JP4100941B2 - Manufacturing method of liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a liquid crystal display which has high reliability by improving display characteristics simply and surely without generating inconvenience such as image persistence in display. <P>SOLUTION: In the liquid crystal display device, a polymer structure for alignment control is formed by applying an AC voltage having a frequency equal to or higher than 60 Hz being a frequency being twice as high as that in ordinary drive to a liquid layer and by maintaining the applied state. Thus, the alignment of liquid crystal molecules are not stipulated by the switching of the AC voltage but by middle states at the time of respective switching and the liquid crystal display device in which image persistence is very small and the disturbance of alignment is not generated is obtained. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and a method of manufacturing the same, and more particularly, a liquid crystal display device that controls the alignment of liquid crystal molecules by utilizing the alignment regulating force of a polymer structure that is a vertical alignment type and formed by photopolymerization. Is targeted.
[0002]
[Prior art]
Conventionally, as a liquid crystal display (LCD) using an active matrix, a liquid crystal material having a positive dielectric anisotropy is aligned horizontally in a dark state so as to be twisted by 90 degrees between opposing substrates. TN mode liquid crystal display devices are widely used.
[0003]
This TN mode liquid crystal display device has a problem that the viewing angle characteristic is inferior, and various studies have been made to improve the viewing angle characteristic. Therefore, as an alternative method, a liquid crystal material having negative dielectric anisotropy is vertically aligned, and the liquid crystal molecules at the time of voltage application are applied by protrusions and slits provided on the substrate surface without subjecting the alignment film to rubbing treatment. An MVA (Multi-domain Vertical Alignment) system that regulates the tilt direction in a plurality of directions has been developed, and has succeeded in greatly improving the viewing angle characteristics.
[0004]
[Problems to be solved by the invention]
The MVA type liquid crystal display device is superior in viewing angle characteristics as compared with the conventional TN type, but has the disadvantages of low white luminance and dark display. This is mainly because the banks and slits are the division boundaries of the liquid crystal alignment, and this portion appears to be optically dark, resulting in low white display transmittance. To improve this, the gap between the banks and slits should be wide enough, but in this case, there will be fewer banks and slits controlling the liquid crystal alignment, so it will take time to stabilize the alignment, Response speed is slow.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and is a method for manufacturing a liquid crystal display device that improves display characteristics easily and reliably without causing inconveniences such as burn-in on a display and realizes a highly reliable liquid crystal display. It aims to provide a method.
[0006]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has conceived the following aspects of the invention.
[0007]
According to the method for manufacturing a liquid crystal display device of the present invention, a first substrate having a first electrode and a second substrate having a second electrode are arranged with a liquid crystal layer formed of an alignment film and a vertically aligned liquid crystal. The liquid crystal display device is disposed opposite to each other, and the liquid crystal layer made of liquid crystal mixed with a monomer for aligning liquid crystal molecules in a predetermined direction is formed between the first substrate and the second substrate. In the state of being sandwiched between them, while applying an alternating voltage between the substrates, the monomer is polymerized to form a polymer structure of a predetermined alignment pattern, and when the alignment of liquid crystal molecules is regulated by the polymer structure, The frequency of the alternating voltage is controlled to a value such that the switching speed of the alternating voltage is greater than the response speed of the liquid crystal molecules, and the burn-in rate is adjusted to 5% or less .
[0008]
Specifically, the frequency of the AC voltage is preferably 60 Hz to 1 kHz.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
-Basic outline of the present invention-
First, the basic outline of the present invention will be described.
The inventors of the present invention have improved the MVA liquid crystal display device to increase the aperture ratio, increase the brightness, and improve the level of cost by mixing a monomer that undergoes photopolymerization or thermal polymerization into the liquid crystal. An alignment regulation technique has been developed that obtains stable alignment by polymerizing monomers while applying a predetermined voltage between the substrates.
[0010]
However, it has been clarified that the alignment regulation technique has a problem that the degree of burn-in of the liquid crystal panel during driving is worse than that of a panel that does not use a method of solidifying with a monomer material or the like.
[0011]
The image sticking ratio α of the panel is obtained as follows.
A black and white checker pattern is displayed in the display area of the liquid crystal display device for a long time. Thereafter, a predetermined halftone is displayed on the entire display area, the difference (β−γ) between the brightness β of the white display area and the brightness γ of the black display area is obtained, and the brightness difference (β−γ) is displayed in black. Divide by the luminance γ of the area to obtain the burn-in rate.
That is,
Image sticking rate α = ((β−γ) / γ) × 100 (%)
Defined in
[0012]
If the burn-in rate α is about 5 to 6%, there is no practical problem, but if it is about 10%, the user will be concerned about the image burn-in phenomenon and cannot be ignored.
[0013]
Usually, when driving a liquid crystal display device, an AC voltage is applied to the liquid crystal layer to prevent burn-in. However, since the pair of substrates sandwiching the liquid crystal layer has different layer structures and formed electrodes, polarity is generated between the substrates, which affects the AC voltage. As a result, even when an AC voltage having a certain value is applied to the liquid crystal display device from the external voltage application device, the voltage applied to the liquid crystal layer has two values that differ depending on the switching of the AC voltage. As the voltage value changes, the alignment and state of the liquid crystal change.
