JPH10319406A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device having a high picture quality and a high productivity, by which unevenness of display caused by burnt afterimage is reduced in a device using a lateral electric field mode by setting a glass transition temperature of an oriented film placed between a liquid crystal layer and at least one of substrates to more than a specific value. SOLUTION: A glass transition temp. Tg of an oriented film placed between a liquid crystal layer and at least one of a pair of substrates holding the liquid crystal layer is set to >=300 deg.C. For a method of varying an optical characteristic according to molecule orientation condition of the liquid crystal layer, a pair of polarizing plates are used of which polarization axes are perpendicular to each other. Further, when a refractive index anisotropy of liquid crystal composition is expressed by Δn and a thickness of the liquid crystal layer is expressed by (d), it is desirable that a parameter Δn.d satisfies 0.2 μm<Δn.d<0.5 μm. Moreover, it is desirable that at least one of the oriented films on the substrates is an organic high molecular compound such as polyamic acid imide series, polyimide series, etc., of which a weight-average molecular weight is 10000-300000.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device, and more particularly to an in-plane switching type active matrix type liquid crystal display device in which an electric field is applied in a direction substantially parallel to a substrate plane to drive liquid crystal.

[0002]

2. Description of the Related Art Display of a liquid crystal display device is performed by changing the alignment direction of liquid crystal molecules by applying an electric field to the liquid crystal molecules of a liquid crystal layer sandwiched between substrates, and thereby changing the optical characteristics of the liquid crystal layer. Will be

A conventional active matrix type liquid crystal display device has a twisted nematic (TN) display system in which a direction of an electric field applied to the liquid crystal is set to a direction substantially perpendicular to a substrate interface, and a display utilizing the optical rotation of the liquid crystal is performed. Is represented by On the other hand, a method of making the direction of the electric field applied to the liquid crystal using a comb electrode substantially parallel to the substrate interface and performing display using the birefringence of the liquid crystal (transverse electric field method) is disclosed in, for example, Japanese Patent Publication No. 63-2190.
No. 7 and Japanese Patent Application Laid-Open No. 5-505247. The horizontal electric field method has advantages such as a wide viewing angle and a low load capacity as compared with the conventional TN method, and is a promising technology as an active matrix type liquid crystal display device.

With the recent increase in response speed of liquid crystal display devices,
An image burn-in phenomenon called an afterimage of the liquid crystal display element has become evident, leading to a reduction in yield as one cause of display failure. This phenomenon of image burning, that is, the afterimage problem,
Usually, this occurs when a region where the response is extremely slow compared to the liquid crystal response speed of about 50 milliseconds occurs.

Although the causes of these occurrences in the conventional TN type liquid crystal display device have not been completely elucidated, it is presumed that DC charges generated from a thin film transistor (TFT) accumulate in a pixel and occur. That is, an effective voltage is applied to the liquid crystal layer by maintaining the potential at the time of voltage application without being canceled within the response time at the interface between the alignment film on the pixel electrode and the liquid crystal alignment film. It is said to be caused by The correlation between such an afterimage phenomenon and a residual DC voltage component has been examined, and it is now beginning to be understood that the residual image voltage is improved as the residual DC voltage is reduced. For this reason, a conventional TN type alignment film is required to have a property that DC charges are hardly accumulated.

[0006]

On the other hand, even in the above-mentioned in-plane switching method, a phenomenon of image sticking (afterimage) occurs, which causes a decrease in black level and contrast, resulting in a decrease in image quality and a yield, resulting in a decrease in mass productivity. There's a problem. Therefore, when the DC voltage remaining on the pixel electrode, which was correlated with the afterimage phenomenon in the conventional TN mode, was also measured in the lateral electric field mode, (1) the residual DC voltage value between the liquid crystal display element in which the afterimage occurs and the liquid crystal display element not generating (2) It was found that in this horizontal electric field method, image sticking persisted semi-permanently and caused a significant decrease in contrast. From the above points, it is considered that the afterimage and burn-in phenomenon of the in-plane switching method is based on a mechanism peculiar to the in-plane switching method, which is completely different from the conventional TN mode, and the problem of image sticking and afterimage peculiar to the in-plane switching method is solved. Is required.

Accordingly, an object of the present invention is to solve the above-mentioned problems in an active matrix type liquid crystal display device using a horizontal electric field method, to reduce display unevenness due to image sticking afterimage, to achieve high image quality and excellent mass productivity. To provide an active matrix type liquid crystal display device.

[0008]

According to an active matrix type liquid crystal display device of the present invention, an alignment film glass is disposed between a liquid crystal layer and at least one of a pair of substrates sandwiching the liquid crystal layer. The transition temperature Tg is set to 300 ° C. or higher.

