WO2012108311A1

WO2012108311A1 - Liquid crystal display

Info

Publication number: WO2012108311A1
Application number: PCT/JP2012/052240
Authority: WO
Inventors: 敢三宅; 井上　威一郎; 寺下　慎一; 宮地　弘一; 宏一松橋
Original assignee: シャープ株式会社
Priority date: 2011-02-08
Filing date: 2012-02-01
Publication date: 2012-08-16

Abstract

The objective of the present invention is to provide a liquid crystal display that has a novel display mode able to achieve high transmittance, high contrast, and high orientation stability. The liquid crystal display is provided with a liquid crystal cell and a polarizing plate. The liquid crystal cell is provided with: a first substrate and a second substrate that are configured containing a plurality of pixels; a vertically-oriented liquid crystal layer containing a liquid crystal molecule; a first orientation film provided to the surface on the liquid-crystal-layer-side of the first substrate; and a second orientation film provided to the surface on the liquid-crystal-layer-side of the second substrate. Each of the plurality of pixels has at least one orientation region, and in the orientation regions, the long axis direction of the liquid crystal molecules has a pre-tilt angle with respect to the first and second substrate surfaces. The orientation projecting the long axis direction of the liquid crystal molecules in the vicinity of the first orientation film to the first substrate surface, and the orientation projecting the long axis direction of the liquid crystal molecules in the vicinity of the second orientation film to the second substrate surface intersect each other, and the polarizing plate necessitates a circular polarizing plate provided on the observer side of the liquid crystal cell.

Description

LCD display

The present invention relates to a liquid crystal display including a liquid crystal cell and a polarizing plate. More specifically, the present invention relates to a VATN (Vertical Aligned Twisted Nematic) mode having a vertically aligned liquid crystal layer, and particularly to a liquid crystal display suitable for small and medium sized liquid crystal applications such as mobile devices, electronic books, and PC monitors. It is.

A liquid crystal display is configured by sandwiching a liquid crystal display element between a pair of substrates such as a glass substrate, and has a feature of being thin, light and low power consumption. Liquid crystal displays are indispensable for daily life and business because they are used for mobile applications, various monitors, televisions, etc., taking advantage of these features. In recent years, along with the growing demand for small and medium-sized liquid crystal displays due to the development of portable electronic devices and market development, they are used for mobile devices, electronic books, photo frames, IA (industrial equipment), PC (personal computer) monitor applications, etc. Widely adopted. In order to exhibit various display characteristics corresponding to these various uses, liquid crystal displays in various display modes (generally also referred to as liquid crystal display panels) have been studied. In each display mode, an electrode arrangement and / or a substrate design specific to each display mode is employed in order to change the optical characteristics of the liquid crystal layer.

Among the conventional liquid crystal displays, as a display mode that can be applied to a small and medium-sized liquid crystal display, for example, a CPA (ContinuousConPinwheel Alignment) mode can be cited. As a liquid crystal display suitable for such a CPA mode, a liquid crystal layer having a vertical alignment type liquid crystal layer, and having an alignment control structure in the liquid crystal layer that expresses an alignment control force that takes a radially inclined alignment state when a voltage is applied. A display device is disclosed (for example, see Patent Document 1).

As in the liquid crystal display of the CPA mode, a liquid crystal layer containing liquid crystal molecules having negative dielectric anisotropy is sandwiched between an active matrix substrate and a counter substrate, as in the above-described configuration of the liquid crystal display device. Are provided with pixel electrode and TFT scanning wiring (gate bus line), and the opposing substrate has a convex portion which is an alignment regulating structure for stabilizing the radial tilt alignment in a region corresponding to the center of the opposing electrode and the liquid crystal domain. A liquid crystal display device in which a vertical alignment film is provided on the surface of the active matrix substrate and the counter substrate on the liquid crystal layer side is disclosed (for example, see Patent Document 2). This liquid crystal display device includes a polymer structure formed on a vertical alignment film, and the orientation of the pretilt direction of liquid crystal molecules around the polymer structure is the same as the tilt direction when a voltage is applied even in the absence of voltage application. It is defined in the same direction. The polymer structure is formed by previously mixing a polymerizable composition (polymerizable monomer or oligomer) into the liquid crystal material constituting the liquid crystal layer and polymerizing the polymerizable composition with ultraviolet light irradiation. . This polymerization process is also referred to as a PSA (Polymer-Sustained Alignment) process.

Furthermore, the present invention relates to a liquid crystal display that operates in a so-called VA (Vertically Aligned) mode in which liquid crystal molecules having negative dielectric anisotropy are aligned in a substantially vertical direction with respect to the panel surface of the liquid crystal display, and the liquid crystal molecules form a twist angle. In addition, a liquid crystal display device in which liquid crystal molecules are aligned in a direction substantially perpendicular to a pair of substrates is disclosed (see, for example, Patent Documents 3 and 4). Patent Document 3 describes that in this liquid crystal display device, response speed, viewing angle, and contrast are optimized.
In addition, in a conventional TN (Twisted Nematic) mode liquid crystal display, a configuration using an elliptically polarizing plate is disclosed (see, for example, Patent Documents 5 to 7), and these documents particularly describe a TN mode liquid crystal display device. Describes that the viewing angle of contrast can be expanded. Hereinafter, the TN mode using an elliptically polarizing plate is also referred to as an elliptically polarized TN mode.

JP 2002-202511 A JP 2009-122254 A Japanese Patent No. 3282986 Special table 2008-538819 JP 2006-301579 A JP 2008-116984 A JP 2009-75533 A

As the demand for liquid crystal displays increases, the development of small and medium-sized liquid crystal displays such as mobile devices, electronic books, and PC monitors is particularly remarkable, and there is a demand for the supply of liquid crystal displays with high transmittance, high contrast, and high alignment stability. Is growing.
In such a liquid crystal display, how to configure the liquid crystal cell and the polarizing plate is an important examination item. Polarizers are roughly classified into circular polarizers and linear polarizers. Hereinafter, a method using a linearly polarizing plate is also referred to as a linearly polarizing mode, and a method using a circularly polarizing plate is also referred to as a circularly polarizing mode. For example, as a combination of the kind of polarizing plate and the display mode of the liquid crystal cell, a combination of a CPA mode, which is one typical display mode, and a circularly polarizing plate can be considered.

However, when the circularly polarizing plate and the CPA mode are combined, there is a problem that the display is crushed at a low gradation at an oblique viewing angle, and there is a problem that the transmittance is reduced due to the rivet that is an alignment regulating structure. The reason is as follows. That is, the problem that the display is crushed at a low gradation is caused by the fact that the pretilt angle of the CPA mode is 90 °, and the direction in which the liquid crystal molecules are tilted is not determined near the threshold when a voltage is applied. The rivet serves as a trigger for the liquid crystal molecules to fall radially around the rivet. In the case of the CPA mode, as shown in FIG. 4, in the graph showing the relationship of voltage (liquid crystal drive voltage) -transmitted light intensity, the transmitted light intensity changes sharply near the threshold at which the alignment characteristics of the liquid crystal change. Therefore, the smoothness of gradation expression is lost in the vicinity of such an inflection point, and gradation jumping and / or collapse occurs. Further, if the graph is shifted to the left or right even a little, the difference in transmitted light intensity increases before and after the shift. Therefore, an afterimage is likely to occur.

In the CPA mode using the circular polarizing plate as described above, if the pretilt angle is smaller than 90 °, that is, if the liquid crystal molecules are tilted from the normal direction of the panel surface, the above-described problems are solved.
Therefore, it is conceivable to give a pretilt angle of less than 90 ° to the CPA mode, but as such a technique, it has already been proposed to use the PSA technique (see, for example, Patent Document 2). However, the rivet still cannot be removed, and there is a transmittance loss corresponding to the area of the rivet as a protrusion as shown in FIG.
In addition, problems unique to the PSA technology are newly generated. Such problems include the occurrence of image sticking due to the residual monomer in the liquid crystal layer, a decrease in reliability caused by decomposition or degradation of the liquid crystal due to ultraviolet irradiation, and a decrease in reliability due to the residual monomer. In view of these current conditions, a display mode that can be manufactured by a more reliable and simple process is required.

On the other hand, Patent Document 3 discloses an embodiment using a linearly polarizing plate in a liquid crystal display device that combines the VA mode and the TN mode as described above, and optimizes contrast, viewing angle characteristics, and response characteristics. Is disclosed. Hereinafter, a mode in which the VA mode and the TN mode are combined is also referred to as a VATN (Vertical Aligned Twisted Nematic) mode, and a VATN mode using a linearly polarizing plate is also referred to as a linearly polarized VATN mode. However, in such a linearly polarized light VATN mode, in order to improve the viewing angle characteristics, when domain division (for example, four-domain division) in which a plurality of regions having different alignment characteristics of liquid crystal molecules is performed in one pixel is performed, There arises a problem in that a boundary between matching domains (domain boundary) and a dark line generated at an edge of a pixel lowers the transmittance. Further, when the pretilt angles are different between the upper and lower substrates due to process factors, the transmittance decreases. For this reason, a process margin is narrow and it becomes necessary to strictly perform production process management for providing a high-quality liquid crystal product. In the case of the linearly polarized VATN mode, the transmittance decreases as described above as the pretilt angle increases. Conversely, the transmittance increases as the pretilt angle decreases. The birefringence felt by the lens increases, so that light leakage increases, resulting in a decrease in contrast.
Even in the elliptically polarized TN mode, when domain division is performed in order to improve viewing angle characteristics, a defect line (dark line) is generated at the domain boundary, resulting in a decrease in contrast and / or transmittance. Even without domain division, the horizontal alignment mode represented by the TN mode has a lower contrast than the VA (vertical alignment) mode.

Furthermore, in recent years, touch panel type liquid crystal displays have become widespread rapidly, and in particular, the demand for medium- and small-sized liquid crystal panels having a touch panel function has been greatly increased. Under such circumstances, when the surface of the liquid crystal panel is pressed with a finger or a pen, the liquid crystal alignment is disturbed by the pressing, and the problem that the alignment does not return to the original state has been clarified.
Thus, although the detailed cause of the problem that the display is disturbed when the panel surface is pressed is unknown, in the case of the CPA mode, the pretilt angle is 90 °, that is, the vertical direction in which the liquid crystal molecules have no tilt with respect to the substrate surface. Since the alignment is disturbed, it takes a long time to restore the alignment disorder, and the alignment is not stable (it takes a long time to restore the alignment).

Among various modes as described above, there is a possibility that high transmittance can be achieved by combining a circularly polarizing plate with the conventional CPA mode and further adopting PSA technology. It has been found that if only a circularly polarizing plate is combined, the gradation display will be crushed and the transmittance will be reduced by rivets, and even if the PSA technology is adopted, problems will arise. Also in the linear polarization VATN mode, the transmittance decreases due to the dark line at the pixel edge, the process margin decreases due to the difference in the pretilt angle between the upper and lower substrates, the transmittance decreases due to the size of the pretilt angle, the contrast decreases, and the liquid crystal changes when the panel surface is pressed. It has been found that there is a problem of alignment stability. And the said subject was analyzed in detail and earnestly examined regarding the combination of a display mode and a polarizing plate.

The present invention has been made in view of the above-described present situation, and an object thereof is to provide a liquid crystal display of a new display mode that can realize high transmittance, high contrast, and high alignment stability. Preferably, high transmittance and high contrast can be realized. In a domain-divided configuration, the transmittance decreases when the pretilt angle is large, and the contrast decreases when the pretilt angle is small. It is possible to solve the problem that it is not possible to achieve a configuration that can achieve both the contrast and the problem with the PSA technology, the process margin decreases due to the difference in the pretilt angle between the upper and lower substrates, and the transmittance decreases due to the size of the pretilt angle Another object of the present invention is to provide a liquid crystal display of a new display mode that can solve the problems such as the reduction in contrast and the stability of alignment of the liquid crystal when the panel surface is pressed.

