WO2012118006A1 - Liquid crystal display - Google Patents

Abstract

The present invention provides a liquid crystal display wherein a display failure such as flicker or image burn-in does not easily occur. This liquid crystal display is provided with: a pair of substrates (1, 2) and a liquid crystal layer (30) that is sandwiched between the pair of substrates. A liquid crystal compound (5) contained in the liquid crystal layer is aligned substantially perpendicular to the surfaces of the pair of substrates when no voltage is applied thereto. One of the pair of substrates, the substrate (1) has a pair of electrodes (15, 16), and the alignment of the liquid crystal compound (5) is controlled by the electric field generated by the pair of electrodes. The liquid crystal layer (30) has positive dielectric anisotropy, and the liquid crystal layer (30) has a specific resistance of 1.5 × 10¹⁴ Ω·cm or more.

Description

LCD display

The present invention relates to a liquid crystal display. More specifically, the present invention relates to a liquid crystal display suitable for a transverse bend alignment (TBA) mode.

A liquid crystal display is a display device with low power consumption, and can be reduced in weight and thickness, so that it is widely used for televisions, monitors for personal computers, and the like.

The display method of the liquid crystal display is determined by how the liquid crystals (liquid crystal compounds) are arranged. Conventionally used liquid crystal display methods include, for example, a TN (TwistedistNematic) mode liquid crystal display or a VA (Vertical Alignment) mode in which an electric field in a direction perpendicular to the substrate is applied to align liquid crystals. Can be mentioned. In addition, a display method in which an electric field (lateral electric field) in a direction parallel to the substrate is applied to align liquid crystals (see, for example, Patent Document 1), or a horizontal electric field is applied to liquid crystal with vertical alignment is driven. Also known is a transverse bend alignment (TBA) mode.

Here, the liquid crystal display described in Patent Document 1 in which a lateral electric field is applied to the liquid crystal will be described in detail with reference to FIG. The liquid crystal display includes a liquid crystal layer 230 sandwiched between a pair of transparent substrates 211 and 221. A common electrode 216, a dielectric layer 218, a pixel electrode 215, and an alignment film 212 are formed in this order on the liquid crystal layer side main surface of the transparent substrate 211, and a polarizing plate 241 is attached to the opposite main surface. The On the other hand, an alignment film 222 is formed on the main surface of the transparent substrate 221 on the liquid crystal layer side, and a polarizing plate 251 is attached to the main surface on the opposite side. As shown in FIG. 10, an electric field (lateral electric field) in a direction parallel to the transparent substrates 211 and 221 is applied to the liquid crystal layer 230 by the pixel electrode 215 and the common electrode 216, and the liquid crystal is aligned. Moreover, in the liquid crystal display described in Patent Document 1, it is disclosed that the specific resistance of the liquid crystal is 1 × 10 ⁹ Ω · cm or more and 1 × 10 ¹⁴ Ω · cm or less.

Further, in a TBA mode liquid crystal display, a lateral electric field is applied to a liquid crystal having positive dielectric anisotropy and aligned in a vertical direction in a state where no voltage is applied.

Japanese Patent Laid-Open No. 7-306417

However, in the liquid crystal display in these various display modes, display defects such as flicker and burn-in caused by the liquid crystal layer may occur. Since these display defects lower the display quality, it has been required to suppress the occurrence of defects due to the liquid crystal layer and to sufficiently exhibit excellent display performance.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a TBA mode liquid crystal display in which display defects such as flicker and burn-in caused by a liquid crystal layer are unlikely to occur.

When the present inventors examined the cause of occurrence of flicker and image sticking, it was found that the cause is impurity ions in the liquid crystal layer. Specifically, flicker is generated when a direct current component due to impurity ions rides on an alternating current signal for driving the liquid crystal and the alternating current signal is not symmetric. Further, image sticking occurs due to an electric field generated by accumulation of impurity ions in the liquid crystal layer at the interface between the alignment film and the liquid crystal layer. The inventors of the present invention have focused on the fact that the liquid crystal material is deteriorated by ultraviolet irradiation, and as a result, impurity ions are generated. Furthermore, as a result of intensive studies by the present inventors, the impurity ions are: (1) a liquid crystal produced by a liquid crystal dropping method (ODF; One drop fill process) in which a seal pattern is formed by an ultraviolet curable sealing material. It has been found that this occurs due to the ultraviolet rays irradiated in the manufacturing process of the display, or (2) the manufacturing process of the liquid crystal display which has an inlet and is sealed with an ultraviolet curable resin. Hereinafter, impurity ions generated in the liquid crystal layer due to ultraviolet rays irradiated in the manufacturing process of the liquid crystal display will be described as an example.

Here, the liquid crystal dropping method will be described with reference to FIG. FIG. 8 is a schematic cross-sectional view of a liquid crystal display in a mode in which liquid crystal molecules are vertically aligned with respect to a substrate during ultraviolet irradiation in the liquid crystal dropping method. In order to fabricate a liquid crystal display using the liquid crystal dropping method, first, the common electrode 116 is formed on the liquid crystal layer 130 side of the transparent substrate 121, and the alignment film 122 is further formed on the common electrode 116 (liquid crystal layer 130 side). To do. A dielectric layer 118 is formed on the liquid crystal layer 130 side of the transparent substrate 111, a pixel electrode 115 is formed on the dielectric layer 118 (liquid crystal layer 130 side), and further on the pixel electrode 115 (liquid crystal layer 130 side). An alignment film 112 is formed. Next, an ultraviolet curable sealant is applied to one of the transparent substrates 111 and 121 to form a seal pattern 123. Thereafter, a fine droplet of a liquid crystal material is dropped and applied onto the entire surface of the transparent substrate 111 or 121 on which the seal pattern 123 is formed with the UV curable sealing material being uncured, and the other transparent substrate is overlaid. As shown in FIG. 3, the seal pattern 123 is cured by irradiating with an ultraviolet ray 106. Further, when the ultraviolet curable sealing material has thermosetting properties in addition to ultraviolet curable properties, it is further heated to perform the main curing. Note that a color filter layer may exist between the transparent substrate 121 and the common electrode 116, and the unevenness of the color filter layer itself is flattened between the color filter layer and the common electrode 116, and the color filter layer There may be a dielectric layer for preventing elution of impurities. In general, in the liquid crystal dropping method, the liquid crystal material is dropped directly onto the transparent substrate, so that the liquid crystal display can be manufactured in a shorter time than the liquid crystal injection method in which the liquid crystal material is injected by capillary action.

