JPH0469926B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid crystal element used in a liquid crystal display element, a liquid crystal light shutter, etc., particularly a liquid crystal element using ferroelectric liquid crystal, and more specifically relates to a method for improving the initial alignment state of liquid crystal molecules. This invention relates to a liquid crystal element with improved display characteristics. [Prior Art] Clark and Lagerwall proposed a type of display element that utilizes the refractive index anisotropy of a ferroelectric liquid crystal element to control transmitted light in combination with a polarizing element. (Japanese Unexamined Patent Publication No. 107216/1983, US Pat. No. 4,367,924, etc.). This ferroelectric liquid crystal generally has a chiral smectic C phase (SmC*) or H phase (SmH*) in a specific temperature range, and in this state, it responds to an applied electric field to produce a first optical It has the property of being in either an optically stable state or a second optically stable state and maintaining that state when no electric field is applied, that is, it has bistability, and it also responds quickly to changes in the electric field. , and is expected to be widely used as high-speed and memory-type display elements. In order for an optical modulation element using this bistable liquid crystal to exhibit predetermined driving characteristics, the liquid crystal placed between a pair of parallel substrates must maintain the above two stable characteristics, regardless of the applied state of the electric field. It is necessary that the molecules be in such a state that conversion between states can occur effectively. For example, for ferroelectric liquid crystals with SmC* or SmH* phase, SmC* or
It is necessary to form a region (monodomain) in which the liquid crystal molecular phase having the SmC* phase is perpendicular to the substrate surface, and the liquid crystal molecular axes are arranged approximately parallel to the substrate surface. By the way, as a method for aligning ferroelectric liquid crystal,
Generally, a method using an alignment control film subjected to uniaxial alignment treatment such as rubbing treatment or oblique evaporation treatment is known. Most of these conventional alignment methods have been applied to ferroelectric liquid crystals having a helical structure that does not exhibit bistability. For example, the alignment method disclosed in European Patent Publication No. 91661 and Japanese Patent Application Laid-Open No. 60-230635 uses polyimide, polyamide or Orientation was controlled by a polyvinyl alcohol film. However, when the conventional alignment control film as described above is applied to control the alignment of a ferroelectric liquid crystal with a non-helical structure exhibiting bistability as announced by Clark and Lagauer, the following problems arise. It had [Problems to be Solved by the Invention] According to experiments conducted by the present inventors, the tilt angle θ( Part 3 mentioned below
The angle θ shown in the figure) is smaller than the tilt angle of the ferroelectric liquid crystal with a helical structure (the angle that is half the apex angle of the triangular pyramid shown in Figure 2 below). There was found. In particular, the tilt angle θ of a ferroelectric liquid crystal with a non-helical structure obtained by alignment using a conventional alignment control film is generally about several degrees, and the transmittance at that time is about 3 to 5% at most. . Thus, according to Clark and Lagauer, the tilt angle of a ferroelectric liquid crystal with a non-helical structure that achieves bistability should be the same as the tilt angle of a ferroelectric liquid crystal with a helical structure. However, in reality, the tilt angle θ in the non-helical structure is smaller than that in the helical structure. That is,
In order for the tilt angle θ to take the maximum tilt angle, the composition of liquid crystal molecules must be in the uniform orientation shown in Figure 4, but in reality, each adjacent liquid crystal is aligned as shown in Figure 5. There was a problem in that it was not possible to form a sufficiently large tilt angle θ because the molecules were in a splay orientation state caused by being twisted and oriented at a twist angle α. In addition, a liquid crystal element in a splayed alignment state exhibits an optical response characteristic to a pulse signal as shown in FIG. 7, and this optical response characteristic causes flickering on the display screen when multiplexing driving is performed. The point was hot. It is therefore an object of the present invention to solve the aforementioned problems, namely that at least two stable states;
In particular, the object of the present invention is to provide a liquid crystal element in which the tilt angle of a non-helical ferroelectric liquid crystal realizing bistability is increased, thereby improving the transmittance when the pixel shutter is opened. Another object of the present invention is to provide a liquid crystal element that does not cause flickering on the screen during multiplexing driving. [Means for Solving the Problem] and [Operation] That is, the present invention provides a ferroelectric liquid crystal element in the uniform alignment state shown in FIG. 4 by using the specific alignment control film described below. Accordingly, it is possible to realize a liquid crystal element that exhibits optical response characteristics to pulse signals as shown in FIG. 6 and that does not cause flickering on the screen during multiplexing drive. The specific alignment control film used in the present invention can be obtained from a modified resin containing a structural unit represented by the following general formula () as a side chain, and can be used to control the ferroelectric liquid crystal element in the uniform alignment state described above. It can be realized. general formula In the formula, R ₁ , R ₂ and R ₃ are hydrogen atoms, alkyl groups (methylethyl, propyl, butyl, amyl, hexyl, decyl, octadecyl, etc.), aromatic groups (phenyl, xylyl, tolyl, biphenyl,
naphthyl, anthralyl, alkoxyphenyl,
chlorophenyl, bromophenyl, etc.) or active groups (hydroxy, amino, alkoxy, cyano, mercapto, trifluoromethyl,
glycidyl, etc.). In particular, the above-mentioned active group is preferably substituted at the terminal of the alkyl group. As the main chain of the resin mentioned above, a polyamide chain, a polyethylene chain, a polyethylene oxide chain, etc. can be used, and a linear chain is particularly preferable. Specific examples of the resin used in the alignment control film of the present invention are shown below.

