JP4937787B2 - Liquid crystal display device and manufacturing method thereof - Google Patents

Description

  In the present invention, a liquid crystal material containing a polymerizable component (such as a monomer or oligomer) that is polymerized by light or heat is sealed between substrates, and the voltage applied to the liquid crystal layer is adjusted (the applied voltage is 0 (zero)). Hereinafter, a liquid crystal display device (LCD) that polymerizes a polymerizable component and defines the orientation direction of liquid crystal molecules during driving, and its It relates to a manufacturing method.

  As a liquid crystal display device having superior viewing angle characteristics as compared with a conventional TN (twisted nematic) mode LCD, an IPS mode (In−) in which a liquid crystal having positive dielectric anisotropy is horizontally aligned and a lateral electric field is applied. 2. Description of the Related Art (Plane-Switching mode) liquid crystal display devices (hereinafter abbreviated as IPS-LCDs) are known. However, in the IPS-LCD, liquid crystal molecules are switched in a horizontal plane by a comb-shaped electrode, and the aperture ratio of the pixel is remarkably lowered by the comb-shaped electrode, so that a backlight unit having a high light intensity is required.

  On the other hand, a multi-domain vertical alignment mode in which liquid crystals having negative dielectric anisotropy are vertically aligned, and banks (linear protrusions) and electrode cutouts (slits) are provided on the substrate as alignment control structures. A multi-domain vertical alignment mode (hereinafter abbreviated as MVA-LCD) is known. Since the alignment regulating structure is provided, the liquid crystal alignment azimuth during voltage application can be controlled to a plurality of azimuths without applying a rubbing treatment to the alignment film, and the viewing angle characteristics are excellent.

  However, although the reduction in the actual aperture ratio of the pixels due to the protrusions and slits in the MVA-LCD is not as high as that of the comb-shaped electrode of the IPS-LCD, the light transmittance of the panel is lower than that of the TN mode LCD. Therefore, at present, it is considered that MVA-LCD and IPS-LCD are not suitable for notebook computers that require low power consumption.

  Further, the conventional MVA-LCD has a defect that the white brightness is low and the display is dark. The main reason for this is that the upper part of the protrusion and the upper part of the slit are the boundary of the alignment division and dark lines are generated, so that the transmittance at the time of white display is lowered and it looks dark. In order to remedy this drawback, the spacing between the protrusions and slits should be sufficiently wide. However, since the number of protrusions and slits that are alignment regulating structures is reduced, the alignment does not occur even when a predetermined voltage is applied to the liquid crystal. There is a problem that it takes time to stabilize and the response time becomes long.

  In order to solve this problem and to realize an MVA-LCD which can respond with high brightness and high speed, a method for defining the alignment direction of liquid crystal molecules during driving using a polymer has been proposed. In the method of defining the alignment direction of liquid crystal molecules at the time of driving using a polymer, a liquid crystal material in which a polymerizable component such as a monomer or an oligomer (hereinafter abbreviated as a monomer) is mixed with liquid crystal is sealed between substrates. The monomer is polymerized by applying a voltage between the substrates and tilting the liquid crystal molecules. As a result, a liquid crystal layer that tilts at a predetermined pretilt angle even when voltage application is removed is obtained. As the monomer, a material that is polymerized by heat or light (ultraviolet rays) is selected.

  However, in an MVA-LCD manufactured by a method that uses a polymer to define the orientation direction of liquid crystal molecules during driving, if the same image is displayed for a long time, the previous image remains and is visible even if the display is changed. There is a problem that image sticking may occur and display quality deteriorates.

  An object of the present invention is to provide a liquid crystal display device and a method for manufacturing the same, which improve an image sticking phenomenon that occurs based on a method of defining the alignment direction of liquid crystal molecules during driving using a polymer.

  The object is a liquid crystal display device in which a liquid crystal material is sealed between two opposing substrates, the liquid crystal material comprising a polymerizable component that is polymerized by light or heat, a polymerization initiator, and a liquid crystal composition. And the concentration x of the polymerization initiator in the liquid crystal material is 0 ≦ x ≦ 0.002 (wt%).