FIG. 9 is a schematic cross-sectional view of a TBA mode liquid crystal display after ultraviolet irradiation manufactured by a liquid crystal dropping method. In the liquid crystal dropping step, ultraviolet rays are irradiated to cure the seal pattern 123 made of the ultraviolet curable sealing material. At this time, not only the seal pattern 123 but also the liquid crystal layer 130 is irradiated with ultraviolet rays. There is. Then, as shown in FIG. 9, impurity ions 131 are generated from the liquid crystal compound 105 included in the liquid crystal layer 130.

Similarly, in the liquid crystal injection method, when the injection port is sealed with an ultraviolet curable resin, the liquid crystal layer near the injection port may be irradiated with ultraviolet rays to generate impurity ions.

The present inventors have found that flicker and image sticking become noticeable when the amount of impurity ions generated exceeds a predetermined amount. Furthermore, when the generation amount of impurity ions due to ultraviolet rays is relatively large, the resistance of the liquid crystal layer becomes small, so that the specific resistance of the liquid crystal layer becomes small. Conversely, the generation amount of impurity ions due to ultraviolet rays is small. It has been found that when the amount is relatively small, the specific resistance of the liquid crystal layer increases because the resistance of the liquid crystal layer increases. At the same time, the inventors have a correlation between the specific resistance of the liquid crystal layer and the residual DC voltage, and when the residual DC voltage is 200 mV or less, there is no flicker or burn-in that reduces display performance. I found. That is, for example, when the specific resistance of the liquid crystal layer falls below a certain value due to ultraviolet irradiation, it has been found that the residual DC voltage becomes larger than 200 mV, and flicker and image sticking become noticeable. As a result of further intensive studies, it has been found that flicker and / or image sticking become noticeable when the specific resistance of the liquid crystal layer is less than 1.5 × 10 ¹⁴ Ω · cm. From the above, the present inventors can simultaneously reduce the residual DC voltage to 200 mV or less by forming a liquid crystal layer using a liquid crystal material having a specific resistance of at least 1.5 × 10 ¹⁴ Ω · cm or more. The inventors have found that the occurrence of flicker and / or burn-in can be suppressed and have conceived that the above-mentioned problems can be solved brilliantly, and have reached the present invention.

That is, an aspect of the present invention is a liquid crystal display including a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates, wherein the liquid crystal compound included in the liquid crystal layer is the pair of substrates when no voltage is applied. The substrate is oriented substantially perpendicularly to the substrate surface, and one of the pair of substrates has a pair of electrodes, and the pair of electrodes are opposed to each other with a gap in plan view. The orientation of the liquid crystal compound is controlled by the electric field generated by the electrode, the dielectric anisotropy of the liquid crystal layer is positive, and the liquid crystal layer has a specific resistance of 1.5 × 10 ¹⁴ Ω · cm or more. A liquid crystal display (hereinafter also referred to as “liquid crystal display of the present invention”).

In the liquid crystal display of the present invention, “the liquid crystal compound contained in the liquid crystal layer is aligned substantially perpendicular to the pair of substrate surfaces when no voltage is applied” specifically means that the pretilt angle of the liquid crystal layer is It is more preferably 86 ° (more preferably 88 °) or more and 90 ° or less. If the angle is less than 86 °, the front contrast is significantly reduced.

The configuration of the liquid crystal display of the present invention is not particularly limited by other components as long as such components are essential.

The preferable form in the liquid crystal display of this invention is demonstrated in detail below. In addition, the following preferable forms may be mutually combined suitably, and the form which combined the following two or more preferable forms with each other is also one of the preferable forms.

The dielectric constant anisotropy Δε of the liquid crystal layer is preferably 15 ≦ Δε ≦ 25 at 25 ° C. Such a liquid crystal layer can be suitably used for the liquid crystal display of the present invention.

The liquid crystal layer preferably has a specific resistance change rate of 32% or less before and after UV irradiation, and the specific resistance change rate is preferably as small as possible. Note that the small change rate of the specific resistance before and after the ultraviolet irradiation means that the amount of impurity ions generated by the ultraviolet irradiation is small, and the deterioration of display quality such as image sticking and flicker is more effectively suppressed. be able to.

The other of the pair of substrates (the one of the pair of substrates that does not have the pair of electrodes) preferably includes an electrode that covers at least the display region. Thereby, an oblique electric field can be applied to the liquid crystal layer. That is, the alignment of the liquid crystal compound in the liquid crystal layer can be controlled by this electrode and the pair of electrodes. Moreover, the response speed can be improved.