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〔Example〕

Hereinafter, the present invention will be explained by giving specific examples and comparative examples. Example 1 A liquid crystal element was manufactured using a polyamic acid resin having a degree of polymerization of 1500 shown below as an alignment film. Two 0.7 mm thick glass plates were prepared, and an ITO film was formed on each glass plate. A solution prepared by dissolving 2% by weight of the polyamic acid in dimethylacetamide was applied onto each of the ITO film-coated glass plates using a spinner at a rotation speed of 2000 rpm for 90 seconds. After the film was formed, it was heated and baked at 180°C for about 1 hour. The thickness of the coating film at this time was approximately 400 Å. After this firing, the coating was rubbed with acetate flocked cloth, then washed with isopropyl alcohol solution, and alumina beads with an average particle size of about 1 μm were sprinkled on one glass plate. A cell was created by stacking two glass plates so that the glass plates were parallel to each other. The cell thickness of this cell was measured using a Bereck phase plate (measurement based on phase difference) and was found to be approximately 1 μm. This cell is "CS-1011" manufactured by Chitsuso Co., Ltd.
(Product Name) was injected under vacuum in an isotropic phase and then slowly cooled from the isotropic phase to 60°C at a rate of 0.5°C/h, thereby making it possible to achieve orientation. Subsequent experiments were conducted at 60°C. The phase change of "CS-1011" mentioned above was as follows. SmC＊56℃ ―――→ ←――― 53℃SmA78℃ ―――→ ←――― 76℃Ch94℃ ――――→ ←――― 90℃Iso (SmA: Smectic A phase, Ch: Cholesteric phase , Iso; indicates an isotropic phase) When this cell was observed under crossed nicol conditions, monodomains were obtained that formed a chiral smectic C phase with a uniform, defect-free, non-helical structure. Next, apply a frequency of 70V to the liquid crystal cell described above.
A high electric field alternating current of 70 Hz was applied for about 1 minute (alternating current application pretreatment). When we measured the tilt angle θ at this time, we found that
It was 18 degrees. This tilt angle θ is determined by applying a pulsed electric field (10 V, 500 μsec) to the liquid crystal cell, aligning the direction of the liquid crystal molecules to one stable state, and then rotating the liquid crystal cell under crossed Nicols to obtain the lowest amount of transmitted light. Find the position where the dark state occurs, then apply a pulsed electric field (-10V, 500μsec) with the opposite polarity to the previous pulse.
By applying , the liquid crystal cell is transferred to the other stable molecular alignment state and becomes a bright state, and then measurement can be performed by rotating the liquid crystal cell again and finding the angle at which it becomes a dark state again. . The positions of these two re-dark states correspond to the detection of a stable average molecular axis of the liquid crystal, and the angle between these two states corresponds to the tilt angle 2θ. It was found that the liquid crystal cell of this example maintained a tilt angle of 18° for a period of one week or more. Furthermore, when the liquid crystal element of this example was multiplexed and driven under the following driving conditions, a flicker-free display screen was formed. Driving conditions (1) 1st step; pulse width 500μsec for all scanning lines,
Pulse width for 10V signal and all signal lines
Apply a signal of -5V for 500μsec at once. (2) Second step: Pulse width as scanning selection signal
Using 500μsec and voltage of 10V, this signal is sequentially applied to the scanning lines, and in synchronization with this scan selection signal, a signal of pulse width of 500μsec and voltage of 5V and a signal of pulse width of 500μsec and voltage of -5V are selectively output. Apply to the line. Examples 2 to 4 Cells similar to those in Example 1 were prepared using the three types of resins shown in Table 1, and the same AC pretreatment as in Example 1 was performed. The tilt angle θ at that time and the tilt angle θ after being left for one week were measured. These results are shown in Table 1. A display screen was formed from each of these liquid crystal cells by multiplexing drive similar to that in Example 1, and there was no flicker during writing in any of them even one week after the alternating current application process.

