JPH11258639A - Chiral smectic liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element capable of suppressing the hysteresis characteristic by the spontaneous polarization of chiral smectic liquid crystals. SOLUTION: The liquid crystal display element formed by holding the chiral smectic liquid crystals between a pair of substrates contains a cyclic ether in the chiral smectic liquid crystals and the difference in the temp. at which a cholesteric phase or smectic phase appears from an isotropic phase in a cooling process of the case the liquid crystals do not contain the cyclic ether is <=1.5 deg.C. In such a case, the chiral smectic liquid crystal element provided with a cell thickness gradient within pixels is preferable and the content of the cyclic ether is preferably at least >=0.5 wt.%. The size of the ring of the cyclic ether is 5 to 6 and a cyclocycle or alkyl group is preferably incorporated into the ornamental group. The element has preferably an alignment layer on at least one substrate and electrical conductivity is preferably imparted to this alignment layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a chiral smectic liquid crystal display device.

[0002]

2. Description of the Related Art Chiral smectic liquid crystal display devices are
There are advantages such as quick response and display memory effect. In this chiral smectic liquid crystal display device, the display state is performed by alternately changing the orientation state of the liquid crystal molecules by inverting the polarity of the applied voltage, so that the direction of the spontaneous polarization of the liquid crystal molecules is alternately inverted.

[0003] In an actual chiral smectic liquid crystal display device, in order to switch between two bistable states, gradation display is performed by a pixel division method or the like.
It has been proposed to perform a gradation display by a cell thickness gradient method in which a gradient is applied to the cell thickness and a distribution is provided in the pixel (for example, Japanese Patent Application Laid-Open No. Sho 62-145216).

[0004]

However, in the cell thickness gradient method, since a driving threshold distribution is provided in a pixel to perform area gradation, in a chiral smectic liquid crystal exhibiting a hysteresis characteristic by spontaneous polarization, the hysteresis characteristic is reduced as much as possible. There was a problem to do.

The present invention has been made in order to solve such problems of the prior art. By adding a cyclic ether to a chiral smectic liquid crystal, the hysteresis characteristic of the chiral smectic liquid crystal due to natural polarization is suppressed. It is an object of the present invention to provide a liquid crystal display device capable of performing the above.

[0006]

That is, the present invention relates to a liquid crystal display device in which a chiral smectic liquid crystal is sandwiched between a pair of substrates. A chiral smectic liquid crystal display device characterized in that the difference in the temperature at which a cholesteric phase or a smectic phase appears from an isotropic phase is 1.5 ° C. or less.

In the present invention, a chiral smectic liquid crystal display device having a cell thickness gradient in a pixel is preferable.
The content of the cyclic ether is preferably at least 0.5% by weight or more. The ring size of the cyclic ether is preferably 5 to 6, and the modifying group preferably contains a cyclo ring or an alkyl group. Preferably, at least one of the substrates has an alignment film, and the alignment film is provided with conductivity.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The chiral smectic liquid crystal display device of the present invention is a liquid crystal display device in which a chiral smectic liquid crystal is sandwiched between a pair of substrates, wherein the chiral smectic liquid crystal optimally contains a cyclic ether and the phase transition temperature does not contain the cyclic ether. By making the change not so large compared to the case, the relaxation time of the hysteresis of the chiral smectic liquid crystal is shortened, especially in an element with a cell thickness gradient in the pixel, and the hysteresis characteristic due to natural polarization is suppressed. It is characterized by.

As the cyclic ether used in the present invention, an ether compound which completely melts in a chiral smectic liquid crystal and does not cause deterioration in alignment is used. Specific examples of the cyclic ether are shown below.

[0010]

Embedded image

[0011]

Embedded image

Among the above cyclic ethers, compounds having a ring size of the cyclic ether of 5 to 6 and containing a cyclo ring or an alkyl group in the modifying group are preferred. The content of the cyclic ether contained in the chiral smectic liquid crystal is at least 0.5% by weight or more, preferably 0.1 to
A range of 1% by weight is desirable.

