JPH10148834A - Liquid crystal element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the coloration of a cell by a fluctuation in the cell thickness of a liquid crystal display element formed by using chiral smectic liquid crystals. SOLUTION: Electrodes 12a are formed on a substrate 11a and an insulating film 13a having projecting parts on its substrate by coexistence of particulates 19 is formed thereon. An orientation control film having projecting parts on its surface by reflecting the projecting parts described above is further formed thereon. The films of the surface projecting parts are peeled and hole parts are formed at the orientation control film 14a by subjecting the orientation control film to a rubbing treatment. The parts where a pretilt angle turns zero are formed in these hole parts to prevent the movement of liquid crystal molecules.

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 having a cell structure suitable for a chiral smectic liquid crystal.

[0002]

2. Description of the Related Art Clark and Lagerwall have proposed a display device of a type that controls transmitted light in combination with a polarizing element by utilizing the refractive index anisotropy of chiral smectic liquid crystal molecules (Clarke and Lagerwall). JP-A-56-107216, U.S. Pat.
369924, etc.). The chiral smectic liquid crystal generally exhibits a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) in a specific temperature range, and in this state, responds to an applied electric field to produce a first phase.
Has a property of taking one of the optically stable state and the second optically stable state and maintaining the state when no electric field is applied, that is, has a bistable property, and has a quick response to a change in the electric field. Therefore, wide use as a high-speed and storage type display element is expected.

[0003]

However, when the liquid crystal cell constituted by using the above-mentioned chiral smectic liquid crystal is driven for a long time, the cell thickness at the cell edge gradually increases, and it becomes yellowish. Occurs.

It is an object of the present invention to provide a liquid crystal device which solves such a problem and prevents a coloring phenomenon at an end portion.

[0005]

The present invention firstly provides a liquid crystal element. A pair of electrode substrates provided with an electrode, an insulating film, and an alignment control film in that order on a substrate are opposed to each other. A liquid crystal element, wherein at least one of the alignment control films has a hole having a diameter of 0.1 to 10 μm.
A liquid crystal element having a density of 0000 / mm ² or more.

A second aspect of the present invention is the above-mentioned method for manufacturing a liquid crystal element, wherein an electrode is formed on a substrate, and then fine particles are mixed to form an insulating film having projections on the surface. An orientation control film having a convex portion on the surface is formed thereon by reflecting the convex portion of the insulating film, and the orientation control film of the convex portion on the surface is peeled off by rubbing the orientation control film. A method for manufacturing a liquid crystal element, wherein a hole is formed in an alignment control film.

[0007]

According to the study of the present inventor, the increase in the cell thickness at the cell edge described above is caused by the fact that the liquid crystal itself moves in a specific direction between the liquid crystal cells by driving, so that the cell edge is increased. It was noted that the pressure at the cell increased and as a result the cell thickness increased. It is presumed that the cause of the generation of the force for moving the liquid crystal molecules in the liquid crystal cell is an electrodynamic effect generated by the fluctuation of the dipole moment of the liquid crystal molecules due to the alternating electric field generated by the driving pulse.

Further, according to an experiment conducted by the present inventor, FIG.
As shown in (A), the moving direction 22 is the rubbing direction 2
0 and the average molecular axis directions 21 and 21 ′ of the liquid crystal molecules. Since the moving direction of the liquid crystal molecules depends on the rubbing direction in this way, it is presumed that the phenomenon depends on the state of pretilt at the substrate interface. The average molecular axis directions 21, 21 'indicate the average molecular positions of the chiral smectic liquid crystal molecules in the bistable state.

Here, for example, when an appropriate AC electric field is applied such that the liquid crystal does not switch in the state where the average molecular axis direction is indicated by 21, the liquid crystal molecules move in the direction of arrow 22. However, here, the case where a liquid crystal material having a negative spontaneous polarization direction is used is described. Further, this liquid crystal movement phenomenon depends on the alignment state of the cell.

The orientation including the chevron structure of the smectic layer as shown in FIG. 3 can be explained by two types of orientation models C1 and C2. In FIG. 3, 31 is a smectic layer,
32 indicates a C1 alignment region, and 33 indicates a C2 alignment region. Smectic liquid crystals generally have a layered structure, but the transition from SmA to SmC or SmC ^* reduces the layer spacing.
As shown in FIG. 3, the layer has a structure (chevron structure) bent at the center between the upper and lower substrate interfaces 36a and 36b. As shown in the figure, there are two bending directions, C1 and C2. However, as is well known, the liquid crystal molecules at the substrate interface form an angle with the substrate by rubbing (pretilt), and the inclination direction is the rubbing direction. The liquid crystal molecule tip side is raised toward A (the tip is floating). Due to this pretilt, the C1 orientation and the C2 orientation are not equivalent in elastic energy, and transition occurs at a certain temperature as described above. In addition, transition may occur due to mechanical strain.