The inventors of the present invention have studied various combinations of the display mode and the polarizing plate. As described above, the liquid crystal display adopting the CPA mode and the circular polarizing plate and further adopting the PSA technology and the linear polarization VATN mode liquid crystal display are described above. Since such a problem to be improved arises, attention was paid to further room for optimization in optimizing the display mode and the polarizing plate. Then, by using the circularly polarized VATN mode or the circularly polarized VAECB (Vertical Alignment Electrically Controlled Birefringence) mode, it is found that an unexpected display characteristic is expressed from the combination of the display mode and the polarizing plate, and For example, even if domain division for improving the viewing angle is adopted, it has been found that, unlike the linearly polarized VATN mode, the problem of transmittance reduction can be solved, and the above problem can be solved brilliantly. The present invention has been achieved.

One aspect of the present invention is a liquid crystal display that uses a circularly polarized VATN mode or a circularly polarized VAECB mode as a new display mode. Hereinafter, the liquid crystal display according to the present invention is also expressed as a circularly polarized VATN mode or a circularly polarized VAECB mode. In the circularly polarized VATN mode, liquid crystal molecules are twisted and aligned as in the general TN mode, but the pretilt angle is about 5 ° in the TN mode, and the pretilt angle is large in the circularly polarized VATN mode ( In a preferred embodiment, about 80 ° or more). Originally, a liquid crystal element combining a TN mode with a circularly polarizing plate cannot be used as a display element. This is because in order to achieve high transmittance in the circularly polarized light mode, it is necessary that the liquid crystal layer does not contain a twist component. In order to allow a liquid crystal element combining a TN mode and a circularly polarizing plate to function as a display element, a seemingly impossible configuration is required in which an orientation with less twisted components is achieved from the twisted initial orientation. In the CPA mode, since there is no twist component, if a circularly polarizing plate is adopted in the CPA mode, high transmittance can be obtained from that point alone. On the other hand, in the VATN mode, since the liquid crystal molecules are usually twisted at a predetermined angle (for example, 90 °) between the upper and lower substrates, it is expected that the transmittance is lower than that in the CPA mode. However, by selecting an optimal pretilt angle in the circularly polarized VATN mode, the torsional component can be remarkably reduced, higher transmittance can be achieved than in the CPA mode, and the display is crushed at an oblique viewing angle at a low gradation. It was found that such a problem can be solved. Further, the circularly polarized VAECB mode does not include a twist component, and the circularly polarized VAECB mode is characterized by a large pretilt angle (in the preferred embodiment, approximately 80 ° or more), which is higher transmission than the CPA mode. It is possible to solve the problem that the display is crushed at an oblique viewing angle at a low gradation. Furthermore, in these methods, it is not necessary to employ the PSA technology. In that case, since there is no ultraviolet irradiation to the liquid crystal layer in the PSA process, the voltage holding ratio (VHR: VoltageＶHolding Ratio) does not decrease, Since an additive such as a monomer is not added to the liquid crystal material, that is, no residual monomer is contained in the liquid crystal layer, a highly reliable liquid crystal display can be manufactured. Furthermore, it is not necessary to arrange a protrusion (rivet) in the pixel. In that case, a decrease in the transmittance due to the protrusion is suppressed, and the transmittance becomes higher.

In the liquid crystal display according to the present invention, in the VATN mode or VAECB mode as described above, a circularly polarizing plate is used instead of only a linearly polarizing plate. Further, by optimizing the pretilt angle, a high transmittance higher than that of the linearly polarized VATN mode can be achieved. As described above, when the circularly polarizing plate is used in the VATN mode and the VAECB mode, it should be noted that the transmittance hardly decreases even if the tilt angles (pretilt angles) of the liquid crystal molecules with respect to the upper and lower substrates are different from each other due to process factors. Can be mentioned. That is, unlike the linearly polarized VATN mode and the linearly polarized VAECB mode, the difference between the pretilt angles on the upper and lower substrates is not easily affected, and thus such a difference in the pretilt angle occurs in the production process. And a new feature that the process margin is wide can be added to the VATN mode and the VAECB mode.

The essential configuration of the liquid crystal display according to the present invention is as follows.
That is, another aspect of the present invention is a liquid crystal display including a liquid crystal cell and a polarizing plate,
The liquid crystal cell includes a first substrate and a second substrate including a plurality of pixels, a vertically aligned liquid crystal layer including liquid crystal molecules provided between the substrates, and a liquid crystal layer side of the first substrate. A first alignment film provided on the surface of the second substrate, and a second alignment film provided on the surface of the second substrate on the liquid crystal layer side,
Each of the plurality of pixels has one or more alignment regions,
In the alignment region, the major axis direction of the liquid crystal molecules has a pretilt angle with respect to the first and second substrate surfaces, and the major axis direction of the liquid crystal molecules in the vicinity of the first alignment film is projected onto the first substrate surface; The direction in which the major axis direction of the liquid crystal molecules in the vicinity of the second alignment film is projected on the surface of the second substrate intersects each other,
The polarizing plate is a liquid crystal display in which a circularly polarizing plate provided on the viewer side of the liquid crystal cell is essential.

Yet another aspect of the present invention is a liquid crystal display comprising a liquid crystal cell and a polarizing plate,
The liquid crystal cell includes a first substrate and a second substrate including a plurality of pixels, a vertically aligned liquid crystal layer including liquid crystal molecules provided between the substrates, and a liquid crystal layer side of the first substrate. A first alignment film provided on the surface of the second substrate, and a second alignment film provided on the surface of the second substrate on the liquid crystal layer side,
Each of the plurality of pixels has one or more alignment regions,
In the alignment region, the major axis direction of the liquid crystal molecules has a pretilt angle with respect to the first and second substrate surfaces, and the major axis direction of the liquid crystal molecules in the vicinity of the first alignment film is projected onto the first substrate surface; The major axis direction of the liquid crystal molecules in the vicinity of the second alignment film is parallel to and opposite to the directions projected on the second substrate surface,
The polarizing plate is a liquid crystal display in which a circularly polarizing plate provided on the viewer side of the liquid crystal cell is essential.
The liquid crystal display according to the present invention will be described in detail below. Hereinafter, the first and second substrates are also referred to as upper and lower substrates, one of the first and second substrates is also referred to as an upper substrate, and the other as a lower substrate.

The liquid crystal display according to the present invention is a vertical alignment mode liquid crystal display, and includes a VATN mode or VAECB mode liquid crystal cell and a circular polarizer on the viewer side of the liquid crystal cell.
The VATN mode is a kind of display mode of a liquid crystal display and is classified as a TN mode. In the VATN mode, the major axis direction of the liquid crystal molecules in the liquid crystal layer is usually the alignment regulation of the alignment film in a state where the voltage in the liquid crystal layer is less than the threshold voltage, preferably in a state where no voltage is applied to the liquid crystal layer. Force is perpendicular to the substrate surface by force, has a pretilt angle to the substrate surface, and twists the orientation of the major axis direction of the liquid crystal molecules projected on the substrate surface in the vicinity of the alignment film surfaces of the upper and lower substrates. It is in the state. A state where the voltage in the liquid crystal layer is lower than the threshold voltage and a state where no voltage is applied to the liquid crystal layer are collectively referred to as an off state. The VAECB mode is a kind of display mode of a liquid crystal display and is classified as an ECB mode. In the above-described VAECB mode, the major axis direction of the liquid crystal molecules in the liquid crystal layer usually has a pretilt angle with respect to the substrate surface while the major axis direction of the liquid crystal layer has a vertical alignment with respect to the substrate surface by the alignment regulating force of the alignment film. In addition, the directions in which the major axis directions of the liquid crystal molecules in the vicinity of the alignment film surfaces of the upper and lower substrates are projected on the substrate surface are parallel and opposite to each other. In such a production process of the VATN mode and the VAECB mode, for example, a vertical alignment film may be formed on both substrates and an alignment process (preferably a photo alignment process) for providing a pretilt angle may be performed.
The VATN mode and VAECB mode liquid crystal layers are usually configured to include nematic liquid crystal molecules having negative dielectric anisotropy.

The liquid crystal cell includes a plurality of pixels each having one or more alignment regions (domains), and has a vertical alignment type liquid crystal layer as described above sandwiched between first and second substrates.

In the circularly polarized VATN mode, normally, in the off state, the orientation in which the major axis direction of the liquid crystal molecules in the vicinity of the first alignment film is projected onto the surface of the first substrate and the major axis direction of the liquid crystal molecules in the vicinity of the second alignment film are in the second state. The directions projected on the substrate surface intersect each other. In other words, in the circularly polarized VATN mode, the orientation direction of the liquid crystal molecules near the first substrate and the orientation direction of the liquid crystal molecules near the second substrate are set to intersect each other in each domain. The angle (intersection angle) formed by both positions is not particularly limited and can be set as appropriate. The feature of the circularly polarized VATN mode according to the present invention that the allowable range of the difference in pretilt angle between the upper and lower substrates is wider than that of the linearly polarized VATN mode is a feature unique to the circularly polarizing plate, and this feature is the circularly polarized VATN according to the present invention. The mode reflects the fact that the transmittance is high regardless of the orientation direction of the liquid crystal molecules. That is, even if the angle formed by the orientation directions of the liquid crystal molecules on the upper and lower substrates is deviated from 90 °, only the orientation direction of the liquid crystal molecules is changed. In the circularly polarized VATN mode according to the present invention, the transmittance remains high. Therefore, the allowable range of the crossing angle is wider than that of the linearly polarized VATN mode. More specifically, the crossing angle can be set within a range of 30 ° or more and less than 180 ° (for example, 179.9 ° or less). However, from the viewpoint of using the production line of the linearly polarized VATN mode, it is preferably set within a range allowed in the normal linearly polarized VATN mode. More specifically, the crossing angle is from 90 °. It is preferably within a range of ± 5 ° (85 to 95 °).

In the circularly polarized VAECB mode, normally, in the off state, the orientation in which the major axis direction of the liquid crystal molecules in the vicinity of the first alignment film is projected onto the surface of the first substrate and the major axis direction of the liquid crystal molecules in the vicinity of the second alignment film are in the second state. The directions projected on the substrate surface are parallel and opposite to each other. In other words, in the circularly polarized VAECB mode, the angle formed by the orientation direction of the liquid crystal molecules near the first substrate and the orientation direction of the liquid crystal molecules near the second substrate is substantially 180 ° (for example, 179 in each domain). Is set to be larger than .9 °).

In a normal embodiment, in one domain in one pixel, the pretilt directions of the liquid crystal molecules in the vicinity of the alignment film on the upper substrate are the same, that is, aligned, and the liquid crystal molecules in the vicinity of the alignment film on the lower substrate are aligned. The pretilt directions are the same, ie, aligned. When one pixel has two or more domains, the pretilt direction of the liquid crystal molecules in the vicinity of the alignment film on the upper substrate and the pretilt direction of the liquid crystal molecules in the vicinity of the alignment film on the lower substrate are divided into one domain and the other domain. At least one of them will be different from each other. Having two or more domains in one pixel is also called orientation division.

The pretilt angle in the liquid crystal display according to the present invention is an angle formed between the surface of the substrate (alignment film) and the major axis direction of the liquid crystal molecules in the vicinity of the alignment film inclined with respect to the surface of the substrate (alignment film) in the off state. It is. If it demonstrates using FIG. 3, in the said OFF state, it is a polar angle which the long axis of a liquid crystal molecule makes with respect to a substrate (alignment film) surface, Comprising: It is an angle which exceeds 0 degree and is less than 90 degrees. Regardless of the off state or the on state, the angle formed by the substrate (alignment film) surface and the major axis direction of the liquid crystal molecules in the vicinity of the alignment film is referred to as a tilt angle or a polar angle.

