WO2012060302A1

WO2012060302A1 - Liquid crystal display device

Info

Publication number: WO2012060302A1
Application number: PCT/JP2011/074979
Authority: WO
Inventors: 伊藤　昌稔
Original assignee: シャープ株式会社
Priority date: 2010-11-02
Filing date: 2011-10-28
Publication date: 2012-05-10

Abstract

A liquid crystal display device (100) comprises: a pair of substrates (110, 120); a liquid crystal layer (140) sandwiched between the pair of substrates; a seal material (130) provided so as to surround the liquid crystal layer (140); a plurality of spacers (132) provided so as to define the spacing between the pair of substrates; an alignment film (114) provided on the liquid crystal layer side of at least one of the pair of substrates; and an alignment maintaining layer (116) including a polymer formed by polymerizing a polymerizable compound, the alignment maintaining layer (116) being provided to the liquid crystal layer side of the alignment film (114). A cell-thickness varying part (50) in which the spacing between the pair of substrates decreases in the direction of the seal material (130) is formed in the vicinity of the seal material (130); and the cell-thickness variance (∆h/W) of the cell-thickness varying part (50) is 0.01% or less, where ∆h is the reduction in cell thickness in the direction perpendicular to the substrate, and W is the width of the cell-thickness varying part in the in-plane direction of the substrate.

Description

Liquid crystal display

The present invention relates to a liquid crystal display device, and more specifically, to a liquid crystal display device using PSA technology.

・・・ Liquid crystal display devices are becoming more sophisticated as their applications expand. In particular, display modes such as MVA (Multi-domain Vertical Alignment) and IPS (In-Plane-Switching) having a wide viewing angle characteristic have been developed, and further improvements are in progress.

In order to improve the display quality of a liquid crystal display device, it is necessary to precisely control the thickness of the liquid crystal layer (sometimes called "cell thickness" or "cell gap") in any display mode. is necessary. In particular, in a large liquid crystal display device, it is necessary to uniformly control the cell gap over a large area.

The cell gap is controlled by, for example, a spacer disposed between a pair of substrates facing each other with a liquid crystal layer interposed therebetween. In recent years, a method of forming columnar spacers on a substrate by a photolithography process using a photosensitive material has been adopted. The spacer formed in this way is called a columnar spacer or a photo spacer (PS).

A photo spacer may be arranged not only in a display area (effective display area) for displaying an image or the like but also in a frame area (peripheral area) outside the photo spacer. However, the structure of the frame area is significantly different from the structure of the display area. For this reason, if the photo spacers are similarly formed in the frame region and the display region in the same manner, the spacers may not perform a desired function in the frame region, and the cell gap may become non-uniform.

Japanese Patent Application Laid-Open No. 2004-228561 has a mode in which the cell thickness is non-uniform because the insulating film provided between the active element and the pixel electrode is formed in a tapered shape in the frame region where the photo spacer is provided. It is shown. When an area where the cell thickness is not constant is used for display, the display quality is lowered. For this reason, in the display device described in Patent Document 1, by defining a lower limit of the width of the frame area, an area where the cell thickness is not uniform is not included in the display area.

However, when the liquid crystal display device is designed so as to define the lower limit of the width of the frame area as described above, it cannot meet the demand for reducing the width of the frame area. In a liquid crystal display device, it is desired to reduce the area that does not contribute to display as much as possible, and the frame area is becoming narrower year by year. According to the lower limit of the width of the peripheral area described in Patent Document 1, it may be difficult to set the frame area narrow.

Patent Document 2 describes a technique for narrowing the frame area. A drive circuit may be provided in the seal region as the frame is narrowed. However, since the wiring specifications are different on each side of the liquid crystal panel, the cell thickness in the vicinity of the seal region may be different on each side. Further, when glass fibers as spacers are mixed in the sealing material, there is a possibility that the underlying TFT element or the like may be destroyed under load. In consideration of these points, in Patent Document 2, a uniform cell thickness is realized by providing a spacer during sealing without adding a spacer to the sealing material. Patent Document 2 also describes a technique for suppressing variation in the cell thickness in the peripheral portion by using a spacer (for example, a wall-like spacer) having a different form from the display area in the frame area.

JP 2006-58329 A Japanese Patent Laid-Open No. 10-153797

The cell thickness in the frame area can change due to various factors. In particular, when the frame region is set to be narrow, even if a photo spacer is arranged, the shape (height and film thickness) of the spacer and the underlying film is not appropriate. Could not be controlled. Therefore, it is not easy to actually make the cell thickness constant. The allowable cell thickness variation may vary depending on the operation mode and configuration of the liquid crystal display device. For this reason, the display quality in this region may be deteriorated. Therefore, there has been a problem of improving the display quality particularly at the end of the display area (boundary with the frame area) while realizing a narrow frame area.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal display device capable of improving the display quality even when the frame area is narrow.

