JPH09211462A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the device which enables a halftone display and shows excellent viewing angle characteristics by combining the device with a TFT(thin film transistor) device or the like. SOLUTION: In this device having two orientation control films and a liquid crystal layer between a pair of substrates each of which is provided with one of a pair of electrode layers, the liquid crystal layer contains at least a photo- cured material that is produced from a photo-curable composition contg. a liquid-crystalline (meth)acrylate, and a ferroelectric liquid crystal. Also, at the time of applying no voltage to between the pair of electrode layers, the angle between the orientational direction of the liquid crystal skeleton of the liquid- crystalline (meth)acrylate and the orientational direction of the ferroelectric liquid crystal is <=5 deg.. Thus, a halftone display can be obtained in the liquid crystal display device using the ferroelectric liquid crystal.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a liquid crystal display element, and more particularly to a ferroelectric liquid crystal display element.

2. Description of the Related Art A liquid crystal display device using a ferroelectric liquid crystal proposed by Clark and Lagerwall (JP-A-56-56).
No. 107216) has bistability and has a fast response to a change in an electric field, and therefore is expected to be applied as a liquid crystal display device having a large screen and high definition.
However, since it has bistability, there is a problem that it is difficult to display halftones.

The problem to be solved by the present invention is to provide a technique capable of displaying a halftone in a liquid crystal element using a ferroelectric liquid crystal.

The inventors of the present invention have made earnest studies on the structure of a liquid crystal layer in a liquid crystal element in order to solve the above-mentioned problems, and as a result, have found that the problem is that liquid crystallinity (meta) is present in the liquid crystal layer.
It has been found that the problem can be solved by including a photocured product of a photocurable composition containing an acrylate, and the present invention has been provided. That is, in a liquid crystal element having an alignment control film and a liquid crystal layer between a substrate having a pair of electrode layers,
The liquid crystallinity in a state where the liquid crystal layer contains a photocured product of a photocurable composition containing at least a liquid crystalline (meth) acrylate and a ferroelectric liquid crystal material, and a voltage is not applied between the pair of electrode layers. Provided is a liquid crystal display device characterized in that an angle formed by an alignment direction of a liquid crystal skeleton of (meth) acrylate and an alignment direction of a ferroelectric liquid crystal material is within 5 degrees. The liquid crystal display device of the present invention contains a photo-cured product of a photo-curable composition containing a liquid crystal (meth) acrylate dispersed in a liquid crystal layer, and contains the liquid crystal layer to form a ferroelectric liquid crystal material having a polymer chain having a liquid crystal skeleton. Due to the effect of stabilizing the alignment of the liquid crystal, the alignment between the liquid crystal skeleton of the liquid crystalline (meth) acrylate and the alignment direction of the ferroelectric liquid crystal material is within 5 degrees in the same alignment state when no voltage is applied. When the voltage is applied, the angle between the alignment direction of the ferroelectric liquid crystal material and the alignment direction of the liquid crystal skeleton of the liquid crystal (meth) acrylate is not less than 5 degrees due to the spontaneous polarization of the ferroelectric liquid crystal. The property that the angle formed by the alignment direction of the ferroelectric liquid crystal material and the alignment direction of the liquid crystal skeleton of the liquid crystal (meth) acrylate is continuously changed by the change of the voltage is imparted. Therefore, the liquid crystal display element of the present invention is, for example, 2
By using a sheet of polarizing plate, the amount of transmitted light can be continuously controlled by changing the applied voltage, and halftone display is possible without using special means such as area gradation. Is. The orientation of the liquid crystal skeleton of the photocured product of the photocurable composition containing the liquid crystalline (meth) acrylate is such that the response of the ferroelectric liquid crystal material to the electric field is not impaired and the ferroelectric liquid crystal material is uniform. In order to obtain a uniform alignment state, it is preferable that the alignment is horizontal and uniform with respect to the surface of the substrate having the electrode layer, and the direction of the uniaxial alignment matches the easy axis of the alignment control film. .
Further, in order to obtain good display characteristics, the angle formed by the alignment direction of the liquid crystal skeleton of the liquid crystal (meth) acrylate contained in the liquid crystal layer (director) and the alignment direction of the ferroelectric liquid crystal material (director). It is preferably within 5 degrees, and more preferably the alignment direction of the liquid crystal skeleton and the alignment direction of the ferroelectric liquid crystal material are the same. Usually, the liquid crystal display element of the present invention is used in combination with two polarizing plates, but the polarization axis of at least one polarizing plate is set to be parallel or perpendicular to the alignment direction of the ferroelectric liquid crystal material in the liquid crystal layer. Preferably. Further, since the liquid crystal display element of the present invention does not have bistability, it can be driven by using an active element such as a MIM (metal insulator metal) element, a TFT (thin film transistor) element or a thin film diode element. preferable. Further, the concentration of the photocured product of the photocurable composition containing the liquid crystal (meth) acrylate in the liquid crystal layer is
It is preferably adjusted to 0.1 to 10% by weight, and 0.5
To 7% by weight is more preferable, and 1 to 5% by weight is particularly preferable. If the liquid crystallinity (meta) in the liquid crystal layer
When the concentration of the photo-cured product of the photo-curable composition containing acrylate is lower than 0.1%, the alignment direction of the liquid crystal skeleton of the liquid crystalline (meth) acrylate contained in the liquid crystal layer and the alignment of the ferroelectric liquid crystal material. The angle formed by the directions cannot be stabilized within 5 degrees, and if it exceeds 10%, the drive voltage increases. Examples of the liquid crystal (meth) acrylate contained in the photocurable composition include those represented by the general formula (I).

