length on the side (a) of the spacer 307 along the direction perpendicular to the uniaxial orientation treatment direction 312 is specified at 0-20mum. The generation of orientation defects is thoroughly eliminated if the length (b) of the component in parallel with the direction 312 of the spacer 307 is made more particularly preferably <=300mum.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal element applied to a liquid crystal display element, a liquid crystal-optical shutter array, etc. This invention relates to a liquid crystal element with improved display and driving characteristics.

[Conventional technology]

Conventional liquid crystal elements include, for example, M, Shut (M,
8chadt) and double 21, Helfrich (W,
He1frich) 1 Applied Physics
Letters” (@Applied Physics L
etters”) Volume 18, No. 4 (February 1, 1971
(published on the 5th).

1 Voltage Dependent Optical Activity - of a Twisted Nematic Liquid Crystal” (@Vo
ltage Dependent Optical Ac
tivity of a Twisted Nemat
Twisted nematic shown in icLiquid Crystal
c) Those using liquid crystal are known. This TN liquid crystal has a problem in that crosstalk occurs during time division driving using a matrix electrode structure with high pixel density, so the number of pixels is limited.

Furthermore, a display element is known in which a switching element using a thin film transistor is connected to each pixel, and each pixel is switched. However, the process of forming the thin film transistor on the substrate is extremely complicated, and it is difficult to use a display element with a large area. There are some problems that make it difficult to create.

Clark (C1
ark) and Lagerwall
(Japanese Unexamined Patent Publication No. 56-107216, US Pat. No. 4,367,924, etc.). As a liquid crystal having bistability, a ferroelectric liquid crystal having a chiral smectic C phase (SmC") and an H phase (8 mH") is generally used. The film thickness of this liquid crystal is kept small enough to release the helical structure of the ferroelectric liquid crystal, thus creating a bistable state consisting of a first optically stable state and a second optically stable state in response to an electric field. Motsukotok becomes. Therefore, unlike the optical modulation element used in the above-mentioned TN-type liquid crystal, for example, the liquid crystal is oriented in a first optically stable state with respect to one electric field vector, and in a first optically stable state with respect to the other electric field vector. The liquid crystal is aligned in the optically stable state 11 of 2.

[Problem that the invention seeks to solve]

In order for the optical modulation element using the above-mentioned bistable liquid crystal to exhibit predetermined drive characteristics, the liquid crystal placed between a pair of parallel substrates must be effectively converted between two stable alignment states. It is necessary for the molecules to be arranged in a state similar to that occurring in

However, the chiral smectic liquid crystal device in which the helical structure is released and bistability is imparted as described above is extremely difficult to manufacture. In other words, the research conducted by the present inventors has shown that in order to ensure the bistability of the chiral smectic liquid crystal described above, it is necessary to reduce the film thickness of the liquid crystal (corresponding to the distance between the pair of substrates). However, it has been found that the thinner the film thickness is, the more groups that generate orientation defects tend to increase. Moreover, it was discovered that the occurrence of the alignment defects mentioned above was caused by the presence of a spacer, which was placed to maintain a uniform liquid crystal film thickness over the entire surface of the device. .

Therefore, in view of the above-mentioned circumstances, it is an object of the present invention to provide a liquid crystal such as a ferroelectric liquid crystal, particularly a bistable liquid crystal, as an optical shutter having a high shutter speed for display elements having high-speed response, high-density pixels, and a large area. To provide a liquid crystal element that can fully exhibit its characteristics by improving the monodomain formation property or initial orientation, which has been a problem in the past in an optical modulation element using a ferroelectric liquid crystal having properties. It is in.

[Means and effects for solving the problems] The present invention provides that although the spacers described above are present in the liquid crystal, particularly in the ferroelectric liquid crystal imparted with bistability, the entire surface of the liquid crystal element is The first type has no alignment defects and exhibits good bistability over a period of time, and has fine protrusions that serve as spacers and is uniaxially aligned in one direction. In a liquid crystal element having a substrate and a substrate of Pa2 opposite to the first substrate, and in which a liquid crystal is disposed between the first substrate and the second substrate, a direction perpendicular to the uniaxial alignment treatment direction; The length of the side of the protrusion along the line is 0 μm to 2
It is characterized in that it is 0 μm (0/Jm means the apex when a polygonal prism is used as a protrusion, or the contact point when a cylindrical body or an inert cylindrical body is used as a protrusion).