The liquid crystal display device of the present invention includes a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, a sealing material provided so as to surround the liquid crystal layer, and the pair of substrates. A plurality of spacers provided so as to define the distance between the substrates, an alignment film provided on the liquid crystal layer side of at least one of the pair of substrates, and provided on the liquid crystal layer side of the alignment film A liquid crystal display device comprising an alignment maintaining layer and an alignment maintaining layer containing a polymer formed by polymerizing a polymerizable compound, wherein the sealing material is provided in the vicinity of the sealing material A cell thickness variation portion in which a distance between the pair of substrates decreases toward the substrate, and a ratio of a cell thickness decrease Δh in the substrate vertical direction of the cell thickness variation portion to a width W in the substrate in-plane direction. Cell thickness fluctuation rate Δh / W is 0.01% or less.

In a preferred embodiment, a display area for displaying and a peripheral area located outside the display area are defined, and the cell thickness variation portion is in the vicinity of a boundary between the display area and the peripheral area. Is formed.

In a preferred embodiment, the spacer is formed in both the display region and the peripheral region, and the spacer formed in the peripheral region is lower than the spacer formed in the display region, and The cell thickness decrease Δh is determined according to the difference between the height of the spacer formed in the region and the height of the spacer formed in the display region.

In a preferred embodiment, the spacer formed in the peripheral region is formed in a central portion of the peripheral region.

In a preferred embodiment, one of the pair of substrates includes a planarization film provided on the liquid crystal layer side, and the planarization film has different thicknesses in the display region and the peripheral region. The cell thickness decrease Δh is determined according to the difference in thickness of the planarization film.

In a preferred embodiment, the liquid crystal layer is a vertical alignment type liquid crystal layer, and the alignment film is a vertical alignment type alignment film, and the cell thickness in the peripheral region is the cell thickness in the display region. Smaller than.

According to the present invention, in a liquid crystal display device that regulates the alignment state of liquid crystal molecules by a polymer obtained by polymerizing a polymerizable compound mixed in a liquid crystal material, narrowing of the frame is achieved, particularly in the vicinity of the frame region. A decrease in display quality can be suppressed.

FIG. 7 is a schematic diagram showing a process for manufacturing a liquid crystal cell by an ODF method, and (a) to (d) show different processes. 1 is a diagram illustrating a cross section of a liquid crystal display device according to Embodiment 1. FIG. FIG. 6 is a diagram illustrating a cross section of a liquid crystal display device according to a second embodiment. It is sectional drawing which shows the structure in the frame area | region of a liquid crystal display device, (a) shows the case where the photo spacer is not provided in the frame area, (b) is an embodiment in which the photo spacer is provided in the frame area. 3 shows a liquid crystal display device according to FIG. (A) And (b) is a top view which shows arrangement | positioning of the photo spacer in the frame area | region of the liquid crystal display device which concerns on Embodiment 3. FIG.

Polymer Sustained Alignment Technology (hereinafter referred to as “PSA technology”) has been developed as a technology for controlling the pretilt direction of liquid crystal molecules. PSA technology typically irradiates a liquid crystal layer mixed with a small amount of a photopolymerizable compound with ultraviolet light while applying a predetermined voltage, and the orientation of liquid crystal molecules is controlled by the photopolymer produced. Technology. In the present specification, a layer formed from a photopolymer is referred to as an alignment sustaining layer.

When the PSA technique is used, the alignment state of the liquid crystal molecules when the photopolymer is generated is maintained (stored) even in the state where no voltage is applied. Therefore, the PSA technique has an advantage that the alignment state of the liquid crystal molecules can be adjusted by controlling the electric field formed in the liquid crystal layer. The PSA technique is suitable for forming a vertical alignment type liquid crystal layer in which the pretilt direction is difficult to control by rubbing the alignment film. The PSA technique is described in, for example, Japanese Patent Application Laid-Open No. 2002-357830.

However, in a liquid crystal display device manufactured using the PSA technology, when trying to realize a narrow frame, the display quality may be deteriorated particularly in the vicinity of the frame region. The reason for this will be described below by the inventors.

FIGS. 1A to 1D schematically show an example of a process for manufacturing a liquid crystal panel using the PSA technique by an ODF (One Drop Fill) method.

First, as shown in FIG. 1A, for example, an ultraviolet curable sealing material 12 is applied to the peripheral portion of the counter substrate 10 provided with a color filter and an alignment film. The sealing material 12 is applied on the counter substrate 10 so as to have a width of 200 μm to 400 μm using, for example, a dispenser device. In addition, a liquid crystal material LC containing a photopolymerizable compound is dropped into a region surrounded by the sealing material 12.

