JP2008299290A - Liquid crystal display - Google Patents

Abstract

Provided is a liquid crystal display device capable of preventing a reduction in luminance and contrast ratio of transmissive display and capable of performing transmissive display with a wide viewing angle.
A vertical alignment mode liquid crystal display device in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display area and a reflective display area are provided. The liquid crystal display device has a λ / 4 retardation layer in a reflective display region between a back substrate or a front substrate and a liquid crystal layer, and a liquid crystal display in a transmissive display region between the back substrate or the front substrate and the liquid crystal layer. There is no retardation layer other than the layer, and in the transmissive display region between the back substrate and the back polarizer, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the back polarizer, and the substrate method This is a liquid crystal display device having a back biaxial retardation layer having a minimum main refractive index in the line direction.
[Selection] Figure 1

Description

The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device suitable for mobile devices such as mobile phones.

Liquid crystal display devices are used in a wide range of fields, taking advantage of their thinness, light weight, and low power consumption, and in recent years, they are increasingly installed in mobile devices such as mobile phones. However, since mobile devices are often used outdoors, from the viewpoint of preventing reflections and reducing power consumption, display is performed using both external light and a backlight. Liquid crystal display devices have been developed.

In a transflective liquid crystal display device, when performing display in the vertical alignment (VA) method, which is a normally black mode, a λ / 4 retardation plate is disposed in the reflective display region in order to effectively perform reflective display. There is a need to. The λ / 4 retardation plate gives a λ / 4 retardation (retardation) between two polarization components that vibrate in a direction perpendicular to each other with respect to the transmitted light of wavelength λ, and can be made into circularly polarized light. . In reflective display, by using a λ / 4 retardation plate, a normally black mode is possible, and a contrast ratio can be ensured.

However, when the λ / 4 retardation plate is disposed on the front surface of the transflective liquid crystal display panel, generally, a circular polarizer including a linear polarizer and a λ / 4 retardation plate is used as the liquid crystal display panel. The λ / 4 phase difference plate is disposed not only in the reflective display area but also in the transmissive display area. Therefore, the circular polarizer disposed in the transmissive display region may cause a reduction in the contrast ratio of the transmissive display.

As a countermeasure, by arranging a λ / 4 plate between the polarizer disposed on the back side of the liquid crystal display panel and the liquid crystal display panel, the λ / 4 plate disposed on the observation surface side in the transmissive display region. A method for canceling the phase difference is also disclosed. However, since this method cancels out the phase difference generated in the λ / 4 plate on the back side with the λ / 4 plate on the observation surface side, the phase difference values of the respective λ / 4 plates are exactly the same. Need to be. For example, when the value of the phase difference of the λ / 4 plate arranged on the observation surface side is 5 nm different from the λ / 4 plate arranged on the back side, the contrast ratio of the transmissive display may be reduced to half or less. is there. For this reason, there is room for improvement in that high-quality quality control is required for the λ / 4 plate, resulting in an increase in cost.

Therefore, a technique for preventing a reduction in contrast ratio by disposing a λ / 4 phase difference plate only in a reflection region in the panel is disclosed (for example, see Patent Documents 1 to 4). These are structures in which a liquid crystalline polymer is patterned inside the panel in order to arrange the λ / 4 plate only in the reflective portion, and since the λ / 4 plate is not arranged in the transmissive display region, Decrease in the contrast ratio of the transmissive display can be prevented.

Further, as a method of expanding the viewing angle of the liquid crystal display device, a retardation plate for compensating the viewing angle is provided between the back substrate and the back polarizer, or between the back substrate and the back substrate, and the front substrate and the front polarization. There is disclosed a method of arranging both of them between the child (see, for example, Patent Documents 5 and 6).
JP 2003-322857 A JP 2004-317611 A JP 2006-221189 A Japanese Patent Application Laid-Open No. 2006-276697 JP 2007-101874 A Japanese Patent No. 3544629

However, in Patent Documents 1 to 4, although it is possible to prevent a decrease in luminance and contrast ratio of transmissive display, no consideration is given to compensating the viewing angle of transmissive display, and when viewed from an oblique direction. There is a risk of gradation inversion. In Patent Documents 5 and 6, although the viewing angle is compensated, a retardation plate made of a λ / 4 wavelength plate or the like is also provided in the transmissive display region. The ratio may be reduced.

The present invention has been made in view of the above situation, and provides a liquid crystal display device capable of preventing a decrease in luminance and contrast ratio of transmissive display and performing transmissive display with a wide viewing angle. It is intended.