As an index for measuring the influence on the orientation of the chiral smectic liquid crystal composition containing a cyclic ether, a phase transition (isotropic phase) between the liquid crystal composition containing the cyclic ether and the liquid crystal composition not containing the cyclic ether is used as an index. The temperature difference Δ _iso is used as the determination means. As a measuring method, a liquid crystal composition containing a cyclic ether is cooled (cooling point) by DSC (thermal scanning analysis).
t). As shown in Example 1 and Comparative Example 1 below, the cyclic ether has a ring size of 5 to 6, and is a cyclic ether containing a cyclo ring or an alkyl group in the modifying group, and has a small temperature difference _Δiso. Good results were obtained.

The switching characteristics of a chiral smectic liquid crystal composition containing a cyclic ether are as follows.
The measurement was performed by the following method. First, a gradient cell having a distribution in the thickness of a liquid crystal layer for injecting the liquid crystal composition containing the cyclic ether was prepared.

FIG. 1 is a plan view of a liquid crystal display device of the present invention.
In particular, FIG. 2 schematically shows an example of the arrangement of electrodes and color filters. FIG. 2 is a cross-sectional view taken along the line AA ′, and FIG.
It is a sectional view taken on the line B '. In FIG. 1, scanning lines Sn... And information lines I
_11, I _12, region and I ₁₃ is to a set of RGB surrounded by a broken line that intersects P is l pixels. 2 and 3, la and lb are insulating substrates, 2 is an undercoat layer, 3 is a color filter, 4 is a columnar film, 5 is an organic film,
6a and 6b are transparent electrodes (the transparent electrodes 6a correspond to the scanning lines Sn..., The transparent electrodes 6b correspond to the information lines I ₁₁ ... I ₂₁ ), 7a and 7b are auxiliary electrodes, and 8a and 8b are short-circuit prevention layers. , 9a and 9b are rough surface forming layers, 10a and 10b are alignment layers, 11 is an adhesive bead, 12 is a spacer bead, 13 is a liquid crystal layer, 14 is a light shielding layer, and 15 is an uneven shape. Upper side of the LCD (color filter 3
Is referred to as a first substrate, and the lower side is referred to as a second substrate. still,
FIG. 1 is a plan view seen from the first substrate side.

Hereinafter, each part of the liquid crystal display element shown in FIGS. 1 to 3 will be described in detail along with the manufacturing process. First, the first substrate side will be described.

Step-a As the insulating substrate la, a commercially available glass for liquid crystal can be generally used, and examples thereof include blue plate glass and non-alkali glass. Preferably, one having one surface polished is used. Further, the thickness and size are appropriately selected depending on the screen size and the number of panels to be taken from one sheet. For example, in the case of manufacturing a liquid crystal element having a large screen (14.8 inches), 1. The one having a thickness of about 1 mm is used.

Step-b In the present invention, preferably, an undercoat layer 2 is provided on the surface of the insulating substrate la to prevent elution of alkali from the glass. As the undercoat layer 2, SiO ₂
Is preferably used and has a thickness of 200 to 1000 °.

Step-c The insulative substrate la having the undercoat layer 2 formed on the surface is cleaned at a suitable number of times and in combination by using at least one of a pure water shower, pure water + ultrasonic cleaning, and a brush.
After drying, organic matter is removed by irradiation with ultraviolet rays.

Step-d The light-shielding layer 14 shown in FIG. 3 is a stripe pattern (plaque stripe). In addition, a desired shape such as an ordinary black matrix can be used as appropriate. Light shielding layer 14
As a material for the above, a metal such as Cr or Mo, or an alloy thereof, Cr ₂ O _{3 as} an oxide, or an organic material such as a resin in which a black pigment is dispersed can be used. The thickness is set in the range of 500 to 1500 ° according to the light shielding ability of the material. For example, when metal is used, a light-shielding effect can be obtained even if the thickness is small. In the present invention, a Mo—Ta alloy layer is preferably used, and preferably a thickness of 1000 ° or less. The light-shielding layer 14 is obtained by laminating the material over the entire surface of the substrate by sputtering, coating, or the like, and then patterning. Specifically, a resist selected based on the adhesion to the material is applied to the surface of the light-shielding layer by a spinner, printing, or the like, prebaked at 70 to 120 ° C, exposed at 90 to 120 mJ, developed, washed, and dried. Then, the substrate is etched with an etching solution such as an acid corresponding to the material of the light-shielding layer, washed, the resist is peeled off, and further washed.