Next, as shown in FIG. 1B, another substrate 20 (here, the TFT substrate 20) is bonded to the counter substrate 10 onto which the liquid crystal material LC has been dropped. Immediately after this, the liquid crystal material LC sandwiched between the substrates flows while concentrically spreading toward the peripheral portion of the substrate (the portion provided with the sealing material 12) unless there is a particular feature on the substrate surface shape. This bonding step is performed in a vacuum atmosphere (pressure P ₀ ).

Thereafter, as shown in FIG. 1C, the sealing material 12 is cured by selectively irradiating the sealing material 12 with ultraviolet rays 30 at atmospheric pressure (pressure P ₁ ). Furthermore, if necessary, a heat treatment for promoting the curing of the sealing material 12 is performed. The sealing material 12 is hardened by being stretched so that the width thereof becomes, for example, about 1 mm through the bonding step and the curing step. In this way, the liquid crystal material LC is sealed between the pair of substrates, and a liquid crystal layer is formed. The alignment state of the liquid crystal molecules is regulated by the alignment film provided on the

substrates

10 and 20.

Thereafter, a voltage is applied between the electrodes as necessary to bring the liquid crystal material into a predetermined alignment state, and then the polymerizable compound in the liquid crystal layer is polymerized by a photopolymerization process (not shown). The polymer obtained in this manner forms an alignment maintaining layer that controls the alignment of liquid crystal molecules.

As described above, in the ODF method, the liquid crystal material LC is applied between the substrates immediately before the substrate bonding step (FIG. 1B) and the sealing material curing step (FIG. 1C) (hereinafter referred to as these The process may be referred to as a liquid crystal cell formation process). For this reason, in the liquid crystal cell forming step, the liquid crystal material LC flows between the substrates.

In the sealing material curing step (FIG. 1C), ideally, only the sealing material 12 is irradiated with the ultraviolet rays 30. However, even when, for example, a mask or the like is provided to selectively irradiate the sealing material 12 with the ultraviolet rays 30, particularly when the frame space is narrow and the sealing material and the display area are close to each other, the liquid crystal material LC There is a possibility that a part of ultraviolet rays is irradiated. At this time, the polymerizable compound (monomer and / or oligomer) contained in the liquid crystal material LC may be polymerized. Further, when the sealing material 12 is cured by heat treatment as described above, the polymerizable compound in the liquid crystal layer may be polymerized with a slight amount. Thereby, a polymer is formed at the alignment film interface.

For example, a BM (black matrix) may be provided between the sealing material 12 and the counter substrate 10 (immediately below the sealing material), but in order to realize a narrow frame, a frame formed on the TFT substrate 20 A sealing material 12 is disposed on the wiring in the region. In order to cure the sealing material 12, it is necessary to irradiate ultraviolet rays through the wiring from the TFT substrate 20 side where the BM is not provided. At this time, since a part of the irradiation light in the vicinity of the sealing material 12 may be blocked by the wiring, it is necessary to irradiate a higher dose of ultraviolet rays in order to sufficiently cure the sealing material 12. As a result, the polymerizable compound contained in the liquid crystal material in the vicinity of the sealing material 12 becomes more easily polymerized.

When a polymer (polymer) is formed by polymerization of the polymerizable compound, as shown in FIG. 1 (d), in the manufactured liquid crystal cell, unevenness (flow) according to the change in the flow rate (flow velocity) of the liquid crystal material. ) 40 may be observed. The occurrence of such unevenness 40 is a specific problem that occurs when the sealing material 12 is cured when the liquid crystal material contains a polymerizable compound. When the liquid crystal material does not contain a polymerizable compound, after the liquid crystal material is sealed in the liquid crystal cell, the disorder of the alignment direction of the liquid crystal molecules can be normalized by heat treatment or the like. However, in a liquid crystal display device using the PSA technology, polymerization of monomers is caused by UV (ultraviolet) irradiation and heat treatment, and as a result, disorder of alignment of liquid crystal molecules due to flow of the liquid crystal material remains.

Unevenness (hereinafter sometimes referred to as PSA unevenness) 40 caused by unintended polymerization and corresponding to a change in the flow rate of the liquid crystal material is significantly observed in the frame region R1 around the display region R2. This seems to be partly due to the fact that the liquidity of the liquid crystal material is greatly reduced (varied) in the frame region R1. That is, in the liquid crystal cell forming process, the cell gap in the vicinity of the sealing material, which will be described later, or the pressure in the void portion in the cell not filled with liquid crystal (initially P ₀ ) gradually increases in the sealing material curing process. It is considered that the flow (spreading) speed of the liquid crystal in the frame region R1 decreases due to a decrease in the difference between this pressure and the atmospheric pressure P ₁ received by the substrate surface.

Therefore, the present inventor considered to suppress a decrease in the liquid crystal flow rate in the frame region R1.