[0014]
For this reason, when an alternating voltage with a frequency of 30 Hz for normal driving is applied to the liquid crystal layer and a polymer structure for alignment control is formed while maintaining the applied state, alignment disturbance caused by instantaneous voltage change remains. The orientation direction is defined as it is. When the alignment disorder occurs, image sticking is observed in the liquid crystal display device and display characteristics are deteriorated.
[0015]
The present inventor has conceived to increase the frequency of the AC voltage applied to the liquid crystal layer in order to suppress burn-in.
Therefore, when the relationship between the frequency of the AC voltage and the burn-in rate was examined, as shown in FIG. 1, the frequency of the AC voltage was 60 Hz, and the burn-in rate showed a minimum value of 5% or less. When the frequency is further increased, the burn-in rate gradually increases (at 1 kHz, the frequency is approximately equivalent to 30 Hz), so the appropriate frequency range is 60 Hz to 1 kHz.
[0016]
The change in the burn-in rate is because the response speed of the liquid crystal molecules cannot catch up with the switching speed of the AC voltage when the frequency of the AC voltage is larger than that of normal driving, for example, about twice (60 Hz). For this reason, the orientation of the liquid crystal molecules is defined by an intermediate state at the time of each switching, regardless of the switching of the AC voltage. By forming the polymer in this state, it is possible to obtain a liquid crystal display device with good display characteristics with little image sticking and no alignment disorder.
[0017]
-Specific Embodiment-
Based on the basic outline of the present invention described above, specific embodiments will be described. Here, a liquid crystal display device having a main configuration as shown in FIG. 2 is targeted.
[0018]
The liquid crystal display device includes a pair of transparent glass substrates 11 and 12 facing each other with a predetermined interval, and a liquid crystal layer 13 sandwiched between the transparent glass substrates 11 and 12. The transparent glass substrates 11 and 12 are bonded and fixed by a sealing material (not shown).
[0019]
On one transparent glass substrate (TFT substrate) 11, a plurality of pixel electrodes 15 made of ITO and thin film transistors (TFT: not shown) serving as active elements are formed via an insulating layer 14. A transparent vertical alignment film 16 a is formed so as to cover 15, and a color filter 17 (and a black matrix not shown) and a common electrode (counter electrode) 18 are formed on the other transparent glass substrate (CF substrate) 12. The vertical alignment film 16b is sequentially stacked. Then, the vertical alignment films 16 a and 16 b are abutted so as to sandwich the liquid crystal layer 13, the glass substrates 11 and 12 are fixed by a sealing material, and polarizers 19 and 20 are provided outside the substrates 11 and 12. The pixel electrode 15 is formed together with an active matrix (TFT matrix), and in the illustrated example, the data bus line 21 to which the drain electrode of the TFT is connected is shown. Although not shown, gate bus lines to which the gate electrodes of the TFTs are connected are also formed. Note that the electrode may be provided only on one substrate.
[0020]
The liquid crystal layer 13 is formed by injecting liquid crystal from a liquid crystal injection port provided in the sealing material. In the present embodiment, the liquid crystal is a mixture of monomers that are photopolymerized or thermally polymerized. Further, the pixel electrode 15 is formed with fine slits 15a for forming an alignment pattern, for example, as shown in FIG. Then, as shown in FIG. 4, the monomer is polymerized by applying UV irradiation or heat treatment while applying a predetermined AC voltage to the injected liquid crystal, in this embodiment, an AC voltage of 60 Hz to 1 kHz, thereby slitting the monomer 15a. The polymer structure 13a regulated by the alignment pattern is formed on the surface layer of the liquid crystal layer 13 (surfaces of the vertical alignment films 16a and 16b), and the liquid crystal molecules are aligned according to the alignment pattern by the polymer structure. .
[0021]
In this embodiment, a liquid crystal display device having a pixel pitch of 297 μm and a pixel number of 1024 × 768 was actually manufactured.
On one substrate (TFT substrate), a pixel electrode formed with a TFT element, a data bus line, a gate bus line, and a fine slit for regulating alignment was formed. A color filter and a common electrode were formed on the other substrate (CF substrate). As the substrate material, a glass substrate OA-2 (manufactured by Nippon Electric Glass) having a thickness of 0.7 mm was used. The fine slit was formed to extend from the center of the pixel in four directions (upper right, lower right, upper left, lower left). The slit width was 3 μm and the distance between the slits was 3 μm. A vertical alignment film (polyimide material) was formed on these substrates using a printing method, and heat treatment was performed at 180 ° C. for 60 minutes. These substrates were bonded together via a spacer (made by Sekisui Fine Chemical) having a diameter of 4 μm to produce an empty cell. A liquid crystal panel with a negative dielectric anisotropy added with a small amount of a photopolymerizable monomer was injected into the cell thus obtained to produce a liquid crystal panel. The addition amount of the photopolymerizable monomer was 0.3 wt%.