The liquid crystal display of the present invention preferably has a sealing member that encloses the liquid crystal layer (or liquid crystal) between the pair of substrates, and the sealing member does not have a liquid crystal inlet sealing member. A liquid crystal display that does not have an injection port for injecting liquid crystal material between substrates drops liquid crystal material on one of a pair of substrates, and seals the substrate on which the liquid crystal material is dropped with the other substrate. However, the liquid crystal layer may be irradiated with ultraviolet rays that are irradiated to cure the sealing material. At this time, even if the liquid crystal layer is irradiated with ultraviolet rays, flicker and image sticking can be suppressed if the specific resistance of the liquid crystal layer is 1.5 × 10 ¹⁴ Ω · cm or more. As described above, in the liquid crystal display in which the liquid crystal layer may be damaged by the ultraviolet irradiation in the manufacturing process, it is possible to particularly suitably suppress the deterioration of the display characteristics.

Another aspect of the present invention is surrounded by (1) a step of applying an ultraviolet curable sealing material (ultraviolet curable sealing material) to the first substrate, and (2) the sealing material of the first substrate. Or a step of dropping a liquid crystal material into a region of the second substrate facing the region surrounded by the sealing material of the first substrate, and (3) the first substrate so that the liquid crystal material is interposed A step of bonding a second substrate to one substrate; and (4) irradiating the sealing material between the first substrate and the second substrate bonded to each other with ultraviolet rays to cure the sealing material. A liquid crystal display manufacturing method including a step, wherein a specific resistance of the liquid crystal layer made of the liquid crystal material after the step (4) is 1.5 × 10 ¹⁴ Ω · cm or more (hereinafter referred to as a liquid crystal display manufacturing method). , "Method of manufacturing the liquid crystal display of the present invention Also referred to as ".) A.

In the step (4), the sealing material is irradiated with ultraviolet rays. At this time, the liquid crystal layer may be irradiated with ultraviolet rays. At this time, if the specific resistance of the liquid crystal layer after ultraviolet irradiation is kept at 1.5 × 10 ¹⁴ Ω · cm or more, even if the liquid crystal layer is irradiated with ultraviolet rays, display defects such as flicker and burn-in may occur. Generation | occurrence | production can be suppressed. Therefore, the manufacturing method of the liquid crystal display of this invention can be used suitably for the manufacturing method of the liquid crystal display accompanied by ultraviolet irradiation.

The manufacturing method of the liquid crystal display of the present invention is not particularly limited by other steps as long as such a step (in particular, a step of irradiating the sealing material with ultraviolet rays) is included as an essential step. Moreover, the preferable form in the liquid crystal display of this invention is applicable also to the manufacturing method of the liquid crystal display of this invention.

According to the present invention, it is possible to provide a liquid crystal display in which display defects such as flicker and burn-in are unlikely to occur, and a manufacturing method thereof.

3 is a schematic plan view of the liquid crystal display of Embodiment 1. FIG. FIG. 2 is a schematic cross-sectional view taken along the line AB in FIG. 1 and shows a state when a voltage is applied. FIG. 2 is a schematic cross-sectional view taken along the line AB in FIG. 1 and shows a state when no voltage is applied. The graph which shows the relationship between the specific resistance ((rho)) of the liquid crystal layer of the liquid crystal display produced using the liquid crystal material A, and the liquid crystal display produced using the liquid crystal material B, and the ultraviolet irradiation amount (UV irradiation amount). It is. 6 is a graph showing the relationship between the specific resistance (ρ) of the liquid crystal layer and the residual DC voltage (r−DC) in a liquid crystal display manufactured using the liquid crystal material A and a liquid crystal display manufactured using the liquid crystal material B. is there. 6 is a schematic cross-sectional view of a liquid crystal display according to Embodiment 2. FIG. 6 is a schematic plan view of a liquid crystal display according to Embodiment 2. FIG. It is a cross-sectional schematic diagram of the liquid crystal display during ultraviolet irradiation in the liquid crystal dropping method. It is a cross-sectional schematic diagram of the liquid crystal display after ultraviolet irradiation in the liquid crystal dropping method. 2 is a schematic cross-sectional view of a liquid crystal display described in Patent Document 1.

Hereinafter, the present invention will be described in more detail with reference to embodiments, but the present invention is not limited only to these embodiments.

(Embodiment 1)
The liquid crystal display according to this embodiment applies an electric field (lateral electric field) in the substrate surface direction (direction parallel to the substrate surface) to the liquid crystal layer, and controls the liquid crystal orientation to display an image. Among the methods, a transmissive liquid crystal display adopting a method called a TBA method (TBA mode).

In FIG. 1 below, one picture element (sub-pixel) is mainly illustrated. However, the display area (image display area) of the liquid crystal display according to the present embodiment is composed of a plurality of picture elements. A plurality of pixels are provided in a matrix. The display area includes a plurality of pixels and displays an image. However, when a light shielding area is provided within a picture element and / or between adjacent picture elements, the display area is an area including such a light shielding area. is there.

As shown in FIGS. 2 and 3, the liquid crystal display according to the present embodiment includes a liquid crystal display panel 100. The liquid crystal display panel 100 includes an active matrix substrate 1 that is a pair of substrates arranged opposite to each other, and an opposing substrate. It has a substrate 2 and a liquid crystal layer 30 sandwiched between them.

On the outer main surface of the active matrix substrate 1 and the counter substrate 2 (on the side opposite to the liquid crystal layer 30), a pair of polarizing plates 41 and 51 are provided. The polarizing plates 41 and 51 are arranged in crossed Nicols.

The substrates 1 and 2 are bonded together by a sealing member provided so as to surround the display area. Moreover, the board | substrates 1 and 2 are facing through spacers, such as a plastic bead. A vertical alignment type liquid crystal layer 30 is formed in the gap between the substrates 1 and 2 as a display medium constituting the optical modulation layer.