In the frame region R1, the cell thickness often decreases toward the portion where the sealing material 12 is provided. For example, such a change in cell thickness occurs because the photo spacer provided in the frame region R1 is formed lower than the photo spacer in the display region R2. In particular, in the vicinity of the sealing material 12, the cell thickness may decrease rapidly. In the region where the cell thickness is decreasing, the fluidity of the liquid crystal material is decreased. When the fluidity of the liquid crystal material is drastically lowered, when the photopolymerizable compound contained in the liquid crystal material LC is polymerized, PSA unevenness (disturbance in the orientation of the liquid crystal molecules, For example, it is considered that the orientation azimuth, the orientation axis center disturbance, and the tilt angle variation 40) occur. The orientation direction refers to a component in the liquid crystal layer plane (in the substrate plane) among vectors indicating the alignment direction of liquid crystal molecules.

Since the flow trajectory is particularly easily observed in the region (frame region) R1 in the vicinity of the sealing material 12, in the liquid crystal display device using the PSA technology, it is possible to suppress the decrease in the cell thickness in the region R1 to a predetermined level. It seems to be effective to suppress the occurrence of the trajectory. More specifically, in a region where the cell thickness decreases toward the outside of the substrate (referred to as a cell thickness variation portion in this specification), the cell thickness variation (cell thickness difference) in the substrate vertical direction is the substrate surface. It has been found that when the cell thickness variation is 0.01% or less with respect to the width of the cell thickness variation portion in the inward direction, it is possible to suppress a rapid drop in liquid crystal fluidity and to reduce the occurrence of a flow locus.

As described above, after forming the liquid crystal cell to limit the cell thickness reduction, the alignment maintaining layer is formed on the alignment film by irradiating the photopolymerizable compound in the liquid crystal layer with ultraviolet rays by the PSA technique, Regulates the pretilt angle of liquid crystal molecules. Even after such a PSA process, the display quality in the vicinity of the frame region R1 is prevented from being lowered. Therefore, even when the PSA technology is used, it is possible to manufacture a narrow frame liquid crystal display device with improved display quality.

Hereinafter, although an embodiment of the present invention is described, the present invention is not limited to this.

(Embodiment 1)
FIG. 2 shows an end cross-section of the liquid crystal display device 100 of the first embodiment. The liquid crystal display device 100 includes a TFT substrate 110, a counter substrate 120, and a vertical alignment type liquid crystal layer 140 sandwiched therebetween, and operates in a VA (Vertical Alignment) mode. The liquid crystal display device 100 is provided with matrix-like pixels along a plurality of rows and a plurality of columns.

The TFT substrate 110 has a transparent substrate 112 and a vertical alignment film 114. On the vertical alignment film 114, an alignment maintaining layer 116 formed by polymerizing a photopolymerizable compound (for example, a photopolymerizable monomer) is provided. The TFT substrate 110 has at least one thin film transistor and a pixel electrode (both not shown here) provided for each pixel.

The counter substrate 120 includes a transparent substrate, a counter electrode formed on the transparent substrate, a vertical alignment film, and the like (not shown). In addition, an alignment maintaining layer (not shown) is formed on the liquid crystal layer 140 side of the vertical alignment film. Furthermore, in the present embodiment, the counter substrate 120 is provided with a color filter (not shown).

Further, polarizing plates (not shown) are provided on the outer surfaces of the TFT substrate 110 and the counter substrate 120 so that their polarization axes are substantially orthogonal to each other.

The liquid crystal layer 140 contains a nematic liquid crystal material having negative dielectric anisotropy. The surface on the liquid crystal layer side of the alignment film is subjected to an alignment treatment so that the pretilt angle of the liquid crystal molecules is substantially vertical. The pretilt angle of the liquid crystal molecules is an angle formed between the main surface (or substrate surface) of the alignment film and the major axis of the liquid crystal molecules. The pretilt angle of the liquid crystal molecules is typically regulated by the alignment maintaining layer 116 so as to be slightly tilted from the substrate vertical direction.

Here, the photopolymerizable compound contained in the liquid crystal material LC will be described in detail.

The photopolymerizable compound is dissolved in the liquid crystal compound, and a mixture of the photopolymerizable compound and the liquid crystal compound is used as the liquid crystal material. An alignment maintaining layer is formed by polymerizing the photopolymerizable compound in the liquid crystal material, and a liquid crystal layer is formed from the mixture. The liquid crystal layer may contain a photopolymerizable compound that has not been polymerized.

As the photopolymerizable compound, a polymerizable monomer having at least one ring structure or condensed ring structure and two functional groups directly bonded to the ring structure or condensed ring structure is used. For example, the photopolymerizable monomer is selected from those represented by the following general formula (1).
P ¹ -A ^1- (Z ¹ -A ² ) _n -P ² (1)

In the general formula (1), P ¹ and P ² are functional groups, each independently being an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group or an epoxy group, and A ¹ and A ² are ring structures. Each independently represents a 1,4-phenylene or naphthalene-2,6-diyl group, Z ¹ represents a —COO— or —OCO— group or a single bond, and n represents 0, 1, or 2.