Embedded image (In the formula, X represents a hydrogen atom or a methyl group, and the 6-membered rings A, B and C are each independently

Embedded image , N is an integer of 0 or 1, and m is 1 to 4
Wherein Y ¹ and Y ² are each independently a single bond, -CH ₂ CH _2- , -CH ₂ O-, -OCH _2- , -C
OO-, -OCO-, -C≡C-, -CH = CH-,-
CF = CF -, - (CH 2) 4 -, - CH 2 CH 2 CH 2 O
_{-, - OCH 2 CH 2 CH} 2 -, - CH 2 = CHCH 2 CH 2
- or -CH ₂ CH ₂ CH = CH- and represents, Y ³ represents a hydrogen atom, a halogen atom, a cyano group, an alkyl group, an alkoxy group having 1 to 20 carbon atoms, alkenyl or alkenyloxy group. )). Among them, particularly in the general formula (I), the 6-membered rings A, B and C are each independently,

[Chemical 6] And m represents an integer of 1 or 2, Y ¹ and Y ² each independently represent a single bond or —C≡C—, and Y
^A compound in which ³ represents a halogen atom, a cyano group, an alkyl group having 1 to 20 carbon atoms or an alkoxy group is preferable.
Although representative examples of such compounds and their phase transition temperatures are shown, the monofunctional acrylate or monofunctional methacrylate compounds that can be used in the present invention are not limited to these compounds.

Embedded image

Embedded image

Embedded image (In the above, the cyclohexane ring represents a transcyclohexane ring, C in the phase transition temperature scheme is a crystalline phase, N
Represents a nematic phase, S represents a smectic phase, I represents an isotropic liquid phase, and the numbers represent phase transition temperatures. The ferroelectric liquid crystal material contained in the liquid crystal layer can be used without particular limitation as long as it is generally recognized as a ferroelectric liquid crystal in this technical field. It is preferable to use a material that exhibits a smectic A phase and a nematic phase in the temperature region above the chiral smectic C phase. The concentration of the ferroelectric liquid crystal material in the liquid crystal layer is preferably 90 to 99.9% by weight, 93 to 9% by weight.
9.5 wt% is more preferable, and 95 to 99 wt% is more preferable. As the alignment control film, a conventionally used rubbing-treated polyimide alignment film can be used without particular limitation. It is also possible to use an alignment control film which is obtained by irradiating a polyvinyl cinnamate thin film, a polyimide thin film, or the like with polarized ultraviolet light and which has not been rubbed. The thickness of the liquid crystal layer depends on the anisotropy of the refractive index of the ferroelectric liquid crystal used, but is preferably 1 to 20 μm,
1.5 to 10 microns is more preferred, 1.5 to 6
Micron is particularly preferred. The liquid crystal display element of the present invention can be manufactured, for example, by the method described below. First, a photocurable composition containing a liquid crystal (meth) acrylate and a liquid crystal composition containing a ferroelectric liquid crystal material are injected between a pair of electrodes and a substrate having an alignment control film, and the injected liquid crystal is further injected. The photocurable composition containing a liquid crystalline (meth) acrylate is polymerized by irradiating the injected liquid crystal composition with an ultraviolet ray or an electron beam while keeping the composition exhibiting a smectic A phase or a nematic phase. The liquid crystal display device of the present invention can be manufactured by obtaining a photocured product. That is, a photocurable composition containing a liquid crystalline (meth) acrylate and a liquid crystal composition containing a ferroelectric liquid crystal material are uniaxially aligned in the easy axis direction of the alignment control film in the smectic A phase or nematic phase, In this state, ultraviolet rays or electron beams are irradiated to fix the liquid crystal skeleton of the liquid crystalline (meth) acrylate in a state where it is aligned with the easy axis direction of the alignment control film. As a result, the angle between the orientation direction of the liquid crystal skeleton of the liquid crystal (meth) acrylate and the orientation direction of the ferroelectric liquid crystal material is changed by the polymer stabilizing effect of the photocured product having the liquid crystal skeleton of the liquid crystal (meth) acrylate. It can be controlled within 5 degrees, preferably in the same direction. Therefore, it is preferable to use a ferroelectric liquid crystal material that exhibits a smectic A phase in a temperature range above the chiral smectic C phase,
More preferably, it is preferable to use a material that exhibits a smectic A phase and a nematic phase in a temperature range above the smectic C phase in order to obtain a good orientation state. The photocurable composition containing a liquid crystalline (meth) acrylate is preferably a photocurable composition having liquid crystallinity so as not to impair the liquid crystallinity of the ferroelectric liquid crystal material. Those having a nematic liquid crystal phase are more preferable, and those having a smectic A liquid crystal phase are particularly preferable. A stabilizer may be added to the photocurable composition containing a liquid crystal (meth) acrylate and the liquid crystal composition containing a ferroelectric liquid crystal material for the purpose of improving the storage stability. As the stabilizer that can be used here, for example, known hydroquinone, hydroquinone monoalkyl ethers, tert-butylcatechols and the like can be selected and used. Further, the addition amount thereof is preferably 0.05% by weight or less based on the photocurable composition contained in the liquid crystal composition. Further, the irradiation dose of ultraviolet rays or electron beams in the process of polymerizing the photocurable composition depends on the concentration of the liquid crystal composition and the photopolymerization initiator used, but is in the range of 50 to 10000 mJ / cm ² . preferable. UV or electron beam irradiation dose is 50mJ / c
When it is m ² or less, the photocurable composition does not cure sufficiently,
After the manufacturing, the change with time became large and 10,000m
When it is J / cm ² or more, the liquid crystal composition itself tends to deteriorate.