As a method of changing the optical characteristics according to the molecular orientation state of the liquid crystal layer, a pair of polarizing plates whose polarization axes are substantially orthogonal to each other is used. Furthermore, when the refractive index anisotropy of the liquid crystal composition is Δn and the thickness of the liquid crystal layer is d, it is preferable that the parameter Δn · d satisfies 0.2 μm <Δnd <0.5 μm.

At least one of the alignment films formed on each of the substrates is made of an organic polymer compound having a weight average molecular weight of 10,000 or more and 300,000 or less, more specifically, a polyamic imide type, a polyimide type, It is preferable to use a polyimidesiloxane-based or polyamideimide-based organic polymer.

The molecular weight distribution of these organic polymers is preferably those having a dispersion coefficient expressed by the ratio of weight average molecular weight / number average molecular weight of 2 or less.

Further, according to an embodiment of the present invention, the alignment film comprises a diamine compound represented by the chemical formula H ₂ NR—NH ₂ and a diamine compound represented by the chemical formula:

[0013]

Embedded image

A dehydration-closed organic polymer of a polyamic acid composed of tetracarboxylic dianhydride represented by the following formula, wherein R and X in the repeating structure are provided with a bonding group capable of rotating the molecular axis of the polymer, -O -, - S -, - CH 2 -, -
_{C (CH 3) 2 -,} - C (CF 3) 2 -, - SO 2 -, meta bonds,
The number of ortho bonds is 3 or less in total.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of operation of a lateral electric field system as a premise of the present invention will be described with reference to FIG. FIG.
1A and 1B are side sectional views showing the operation of liquid crystal within one pixel of a liquid crystal element of a horizontal electric field method, and FIGS. 1C and 1D are front views thereof.

FIG. 1A is a cross-sectional view of the cell side when no voltage is applied.
FIG. 1C shows a front view at that time. Linear electrodes 1 and 4 are formed inside one of the substrates, and the substrate surface is an alignment film 5 on both of the paired substrates, and a liquid crystal composition is sandwiched between the substrates (in this example, in this example). The dielectric anisotropy is assumed to be positive, but in a negative liquid crystal composition, the transverse electric field method can be similarly realized only by changing the directions of the long axis and the short axis of the liquid crystal molecules.)

The rod-like liquid crystal molecules 6 are bonded to the alignment film 5 at the interface between the two substrates at the longitudinal direction of the electrodes 1 and 4 (FIG. 1).
(C) Front view), the orientation is controlled in the direction 10 having a slight angle, and when no electric field is applied, the liquid crystal layer is oriented almost uniformly in this direction. Here, different potentials are applied to the pixel electrode 4 and the common electrode 1, respectively.
When an electric field 9 is applied to the liquid crystal composition layer due to the potential difference between them, the interaction between the dielectric anisotropy of the liquid crystal composition and the electric field causes the liquid crystal molecules to change as shown in FIGS. 1 (b) and (d). Change its direction to the direction of the electric field. At this time, the optical characteristics of the present liquid crystal element change due to the refractive anisotropy of the liquid crystal composition layer and the action of the polarizing plate 8, and display is performed by the change. FIG. 2 is a graph schematically showing a relationship between an applied voltage between electrodes of a liquid crystal display device of a horizontal electric field type and a display luminance thereof. The solid line in FIG. 2A shows the initial basic characteristics, and the dotted line in FIG. 2B shows the voltage / luminance characteristic curve when a typical afterimage is shown. As described above, the afterimage and the image printing phenomenon show remarkable luminance fluctuation in the halftone area.

Here, the mechanism of the afterimage phenomenon will be considered.

It is known that the alignment regulating force (coupling force) due to the bonding between the alignment film and the liquid crystal molecules varies greatly depending on the alignment film material and the rubbing treatment conditions. It also depends on the direction of the orientation change. Considering a liquid crystal material having a positive dielectric anisotropy that is oriented almost horizontally on the surface, the direction of change in the orientation of liquid crystal molecules on the substrate surface caused by the application of an electric field is such that an electric field is applied almost perpendicular to the substrate interface. In the TN mode, the substrate rises from the substrate surface (in the polar angle direction shown in FIG. 3), and in the lateral electric field mode in which the electric field is applied almost parallel to the substrate interface, the in-plane direction of the substrate (in-plane twist shown in FIG. 3) Rotation direction). Therefore, in the conventional TN mode, it is considered that the difficulty in returning the alignment change of the liquid crystal molecules in the polar angle direction corresponds to image burn-in and an afterimage, which is caused by the DC potential remaining near the upper and lower counter electrodes.

On the other hand, in the horizontal electric field method, image burning,
The afterimage corresponds to the difficulty of returning the twist deformation of the liquid crystal molecules in the in-plane direction of the substrate. Also, as described above, since there is no correlation between the afterimage and the DC potential remaining near the pixel electrode,
This is considered to be based not on the electrical factor but on the interaction of the liquid crystal / alignment film interface.