In the general formula (1), P ¹ and P ² are preferably acrylate groups, Z ¹ is preferably a single bond, and n is preferably 0 or 1. A preferable monomer is, for example, a compound represented by the following formula.

In the structural formulas (1a) to (1c), P ¹ and P ² are as described in the general formula (1), and particularly preferable P ¹ and P ² are acrylate groups. Further, among the above compounds, the compounds represented by Structural Formula (1a) and Structural Formula (1b) are very preferable, and the compound of Structural Formula (1a) is particularly preferable.

Hereinafter, the configuration of the peripheral part of the liquid crystal display device 100 will be described in more detail.

The liquid crystal display device 100 is divided into a display area R2 for displaying images, videos, and the like, and a frame area (or a peripheral area) R1 on the outside thereof. In the frame region R <b> 1, a sealing material 130 for sealing the liquid crystal layer 140 is provided between the

substrates

110 and 120 so as to surround the liquid crystal layer 140.

In this embodiment, the sealing material 130 is an ODF sealing material (after curing) used in the steps shown in FIGS. The sealing material 130 is formed by a photocuring process and a heat curing process. However, the sealing material 130 is not limited to this, and may be of an ultraviolet curing type, a thermosetting type, or a combination type. The width of the sealing material 130 is set to 1000 μm (1 mm), for example.

Further, between the TFT substrate 110 and the counter substrate 120, a photo spacer (PS) 132 is provided in both the frame region R1 and the display region R2. The photo spacer 132 defines an interval (cell gap d) between the TFT substrate 110 and the counter substrate 120. The photo spacer 132 is produced, for example, by patterning a photosensitive resin layer (resist material) formed on the counter substrate 120 by a spin coating method or the like by a photolithography method or the like. By appropriately performing patterning, a desired number of photo spacers 132 can be formed at a desired position on the substrate. Further, the height of the photo spacer 132 to be formed can be controlled by changing the thickness of the photosensitive resin layer. In this embodiment, using the photo spacer 132, the cell gap d in the display region R2 is set to about 3.0 μm.

In the liquid crystal display device 100 of the present embodiment, there is a portion 50 where the cell thickness d decreases in the vicinity of the area where the sealing material 130 is provided. In this specification, this portion is called a cell thickness variation portion.

In the cell thickness varying portion 50, the cell thickness is reduced because the photo spacer 132a is formed relatively low. The reason why the photo spacer 132a is formed low in this way is considered that the film thickness of the photosensitive resin layer described above decreases toward the outside of the liquid crystal cell in the frame region R1.

This is considered to be caused in the frame region R1 because the structure inside the liquid crystal cell and the structure outside the liquid crystal cell (here, meaning the part outside the sealing material 130) are greatly different. In FIG. 2, the TFT substrate 110 and the counter substrate 120 are shown as being cut at the end of the sealing material 130, but in an actual manufacturing process, a plurality of large substrates are formed on a large mother substrate. In many cases, a structure corresponding to the liquid crystal panel is provided and then divided into each liquid crystal panel. In this case, in the manufacturing process of the TFT substrate 110 and the counter substrate 120, there are continuous portions (portions not shown in FIG. 2) of the TFT substrate 110 and the counter substrate 120 in the region outside the sealing material 130. is doing. In this specification, this portion is called the outside of the liquid crystal cell.

Inside the liquid crystal cell, elements and electrodes, an alignment film, a color filter, and the like are provided on the TFT substrate 110 and the counter substrate 120. Therefore, the density inside the liquid crystal cell is in a high state. On the other hand, although the terminal part etc. for connecting with a drive circuit are provided in the liquid crystal cell outer side, there are almost no other structures and its density is low.

It seems that the thickness of the photosensitive resin layer varies due to the difference in structure between the liquid crystal cell inner side and the liquid crystal cell outer side. For example, when there is no dense base film outside the liquid crystal cell, the photosensitive resin after coating is caused by a difference in the film thickness of the base film or liquid leakage during coating (for example, spin coating) (concave portion on the coating surface). It seems that the thickness of the layer varies. In particular, when a liquid crystal display device is manufactured so that the frame region R1 becomes narrow, the thickness of the resin layer often decreases rapidly in the vicinity of the sealing material 130.

When the thickness of the resin layer is not constant and the photo spacer 132 is formed by photolithography, the height of the photo spacer 132a in the frame region R1 becomes lower than the height of the photo spacer 132 in the display region R2. In particular, when the frame region R1 is narrow, the height of the photo spacer 132a formed in the vicinity of the sealing material 130 tends to be lower than that of the photo spacer 132 formed in the display region R2.