When the layer structure shown in FIG. 3 is viewed in a plan view, the boundary 34 at the time of shifting from the C1 orientation to the C2 orientation in the rubbing direction A is called a lightning defect in a zigzag lightning shape,
The boundary 35 at the transition from C2 to C1 is wide and gently curved and is called a hairpin defect.

A pair of substrates which are substantially parallel to each other and have been subjected to uniaxial alignment processing in the same direction for aligning the chiral smectic liquid crystal are provided. The pretilt angle of the chiral smectic liquid crystal is α, and the tilt angle (1/1 of the cone angle) 2)
Θ, and the tilt angle of the SmC ^* layer is δ, and if the SmC ^* layer has an orientation state represented by Θ <α + δ, there are four more states having a chevron structure in the C1 orientation state.

The four C1 orientation states are different from the conventional C1 orientation state, and two of the four C1 orientation states are bistable states (uniform states).
Is formed. Here, if the tilt angle of apparent when no electric field and theta _a, among the four states in C1 alignment state, Θ <θ _a <a state indicating theta / 2 in relation uniform states.

In the uniform state, it is considered from the optical properties that the director is not twisted between the upper and lower substrates. FIG. 4A is a schematic diagram showing the arrangement of directors at each position between substrates in each state of C1 orientation. In the figure, reference numerals 41 to 44 show the state in which the director is projected on the bottom surface of the cone in each state and viewed from the bottom direction. 41 and 42 are splay states, and 43 and 44 are arrangements of directors considered to be in a uniform state. It is. As can be seen from the figure, in the two states 43 and 44 of the uniform, the liquid crystal molecules at the interface between the upper and lower substrates are replaced with the positions in the spray state. FIG. 4B shows the C2 orientation, and there are two states 45 and 46 by internal switching without interface switching. The uniform state of the C1 orientation produces _a larger tilt angle θa than the conventionally used bistable state in the C2 orientation, resulting in high luminance and high contrast.

As shown in FIG. 2, in the actual liquid crystal cell, for example, if the position of the liquid crystal molecule is in the state indicated by the arrow 21 in the entire cell, the movement of the liquid crystal molecule is caused by the arrow 22
Liquid crystal moves in the direction of. As a result, as shown in FIG. 2B, the cell thickness of the region 23 increases with time, and coloring occurs. When the liquid crystal molecules are in the state shown by the arrow 21 ', the moving direction under the AC electric field is reversed, but in any case, the liquid crystal moves in the direction perpendicular to the rubbing direction 20, that is, in the smectic layer. Occurs.

The inventor of the present invention has proposed that by providing a hole of an appropriate size in the alignment control film, since the state of the movement of the liquid crystal described above strongly depends on the physical condition of the substrate interface, ie, the surface of the alignment control film. The pretilt angle is locally set to 0 in the hole, thereby reducing the movement of the liquid crystal.

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

As shown in FIG. 1, this liquid crystal cell comprises a pair of parallel upper and lower substrates 11a and 11b, and a wiring having a thickness of about 400 to 300
It has 0 ° transparent electrodes 12a and 12b. A chiral smectic liquid crystal 15 having a non-helical structure having two stable states is sandwiched between the upper substrate 11a and the lower substrate 11b. Specifically, in addition to SmC ^* and SmH ^* ,
Phase (SmI ^* ), K phase (SmK ^* ) and G phase (SmG ^* )
Liquid crystal can be used.

In the present invention, it is particularly preferable to use a liquid crystal exhibiting a cholesteric phase at a high temperature side, for example, a pyrimidine-based mixed liquid crystal A having a phase transition temperature and physical properties shown in the following table. it can.

[0020]

[Table 1]

On the transparent electrodes 12a and 12b, for example, insulating films 13a and 13b each having a thickness of 100 to 3000 ° are provided.
Are formed. 14a and 14b are alignment control films, each having a thickness of 50 to 1000 °. Usually, a high molecular polymer is used, but in the device of the present invention,
An orientation control film that gives a high pretilt angle, such as a fluorine-containing polyimide, is preferable.