The inventors of the present invention have conducted intensive studies, and as a result, the occurrence of image sticking and afterimage in the lateral electric field method is controlled by controlling the orientation of the liquid crystal molecules by the rotational torque generated based on the in-plane torsional deformation of the liquid crystal molecules. The surface of the alignment film is elastically deformed,
If the deformation / creep appears as a polymer-specific elastic aftereffect (after delayed elastic deformation), that is, as an afterimage that recovers with a finite delay time as a residual strain, or as an image burn-in phenomenon as a permanent deformation Was interpreted.

Therefore, as a countermeasure to reduce the occurrence of such an afterimage phenomenon, the hardness (elastic modulus) of the alignment film is increased to form a highly elastic polymer surface which is hardly affected by the rotation torque caused by driving the liquid crystal molecules. It is considered to be effective to perform the operation or to form a state in which the torsional coupling at the interface is weak so that the rotation torque of the liquid crystal layer is not easily transmitted to the alignment film layer.

As a specific measure for increasing the elastic modulus of the alignment film, it is desirable that the polymer constituting the alignment film has a rigid and highly linear molecular structure, and that the molecular weight be as large as possible. Is preferred. Further, it is preferable to use a monodispersed system. It is also possible to construct a higher-order network by photocrosslinking reaction after the application of an alignment film, baking hardening, and rubbing alignment treatment to mechanically increase the strength. Molecular weight 10,000
By making it larger than 00, the cohesive force between the polymer chains can be increased and the elastic modulus can be increased. However, on the other hand, when the molecular weight is 300,000 or more, entanglement of polymer chains may occur in the melt state of the alignment film varnish, and packing with high polymer chain density may be prevented. It is also known that the elastic modulus of the polymer alignment film is greatly affected by surrounding environmental conditions, particularly temperature.

From this viewpoint, the glass transition point Tg of the polymer of the alignment film other than the elastic modulus is an index for selecting the high elastic modulus alignment film as described above. The higher the Tg, the higher the elastic modulus of the alignment film is guaranteed. The correlation between the magnitude of this Tg and the magnitude of the afterimage of the in-plane switching method, which is an object of the present invention, shows that an alignment film having a Tg of more than 300 ° C. can reduce the afterimage to an extent that the allowable value of the display performance is satisfied. I understood. Therefore, a polymer having a Tg of the alignment film of 300 ° C. or more is desirable. This Tg is a bulk value of the polymer of the alignment film, and the Tg of the surface of the alignment film related to the interface of the liquid crystal alignment film is expected to decrease by about 100 ° C. even if it is largely estimated. Therefore, the operation is actually guaranteed at -30 ° C.
It is considered that the elastic modulus of the surface of the alignment film hardly decreases in the temperature range from 70 to 70 ° C.

Further, a bonding group capable of rotating the molecular axis of the polymer, —O—, —S—, —CH ₂ —, —C (CH ₃ ) ₂ —,
It is desirable that the total number of —SO ₂ −, meta bond and ortho bond is 3 or less. This is because diffusion between polymer main chains hardly occurs, but the presence of a large number of the above-described bonding groups facilitates rotation around the molecular axis and enables local thermal motion, and thus the elasticity of the alignment film polymer is increased. This results in a lower rate. Such a phenomenon is known as side chain sub-dispersion appearing in the temperature characteristics of the elastic modulus.

In the alignment film used in the conventional TN method, a method of introducing a linear alkyl group or the like into a side chain is used to control a tilt angle. In order to maintain the above, also from the above point of view, a polymer having no long-chain branched side-chain functional groups such as a linear alkyl group that generates a tilt angle, or a polymer having no bulky side-chain substituents. It is suitable.

From the above viewpoints, the compounds of the amine component and other copolymerizable compounds which are synthetic materials for the alignment film used in the present invention include, for example, p-phenylenediamine and m-phenylene as aromatic diamines. Diamine, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,6-diaminotoluene, diaminodulene,
Benzidine, O-tolidine, 3,3'-dimethoxybenzidine, 4,4 "-diaminoterphenyl, 1,5-diaminonaphthalene, 2,7-diaminofluorene, 4,
4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,5-diaminopyridine, 4,4 '
-Bis (p-aminophenoxy) biphenyl, 2,2-
Bis {4- (p-aminophenoxy) phenyl} propane, 2,2-bis {4- (p-aminophenoxy) phenyl} hexafluoropropane, 4,4′-bis (m-
Aminophenoxy) diphenylsulfone and the like, but are not limited thereto.

