JP3192780B2 - Twisted nematic liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a twisted nematic liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device has a so-called super twisted nematic (STN) mode or a twisted nematic (TN) driven by a thin film transistor (TFT).
With the development of the mode liquid crystal display device, for example, it has become indispensable as a display component of a word processor or a personal computer.

[0003] Among them, a TN liquid crystal display element driven by a TFT has been developed in recent years to realize a high speed, a high contrast ratio, and a multi-gradation.

[0004]

In a TFT-driven liquid crystal cell, a reverse tilt occurs around a pixel electrode at a high temperature, resulting in a decrease in contrast and a change in the viewing angle direction .
This may cause display quality degradation. It is said that these are phenomena that occur because the pretilt angle at the interface of the alignment film is not sufficiently large.

In order to solve such a problem , an appropriate alignment film is selected, in particular, a ring-closed polyimide is employed, and a ratio (d / p) of a liquid crystal layer thickness to a liquid crystal twist pitch is used. the measures such as selecting the appropriate one has been studied as a. However, it was difficult for these measures to sufficiently suppress the occurrence of reverse tilt.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a twisted nematic liquid crystal display device in which a nematic liquid crystal layer twisted by approximately 90 degrees is sandwiched between substrates with electrodes. in, the liquid crystal layer is viewed contains 0.1 to 5 wt% of the crosslinked polymer, the polymer rack
The bridge contains a liquid crystalline monomer as its polymerization component.
There is provided a twisted nematic liquid crystal display element characterized in that.

Here, the crosslinked polymer is a homopolymer or a copolymer of a monomer having two or more polymerizable functional groups in a molecule. The crosslinked polymer may be a copolymer of a monomer having one polymerizable functional group in the molecule and a monomer having two or more polymerizable functional groups in the molecule. However, in order to crosslinked polymer is substantially insoluble in the liquid crystal, the content of the polymerization component based on a monomer having two or more in its molecule a polymerizable functional group in the crosslinked polymer <br/> It is preferably at least 15% by weight.

The amount of the crosslinked polymer is 0.1 to 5 % by weight based on the liquid crystal layer. If the amount is less than 0.1%, the effect of suppressing reverse tilt generation is not sufficient, and if it exceeds 5%, light scattering due to the presence of the crosslinked polymer increases.
Not suitable . Although the amount of light scattering also depends on the refractive index of the crosslinked polymer, it is preferable that the haze value when no voltage is applied is suppressed to 5% or less.

The polymerization reaction for forming the polymer crosslinked product is preferably chain polymerization, polyaddition, or the like. On the other hand, a reaction such as polycondensation in which volatiles such as water are generated during the polymerization and a reaction in which by-products which adversely affect the liquid crystal characteristics are generated are not preferable. This is because there is a possibility that voids may be generated in the element and that the liquid crystal characteristics may be deteriorated.

In order to produce the twisted nematic liquid crystal display element of the present invention, a liquid crystal is mixed with a compound such as a monomer or oligomer which forms a crosslinked polymer, and the mixture is made into a solution state. , And then a photo-curing, a thermo-curing, an electron beam curing, a curing by mixing two liquids, a solidification by cooling, or the like may be used to form a crosslinked polymer.

[0011] In particular, it is preferable to use a photocurable resin as a crosslinked polymer because it can be solidified in a short time without being affected by heat. In this case, it can be usually performed by irradiating ultraviolet rays of about 0.1 to 10 mJ / cm ² .

Representative examples of monomers and oligomers having two or more polymerizable functional groups in the molecule are described below.

The first group is a styrene derivative represented by Chemical Formula 1. Here, n and k are 0 or 1,
Does not. m is 0 or 1, A is —CH ₂ —,
-CO-O -, - O- CO -, - CH 2 -CH 2 -, -
And a linking group such as CH ₂ —O— and —O—CH ₂ —. Specific compounds of Formula 1 include divinylbenzene and the like.

[0014]

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The second group is a diac relay represented by Chemical Formula 2.
It is a kind . Here, X is a hydrogen atom, a fluorine atom or a methyl group. B represents a diol residue. the above
The diacrylates may form a compound having a molecular weight of 500 to tens of thousands generally called an acrylic oligomer by polymerization.

[0016]

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The crosslinked polymer in the present invention, Ru der those containing a liquid crystalline monomer as a polymerizable component. Thereby, change in the clear ring points between the mixed solution and the original liquid crystal is reduced, thus, also reduced the change in helical pitch.