As described above, the liquid crystal display according to the present embodiment includes a pair of polarizing plates 41 and 51 arranged in a crossed Nicols manner and a vertical alignment type liquid crystal layer 30, and thus becomes a normally black mode liquid crystal display.

As shown in FIG. 2, the counter substrate 2 includes a colorless and transparent transparent substrate 21 made of glass, plastic, or the like. On the main surface on the liquid crystal layer 30 side of the transparent substrate 21, black that shields between pixels. A matrix (BM) layer, a plurality of color layers (color filters) provided in each pixel, a dielectric layer (insulating layer) 18 covering the BM layer and the color layers, and a liquid crystal layer 30 covering these components And an alignment film 22 provided on the side surface. The BM layer is formed from an opaque metal such as Cr, an opaque organic film such as an acrylic resin containing carbon, and the like, and is formed at the boundary between adjacent picture elements. On the other hand, the color layer is used for color display, and is formed of a light-transmitting organic film such as an acrylic resin containing a pigment, and is mainly formed in the pixel region. The dielectric layer 18 is formed from a thermosetting acrylic resin, a photocurable acrylic resin, or the like. The dielectric layer 18 need not be provided, but is preferably provided from the viewpoint of flattening the irregularities of the BM layer and the color layer itself and preventing impurity elution from the BM layer and the color layer. In the counter substrate 2, a second common electrode (counter electrode) may be formed on the liquid crystal layer 30 side of the transparent substrate 21 in addition to the common electrode 16 described later. In this case, the second common electrode is formed between the transparent substrate 21 and the dielectric layer 18 so as to cover the picture element. As a result, the electric field generated between the pixel electrode 15 and the common electrode 16 both formed in a comb-teeth shape in the active matrix substrate 1 and the second common electrode formed so as to cover the picture element in the counter substrate 2 is controlled. Thus, the transmittance can be further improved. Note that an optical film such as a retardation plate may be provided between the transparent substrate 21 and the polarizing plate 51.

As described above, the liquid crystal display of the present embodiment is a color liquid crystal display (active matrix liquid crystal display for color display) having a color layer on the liquid crystal layer 30 side of the counter substrate 2, and is R (red), G (green). ), B (blue), one pixel is composed of three picture elements that output each color light. In addition, the kind and number of the color of the picture element which comprises each pixel are not specifically limited, It can set suitably. That is, in the liquid crystal display of the present embodiment, each pixel may be composed of, for example, three color pixels of cyan, magenta, and yellow, or four or more color pixels (for example, R, G, B, and Yellow). The liquid crystal display of the present embodiment may be a monochrome liquid crystal display. In this case, it is not necessary to form a color layer on the counter substrate 2.

On the other hand, the active matrix substrate 1 includes a colorless and transparent transparent substrate 11 made of glass, plastic or the like. On the main surface of the transparent substrate 11 on the liquid crystal layer 30 side, a gate bus line 26, a Cs bus line, and a source bus are provided. Line 24, thin film transistor (TFT) 23 which is a switching element and is provided for each pixel, drain wiring (drain) 25 connected to each TFT 23, and provided separately for each pixel The pixel electrode 15, the common electrode 16 provided in common to each pixel, and the alignment film 12 provided on the surface on the liquid crystal layer 30 side so as to cover these components. Note that an optical film such as a retardation plate may be provided between the transparent substrate 11 and the polarizing plate 41.

The alignment films 12 and 22 provided on the active matrix substrate 1 and the counter substrate 2 are vertical alignment films, and are formed by coating from a general alignment film material such as polyimide. The vertical alignment film is not usually rubbed, but can align liquid crystal compounds (liquid crystal molecules) substantially perpendicular to the film surface when no voltage is applied. Therefore, as shown in FIG. 3, the liquid crystal compound 5 is aligned substantially perpendicular to the surfaces of the substrates 1 and 2 when no voltage is applied.

An image signal (video signal) is supplied to the pixel electrode 15 via a TFT 23 from a source bus line 24 extending in the vertical direction between adjacent picture elements. Thus, a rectangular wave is applied to the pixel electrode 15 according to the image signal. Each pixel electrode 15 is electrically connected to the drain wiring 25 of the TFT through a contact hole provided in the interlayer insulating film. The common electrode 16 is supplied with a common signal common to the picture elements. Further, the common electrode 16 is connected to a common voltage generation circuit and is set to a predetermined potential (typically 0 V).

The source bus line 24 is connected to a source driver (data line driving circuit). A gate bus line 26 connected to a gate driver (scanning line driving circuit) extends in the left-right direction between adjacent picture elements. The gate bus line 26 also functions as a gate of the TFT 23, and a scanning signal supplied in a pulse manner from the gate driver to the gate bus line 26 at a predetermined timing is applied to each TFT 23 in a line sequential manner. An image signal supplied from the source bus line 24 is applied at a predetermined timing to the pixel electrode 15 connected to the TFT 23 which is turned on for a certain period by the input of the scanning signal.

Further, the image signal of a predetermined level written in the liquid crystal layer 30 is held for a certain period between the pixel electrode 15 to which the image signal is applied and the common electrode 16. Here, in order to prevent the stored image signal from leaking, a storage capacitor is formed in parallel with the liquid crystal capacitor formed between the pixel electrode 15 and the common electrode 16. In each picture element, the storage capacitor is formed between the drain wiring 24 of the TFT 23 and the Cs bus line provided in parallel with the gate bus line 26. Note that the Cs bus line is also connected to the common voltage generation circuit in the same manner as the common electrode 16.