On the other hand, the acid component compound and other copolymerizable compounds include, for example, aromatic tetracarboxylic dianhydride such as pyromellitic dianhydride, methyl-pyromellitic dianhydride and dimethylene trimellitate. Tetate dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, dimethylene trimellitate dianhydride 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ', 4,4'-biphenylsulfonetetracarboxylic dianhydride, 3,3', 4,4'-diphenylethertetracarboxylic Acid dianhydride, 3,3 ', 4
Examples of 4'-diphenylmethanetetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride include 1,2,3,
4-butanetetracarboxylic dianhydride, 1,2,3,4
-Biscyclobutanetetracarboxylic dianhydride, 1,
Examples include, but are not limited to, 2,3,4-cyclopentanetetracarboxylic dianhydride.

As the solvent, for example, polar N-methyl-2-pyrrolidone, dimethylformamide,
Dimethylacetamide, dimethylsulfoxide, sulfolane, butyllactone, cresol, phenol,
Cyclohexanone, dimethylimidazolidinone, dioxane, tetrahydrofuran, butylcellosolve, butylcellosolve acetate, acetophenone, and the like can be used.

Further, amino-based silane coupling agents such as γ-aminopropyltriethoxysilane, δ-aminopropylmethyldiethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, etc. , An epoxy silane coupling agent, a titanate coupling agent, a surface treatment agent such as aluminum alcoholate, aluminum chelate and zirconium chelate can be mixed or reacted. The formation of the alignment film can be performed by general spin coating, printing, brush coating, spraying, or the like.

As the liquid crystal used, for example, 4-substituted phenyl-4'-substituted cyclohexane, 4-substituted cyclohexyl-4'-substituted cyclohexane, 4-substituted phenyl-
4'-substituted dicyclohexane, 4-substituted dicyclohexyl-4'-substituted diphenyl, 4-substituted-4 "-substituted terphenyl, 4-substituted biphenyl-4'-substituted cyclohexane, 2- (4-substituted phenyl) -5 -Pyrimidine, 2
-(4-substituted dioxane) -5-phenyl, 4-substituted benzoic acid-4'-phenyl ester, 4-substituted cyclohexanecarboxylic acid-4'-substituted phenyl ester, 4-substituted cyclohexanecarboxylic acid-4'-substituted biphenyl Ester, 4- (4-substituted cyclohexanecarbonyloxy) benzoic acid-4'-substituted phenyl ester, 4- (4
-Substituted cyclohexyl) benzoic acid-4'-substituted phenyl ester, 4- (4-substituted cyclohexyl) benzoic acid-
4'-substituted cyclohexyl ester, 4-substituted-4'-
Substituted biphenyls and the like can be mentioned. Among these compounds, an alkyl group,
A multi-component mixed liquid crystal composition having an alkoxy group, an alkoxymethylene group, a cyano group, a fluorine group, a difluorine group, and a trifluorine group is used.

An embodiment of the present invention will be described specifically.

(Example 1) As a substrate, a thickness of 1.1 mm was used.
Using two transparent glass substrates whose surfaces have been polished, a thin film transistor and a wiring electrode to which a lateral electric field can be applied are formed on one of these substrates, and an insulating layer made of silicon nitride is formed on the uppermost surface thereof. A protective film was formed.

FIG. 4 shows the structure of the thin film transistor and various electrodes as a front view as viewed from a direction perpendicular to the substrate surface and side sectional views along AA 'and BB' in the front view.

The thin film transistor element 14 comprises a pixel electrode (source electrode) 4, a signal electrode (drain electrode) 3, a scanning electrode (gate electrode) 12, and amorphous silicon 13.

The common electrode 1 and the scanning electrode 12, and the signal electrode 3 and the pixel electrode 4 were formed by patterning the same metal layer.

The pixel electrodes 4 are arranged between the three common electrodes 1 in the front view.

The pixel pitch is in the horizontal direction (that is, the signal electrode 3).
Is 100 μm, in the vertical direction (that is, between the scanning electrodes 12).
Is 300 μm.

As for the electrode width, a scanning electrode, a signal electrode, and a common electrode wiring portion (a portion extending in parallel with the scanning wiring electrode), which are wiring electrodes extending over a plurality of pixels, are widened to avoid line defects. The widths are 10 μm, 8 μm, and 8 μm, respectively.

On the other hand, the widths of the pixel electrodes independently formed for each pixel in order to improve the aperture ratio and the portions of the signal wiring electrodes of the common electrodes extending in the longitudinal direction are slightly narrowed, and each is 5
μm and 6 μm. By reducing the width of these electrodes, the possibility of disconnection due to the incorporation of foreign matter and the like increases, but in this case, only one pixel is partially missing and no line defect occurs.

The signal electrode 3 and the common electrode 1 were spaced apart by 2 μm via an insulating film.

The number of pixels is 640 × 3 (R, G, B) signal wiring electrodes and 480 wiring electrodes.
It was set to 3 × 480.