Note that the technical range in terms of vertical alignment is not limited to being strictly vertical, but within the range allowed in the normal VATN mode and / or VAECB mode, the vertical alignment is near the substrate (alignment film). Anything that can be evaluated is acceptable. Preferably, the pretilt angle of the liquid crystal molecules in the vicinity of the first alignment film and the pretilt angle of the liquid crystal molecules in the vicinity of the second alignment film are 80 ° or more and 89.9 ° or less, respectively.
Further, the configuration of the liquid crystal display according to the present invention is not particularly limited by other components as long as the components described above are essential.
The liquid crystal display according to the present invention may be a liquid crystal panel, a liquid crystal display element, or a liquid crystal display device.
Other preferred modes in the circularly polarized VATN mode will be described in detail below. Various forms shown below may be combined as appropriate.

In one preferred embodiment of the liquid crystal display according to the present invention, the pretilt angle has a form in which the difference between the vicinity of the first alignment film and the vicinity of the second alignment film is less than 1.0 ° (pretilt angle vertically symmetrical form). Also called). In this mode, in the VATN mode, the pretilt angle of the liquid crystal molecules on the first alignment film and the pretilt angle of the liquid crystal molecules on the second alignment film are substantially the same, that is, the pretilt angles on the upper and lower substrates are substantially the same. It is evaluated that it is the same. In this case, the transmittance is more susceptible to the influence of the pretilt angle than in a form in which the pretilt angles on the upper and lower substrates described later are substantially different from each other. The larger the pretilt angle, the higher the transmittance and the brighter.

With regard to the pretilt angle, particularly when the pretilt angles on the upper and lower substrates are substantially the same, the following preferred embodiments can be mentioned.
First, the pretilt angle is 84 ° or more and less than 90 ° (for example, 89.9 ° or less), that is, the pretilt angle of the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film. Are pre-tilt angles of 84 ° or more and less than 90 ° (for example, 89.9 ° or less). In this embodiment, a higher contrast can be realized at 84 ° or more as compared with the linearly polarized VATN mode, and the contrast increases as the pretilt angle increases, and reaches a peak state around 90 °.

Second, the pretilt angle is 86 ° or more, that is, the pretilt angle of the liquid crystal molecules near the first alignment film and the pretilt angle of the liquid crystal molecules near the second alignment film are each 86 ° or more. It is a form. In this embodiment, a higher transmittance can be realized as compared with the embodiment in which the circularly polarizing plate is combined with the CPA mode, and the transmittance is improved as the pretilt angle is increased.

Thirdly, the pretilt angle is 89.7 ° or less, more preferably the pretilt angle is 89.5 ° or less, that is, the pretilt angle of the liquid crystal molecules in the vicinity of the first alignment film, The pretilt angles of the liquid crystal molecules in the vicinity of the bi-alignment film are each 89.7 ° or less, more preferably 89.5 ° or less. In this embodiment, display disturbance due to pressing on the liquid crystal display can be improved. In the circularly polarized light VATN mode, the smaller the pretilt angle, the greater the alignment regulating force acting in the direction of the pretilt azimuth angle, which is considered to be due to the strong restoring force against the alignment disturbance caused by pressing. In addition, since the pretilt angle is less than 90 °, the time from when the orientation is disturbed by pressurization until the orientation is restored can be remarkably improved. In such a form, in addition to being able to achieve high transmittance and high contrast, coupled with high alignment stability, it is possible to improve display performance in applications where the surface of the liquid crystal display is pressed, especially This is suitable for a small-sized liquid crystal display of a touch panel type.

In one embodiment, the polarizing plate further includes a circularly polarizing plate provided on the back side of the liquid crystal cell. In this embodiment, the liquid crystal display according to the present invention further includes a circularly polarizing plate provided on the back side of the liquid crystal cell. In the liquid crystal display according to the present invention, it is essential to provide a circularly polarizing plate on the viewer side of the liquid crystal cell, but whether to provide a circularly polarizing plate on the back side of the liquid crystal cell is as follows. It depends on whether the display method of the display is a transmission type or a reflection type. In other words, the liquid crystal display according to the present invention may be a transmissive liquid crystal display device that performs display by transmitting light from the backlight through the liquid crystal cell, and the external light is incident on the liquid crystal cell and reflected. A reflective liquid crystal display device that performs display may be used, or a combination of the two may be a transflective type that includes a region that displays by transmission (transmission region) and a region that performs display by reflection (reflection region). You may apply to a liquid crystal display device. In the case of the transmission type, it is preferable to provide a circularly polarizing plate on both sides of the observer side and the back side of the liquid crystal cell. In the case of the reflection type, it is preferable to provide a circularly polarizing plate only on the viewer side of the liquid crystal cell. In addition, in the semi-transmissive type, when the incident light that has passed through the liquid crystal layer is reflected by the substrate, if a circularly polarizing plate is provided on both the viewer side and the back side of the liquid crystal cell, the transmitted light is transmitted on the back side in the transmissive region. The light passes through the circularly polarizing plate, the liquid crystal layer, and the circular polarizing plate on the viewer side in this order. In the reflection region, incident light passes through the circular polarizing plate and the liquid crystal layer on the viewer side in this order, and then is reflected by the substrate. Is preferable because it passes through the liquid crystal layer and the circular polarizing plate on the viewer side in this order.
Thus, in any of the transmissive type, the reflective type, and the transflective type, the light emitted from the liquid crystal cell to the viewer side is similarly affected by the circularly polarizing plate.

The liquid crystal cell is one embodiment in which the retardation of the liquid crystal layer is preferably 315 to 385 nm. The retardation of the liquid crystal layer is determined by (cell thickness) × (Δn) (Δn is refractive index anisotropy) and is related to the transmittance. Therefore, the graph showing the relationship between transmittance and retardation may be set so that the retardation becomes higher. In the case of the circularly polarized VATN mode, the optimum retardation is 350 nm. However, since the cell thickness of a liquid crystal cell (liquid crystal panel) generally has a process margin of about ± 10%, it may be 350 ± 35 nm. preferable. In this range, it is possible to achieve a high transmittance as compared with a mode in which a circularly polarizing plate is combined with the CPA mode.
The retardation setting is effective when applied to a transmission region of a transmissive liquid crystal display device and a transflective liquid crystal display device, but is also applicable to a reflective type and a transflective type. The preferred retardation range of the liquid crystal layer in the reflective region of the reflective liquid crystal display device and the transflective liquid crystal display device is half of the transmissive type, that is, (350 ± 35) / 2 nm.

Furthermore, as one of preferred embodiments of the liquid crystal display according to the present invention, the pretilt angle has a form in which the difference between the vicinity of the first alignment film and the vicinity of the second alignment film is 1.0 ° or more (pretilt angle up and down Also referred to as an asymmetric form). In this mode, in the VATN mode, the pretilt angle of the liquid crystal molecules on the first alignment film and the pretilt angle of the liquid crystal molecules on the second alignment film are substantially different from each other, that is, the pretilt angles on the upper and lower substrates are substantially different. It is evaluated that they are different. In this case, although the dependency of the transmittance on the pretilt angle is less than that of the above-described form in which the pretilt angles on the upper and lower substrates are substantially the same, the transmittance is higher and brighter as the pretilt angle is larger. As described above, according to the circularly polarized VATN mode according to the present invention, it is possible to maintain a high transmittance even with respect to the pretilt angle up / down asymmetry when there is a difference between the pretilt angles in the upper and lower substrates in the production process. It is possible to widen the process margin.

With respect to the pretilt angle, the following preferred embodiments can be cited particularly when the pretilt angles on the upper and lower substrates are substantially different from each other.
The pretilt angle is such that the angle in the vicinity of one alignment film is not less than 84 ° and less than 90 ° (for example, 89.9 ° or less), that is, the pretilt angle of the liquid crystal molecules in the vicinity of the first alignment film and the second alignment film Of the pretilt angles of the liquid crystal molecules in the vicinity, one of the pretilt angles (also referred to as pretilt angle (A)) is 84 ° or more and less than 90 ° (for example, 89.9 ° or less), and the other pretilt angle ( The pretilt angle (also referred to as “B”) is less than 90 ° (for example, 89.9 ° or less). In this embodiment, the pretilt angle (A) is 84 ° or more, and higher contrast can be realized as compared with the linear polarization VATN mode. The larger the pretilt angle (A), the higher the contrast, and in the vicinity of 90 ° It becomes a peak state.

The lower limit of the preferable range of the pretilt angle (A) may be 80 ° or more. In this case, higher transmittance can be realized as compared with a mode in which a circularly polarizing plate is combined with the CPA mode. it can. The upper limit of the preferable range of the pretilt angle (A) may be 89.7 ° or less, and more preferably 89.5 °.
The lower limit of the pretilt angle (B) is preferably 75 ° or more, more preferably 80 ° or more, and even more preferably 88 ° or more. The upper limit of the pretilt angle (B) is preferably the upper limit. May be 89.7 ° or less, and more preferably 89.5 °.
By setting the upper limit value of the preferable range of the pretilt angles (A) and (B) as described above, it is possible to improve display disturbance due to pressing on the liquid crystal display.

In order to express the pretilt angle in the pretilt angle vertically symmetrical form and the pretilt angle vertically asymmetrical form, in general, in the case of the pretilt angle vertically symmetrical form, both the pretilt angles on the upper and lower substrates are less than 90 °. In the case of a pretilt angle up / down asymmetric configuration, the pretilt angle may be less than 90 ° (for example, 89.9 ° or less) in at least one of the upper and lower substrates. However, the liquid crystal display according to the present invention is applied to the VATN mode or the VAECB mode in which the pretilt angles are both less than 90 ° (for example, 89.9 ° or less) on the upper and lower substrates. In other words, in order for the pretilt angle to be expressed, it is generally sufficient that the pretilt angle in one of the pair of substrates is 90 ° or less and the pretilt angle in the other substrate is less than 90 °. The pretilt angle may be 90 ° in any one of the pair of substrates, and the pretilt angle may be less than 90 ° in the other substrate. However, the VATN mode or the VAECB mode is employed in the liquid crystal display according to the present invention in order to further exhibit the advantages of the pretilt angle for obtaining a wide viewing angle and high-speed response.
Note that a form in which the pretilt angle is approximately 90 ° (for example, larger than 89.9 °) in any one of the pair of substrates is VAHAN (Vertical Alignment Hybrid Aligned) in which the pretilt angle is less than 90 ° only on one side substrate. Nematic or HAN orientation) mode. A liquid crystal display including such a VAHAN mode liquid crystal cell and a circularly polarizing plate on the viewer side of the liquid crystal cell can also exhibit good performance in both contrast and transmittance.

Regarding the measurement of the pretilt angle, it is possible to measure the pretilt angle not only in the case of the pretilt angle vertically symmetrical form but also in the case of the pretilt angle vertically asymmetrical form. In the case of the pretilt angle up-down asymmetrical form, after disassembling the upper and lower substrates, producing a liquid crystal cell using each substrate and injecting liquid crystal, producing a liquid crystal cell between upper substrates and a liquid crystal cell between lower substrates If the respective pretilt angles are measured, the pretilt angle of the liquid crystal molecules in the vicinity of the first alignment film and the pretilt angle of the liquid crystal molecules in the vicinity of the second alignment film can be measured.

Also in the pretilt angle up / down asymmetric form, it is one preferred embodiment that the polarizing plate further includes a circularly polarizing plate provided on the back side of the liquid crystal cell. The details are the same as the pretilt angle vertically symmetrical form described above. In addition, the pretilt angle up / down asymmetric configuration can also be applied to transmissive, reflective, and transflective liquid crystal display devices, as described above.

Further, even in the pretilt angle up / down asymmetrical form, the liquid crystal cell is preferably one in which the retardation of the liquid crystal layer is 315 to 385 nm.
The details are the same as the pretilt angle vertically symmetrical form described above. Note that the retardation range can be applied to the pretilt angle up / down asymmetric configuration as in the case of the pretilt angle up / down symmetry for the following reason. That is, as shown in FIG. 22, even in the pretilt angle up / down asymmetrical form, the inclination of the graph showing the relationship between the director azimuth angle (pretilt azimuth angle of liquid crystal molecules) -cell thickness, that is, the effective retardation is hardly changed. Only the average azimuth angle of the liquid crystal molecules changes greatly. Therefore, in the circularly polarized light mode, the retardation range can be applied because the axial orientation (= average azimuth angle) of the birefringent medium (= liquid crystal molecules) is not dependent on the transmittance in principle.