The pixel electrode 15 is formed of a transparent conductive film such as ITO, a metal film such as aluminum or chromium, and the like. The shape of the pixel electrode 15 when the liquid crystal display panel 100 is viewed from above is a comb-like shape.

The common electrode 16 is also formed of a transparent conductive film such as ITO, a metal film such as aluminum, and the like, and the shape of the common electrode 16 when the liquid crystal display panel 100 is viewed in plan is a comb-like shape.

Further, the pixel electrodes 15 and the common electrodes 16 are alternately arranged with a constant interval. In other words, the comb-like pixel electrode 15 and the comb-like common electrode 16 are arranged to face each other in a direction in which the comb teeth mesh with each other.

The width (minimum width) of the pixel electrode 15 and the common electrode 16 is, for example, 2 to 5 μm (preferably 2 to 3 μm). If it exceeds 5 μm, the aperture ratio decreases and the transmittance decreases. Moreover, there exists a possibility that yields, such as a disconnection, may fall that it is less than 2 micrometers.

In addition, the present embodiment includes a case where each picture element includes a plurality of regions having different intervals between the pixel electrode 15 and the common electrode 16 (hereinafter also simply referred to as electrode intervals). That is, in each picture element, a region having a relatively narrow electrode interval (region of Sn) and a region having a relatively large electrode interval (region of Sw) may be formed. Thereby, since the threshold value of the VT characteristic in each region can be made different, the slope of the VT characteristic (VT curve) of the entire picture element particularly at a low gradation can be made gentle. As a result, the occurrence of whitening can be suppressed and the viewing angle characteristics can be improved. White floating is a phenomenon in which a display that should appear dark appears to be whitish when the viewing direction is tilted obliquely from the front in a state where a relatively dark display with low gradation is performed.

The liquid crystal display of this embodiment applies an image signal (voltage) to the pixel electrode 15 via the TFT 23, so that the surface of the substrate (the active matrix substrate 1 and the counter substrate 2) is between the pixel electrode 15 and the common electrode 16. An electric field (lateral electric field) in a direction (horizontal direction, a direction parallel to the substrate surface) is generated. Then, the liquid crystal is driven by this electric field, and an image is displayed by changing the transmittance of each picture element.

More specifically, the liquid crystal display of this embodiment forms a distribution of electric field strength in the liquid crystal layer 30 by applying an electric field. This causes distortion of the alignment of the liquid crystal compound. Then, the retardation of the liquid crystal layer 30 is changed using the distortion. More specifically, the initial alignment state of the liquid crystal layer 30 is vertical alignment. When a voltage is applied between the comb-like pixel electrode 15 and the common electrode 16, a parabolic electric field is formed between the electrodes 15 and 16. This electric field is generally called a horizontal electric field because it becomes an electric field (horizontal electric field) substantially horizontal to the main surfaces of the substrates 1 and 2 in the light transmission region of the liquid crystal layer 30. As a result, the liquid crystal compounds are arranged in a bow shape (bend orientation), and two domains whose director directions are 180 ° different from each other are formed between the electrodes 15 and 16 as shown in FIG.

In the region where the two domains are adjacent (usually on the center line of the gap between the pixel electrode 15 and the common electrode 16), the liquid crystal compound is always aligned vertically regardless of the applied voltage value. Therefore, a dark line (dark line) is always generated in this region (boundary) regardless of the applied voltage value. In addition, a horizontal electric field is not generated on the pixel electrode 15 and the common electrode 16, and the liquid crystal compound remains vertically aligned, and a dark line is always generated on the pixel electrode 15 and the common electrode 16.

The structure of the liquid crystal display according to the first embodiment has been described above with reference to FIGS. 1, 2, and 3. Below, the manufacturing method of the liquid crystal display of Embodiment 1, especially the bonding process by the liquid crystal dropping method (ODF; One drop fill process) of a liquid crystal display panel is demonstrated. Note that each of the active matrix substrate 1 and the counter substrate 2 can be manufactured by a conventionally known method.

In the bonding step, first, an ultraviolet curable sealant is applied to either the active matrix substrate 1 or the counter substrate 2 so as to surround the display region, thereby forming a rectangular frame-shaped seal pattern. An injection port for injecting the liquid crystal material is not formed in the seal pattern. The ultraviolet curable sealing material has a property of being cured by ultraviolet rays (ultraviolet curable). The ultraviolet curable sealant may have a property of being cured by heating (thermosetting) in addition to the ultraviolet curable property. Thereafter, fine droplets of the liquid crystal material are dropped and applied onto the entire surface of the active matrix substrate 1 or the counter substrate 2 on which the seal pattern is formed, with the UV curable sealing material being uncured, and then the other substrate is overlaid. Thereafter, for example, using an ultra-high pressure UV lamp as a light source, UV irradiation is performed with an energy of, for example, about 10 to 15 J to cure the seal pattern and simultaneously form the liquid crystal layer 30 with a desired cell thickness. In this way, the liquid crystal material is sealed in a region between the substrates 1 and 2 and surrounded by the seal member. Further, the sealing member does not have a liquid crystal inlet sealing member. The sealing member is a cured product of the sealing material, and the liquid crystal inlet sealing member is a member for sealing the inlet. Further, the liquid crystal material may be dropped and applied to the active matrix substrate 1 or the counter substrate 2 on which no seal pattern is formed. In this case, the liquid crystal material is dropped into a region corresponding to the region surrounded by the seal pattern.