  A liquid crystal display device and a method for manufacturing the same according to an embodiment of the present invention will be described with reference to FIGS. First, an outline of the liquid crystal display device and the manufacturing method thereof according to the present embodiment will be described with reference to FIG. FIG. 1 shows a state in which one pixel 2 of the liquid crystal display device according to the present embodiment is viewed in the normal direction of the substrate surface. A pixel 2 is formed in a rectangular region defined by a gate bus line 4 and a drain bus line 6 that intersect with each other via an insulating film (not shown). In the upper left of the pixel 2 in the figure, a TFT 16 that functions as a switching element for applying a gradation voltage to a pixel electrode described later is formed. In the pixel 2, cross-shaped connection electrodes 12 and 14 that are divided into four alignment domains having the same outer periphery are formed. The connection electrode 12 is formed in parallel with the drain bus line 6 at approximately the center in the pixel 2, and the connection electrode 14 is formed on the storage capacitor bus line 18 that substantially crosses the center in the pixel 2.

  A plurality of striped electrodes 8 having a fine electrode pattern are repeatedly formed at an angle of approximately 45 ° from the connection electrodes 12 and 14. The connection electrodes 12 and 14 and the plurality of stripe electrodes 8 constitute a pixel electrode. The striped electrode 8 at the upper left in the figure is electrically connected to the source electrode of the TFT 16. A space 10 is formed between the adjacent striped electrodes 8 with the electrodes removed. The stripe-shaped electrode 8 and the space 10 constitute an alignment regulating structure. Of course, instead of the striped electrode 8 and the space 10 in FIG. 1, fine linear protrusions may be formed on the pixel electrode formed on the entire surface of the pixel 2. Although illustration is omitted, an insulating structure or a slit (a part of the common electrode partially removed by patterning) is also formed on the counter substrate corresponding to the alignment regulating structure formed on the pixel electrode side. Of course.

  After forming such a fine line and space pattern on the pixel electrode of the pixel 2 of the TFT substrate, a vertical alignment film is formed on the opposing surface of the TFT substrate and the opposing substrate. Various materials can be applied as the material of the vertical alignment film, but a polyamic acid type alignment film can be used as an example.

  Next, the negative type liquid crystal having negative dielectric anisotropy is sealed and the two substrates are bonded together. In the negative liquid crystal, a polymerizable component is mixed in a predetermined ratio. As the polymerizable component, a diacrylate monomer is used.

  FIG. 2 shows a process of irradiating ultraviolet rays while applying a voltage to the liquid crystal layer of the LCD panel. As shown in FIG. 2, the LCD panel is placed in the chamber of the ultraviolet irradiation device 32. The liquid crystal molecules in the liquid crystal composition before polymerizing the monomers in the LCD panel are aligned substantially perpendicular to the substrate surface. Next, a voltage is applied from the voltage application device 30 between the electrodes 34 and 36 provided on both substrates of the LCD panel. Thus, a voltage is applied to the liquid crystal layer 38 sealed between the electrodes 34 and 36, and the liquid crystal molecules in the pixel 2 are tilted in a predetermined direction. While continuing to apply a voltage from the voltage application device 30, ultraviolet light (UV light) is irradiated toward the LCD panel surface from a high-pressure mercury lamp (not shown) of the ultraviolet irradiation device 32. As a result, the liquid crystal material to which the monomer has been added is irradiated with ultraviolet light, the monomer is polymerized and polymerized, and the alignment direction of the liquid crystal molecules during normal driving is defined.

  FIG. 3 shows a state in which one pixel 2 of the MVA-LCD having another configuration is viewed in the normal direction of the substrate surface. The configuration shown in FIG. 3 is characterized in that the pixel electrode 3 on the TFT substrate side on which the TFT 16 is formed is a striped electrode having a line and space pattern. As shown in FIG. 3, the pixel electrode 3 includes a striped electrode 8 and a space 10 in which a line and space pattern is formed in parallel to the drain bus line 6.