In the liquid crystal display according to the present invention, alignment division (divided domain) in which a plurality of regions (domains) having different alignment directions of liquid crystal molecules in one pixel can be applied. be able to.
That is, each of the plurality of pixels preferably has two or more alignment regions, and more preferably has four or more alignment regions. From the viewpoint of improving the viewing angle characteristics, the efficiency of the production process, and the like, a particularly preferred embodiment is a form in which each of the plurality of pixels has four alignment regions.

As described above, the configuration in which the divided domain configuration is adopted in the circularly polarized VATN mode is effective for a new problem found when the divided domain configuration is adopted in the linearly polarized VATN mode. That is, in the linearly polarized light VATN mode, new problems have been found that cause a reduction in transmittance and low contrast due to the dark line at the boundary dividing one pixel into a plurality of domains. On the other hand, in the case of a single domain having only one orientation azimuth area per pixel, there is no boundary between the domains, so that the transmittance and contrast are not greatly lowered even if the pretilt angle is high. The liquid crystal display according to the present invention has a technical significance with respect to a display mode such as a conventional CPA mode, whether or not a divided domain configuration is adopted, but adopts a divided domain configuration. In this case, it is effective for the above-described new problem, and therefore has a greater technical significance.

Further, when adopting the configuration of the divided domain, the range of the optimum pretilt angle of the linearly polarized VATN mode and the optimum pretilt angle of the circularly polarized VATN mode are different. In the single domain, the same characteristic is exhibited that the optimum pretilt angle of both is better as it is closer to 90 °. On the other hand, in the multi-domain employing the divided domain configuration, the optimum pretilt angles of both are different. Therefore, the optimum configuration of the liquid crystal display according to the present invention has an important technical significance not only by changing the linearly polarized VATN mode polarizing plate to a circularly polarizing plate but also by optimizing the pretilt angle. It will be.
Thus, the preferred embodiment of the liquid crystal display according to the present invention is particularly suitable for these in that it can solve a new problem found in the circularly polarized CPA mode and / or the linearly polarized VATN mode. It has a useful configuration.

The liquid crystal display according to the present invention may be a monochrome display liquid crystal display or a color display liquid crystal display in which each pixel includes a plurality of sub-pixels. When the liquid crystal display according to the present invention is applied to a color display liquid crystal display, each pixel described above can be read as a sub-pixel.

Various preferable modes in the circularly polarized VATN mode can be similarly applied to the circularly polarized VAECB mode, and the same result can be obtained.

ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display of the novel display mode which can implement | achieve high transmittance | permeability, high contrast, and high orientation stability can be provided. In addition, according to a preferred embodiment of the present invention, high transmittance and high contrast can be realized. In a domain-divided configuration, when the pretilt angle is large, the transmittance is decreased, and when the pretilt angle is small. It is possible to solve the problem that it is not possible to achieve a configuration in which both the transmittance and the contrast can be achieved due to the decrease in contrast, and the problem associated with the PSA technology and the reduction in process margin due to the difference in the pretilt angle between the upper and lower substrates Further, it is possible to provide a liquid crystal display of a new display mode that can solve new problems such as a decrease in transmittance due to the size of the pretilt angle, a decrease in contrast, and stability of alignment of liquid crystal when the panel surface is pressed.

It is the (a) plane schematic diagram of the liquid crystal cell in the circular polarization CPA mode which is a comparative form (comparative example 1) of this invention, (b) A cross-sectional schematic diagram, (c) The enlarged plane schematic diagram of a rivet. It is a perspective conceptual diagram which shows the relationship between the circularly-polarizing plate in the circular polarization CPA mode which is a comparative form (comparative example 1) of this invention, and the liquid crystal cell of CPA mode. It is a conceptual diagram which shows the definition of the angle in this specification. It is a graph which shows the result of having simulated the relationship of the voltage-transmitted light intensity in the circular polarization CPA mode which is a comparative form (comparative example 1) of this invention. It is a schematic diagram for demonstrating the domain division | segmentation in the circular polarization | polarized-light VATN mode which is embodiment (Example 1) of this invention, (a) Plane | planar schematic diagram (D1, D2, D3, D4 in one pixel) of a liquid crystal cell 4 domains), (b) a schematic cross-sectional view (two domains D1 and D2), and (c) a schematic cross-sectional view (two domains D3 and D4). It is a figure which illustrates alignment division in an embodiment of the present invention, and (a) is one pixel in the state where AC voltage more than a threshold was applied between a pair of substrates in the form where a liquid crystal display has four domains. Or (b) is a schematic plan view showing the direction of an average liquid crystal director in one subpixel), the direction of optical alignment treatment for a pair of substrates (upper and lower substrates), and the domain division pattern. It is a schematic diagram which shows the absorption-axis direction of the linearly-polarizing plate which comprises the circularly-polarizing plate provided in the liquid crystal display shown by a). In (a), the solid line arrow indicates the direction of the photo-alignment process for the lower substrate (for example, the drive element substrate), and the dotted line arrow indicates the direction of the photo-alignment process for the upper substrate (for example, the color filter substrate). . FIG. 7A is a diagram illustrating alignment division in an embodiment of the present invention, and FIG. 6A is a diagram in which an AC voltage equal to or higher than a threshold value is applied between a pair of substrates when the liquid crystal display has four domains different from those in FIG. 6. FIG. 6 is a schematic plan view showing the direction of an average liquid crystal director in one pixel (or one sub-pixel) in a state where it is aligned, the direction of photo-alignment treatment for a pair of substrates (upper and lower substrates), and domain division patterns; (B) is a schematic diagram which shows the absorption-axis direction of the linearly-polarizing plate which comprises the circularly-polarizing plate provided in the liquid crystal display shown to (a), (c) is more than a threshold value between a pair of board | substrates. It is a cross-sectional schematic diagram in the GH line of (a) when an AC voltage is applied, and shows the alignment direction of liquid crystal molecules. In addition, in (a), a dotted line arrow shows the direction of the optical alignment process with respect to a lower board | substrate (for example, drive element board | substrate), and a solid line arrow shows the direction of the optical alignment process with respect to an upper board | substrate (for example, color filter board | substrate). . Moreover, in (c), a dotted line shows the boundary between domains. It is a graph which shows the result of having simulated the relationship of the voltage-transmitted light intensity in the circularly polarized light VATN mode which is embodiment (Example 1) of this invention. It is a perspective conceptual diagram which shows the relationship between the linearly-polarizing plate in the linearly polarized light VATN mode which is a comparative form (comparative example 2) of this invention, and the liquid crystal cell of VATN mode. In the linearly polarized light VATN mode which is the comparative form (Comparative Example 2) of the present invention, one pixel when the pretilt angle is changed in the range of 75 ° to 89.8 ° and the liquid crystal display is viewed from the normal direction when a voltage is applied. The brightness simulation result in is shown. It is a graph which shows the pretilt angle-contrast ratio in the linearly polarized light VATN mode which is a comparative form (comparative example 2) of this invention. It is a perspective conceptual diagram which shows the relationship between the circularly-polarizing plate in the circularly polarized light VATN mode which is embodiment (Example 2) of this invention, and the liquid crystal cell of VATN mode. In the circularly polarized VATN mode according to the embodiment (Example 2) of the present invention, one pixel when the pretilt angle is changed in the range of 75 ° to 89.8 ° and the liquid crystal display is viewed from the normal direction when a voltage is applied. The brightness simulation result in is shown. 6 is a graph showing a pretilt angle-contrast ratio in a circularly polarized VATN mode according to an embodiment (Example 2) of the present invention. The relationship between the voltage and the transmitted light intensity in the circularly polarized TN mode which is the comparative form (Comparative Example 3) of the present invention, and the relationship between the voltage and the transmitted light intensity in the circularly polarized VATN mode which is the embodiment of the present invention (Example 2). It is a graph which shows. It is a conceptual diagram which shows the display principle of the normal linearly polarized light TN mode which is a comparative form (comparative example 3) of this invention. (A) is a state when no voltage is applied to the liquid crystal panel, and (b) is a state when a voltage is applied to the liquid crystal panel. It is a conceptual diagram which shows the principle that the liquid crystal element of the circularly polarized light TN mode which is a comparative form (comparative example 3) of this invention does not become a display element. (A) is a state when no voltage is applied to the liquid crystal panel, and (b) is a state when a voltage is applied to the liquid crystal panel. An example showing that the pretilt azimuth angle of liquid crystal molecules is twisted between the upper and lower substrates in the liquid crystal cell of the circularly polarized VATN mode (in the case of the pretilt angle vertically symmetrical form) which is an embodiment of the present invention (Example 3). FIG. In the circularly polarized VATN mode (in the case of the pretilt angle vertically symmetrical form) which is an embodiment (Example 3) of the present invention, both the pretilt angles of the liquid crystal molecules on the upper and lower substrates are changed from 75 ° to 89.8 °. It is a graph which shows distribution of the pretilt azimuth angle of a liquid crystal molecule. In the circular polarization CPA mode which is a comparative form of the present invention (Comparative Example 4), a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied is shown. Concept of an example showing that the pretilt azimuth angle of liquid crystal molecules is twisted between the upper and lower substrates in a liquid crystal cell of circularly polarized VATN mode (in the case of a pretilt angle up-and-down asymmetry) which is an embodiment of the present invention (Example 4) FIG. In the circularly polarized VATN mode (in the case of the pretilt angle asymmetrical form) that is an embodiment of the present invention (Example 4), the pretilt angle is fixed to 88 ° on the lower substrate, and the pretilt angle on the upper substrate is from 75 ° to 89.89. It is a graph which shows distribution of the director azimuth angle when it changes to 8 degrees. In the circularly polarized VATN mode (in the case of a pretilt angle up-down asymmetric configuration) that is an embodiment of the present invention (Example 5), the pretilt angle is fixed to 88 ° on the lower substrate, and the pretilt angle on the upper substrate is 75 ° to 90 °. The brightness simulation results for one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied are shown in FIG. Transmitted light in the circularly polarized VATN mode (in the case of the pretilt angle vertically symmetrical form and vertically asymmetrical form) which is an embodiment of the present invention (Examples 2 and 5) and the linearly polarized VATN mode which is a comparative form (Comparative Example 2) It is the graph which showed the pretilt angle dependence of intensity | strength compared. It is a graph which shows the pretilt angle-contrast ratio in the circularly polarized light VATN mode (in the case of a pretilt angle up-down asymmetrical form) which is embodiment (Example 5) of this invention. It is a graph which shows the retardation dependence of the transmitted-light intensity | strength in the circularly polarized light VATN mode (in the case of a pretilt angle up-down asymmetrical form) which is embodiment (Example 6) of this invention. It is a cross-sectional conceptual diagram of the liquid crystal cell in the circular polarization VATN mode which is embodiment (Example 7) of this invention. In embodiment (Example 7) of this invention, it is a plane conceptual diagram which shows the relationship between the rough shape of a liquid crystal cell, and a pressurization point. In the embodiment of the present invention (Example 7), it is a graph showing the relationship between the pretilt angle-the alignment return time after pressurization. It is a schematic diagram for demonstrating the domain division | segmentation in the circularly polarized light VATN mode which is embodiment (Example 8) of this invention, and is a plane schematic diagram (4 domains of D1, D2, D3, D4 in one pixel) ). In the circular polarization VATN mode which is an embodiment of the present invention (Example 8), a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied is shown. It is a schematic diagram for demonstrating the domain division | segmentation in the circular polarization | polarized-light VATN mode which is embodiment (Example 9) of this invention, and is a plane schematic diagram (4 domains of D1, D2, D3, and D4 in one pixel) ). In the circular polarization VATN mode which is an embodiment of the present invention (Example 9), a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied is shown. It is a schematic diagram for demonstrating the domain division | segmentation in the circularly polarized light VAECB mode which is embodiment (Example 10) of this invention, and is a plane schematic diagram (4 domains of D1, D2, D3, and D4 in one pixel) ). In the circular polarization VAECB mode which is an embodiment of the present invention (Example 10), a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied is shown.

