JPH08211413A - Ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE: To provide a ferroelectric liquid crystal display element sufficiently ameliorated of the degradation in the display grade by sticking which is a deterioration in display with lapse of time without coloration of electrodes and deterioration in an initial threshold characteristic even if the element is driven for a long time or makes the same display over a long time. CONSTITUTION: This ferroelectric liquid crystal display element consists of a pair of substrates 1 with electrode 2 at least one of which are transparent and a ferroelectric liquid crystal compsn. 3 held between these substrates 1. The ferroelectric liquid crystal compsn. 3 of the ferroelectric liquid crystal display element consists of ferroelectric liquid crystals and 0.1 to 10wt.%, by the weight of the ferroelectric liquid crystals, an epoxy compd. having bivalent or higher valency epoxy groups and specific resistance at room temp. of >=10<8> Ω.cm and does not include the hardener of the epoxy compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device which is preferably used as a display device for various liquid crystal displays.

[0002]

2. Description of the Related Art Ferroelectric liquid crystals have advantages such as faster response speed than conventional nematic liquid crystals and simple matrix drive utilizing their bistability. Is expected. But,
It is said that a display using a ferroelectric liquid crystal becomes uni-stable if it is driven for a long time or left in the same display for a long time, and the bistability deteriorates with time (burning phenomenon). There was a problem. Therefore, the life of a display using a ferroelectric liquid crystal is short, which is a great obstacle to practical use.

Although the cause of the image sticking phenomenon is not well understood, the impurity ions in the liquid crystal are unevenly distributed by the spontaneous polarization of the ferroelectric liquid crystal, and the internal electric field due to the uneven distribution of the ions makes the liquid crystal monostable. It is said that this is one of the causes. Therefore, a technique for sufficiently purifying the liquid crystal or eliminating an image sticking by adding an ion adsorbent to the liquid crystal is disclosed in, for example, JP-A-54-
59244, JP-A-63-163426,
It is described in JP-A-5-88148. However, the ion removal alone does not provide a sufficient effect, and the image sticking phenomenon cannot be sufficiently eliminated. On the other hand, JP-A-2-1516
JP-A-83-223440, JP-A-4-223440, etc. describe a technique for eliminating the image sticking phenomenon by adding an epoxy compound or an amine compound to the ferroelectric liquid crystal. It is stated that this technique eliminates the image sticking phenomenon not by the effect of detoxifying the ions but by the effect of modifying the surface of the alignment film with an epoxy compound and relaxing the interaction between the liquid crystal molecule side surfaces. ing. But,
As a result of studies by the present inventors, this technique has no effect when an epoxy compound having only a monovalent epoxy group is used, and such a property is exhibited only in a compound having a divalent or higher valent epoxy group. I found something. In addition, when the epoxy compound contains a large amount of impurities and the specific resistance of the epoxy compound itself is small, if these epoxy compounds are added to the liquid crystal, seizure due to impurity ions, electrode coloring, deterioration of initial bistability, etc. Problem arises.

Further, Japanese Patent Laid-Open No. 2-36229 discloses that
A technique of blending a crosslinkable resin with a ferroelectric liquid crystal composition and polymerizing it with a curing agent to improve mechanical strength is disclosed, and an epoxy resin is mentioned as an example of the crosslinkable resin. No mention is made of the elimination of the sticking phenomenon. Further, the epoxy resin used in this method is a thermosetting resin containing a curing agent, and it takes a long time to cure the epoxy resin after the liquid crystal is aligned and crosslinked without disturbing the alignment state. However, it is not preferable from the viewpoint of productivity.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to prevent electrode coloring and deterioration of initial threshold characteristics even when driven for a long time or the same display is performed for a long time. It is an object of the present invention to provide a ferroelectric liquid crystal display element in which the deterioration of the display quality due to the burn-in phenomenon, which is a display deterioration phenomenon over time, is sufficiently improved without being caused.

[0006]

As a result of studies to solve the above problems, the present inventors have found that an epoxy compound having a divalent or higher valent epoxy group and having a specific resistance of a certain value or higher is ferroelectric. It was found that a ferroelectric liquid crystal display device capable of sufficiently preventing the image sticking phenomenon and maintaining an excellent display quality for a long period of time can be obtained by using a liquid crystal material blended in a liquid crystal composition. The present invention has been completed based on the above.