The alignment film used was prepared by dissolving 1.0 mol% of p-phenylenediamine in N-methyl-2-pyrrolidone and adding 1 mol% of pyromellitic dianhydride thereto.
The mixture was reacted at 0 ° C. for 12 hours to obtain a polyamic acid varnish having a weight average molecular weight in terms of standard polystyrene of about 250,000 and a weight average molecular weight / number average molecular weight (Mv / Mn) of about 1.8. After diluting the varnish to a concentration of 6%, adding 0.3% by weight of γ-aminopropyltriethoxysilane in solid content, forming a print, and performing a heat treatment at 220 ° C. for 30 minutes to obtain a dense polyimide alignment of about 800 °. A film was formed.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same manufacturing method as above was measured, it was found to be about 38
0 ° C. was indicated.

Next, the surface of the alignment film was rubbed with a buff cloth attached to a rubbing roller to give a liquid crystal alignment film.

On the other substrate, a color filter with a light-shielding layer was formed, a polyimide alignment film was formed on the outermost surface in the same manner as described above, and a liquid crystal alignment ability was imparted by a rubbing treatment.

In this embodiment, the rubbing method is used as a method for imparting alignment ability. However, other than that, for example, an ultraviolet-curable resin solution is applied to form an alignment film, which is irradiated with polarized ultraviolet light to cause a photochemical reaction. Then, a method of imparting liquid crystal alignment ability by applying the method and a method of using a multilayer film having good alignment property formed by pulling up an organic molecular film spread on a water surface onto a substrate can be used.

In particular, the latter two methods are alignment control methods in which it has conventionally been difficult to provide a sufficiently large interface tilt angle, but in the lateral electric field method, a vertical electric field method represented by a conventional TN method is used. Unlike in principle, an interface tilt angle is not required in principle, so that practicality such as mass productivity can be improved by combination with the horizontal electric field method.

Next, a sealing agent is applied to the periphery of the two substrates with the surfaces having the liquid crystal alignment ability facing each other and a spacer made of dispersed spherical polymer beads interposed therebetween. The cell was assembled. The rubbing directions of the two substrates were substantially parallel to each other, and the angle between the rubbing directions and the direction of the applied lateral electric field was 75 °. The dielectric anisotropy Δ
ε is positive and its value is 10.2 (1 kHz, 20 ° C.)
The refractive index anisotropy Δn is 0.075 (wavelength 590 nm, 20
C) was injected in vacuum and sealed with a sealing material made of an ultraviolet-curable resin. A liquid crystal panel having a liquid crystal layer thickness (gap) of 4.8 μm was manufactured. The retardation (Δnd) of this panel is 0.36 μm. This panel is composed of two polarizing plates (G1220D manufactured by Nitto Denko Corporation).
U), the polarization transmission axis of one of the polarizing plates was substantially parallel to the rubbing direction, and the other was perpendicular to it.

Thereafter, a drive circuit, a backlight and the like were connected to form a module, and an active matrix type liquid crystal display device was obtained. In the present embodiment, the normally closed characteristic is used in which dark display is performed at a low voltage and bright display is performed at a high voltage.

In order to quantitatively measure the image sticking and the afterimage of the liquid crystal display device manufactured as described above, evaluation was performed using an oscilloscope combined with a photodiode. First,
A window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched so that the afterimage is most noticeable, in which the luminance is 10% of the maximum luminance.
The time until the pattern at the edge of the window disappears is evaluated as an afterimage time, and the magnitude ΔB / B of the luminance variation of the luminance B between the afterimage portion of the window and the peripheral halftone portion.
(10%) was evaluated as an afterimage intensity. However, the afterimage intensity allowed here is 3% or less.

The result is taken as the residual image intensity ΔB, which is the luminance variation.
/ B (10%) was about 2%, and the time until the afterimage disappeared was about 50 ms, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 ms. In the image quality afterimage inspection by visual inspection, no display unevenness due to image burn-in and afterimage was observed, and high display characteristics were obtained.
As described above, by using the alignment film, a liquid crystal display device in which image sticking and image display defects are reduced can be obtained.

(Example 2) Except for the alignment film used, Example 1 was used.
In the same manner as described above, 1.0 mol% of m-phenylenediamine was dissolved in N-methyl-2-pyrrolidone, and
1.0 mol% of 3 ', 4,4'-diphenylethertetracarboxylic dianhydride was added and reacted at 40 ° C for 6 hours.
Standard polystyrene equivalent weight average molecular weight of about 21,000
A polyamic acid varnish having a weight average molecular weight / number average molecular weight (Mv / Mn) of about 1.5 was obtained. 6 of this varnish
%, And 0.3% by weight of solid content of γ-aminopropyltriethoxysilane was added.
A heat treatment was performed at 30 ° C. for 30 minutes to form a dense polyimide alignment film of about 700 °.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same manufacturing method as above was measured, it was found to be about 31.
0 ° C. was indicated.