At this time, the specific resistance of the liquid crystal layer 30 is 1.5 × 10 ¹⁴ Ω · cm or more, and since the amount of impurity ions in the liquid crystal layer is small, occurrence of flicker and image sticking can be suppressed. The upper limit of the specific resistance of the liquid crystal layer 30 is preferably as high as possible from the viewpoint of reducing the amount of impurity ions in the liquid crystal layer 30, but the characteristics of the liquid crystal material and the characteristics of the alignment films 12 and 22 are considered. Then, the upper limit value of the specific resistance of the liquid crystal layer 30 is preferably set to about 1.0 × 10 ¹⁵ Ω · cm. The reason will be described below. The magnitude of the residual DC voltage varies depending not only on the amount of impurity ions in the liquid crystal layer but also on the combination of the liquid crystal material and the alignment film. Theoretically, the dielectric constant of the alignment film and the specific resistance of the alignment film If the product and the product of the dielectric constant of the liquid crystal material and the specific resistance of the liquid crystal material are the same, the residual DC component resulting from the combination will not occur. The dielectric constant of a general alignment film is approximately the same as the dielectric constant of all liquid crystal materials including the liquid crystal material used in this embodiment, and the specific resistance of the general alignment film is approximately 1.0 × 10 10. It falls within the range of ¹⁵ Ω · cm or less. Therefore, when a general alignment film material is used, the specific resistance of the liquid crystal layer 30 is 1.0 × 10 ¹⁵ Ω · cm or less from the viewpoint of more effectively suppressing the occurrence of flicker and image sticking. Is preferred. In the present embodiment, the specific resistance of the liquid crystal layer 30 may be 5.0 × 10 ¹⁴ Ω · cm or less, or 3.0 × 10 ¹⁴ Ω · cm or less.

The liquid crystal material (liquid crystal composition) of the liquid crystal layer 30 has a phenyl-bicyclohexane-based, phenyl-biphenyl-based, bicyclohexane-based, or terphenyl-based structure in the core, and an alkyl group or an alkoxy group at the terminal or in the middle. And having a refractive index anisotropy. The liquid crystal material includes a liquid crystal compound having a polar group such as a fluoro group at the terminal or in the middle, and has positive dielectric anisotropy. Further, the liquid crystal material includes a liquid crystal compound having a viscosity reducing effect for decreasing the viscosity. The above liquid crystal compound preferably has light resistance. Thereby, even if intense ultraviolet rays are irradiated, generation of impurity ions can be effectively suppressed.

The dielectric anisotropy Δε of the liquid crystal layer 30 is not particularly limited, but is preferably a large value, specifically, 15 to 25 (preferably 18 to 22) at 25 ° C. If it exceeds 25, it becomes difficult to maintain the desired liquid crystal phase and the viscosity becomes high, resulting in a slow response speed. If it is less than 15, the VT (voltage-transmittance) characteristics shift to the high voltage side and transmit. The rate will drop.

Furthermore, the liquid crystal layer 30 preferably has a specific resistance change rate of 32% or less before and after ultraviolet irradiation, and the smaller the specific resistance change rate, the more preferable. The small rate of change in specific resistance before and after UV irradiation means that the amount of impurity ions generated by UV irradiation is small, and it is possible to more effectively suppress deterioration in display quality such as image sticking and flicker. it can. From such a viewpoint, the lower limit of the rate of change in specific resistance is not particularly limited.

As shown in FIG. 3, the liquid crystal compound 5 in the liquid crystal layer 30 is homeotropic when no voltage is applied (when an electric field is not generated by the electrodes 15 and 16) due to the alignment regulating force of the alignment films 12 and 22. Indicates orientation. The pretilt angle of the liquid crystal layer 30 is 86 ° or more (preferably 88 ° or more) and 90 ° or less. If the angle is less than 86 °, the front contrast is significantly reduced.

Hereinafter, the liquid crystal display according to Embodiment 1 was produced, and the specific resistance and residual DC voltage of the liquid crystal layer were measured.

[Measurement of resistivity of liquid crystal layer]
The specific resistance of the liquid crystal layer was measured using a TFT liquid crystal panel evaluation apparatus LCM-3 type (manufactured by Toyo Technica Co., Ltd.). This apparatus can measure specific resistance in a state of a liquid crystal layer, that is, in a state where a liquid crystal material is sandwiched between substrates. Under a temperature condition of 70 ° C., a resistance value was measured by applying a triangular wave voltage of 0.01 V of 0V-10V to the liquid crystal display panel, and a specific resistance was calculated from resistance value × electrode area / electrode interval.

[Measurement of change in residual DC voltage]
The residual DC voltage was determined by the flicker elimination method [Operation I] described in WO2007 / 141935. Specifically, a DC offset voltage is applied to the liquid crystal cell at 2 V for 2 hours, and then the liquid crystal cell is driven with a rectangular wave voltage (V _15% , 30 Hz) to apply a DC offset voltage to be applied so that flicker is not observed. The DC offset voltage was adjusted to be the residual DC voltage. In addition, the measurement was performed in 25 degreeC, and the self-made apparatus comprised including the generator, the photomultiplier, the oscilloscope, and the computer which controls these was used. It is considered that the residual DC voltage increases as the amount of impurity ions in the liquid crystal layer increases. That is, the higher the residual DC voltage, the more easily the deterioration of display quality is observed.