〔Example〕

Hereinafter, the present invention will be described in further detail with reference to the drawings as necessary.

FIG. 1 schematically depicts an example of a cell for explaining the operation of a ferroelectric liquid crystal. A substrate (glass plate) covered with an electrode 21a, between which a liquid crystal molecular layer 22 is oriented perpendicularly to the glass surface.
H-phase liquid crystal is sealed. A thick line 23 represents a liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (on P) 24 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the liquid crystal molecules 23 are aligned so that the dipole moment (P) 24 is all oriented in the direction of the electric field. You can change direction.

23 liquid crystal molecules have an elongated shape and exhibit high refractive anisotropy in the long and short axis directions [1. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface,
It is easy to understand that this is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage.

The thickness of the liquid crystal cell used in the liquid crystal element of the present invention can be made sufficiently thin (for example, 10 μm or less). As the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unravels due to the wall effect between the substrates, which are spaced sufficiently apart, even when no electric field is applied, as shown in Figure 2. structure can be adopted.

Its dipole moment) Pa or pb upwards (34a
) or downward (34b). As shown in FIG. 2, voltage application means 31a and 31 apply a voltage field Ha or gb of different polarity above a certain threshold to such a cell.
b, the dipole moment changes its direction upward 34a or downward 34b in response to the electric field vector across the electric field Ea and Eb, and accordingly, the liquid crystal molecules
Either the stable state 33a or the second stable state 33b is oriented in one direction.

As mentioned earlier, there are two advantages to using such ferroelectricity as an optical modulation element.

The first is that the response speed is extremely fast, and the second is that the alignment of liquid crystal molecules has bistability. To further explain the second point, for example with reference to FIG. 2, the electric field Ea
When the electric field is applied, the liquid crystal molecules are aligned in the first stable state gaaa, but this state 'g is stable even when the electric field is turned off. Furthermore, when an electric field Bb in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 33b and change their orientation, but they remain in this state even after the electric field is turned off. Further, as long as the applied electric field Ba does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable that the cell be as thin as possible.

FIG. 3 specifically shows the liquid crystal element of the present invention.
FIG. 3(A) is a sectional view thereof, and FIG. 3(B) is a plan view thereof.

300 liquid crystal elements shown in FIG. 3, a substrate 3 (10) (preferably made of flexible glass or flexible plastic) and a substrate 3
02 (preferably, glass plate),
The substrate 3 (10) has a striped transparent electrode 303,
An alignment control film 304 made of an insulating material is coated thereon.

In addition, the substrate 302 has a striped transparent electrode 305 orthogonal to the transparent electrode 303, a spacer 307 made of an insulating material thereon, and an alignment control film that is subjected to uniaxial alignment treatment (rubbing treatment, etc.) in the 312 direction. A membrane 306 is applied.

The spacer 307 used in the present invention is made of polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, etc. on the substrate 302 on which the alignment control film 306 is formed.
Insulating coatings formed from resins such as polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, Urya resin, acrylic resin, or Si0, 8i02, T
It is obtained by forming an inorganic insulating film such as iO, etc., and then etching it into a predetermined shape using a conventional photo-IJ process.

At this time, the dry film thickness of the insulating film that becomes the spacer 307 corresponds to the height of the spacer.

In the present invention, the length of the side a of the spacer 3070 along the direction perpendicular to the uniaxial alignment treatment direction 312 described above is (10) 1 m.
~20 μm, particularly preferably the length b of the component in the direction parallel to the uniaxial alignment treatment direction 312 in the spacer 307
When it is set to 300 μm or less, no alignment defects can occur. This point will be explained in more detail below.

In a preferred embodiment of the present invention, if the spacers 307 are provided at a rate of 0.1 to 100 spacers per 1 mm'' of the plane of the liquid crystal element 300, the occurrence of alignment defects can be effectively prevented. , the plane of the liquid crystal element 300 is 1 mm
"If the spacers 307 are provided at a ratio of 0.5 to 50, the thickness of the liquid crystal film will be increased when the distance between the substrate 3 (10) and 302 is sufficiently small (0.5 μm to 5 μm). It is possible to completely eliminate the occurrence of orientation defects in the bistable monodomains.