[0018]

In particular, the above liquid crystalline monomer is obtained by adding 3% by weight of the liquid crystalline monomer to the original liquid crystal.
Preferably, the change of the clearing point of the mixed solution with respect to the clearing point of the original liquid crystal is 3 ° C. or less. This is because a change in the helical pitch verge Umate can be reduced.

Further, the polymer crosslinked product contains a liquid crystal monomer as a polymerization component thereof,
By polymerizing while applying an electric field during polymerization,
There is also an advantage that the haze value is minimized when a voltage is applied, and a transparent element can be obtained from any angle.

In this case , there is also an effect of increasing the pretilt angle. Conventionally, in order to increase the pretilt angle, but selection improvements and the liquid crystal alignment film has been energetically carried out, For example <br/>, when an alignment film of a high pretilt angle, the display device surface The unevenness of the pretilt angle tends to occur, and uniform display over the entire surface is difficult.

[0022] When manufacturing the liquid crystal display device of the present invention, by polymerizing while applying an electric field at the time of polymerization, it is possible to uniform display over the entire surface unevenness of a pretilt angle hardly occurs in the display device surface.

The voltage applied during polymerization depends on the dielectric anisotropy and elastic constant of the liquid crystal used, and the thickness of the element, but is preferably 0.3 volts or more and 150 volts or less. 0.3 volts In the following, the reverse tilt to increase the flop Rechiruto angle
It is difficult to obtain the suppression effect. In principle, the upper limit is not limited as long as the element is not destroyed, but may be 150 volts or less in view of simplicity. A sufficient effect can be obtained with about 10 volts.

The power applied during polymerization may be DC or AC. In the case of AC, the frequency is 10
0 kHz or less, usually 10 to 100 Hz is good.

The original of adding crosslinked polymer liquid crystal is, as long as it usually can be used as twisted nematic liquid crystal display element, that it used both.

The mixture of the liquid crystal and the monomer or oligomer for forming a crosslinked polymer includes, in addition to a polymerization initiator such as photopolymerization, ceramic particles for controlling the distance between substrates, plastic particles, spacers such as glass fibers, and pigments. , Dyes, viscosity modifiers, and other additives that do not adversely affect the performance of the present invention can be added.

The basic structure of a liquid crystal cell sandwiching the above liquid crystal layer is as follows. ITO patterned with a desired pattern on the surface of a substrate such as plastic or glass
A transparent electrode such as (In ₂ O ₃ —SnO ₂ ) or SnO ₂ is provided to form a substrate with electrodes. The electrode layers are arranged in a matrix in which electrode groups face each other in accordance with the display, so that ON / OFF of each dot can be controlled. As a method for forming the electrode layer, aspects or al to achieve a uniform layer thickness, deposition method, sputtering method or the like is preferably used, in particular this
Not limited to

In the present invention, if necessary,
Also SiO ₂ to lower, TiO ₂ or the like of the insulating film, retardation film, polarizing film, a reflecting film, a photoconductive film and the like may be formed. In particular, when the device is driven by providing an active element such as a TFT, a MIM, or a thin film diode, the above-described reverse tilt is likely to occur, and the effect of the present invention is large.

On the surface of the substrate with electrodes, there is formed an orientation control film composed of a film of rubbed polyimide or polyamide or a film of obliquely deposited SiO or the like. 2
A plurality of the substrates are prepared, and the liquid crystal layer described above is sandwiched therebetween.

[0030] Incidentally, or an insulating film such as _{TiO 2, SiO 2, Al 2} O 3 in order to prevent inter-substrate short circuit between the electrode and the alignment layer, Al to the transparent electrode, Cr, such as Ti Low A resistance lead electrode may be provided.

A pair of polarizing plates is arranged on both outer sides of the substrate. It is general that the polarizing plate itself is also arranged outside the substrate constituting the cell, but if performance permits, the substrate itself may be formed of a polarizing plate or provided as a polarizing layer between the substrate and the electrode. Is also good.

Further, it is possible to use a color filter in combination. By forming the color filter on the inner surface of the cell, a more accurate color display can be achieved without causing a shift due to a viewing angle. Specifically, it may be formed below the electrode, or may be formed above the electrode.
Moreover, and a color filter for correcting color, or a combination of color and polarization plate, or the addition of the dye in the liquid crystal layer may be or using an illumination having a wavelength distribution of JP <br/> constant.

Driving means for applying a voltage to the electrodes of the liquid crystal cell having such a configuration is connected to perform driving. That is, an external circuit board made of a flexible board or the like is connected to the connection terminal portion led to the end of the board via anisotropic conductive rubber, using heat seal, anisotropic conductive adhesive, or a TAB board. Or to connect.