As in Example 1, in order to quantitatively measure the image burn-in and the afterimage of the liquid crystal display device manufactured as described above, evaluation was performed using an oscilloscope combined with a photodiode. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched so that the afterimage is most noticeable, in this case, the luminance is 10% of the maximum luminance. The time until disappears was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion of the window and the peripheral halftone portion was evaluated as the afterimage intensity.
However, the afterimage intensity allowed here is 3% or less.

The result is represented by an afterimage intensity ΔB which is a luminance variation.
/ B (10%) was about 3%, and the time until the afterimage disappeared was about 56 milliseconds, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 milliseconds. In the image quality afterimage inspection by visual inspection, no display unevenness due to image burn-in and afterimage was observed, and high display characteristics were obtained.
As described above, by using the alignment film, a liquid crystal display device in which image sticking and image display defects are reduced can be obtained.

Example 3 Example 1 except for the alignment film used.
In the same manner as described above, 1.0 mol% of 4,4'-diaminodiphenylmethane was dissolved in a mixed solvent of N-methyl-2-pyrrolidone and dimethylacetamide.
3,4-cyclopentanetetracarboxylic dianhydride 1.
0 mol%, and reacted at 30 ° C. for 12 hours to obtain a standard polystyrene reduced weight average molecular weight of about 15,000 to 25.
A polyamic acid varnish of 000 was prepared. Thereafter, the varnish was fractionated into a monodispersed polyamic acid varnish having a weight average molecular weight of about 200,000 and a weight average molecular weight / number average molecular weight (Mv / Mn) of 1.05 using gel permeation chromatography. The varnish was diluted to a concentration of 6%, and γ-aminopropyltriethoxysilane was added at a solid content of 0.1%.
After the addition of 3% by weight, printing was performed, and a heat treatment was performed at 220 ° C. for 30 minutes to form a dense polyimide alignment film of about 700 °.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same manufacturing method as above was measured, it was found to be about 38
0 ° C. was indicated.

As in Example 1, in order to quantitatively measure the image sticking and the afterimage of the liquid crystal display device thus manufactured, evaluation was performed using an oscilloscope combined with a photodiode. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched so that the afterimage is most noticeable, in this case, the luminance is 10% of the maximum luminance. The time until disappears was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion of the window and the peripheral halftone portion was evaluated as the afterimage intensity.
However, the afterimage intensity allowed here is 3% or less.

The result is taken as the residual image intensity ΔB, which is the luminance variation.
/ B (10%) was about 2%, and the time until the afterimage disappeared was about 48 milliseconds, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 milliseconds. In the image quality afterimage inspection by visual inspection, no display unevenness due to image burn-in and afterimage was observed, and high display characteristics were obtained.
As described above, by using the alignment film, a liquid crystal display device in which image sticking and image display defects are reduced can be obtained.

Example 4 Example 1 except for the alignment film used.
In the same manner as described above, 1.0 mol% of 4-fluoro-metaphenylenediamine was dissolved in N-methyl-2-pyrrolidone, and 3,3 ', 4,4'-biscyclobutanetetracarboxylic dianhydride was added thereto. Add 1.0 mol% and add 8% at 20 ° C.
The reaction was carried out at 100 ° C. for 2 hours to obtain a polyamideimide having a weight average molecular weight in terms of standard polystyrene of about 12,000 and a weight average molecular weight / number average molecular weight (Mv / Mn) of 1.95. This varnish was diluted to a concentration of 6% and γ-
After adding aminopropyltriethoxysilane at a solid content of 0.3% by weight, printing was performed and heat treatment was performed at 200 ° C. for 30 minutes to form a dense polyamideimide alignment film of about 600 °. A 4.0 μm liquid crystal display device was produced.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same manufacturing method as above was measured, it was found to be about 31.
0 ° C. was indicated.

As in Example 1, evaluation was performed using an oscilloscope combined with a photodiode in order to quantitatively measure the image sticking and afterimage of the liquid crystal display device manufactured as described above. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched so that the afterimage is most noticeable, in this case, the luminance is 10% of the maximum luminance. The time until disappears was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion of the window and the peripheral halftone portion was evaluated as the afterimage intensity.
However, the afterimage intensity allowed here is 3% or less.

The result is converted into a residual image intensity ΔB which is a luminance variation.
/ B (10%) was about 3%, and the time until the afterimage disappeared was about 60 milliseconds, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 milliseconds. In the image quality afterimage inspection by visual inspection, no display unevenness due to image burn-in and afterimage was observed, and high display characteristics were obtained.
As described above, by using the alignment film, a liquid crystal display device in which image sticking and image display defects are reduced can be obtained.