That is, the present invention relates to a ferroelectric liquid crystal display device comprising a pair of substrates with electrodes, at least one of which is transparent, and a ferroelectric liquid crystal composition sandwiched between the substrates. The composition has a ferroelectric liquid crystal and a divalent or higher valent epoxy group, a specific resistance at room temperature of 10 ⁸ Ω · cm or more, and 0.1 to 10% by weight of epoxy based on the weight of the ferroelectric liquid crystal. It is intended to provide a ferroelectric liquid crystal display device comprising a compound and containing no curing agent for the epoxy compound.

The ferroelectric liquid crystal composition used in the present invention comprises a ferroelectric liquid crystal and an epoxy compound having a divalent or higher valent epoxy group and having a specific resistance at room temperature of 10 ⁸ Ω · cm or more. It exhibits a dielectric liquid crystal property. It should be noted that this ferroelectric liquid crystal composition does not contain a curing agent for the epoxy compound.

The liquid crystal component used in the ferroelectric liquid crystal composition, that is, the ferroelectric liquid crystal is not particularly limited as long as it exhibits ferroelectricity. For example, only one type of low molecular weight or polymer liquid crystal exhibiting ferroelectricity may be used, or a liquid crystal composition comprising two or more types of polymer liquid crystal exhibiting ferroelectricity and / or low molecular weight liquid crystal. Further, in order to improve the response speed of the ferroelectric liquid crystal display element, a low-molecular liquid crystal that does not exhibit ferroelectricity may be blended, and further, in order to improve the strength of the ferroelectric liquid crystal display element. Alternatively, a polymer substance that does not exhibit liquid crystallinity may be blended.

In the present invention, in particular, a ferroelectric liquid crystal comprising a ferroelectric polymer liquid crystal and a low molecular weight liquid crystal, wherein the proportion of the ferroelectric polymer liquid crystal in the ferroelectric liquid crystal is usually 10% by weight or more. A ferroelectric liquid crystal of 10 to 99% by weight, more preferably 10 to 70% by weight, is preferably used. When the ferroelectric liquid crystal containing 10% by weight or more of the ferroelectric polymer liquid crystal is used, a ferroelectric liquid crystal display device having high mechanical strength and high impact resistance can be obtained. The low-molecular liquid crystal used in combination with the ferroelectric polymer liquid crystal may or may not exhibit ferroelectricity,
There is no particular limitation.

The ferroelectric polymer liquid crystal is not particularly limited, and examples thereof include polyacrylate main chain, polymethacrylate main chain, polychloroacrylate main chain, polyoxirane main chain, polysiloxane main chain, polyester main chain, polysiloxane. A side chain type ferroelectric polymer liquid crystal composed of a main chain such as an olefin main chain and a liquid crystal side chain is preferably used.

The ferroelectric polymer liquid crystal generally has a weight average molecular weight of 1,000 to 1,000,000, preferably 1,000.
Those having 100,000 to 100,000 are preferably used.

Specific examples of the side chain type ferroelectric polymer liquid crystal preferably used in the present invention are shown below.

Examples of the polyacrylate main chain type ferroelectric polymer liquid crystal include those having the following repeating units.

[0015]

Embedded image Examples of the polymethacrylate main chain ferroelectric polymer liquid crystal include those having the following repeating units.

[0016]

Embedded image Examples of the polychloroacrylate main chain ferroelectric polymer liquid crystal include those having the following repeating units.

[0017]

[Chemical 4] Examples of the polyoxirane main chain ferroelectric polymer liquid crystal include those having the following repeating units.

[0018]

Embedded image Examples of the polysiloxane main-chain ferroelectric polymer liquid crystal include those having the following repeating units.

[0019]

[Chemical 6] Examples of the polyester main chain type ferroelectric polymer liquid crystal include those having the following repeating units.

[0020]

[Chemical 7] Examples of the polysiloxane-olefin main chain ferroelectric polymer liquid crystal include those having the following repeating units.

[0021]

Embedded image Here, x: y = 19: 1 to 7: 3 (molar ratio).