The cell thickness variation is the ratio between the cell thickness decrease Δh in the substrate vertical direction in the cell thickness variation portion 50 and the width (width of the cell thickness variation portion 50) W of the portion where the cell thickness is decreased in the in-plane direction of the substrate. It is specified as a rate (%). In the present embodiment, the cell thickness variation portion 50 corresponds to a portion where the photo spacer 132 is formed low. The cell thickness decrease Δh corresponds to a difference in height (height variation) of the photo spacer. In FIG. 2, only one photo spacer 132a formed low is shown, but a plurality of photo spacers may be formed low. In this case, the cell thickness decrease Δh is defined as the difference in height between the photo spacer formed in the uniform cell thickness region and the lowest photo spacer in the peripheral region.

When the width W of the cell thickness variation portion 50 is 2000 μm, the cell thickness decrease is the difference between the height of the photo spacer 132 in the region where the cell thickness is constant and the height of the photo spacer 132a in the region where the cell thickness decreases. Table 1 below shows Δh, the cell thickness fluctuation rate, and the occurrence of PSA unevenness (liquid crystal flow unevenness). In Table 1 below, the case where PSA unevenness is confirmed is indicated by x, and the case where no PSA unevenness is confirmed is indicated by ◯.

As can be seen from Table 1, when the cell thickness fluctuation rate is 0.01% or less, liquid crystal flow unevenness does not occur, and the display quality of the liquid crystal display device can be improved. In order to more reliably prevent the occurrence of PSA unevenness, the cell thickness fluctuation rate is preferably 0.005% or less.

However, in the case of a liquid crystal display device operating in the VA mode, the display quality is greatly lowered when the outer cell thickness is increased. In the VA mode, the liquid crystal display device is generally displayed in normally black (black state when no voltage is applied), but when the outer cell thickness is larger, the display is whiter (brighter) than the color that should be originally displayed. White unevenness occurs. When the outer cell thickness is smaller, it is displayed darker (darker) than the color that should originally be displayed, but the luminance is lower and less noticeable than white unevenness. Therefore, in order to perform display with higher quality, it is necessary to avoid that the cell thickness on the peripheral region side becomes larger than the cell thickness on the display region side.

For this reason, when the cell thickness fluctuates as described above, it is desirable that the variation rate is suppressed to 0.01% or less, and the cell thickness in the frame region is less than or equal to the cell thickness in the display region. . In practice, it is extremely difficult to reduce the cell thickness variation rate to 0% due to the fact that a manufacturing process margin is set and thermal expansion of the liquid crystal layer may occur. For this reason, it is practically preferable to set the cell thickness in the frame region to be smaller than the cell thickness in the display region. Therefore, the cell thickness variation rate is set to 0.002% or more, for example. In this way, it is possible to prevent the outer liquid crystal layer from becoming thicker due to various factors, thereby improving the display quality in the VA mode.

Next, a specific method for controlling the cell thickness variation rate will be described.

In order to make the cell thickness fluctuation rate 0.01% or less, it is conceivable to suppress a decrease in the height of the photo spacer 132 in the frame area. For this purpose, a photosensitive resin layer for forming the photo spacer 132 may be provided in the frame region R1 in the same thickness as the display region R2.

As a method for suppressing variation in the height of the photo spacer, it is conceivable to provide a structure similar to that in the liquid crystal cell outside the liquid crystal cell. As described above, on the mother substrate, there is a portion continuous with the counter substrate 120 in a region outside the sealing material 130 that is not shown in FIG. Therefore, in the state before dividing into each panel, for example, a color filter provided in the liquid crystal cell, an insulating film (underlayer of the photo spacer), and the like are provided outside the sealing material 130 in the same manner as in the liquid crystal cell. It is possible.

In this manner, the photosensitive resin layer for forming the photo spacer can be provided with a uniform thickness if the underlying surface is relatively flat before the photo spacer is formed. The height of the photo spacer can be made uniform.

In addition, in order to make the cell thickness uniform, not only the height of the photo spacer itself but also the thickness of the underlying layer disposed below it is important. That is, it is important that the distance between the apex portion of the photospacer and the substrate surface (the sum of the height of the photospacer and the height of the structure disposed thereunder) is uniform. Therefore, when a structure is provided outside the liquid crystal cell, the distance from the substrate to the top of the photospacer should be uniform, including not only the height of the photospacer itself but also the underlying film provided below it. Therefore, it is desirable to control the height of the photo spacer, the thickness of the base film, and the like.

For example, a wall-like structure may be provided outside the liquid crystal cell. This wall-shaped structure prevents a decrease in thickness outside the liquid crystal cell (a decrease in local leveling on the coating surface) when a photosensitive resin layer for a photospacer is provided by a spin coating method or the like. It is provided as follows. Also, when forming the underlayer of the photo spacer, the underlayer can be formed with a more uniform thickness inside and outside the cell. In this way, it is possible to make the distance from the substrate to the top of the photo spacer relatively uniform.