Step-e In the present invention, the color filter 3 forms green (G), red (R), and blue (B). As a forming method, there are a dyeing method, a pigment dispersion method, an electrodeposition method, and the like, and any of the methods can be used in the present invention. The pigment dispersion method will be described as an example. A color resist of a photosensitive resin in which a desired pigment is dispersed is coated with a spinner, a coater or the like to a thickness of 1.0 to 2. μm,
After leveling at a certain temperature, pre-baking is performed at about 80 ° C. At this time, the temperature, the holding time, and the thickness to be applied are appropriately selected depending on the resist material. Then 200-10
Exposure at 00 mJ. Since the exposure degree differs in sensitivity among R, G, and B, it is adjusted by changing the exposure time. After exposure, develop with a developing solution, a method, and a temperature according to the resist material.
Post-bake at 250 ° C. and wash. Each color filter is formed with a gap of several μm so as not to be in contact with the previously formed light shielding layer 14 and the adjacent color filter. Further, the whole is formed so as to be wider than the display area and not to be applied to a sealant described later. In addition, the above-described forming process is sequentially performed for each color, and the order is appropriately selected depending on a material to be used.

Step-f Next, the columnar film 4 is formed. In the present invention, the photosensitive resin of the color filter (W) to which no pigment is added is used for the columnar film, but any inorganic or organic substance can be used as long as it can withstand the subsequent steps and has heat resistance and chemical resistance.

The color resist of the photosensitive resin of the filter (W) to which no pigment is added is coated with a spinner, a coater or the like to a thickness of 1.0 to 2. μm, leveling at a constant temperature, and pre-baking at around 80 ° C. At this time, the temperature, the holding time, and the thickness to be applied are appropriately selected depending on the resist material. Next, exposure is performed at 200 to 1000 mJ. After exposure, development is performed with a developing solution, method and temperature according to the resist material, post-baked at 120 to 250 ° C., and washed. The number of columnar films 4 may be the same or different for each color.

The columnar shape of each columnar film 4 is 3 μm or more in width, preferably 3 to 5 μm, on the previously formed color filter.
At 0 μm, the height varies depending on the size of the pixel, but is 1 μm or more and the interval is 200 μm or less, preferably 10 to 200 μm.
It is formed to have a thickness of μm. The width of each columnar film may be the same, or may be made of two or more different films. The intervals between the individual columnar films may be the same, or may be two or more different ones.

Step-g Next, an organic film 5 for filling the gaps between the columnar films and making the surface uneven with a gentle gradient is formed. In the present invention, the organic film 5 has a thickness of 0.5 μm or more, preferably 0.8 to 1.5 μm, a spinner, printing,
After applying an organic film agent with a coater or the like, the layer is formed by leveling at 60 to 150 ° C. and post-baking at 150 to 330 ° C. if necessary (these temperatures are set depending on the material). The material is color filter 3
And a step caused by the light shielding layer 14 can be flattened.
Any material can be used as long as it can withstand the subsequent steps and has heat resistance and chemical resistance. Specific examples include acrylic resins, polyamides, epoxy resins, organic silane resins, silicon resins, and the like. Among them, organic silane resins are preferably used. It is preferable that the columnar film and the organic film laminated thereon have different materials.

The viscosity of the coating liquid for the organic film laminated on the columnar film is 5 to 100 cp (30 ° C.), preferably 2 to 100 cp (30 ° C.).
0 to 40 cp (30 ° C.) is desirable. Further, in the liquid crystal device of the present invention, the diameter of the spacer beads 12 described later is larger than the thickness of the liquid crystal layer 13 and the spacer beads 12
Is desirably fixed so as to be embedded in both substrates. Therefore, it is desirable that the substrate is flexible enough to fill the spacer beads, and the hardness of the laminated organic film 5 is 5
It is preferably in the range of H or less. Further, it is preferable to form up to the lower side of the sealant. With this configuration, liquid crystal can be easily injected, and defective products due to defective injection of liquid crystal during manufacturing can be prevented.