In the repeating unit of the above ferroelectric polymer liquid crystal, the side chain skeleton may be replaced with a biphenyl skeleton, a phenylbenzoate skeleton, a biphenylbenzoate skeleton, or a phenyl-4-phenylbenzoate skeleton. The benzene ring in the skeleton may be replaced with a pyrimidine ring, a pyridine ring, a pyridazine ring, a pyrazine ring, a tetrazine ring, a cyclohexane ring, a dioxane ring, a dioxaborinane ring, or a halogen group such as fluorine or chlorine or a cyano group. Also, a 1-methylalkyl group, a 2-fluoroalkyl group, a 2-chloroalkyl group,
2-chloro-3-methylalkyl group, 2-trifluoromethylalkyl group, 1-alkoxycarbonylethyl group, 2-alkoxy-1-methylethyl group, 2-alkoxypropyl group, 2-chloro-1-methylalkyl group ,
It may be replaced with an optically active group such as a 2-alkoxycarbonyl-1-trifluoromethylpropyl group. Further, the length of the spacer may be changed within a range of 2 to 30 in methylene chain length.

These polymer liquid crystals are typical of ferroelectric polymer liquid crystals, and the ferroelectric polymer liquid crystals that can be used in the present invention are not limited to these.

Further, these ferroelectric polymer liquid crystals are
They may be used alone or in combination of two or more.

Examples of the ferroelectric low-molecular liquid crystal compound include Schiff base ferroelectric low-molecular liquid crystal compounds represented by the following formula, azo and azoxy ferroelectric low-molecular liquid crystal compounds, biphenyl and aromatic ester strong compounds. Examples thereof include a dielectric low molecular weight liquid crystal compound, a ferroelectric low molecular weight liquid crystal compound having a ring substituent such as halogen and a cyano group, and a ferroelectric low molecular weight liquid crystal compound having a heterocycle.

Examples of the Schiff base type ferroelectric low molecular weight liquid crystal compound include the following compounds (1 to 4).

[0027]

[Chemical 9] Examples of the azo and azoxy ferroelectric low-molecular liquid crystal compounds include the following (5) and (6).

[0028]

[Chemical 10] Examples of the biphenyl and aromatic ester-based ferroelectric low-molecular liquid crystal compounds include the following compounds (7) and (8).

[0029]

[Chemical 11] Examples of the ferroelectric low molecular weight liquid crystal compound into which a ring substituent such as halogen or cyano group is introduced include the following compounds (9) to (11).

[0030]

[Chemical 12] Examples of the ferroelectric low molecular weight liquid crystal compound having a heterocycle include compounds (12) and (13) shown below.

[0031]

[Chemical 13] Note that these compounds are representative of ferroelectric low-molecular liquid crystal compounds, and the ferroelectric low-molecular liquid crystal compounds that can be used in the present invention are not limited to these structural formulas. Further, these ferroelectric low molecular weight liquid crystal compounds may be used alone or in combination of two or more.

Examples of the liquid crystal compound having no ferroelectricity that can be used in the present invention by blending with the ferroelectric polymer liquid crystal or the ferroelectric low molecular weight liquid crystal compound include the following smectic low molecular weight liquid crystal compounds. .

[0033]

Embedded image Note that these compounds are typical liquid crystal compounds that do not exhibit ferroelectricity, and liquid crystal compounds that do not exhibit ferroelectricity that can be used in the present invention are not limited to these. These liquid crystal compounds may be used alone or in combination of two or more.

The epoxy compound used in the ferroelectric liquid crystal composition is an epoxy compound having a divalent or higher valent epoxy group and having a specific resistance at room temperature of 10 ⁸ Ω / cm or more. Here, "having a divalent or higher valent epoxy group" means 1
It means having two or more epoxy groups per molecule. An epoxy compound having only one epoxy group in one molecule has no effect of reducing seizure. Further, if the specific resistance of the epoxy compound at room temperature is less than 10 ⁸ Ω / cm, problems such as seizure due to impurity ions and coloring of electrodes occur. The preferred value of the specific resistance at room temperature of the epoxy compound used in the present invention is 10 ⁸ to 10 ¹⁵ Ω.
/ Cm, more preferably 10 ⁸ to 10 ¹³ Ω / cm.