  Each striped electrode 8 is electrically connected by a connection electrode 14 formed substantially in the center of the pixel 2 and parallel to the gate bus line 4. A part of the striped electrode 8 is connected to a source electrode 22 disposed opposite to the drain electrode 20 of the TFT 16.

  A linear protrusion extending in parallel with the gate bus line 4 is formed at a position facing the connection electrode 14 in the center of the pixel region of the counter substrate (not shown). The alignment protrusion direction of the liquid crystal molecules can be more clearly determined by the linear protrusion.

  In the same manner as the configuration shown in FIG. 2, a voltage is applied to a liquid crystal layer (not shown) so that liquid crystal molecules in the pixel 2 are tilted in a predetermined direction, and the liquid crystal material to which the monomer is added is irradiated with ultraviolet light. By polymerizing the monomer, stabilization of the pretilt angle and / or orientation orientation of the liquid crystal molecules can be realized.

  In the LCD manufactured by the manufacturing method described above, various monomers and polymerization initiators are used in order to reduce image sticking phenomenon caused by adopting a method of defining the alignment direction of liquid crystal molecules during driving using a polymer. And liquid crystal compositions (liquid crystal molecules) were studied. As a result, it was found that the polymerization initiator is effective in reducing the optimum ultraviolet irradiation amount and increasing the production efficiency, but causes image burn-in. In the case of an LCD that uses a polymer to define the alignment direction of liquid crystal molecules when a voltage is applied, if the concentration of the polymerization initiator that helps start the polymerization of the monomer during UV irradiation is high, the time required for the polymerization is shortened, but it has been completed. The image sticking phenomenon of the LCD display image is relatively deteriorated. Further, when no polymerization initiator is added to the liquid crystal material, the time required for the polymerization becomes longer, but the degree of image sticking phenomenon of the display image of the completed LCD is relatively reduced. Therefore, in order to improve the seizure phenomenon, the concentration of the polymerization initiator is preferably low.

That is, the image sticking phenomenon can be reduced by adding no monomer polymerization initiator in the liquid crystal material or polymerizing the monomer with a very small addition amount.
The concentration x (wt%) of the polymerization initiator in the liquid crystal material before polymerization, the concentration y in the liquid crystal material before polymerization of the monomer, the concentration z in the liquid crystal material before polymerization of the liquid crystal composition, When the seizure rate α is set, the concentration x of the polymerization initiator is preferably 0 ≦ x ≦ 0.002 (wt%). In particular, when x = 0, the image sticking rate α is the lowest. The monomer concentration y is preferably 0.1 wt% or more and 10 wt% or less from the viewpoint of the image sticking rate α.

The image sticking rate α is obtained as follows. A black and white checker pattern is displayed on the LCD display area 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 (%)
It is.

  FIG. 4 shows the relationship between the concentration of the polymerization initiator and the seizure rate. In FIG. 4, the horizontal axis represents the concentration (wt%) of the polymerization initiator, and the vertical axis represents the seizure rate (%). As described above, the concentration of the polymerization initiator is preferably 0.002 wt% or less, and the image sticking rate α is lowest when no polymerization initiator is added to the liquid crystal material. From the viewpoint of a general observer, if the image sticking ratio α of the LCD is about 5 to 6%, there is no practical problem, and if it becomes about 10%, the image sticking phenomenon will be anxious. From the graph shown in FIG. 4, if the polymerization initiator concentration is 0.002 wt% or less, the seizure rate is 6% or less, and a practically satisfactory characteristic can be obtained. When the polymerization initiator concentration is 0%, that is, when no polymerization initiator is used, an extremely low seizure rate α of about 3% can be obtained.

  The liquid crystal display device according to the present embodiment and the method for manufacturing the same will be specifically described below using examples and comparative examples. In all the following examples and comparative examples, the MVA-LCD having the structure shown in FIG. 1 is used. That is, a vertical alignment film is formed, and the liquid crystal has negative dielectric anisotropy. In addition, the two polarizing plates opposed to each other with both substrates interposed therebetween are in a normally black mode in which the crossed Nicols are arranged and black display is performed when no voltage is applied. In addition, the polarization axis of a polarizing plate (not shown) is oriented in a direction substantially parallel or orthogonal to each bus line. The panel size is 15 inches diagonal and the resolution is XGA.

