JP3642575B2 - Liquid crystal display element - Google Patents

Description

  The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element having high voltage holding characteristics.

In recent years, liquid crystal display elements are becoming mainstream for use in TFT drive panels that can be manufactured to be thin and lightweight and that can provide clear images. In order to obtain a bright and clear image with the TFT drive panel, it is important to hold the written information for as long as possible other than the writing time. Therefore, the electrical resistance value of the liquid crystal layer of the liquid crystal display element needs to be sufficiently high. However, since the ionic impurities are present in a small amount in the liquid crystal layer, the electric resistance value of the liquid crystal layer is not sufficiently high.

In a general liquid crystal display element, ions are brought into the liquid crystal layer when Na ⁺ or the like is mixed in the manufacturing process. For this, various investigations such as improvement of the manufacturing process and development of liquid crystals that are difficult to take in ions have been made, but it is very difficult to prevent the mixing of very few ions, so the yield is poor, There is a problem that the cost becomes high.

On the other hand, in the guest-host type liquid crystal display element, ions are brought into the liquid crystal layer by the generation of ionic impurities due to photodegradation of the dye, in addition to the mixing of ions in the manufacturing process.

The TFT drive panel using the guest-host type liquid crystal display element has advantages that a bright and clear image can be obtained, a viewing angle is wide, and that it is thin and light. Therefore, a guest-host type liquid crystal display element is expected as an ideal element that constitutes a display panel mounted on a portable device or the like.

However, in the guest-host type liquid crystal display element, as described above, ionic impurities are generated due to decomposition of the dye, in addition to the mixing of ions in the manufacturing process, so that the liquid crystal layer is easily contaminated by ions. Therefore, in the guest-host type liquid crystal display element, the electric resistance value is greatly reduced, and thus the voltage holding characteristic is particularly deteriorated. This is the guest
This greatly hinders the marketability of host-type liquid crystal display elements.

  An object of the present invention is to provide a liquid crystal display element having high voltage holding characteristics.

The present invention relates to a pair of substrates disposed opposite to each other and having an electrode on the opposite surface, at least one of which is transparent, sandwiched between the pair of substrates, a liquid crystal material containing a dichroic dye, and an ion trapping property A liquid crystal display element comprising: a liquid crystal layer including a substance.

In the liquid crystal display device according to the present invention, the ion-trapping substance is selected from the group consisting of a compound represented by the following chemical formula 1, a compound represented by the following chemical formula 2, a compound represented by the following chemical formula 3, and derivatives thereof.

(However, R in Chemical Formula 1 and Chemical Formula 2 ⁵ , R ⁶ , R ⁷ Is at least one organic group selected from a cyano group, an alkyl group, a phenyl group, and a phenyl group in which hydrogen is substituted with a cyano group)

In the liquid crystal display element according to the present invention, the liquid crystal material is included in a microcapsule,
The ion promoting substance is contained in the coating film of the microcapsules or in a binder resin existing between the microcapsules.

According to the present invention, since the electrical resistivity of the liquid crystal layer is hardly lowered, a liquid crystal display element having high information retention characteristics can be provided.

Hereinafter, the liquid crystal display element of the present invention will be described in more detail with reference to the drawings. At least one of the pair of substrates used in the liquid crystal display element of the present invention needs to be transparent. When this element is used as a reflective liquid crystal display element, a substrate in which an electrode such as aluminum or copper is formed on one main surface and a reflecting plate is provided if necessary can be used for the one substrate. .

As a transparent substrate used in the liquid crystal display element of the present invention, IT, on at least one main surface of an insulating transparent substrate such as glass, acrylic resin, polycarbonate, and polyethylene,
There may be mentioned those in which a transparent electrode such as O is formed. When this element is used as a transmissive liquid crystal display element, this transparent substrate is used for both of the pair of substrates.

As the above-described substrate, an appropriate one is selected according to a display method, and an alignment film surface in contact with the liquid crystal layer is subjected to an alignment treatment as necessary. In the liquid crystal display element of the present invention, the liquid crystal compound contained in the liquid crystal material is not particularly limited, and a liquid crystal compound generally used in each display method can be used.