The epoxy compound used in the present invention is not particularly limited as long as the above conditions are satisfied,
It can be appropriately selected and used from known ones.
Preferably, a low molecular weight epoxy compound satisfying the above conditions is used. When the epoxy compound is polymerized to form a resin (epoxy resin), the effect of reducing image sticking is small, and the epoxy resin may cause phase separation from the liquid crystal, resulting in a reduction in contrast. Specific examples of the epoxy compound preferably used in the present invention include those represented by the following formulas 1 to 3.

[0036]

[Chemical 15] The epoxy compounds may be used alone or in combination of 2
You may use together 1 or more types.

The compounding amount of the epoxy compound is 0.1 to the ferroelectric liquid crystal (total amount of liquid crystal material).
10% by weight, preferably 0.5-5% by weight is used.
If the amount of the epoxy compound is less than 0.1% by weight, there is no effect of preventing seizure, and if it exceeds 10% by weight, the ferroelectric liquid crystal composition is phase-separated and the contrast is lowered or liquid crystallinity is deteriorated. It may disappear.

The ferroelectric liquid crystal composition used in the present invention may be blended with additives used in liquid crystal display devices in addition to the above components, as long as the object of the present invention is not hindered. . Examples of such additives include dichroic dyes such as anthraquinone dyes, azo dyes, diazo dyes, and merocyanine dyes.

FIG. 1 is a partial cross-sectional view showing one embodiment of the ferroelectric liquid crystal display device of the present invention. Two electrodes 2 facing each other are shown.
The ferroelectric liquid crystal composition 3 is sandwiched between the attached substrates 1.

The substrate of the electrode-attached substrate is not particularly limited, and may be appropriately selected and used from those known as substrates for liquid crystal display elements such as glass and plastic. Examples of materials for the plastic substrate include crystalline polymers such as uniaxially or biaxially oriented polyethylene terephthalate (PET), non-crystalline polymers such as polysulfone (PS) and polyethersulfone (PES), polyolefins such as polyethylene and polypropylene, and the like. Polyarylate (P
Examples thereof include Ar), polycarbonate (PC), and polyamide such as nylon. From the viewpoint of high productivity of the liquid crystal display element, it is preferable to use a flexible substrate such as a plastic film. The thickness of the substrate is usually 1 μm to
10 mm, preferably 10 μm to 1 mm.

In the present invention, the two substrates with electrodes may be made of the same material as each other or may be made of different materials. It is transparent and is provided with an optically transparent or semitransparent electrode.

Specific examples of the transparent or translucent electrode include, for example, a tin oxide film called an NESA film, an indium oxide film, an ITO film made of a mixture of indium oxide and tin oxide, and a vapor deposition film of gold or titanium. , Or other thin film metal or alloy such as aluminum. The shape of these electrodes is not particularly limited, and may be the entire surface on a predetermined surface of the substrate, the stripe shape, or any other desired shape. .

The layer thickness of the ferroelectric liquid crystal composition is usually
0.5 to 10 μm, preferably 0.5 to 5 μm is suitable.

FIG. 2 is a partial cross-sectional view showing another example of the ferroelectric liquid crystal display element of the present invention. Two electrodes 2
An insulating film 4 is provided on each electrode surface of the attached substrate 1, and an alignment film 5 is further provided on the insulating film 4.
6 is a spacer for keeping the cell gap between the electrodes constant and preventing a short circuit between the electrodes.

The spacer is not particularly limited as long as it is usually used in a liquid crystal display device, but is made of silica or plastic having solvent resistance, and spherical spacers are used for a ferroelectric liquid crystal display device by a continuous process. It is suitable for the manufacturing method and is preferably used. Specific examples of suitable materials for the spherical spacers include inorganic materials such as silica and divinylbenzene-based or polystyrene-based polymer beads. The particle size of the spherical spacer is not particularly limited, but usually about 1 to 5 μm is preferable. If the cell gap can be maintained without using the spacer, the spacer may not be used.