The height difference of the unevenness of the organic film laminated on the columnar film is smaller than the height difference of the unevenness of the columnar film, and the height difference of the unevenness of the organic film stacked on the columnar film is not less than 1/3 of the cell gap. Is preferred.

Further, the organic film to be laminated may be composed of two or more layers, and the kind of the organic film to be laminated may be different. Further, an inorganic film may be present between the two or more stacked organic films.

The above is the process for the first substrate only, and the following processes are common to the first and second substrates. Also, the second
The same material as the insulating substrate la of the first substrate is used for the insulating substrate lb of the substrate.

Step-h As the transparent electrodes 6a and 6b, for example, an ITO layer is formed by sputtering, vapor deposition, firing or the like. Preferably, In ₂ O ₃
Although SnO ₂ is used in an amount of ₅ to 10% by weight, it may be appropriately selected depending on transmittance and conductivity. The thickness of the transparent electrodes 6a and 6b is 300 to 3000 °, and the thickness is also selected according to the optical characteristics and resistance of the liquid crystal used. The ITO layer is formed into a desired shape by re-patterning by photolithography similarly to the light shielding layer 14. However,
As an etching solution, an aqueous solution of iron chloride, hydroiodic acid, hypophosphorous acid, or the like is used.

Step-i Auxiliary electrodes 7a and 7b for reducing the wiring resistance of the transparent electrodes 6a and 6b are formed. The material is metal, Cr, Al, M
o, an alloy thereof, Mo-Ta, or the like is used. Further, a multilayer structure may be adopted in consideration of the adhesion to the transparent electrodes 6a and 6b, the resistance, and the adhesion to the resist. Specifically, it is Mo / Al, Mo / A1 / Mo-Ta, or the like. In particular, in the case of a multi-layer configuration, since the etching speed differs depending on the material, the material is selected in consideration of the etching in the subsequent process. For example, when simultaneously etching the above three-layer structure, Mo-Ta 5-10% / Al alloy / Mo-Ta
10 to 20% has good compatibility with the etching solution. Further, the multilayer structure may be formed by laminating while etching each layer.

The above-mentioned metal is laminated on the entire surface of the substrate, and the steps of resist coating, exposure, development, post-baking, etching and resist peeling are sequentially performed to overlap the transparent electrode 6a and to form an opening on the color filter 3. And an auxiliary electrode 7b overlapping the end of the transparent electrode 6b.

Step-j The short prevention layers 8a and 8b are formed on the wiring. The short-circuit preventing layers 8a and 8b are insulating layers for preventing a short circuit between the upper and lower substrates, and an organic or inorganic insulating film is formed on the entire surface of the substrate by sputtering, coating, baking, or the like. Specifically, Ti—Si, SiO ₂ , TiO ₂ , and Ta ₂ O ₅ are used, and these can be used in a single layer or a multilayer. For example, Ta ₂ O ₅ is sputtered from 500 to 1200.
A multi-layer structure in which a coating type insulating film solution such as Ti-Si is printed and baked after being formed to a thickness of Å to form an insulating layer having a thickness of 500 to 1,000 好 ま し く is preferably used. The short prevention layers 8a and 8b are formed up to the outside of a sealing region described later.

Step-k In order to prevent the movement of liquid crystal molecules, the rough surface forming layers 9a and 9b
May be formed to roughen the surface of the alignment film. Rough surface forming layer 9a, 9b is a SiO ₂ beads having a particle size 150~500Å Ti-Si = 1: 5~3 on the insulating film a solution of 1 ratio
It is obtained by dispersing 0 wt%, printing and baking using a color developing plate. The film thickness is preferably 50 to 300 °, and is formed to the outside of the sealing region.