Further, as the shape of the spacer 307 used in the present invention, in addition to the above-mentioned quadrangular prism, a cylinder, an inert cylinder, and a hexagonal prism shown in FIGS. 4 to 6 can be used. Figures 4 to 6
A, b, and 312 in the figure mean the same as a, b, and 312 in FIG. 3.

In particular, a in FIGS. Further, C in FIG. 5 represents the short axis of the cylindrical body, which is perpendicular to the uniaxial orientation processing direction 312. The hexagonal prism shown in FIG. 6 is formed with a width d and a length b,
The direction of the width d is perpendicular to the direction 312 of the uniaxial alignment process.

In the case of the cylindrical body shown in FIG. 4, the spacers 307 described above are provided at a pitch of 5 to 50 times, preferably 10 to 20 times, the length b, and have a length corresponding to the diameter in the plane of the substrate. It is preferable that b is 50 μm or less. In the case of the inertia cylindrical body shown in Fig. 5, the pitch is 5 to 50 times the length dc, preferably 10 to 20 times the length dc, and the long axis corresponding to the component parallel to the rubbing direction is 300 μm or less. It is preferable. In the case of the hexagonal prism shown in Fig. 6, they are provided at a pitch of 5 to 50 times the length d, preferably 10 to 20 times, and the length b corresponding to the component parallel to the rubbing direction is 300 μm or less. It is preferable that

Further, the liquid crystal shown in FIG. 3, particularly the ferroelectric Kyra A/smectic liquid crystal 308#-1, and the periphery of the substrates 3 (10) and 302 are sealed with a sealing material 309 (e.g., epoxy adhesive).

300 liquid crystal elements of the present invention, 31 cross-niffle polarizers
0 and 311 are arranged on both sides of the substrates 3 (10) and 302, respectively.

Moreover, the alignment control film 304 used in the liquid crystal element 300 of the present invention
and 306 are coated, for example, by vapor deposition, using compounds such as - silicon oxide, silicon dioxide, aluminum oxide, zirconia, magnesium heptadide, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, etc. It can be obtained by forming. In addition, for example, polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyvaraxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide,
It can also be formed as a coating film of resins such as polystyrene, cellulose resin, melamine resin, urea resin, and acrylic resin. The thickness of the alignment control films 304 and 306 depends on the charge injection prevention ability of the material and the thickness of the liquid crystal layer, but is usually 508 to 5μ, preferably 500A to 500μ.
It is set within the range of 0A.

The alignment control films 304 and 306 can have the effect of aligning the molecular direction of the uniaxial liquid crystal (smectic A phase, nematic phase, etc. that appears at a higher temperature than the ferroelectric chiral smectic liquid crystal phase) in one direction. . As a specific uniaxial alignment treatment method, a method of rubbing the plane of the substrate in one direction or an oblique vapor deposition method can be used (in the figure, the rubbing direction is 312 degrees).

The ferroelectric chiral smectic liquid crystal 308 used in the liquid crystal element 300 of the present invention is cooled (slow cooling;
Isotropic phase (Iso) → cholesteric phase (ah) → smectic A phase (8 mA) under
Preferably, those that cause a phase transition from → chiral smectic phase or those that cause a phase transition from Tokichitic phase → 8 mA → chiral smectic phase.

Hereinafter, the present invention will be explained according to examples.

Examples 1 to 23 A polyimide forming solution (pyromellitic dianhydride and
, 4'-N-methylpyrrolidone solution of polyamic acid obtained by dehydration condensation with diaminodiphenyl ether) was coated to give a film thickness of 150 OA after heat curing, and then heat cured to form a polyimide film. Two glass substrates provided with this polyimide film were prepared. Among these two glass substrates, one glass plate was coated with another polyimide forming liquid (rPIQJ, manufactured by Hitachi Chemical Co., Ltd.) so that the film thickness after curing was 1 μm.

Next, a positive resist solution (O@ manufactured by Hipley Co., Ltd.
AZ1350') was applied using a spinner and prebaked.

This resist layer was exposed to light using a mask with a maximum pitch of 3 mm. The shape of the mask used in this case was square or rectangular, and the lengths corresponding to a and b in FIG. 3 were set to the values shown in Table 1. Next, a developer containing tetramethylammonium hydroxide "MF31" was applied.
By etching at 2", the resist film in the exposed area and the underlying polyimide film are etched to form through holes. After washing and drying, the resist film in the unexposed area is removed using methyl ethyl ketone. Thereafter, it was cured by heating at 200°C for 60 minutes and 350t4' for 30 minutes to form a spacer of polyimide isoindoquinazolinedione.