The insulating film is for preventing a short circuit between the opposing electrodes, and if there is no risk of short circuit, the insulating film may not be provided. The material of the insulating film is not particularly limited as long as it is one normally used for liquid crystal display elements,
Examples thereof include inorganic vapor deposition films such as SiO _x , and various polymer films such as acrylic, nylon, and epoxy polymer films.

The alignment film is not particularly limited as long as it is usually used for a liquid crystal display device, and a polymer film such as polyimide or polyvinyl alcohol is unidirectionally rubbed, or silicon oxide is obliquely vapor-deposited. Various alignment films can be used. In addition, shear orientation and shear orientation by bending described in JP-A No. 2-10322,
When aligning with an alignment method by applying shear and voltage,
The alignment film may not be provided.

In the ferroelectric liquid crystal display device of the present invention, a ferroelectric liquid crystal composition and, if necessary, a spacer are arranged between two electrode-attached substrates provided with an insulating film and an alignment film, if necessary. Manufactured by orienting the ferroelectric liquid crystal composition.

The arrangement method of the ferroelectric liquid crystal composition is as follows:
There is no particular limitation, and a vacuum injection method, a coating method on an electrode substrate, or the like can be appropriately selected according to the properties of the ferroelectric liquid crystal composition. In the case of the coating method, the ferroelectric liquid crystal composition may be applied in a molten state by heating or the like, or the ferroelectric liquid crystal composition may be dissolved in a solvent and applied as a solution.
The solvent is not particularly limited as long as it does not dissolve the substrate or the insulating film and the alignment film provided as necessary, but dissolves the ferroelectric liquid crystal composition. Usually, acetone, methyl ethyl ketone, toluene, xylene, dichloromethane, chloroform, tetrahydrofuran, ethyl acetate, a mixed solvent thereof or the like is preferably used.

The method of disposing the spacer is not particularly limited, and may be fixed on the substrate with electrodes in advance before disposing the ferroelectric liquid crystal composition, or may be mixed in the ferroelectric liquid crystal composition. The ferroelectric liquid crystal composition may be arranged at the same time as the arrangement, or after the ferroelectric liquid crystal composition or its solution is applied, it may be arranged on the coating layer and embedded and fixed. .

Further, the ferroelectric liquid crystal display element of the present invention is
It is preferable to seal the ferroelectric liquid crystal composition so that it does not flow out of the element, but if the ferroelectric liquid crystal composition is not likely to flow out and the element can be kept stable, do not seal it. May be.

[0052]

The present invention will be described in more detail below with reference to examples of the present invention and comparative examples thereof, but the present invention is not limited to these examples.

Examples 1 to 3 and Comparative Examples 1 to 6 Ferroelectric polymer liquid crystal A and low molecular weight liquid crystals B, C and D shown below were 0.6 g, 0.2 g, 0.1 g and 0.1, respectively.
g (total weight of liquid crystal: 1 g) was weighed and used as a 20 wt% acetone solution. As Examples and Comparative Examples, the epoxy compounds shown in Table 1 and the following formulas 1 to 6 were added in the proportions shown in Table 1 (10 mg in the case of 1%) to prepare acetone solutions of 6 types of ferroelectric liquid crystal compositions. Prepared. The specific resistance of each epoxy compound is also shown in Table 1. The specific resistance is a value measured with an impedance meter at a frequency of 1 Hz at room temperature.

[0054]

Embedded image

[0055]

[Chemical 17] The phase transition behaviors of the above 6 types of ferroelectric liquid crystal compositions are shown below. Phase transition behavior of the ferroelectric liquid crystal composition containing Celoxide 2021P used in Example 1

[0056]

Embedded image Phase transition behavior of the SR-HHPA-containing ferroelectric liquid crystal composition used in Example 2

[0057]

[Chemical 19] Phase transition behavior of the ferroelectric liquid crystal composition containing Epolite 3002 used in Example 3

[0058]

Embedded image Phase transition behavior of the ferroelectric liquid crystal composition used in Comparative Example 1

[0059]

[Chemical 21] Phase transition behavior of the ferroelectric liquid crystal composition containing celoxide 2021P used in Comparative Example 2

[0060]

[Chemical formula 22] Phase transition behavior of the ferroelectric liquid crystal composition containing celoxide 2021P used in Comparative Example 3