Step-1 Alignment films 10a and 10b for controlling alignment of liquid crystal molecules
To form The material of the alignment film is selected from polyvinyl alcohol, polyimide, polyamide imide, polyamide and the like, and is coated or printed on the entire surface of the substrate.
Baking is performed at 0 ° C. to form an insulating layer with a thickness of 50 to 100 ° outside the sealing region. A roller around which a brushed rubbing cloth is wound is pressed against the surface of the insulating layer, and a rotation speed of 500 to
While rotating at 2,000 rpm, the surface of the insulating layer is subjected to a rubbing treatment to form alignment films 10a and 10b. The material of the rubbing cloth is selected from natural fibers such as cotton, and synthetic fibers such as aramid, nylon, rayon, Teflon, polypropylene, and acrylic. Among them, aramid fibers are preferably used. The rotation direction and the feed speed of the roller are appropriately selected depending on the degree of the rubbing treatment. After the rubbing treatment, both substrates are washed. Step-m Adhesive beads 11 on one substrate, preferably the surface of the first substrate
Spray. The adhesive beads 11 are formed of an adhesive made of, for example, a thermosetting resin that does not affect the liquid crystal, such as an epoxy resin or an acrylic resin. The diameter of the adhesive beads 11 is 3
７7 μm is preferred, dispersed in a solvent such as isopropyl alcohol, and sprayed at about 50 to 130 particles / mm ² .
The adhesive beads 11 are adhered to both substrates after the substrates are sealed. As will be described later, the cutting positions of the first substrate and the second substrate are shifted to expose the terminals at the ends of the substrate. If the adhesive bead 11 is present, the part to be cut off is the adhesive bead 11
It is preferable that the adhesive bead 11 does not exist in a region to be cut off by cutting, and it is preferable that the adhesive bead 11 be sprayed only in a sealing region.

Step-n A seal pattern is drawn on the surface of the other substrate, preferably the second substrate, with a sealant (not shown) while leaving an injection port.
As the sealing agent, for example, a thermosetting epoxy resin is used, and drawing is performed by a dispenser. The drawing method is not limited to this, and can be appropriately selected according to the material of the sealing agent such as screen printing. The width may be set in consideration of the cell thickness or the thickness at the time of printing.

Step-o Spacer beads 12 are sprayed on the surface of the substrate on which the sealant has been drawn. The diameter of the spacer beads 12 is selected to be larger than the cell thickness, but is preferably in the range of 0.1 to 3.5 μm. For example, when the cell thickness is 1 μm, 1.
A bead having a diameter of about 2 to 1.3 μm is selected. As the material of the beads, silica beads and alumina beads are preferably used, and the beads are dispersed in ethanol or the like and dispersed over the entire surface of the substrate so as to be 100 to 700 beads / mm ² . In the present invention, by using beads having a diameter larger than the liquid crystal layer thickness as spacers, the beads are fixed between the substrates in a state that the beads are embedded in the surface of the substrate in the middle, so that the movement of the beads after sealing is reduced. And a uniform liquid crystal layer thickness is maintained.

Step-p The substrate on which the adhesive beads 11 are sprayed is fixed, and the substrate on which the spacer beads 12 are sprayed is aligned with the alignment films 10a and 10b.
The adhesive beads 11 and the sealing agent are cured by heating them for 10 to 120 minutes while pressing each other so that they are on the inside, and the substrates are adhered to each other. That is, the adhesive beads 11 and the spacer beads 12 are scattered on another substrate, and the substrate on which the adhesive beads 11 are scattered is fixed and bonded, so that there is no fear that the adhesive beads 11 are biased or detached from the substrate surface. . Further, since the spacer beads 12 are much smaller in diameter than the adhesive beads 11 and adhere to the surface of the substrate even when the substrate is turned over, the spacer beads 12 are not biased or fall off the substrate. According to this step, the substrates are bonded together in a state where both the adhesive beads 11 and the spacer beads 12 are uniformly dispersed.

Step-q Scribing is performed by shifting the cutting position between the first substrate and the second substrate so that the mounting terminal portion is exposed, and an extra substrate is removed.

Step-r A liquid crystal is injected into the liquid crystal cell obtained in the above step. First,
The liquid crystal cell is placed in a vacuum device, and the liquid crystal is attached to the injection port with the inside of the cell being sufficiently evacuated. Next, pressure is gradually applied in this state, and the liquid crystal is drawn into the liquid crystal cell at a constant speed as much as possible.

A gradient cell was prepared in this manner, and an experiment was conducted on the hysteresis characteristics using the gradient cell.