Comparative Example 1 1.0 mol% of 2,2-bis {4- (p-aminophenoxy) phenyl} propane
1.0 mol% of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride was polymerized in N-methyl-2-pyrrolidone at 20 ° C. for 10 hours to obtain a standard polystyrene equivalent weight average molecular weight of about 200. Thus, a polyamic acid varnish having a weight average molecular weight / number average molecular weight (Mv / Mn) of about 1.9 was obtained. After diluting the varnish to a concentration of 6%, adding 0.3% by weight of γ-aminopropyltriethoxysilane in solid content, forming a print, and performing a heat treatment at 220 ° C. for 30 minutes to obtain a dense polyimide alignment of about 800 °. A film was formed.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same method as described above was measured,
0 ° C. was indicated.

Next, a liquid crystal display device was prepared using this alignment film material in the same manner as in Example 1, and the image printing and afterimage of the liquid crystal display device were quantitatively measured and evaluated. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched to the halftone display where the afterimage is most noticeable.
The time until the pattern at the edge of the window disappeared was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion and the peripheral halftone portion of the window was evaluated as an afterimage intensity. However, the afterimage intensity allowed here is 3% or less.

As a result, the afterimage intensity ΔB, which is the luminance variation,
/ B (10%) was as large as about 5%, and it took about 60 minutes until the afterimage disappeared. Even in the visual image quality afterimage inspection, it was confirmed as a clear image burn-in and display unevenness due to the afterimage. As described above, by using the alignment film, image sticking and a display defect due to an afterimage were conspicuous.

Comparative Example 2 0.5 mol% of 2,2-bis [4- (p-aminophenoxy) phenyl] octane
0.5 mol% of 4,4'-diaminodiphenylmethane,
1.0 mol% of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is dissolved in N-methyl-2-pyrrolidone in 2 mol%.
Polymerization was carried out at 0 ° C. for 8 hours to obtain a polyamic acid varnish having a standard polystyrene equivalent weight average molecular weight of about 40,000 and a weight average molecular weight / number average molecular weight (Mv / Mn) of about 1.8. After diluting the varnish to a concentration of 6%, adding 0.3% by weight of γ-aminopropyltriethoxysilane in solid content, forming a print, and performing a heat treatment at 200 ° C./30 minutes to obtain a dense polyimide alignment of about 800 °. A film was formed.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same manufacturing method as above was measured,
0 ° C. was indicated.

Next, a liquid crystal display device was prepared using this alignment film material in the same manner as in Example 1, and the image printing and afterimage of the liquid crystal display device were quantitatively measured and evaluated. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched to the halftone display where the afterimage is most noticeable.
The time until the pattern at the edge of the window disappeared was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion and the peripheral halftone portion of the window was evaluated as an afterimage intensity. However, the afterimage intensity allowed here is 3% or less.

As a result, the afterimage intensity ΔB, which is the luminance variation,
/ B (10%) was as large as about 8%, and it took about 120 minutes for the afterimage to disappear. Even in the visual image quality afterimage inspection, it was confirmed as a clear image burn-in and display unevenness due to the afterimage. As described above, by using the alignment film, image sticking and a display defect due to an afterimage were conspicuous.

Comparative Example 3 1.0 mol% of 2,2-bis [4- (p-aminophenoxy) phenyl] hexafluoropropane and 1.0 mol% of 4,4′-diaminodiphenyl ether were added to N 20 ° C. in methyl-2-pyrrolidone
For 6 hours, the standard polystyrene-equivalent weight average molecular weight is about 8000, and the weight average molecular weight / number average molecular weight (Mv
/ Mn) of about 3.5 was obtained. After diluting the varnish to a concentration of 6%, adding 0.3% by weight of γ-aminopropyltriethoxysilane in solid content, forming a print, and performing a heat treatment at 200 ° C./30 minutes to obtain a dense polyimide alignment of about 800 °. A film was formed.

When the glass transition temperature Tg of the polyimide alignment film obtained by the same manufacturing method as above was measured,
0 ° C. was indicated.

Next, a liquid crystal display device was prepared using this alignment film material in the same manner as in Example 1, and the image printing and afterimage of the liquid crystal display device were quantitatively measured and evaluated. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched to the halftone display where the afterimage is most noticeable.
The time until the pattern at the edge of the window disappeared was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion and the peripheral halftone portion of the window was evaluated as an afterimage intensity. However, the afterimage intensity allowed here is 3% or less.

As a result, the afterimage intensity ΔB, which is the luminance variation,
/ B (10%) was as large as about 6%, and it took about 100 minutes for the afterimage to disappear, and it was confirmed by visual inspection of the image quality afterimage that the image was clearly printed and uneven display due to the afterimage was observed. As described above, by using the alignment film, image sticking and a display defect due to an afterimage were conspicuous.