The present invention will be described below in more detail with reference to Examples of the present invention. However, the invention is not limited to these examples. (Example 1) On one side of a 1.1 mm-thick glass substrate on which an ITO (indium tin oxide) transparent electrode was formed,
A solution of polyvinyl cinnamate dissolved in N-methylpyrrolidinone (NMP) at a concentration of 2% was applied using a spin coater. Then, the substrate coated with polyvinyl cinnamate was heated at 180 ° C. for 1 hour to be dried. After cooling the dried substrate to room temperature, the center wavelength 3
It was irradiated with polarized ultraviolet light having an intensity of about 30 mW / cm ² at 13 nm for 2 minutes. The two substrates thus obtained, each having an ITO transparent electrode on which a polyvinyl cinnamate thin film was formed, were made to face each other with a gap of 1.7 microns so that the surface on which the polyvinyl cinnamate thin film was formed faced inward. A cell (A) was produced. At this time, the liquid crystal cell (A) 2
The substrates were set so that the vibration directions of the polarized ultraviolet rays upon irradiation with the polarized ultraviolet rays were in the overlapping directions. next,
Liquid crystalline acrylate compound (a)

Embedded image 49.5 parts by weight of the liquid crystal acrylate compound (d)

Embedded image 49.5 parts by weight and a photopolymerization initiator "IRGACURE 65
1 "(manufactured by Ciba Geigy) to prepare a photocurable composition (I). The photocurable composition (I) exhibited nematic liquid crystallinity in the range of room temperature to 46 ° C. 3 parts by weight of this photocurable composition (I) and a ferroelectric liquid crystal "CS-
Liquid crystal composition (L-1) consisting of 97 parts by weight of "1014" (manufactured by Chisso) was prepared. Next, the liquid crystal cell (A) is heated to 85 ° C.
While maintaining the liquid crystal composition (L-1), the liquid crystal composition (L-1) is injected as it is in the isotropic liquid phase, and then the temperature is gradually lowered to 60 ° C. to remove the liquid crystal composition (L-1) from the isotropic liquid phase. The nematic phase was further changed to the smectic A phase.
The liquid crystal composition (L-1) injected into the liquid crystal cell (A) was mixed with 60
The photocurable composition (I) contained in the liquid crystal composition was photocured by irradiating it with ultraviolet rays having a central wavelength of 365 nm and an intensity of 40 mW / cm ^{2 in} a state of showing a smectic A phase. . After cooling to room temperature, the obtained liquid crystal element was observed with a polarizing microscope.As a result, the ferroelectric liquid crystal had a uniform uniaxial orientation, and the direction was the vibration direction of the polarized UV when the polyvinyl cinnamate was irradiated with the polarized UV. And made a right angle. Further, by observing the orientation of the liquid crystal skeleton of the liquid crystalline acrylate cured product by raising the temperature of the obtained liquid crystal element to near the clearing point under a polarizing microscope, the orientation of the liquid crystal skeleton of the liquid crystalline acrylate cured product was It was confirmed that it was in the same direction as the alignment direction of the ferroelectric liquid crystal.
Fig. 1 shows the case where the obtained liquid crystal element is sandwiched between two orthogonal polarizing plates, and the alignment direction of the ferroelectric liquid crystal in the state where no voltage is applied is aligned with the polarization axis of the polarizing plate. The electro-optical characteristics of the liquid crystal display device of the present invention are shown. Further, in FIG. 2, the obtained liquid crystal element was sandwiched between two orthogonal polarizing plates, and the alignment direction of the ferroelectric liquid crystal in the state where a voltage of −5 V was applied was aligned with the polarization axis of the polarizing plate. The electro-optical characteristics of the liquid crystal display device of the present invention at the time are shown. From the above figures, it can be seen that the liquid crystal display element of the present invention can control the transmittance by changing the applied voltage, that is, it is possible to perform halftone display. (Comparative Example 1) While maintaining the same liquid crystal cell (A) as that manufactured in Example 1 at 85 ° C, the ferroelectric liquid crystal "CS-1" was used.
014 ”(manufactured by Chisso) is injected as isotropic liquid phase,
After that, the temperature was gradually lowered to room temperature to cause the ferroelectric liquid crystal "CS-1014" to undergo a phase transition from the isotropic liquid phase to the chiral smectic C phase via the nematic phase and the smectic A phase. When a voltage was applied to the obtained liquid crystal element under a polarization microscope, optical switching behavior based on bistability was observed, and halftone display was not obtained.