[Example 1]
A liquid crystal material in which 0.3 wt% of a photocurable diacrylate monomer having a molecular weight of about 350 was mixed with a liquid crystal composition having an average molecular weight of about 350, and a liquid crystal material mixed with 0.006 wt% of a polymerization initiator was sealed between the substrates. Next, the monomer was polymerized in a state where a voltage was applied to the liquid crystal layer, and the direction in which the liquid crystal molecules fell was stored. The ultraviolet rays for polymerizing the monomer are irradiated at room temperature (20 ° C.), and the irradiation energy is 10 J / cm ² (using the same ultraviolet irradiation apparatus as in Comparative Example 1 below, the ultraviolet irradiation time in Comparative Example 1). Irradiation for 10 times). The burn-in rate α measured after displaying the black and white checker pattern for 48 hours on the completed MVA-LCD was 15%.

[Example 2]
The liquid crystal composition having an average molecular weight of about 350 was mixed with 0.3 wt% of a photocurable diacrylate monomer having a molecular weight of about 350, and a liquid crystal material not mixed with any polymerization initiator was sealed between the substrates. Next, the monomer was polymerized in a state where a voltage was applied to the liquid crystal layer, and the direction in which the liquid crystal molecules fell was stored. The ultraviolet rays for polymerizing the monomers are irradiated at room temperature (20 ° C.), and the irradiation energy is 100 J / cm ² (using the same ultraviolet irradiation apparatus as in Comparative Example 1 below, the ultraviolet irradiation time in Comparative Example 1). Irradiated 100 times longer). The burn-in rate α measured after displaying the black and white checker pattern for 48 hours on the completed MVA-LCD was 3%.

[Comparative Example 1]
A liquid crystal material in which 0.3 wt% of a photocurable diacrylate monomer having a molecular weight of about 350 was mixed with a liquid crystal composition having an average molecular weight of about 350, and a liquid crystal material mixed with 0.008 wt% of a polymerization initiator was sealed between the substrates. Next, the monomer was polymerized in a state where a voltage was applied to the liquid crystal layer, and the direction in which the liquid crystal molecules fell was stored. The ultraviolet rays for polymerizing the monomer are irradiated at room temperature (20 ° C.), and the irradiation energy is 1 J / cm ² . The burn-in rate α measured after displaying a black and white checker pattern for 48 hours on the completed MVA-LCD was 35%.

  Under either condition, the LCD panel after the ultraviolet irradiation was able to obtain almost the same optical characteristics. As shown in Examples 1 and 2 and Comparative Example 1, if the polymerization initiator concentration is lowered or no polymerization initiator is added at all, the burn-in phenomenon of the display image of the completed LCD is greatly reduced. Can be made.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, although diacrylate is used as a monomer in the above embodiment, the present invention is not limited to this. For example, triacrylate may be used as a polymerizable component as a polyfunctional polymer.

  In the above embodiment, the monomer is exemplified as a polymerizable component for stabilizing liquid crystal alignment using a polymer. However, the present invention is not limited to this, and an oligomer or a mixture of an oligomer and a monomer is used. Of course, it may be used as a polymerizable component.

The liquid crystal display device and the manufacturing method thereof according to the embodiment described above are summarized as follows.
(Appendix 1)
A liquid crystal display device in which a liquid crystal material is sealed between two opposing substrates,
The liquid crystal material is
A polymerizable component that is polymerized by light or heat, a polymerization initiator, and a liquid crystal composition,
The concentration x of the polymerization initiator is
0 ≦ x ≦ 0.002 (wt%)
A liquid crystal display device characterized by

(Appendix 2)
In the liquid crystal display device according to appendix 1,
The liquid crystal display device, wherein the polymerizable component is polymerized by irradiation with ultraviolet rays.