[0077]

According to the present invention, it is possible to reduce the image sticking and the afterimage phenomenon peculiar to the lateral electric field method due to the elastic deformation of the alignment film surface induced by the in-plane twist rotation torque of the liquid crystal molecules at the liquid crystal / alignment film interface. As a result, an active matrix type liquid crystal display device having high image quality and excellent mass productivity with less display unevenness due to image sticking and afterimage phenomenon can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an operation of a liquid crystal in a liquid crystal display device of the present invention.

FIG. 2 is a diagram illustrating electro-optical characteristics of the present invention.

FIG. 3 is a diagram showing polar coupling and torsional coupling between liquid crystal molecules and a substrate surface.

4A and 4B are diagrams showing the structure of a thin film transistor, an electrode, and a wiring according to the present invention, wherein FIG. 4A is a front view, and FIG.

[Description of Signs] 1 ... Common electrode (common electrode), 2 ... Gate insulating film, 3 ...
Signal electrode (drain electrode), 4 ... pixel electrode (source electrode), 5 ... alignment film, 6 ... liquid crystal molecules in liquid crystal composition layer, 7
... Substrate, 8 ... Polarizing plate, 9 ... Electric field direction, 10 ... Direction of molecular long axis alignment on interface (rubbing direction), 11 ... Polarizing plate polarized light transmission axis direction, 12 ... Scanning electrode (gate electrode), 13 ... Amorphous silicon , 14 ... Thin film transistor element.

Continuing from the front page (72) Inventor Hisao Yokokura 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (10)

[Claims] 1. A pair of substrates, at least one of which is transparent; a liquid crystal layer disposed between the pair of substrates; and a liquid crystal layer formed on one of the pair of substrates, and is predominantly parallel to the substrate surface. Electrode group for applying an electric field having various components to the liquid crystal layer, and a plurality of active elements connected to electrodes corresponding to these electrode groups; and at least one of the liquid crystal layer and the pair of substrates. An alignment film disposed between the substrate and an optical unit that changes optical characteristics according to a molecular alignment state of the liquid crystal layer formed on at least one of the pair of substrates; An active matrix liquid crystal display device, wherein the glass transition temperature Tg of the film is 300 ° C. or higher. 2. The optical device according to claim 1, wherein the optical means is a pair of polarizing plates provided between the liquid crystal layer and the pair of substrates, and their polarization axes are substantially orthogonal to each other. Active matrix type liquid crystal display device. 3. The parameter Δn · d when the refractive anisotropy of the liquid crystal layer is Δn and the thickness is d.
Satisfies 0.2 μm <Δnd · 0.5 <0.5 μm. 4. An active matrix liquid crystal display device according to claim 1, wherein at least one of said alignment films is made of a polyamic imide-based, polyimide-based, polyimidesiloxane-based, or polyamide-imide-based organic polymer. . 5. The active matrix type liquid crystal display device according to claim 4, wherein the organic polymer has a weight average molecular weight of 10,000 to 300,000. 6. The active matrix type according to claim 1, wherein at least one of the alignment films is an organic polymer having a dispersion coefficient represented by a ratio of weight average molecular weight / number average molecular weight of 2 or less. Liquid crystal display. 7. An active matrix liquid crystal display device having a plurality of thin-film semiconductor transistors, wherein at least one of the substrates is a pair of transparent substrates, a liquid crystal layer disposed between the pair of substrates, and one of the pair of substrates. An electrode structure formed on the substrate for applying an electric field having a component predominantly parallel to the substrate surface to the liquid crystal layer; and an electrode structure disposed between the liquid crystal layer and the pair of substrates. A pair of alignment films, wherein the alignment film is formed of a diamine compound represented by the chemical formula H ₂ N—R—NH ₂ and a chemical formula: Is a dehydration-closed organic polymer of a polyamic acid composed of a tetracarboxylic dianhydride represented by the following formula, wherein R and X in the repeating structure have a bonding group capable of rotating the molecular axis of the polymer, -O -, - S -, - CH 2 -, - C (CH 3) 2
_{-, - C (CF 3)} 2 -, - SO 2 -, meta coupling, an active matrix type liquid crystal display device, wherein the ortho bond is 3 or less in total. 8. The active matrix type liquid crystal display device according to claim 7, wherein a glass transition temperature Tg of said alignment film is 300 ° C. or higher. 9. The active matrix type liquid crystal display device according to claim 7, wherein the organic polymer has a weight average molecular weight of 10,000 or more and 300,000 or less. 10. The active matrix type according to claim 7, wherein at least one of the alignment films is an organic polymer having a dispersion coefficient represented by a ratio of weight average molecular weight / number average molecular weight of 2 or less. Liquid crystal display.