[0061]

[Chemical formula 23] Phase Transition Behavior of Styrene Oxide-Containing Ferroelectric Liquid Crystal Composition Used in Comparative Example 4

[0062]

[Chemical formula 24] Phase Transition Behavior of Ferroelectric Liquid Crystal Composition Containing Celloside 2000 Used in Comparative Example 5

[0063]

[Chemical 25] Phase transition behavior of the ferroelectric liquid crystal composition containing ethylene glycol diglycidyl ether used in Comparative Example 6

[0064]

[Chemical formula 26] An acetone solution of each of the above-mentioned ferroelectric liquid crystal compositions is impregnated in an impregnating material, and a glass substrate with an ITO electrode is coated with the impregnating material using the impregnating coating method.
Of silica spacer was attached. The coating layer was heated to 120 ° C., and another glass substrate with an ITO electrode was laminated on the formed liquid crystal layer. No insulating film or alignment film was provided on this glass substrate, and the liquid crystal layer and the ITO electrode formed a direct interface. While cooling this liquid crystal element, 30V, 30
While applying a square wave of Hz, an orientation treatment was performed by applying a shear deformation of about 0.5 mm 10 times. Further cooling to room temperature, sealing the periphery of the substrate with an epoxy adhesive, Example 1
Nine ferroelectric liquid crystal display devices of 3 and Comparative Examples 1 to 6 were obtained.

In all the examples and comparative examples, the initial bistability and the presence or absence of electrode coloring were examined. The initial bistability was observed in a liquid crystal element arranged such that a dark state was produced when a positive voltage was applied between the crossed polarizing plates approximately one hour after the liquid crystal element was manufactured, as shown in FIGS. 3 and 5. Square wave (pulse width 1
ms, voltage ± 30 V) was applied to write the liquid crystal element in the bright state and the dark state, and whether the state was maintained thereafter was evaluated by measuring the change in transmitted light intensity. FIG. 4 shows an example of the change over time of the transmitted light intensity after writing in the bright state by applying the single rectangular wave shown in FIG. 3, and FIG. 6 shows the transmitted light after writing in the dark state by applying the single rectangular wave shown in FIG. An example of changes in strength over time is shown. As the evaluation standard value, the M value represented by the following formula was used. M (%) = {[S B (192) -S D (192)] / [S
_{B (2) -S D (2} )]} × 100 wherein, S _B (t) and S _D (t) is the transmitted light intensity of the bright state and dark state after the rectangular wave is applied t msec .

On the other hand, the electrode coloring is a phenomenon in which the transparent electrode is colored by repeated driving, and it is considered to be an oxidation-reduction reaction due to a current flowing between the upper and lower substrates. As a test method for electrode coloring, a DC electric field of 30 V was applied for 200 hours, and the difference in color between the electrode before the test and after the DC electric field was applied was determined by CIE1 which was determined by the International Commission on Illumination (CIE).
976L ^* a ^* b ^* color space based color difference ΔE _ab (eg,
(Company) Color Materials Association: "Color Material Engineering Handbook", Asakura Shoten (1989)). In Table 1, ΔE _ab >
In the case of 2, the evaluation result is shown by x, and in the case of ΔE _ab ≦ 2, it is shown by o.

In Comparative Example 3, since the amount of the epoxy compound added was too large, phase separation occurred and sufficient contrast could not be obtained. On the other hand, in Comparative Example 6, the specific resistance of the epoxy compound was low, which caused electrode coloring. Also, the initial bistability was not good. It was confirmed that the initial bistability was good except for Comparative Examples 3 and 6 and that no electrode coloring occurred except for Comparative Example 6.

Samples other than Comparative Examples 3 and 6 were darkened by the single-shot rectangular wave shown in FIG. 7 and left at room temperature for 1000 hours, and the threshold characteristics were measured.
The threshold characteristic was measured by the method described below.