Embodiments will be described below, and the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited only to these embodiments.
The order of explanation of the embodiment of the present invention (example) and the comparative form (comparative example) is comparative examples and examples in order to make it easy to grasp the features of the embodiment of the present invention as compared with the comparative form. Will be described in the order.

(Comparative Example 1)
Circularly polarized CPA mode liquid crystal cell The alignment simulation of the liquid crystal was performed by “LCDMASTER Prime 3D ver. 4.97 (trade name, manufactured by Shintech Co., Ltd.)”. The calculation conditions are as follows.
The cell size was calculated at 50 μm × 60 μm, and the cell thickness was calculated at a liquid crystal layer thickness of 1.5 μm.
The liquid crystal used is MBBA (N- (4-Methoxybenzylidene) -4-n-butylanline), refractive index anisotropy Δn = 0.255, dielectric anisotropy Δε = −0.5, pretilt angle is Calculated at 90 °. The calculated wavelength is 550 nm.
A CPA mode liquid crystal cell 10B as shown in FIG. 1 was used. FIG. 1A is a schematic plan view of the relationship between the liquid crystal layer and the rivet in the liquid crystal cell as viewed from the viewer side of the liquid crystal cell (normal direction of the upper substrate). FIG. 1B is a schematic cross-sectional view taken along the line AB of FIG. FIG. 1C is an enlarged schematic plan view of the rivet shown in FIG.

On the upper substrate (observer side substrate such as a glass substrate) 1, a projection (rivet) 7 is arranged at the center of the unit cell, the thickness of the rivet 7 is 0.5 μm, and the taper angle of the rivet 7 is 50 °. is there. Further, the transparent electrode (for example, ITO film) 3 and the alignment film 5 are disposed on the entire surface (solidly). The thicknesses are about 100 to 2000 mm, and are sufficiently small with respect to the thickness of the liquid crystal layer 9 being 1.5 μm, so that the thickness is set to be infinite in the calculation. Only the transparent electrode (for example, ITO film) 4 and the alignment film 6 are disposed on the lower substrate (back side substrate, for example, glass substrate) 2. The transparent electrode 4 has a size of 48 μm × 58 μm 1 μm inside the unit cell boundary. The alignment film 6 is solid (no breaks) and is disposed on the entire surface. The thickness of each of the transparent electrode 4 and the alignment film 6 is set to an infinite thickness for the same reason as the upper substrate 1.
In FIG. 1A and FIG. 1B, the liquid crystal molecules 8 are oriented radially with respect to the rivets 7 of the upper substrate 1 while being oriented perpendicularly to the

orientation films

5 and 6. It is shown conceptually.

The liquid crystal cell 10B is sandwiched between two circularly

polarizing plates

11a and 11b as shown in FIG. The absorption axes 13a and 13b of the upper and lower linear polarizing plates are orthogonal to each other, and the

slow axes

14a and 14b of the λ / 4 plates laminated adjacent to the respective linear polarizing plates are relative to the absorption axes 13a and 13b. The laminated body has a function as a circularly polarizing plate. The definition of the angle is as shown in FIG.
In FIG. 3, the polar angle is an angle with respect to the substrate surface, and the direction parallel to the substrate surface is 0 °, and the vertical direction (normal direction) is 90 °. Further, the azimuth angle is an angle indicating an azimuth relative to a certain direction in a plane parallel to the substrate surface at 0 °, that is, a reference. When described using (x, y, z) indicating a three-dimensional direction, a polar angle is defined as an angle formed with respect to the x-axis direction in the xy plane, and an azimuth angle is defined with respect to the x-axis direction in the xz plane. It is defined as the angle formed. In FIG. 3, the direction in which both the polar angle and the azimuth angle are 0 ° is indicated by (azimuth angle, polar angle) = (0 °, 0 °).
If the definition of the angle shown in FIG. 3 is applied to the alignment of the liquid crystal molecules, the following is obtained.
That is, in FIG. 3, the polar angle is an angle with respect to the substrate surface in the major axis direction in the liquid crystal molecules, and the azimuth angle is a projection of the major axis direction in the liquid crystal molecules onto the substrate surface, and a certain orientation on the substrate surface is 0. This is the angle indicated by the azimuth projected onto the substrate surface with respect to it.

FIG. 4 shows the result of simulating the relationship between the voltage and the transmitted light intensity when the circularly polarized CPA mode liquid crystal panel is viewed obliquely (polar angle 45 °). In this graph, there is a portion where the transmitted light intensity changes steeply in the vicinity of 4.1V. The smoothness of gradation expression is lost at this location, and gradation jump and / or collapse occurs. Further, if the graph showing the relationship between the voltage and the transmitted light intensity is shifted to the left or right as much as possible, the difference in transmitted light intensity between before and after the shift increases. Therefore, in the circularly polarized CPA mode, there is a problem that an afterimage is likely to occur.

Example 1
Circularly polarized VATN mode liquid crystal cell In the same manner as in Comparative Example 1, a liquid crystal alignment simulation was performed. The calculation conditions are as follows.
The dividing method of the liquid crystal layer 9 is as shown in FIG. 5. The unit cell is divided into four regions (D1 to D4 having the same area), and the pretilt angle of the liquid crystal is set to 88.0 ° (polar angle). . Near the upper substrate 1, the orientations of the pretilt directions of D1 and D3 differ from each other by 180 °, and near the upper substrate 1, the orientations of the pretilt directions of D2 and D4 differ from each other by 180 °. In the vicinity of the lower substrate 2, the pretilt direction orientations of D1 and D2 differ from each other by 180 °, and in the vicinity of the lower substrate 2, the pretilt direction orientations of D3 and D4 differ from each other by 180 °. The absolute values of the twist angles D1 and D2 are 90 °, but the signs are different from each other. The absolute values of the twist angles D3 and D4 are 90 °, but the signs are different from each other. Other conditions such as cell size, cell thickness, liquid crystal, and physical property values thereof are the same as those in Comparative Example 1. However, no rivets are arranged. 5B is a schematic cross-sectional view taken along the line CD in FIG. 5A, and FIG. 5C is a schematic cross-sectional view taken along the line EF in FIG. 5A.

Thus, in the liquid crystal display device of this embodiment, as shown in FIG. 5, in the off state where the voltage applied between the substrates sandwiching the liquid crystal layer is less than the threshold voltage, the first alignment film and the second alignment film are The liquid crystal molecules having negative dielectric anisotropy are aligned in a direction slightly inclined from the direction perpendicular to the substrate surface (alignment film surface). In the off state, the orientation direction of liquid crystal molecules (hereinafter also referred to as upper liquid crystal molecules) in the vicinity of one substrate (alignment film) and the liquid crystal molecules (hereinafter referred to as lower liquid crystal molecules) in the vicinity of the other substrate (alignment film). The orientation directions of the liquid crystal molecules are also substantially orthogonal to each other.
The orientation direction of liquid crystal molecules means the direction shown when the tilt direction of liquid crystal molecules is projected onto the substrate surface. In the off state in which the voltage applied between the substrates sandwiching the liquid crystal layer is less than the threshold voltage, the absolute values of the pretilt direction and the twist angle are as described above, and the upper liquid crystal molecules and the lower liquid crystal molecules are substantially separated from each other. It will be oriented in an orthogonal direction. In this case, if the upper liquid crystal molecules and the lower liquid crystal molecules are aligned in directions substantially perpendicular to each other to the extent that liquid crystal display in the VATN mode is possible, these liquid crystal molecules are completely orthogonal. For example, the orientation orientation of the upper liquid crystal molecules (or the orientation orientation defined by the first orientation film) and the orientation orientation of the lower liquid crystal molecules (or the orientation orientation prescribed by the second orientation film) are, for example, , They may cross each other at 85 ° to 95 °. On the other hand, in the ON state where the voltage applied between the substrates sandwiching the liquid crystal layer exceeds the threshold voltage, the liquid crystal molecules having negative dielectric anisotropy are substantially reduced with respect to the substrate surface according to the applied voltage. It is aligned in the parallel direction and exhibits birefringence with respect to the light transmitted through the liquid crystal layer.

Examples of the alignment-divided VA mode include a VATN mode, a VAECB mode, and a VAHAN mode. In the liquid crystal display according to the present invention, the VATN mode and the VAECB mode to be described later are preferably applied. Become.
When one pixel is divided into four regions (domains) as in the present embodiment, for example, the following method can be employed. A first alignment film is formed on the first substrate, two regions whose alignment directions are different from each other by about 180 ° are formed on the first alignment film, a second alignment film is formed on the second substrate, Two regions in which the orientation directions differ from each other by about 180 ° are formed in the two orientation films. The alignment films may be opposed to each other so that the alignment direction defined by the first alignment film and the alignment direction defined by the second alignment film are orthogonal to each other. Thereby, each region of the alignment film on one substrate is aligned and divided by each region of the alignment film on the other substrate, and four domain regions having different twist directions of liquid crystal molecules can be formed in each pixel.

FIG. 6 and FIG. 7 are conceptual diagrams illustrating an on-state configuration in the orientation division having four domains. FIG. 6 shows a form in which one pixel (or one sub-pixel) is divided vertically and horizontally and divided into approximately four equal parts, and corresponds to the case of this embodiment. FIG. 7 shows another embodiment in which one pixel (or one subpixel) is divided into stripes and divided into approximately four equal parts. FIG. 7C is a schematic cross-sectional view taken along the line GH in FIG. The on state is a state in which a voltage (usually an AC voltage) in the liquid crystal layer is equal to or higher than a threshold voltage, and preferably a voltage is applied to the liquid crystal layer.
In the alignment division mode of FIG. 6, as shown in FIG. 6A, in the ON state, the alignment orientation of the liquid crystal molecules located near the center in the thickness direction of the liquid crystal layer has four domain regions (FIG. 6 ( In a), in i to iv), quadrant domains different from each other, more specifically, substantially orthogonal to each other are formed. Further, as shown in FIG. 6B, when the substrate is viewed in plan, the direction of the photo-alignment treatment with respect to the upper substrate (for example, the color filter substrate) (the dotted arrow in FIG. 6A) is the upper substrate. The same direction as the absorption axis direction (azimuth) 20 of the linearly polarizing plate in the circularly polarizing plate disposed on the side may be the same, and the direction of the photo-alignment treatment with respect to the lower substrate (for example, the drive element substrate) (solid line in FIG. 6A) The arrow) may be in the same direction as the absorption axis direction (orientation) 19 of the linearly polarizing plate in the circularly polarizing plate disposed on the lower substrate side. However, the

absorption axis directions

19 and 20 of the linear polarizing plate are not particularly limited, and may be appropriately rotated from the direction shown in FIG.

At the boundary between the domains, the orientation direction of the liquid crystal molecules on one substrate coincides with the absorption axis direction of the linear polarizing plate, and the orientation direction of the liquid crystal molecules on the other substrate is almost perpendicular to the substrate. It has become. Therefore, when only a linear polarizing plate is arranged in crossed Nicols instead of a circularly polarizing plate (linear polarizing plate and λ / 4 plate) as in this embodiment, the boundary between domains does not transmit light even in the on state. So it becomes a dark line (dark line).

In the alignment division mode of FIG. 7, as shown in FIG. 7A, in the ON state, the alignment direction of the liquid crystal molecules located near the center in the thickness direction of the liquid crystal layer has four domain regions (FIG. 7 ( In a), in i to iv), quadrant domains different from each other, more specifically, substantially orthogonal to each other are formed. Further, as shown in FIG. 7B, in this embodiment, when the substrate is viewed in plan, the direction of the photo-alignment process with respect to the upper substrate (for example, the color filter substrate) (solid arrow in FIG. 7A). ) May be the same direction as the absorption axis direction 20 of the linearly polarizing plate disposed on the upper substrate side, and the direction of the photo-alignment treatment with respect to the lower substrate (for example, the drive element substrate) (dotted line arrow in FIG. 7A). May be in the same direction as the absorption axis direction 19 of the linearly polarizing plate disposed on the lower substrate side. However, as described above, the

absorption axis directions

19 and 20 of the linearly polarizing plate may be appropriately rotated from the direction shown in FIG.