[0022]
Next, UV light was applied to the panel while applying an alternating voltage (10 V) having a frequency of 60 Hz, which is twice that of normal driving, to solidify the photopolymerizable monomer. The amount of light irradiation was about 4000 mJ / cm ² (wavelength 365 nm). There was no disorder in the alignment state in the pixel, and the burn-in rate α measured after displaying the black and white checker pattern for 48 hours was 5%.
[0023]
(Comparative example)
A comparative example of this embodiment will be described. This comparative example is the same as this embodiment except for the following requirements.
The voltage for solidifying the photopolymerizable monomer was an alternating voltage (10 V) with a normal frequency of 30 Hz, and UV light was applied.
[0024]
In this case, unlike the case of the present embodiment, a slight disturbance occurred in the alignment state in the pixel, and the burn-in rate α measured after displaying the black and white checker pattern for 48 hours was 10%.
[0025]
As described above, according to the manufacturing method of the liquid crystal display device of the present embodiment, the display characteristics can be improved easily and reliably without causing inconvenience such as burn-in on the display, and a highly reliable liquid crystal display is realized. It becomes possible.
[0026]
Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.
[0027]
(Supplementary note 1) A method for manufacturing a liquid crystal display device, in which a first substrate having a first electrode and a second substrate having a second electrode are arranged to face each other with an alignment film and a liquid crystal layer interposed therebetween. And
An alternating voltage is applied between the substrates in a state where the liquid crystal layer made of a liquid crystal mixed with a monomer for aligning liquid crystal molecules in a predetermined direction is sandwiched between the first substrate and the second substrate. However, when the monomer is polymerized to form a polymer structure having a predetermined alignment pattern, and the liquid crystal molecules are regulated by the polymer structure,
A method for manufacturing a liquid crystal display device, characterized in that the frequency of the AC voltage is controlled to a value such that the switching speed of the AC voltage is greater than the response speed of liquid crystal molecules.
[0028]
(Additional remark 2) The manufacturing method of the liquid crystal display device of Additional remark 1 characterized by the above-mentioned.
[0029]
(Supplementary note 3) The method for manufacturing a liquid crystal display device according to supplementary note 1 or 2, wherein the frequency of the AC voltage is 60 Hz or more.
[0030]
(Additional remark 4) The frequency of the said alternating voltage is 1 kHz or less, The manufacturing method of the liquid crystal display device of Additional remark 3 characterized by the above-mentioned.
[0031]
(Supplementary note 5) The method for manufacturing a liquid crystal display device according to any one of supplementary notes 1 to 4, wherein a slit for regulating the alignment pattern is formed in the first electrode.
[0032]
(Additional remark 6) The said monomer is polymerized by light irradiation or heat processing, and the said polymer structure is formed, The manufacturing method of the liquid crystal display device of any one of additional marks 1-5 characterized by the above-mentioned.
[0033]
【The invention's effect】
According to the present invention, it is possible to obtain a liquid crystal display device that can easily and surely improve display characteristics and realize a highly reliable liquid crystal display without causing inconvenience such as image sticking to the display.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the relationship between the frequency of an AC voltage and the burn-in rate.
FIG. 2 is a cross-sectional view showing the main configuration of the liquid crystal display device of the present embodiment.
FIG. 3 is a plan view showing a part of a pixel electrode in which fine slits for forming an alignment pattern are formed.
FIG. 4 is a cross-sectional view showing a state when a liquid crystal layer is formed.
[Explanation of symbols]
11 and 12 Transparent glass substrate 13 Liquid crystal layer 13a Polymer structure 14 Insulating layer 15 Pixel electrode 15a Fine slits 16a and 16b Alignment film 17 Color filter 18 Common electrodes 19 and 20 Polarizer 21 Data bus line

Claims (5)

Manufacture of a liquid crystal display device in which a first substrate having a first electrode and a second substrate having a second electrode are arranged to face each other with a liquid crystal layer made of an alignment film and a vertically aligned liquid crystal. A method,
An alternating voltage is applied between the substrates in a state where the liquid crystal layer made of a liquid crystal mixed with a monomer for aligning liquid crystal molecules in a predetermined direction is sandwiched between the first substrate and the second substrate. However, when the monomer is polymerized to form a polymer structure having a predetermined alignment pattern, and the liquid crystal molecules are regulated by the polymer structure,
A method for manufacturing a liquid crystal display device, wherein the frequency of the AC voltage is controlled to a value such that the switching speed of the AC voltage is greater than the response speed of liquid crystal molecules, and the burn-in rate is adjusted to 5% or less .   The method of manufacturing a liquid crystal display device according to claim 1, wherein the AC voltage is a rectangular wave.   The method for manufacturing a liquid crystal display device according to claim 1, wherein the frequency of the AC voltage is 60 Hz or more.   The method of manufacturing a liquid crystal display device according to claim 3, wherein the frequency of the AC voltage is 1 kHz or less.   The method for manufacturing a liquid crystal display device according to claim 1, wherein a slit for regulating the alignment pattern is formed in the first electrode.

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