A liquid crystal display device obtained by injecting a chiral smectic liquid crystal composition containing a cyclic ether into the gradient cell was written by a multiplexing driving method shown in FIG. This is a method in which a bright state and a dark state can be written in one frame, and a 3ΔT driving method that requires 3ΔT for one line scanning period for a writing pulse width ΔT. The voltage is increased until the pixel switches from a dark state (black display state) to a completely bright state (white display state), and from that state (bright state, white display state) to a completely dark state (black display state) The voltage was lowered until switching to.

FIG. 5 is a diagram showing a voltage versus transmittance curve when writing is performed at a specific time. These profiles are shown in FIG. This profile changes over time, and the hysteresis changes accordingly. In FIG. 5, 31
Is a voltage versus transmittance curve from the dark state to the bright state, 32 is a voltage versus transmittance curve from the bright state to the dark state, and 33 is 31 and 32
Is the hysteresis voltage V _his generated by the difference

The shorter the time required for the hysteresis to reach a certain value, the more stable and excellent gradation display becomes possible. The hysteresis and the hysteresis saturation time were measured. On the other hand, some of the cyclic ethers containing a cyclo ring in the modifying group were good. (See Example 2)
Further, in the liquid crystal composition containing the cyclic ether,
Some of the cyclic ethers contained an alkyl group in the modifying group, and the shortening of the saturation time became more remarkable. (See Example 2) Further, when an alignment film having a conductive material was used for the gradient cell, there was a device in which the reduction of the hysteresis relaxation time was further improved.

In order to impart conductivity to the alignment film, for example, a conductive substance may be added to the alignment film. Examples of the conductive substance include fine particles of tin oxide and fine particles in which a conductor is coated on the surface of fine particles of SiO ₂ . The added amount of the conductive substance is preferably 10 to 100% by weight.

As the chiral smectic liquid crystal used in the present invention, a ferroelectric liquid crystal and an antiferroelectric liquid crystal are used.

[0047]

EXAMPLES The present invention will be specifically described below with reference to examples.

Embodiment 1 This embodiment will be described with reference to the liquid crystal display device shown in FIGS. First, SiO ₂ was formed to a thickness of 500 ° as an undercoat layer 2 on the surface of a glass substrate 1 a having a thickness of 1.1 mm. Next, a Mo-Ta alloy layer was formed as the light shielding layer 14 to a thickness of 1000 °.

On top of that, green (G), red (R), blue (B)
Each color filter was formed. As a color filter, a 1 μm-thick photosensitive resin color resist in which pigments of each color (no pigment was added to white (W)) were dispersed by a spinner and patterned.

Next, the columnar film 4 was formed by a color filter (same as W) to which no pigment was added. Next, an organic film 5 was formed to fill the gaps between the columnar films and make the surface uneven with a gentle gradient. As the organic film, an organic silane resin was used and applied by a spinner.

The above is the step for only the first substrate, and the following steps are steps common to the first and second substrates. Transparent electrode 6
As a and 6b, an ITO layer was formed to a thickness of 700 ° by sputtering. Then, the auxiliary electrodes 7a and 7b for lowering the wiring resistance of the transparent electrodes 6a and 6b are formed with a thickness of 2000 mm by M
It was formed with a multilayer structure of o-Ta / Al / Mo-Ta.

On this wiring, Ta ₂ O ₅ was formed as a short prevention layer 8a, 8b to a thickness of 900 ° by sputtering. Furthermore, a coating type insulating film of Ti-Si is printed thereon,
By firing, a film having a thickness of 900 ° was formed.

After the alignment films 10a and 10b made of polyimide polymer are formed on the pair of substrates and rubbed, a 1.5 μm-diameter SiO ₂ bead spacer 12 is sprinkled on the substrates, and an epoxy resin The two substrates were bonded together via a sealing agent composed of: Thus, a gradient cell was created.