FIG. 7 shows the waveform of the voltage applied to the display element when the threshold value is measured when writing from the bright state to the dark state. After a stable bright state was obtained with the first pulse (75 ms, ± 40 V), writing was performed with the second pulse (2.5 ms, ± v (V)). FIG. 8 shows how the light transmission amount of the display element when such a waveform is applied. The transmission amount when the first pulse +40 V is applied is I ₀ +, -40V is applied, the transmission amount is I _0- , + v of the second pulse
(V) is removed and after a sufficient time, the permeation amount is calculated as I ₁
Where, the transmittance T (%) in the bistable state is defined by the following equation.

[0070]

[Equation 1] Then, the v-T curve when v (V) was changed from 0 (V) to 40 (V) was used as the threshold characteristic. FIG. 9 shows how the threshold characteristics of the display element are changed, in which the deterioration of bistability over time is recognized. Such a display element exhibits a steep threshold characteristic immediately after the display element is manufactured as shown by the dotted line in FIG.
As the bistability deteriorates, as shown by the solid line in FIG. 9, the steepness of the threshold characteristic disappears and the threshold shifts.

As a result of measuring the threshold characteristics after 1000 hours, in all of the examples, the threshold characteristics hardly changed from the initial state, and the seizure phenomenon did not occur. On the other hand, in the comparative example, the threshold characteristic was significantly changed, and the seizure phenomenon occurred. An example thereof is shown by the data of Example 1 and Comparative Example 2. FIG. 10 shows data of Example 1 and FIG. 11 shows data of Comparative Example 2. In Table 1, the case where there is almost no change in the threshold characteristic as shown in FIG. 10 is shown as O, and the case where there is a significant change as shown in FIG. From these experiments, the epoxy group has a valence of 2 or more and the resistivity at room temperature is 10 ⁸ Ω.
・ When a specified amount of epoxy compound with a size of cm or more is added,
It was confirmed that the seizure phenomenon was eliminated without deteriorating the initial bistability, and that electrode coloring did not occur.

The above results are shown in Table 1.

[0073]

[Table 1] Example 4 and Comparative Example 7 and Comparative Example 8 In all, the composition of the ferroelectric liquid crystal (liquid crystal mixture component) was the same as that of Examples 1 to 3 and Comparative Examples 1 to 6, and the total liquid crystal weight was Weigh it to 2 g and weigh 3
This was a 0% by weight MEK (methyl ethyl ketone) solution.
In Example 4, an epoxy compound was added as in Example 1, Comparative Example 7 was the same as Comparative Example 1 with no epoxy compound added, and Comparative Example 8 was an epoxy resin containing bisphenol A-type diglycidyl ether (oil Shell Co .:
Epicoat 828), 1-benzyl-2-phenylimidazole as a curing agent (manufactured by Shikoku Kasei: Cureazole 1)
B2PZ) is mixed with the liquid crystal solution in a weight ratio of 1: 1. The mixing amount was 100 mg so as to be 5% by weight with respect to the ferroelectric liquid crystal (liquid crystal mixture component). A liquid crystal panel was produced by teaching the liquid crystal composition thus prepared on a polyether sulfone (PES) substrate with an ITO electrode patterned in a stripe shape by the method described below. It should be noted that SiO _x is used as an insulating layer (thickness: 300 Å) on the substrate. The phase transition behavior of the epoxy resin and the hardener-containing ferroelectric liquid crystal composition used in Comparative Example 8 was as follows.

[0074]

[Chemical 27] The above-mentioned liquid crystal composition is applied on the electrode surface of the PES substrate using a microgravure coater to form a film, and after solvent evaporation (cell thickness: 2.5 μm), the other PES substrate not coated with liquid crystal is laminated. did. Next, while applying a DC voltage of 60 V between the ITO electrodes on both substrates at room temperature, a bending deformation in a certain direction was given to the whole to perform an alignment treatment, thereby obtaining a dot matrix type liquid crystal panel. Example 8
Then, a curing treatment was further performed at 60 ° C. for 5 hours to crosslink the epoxy resin. In Comparative Example 8, the alignment state was disturbed during the curing process, and the contrast was reduced from 25 to 13.