The liquid crystal display element of the present invention is a guest-host type liquid crystal display element, and the liquid crystal material contains a dichroic dye. As the dichroic dye, a dye usually used in a guest-host type liquid crystal display element such as anthraquinones and azo dyes is used.

It has been described above that this dichroic dye is decomposed by light irradiation to generate ionic impurities, which is caused by oxygen present in the liquid crystal layer and is most frequently used as a dichroic dye. It is known that the anthraquinone dyes are decomposed by excited singlet oxygen.

Therefore, by reducing the oxygen concentration in the liquid crystal layer, generation of ionic impurities in the liquid crystal layer due to decomposition of the dichroic dye can be prevented, and a decrease in the electrical resistance value of the liquid crystal layer can be prevented. It can be done.

FIG. 1 shows a cross-sectional view of a liquid crystal display element according to the first embodiment of the present invention. In this figure, an electrode 3 is formed on one main surface of a transparent substrate 1. A transparent substrate 2 is disposed facing the surface of the substrate 1 where the conductive film 3 is formed, and an electrode 4 is formed on the surface of the transparent substrate 2 facing the conductive film 3. An alignment film is formed on the conductive film 3 formed on the substrate 1 (not shown). Between these electrodes 3 and 4, a liquid crystal layer 8 composed of a liquid crystal compound 5, a dichroic dye 6 and an ion-trapping substance 9 is sandwiched to form a liquid crystal display element 13.

Note that the ion trapping substance here refers to a substance having a property of reducing the mobility of ions in the liquid crystal layer by electrically interacting with ions in the liquid crystal layer. The liquid crystal display element of the present invention contains an ion trapping substance in the liquid crystal layer. Therefore, ions that cause a decrease in electrical resistivity in the liquid crystal layer, particularly cations, are trapped in this substance. As a result, the ions behave as if the molecular weight of the ions has increased, the mobility in the liquid crystal layer is reduced, and the electrical resistivity of the liquid crystal layer is not reduced.

As the ion-trapping substance, compounds having a pyridine structure represented by the following chemical formulas 1 and 2,
The compound shown by following Chemical formula 3 and those derivatives can be mentioned.

In the above chemical formulas 1 and 2, R ⁵ , R ⁶ and R ⁷ are a cyano group, Me, Et, and n.
An alkyl group such as -Bu, a phenyl group, and a phenyl group in which hydrogen is substituted with a cyano group or the like;

As the ion-trapping substance, a compound having a large polarity or the like that is adsorbed or coated on the surface of a nonionic polar polymer bonded to the side chain of the polymer or glass fine particles may be used. In this case, since the mobility of cations in the liquid crystal layer is further reduced, it is possible to further prevent the electrical resistivity of the liquid crystal layer from being lowered.

In addition, as an ion-trapping substance, for example, a nonionic polar polymer in which a high-polarity substituent is localized on the surface by ultrasonically dispersing polymer fine particles made of acrylic or the like in a high-polarity solvent such as water In addition, fine particles made of a compound having a large polarity such as an ion exchange resin and an oxide such as silica or alumina can be used.

This ion-trapping substance is preferably contained in an amount of 1 × 10 ⁻² to 2% by weight with respect to the liquid crystal layer. When it is less than 1 × 10 ⁻² wt%, it is not possible to prevent a decrease in the electric resistance value of the liquid crystal layer, and when it exceeds 2 wt%, the orientation of the liquid crystal material is lowered, which is not preferable.

The above-described reducing substance and ion trapping substance can be used in a state dispersed in a liquid crystal material. It is also possible to include these substances in the alignment film. In this case, since the reducing or ion-trapping substance is not present in the liquid crystal material, the orientation of the liquid crystal material is not affected.

In the liquid crystal display element according to the present invention, the liquid crystal material may be microencapsulated. In this case, a microcapsule 16 shown in FIG. 2A containing the above-described ion-trapping substance 15 in the coating 14 and including the liquid crystal materials 5 and 6 in the coating 14 can be used. FIG.
), It is preferable to form a liquid crystal layer with the microcapsules 16 because the orientation of the liquid crystal material is not affected.