In the off state in the form of these alignment divisions, the major axis direction of the liquid crystal molecules is tilted with a pretilt angle with respect to the upper and lower substrates by the alignment regulating force of the alignment film, and twisted by approximately 90 ° between the upper and lower substrates. There will be four different orientation states in the four domains.
In the ON state, the major axis direction of the liquid crystal molecules changes under the influence of the electric field. In this case, too, for example, as schematically shown in FIG. Thus, there are four orientation states different in four domains.

Note that, regarding a preferable mode of the liquid crystal cell in the liquid crystal display according to the present invention, one of the first substrate and the second substrate is a thin film transistor (hereinafter also referred to as TFT) which is a switching element and a pixel electrode is a matrix. A TFT array substrate provided in a shape is preferable.
The other of the first substrate and the second substrate is preferably a color filter substrate (hereinafter also referred to as a CF substrate) having a color filter and a common electrode. Thus, the liquid crystal display according to the present invention is preferably an active matrix liquid crystal display, but may be a simple matrix liquid crystal display. In the case of a simple matrix type liquid crystal display, normally, the first substrate and the second substrate are a substrate provided with a stripe-shaped signal electrode (column electrode), and a stripe-shaped scanning electrode so as to be substantially orthogonal to the signal electrode. It becomes a combination with a substrate provided with (row electrode). In the case of an active matrix liquid crystal display, the pixels in these liquid crystal displays are defined by a pixel electrode and a common electrode facing the pixel electrode. Further, in a simple matrix type liquid crystal display, it is defined by the intersection of a striped signal electrode and a scanning electrode.

In the present embodiment, the configuration of the circularly polarizing plate is the same as that of Comparative Example 1. It should be noted that the VATN modes described in Patent Document 3 and Patent Document 4 are described on the assumption that a linearly polarizing plate is used. In particular, Patent Document 3 presents a configuration in which a phase difference plate is disposed between a linearly polarizing plate and a liquid crystal cell. This is a configuration intended to improve the viewing angle characteristics of the linearly polarized VATN mode. That is, the absorption axis of the linear polarizing plate is parallel to or orthogonal to the slow axis of the retardation plate.
On the other hand, in this example, a retardation plate is arranged between the linear polarizing plate and the liquid crystal cell, but the absorption axis of the linear polarizing plate and the slow axis of the retardation plate are 45 ° or −45 °. The phase difference is substantially specified as λ / 4, and the configuration is for the circular polarization mode. That is, the circularly polarizing plate in this example has the same configuration as the circularly

polarizing plates

11a and 11b in the circularly polarized CPA mode shown in FIG. However, the configuration of the circularly polarizing plate in the liquid crystal display according to the present invention may be anything as long as it generates circularly polarized light. For example, a structure having a helical structure at an optical pitch (for example, cholesteric liquid crystal) may be used. When the liquid crystal display according to the present invention includes a pair of circularly polarizing plates, the liquid crystal display usually includes a right polarizing plate and a left polarizing plate, and both polarizing plates are arranged in crossed Nicols.

The circularly polarizing plate is preferably composed of a combination of a linearly polarizing plate (polarizer) and a λ / 4 plate. Hereinafter, this case will be described in detail. From the viewpoint of realizing a white display state with high transmittance and a substantially complete black display state, the in-plane slow axes of the first (observer side) and second (back side) λ / 4 plates are the first ( Most preferably, it has a relative angle of 45 ° (+ 45 ° or -45 °) with the absorption axis of the linear polarizer on the viewer side and the second (back side), but it reduces the contrast ratio in the front direction. As long as it is within the range, it may be slightly deviated from 45 °. Specifically, when the substrate surface of the liquid crystal cell is viewed in plan, the angle formed by the in-plane slow axis of the first λ / 4 plate and the absorption axis of the first linear polarizing plate, and the second The angles formed by the in-plane slow axis of the λ / 4 plate and the absorption axis of the second linearly polarizing plate are each preferably in the range of 45 ° to ± 2 ° (43 ° to 47 °). Similarly, when the substrate surface of the liquid crystal cell is viewed in plan, the angle formed by the in-plane slow axis of the first λ / 4 plate and the in-plane slow axis of the second λ / 4 plate is 90 °. To ± 1 ° (89 ° to 91 °). The λ / 4 plate is a phase difference plate that generates a phase difference of approximately ¼ wavelength with respect to a light wave having a set wavelength. The λ / 4 plate is approximately ¼ wavelength (accurately at 137.5 nm with respect to light having a wavelength of 550 nm). It is a layer having an optical anisotropy of greater than 115 nm and smaller than 160 nm, and is synonymous with a λ / 4 retardation film and a λ / 4 retardation plate. A linear polarizing plate (linear polarizer) is an element having a function of changing natural light into linearly polarized light. Typically, a polyvinyl alcohol (PVA) film obtained by adsorbing and orienting an anisotropic material such as an iodine complex having dichroism can be used. Usually, a protective film such as a triacetyl cellulose (TAC) film is laminated on both sides of the PVA film and used for practical use.

FIG. 8 is a graph showing a result of simulating the relationship between the voltage and the transmitted light intensity when the circularly polarized VATN mode liquid crystal panel is viewed obliquely (polar angle 45 °) as in Comparative Example 1. In this graph, the sharply changing portion near 4.1 V disappears, and the smoothness of gradation expression can be realized, and gradation jumping and / or collapse are not substantially generated. In addition, there is an advantage that an afterimage is not easily produced. Since this has a pretilt angle (88.0 ° in this embodiment), the direction in which the liquid crystal molecules are tilted in the vicinity of the threshold is defined in advance in a specific direction, and the liquid crystal molecules are tilted according to the applied voltage. Because.
The configuration of the circularly polarized VATN mode in the above embodiment can be similarly applied to the circularly polarized VAECB mode, and the same result can be obtained.

(Comparative Example 2)
Relationship between pretilt angle of linearly polarized VATN mode, transmittance and contrast The VATN mode liquid crystal cell 10A having a cell thickness of 2 μm is the same as in Example 1 except that it is not a circularly polarized mode but a linearly polarized mode. The structure of the liquid crystal display element is shown in FIG. The liquid crystal cell 10A is sandwiched between two linearly

polarizing plates

12a and 12b as shown in FIG. 9, and the absorption axes 13a and 13b of the upper and lower linearly

polarizing plates

12a and 12b are orthogonal to each other. Using this linearly polarized VATN mode liquid crystal display element, the result of the simulation when the pretilt angle is changed in the range of 75 ° to 89.8 ° when the white display voltage (= 6V) is applied is shown in FIG. Shown in FIG. 10 is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied. The pretilt angle is 89.8 ° in FIG. 10A and 88 in FIG. 0.0 °, 86.0 ° in FIG. 10 (c), 84.0 ° in FIG. 10 (d), 82.0 ° in FIG. 10 (e), 80.0 ° in FIG. 10 (f), FIG. In (g), it is 75.0 °.

From FIG. 10, it can be seen that, when a voltage is applied, the linearly polarized VATN mode is preferably brighter (higher transmittance) as the pretilt angle is smaller.
This is because as the pretilt angle is larger, the dark line on the domain-divided boundary becomes thicker and the orientation of the pixel edge is disturbed by the effect of the oblique electric field around the pixel. The larger the pretilt angle, the lower the alignment regulating force acting in the direction of the pretilt azimuth angle, so the force that constrains the alignment azimuth of the liquid crystal molecules in the specified azimuth angle direction becomes weaker. Leads to an increase in
Conventionally, since this effect is not taken into consideration, it has been considered that the higher the pretilt angle, the better. However, it can be seen that the reverse phenomenon occurs in the pixels obtained by actual domain division.
However, on the contrary, the smaller the pretilt angle, the better the performance, but the smaller the pretilt angle, the greater the birefringence felt by the propagating light when no voltage is applied, so the light leakage increases, resulting in a contrast increase. Bring about a decline. This graph is shown in FIG.

In FIG. 11, the horizontal axis indicates the pretilt angle (pretilt angle / deg.), And the vertical axis indicates the contrast ratio (Contrast ratio).
The contrast has an extreme value, and shows a maximum value when the pretilt angle is around 86 °.
That is, the most preferred pretilt angle in the linearly polarized VATN mode is around 86 °. If the pretilt angle is too larger than this value, the dark line on the domain-divided boundary becomes thicker when a voltage is applied, and the pixel edge orientation is disturbed by the effect of the oblique electric field around the pixel. Lowers, resulting in a decrease in contrast. On the other hand, when the pretilt angle is smaller than 86 °, the birefringence felt by the propagating light becomes large when no voltage is applied, so that light leakage increases, resulting in a decrease in contrast.

(Example 2)
Relationship between Pretilt Angle, Transmittance, and Contrast of Circularly Polarized VATN Mode A liquid crystal display element having the same configuration as that of Comparative Example 2 except that a VATN mode liquid crystal cell 10A is sandwiched from both sides by circularly

polarizing plates

11a and 11b is shown in FIG. Shown in The absorption axes 13a and 13b of the upper and lower linear polarizing plates are orthogonal to each other, and the

slow axes

14a and 14b of the λ / 4 plates laminated adjacent to the respective linear polarizing plates are relative to the absorption axes 13a and 13b. Are arranged in a direction that forms an angle of 45 °. Using this circularly polarized VATN mode liquid crystal display element, the pixel when the white display voltage (= 6 V) is applied is changed in the pretilt angle in the range of 75 ° to 89.8 °, and the simulation result is shown in FIG. Shown in FIG. 13 is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied. The pretilt angle is 89.8 ° in FIG. 13A and 88 in FIG. 13B. 0.0 °, 86.0 ° in FIG. 13 (c), 84.0 ° in FIG. 13 (d), 82.0 ° in FIG. 13 (e), 80.0 ° in FIG. 13 (f), FIG. In (g), it is 75.0 °.

FIG. 13 shows that the circularly polarized VATN mode becomes brighter (the transmittance is higher) as the pretilt angle is larger. In addition, the brightness is less dependent on the alignment direction of the liquid crystal, and it is not affected by the dark lines at the domain boundary and the disturbance in the alignment around the pixels, which are noticeable in the linearly polarized VATN mode. Recognize. In the circular polarization mode, the alignment direction of the liquid crystal molecules does not depend on the transmittance, so that no dark line is generated due to the alignment direction of the liquid crystal molecules. The reason why the circularly polarized VATN mode is bright can be explained from the result of Example 3 described later. A graph of the pretilt angle dependence of contrast is shown in FIG.

In FIG. 14, the horizontal axis represents a pretilt angle (pretilt angle / deg.), And the vertical axis represents a contrast ratio.
Unlike Comparative Example 2, the larger the pretilt angle, the better. Further, a high contrast can be achieved with respect to Comparative Example 2. The maximum value 3500 in FIG. 11 in the linearly polarized VATN mode of Comparative Example 2 can be achieved at a pretilt angle of 84 ° or more in the circularly polarized VATN mode. From this, it can be seen that the pretilt angle is preferably 84 ° or more.

(Comparative Example 3)
Comparison between linearly polarized light and circularly polarized light in TN mode With the same configuration as in Example 2, the liquid crystal was set to 5 CB, and the pretilt angle was set to 5 °. This pretilt angle is a value of a general TN mode. The relationship between voltage and transmitted light intensity at this time is shown in FIG.
Comparative Example 3 does not function as a liquid crystal display element. Originally, a TN mode using a circularly polarizing plate (also referred to as a circularly polarized TN mode) cannot be used as a display element. The principle of this reason is shown in FIGS.