First, a plurality of liquid crystal displays were manufactured using a liquid crystal material A having a dielectric anisotropy Δε of 16 and an initial specific resistance of 2.42 × 10 ¹⁴ Ω · cm as a liquid crystal material forming a liquid crystal layer. . These liquid crystal displays were manufactured by a liquid crystal dropping method (ODF) with a seal pattern formed by an ultraviolet curable sealing material. At this time, in order to cure the sealing material, the sealing material and the liquid crystal layer were irradiated with ultraviolet rays. The specific resistance of the liquid crystal layer decreases with the irradiation amount of ultraviolet light, and the specific resistance of the liquid crystal layer is 1.67 × 10 ¹⁴ Ω · cm when irradiated with ultraviolet light having an energy of 12 J. The specific resistance of the layer was 4.10 × 10 ¹³ Ω · cm. The specific resistance change rate before and after UV irradiation was 31.1% for 12J irradiation and 83% for 60J irradiation, respectively. Hereinafter, the above-mentioned liquid crystal display produced by using the liquid crystal material A and irradiating the sealing material and the liquid crystal layer with ultraviolet rays having 12 J energy is referred to as the liquid crystal display A after being irradiated with 12 J ultraviolet rays. The liquid crystal display produced by irradiating the material and the liquid crystal layer with ultraviolet rays having energy of 60 J is referred to as a liquid crystal display A after irradiation with ultraviolet rays of 60 J. The initial specific resistance of the liquid crystal material A was measured with a liquid crystal display produced by irradiating only the sealing material with ultraviolet rays. Hereinafter, the liquid crystal display manufactured by using the liquid crystal material A and irradiating only the sealing material with ultraviolet rays is referred to as the liquid crystal display A before the ultraviolet irradiation. From the value of specific resistance, the liquid crystal display A before ultraviolet irradiation and the liquid crystal display A after 12J ultraviolet irradiation correspond to the liquid crystal display of Embodiment 1 according to the present invention, and the liquid crystal display A after 60 J ultraviolet irradiation is This corresponds to a comparative liquid crystal display.

The residual DC voltage in each liquid crystal display A was measured before ultraviolet irradiation, after 12 J ultraviolet irradiation, and after 60 J ultraviolet irradiation. The residual DC voltage of the liquid crystal display A before the ultraviolet irradiation was 130 mV, the residual DC voltage of the liquid crystal display A after the ultraviolet irradiation of 12 J was 180 mV, and the residual DC voltage of the liquid crystal display A after the ultraviolet irradiation of 60 J was 780 mV. .

Next, a plurality of liquid crystal displays are manufactured by using a liquid crystal material B having a dielectric anisotropy Δε of 18 and an initial specific resistance of 2.45 × 10 ¹⁴ Ω · cm as a liquid crystal material forming a liquid crystal layer. did. The liquid crystal material B has an initial specific resistance that is substantially the same as that of the liquid crystal material A, but is a liquid crystal material that is more likely to generate impurity ions when irradiated with ultraviolet light than the liquid crystal material A. The liquid crystal display produced using the liquid crystal material B is the same as the liquid crystal display produced using the liquid crystal material A, except that the liquid crystal material B is used instead of the liquid crystal material A. The specific resistance of the liquid crystal layer was decreased with the amount of ultraviolet irradiation to the sealing material and the liquid crystal layer, and the specific resistance of the liquid crystal layer was decreased to 5.29 × 10 ¹³ Ω · cm by ultraviolet irradiation with 12 J energy. Hereinafter, the liquid crystal display produced by using the liquid crystal material B and irradiating the sealing material and the liquid crystal layer with ultraviolet rays having 12 J energy will be referred to as the liquid crystal display B after the ultraviolet irradiation with 12 J. The initial specific resistance of the liquid crystal material B was measured by a liquid crystal display produced by irradiating only the sealing material with ultraviolet rays. Hereinafter, the liquid crystal display produced by using the liquid crystal material B and irradiating only the sealing material with ultraviolet rays will be referred to as the liquid crystal display B before ultraviolet irradiation. From the value of the specific resistance, the liquid crystal display B before the ultraviolet irradiation corresponds to the liquid crystal display of Embodiment 1 according to the present invention, and the liquid crystal display B after the 12J ultraviolet irradiation corresponds to the liquid crystal display of the comparative form.

The residual DC voltage in each liquid crystal display B before ultraviolet irradiation and after 12J ultraviolet irradiation was measured. The residual DC voltage of the liquid crystal display before UV irradiation was 200 mV, and the residual DC voltage of the liquid crystal display after UV irradiation of 12 J was 680 mV.

Table 1 shows the specific resistance and residual DC voltage of the liquid crystal layer in each liquid crystal display using the liquid crystal materials A and B.

FIG. 4 shows the relationship between the specific resistance (ρ) of the liquid crystal layer of the liquid crystal display manufactured using the liquid crystal material A and the liquid crystal display manufactured using the liquid crystal material B and the irradiation amount of ultraviolet rays (UV irradiation amount). It is a graph which shows a relationship. As shown in FIG. 4, the specific resistance of the liquid crystal layer decreased as the amount of ultraviolet irradiation increased.

FIG. 5 shows the relationship between the specific resistance (ρ) of the liquid crystal layer and the residual DC voltage (r−DC) in the liquid crystal display manufactured using the liquid crystal material A and the liquid crystal display manufactured using the liquid crystal material B. It is a graph which shows. The residual DC voltages of the liquid crystal display A before ultraviolet irradiation, the liquid crystal display A after 12J ultraviolet irradiation, and the liquid crystal display B before ultraviolet irradiation are 130 mV, 180 mV, and 200 mV, respectively, and display quality such as flicker and burn-in A decrease in was not observed. On the other hand, the liquid crystal display A after UV irradiation of 60J and the liquid crystal display B after UV irradiation of 12J are large in residual DC voltages of 780 mV and 680 mV, respectively, and it is considered that a large amount of impurity ions were generated by the UV irradiation. In all cases, a decrease in display quality such as flicker and burn-in was observed. Therefore, when the residual DC voltage is 200 mV or less, that is, as shown in FIG. 5, when the specific resistance of the liquid crystal layer is 1.5 × 10 ¹⁴ Ω · cm or more, the display quality is kept good.