As shown in FIG. 3, the liquid crystal layer 8 may be configured by dispersing the microcapsules 18 including the liquid crystal materials 5 and 6 and the ion trapping substance 15 in the medium 19. When the liquid crystal display element 20 is configured in this manner, the orientation of the liquid crystal material is not affected, which is preferable. In this case, deterioration of the retention rate due to the binder resin can be prevented. As a medium in which the microcapsules are dispersed in the liquid crystal layer, a commonly used medium such as polyvinyl alcohol or cellulose can be used.

  Examples of the present invention will be described below.

(Comparative example)
A liquid crystal display element was produced as follows.

First, a glass substrate with an ITO film formed on one main surface is used as a transparent substrate.
A film made of polyimide having a thickness of 1000 angstroms was formed on the surface on which the O film was formed. Furthermore, an alignment film was formed by subjecting this coating to a horizontal alignment treatment by a rubbing method.

As described above, an alignment film is formed on two transparent substrates, an epoxy adhesive is applied to the periphery of the surface on which the coating on one substrate is formed, and the surface on which the coating on the other substrate is formed A spacer having an average particle size of 10 μm was sprayed on the substrate. The two substrates were bonded to each other so that the respective alignment films face each other and the alignment directions of the respective alignment films were parallel to each other, thereby manufacturing a cell.

Next, a liquid crystal material was prepared by mixing the liquid crystal compound ZLI-2293 (Chisso Chemical Industries) with a dichroic dye represented by the following chemical formula 4 at a ratio of 1.0% by weight with respect to the liquid crystal compound. In addition,
In this dichroic dye, R8 and R9 are both ethyl groups, R8 is an ethyl group and R9 is a t-Bu group,
And a mixture of compounds in which R8 and R9 are both t-Bu groups,
1: 2: 1.

This mixture was injected into the cells bonded together as described above in a vacuum, and this was sealed to produce a liquid crystal display element. When the oxygen concentration contained in the liquid crystal layer of this liquid crystal display element was examined, it was 1 × 10 ⁻² mol / l.

About the liquid crystal display element of the comparative example 1 produced as mentioned above, after irradiating 100,000 lux sunlight for 10 hours, respectively, the voltage of 5V was applied on 24 degreeC temperature conditions, and voltage application By measuring the voltage after 16.7 msec from the stop, 16.
The voltage holding ratio after 7 msec was examined. The result was 70.5%.
(Example 1)
A liquid crystal display device was produced in the same manner as in the comparative example, except that a pyridine derivative represented by the following chemical formula 5 was mixed with the liquid crystal material at a ratio of 2% by weight with respect to the liquid crystal compound.

(Example 2)
A liquid crystal display device was produced in the same manner as in Example 1 except that the crown ether represented by the chemical formula 3 was mixed at a ratio of 2% by weight with respect to the liquid crystal compound instead of the pyridine derivative represented by the chemical formula 5. .

(Example 3)
A liquid crystal display device was produced in the same manner as in Example 1 except that the pyridine derivative was coated on glass fine particles.

That is, instead of directly mixing the pyridine derivative represented by the chemical formula 5 with the liquid crystal material,
The above-mentioned pyridine derivative was coated on glass fine particles having an average particle size of 0.2 μm, and this was mixed with the liquid crystal material so as to contain 2.0% by weight with respect to the liquid crystal material.

(Example 4)
A liquid crystal display device was produced in the same manner as in the comparative example, except that a mixture of 1.5% by weight pyridine derivative represented by the above chemical formula 5 and 60% by weight polyimide was used as the material for the alignment film.

(Example 5)
A liquid crystal material was prepared by mixing the liquid crystal compound ZLI-2293 (Chisso Chemical Industries) with the dichroic dye represented by the above chemical formula 4 at a ratio of 1.0% by weight with respect to the liquid crystal compound. This liquid crystal material is 10
It put into the processing container maintained at 0 degreeC, and stirred under pressure reduction conditions of 1 * 10 < ^-6 > Torr. After stirring for 3 hours, xenon gas was introduced into the processing container, and the inside of the processing container was returned to normal pressure. By repeating the above operation three times, oxygen in the liquid crystal material was replaced with xenon.