FIG. 16 shows a display principle of a liquid crystal display in a normal TN mode (also referred to as a linearly polarized TN mode) using a linearly polarizing plate. The liquid crystal layer rotates light when no voltage is applied, and functions as an optical shutter by turning on and off the voltage. In FIG. 16, (a) is when no voltage is applied, and (b) is when voltage is applied. In FIG. 16, left and right linearly polarized light means linearly polarized light that oscillates in the left and right direction, and left and right linearly polarized light means linearly polarized light that transmits left and right linearly polarized light.

FIG. 17 shows a circularly polarized TN mode liquid crystal element. When no voltage is applied, the liquid crystal molecules in the liquid crystal layer are twisted and have the role of rotating light, but right circularly polarized light is incident on the liquid crystal layer, so only the phase changes even if the right circularly polarized light is rotated. Thus, there is no change in that right-handed circularly polarized light is emitted. Therefore, the polarization state of right circularly polarized light does not change regardless of the voltage on / off state. Therefore, the right circularly polarized light cannot pass through the left circularly polarizing plate, and the circularly polarized TN mode does not function as a display element. The same applies when the right and left polarizing plates are switched.
This phenomenon is caused by the fact that the optical rotation of the liquid crystal layer causes only a phase shift for circularly polarized light. Therefore, in the TN mode as in Patent Documents 5 to 7, a configuration using an elliptically polarizing plate instead of a circularly polarizing plate has been proposed. However, when the domain division is performed for improving the viewing angle characteristics in the configurations described in these documents, there is a fatal defect that a defect line is generated at the domain boundary, resulting in a decrease in contrast and / or a decrease in transmittance. . Even if domain division is not performed, the horizontal alignment mode typified by the TN mode has the principle drawback that the contrast is lower than that of the VA (vertical alignment) mode. In order to achieve high transmittance and high contrast in the circular polarization mode, it is necessary not to include a twist component as in the CPA mode, and a liquid crystal element combining a TN mode with a circularly polarizing plate is used as a display element. In order to function as an element, a seemingly impossible configuration is required in which an orientation with less twisting component is achieved from the twisted initial orientation. However, if the circularly polarized VATN mode or the circularly polarized VAECB mode according to the present invention is used, the polarization state of the circularly polarized light does not change regardless of the on / off state of the voltage as in the TN mode, and the pretilt angle is further increased. All the above problems can be solved by optimizing. These were first discovered by the present inventors.
Next, configurations and methods for solving these problems in the circularly polarized VATN mode and the circularly polarized VAECB mode and achieving a high transmittance exceeding the CPA mode will be described in the third and subsequent embodiments.

(Example 3)
Distribution of pretilt azimuth angle of liquid crystal molecules in circularly polarized VATN mode (pretilt angle vertically symmetrical form)
FIG. 18 conceptually shows an example showing that the pretilt azimuth angle of liquid crystal molecules is twisted between the upper and lower substrates in a circularly polarized VATN mode liquid crystal cell. The pretilt azimuth angle is an angle indicated by an azimuth obtained by projecting the major axis direction of liquid crystal molecules having a pretilt angle on the substrate surface. In the case of FIG. 18, the pretilt angle is vertically symmetrical. In the VATN mode liquid crystal cell shown in FIG. 18, the distribution of pretilt azimuth angles of liquid crystal molecules inside the liquid crystal layer was simulated. In the upper and lower substrates, the liquid crystal molecules are pretilted in 0 ° azimuth and 90 ° azimuth, respectively, and the liquid crystal molecules are twisted in the liquid crystal layer. The liquid crystal used was MBBA. The cell thickness is 2 μm. The applied voltage is 6V. FIG. 19 shows the distribution of pretilt azimuth angles of liquid crystal molecules when the pretilt angle is changed from 75 ° to 89.8 ° on both the upper and lower substrates.

FIG. 19 is a graph showing the relationship between the internal position of the liquid crystal layer and the azimuth angle of the liquid crystal molecules. The internal position of the liquid crystal layer indicates the distance (μm) from one end to the liquid crystal molecules in the substrate normal direction in the liquid crystal layer. The liquid crystal molecule azimuth indicates the pretilt azimuth (°) of the liquid crystal molecules. This shows how the graph showing the relationship between the internal position of the liquid crystal layer and the liquid crystal molecule azimuth varies depending on the difference in pretilt angle.
When the pretilt angle is 75 °, the liquid crystal molecules are twisted almost uniformly inside the liquid crystal layer, whereas when the pretilt angle is 89.8 °, the liquid crystal molecules are at the interface (in the normal direction of the substrate in the liquid crystal layer). It can be seen that it is largely twisted at the end) but not twisted in most areas. That is, as the pretilt angle increases, the twist is biased toward the interface, and the alignment is uniform in other regions. Therefore, in the circularly polarized VATN mode, the liquid crystal molecules are twisted. I understand that it will become.

(Comparative Example 4)
Transmittance of circularly polarized CPA mode FIG. 20 shows the result of pixel simulation in a liquid crystal display device having the same configuration as in Comparative Example 1 except that the cell thickness is 2 μm.

This is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied.
The central black area is a rivet for CPA alignment of the liquid crystal. The transmittance was 0.359 (air = 1).

Example 4
Distribution of pretilt azimuth angle of liquid crystal molecules in circularly polarized VATN mode
Patent Document 4 discloses a problem that in the VATN mode configuration, when the pretilt angles are different between the upper and lower substrates, the transmittance is significantly reduced. This is because if the pretilt angles at the upper and lower interfaces are different from each other in the linearly polarized light VATN mode, the average direction of the pretilt azimuth angles of the liquid crystal molecules deviates from the direction of 45 ° with respect to the absorption axis of the linearly polarizing plate.
FIG. 21 conceptually shows an example showing that the pretilt azimuth angle of liquid crystal molecules is twisted between the upper and lower substrates in a circularly polarized VATN mode liquid crystal cell. In this embodiment, the pretilt angle was fixed to 88 ° on the lower substrate, and the pretilt angle was changed from 75 ° to 89.8 ° on the upper substrate. The distribution of the pretilt azimuth angle at this time is shown in FIG. Accordingly, in the case of FIG. 21, the pretilt angle is vertically asymmetrical.

FIG. 22 is a graph showing the relationship between the internal position of the liquid crystal layer (the horizontal axis is expressed as “cell thickness”) − liquid crystal molecule azimuth (the vertical axis is expressed as “director azimuth”), as in FIG. The liquid crystal layer internal position indicates the distance (μm) from one end to the liquid crystal molecule in the substrate normal direction in the liquid crystal layer, and the liquid crystal molecule azimuth indicates the pretilt azimuth angle (°) of the liquid crystal molecule. Yes.
It should be noted in FIG. 22 that the slope of the distribution (= degree of twist) does not change much even if the pretilt angle changes, compared to FIG. That is, even if the pretilt angles are different from each other between the upper and lower substrates, it is expected that in the circularly polarized VATN mode, the transmittance remains almost unchanged. This will be described in detail in Example 5. Patent Document 4 describes that in the linearly polarized VATN mode, it is preferable that the difference in pretilt angle between the upper and lower substrates is less than 1 °, but this is also acceptable in the circularly polarized VATN mode. In other words, it is possible to positively make the pretilt angles different between the upper and lower substrates.
Since the circularly polarized VAECB mode does not include a twist component, for example, the pretilt angle is fixed at 90 ° on the lower substrate and the pretilt angle is changed from 75 ° to 89.8 ° on the upper substrate. However, the distribution of director azimuth is constant.

(Example 5)
Relationship between pretilt angle, transmittance and contrast in circularly polarized VATN mode (pretilt angle up / down asymmetry)
FIG. 23 shows the result of pixel simulation when the pretilt angle is fixed to 88 ° on the lower substrate and the pretilt angle is changed from 75 ° to 90 ° on the upper substrate with the same configuration as in the second embodiment.

FIG. 23 is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied. The pretilt angle on the upper substrate is 90.0 ° in FIG. b) 89.8 °, FIG. 23 (c) 88.0 °, FIG. 23 (d) 86.0 °, FIG. 23 (e) 84.0 °, FIG. 23 (f) 82.0 °. In FIG. 23 (g), the angle is 80.0 °, and in FIG. 23 (h), the angle is 75.0 °.
Compared to FIG. 13, it can be seen that the transmitted light intensity is maintained high without depending on the pretilt angle. In particular, the configuration with a pretilt angle of 90.0 ° shows good transmittance despite the VAHAN (Vertical Alignment Hybrid Aligned Nematic) mode in which only one substrate is aligned.

FIG. 24 is a graph showing the dependence of the transmittance on the pretilt angle. The horizontal axis indicates the pretilt angle (pretilt angle / deg.), And the vertical axis indicates the transmitted light intensity (transmittance). The transmitted light intensity is 1 for air.
In Comparative Example 2, the transmittance deteriorates as the pretilt angle increases. In Examples 2 and 5, the transmittance increases as the pretilt angle increases. Example 5 shows the result when the pretilt angle is fixed to 88 ° on one side of the substrate, and shows that the circularly polarized VATN mode maintains a high transmittance without any problem with respect to the pretilt angle up-and-down asymmetry. Yes.
Further, as described in Comparative Example 4, the transmittance in the CPA mode is 0.359, and in order to obtain a transmittance exceeding this, the pretilt angle may be set to 86 ° or more in the configuration of Example 2. In the configuration of the fifth embodiment, the pretilt angle may be set to 80 ° or more. As described above, the circularly polarized VATN mode that does not require rivets has an advantage that a high transmittance can be achieved as compared with the CPA mode that requires rivets described in Comparative Example 4.

In FIG. 25, the horizontal axis indicates the pretilt angle (pretilt angle / deg.), And the vertical axis indicates the contrast ratio (Contrast ratio).
The contrast in the pretilt angle asymmetrical form of the circularly polarized VATN mode also improves as the pretilt angle increases. In particular, a configuration with a pretilt angle of 90 ° indicates a HAN alignment in which the pretilt angle is less than 90 °, that is, the liquid crystal molecules are tilted only on one substrate, indicating that there is no problem in both contrast and transmittance.
When the polar angle (pretilt angle) of the liquid crystal molecules on one substrate side is 90 ° and the polar angle (pretilt angle) of the liquid crystal molecules on the other substrate side is less than 90 °, the liquid crystal molecules are inclined with respect to the substrate surface. The form of the HAN orientation is disclosed as a reference example for the embodiment of the present invention.
The configuration of the circularly polarized VATN mode in the above embodiment can be similarly applied to the circularly polarized VAECB mode, and the same result can be obtained.

(Example 6)
Retardation of circularly polarized VATN mode The configuration differs from Example 2 only in the following points.
The cell thickness is 3.6 μm, the pretilt angle is 88 °, and the applied voltage is 6V.
The physical properties of the liquid crystal were K11 = 14, K22 = 8, K33 = 16, and Δε = 4, and Δn was varied between 0.066 and 0.116 to evaluate the change in transmittance with respect to the retardation of the liquid crystal.

FIG. 26 is a graph showing the retardation dependency of transmittance. The horizontal axis represents retardation (Retardation / nm), and the vertical axis represents transmitted light intensity (transmittance). The transmitted light intensity is 1 for air.
FIG. 26 shows the optimum retardation (cell thickness × Δn) from the viewpoint of transmittance. A more preferable value is 350 nm, but generally, the cell thickness of the liquid crystal panel has a process margin of about ± 10%, so 350 ± 35 nm is preferable. In this range, the transmittance of the CPA mode of Comparative Example 4 exceeds 0.359, which is also preferable in this sense.
The configuration of the circularly polarized VATN mode in the above embodiment can be similarly applied to the circularly polarized VAECB mode, and the same result can be obtained.