The liquid crystal composition in which dicyclo-hexano-18c6, diazodibenzo-18c6, and dibenzo-15c5 were added as cyclic ethers to the gradient cell in the following chiral smectic liquid crystal was added in an amount of 0.5% by weight. (Temperature drop) ΔT _iso between the temperature at which the liquid crystal transitions from the isotropic phase to the cholesteric phase and the temperature at which the liquid crystal to which the cyclic ether is not added at all (the target example) transitions from the isotropic phase to the cholesteric phase during the cooling process. And the results are shown in Table 1 below. The temperature drop was within 1.5 ° C.

The orientation was measured by an optical polarization microscope (manufactured by Olympus Corporation, BH-2, magnification: 100 ×) by cross-nicols of the polarizing plate and transmission observation.

[0056]

[Table 1]

(Note 1) The results of orientation are shown below.

：: Orientation with no zigzag defect X: Orientation with zigzag defect

(Note 2) Cyclic ether

[0060]

Embedded image

(Note 3) Chiral smectic liquid crystal

[0062]

(Equation 1)

Comparative Example 1 In Example 1, the temperature at which the transition from the isotropic phase to the cholesteric phase in the temperature-falling process was completely different for the liquid crystal composition containing 1.0 wt% of the cyclic ether added to the chiral smectic liquid crystal. Table 2 below shows a comparison of the temperature difference (temperature decrease amount) ΔT _iso at which the liquid crystal to which the cyclic ether was not added (the target example) changed from the isotropic phase to the cholesteric phase during the temperature drop process. Temperature drop is 1.5
° C. The orientation was also poor.

[0064]

[Table 2]

Comparative Example 2 As in Example 1, benzo-12 was used as the cyclic ether.
For a liquid crystal composition in which c4, benzo-15c5, and benzo-18c6 were added to chiral smectic liquid crystal in an amount of 0.5% by weight, the temperature at which a transition from an isotropic phase to a cholesteric phase during a temperature drop process occurred, Temperature difference (temperature decrease amount) ΔT _{iso of} the liquid crystal to which was not added (transition example) during the temperature drop process from the isotropic phase to the cholesteric phase
And the results of Table 3 below were obtained. The temperature drop exceeded 1.5 ° C. The orientation was also poor.

[0066]

[Table 3]

[0067]

Embedded image

Therefore, from the results of Example 1 and Comparative Examples 1 and 2, it can be said that a sample having ΔT _iso of 1.5 ° C. or less has good orientation and is suitable for use in a liquid crystal display device. The present inventor believes that the influence of the added cyclic ether on the physical properties of the liquid crystal deteriorates the orientation, and that the physical properties are Δ Δ
T _iso , which was found to be good if 1.5 ° C. or less.

Example 2 To the gradient cell of Example 1, a cyclic ether containing a cyclo ring in the following modifying group (dicyclohexano-18-c
6) The hysteresis characteristics of a chiral smectic liquid crystal composition containing a cyclic ether (diazodibenzo-18-c6) containing 0.5% by weight of an alkyl group in the modifying group were evaluated. FIG. 6 shows the result.

[0070]

Embedded image

Hysteresis Characteristic Evaluation Method The sample shown in FIG. 5 was driven by applying the waveform shown in FIG. 5 to the prepared sample, and the amount of transmitted light T when the drive voltage (V ₂ −V ₄ ) was increased from 0 V to 30 V by 0.1 V at a time. Change curve (31 in FIG. 5)
And the transmitted light amount T when the voltage is lowered by 0.1 V from 30 V
5 (32 in FIG. 5) are measured at the following time intervals, and the voltage values of the curves 31 and 32 when the transmittance is 50% are V ₃₁ and V ₃₂ , respectively, and V _his = 33 = V It was determined hysteresis voltage V _{his-by 31} -V _32.

Time interval from the measurement of the curve 31 to the measurement of the curve 32 1 μsec, 2 μsec, 3 μsec, 5 μsec, 1
0 μsec 20 μsec, 30 μsec, 50 μsec, 100 μsec
sec 0.2msec, 0.3msec, 0.5msec, 1
msec 2msec, 3msec, 5msec, 10ms
ec 20msec, 30msec, 50msec, 100m
0.2 sec, 0.3 sec, 0.5 sec, 1 sec 2 sec, 3 sec, 5 sec, 10 sec
V _his was measured at each point c, and FIG. 6 was measured.