The liquid crystal display element of the present invention is a display element using a ferroelectric liquid crystal, which enables halftone display. Therefore, the liquid crystal display device of the present invention is useful as a display device capable of displaying halftones excellent in viewing angle characteristics by combining with a TFT device or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing electro-optical characteristics of a liquid crystal display element of the present invention in Example 1.

FIG. 2 is a diagram showing electro-optical characteristics of the liquid crystal display element of the present invention in Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Hasebe 7-18-12 Nishibori, Urawa-shi, Saitama Prefecture (72) Haruyoshi Takatsu 3-6-27 Nakahara, Higashiyamato-shi, Tokyo

Claims (7)

[Claims] 1. A liquid crystal device having an alignment control film and a liquid crystal layer between substrates having a pair of electrode layers, wherein the liquid crystal layer contains at least a liquid crystalline (meth) acrylate. The angle between the alignment direction of the liquid crystal skeleton of the liquid crystal (meth) acrylate and the alignment direction of the ferroelectric liquid crystal material in the state in which the ferroelectric liquid crystal material is contained and a voltage is not applied between the pair of electrode layers A liquid crystal display device characterized by being within 5 degrees. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal skeleton of the liquid crystal (meth) acrylate and the ferroelectric liquid crystal material are aligned in the same direction. 3. The liquid crystal display device according to claim 1, wherein the alignment direction of the liquid crystal skeleton of the liquid crystal (meth) acrylate coincides with the easy axis direction of the alignment control film. 4. The concentration of the photocured product of the photocurable composition containing a liquid crystalline (meth) acrylate in the liquid crystal layer is 0.1.
The liquid crystal display device according to claim 1, 2 or 3, wherein the content is 1 to 10% by weight. 5. A liquid crystalline (meth) acrylate is represented by the general formula (I): (In the formula, X represents a hydrogen atom or a methyl group, and the 6-membered rings A, B and C are independently, , N is an integer of 0 or 1, and m is 1 to 4
Wherein Y ¹ and Y ² are each independently a single bond, -CH ₂ CH _2- , -CH ₂ O-, -OCH _2- , -C
OO-, -OCO-, -C≡C-, -CH = CH-,-
CF = CF -, - (CH 2) 4 -, - CH 2 CH 2 CH 2 O
_{-, - OCH 2 CH 2 CH} 2 -, - CH 2 = CHCH 2 CH 2
- or -CH ₂ CH ₂ CH = CH- and represents, Y ³ represents a single bond, -COO -, - OCO- represents, R represents a hydrocarbon group having 1 to 18 carbon atoms. 5. The liquid crystal display device according to claim 1, which is a compound represented by the formula (1). 6. In the general formula (I), the 6-membered rings A, B and C are each independently And m represents an integer of 1 or 2, Y ¹ and Y ² each independently represent a single bond or —C≡C—, and Y
The liquid crystal display element according to claim 5, wherein ³ represents a halogen atom, a cyano group, an alkyl group having 1 to 20 carbon atoms, or an alkoxy group. 7. The element is driven by an active element such as a thin film transistor element, a metal insulator metal element, or a thin film diode element.
3. The liquid crystal display device according to 3, 4, 5 or 6.