As described above, when the liquid crystal material contains a photopolymerizable compound by the PSA technique, the cell thickness variation rate is suppressed to 0.01% or less by appropriately adjusting the height of the photo spacer. It is desirable. When the cell thickness variation rate is set to 0.01% or less, even if a polymer is generated in the liquid crystal layer in the vicinity of the sealing material in the sealing material curing step, unevenness that shows a trace of the flow of the liquid crystal material is exhibited. Does not occur. As a result, even when the frame area is set narrow and the display area is provided at a position relatively close to the sealing material, high-quality display can be performed.

Although an example using a vertical alignment type liquid crystal layer has been described above, the present invention is not limited to this. Even when a horizontal alignment type liquid crystal layer such as an ECB liquid crystal or a TN liquid crystal is used, the unevenness of liquid crystal flow caused by the polymer by the PSA technology is achieved by suppressing the cell thickness fluctuation rate to 0.01% or less. Can be suppressed.

(Embodiment 2)
FIG. 3 shows an end cross section of the liquid crystal display device 200 of the second embodiment. Similar to the liquid crystal display device 100 of the first embodiment, the liquid crystal display device 200 seals the TFT substrate 110, the counter substrate 220, the vertically aligned liquid crystal layer 140 sandwiched therebetween, and the liquid crystal layer 140 between the substrates. It has a sealing material 130 for stopping. The same components as those in the first embodiment are denoted by the same reference numerals.

In the liquid crystal display device 200, the counter substrate 220 has an organic planarization film 222. The organic planarization film 222 functions as a base film in the liquid crystal cell, and a photo spacer 132 is formed on the organic planarization film 222.

Also in the case of forming the organic planarizing film 222, the film thickness tends to decrease in the portion corresponding to the frame region R1 of the counter substrate 220 as in the photo spacer forming process described in the first embodiment. In particular, in the vicinity of the sealing material 130, the film thickness of the organic planarizing film 222 decreases rapidly. As the thickness of the organic planarizing film 222 decreases, the cell thickness decreases in the frame region R1, and the liquid crystal flow slows down.

In FIG. 3, unlike the first embodiment, not the counter substrate 220 but the TFT substrate 110 is bent. The cell thickness variation portion 50 is a portion formed near the outer periphery of the liquid crystal cell, and may be a portion where the cell thickness is reduced, and does not necessarily require deformation of the counter substrate or the TFT substrate. Further, the cell thickness variation portion may be formed with the deformation of both the substrates.

The cell thickness variation is the ratio between the cell thickness decrease Δh in the substrate vertical direction in the cell thickness variation portion 50 and the width (width of the cell thickness variation portion 50) W of the portion where the cell thickness is decreased in the in-plane direction of the substrate. It is specified as a rate (%). Here, the cell thickness decrease Δh is the maximum difference in film thickness of the organic planarization film 222 between the display region R2 and the frame region R1.

When the width W of the cell thickness variation portion 50 is 2000 μm, the cell thickness decrease Δh, which is the difference in the thickness of the organic planarization film 222 in the display region R2 and the frame region R1, the cell thickness variation rate, and the PSA unevenness The occurrence of (liquid crystal flow unevenness) is shown in Table 2 below. In Table 2 below, the case where PSA unevenness is confirmed is indicated by x, and the case where no PSA unevenness is confirmed is indicated by ◯.

As can be seen from Table 2, when the cell thickness fluctuation rate is 0.01% or less, liquid crystal flow unevenness does not occur, and the display quality of the liquid crystal display device can be improved. As described above, in order to suppress the cell thickness variation rate to 0.01% or less, for example, in the same process as that described in the first embodiment, in the step before the organic planarization film 222 is formed, the outside of the liquid crystal cell. A structure similar to that inside the liquid crystal cell may be provided. In addition, a wall-like structure may be provided outside the liquid crystal cell to suppress a decrease in film thickness in this region when the organic planarizing film 222 is formed.

(Embodiment 3)
In the liquid crystal display device of Embodiment 3, the cell thickness variation rate is set to 0.01% or less by appropriately arranging the photo spacers 132 in the frame region R1. Before describing the liquid crystal display device of this embodiment, first, problems that occur when no photo spacer is provided in the frame region R1 will be described.

FIG. 4A shows a change in cell thickness that may occur when no photo spacer is provided in the frame region R1. As shown in FIG. 4A, in the frame region R1, the cell thickness is reduced because there is no support by the photo spacer.

FIG. 4A shows a form in which the sealing material 130 has a height substantially the same as the cell thickness in the display region R2. However, as can be seen from the figure, it is difficult to suppress the cell thickness variation in the frame region only by adjusting the height of the sealing material 130. If there is such a portion where the cell thickness varies, the flow rate of the liquid crystal material may be reduced. In order to prevent deterioration in display quality due to PSA unevenness, it is necessary to suppress this decrease in flow rate. For this purpose, it is important to keep the cell thickness fluctuation rate within a predetermined range. It is.