In the present invention, the orientation control films 14a, 1
4b has a diameter of at least 0.1 (both in FIG. 1).
It is necessary to have 10 μm holes at a density of 10,000 / mm ² or more. Such a hole preferably penetrates to the lower layer in the thickness direction of the orientation control layer,
The lower layer acts on the liquid crystal. If the diameter of the hole exceeds 10 μm, it is not preferable because an alignment defect occurs and a display is adversely affected. On the other hand, when the thickness is less than 0.1 μm, the effect of providing the holes cannot be obtained, which is not preferable. The hole has an effect at a density of 10000 holes / mm ² or more, but the upper limit is 100000 holes / mm ^2.
mm ² or more, and if it exceeds this, there is a possibility that an alignment defect is generated and display is adversely affected.

The hole of the orientation control film can be formed by mixing fine particles 19 into the insulating films 13a and 13b, which are preferably lower layers. That is, the insulating film 1
Projections are formed by the fine particles 19 on the surfaces of 3a and 13b, and projections are also formed on the surfaces of the alignment control films 14a and 14b formed thereon by the projections. By rubbing the alignment control film having the convex portions, the alignment control film of the convex portions is peeled off, and holes are formed.

In the present invention, the particle diameter D of the fine particles 19
Is for forming a convex portion on the surfaces of the insulating films 13a and 13b, and for the thickness di of the insulating film, di <D <50
It is preferably di. As a material for the fine particles, an inorganic material such as SiO ₂ is preferably used.

In the present invention, preferably, the angle between the base cloth of the rubbing cloth used for the rubbing treatment and the pile is set in the range of 70 to 90 °, and the angle is the same over the entire surface of the rubbing cloth. By performing the rubbing treatment in order, the convex portions of the orientation control film can be removed to form the holes. As the rubbing cloth, nylon or modified nylon is preferable.

[0026]

【Example】

[Example 1] A transparent electrode made of ITO was formed on a glass substrate, and an insulating film of a coating and firing type, specifically, a mixed solution of an organic titanium compound and an organic silicon compound was used thereon, in which Ube Nitto Kasei was used. Silica fine particles having a particle size of 2000 ° manufactured by Co., Ltd. were mixed so as to be present at 10,000 particles / mm ² or more after printing, printed and coated at 1,000 ° by an angstromer, and fired at 300 ° C. 1% NMP of a polyamide alignment film LQ1802 manufactured by Hitachi Chemical Co., Ltd.
(N-methylpyrrolidone) solution is applied with a spinner,
Baking was performed at 270 ° C. for 1 hour. Next, the substrate was rubbed. The material of the rubbing cloth is nylon,
Three types of denatured nylon, aramid and cotton, and a woolen fabric having a bristle length of 2 mm were used. Moreover, the thing which adjusted the degree of raising of each cloth to 60 degrees, 70 degrees, 80 degrees, and 90 degrees was used. A schematic diagram of the rubbing device is shown in FIG. FIG.
Reference numeral 51 denotes a substrate, 52 denotes a rubbing roller, and 53 denotes a rubbing cloth. In FIG. 5, for convenience, a transparent electrode,
The insulating film and the orientation control film are omitted. The rubbing conditions were as follows: rotation speed C = 400 rpm, substrate feed speed B = 50 mm /
sec, and the amount of indentation ε is 17
° was appropriately adjusted.

The above-mentioned substrate and another substrate which has been subjected to the same treatment are subjected to the following steps so that the rubbing directions are parallel and the same.
Affixing with a gap of 5 μm to produce a cell,
The aforementioned pyridimine-based mixed liquid crystal A was injected at 90 ° C. to obtain the aforementioned C1 uniform orientation.

Next, the orientation of the entire cell is aligned with the average molecular axis direction 21 in FIG. 2A, and the pulse width Δt = 25 μs
ec, a voltage amplitude V _pp = 40 V, a rectangular wave having a (矩形) duty is applied for about 7 hours, and then a region 23 in FIG.
Was measured, and the percentage increased from the initial stage was calculated. The results are shown in the table below.

[0029]

[Table 2]

As described above, it was found that the rubbing treatment using nylon or aramid, particularly the change in cell thickness at 70 to 90 °, can be reduced.

Further, the present inventor examined the influence of the state of the rubbing cloth on the alignment film. Observation of the state of the holes in the alignment film of each sample by SEM (scanning electron microscope) revealed that almost no holes were found in the alignment control film of the substrate using a cotton rubbing cloth. Also, in the case of nylon and aramid having a degree of raising of 60 °, almost no pores were observed on the entire surface of the cell. On the other hand, nylon and aramid having a brushing degree of 70 to 90 ° have a diameter of 0.1 to 10 °.
μm holes were found to be scattered.