The initial stability of these liquid crystal panels was examined in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 6, and the M value was measured 1000 hours later to measure the deterioration of bistability with time. I examined the change of. In Example 4, there was almost no change in the M value from 97% to 95%, but in Comparative Example 7, 98% to 20%, and in Comparative Example 8, 95% to 57%.
%, And deterioration with time occurred. In parallel with this, the liquid crystal panel is connected to the drive circuit, the drive is actually performed to display the characters, and then left at room temperature for 1000
When another character was displayed after the elapse of time, in Example 4, the character when left as it was was completely erased and a new character could be completely displayed, but in Comparative Example 7 and Comparative Example 8, it was left as it was even after the display was rewritten. The characters that were in the state remained as a burn-in.

[0076]

According to the present invention, even when the display is driven for a long time or the same display is performed for a long time, the coloring of the electrodes and the deterioration of the initial threshold characteristic are not caused, and the display by the burn-in phenomenon which is a display deterioration phenomenon with time is performed. It was possible to provide a ferroelectric liquid crystal display device in which the deterioration of quality was sufficiently improved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing one embodiment of a ferroelectric liquid crystal display element of the present invention.

FIG. 2 is a partial cross-sectional view showing another embodiment of the ferroelectric liquid crystal display element of the present invention.

FIG. 3 is a diagram illustrating a single-shot rectangular wave applied to a ferroelectric liquid crystal display element.

FIG. 4 is a graph showing a change over time in transmitted light intensity after applying the single-shot rectangular wave shown in FIG. 3 to a ferroelectric liquid crystal display device.

FIG. 5 is a diagram illustrating a single-shot rectangular wave applied to a ferroelectric liquid crystal display element.

FIG. 6 is a graph showing a change over time in transmitted light intensity after applying the single-shot rectangular wave shown in FIG. 5 to a ferroelectric liquid crystal display element.

FIG. 7 is a diagram illustrating a waveform of a voltage applied to a ferroelectric liquid crystal display element.

FIG. 8 is a graph showing changes in transmitted light intensity when the voltage of FIG. 7 is applied to the ferroelectric liquid crystal display element.

FIG. 9 is a graph showing how the threshold characteristics of a ferroelectric liquid crystal display device change.

FIG. 10 is a graph showing changes in threshold characteristics of the ferroelectric liquid crystal display element of the present invention.

FIG. 11 is a graph showing how the threshold characteristics of a ferroelectric liquid crystal display device change.

[Explanation of symbols]

 1 Substrate 2 Electrode 3 Ferroelectric Liquid Crystal Composition 4 Insulating Film 5 Alignment Film 6 Spacer

Claims (6)

[Claims] 1. A ferroelectric liquid crystal display device comprising a pair of substrates with electrodes, at least one of which is transparent, and a ferroelectric liquid crystal composition sandwiched between the substrates, wherein the ferroelectric liquid crystal composition comprises: A ferroelectric liquid crystal and an epoxy group having a valence of 2 or more, a specific resistance at room temperature of 10 ⁸ Ω · cm or more, and 0.1 to 10% by weight of an epoxy compound based on the weight of the ferroelectric liquid crystal. A ferroelectric liquid crystal display device characterized by containing no curing agent of the epoxy compound. 2. The epoxy compound comprises at least one epoxy compound represented by the following formulas 1 to 3.
The ferroelectric liquid crystal display device described. Embedded image 3. The ferroelectric liquid crystal according to claim 1 or 2, wherein the ferroelectric liquid crystal in the ferroelectric liquid crystal composition contains 10% by weight or more of a ferroelectric polymer liquid crystal based on the weight of the ferroelectric liquid crystal. Dielectric liquid crystal display device. 4. The ferroelectric liquid crystal in the ferroelectric liquid crystal composition comprises 10 to 100% by weight of a ferroelectric polymer liquid crystal and 90 to 0% by weight of a low molecular weight liquid crystal compound based on the weight of the ferroelectric liquid crystal. The ferroelectric liquid crystal display device according to claim 3, wherein 5. The ferroelectric liquid crystal in the ferroelectric liquid crystal composition comprises 10 to 100% by weight of a ferroelectric polymer liquid crystal and 90 to 0% by weight of a smectic low molecular weight liquid crystal compound based on the weight of the ferroelectric liquid crystal. The ferroelectric liquid crystal display element according to claim 3, which is composed of 6. The substrate according to claim 3, which is a plastic substrate.
The ferroelectric liquid crystal display device described.