From FIG. 6, the relaxation time for each liquid crystal composition was determined. As a result, it can be seen that the resin containing the cyclic ether has a shorter relaxation time than the resin containing no cyclic ether.

As shown in FIG. 6, it can be seen that the relaxation time of V _his is shorter in the sample in which the cyclic ether is added than in the target example (liquid crystal in which no cyclic ether is added). Therefore, a liquid crystal display device having good orientation and good hysteresis characteristics can be obtained with this added sample.

Example 3 A comparison was made of the relaxation times of the gradient cell of Example 1 using an alignment film made of polyimide to which 100 wt% of a conductive material made of tin oxide was added. As a result, it was found that a relaxation time equivalent to that in Example 2 containing a cyclic ether was obtained.

Example 4 In Example 2, a cyclic ether containing an alkyl group in the following modifying group (diazodibenzo-18-c6)

[0077]

Embedded image Of a chiral smectic liquid crystal composition containing 0.3%, 0.5%, 0.7%, and 1.0% was evaluated for hysteresis characteristics. The results are shown in Table 4 and FIG.

[0078]

[Table 4]

From the above results, it can be seen that the inclusion of the cyclic ether in the liquid crystal can improve the hysteresis characteristics. Furthermore, when the content is 0.5% or more, the improvement effect is greater, and the increase in the improvement effect tends to be saturated,
Even when the content is 1.0% or more, there is not much difference in hysteresis characteristics as compared with 0.7%. When the content is 1.0% or more, ΔT _iso becomes larger than 1.5 ° C., and the orientation becomes poor.

[0080]

As described above, in the liquid crystal display device according to the present invention, by adding a cyclic ether to the chiral smectic liquid crystal, the hysteresis characteristic of the chiral smectic liquid crystal due to the spontaneous polarization can be suppressed. For this reason, switching failure (burn-in) after long-time writing can be prevented in the gradient cell having the driving threshold distribution in the pixel, and the area gradation can be further improved. As a result, it was possible to obtain a chiral smectic liquid crystal display element which was excellent for gradation display.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an example of a chiral smectic liquid crystal display device of the present invention.

FIG. 2 is a sectional view of the liquid crystal display device of FIG. 1 taken along the line AA ′.

FIG. 3 is a sectional view taken along line BB ′ of the liquid crystal display device of FIG. 1;

FIG. 4 is a waveform diagram of a driving voltage used in the present invention.

FIG. 5 is a diagram showing a voltage versus transmittance curve when writing is performed at a specific time.

FIG. 6 is a diagram showing the results of hysteresis characteristic evaluation of Example 2.

FIG. 7 is a diagram showing the results of the hysteresis characteristic evaluation of Example 4.

[Explanation of symbols]

 la, lb Insulating substrate 2 Undercoat layer 3 Color filter 4 Columnar film 5 Organic film 6a, 6b Transparent electrode 7a, 7b Auxiliary electrode 8a, 8b Short prevention layer 9a, 9b Rough surface forming layer 10a, 10b Alignment layer 11 Adhesive beads REFERENCE SIGNS LIST 12 spacer beads 13 liquid crystal layer 14 light-shielding layer 15 uneven shape 2 (A) waveform diagram of drive voltage used in the present invention 2 (B) waveform diagram of drive voltage used in the present invention 2 (C) drive used in the present invention Voltage waveform diagram

Claims (5)

[Claims] 1. A liquid crystal display device in which a chiral smectic liquid crystal is sandwiched between a pair of substrates. A chiral smectic liquid crystal display device characterized in that the difference in the temperature at which appears is 1.5 ° C. or less. 2. The chiral smectic liquid crystal display device according to claim 1, wherein a cell thickness gradient is provided in each pixel. 3. The chiral smectic liquid crystal display device according to claim 1, wherein the content of the cyclic ether is at least 0.5% by weight or more. 4. The chiral smectic liquid crystal display device according to claim 1, wherein the ring size of the cyclic ether is 5 to 6, and the modifying group contains a cyclo ring or an alkyl group. . 5. The chiral smectic liquid crystal display device according to claim 1, wherein an alignment film is provided on at least one of the substrates, and the alignment film is provided with conductivity.