(Appendix 3)
In the liquid crystal display device according to appendix 1 or 2,
A concentration y of the polymerizable component in the liquid crystal material is 0.1 ≦ y ≦ 10 (wt%).

(Appendix 4)
In the liquid crystal display device according to any one of appendices 1 to 3,
The liquid crystal display device, wherein the polymerizable component is diacrylate.

(Appendix 5)
In the liquid crystal display device according to any one of appendices 1 to 4,
A liquid crystal display device, wherein liquid crystal molecules in the liquid crystal composition before polymerization of the polymerizable component are aligned substantially perpendicular to the substrate surface.

(Appendix 6)
A liquid crystal material containing a polymerizable component that is polymerized by light or heat is sealed between the substrates,
In the method of manufacturing a liquid crystal display device that regulates the alignment direction of liquid crystal molecules during driving by polymerizing the polymerizable component while applying a voltage to the liquid crystal material,
The method of manufacturing a liquid crystal display device, wherein the concentration x of the polymerization initiator in the liquid crystal material is 0 ≦ x ≦ 0.002 (wt%).

(Appendix 7)
In the method for manufacturing a liquid crystal display device according to appendix 6,
The method for producing a liquid crystal display device, wherein the polymerizable component is polymerized by irradiation with ultraviolet rays.

(Appendix 8)
In the method for manufacturing a liquid crystal display device according to appendix 6 or 7,
The method of manufacturing a liquid crystal display device, wherein the concentration y of the polymerizable component in the liquid crystal material is 0.1 ≦ y ≦ 10 (wt%).

(Appendix 9)
In the method for manufacturing a liquid crystal display device according to any one of appendices 6 to 8,
The method for producing a liquid crystal display device, wherein the polymerizable component is diacrylate.

(The invention's effect)
As described above, according to the present invention, it is possible to improve the image burn-in phenomenon that occurs based on the method of defining the alignment direction of liquid crystal molecules during driving using a polymer.

It is a figure explaining the outline of the liquid crystal display device by one embodiment of this invention, and its manufacturing method. It is a figure which shows the process of irradiating an ultraviolet-ray, applying a voltage to the liquid crystal layer of a LCD panel. It is a figure explaining the outline of another liquid crystal display device by one embodiment of the present invention, and its manufacturing method. It is a figure which shows the relationship between the density | concentration of a polymerization initiator, and the image sticking rate in one embodiment of this invention.

Explanation of symbols

2 Pixel 3 Pixel electrode 4 Gate bus line 6 Drain bus line 8 Striped electrode 10 Space 12, 14 Connection electrode 18 Storage capacitor bus line 20 Drain electrode 22 Source electrode 30 Voltage application device 32 Ultraviolet irradiation device 34, 36 Electrode 38 Liquid crystal layer

Claims (3)

A liquid crystal display device in which a liquid crystal material is sealed between two opposing substrates,
A pixel electrode is formed on at least one of the substrates ,
The pixel electrode, the connection electrode of cruciform, is constituted by a plurality of stripe-shaped electrodes extending from the connection electrode,
The liquid crystal material includes a diacrylate that is polymerized by light or heat, a polymerization initiator, and a liquid crystal composition.
The concentration y of the diacrylate in the liquid crystal material is y = 0.3 (wt%),
The concentration x of the polymerization initiator is 0 ≦ x ≦ 0.002 (wt%),
Liquid crystal molecules in the liquid crystal composition before polymerization of the diacrylate are aligned substantially perpendicular to the substrate surface,
The alignment direction of the liquid crystal molecules at the time of driving is defined by the polymer obtained by polymerizing the diacrylate ,
An alignment film and the polymer are formed in this order on opposite surfaces of the two substrates, respectively. The liquid crystal display device according to claim 1 .
The concentration x of the polymerization initiator is 0 <x ≦ 0.002 (wt%). The liquid crystal display device according to claim 1 or 2 ,
The liquid crystal display device, wherein the diacrylate is polymerized by irradiation with ultraviolet rays.

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