Example 2 The density after printing was adjusted to 5000 or 1000 by adjusting the mixing amount of the silica fine particles in the insulating film.
A cell was manufactured and driven in the same manner as in Example 1 except that the density was set to 0, 20,000 cells / mm ² . The rubbing cloth used was made of nylon and aramid having a raising degree of 90 °. Table 3 shows the results.

[0033]

[Table 3]

As described above, when the amount of fine particles is 500
It can be seen that the effect is small at 0 pieces / mm ² .

Comparative Example 1 A cell was prepared in the same manner as in Example 1 except that fine particles were not mixed into the insulating film and that the rubbing cloth was made of nylon and aramid having a raising degree of 90 °. 3B, the cell thickness in the region of FIG. 3B was increased by about 30% as compared with the initial stage.

[0036]

As described above, according to the present invention,
A coloring phenomenon due to a change in cell thickness over time is prevented, and a liquid crystal element with improved durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of a liquid crystal element of the present invention.

FIG. 2 is an explanatory diagram of a change in cell thickness due to movement of liquid crystal molecules.

FIG. 3 is an explanatory diagram of a smectic layer of a liquid crystal element using a chiral smectic liquid crystal.

FIG. 4 is an explanatory diagram of a liquid crystal alignment state of a liquid crystal element using a chiral smectic liquid crystal.

FIG. 5 is an explanatory diagram of a rubbing process.

[Explanation of symbols]

 11a, 11b Substrate 12a, 12b Transparent electrode 13a, 13b Insulating film 14a, 14b Alignment control film 15 Liquid crystal 16 Sealing material 17 Spacer 18 Adhesive material 19 Fine particles 20 Rubbing direction 21, 21 'Average molecular axis direction 22 Liquid crystal moving direction 23 Cell Thickness change region 31 Smectic layer 32 C1 orientation 33 C2 orientation 34 Lightning defect 35 Hairpin defect 36a, 36b Substrate 41, 42 Spray state 43, 44 Uniform state 45, 46 Uniform state 51 Substrate 52 Rubbing roller 53 Rubbing cloth

Claims (9)

[Claims] 1. A liquid crystal element comprising a pair of electrode substrates having a substrate on which an electrode, an insulating film, and an alignment control film are sequentially provided, and a liquid crystal sealed in a gap therebetween, wherein at least one of the alignment control films is provided. Has a hole having a diameter of 0.1 to 10 μm
A liquid crystal element having a density of not less than ² / mm ² . 2. A projection formed in a lower insulating film fills a hole of the orientation control film, and the projection of the insulating film is formed by fine particles dispersed in the insulating film. The liquid crystal device according to claim 1. 3. The liquid crystal device according to claim 2, wherein the particle diameter D of the fine particles satisfies di <D <50 di with respect to the film thickness di of the insulating film. 4. The liquid crystal device according to claim 1, wherein the liquid crystal is a chiral smectic liquid crystal. 5. The liquid crystal device according to claim 4, wherein the pretilt angle of the liquid crystal is α, the tilt angle is Θ, and the inclination angle of the SmC ^* layer is δ, and the alignment state is represented by Θ <α + δ. 6. The liquid crystal element has at least two stable states, and the relationship between θ _a , which is half the angle formed by the optical axis in each stable state, and the tilt angle 液晶 of the liquid crystal is as _follows : Θ <θ The liquid crystal device according to claim 4, wherein _a <Θ / 2. 7. The method for manufacturing a liquid crystal element according to claim 1, wherein after forming an electrode on the substrate, an insulating film having a convex portion formed on the surface by mixing fine particles is formed. An alignment control film having a convex portion on the surface reflecting the convex portion of the insulating film is formed thereon, and the alignment control film having the convex portion on the surface is peeled off by rubbing the alignment control film, whereby the alignment is performed. A method for manufacturing a liquid crystal element, wherein a hole is formed in a control film. 8. An angle between the base cloth of the rubbing cloth used for the rubbing treatment and the pile is set in the range of 70 to 90 °, and the angle is set in the same direction over the entire surface of the rubbing cloth. And performing the rubbing process in order.
The manufacturing method of the liquid crystal element of the description. 9. The method according to claim 8, wherein the material of the rubbing cloth is nylon or modified nylon.