(Embodiment 2)
The liquid crystal display of the second embodiment is different from the first embodiment in the following points.
That is, the liquid crystal display panel 200 of Embodiment 2 has a counter electrode (second common electrode) on the counter substrate 2 side. Specifically, as illustrated in FIG. 6, the counter electrode 17, the dielectric layer 18, and the alignment film 22 are stacked in this order on the main surface of the transparent substrate 21 on the liquid crystal layer 30 side. Note that a color layer and / or a BM layer may be provided between the counter electrode 17 and the transparent substrate 21.

The counter electrode 17 is formed of a transparent conductive film such as ITO or IZO. As shown in FIG. 7, the counter electrode 17 is formed without a break so as to cover at least the entire display region 6. A predetermined potential common to each pixel (or picture element) is applied to the counter electrode 17. In the frame region of the liquid crystal display panel 200, as with the liquid crystal display panel 100, a seal member 7 that does not have a liquid crystal inlet sealing member is provided.

The dielectric layer 18 is formed from a transparent insulating material. Specifically, it is formed from an inorganic insulating film such as silicon nitride, an organic insulating film such as acrylic resin, or the like. The dielectric layer 18 is formed without a break so as to cover at least the entire display region 6.

On the other hand, the transparent substrate 11 is provided with a pair of comb-like electrodes including the pixel electrode 15 and the common electrode 16 as in the first embodiment, and is further provided with an alignment film 12. Further, polarizing plates 41 and 51 are disposed on the outer main surfaces of the two transparent substrates 11 and 21 (on the side opposite to the liquid crystal layer 30).

The voltage applied to the pixel electrode 15 is different from both the voltage applied to the common electrode 16 and the voltage applied to the counter electrode 17 except during black display.

In the present embodiment, when a voltage is applied, an oblique electric field (an oblique electric field with respect to the main surfaces of the substrates 1 and 2) is formed from the pixel electrode 15 toward the counter electrode 17. Further, a horizontal electric field (electric field substantially parallel to the main surfaces of the substrates 1 and 2) is formed from the pixel electrode 15 toward the common electrode 16. This transverse electric field serves to help form an oblique electric field. Therefore, due to the presence of the lateral electric field, the oblique electric field does not become so weak even if it is separated from the pixel electrode 15. Therefore, the liquid crystal compound that has been vertically aligned when no voltage is applied is aligned parallel to the oblique electric field when the voltage is applied.

Also with the liquid crystal display of this embodiment, flicker and image sticking can be suppressed as in the first embodiment. Further, the response speed can be improved by forming the counter electrode 17.

Further, when the counter electrode 17 is adjacent to the alignment film 22, equipotential lines are concentrated near the interface between the counter substrate 2 and the liquid crystal layer 30. For this reason, the component in the normal direction of the oblique electric field becomes strong in the liquid crystal layer 30, and the liquid crystal compound may not fall sufficiently sideways. On the other hand, in the present embodiment, the dielectric layer 18 is provided on the liquid crystal layer 30 side of the counter electrode 17. Therefore, concentration of equipotential lines near the interface between the counter substrate 2 and the liquid crystal layer 30 can be suppressed. Therefore, the component in the normal direction of the oblique electric field in the liquid crystal layer 30 can be weakened. As a result, the liquid crystal compound can be tilted sideways sufficiently, and the transmittance of the entire picture element can be improved.

Note that the common electrode 16 and the counter electrode 17 may be grounded, and voltages having the same magnitude and the same polarity may be applied to the common electrode 16 and the counter electrode 17.

In the first and second embodiments, the number of regions having different electrode intervals in one picture element is not particularly limited, and may be three or more. Even when there are three or more, the occurrence of whitening can be suppressed and the viewing angle characteristics can be improved in the same manner as in the case of two.

The present application claims priority based on the Paris Convention or the laws and regulations in the country of transition based on Japanese Patent Application No. 2011-041556 filed on February 28, 2011. The contents of the application are hereby incorporated by reference in their entirety.

1: active matrix substrate 2: counter substrate 5, 105: liquid crystal compound 6: display region 7: seal member 11, 21, 111, 121, 211, 221: transparent substrate 12, 22, 112, 122, 212, 222: orientation Films 15, 115, 215: Pixel electrodes 16, 116, 216: Common electrode 17: Counter electrode 18, 118: Dielectric layer 23: Thin film transistor (TFT)
24: source bus line 25: drain wiring 26: gate bus line 30, 130: liquid crystal layers 41, 51, 241, 251: polarizing plate 100, 200: liquid crystal display panel 106: ultraviolet ray 123: seal pattern 131: impurity ions

Claims (4)

A liquid crystal display comprising a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates,
The liquid crystal compound contained in the liquid crystal layer is aligned substantially perpendicular to the pair of substrate surfaces when no voltage is applied,
One of the pair of substrates has a pair of electrodes,
The pair of electrodes are opposed to each other at an interval in a plan view, and the orientation of the liquid crystal compound is controlled by an electric field generated by the pair of electrodes,
The liquid crystal layer has a positive dielectric anisotropy,
The liquid crystal layer has a specific resistance of 1.5 × 10 ¹⁴ Ω · cm or more. 2. The liquid crystal display according to claim 1, wherein the dielectric anisotropy Δε of the liquid crystal layer is 15 ≦ Δε ≦ 25. The liquid crystal display according to claim 1, wherein the other of the pair of substrates has an electrode that covers at least a display region. The liquid crystal display has a seal member that encloses the liquid crystal layer between the pair of substrates,
4. The liquid crystal display according to claim 1, wherein the seal member does not have a liquid crystal inlet sealing member.

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