The present invention can be applied to both a transmission type and a reflection type, and its application range is wide. When the transmission type is used, a light source is arranged on the back side. A light guide and a color filter can be used in combination with the light source . Further, in the case of the transmission type, a background portion other than the pixels can be covered with a light shielding film by printing or the like.

In the present invention, various techniques used in ordinary liquid crystal display elements can be applied as long as the effects of the present invention are not impaired.

[0036]

The reason why a twisted nematic liquid crystal having a suppressed reverse tilt can be obtained by the present invention is not necessarily clear, but is presumed as follows.

Whether or not reverse tilt occurs in a TFT liquid crystal display element or the like is determined by a delicate balance between liquid crystal molecules and an interface of an alignment film in a voltage applied state. The crosslinked polymer in the present invention is considered to have a kind of alignment pinning effect by forming a very weak three-dimensional network structure in the liquid crystal cell and increasing the apparent alignment film interface. .

[0038] That is, the crosslinked polymer, along with a uniform distribution of very small defects, crystal and acts, in a high temperature state or generated in a low temperature state, an effect of preventing the alignment defects to the extent that can be observed it is conceivable that.

[0039]

[Example] Glass substrate (Corning 7059 substrate)
Chromium was deposited thereon to a thickness of 60 nm and patterned to form a gate electrode. Subsequently, a silicon oxynitride film and an amorphous silicon film were deposited by a plasma CVD apparatus.
This was annealed using a laser and then patterned to obtain polycrystalline silicon. Then, phosphorus-doped amorphous silicon and chromium were deposited using plasma CVD and a vapor deposition apparatus, respectively, and were patterned so as to cover the polycrystalline silicon, thereby forming a first layer source electrode and drain electrode. Further, after depositing ITO, pixel electrodes were formed by patterning.

Subsequently, chromium and aluminum were successively vapor-deposited and patterned so as to connect the pixel electrode with the first-layer source electrode and drain electrode, thereby forming a second-layer source electrode and drain electrode. Thereafter, a silicon oxynitride film was deposited again by a plasma CVD apparatus to form a protective film. Further, a polyimide film was applied to a thickness of 0.06 μm and baked to form a film, and this film was rubbed using a nylon thread rubbing cloth of electrostatic flocking to prepare an active matrix substrate.

After a solid ITO electrode is formed on the entire surface, a polyimide film is coated thereon to a thickness of 0.06 μm and baked to form a film. A counter electrode substrate made of the same glass substrate rubbed by using the above and an active matrix substrate manufactured previously are arranged so that the electrode surfaces face each other, and a spacer having a diameter of about 5.0 μm is scattered inside, and the periphery thereof is spread. An empty cell having a substrate gap d of about 5.0 μm was manufactured by sealing with an epoxy-based sealing material except for the injection port.

As a liquid crystal, "ZLI-479" manufactured by Merck Ltd.
After adding a predetermined amount of cholesteric nonanoate as a chiral agent using "2" (trade name), 3% by weight of the compound of formula 3 and 0.03% by weight of benzoin isobutyl ether as a photopolymerization initiator were added. Dissolved uniformly.

[0043]

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This mixture was injected into the empty cell manufactured by the above method from the inlet, and the inlet was sealed. The injected liquid crystal layer had a twist of approximately 90 degrees.

This was irradiated with ultraviolet rays for 30 seconds, and polarizing plates were arranged on both sides of the cell, thereby producing an active matrix liquid crystal display device. When this panel was driven at a high temperature of 70 ° C., good characteristics were obtained without any alignment defect due to reverse tilt around the electrodes, which was a problem in the conventional TFT liquid crystal.

[0046]

According to the present invention, the orientation abnormality of the verge Umate which minimize TN liquid crystal element, such as a reverse tilt is obtained. In particular, the present invention is effective for a TFT element in which a reverse tilt defect easily occurs.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1334 G02F 1/137

Claims (2)

(57) [Claims] 1. A substrate with electrode twisted nematic liquid crystal display device formed by sandwiching a nematic liquid crystal layer twisted approximately 90 ° between, the liquid crystal layer is viewed contains 0.1 to 5 wt% of the crosslinked polymer, The crosslinked polymer forms a liquid crystalline monomer.
A twisted nematic liquid crystal display device comprising a polymerizable component . 2. The method according to claim 1, further comprising a TFT element.
Twisted nematic liquid crystal display element .