Next, a rubbing treatment was performed with a cloth along the sides and a direction perpendicular to the square prism (spacer), followed by washing with water and acetone sequentially, and drying.

Next, the other glass substrate on which the polyimide film described above was provided (after rubbing in advance, epoxy adhesive was applied around it by screen printing except for the injection port) and the four substrates that would become spacers. A cell was created by stacking the glass substrate with a prismatic body and curing the epoxy adhesive. At this time, the cells were assembled so that the rubbing directions applied to the two glass substrates were parallel to each other and the striped pattern electrodes were perpendicular to each other.

Next, this cell is placed in a vacuum chamber, the inside of the cell is sufficiently evacuated, and the liquid crystal material described below is brought into contact with the injection port of the cell to isolate the inside and outside of the cell. When the cell was returned to atmospheric pressure, liquid crystal material was injected into the cell.

This injection step was carried out under conditions where the liquid crystal material was in constant phase (75° C.).

Liquid crystal material After the liquid crystal material is injected into the cell, the injection port is sealed, and the liquid crystal material in the liquid crystal phase is slowly cooled at a rate of about 0.5°C/hour, starting from the liquid crystal phase to the cholesteric phase and then to the smectic phase. A ferroelectric chiral smectic liquid crystal device (memory device) was produced at 28° C. by causing a phase transition in the phase and the chiral smectic C phase.

The alignment state of this liquid crystal element was observed using a polarized light microscope under crossed Nicols. Also, 30 volts and -30 volts are applied to this liquid crystal element.
Bistability was evaluated by applying a voltage of volts.

The results of these experiments are shown in Table 1. In the table, ○ indicates a good alignment state with no alignment defects and also good bistability, while Δ had some alignment defects.
In a sample that shows bistability within a practical range,
This is a sample in which a large number of orientation defects 71 shown in FIG. 7 occur, making it impossible to put it to practical use. Of the numbers in Figure 7, the third
Same as the figure - several items showing the same parts.

Table 1 (1) 5 300 Q(7)
10 100 Q(8)
10 50 Q(10) 2
0 300 Δ(11) 20
150 Δ(16') 25
300 X ('17) 25
150 X (18) 25
100 X (19) 25
50 X(20) 25
25 X(21) 30
200 X (22) 30
50X According to these experiments, by setting the length of side a to 20 μm or less, a liquid crystal element with no alignment defects can be obtained. It can be seen that this is not a major factor in the occurrence of

Examples 24 to 32 In place of the rectangular prism spacer used in Examples 1 to 23, a cylindrical spacer shown in FIG. A liquid crystal device was created using the method described above, and its evaluation was performed. The results are shown in Table 2.

Table 2 (25) 20 Q (28) so 0 (29) 80 Δ (30) 90 Δ
(31) 100 Δ (32) 150
It can be seen that when the diameter (b) was set to 100 μm or less, a practical orientation state and bistability were obtained, and especially when the diameter (b) was set to 50 μm or less, an element with an oriented state with no orientation defects was obtained. .

Examples 33 to 40 Instead of the rectangular prism spacer used in Examples 1 to 23, a cylindrical spacer shown in FIG.
A liquid crystal device was prepared in exactly the same manner except that the liquid crystal device shown in the table was used, and its evaluation was performed. The results are shown in Table 3.

Table 3 (33) 10 5 Q (36) Zoo 50 0 (37) 200 100
Δ(38) 300 1
50 Δ(39) 350
175 X (40)
400 200 X According to these experiments, in a liquid crystal element using a spacer having a spacer cylinder, a practically usable liquid crystal element can be obtained when the length b of the cylinder is 300 μm or less, and especially when the length b is 100 μm. It can be seen that a liquid crystal element with no alignment defects can be obtained when the following conditions are met.

Examples 41 to 67 In place of the square columnar spacers used in Examples 1 to 23, hexagonal columnar spacers shown in FIG. 6 (lengths a, b, and d are shown in Table 4) were used. created a liquid crystal device using exactly the same method and evaluated it. The results are shown in Table 4.