〔Effect of the invention〕

According to the present invention, it is possible to realize a ferroelectric liquid crystal in a uniformly aligned state that can obtain an increased tilt angle, and moreover, it is possible to stably maintain this uniformly aligned state for a long period of time.

[Brief explanation of drawings]

1A and 1B are cross-sectional views showing embodiments of the liquid crystal device of the present invention, FIG. 2 is a perspective view schematically showing a liquid crystal device using a ferroelectric liquid crystal with a spiral structure, and FIG. A perspective view schematically showing a liquid crystal element using a ferroelectric liquid crystal with a non-helical structure, FIG. 4 is a cross-sectional view schematically showing a uniform alignment state, and FIG. 5 is a cross-sectional view schematically showing a splay alignment state. , FIG. 6 is a characteristic diagram showing optical response characteristics in a uniform orientation state, and FIG. 7 is a characteristic diagram showing optical response characteristics in a splay orientation state. 11a...upper substrate, 11b...lower substrate, 12
a, 12b...transparent electrode, 13...ferroelectric liquid crystal, 14a, 14b...alignment control film, 21a, 2
1b...substrate, 22...liquid crystal molecule layer, 22...liquid crystal molecule, 24...dipole moment, 32...vertical layer, 33a...first stable state, 33b...second stable state, 34a ...Upward dipole moment, 34b...Downward dipole moment, ...
Tilt angle in helical structure, θ... Tilt angle in non-helical structure, Ea, Eb... Electric field, 41... Projection of liquid crystal molecules onto vertical layer (C-director), 42...
Tip of liquid crystal molecules relative to vertical layer, 61... Transmittance curve in uniform alignment state, 62, 72...
Pulse, 71...transmittance curve in spray orientation state.

Claims (1)

[Scope of Claims] 1. A liquid crystal element having a pair of parallel substrates and a ferroelectric liquid crystal having a molecular arrangement forming a plurality of layers perpendicular to the planes of the pair of parallel substrates, At least one of the pair of parallel substrates has a resin coating having a structural unit represented by the following general formula in a side chain that preferentially orients the plurality of layers in one direction. A liquid crystal element. general formula (In the formula, R ₁ , R ₂ and R ₃ are hydrogen atoms, alkyl groups,
Indicates an alkyl group having an aromatic group or an alkyl group having an active group. 2. The liquid crystal element according to claim 1, wherein the main chain of the resin is polyamide. 3. The liquid crystal element according to claim 1, wherein the main chain of the resin is polyethylene. 4. The liquid crystal element according to claim 1, wherein the alignment control film has a uniaxial alignment axis. 5. The liquid crystal element according to claim 4, wherein the uniaxial alignment axis is an alignment axis imparted by rubbing treatment. 6. The liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal has a chiral smectic phase. 7 When the ferroelectric liquid crystal has no electric field, at least 2
2. A liquid crystal element according to claim 1, which is a liquid crystal exhibiting two stable alignment states. 8. The liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal with a non-helical structure and has a tilt angle of 18 degrees or more. 9. The liquid crystal element according to claim 1, wherein the active group is substituted at the end of an alkyl group. 10. The liquid crystal device according to claim 9, wherein the active group is a hydroxy group, an alkoxy group, an amino group, a mercapto group, a glycidyl group, a cyano group, or a fluoroalkyl group.