Therefore, as shown in FIG. 4B, it is desirable to reduce the cell thickness variation rate by providing a photo spacer 132a at the center of the frame region R1 and maintaining the distance between the substrates by this photo spacer. However, in the frame region R1, it is desirable to dispose the photo spacer 132a so as not to reduce the fluidity of the liquid crystal.

FIGS. 5A and 5B show the arrangement of the photo spacers 132a in the frame region R1. As shown in FIG. 5A, the photo spacer 132a is provided along the line 11 at the substantially center of the frame region R1 having the width D.

In FIG. 5A, the density is lower than that of the photo spacers 132 provided in the display region R2, and the gaps are further spaced. This is advantageous for suppressing a decrease in the fluidity of the liquid crystal material in the frame region R1. Furthermore, by setting the size (diameter) of the photo spacer 132a to be relatively large, it is possible to prevent deformation due to external pressure or the like, and to prevent its height from fluctuating. Therefore, there is an advantage that the cell gap can be easily maintained at a desired interval.

Further, as shown in FIG. 5B, more photo spacers 132a may be provided. Also in this case, it is desirable to position the center portion of the photo spacer formation region along the center line l1 of the frame region R1. Further, the interval between the photo spacers 132a in the width direction of the frame region R1 may be smaller than the interval between the photo spacers 132 in the display region R2. This provides the advantage that the cell gap can be easily maintained at a desired interval in the frame region. However, it is better not to reduce the distance between the photo spacers 132a in the direction perpendicular to the width direction because the liquid crystal fluidity may be hindered.

As shown in FIGS. 5 (a) and 5 (b), by arranging the photo spacer, it is possible to effectively suppress the reduction in the cell thickness while keeping the liquidity of the liquid crystal material relatively high. As described above, by appropriately arranging the photo spacers, it becomes easy to set the cell thickness variation rate to 0.01% or less. Even when the height of the photo spacer varies, it is possible to effectively suppress the reduction of the cell thickness and to suppress the occurrence of PSA unevenness without significantly impeding the fluidity of the liquid crystal material in this region.

In the above description, the case where the height of the sealing material is substantially the same as the cell thickness of the display area has been described. In that case, it is desirable to provide a photo spacer at a position having a cell thickness obtained by averaging the height of the sealing material and the cell thickness in the display region.

The present invention is widely used in various liquid crystal display devices such as liquid crystal televisions.

50 Cell thickness variation portion 100 Liquid crystal display device 110 TFT substrate 112 Transparent substrate 114 Vertical alignment film 116 Orientation maintaining layer 120 Counter substrate 130

Sealing material

132, 132a Photo spacer 140 Liquid crystal layer R1 Frame region (peripheral region)
R2 display area d Cell gap

Claims

A pair of substrates;
A liquid crystal layer sandwiched between the pair of substrates;
A sealing material provided so as to surround the liquid crystal layer;
Between the pair of substrates, a plurality of spacers provided so as to define an interval between the pair of substrates;
An alignment film provided on the liquid crystal layer side of at least one of the pair of substrates;
An alignment maintaining layer provided on the liquid crystal layer side of the alignment film, the alignment maintaining layer including a polymer formed by polymerizing a polymerizable compound, and a liquid crystal display device comprising:
In the vicinity of the sealing material, a cell thickness variation portion is formed in which the distance between the pair of substrates decreases toward the portion where the sealing material is provided,
A liquid crystal display device having a cell thickness variation rate Δh / W of 0.01% or less, which is a ratio of a cell thickness decrease Δh in the substrate vertical direction and a width W in the substrate in-plane direction of the cell thickness variation portion.
A display area for displaying and a peripheral area located outside the display area are defined, and the cell thickness variation portion is formed in the vicinity of a boundary between the display area and the peripheral area. 2. A liquid crystal display device according to 1.
The spacer is formed in both the display area and the peripheral area,
The spacer formed in the peripheral region is lower than the spacer formed in the display region,
The liquid crystal display device according to claim 2, wherein the cell thickness decrease Δh is determined according to a difference between a height of the spacer formed in the peripheral region and a height of the spacer formed in the display region.
4. The liquid crystal display device according to claim 3, wherein the spacer formed in the peripheral region is formed in a central portion of the peripheral region.
One of the pair of substrates includes a planarization film provided on the liquid crystal layer side,
The planarizing film has different thicknesses in the display region and the peripheral region,
The liquid crystal display device according to claim 2, wherein the cell thickness decrease Δh is determined according to a difference in thickness of the planarizing film.
The liquid crystal layer is a vertical alignment type liquid crystal layer, and the alignment film is a vertical alignment type alignment film,
The liquid crystal display device according to claim 2, wherein a cell thickness in the peripheral region is smaller than a cell thickness in the display region.