Table 4 (41) Zoo 5 500 (44) 300 5150 Δ (45) 300 5200 Δ (46) 350 5175 Δ (47) 400 5200 Δ (53) 350 1 (10) 75 Δ (54)
400 10200 Δ(55) too
20 50 0 (58)
3Q0 20 150 Δ(
59) 300 20 20
0 Δ(60) 350
20. 175 X (61) 40
0 20 200 X(62)
100 25 50
X(63) 200 25
100 X (64) 200
25 150 X (65)
300 25 150
66) 300 25 20
0 X(67) 300
25 175 Although there are almost no problems, it has been found that when b of the polygonal prism is set to 300 μm or more, many alignment defects occur, making it impractical.

From the above examples, when the rubbing direction when producing a liquid crystal element and the length of the side perpendicular to the rubbing direction of the spacer are set to 20 μm or less, no alignment defects occur and good bistability is obtained. It turns out that it can be done. On the other hand, when the length of the aforementioned side exceeded 20 μm, alignment defects occurred from the aforementioned side as shown in FIG. or,
Differences in the alignment state of the liquid crystal were observed with this alignment defect line as a boundary. The difference in alignment state is that although the liquid crystal is uniaxially aligned in each domain, the alignment direction is different between each domain, and the domains are oriented at an angle of 2 to 3 degrees from the rubbing direction. existed. The bistability of each domain under such an orientation state is greatly different, and originally it does not have the memory property of this liquid J & Shiko, and it can perform good display by prescribed driving. I couldn't.

The cause of this orientation defect has not yet been sufficiently analyzed, but according to the inventors' estimation, the length of the side perpendicular to the rubbing direction is 2.
If it exceeds 0 am, the liquid crystal molecules tend to be aligned parallel to the side surface of the spacer on this side, which may impede the uniaxial alignment of the liquid crystal in the entire device. In fact, according to the observations of the present inventors, alignment defects as shown in FIG. 7 commonly occur in element samples with side lengths b exceeding 20 μm.

〔effect〕

Such a phenomenon has not been observed in natic liquid crystals or cholesteric liquid crystals, and also occurs characteristically in chiral smectic liquid crystals when the cell is thin enough to release the helical structure. In the above experiment,
Phenomenologically, if the length of the edge is 20 μm or less, the number of defect-generating groups can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 2 is a perspective view schematically showing another ferroelectric liquid crystal element used in the present invention. FIG. 3(A) is a sectional view of the liquid crystal element of the present invention, and FIG. 3(B) is a cross-sectional view of the liquid crystal element of the present invention.
is its plan view. FIG. 4, FIG. 5, and FIG. 6 are plan views each showing the shape of the spacer used in the present invention. FIG. 7 is an explanatory diagram sketching the state of orientation defects occurring in the comparative element. 1a N to 1

S% mouth

Claims (10)

[Claims] (1) A first substrate having minute protrusions serving as spacers and subjected to uniaxial alignment treatment in one direction, and a second substrate facing the first substrate; In a liquid crystal element in which a liquid crystal is arranged between a first substrate and a second substrate, the length of the side of the protrusion along the direction perpendicular to the uniaxial alignment treatment direction is 0 μm to 20 μm (0 μm is the length of the protrusion). A liquid crystal element characterized in that it is a vertex or a contact point. (2) The length of the side of the protrusion along the direction perpendicular to the uniaxial orientation treatment direction is 0 μm to 20 μm, and the length of the component of the protrusion parallel to the uniaxial orientation treatment direction is 300 μm or less The first claim is
The liquid crystal element described in . (3) The liquid crystal element according to claim 1, wherein the protrusion is a cylindrical body having a diameter within the plane of the substrate of 50 μm or less. (4) The scope of the present invention is that the protrusion is an elliptical cylinder whose long axis is parallel to the uniaxial alignment treatment direction and whose short axis has a length of 50 μm or less. The liquid crystal element according to item 1. (5) The liquid crystal element according to claim 1, wherein the uniaxial alignment treatment is a rubbing treatment. (6) The liquid crystal element according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal. (7) The liquid crystal is a ferroelectric liquid crystal, and the first substrate and the second substrate are held at a spacing sufficiently small to loosen the helical structure of the ferroelectric liquid crystal. The liquid crystal element according to range 1. (8) The liquid crystal element according to claim 6 or 7, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (9) The liquid crystal element according to claim 1, wherein the protrusions are distributed at a rate of 0.1 to 100 per mm^2. (10) The liquid crystal element according to claim 1, wherein the protrusions are distributed at a rate of 0.5 to 50 per mm^2.