A liquid crystal material in which oxygen was substituted with xenon, methyl methacrylate as a thermopolymerizable polymer, polyvinyl alcohol as a surfactant, and benzoin peroxide as a polymerization initiator were mixed in water and stirred with a homogenizer. Further, 10% by weight of a pyridine derivative represented by Chemical Formula 5 was mixed with the liquid crystal material. The liquid crystal material, the thermally polymerizable polymer and the polymerization initiator were mixed at a ratio of 100: 10: 1 by weight, and the surfactant was added at a ratio of 3% by weight with respect to the water mixture. As a result, liquid crystal microcapsules having an average particle size of 10 μm were formed. As a result, the outer wall of the liquid crystal microcapsule contained a pyridine derivative represented by Chemical Formula 9.

Next, a glass substrate having an ITO film formed on one main surface was used as a transparent substrate, and liquid crystal microcapsules were uniformly dispersed on the surface of the transparent substrate on which the ITO film was formed. This is laminated with another transparent substrate so that the respective ITO films face each other, and 300 g / cm ²
A liquid crystal display element having a distance between electrodes of 10 μm was manufactured by thermocompression bonding at a pressure of 120 ° C.

For the liquid crystal display elements of Examples 1 to 5 and Comparative Example manufactured as described above, a voltage of 5 V was applied under each temperature condition of 20 ° C. and 50 ° C., and the voltage application was stopped 16.
By measuring the voltage after 7 msec, the voltage holding ratio after 16.7 msec with respect to the applied voltage was examined.

Furthermore, these liquid crystal display elements were irradiated with sunlight of 100,000 lux for 10 hours, and the voltage holding ratio was similarly examined under temperature conditions of 20 ° C. and 50 ° C. The results are shown in Table 1.

As shown in Table 1, before light irradiation, these elements showed a high voltage holding ratio regardless of the temperature, and the liquid crystal display elements of Examples 1 to 5 were the liquid crystal display elements of the comparative examples. A slightly higher voltage holding ratio is shown.

On the other hand, after light irradiation, the voltage holding ratio at 20 ° C. of the liquid crystal display element of the comparative example is lower by 20% or more than before light irradiation, and the voltage holding ratio at 50 ° C. is 20 ° C. It is reduced to less than half, and the decrease in voltage holding ratio and the increase in temperature dependency due to light irradiation are extremely large. On the other hand, the liquid crystal display elements of Examples 1 to 5 have almost the same voltage holding ratio as before light irradiation,
There is almost no temperature dependence.

1 is a cross-sectional view showing a liquid crystal display element according to the present invention. FIG. 6 is a cross-sectional view showing a liquid crystal display element according to another embodiment of the present invention and a liquid crystal microcapsule used therein. FIG. 10 is a cross-sectional view showing a liquid crystal display element according to still another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Transparent substrate, 3, 4 ... Electrode 5 ... Liquid crystal compound, 6 ... Dichroic dye, 8 ... Liquid crystal layer, 9 ... Ion trapping substance, 13 ... Liquid crystal display element, 14 ... Film, 15 ... Reducing or ion-trapping substance, 16 ... microcapsule, 17 ... liquid crystal display element, 18 ... microcapsule, 1
9 ... medium, 20 ... liquid crystal display element

Claims (2)

A pair of substrates disposed opposite to each other and having an electrode on the opposite surface, at least one of which is transparent, and a liquid crystal material sandwiched between the pair of substrates and containing a dichroic dye and an ion trapping substance Layers,
The ion scavenging substance comprises a compound selected from the group consisting of a compound represented by the following chemical formula 1, a compound represented by the following chemical formula 2, a compound represented by the following chemical formula 3, and derivatives thereof: A liquid crystal display element.

(Wherein R ⁵ , R ⁶ and R ⁷ in Chemical Formula 1 and Chemical Formula 2 are at least one organic group selected from a cyano group, an alkyl group, a phenyl group, and a phenyl group in which hydrogen is substituted with a cyano group)   2. The liquid crystal according to claim 1, wherein the liquid crystal material is contained in a microcapsule, and the ion promoting substance is contained in a film of the microcapsule or in a binder resin present between the microcapsules. Display element.

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