(Example 7)
Two glass substrates with ITO (0.7 mm thickness) were prepared, and a vertical photo-alignment film forming solution was applied onto each substrate by spin coating. The photo-alignment film material contained in this solution is polyamic acid, and is a cinnamic acid derivative containing a functional group that reacts with light in the molecule. After spin coating, this was temporarily dried at 90 ° C. for 1 minute, and then a firing step was performed at 200 ° C. for 60 minutes while purging with nitrogen. The thickness of the alignment film was 100 nm.
Next, a liquid crystal alignment treatment was performed on these substrates. Specifically, an appropriate amount of linearly polarized ultraviolet light having a wavelength of 313 nm was irradiated on the entire surface of the substrate from a direction inclined by 40 ° from the normal line of the substrate. The polarized light at this time was p-polarized light. The amount of UV irradiation was adjusted so that the pretilt angle of the liquid crystal molecules was within the range of 88.6 ° to 89.8 °.
Next, a thermosetting seal (HC1413FP: manufactured by Mitsui Chemicals, Inc.) was printed on one of these substrates using a screen plate. Further, in order to make the thickness of the liquid crystal layer 3.5 μm, 3.5 μm diameter beads (SP-2035: manufactured by Sekisui Chemical Co., Ltd.) were sprayed on the opposite substrate. These two types of substrates were bonded together so that the ultraviolet irradiation azimuths were orthogonal to each other (VATN). Next, the bonded substrate was heated at 200 ° C. for 60 minutes in a furnace purged with nitrogen while being pressurized at 0.5 kgf / cm ² to cure the seal.
Liquid crystal was injected into the cell produced by the above method under vacuum. In this embodiment, MLC6610 (manufactured by Merck) having a negative dielectric anisotropy was used as the liquid crystal. The inlet of the cell into which the liquid crystal was injected was sealed with an ultraviolet curable resin (TB3026E: manufactured by Three Bond Co.). The wavelength of ultraviolet rays irradiated in the sealing process is 365 nm, and the pixel portion is shielded from light so as to remove the influence of ultraviolet rays as much as possible. Next, in order to erase the flow alignment of the liquid crystal, the cell was heated at 130 ° C. for 40 minutes, and the liquid crystal was subjected to a realignment treatment with an isotropic phase. Then, a VATN mode liquid crystal cell without domain division was obtained. The conceptual cross-sectional view is shown in FIG. Between the liquid crystal molecules 8 near the upper (observer side) photo-alignment film (first alignment film) 5 and the liquid crystal molecules 8 near the lower (back-side) photo-alignment film (second alignment film) 6. The absolute value of the twist angle was 90 °, similar to the domain such as D1 in Example 1.
Thus, for the pretilt angle measurement, a liquid crystal cell without domain division was produced. Naturally, it can be easily imagined that the same result as in this embodiment can be obtained even with a liquid crystal cell with domain division. For the measurement of the pretilt angle of the finished liquid crystal cell, Optipro manufactured by Shintech Co., Ltd. was used.

FIG. 28 is a conceptual plan view showing the relationship between the outline of the liquid crystal cell and the pressure point, and the liquid crystal cell viewed from the normal direction with respect to the substrate.
The method for evaluating the afterimage resulting from the pressurization is as follows. First, the cell is sandwiched between two circularly polarizing plates. Next, as shown in FIG. 28, a load of 250 g, approximately 0.3 seconds is applied to one central point (pressing point 15, area 1 mm ² ) of the liquid crystal filling region 16 of 20 mm square surrounded by the thermosetting seal 17 in the cell. Applying pressure results in disturbing the alignment of the liquid crystal. And the time (orientation return time after pressurization) until the orientation is spontaneously restored after that time is measured visually through the circularly polarizing plate. At this time, a rectangular wave of 3 V and 30 Hz was applied to the liquid crystal filling region 16.

FIG. 29 is a graph showing the relationship between the pretilt angle and the alignment return time after pressurization.
Thus, the smaller the pretilt angle, the shorter the alignment return time after pressurization, and the display disturbance improves.
The alignment recovery time deteriorates rapidly when the pretilt angle is 89.7 ° or more, and is saturated in about 2 seconds or less when the pretilt angle is 89.5 ° or less. This time is practically a good display for the use of touch panels and the like. Give performance. In other words, from the viewpoint of alignment stability, a pretilt angle of 89.7 ° or less for rapidly stabilizing the alignment is preferable, and practically 89.5 ° or less is more preferable. The reason why the alignment return time is shortened as the pretilt angle is smaller is that the smaller the pretilt angle, the greater the alignment regulating force acting in the direction of the pretilt azimuth angle, and the stronger the restoring force against the alignment disorder due to pressing. It is.
The configuration of the circularly polarized VATN mode in the above embodiment can be similarly applied to the circularly polarized VAECB mode, and the same result can be obtained.

(Example 8)
Relationship between pretilt direction of circularly polarized VATN mode, transmittance and contrast The configuration of Example 6 is different from that of Example 6 only in the following points.
Δn = 0.096, and the orientation of the pretilt direction on the upper and lower substrates is as shown in FIG. The crossing angle of the azimuths in the pretilt direction of each domain is 120 ° for D1 and D3, and 60 ° for D2 and D4. In FIG. 30, the dotted arrow indicates the orientation in the pretilt direction on the lower substrate side, and the solid arrow indicates the orientation in the pretilt direction on the upper substrate side. FIG. 31 shows a pixel simulation when a white display voltage (= 6 V) is applied.

FIG. 31 is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied. The transmittance is 0.380 (air = 1) and the contrast is 4900, which is superior to that of Comparative Example 4.

Example 9
Relationship between pretilt direction of circularly polarized VATN mode, transmittance and contrast The configuration of Example 8 is different from that of Example 8 only in the following points.
The orientation of the pretilt direction on the upper and lower substrates is as shown in FIG. The crossing angle of the azimuths in the pretilt direction of each domain is 150 ° for D1 and D3, and 30 ° for D2 and D4. In FIG. 32, the dotted arrow indicates the orientation in the pretilt direction on the lower substrate side, and the solid arrow indicates the orientation in the pretilt direction on the upper substrate side. FIG. 33 shows a pixel simulation when a white display voltage (= 6 V) is applied.

FIG. 33 is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied. The transmittance is 0.379 (air = 1) and the contrast is 4900, which is superior to that of Comparative Example 4.

(Example 10)
Transmittance and contrast of circularly polarized VAECB mode The configuration differs from Example 8 only in the following points.
The orientation of the pretilt direction on the upper and lower substrates is as shown in FIG. In each of the domains D1 to D4, the angles formed by the azimuths in the pretilt direction are all 180 °. In FIG. 34, the dotted arrow indicates the orientation in the pretilt direction on the lower substrate side, and the solid arrow indicates the orientation in the pretilt direction on the upper substrate side. They are no longer in VATN mode, but in VAECB mode. FIG. 35 shows a pixel simulation when a white display voltage (= 6 V) is applied.

FIG. 35 is a simulation result of brightness in one pixel when the liquid crystal display is viewed from the normal direction when a voltage is applied. The transmittance is 0.389 (air = 1) and the contrast is 5000, which is superior to that of Comparative Example 4.

This application claims priority based on the Paris Convention or the laws and regulations in the country of transition based on Japanese Patent Application No. 2011-024964 filed on Feb. 8, 2011. The contents of the application are hereby incorporated by reference in their entirety.

1: Upper (observer side) substrate (glass substrate)
2: Lower side (back side) substrate (glass substrate)
3: Transparent electrode (observer side) (ITO film)
4: Transparent electrode (back side) (ITO film)
5: (Light) alignment film (observer side)
6: (Light) alignment film (back side)
7: Projection (rivet)
8: Liquid crystal molecule 9: Liquid crystal layer 10A: Liquid crystal cell (VATN mode)
10B: Liquid crystal cell (CPA mode)
11a: Circularly polarizing plate (observer side)
11b: Circularly polarizing plate (back side)
12a: Linear polarizing plate (observer side)
12b: Linear polarizing plate (back side)
13a: Absorption axis of the linearly polarizing plate (observer side)
13b: Absorption axis of the linearly polarizing plate (back side)
14a: λ / 4 plate slow axis (observer side)
14b: λ / 4 plate slow axis (back side)
15: Pressurization point 16: Liquid crystal filling region 17: Thermosetting seal 18: Average liquid crystal director direction when an AC voltage is applied 19: Absorption axis direction 20 of the linear polarizing plate in the circularly polarizing plate disposed on the lower substrate side : Absorption axis direction of linearly polarizing plate in circularly polarizing plate arranged on upper substrate side

Claims

A liquid crystal display comprising a liquid crystal cell and a polarizing plate,
The liquid crystal cell includes a first substrate and a second substrate including a plurality of pixels, a vertically aligned liquid crystal layer including liquid crystal molecules provided between the substrates, and a liquid crystal layer side of the first substrate. A first alignment film provided on the surface of the second substrate, and a second alignment film provided on the surface of the second substrate on the liquid crystal layer side,
Each of the plurality of pixels has one or more alignment regions,
In the alignment region, the major axis direction of the liquid crystal molecules has a pretilt angle with respect to the first and second substrate surfaces, and the major axis direction of the liquid crystal molecules in the vicinity of the first alignment film is projected onto the first substrate surface. The direction in which the major axis direction of the liquid crystal molecules in the vicinity of the second alignment film is projected on the surface of the second substrate intersects each other,
The liquid crystal display, wherein the polarizing plate is essentially a circular polarizing plate provided on the viewer side of the liquid crystal cell.
2. The liquid crystal display according to claim 1, wherein a difference between the pretilt angle between the vicinity of the first alignment film and the vicinity of the second alignment film is less than 1.0 °.
The liquid crystal display according to claim 1, wherein the pretilt angle is not less than 84 ° and less than 90 °.
The liquid crystal display according to claim 3, wherein the pretilt angle is 86 ° or more.
The liquid crystal display according to claim 3 or 4, wherein the pretilt angle is 89.7 ° or less.
The liquid crystal display according to claim 5, wherein the pretilt angle is 89.5 ° or less.
7. The liquid crystal display according to claim 1, wherein the polarizing plate further includes a circularly polarizing plate provided on the back side of the liquid crystal cell.
The liquid crystal display according to claim 1, wherein the liquid crystal cell has a liquid crystal layer retardation of 315 to 385 nm.
2. The liquid crystal display according to claim 1, wherein the pretilt angle has a difference of 1.0 ° or more between the vicinity of the first alignment film and the vicinity of the second alignment film.
10. The liquid crystal display according to claim 9, wherein the pretilt angle is an angle in the vicinity of one alignment film of 84 ° or more and less than 90 °.
The liquid crystal display according to claim 9 or 10, wherein the polarizing plate further comprises a circularly polarizing plate provided on the back side of the liquid crystal cell.
12. The liquid crystal display according to claim 9, wherein the liquid crystal cell has a liquid crystal layer retardation of 315 to 385 nm.
The liquid crystal display according to any one of claims 1 to 12, wherein each of the plurality of pixels has two or more alignment regions.
The liquid crystal display according to claim 13, wherein each of the plurality of pixels has four or more alignment regions.
The liquid crystal display according to claim 14, wherein each of the plurality of pixels has four alignment regions.
A liquid crystal display comprising a liquid crystal cell and a polarizing plate,
The liquid crystal cell includes a first substrate and a second substrate including a plurality of pixels, a vertically aligned liquid crystal layer including liquid crystal molecules provided between the substrates, and a liquid crystal layer side of the first substrate. A first alignment film provided on the surface of the second substrate, and a second alignment film provided on the surface of the second substrate on the liquid crystal layer side,
Each of the plurality of pixels has one or more alignment regions,
In the alignment region, the major axis direction of the liquid crystal molecules has a pretilt angle with respect to the first and second substrate surfaces, and the major axis direction of the liquid crystal molecules in the vicinity of the first alignment film is projected onto the first substrate surface. The major axis direction of the liquid crystal molecules in the vicinity of the second alignment film is parallel to and opposite to the directions projected on the second substrate surface,
The liquid crystal display, wherein the polarizing plate is essentially a circular polarizing plate provided on the viewer side of the liquid crystal cell.