The inventor has made various studies on a vertical alignment mode liquid crystal display device in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display area and a reflective display area are provided. As a result, attention was paid to the arrangement of each of the λ / 4 retardation layer capable of converting linearly polarized light into circularly polarized light and the layer capable of expanding the viewing angle of transmissive display. A λ / 4 retardation layer is provided in the reflective display region between the back substrate or the front substrate and the liquid crystal layer, and the retardation other than the liquid crystal layer is provided in the transmissive display region between the back substrate or the front substrate and the liquid crystal layer. In the transmissive display region between the back substrate and the back polarizer, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the back polarizer and has the smallest main in the substrate normal direction. By providing the back biaxial retardation layer having a refractive index, it is possible to perform transmissive display with a wide viewing angle and to prevent a decrease in luminance and contrast ratio of the transmissive display. The present inventors have arrived at the present invention by conceiving that it can be solved on a case-by-case basis.

That is, the present invention is a vertical alignment mode liquid crystal display device in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display region and a reflective display region are provided. The liquid crystal display device has a λ / 4 retardation layer in the reflective display region between the back substrate or the front substrate and the liquid crystal layer, and in the transmissive display region between the back substrate or the front substrate and the liquid crystal layer. Has no retardation layer other than the liquid crystal layer, and in the transmissive display region between the back substrate and the back polarizer, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the back polarizer, and It is a liquid crystal display device (hereinafter also referred to as a first liquid crystal display device) having a back biaxial retardation layer having a minimum main refractive index in the substrate normal direction.
The present invention is described in detail below.

The first liquid crystal display device is a vertical alignment mode liquid crystal display in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display area and a reflective display area are provided. Device. In the present specification, a portion from the back substrate to the front substrate in the liquid crystal display device is also referred to as a liquid crystal display panel. The back polarizer and the front polarizer are linear polarizers that can convert unpolarized light into linearly polarized light. The absorption axis of the back polarizer and the absorption axis of the front polarizer are arranged vertically. It is preferable to take a crossed Nicol arrangement. By adopting the crossed Nicols arrangement, the first liquid crystal display device can be a normally black mode liquid crystal display device that displays black when no voltage is applied to the liquid crystal layer. The contrast ratio can be improved as compared with the liquid crystal display device. The back polarizer and the front polarizer may be the same or different, but are preferably the same from the viewpoint of symmetry.

The rear substrate is a rear substrate, and the front substrate is an observation surface substrate. The back substrate and the front substrate are preferably colorless and transparent substrates, and more preferably a glass substrate, a plastic substrate and the like from the viewpoint of cost reduction. The first liquid crystal display device is of a vertical alignment mode in which the major axis of liquid crystal molecules is aligned perpendicular to the substrate normal direction when no voltage is applied to the liquid crystal layer. Therefore, the liquid crystal layer is preferably configured to include liquid crystal molecules having negative dielectric anisotropy. Further, it is preferable that a vertical alignment film is disposed at at least one of a position in contact with the liquid crystal layer between the liquid crystal layer and the back substrate and a position in contact with the liquid crystal layer between the liquid crystal layer and the front substrate. .

The first liquid crystal display device is a transflective liquid crystal display device having a transmissive display area and a reflective display area. In the transmissive display area, display is performed using light incident from the back substrate side, and the reflective display area is displayed. Then, display is performed using light incident from the front substrate side.

In the transmissive display region, the first liquid crystal display device may have a structure in which a back polarizer, a back substrate, a back transparent electrode, a liquid crystal layer, a front transparent electrode, a front substrate, and a front polarizer are arranged in this order. preferable. According to this, transmissive display can be performed by controlling the orientation of the liquid crystal molecules in the liquid crystal layer by applying a voltage to the liquid crystal layer between the back transparent electrode and the front transparent electrode.
In the reflective display area, the first liquid crystal display device has a structure in which (a) a back polarizer, a back substrate, a reflective electrode, a liquid crystal layer, a front transparent electrode, a front substrate and a front polarizer are arranged in this order, or (B) It is preferable that the back polarizer, the back substrate, the reflective layer, the back transparent electrode, the liquid crystal layer, the front transparent electrode, the front substrate, and the front polarizer are arranged in this order. According to this, in the case of having the structure of (a), the light incident from the front substrate side is reflected by the reflective electrode, and a voltage is applied to the liquid crystal layer between the reflective electrode and the front transparent electrode. In the case of having the structure of (b), the light incident from the front substrate side is reflected by the reflective layer, and a voltage is applied to the liquid crystal layer between the back transparent electrode and the front transparent electrode, whereby the liquid crystal layer Reflective display can be performed by controlling the orientation of the liquid crystal molecules therein.

The first liquid crystal display device has a λ / 4 retardation layer in a reflective display region between a back substrate or a front substrate and a liquid crystal layer, and a transmissive display region between the back substrate or the front substrate and the liquid crystal layer. Has no retardation layer other than the liquid crystal layer. The λ / 4 retardation layer gives the light incident on the λ / 4 retardation layer a phase difference of λ / 4 with respect to one wavelength λ in the wavelength range of visible light (range of 380 nm to 780 nm). It is. The wavelength of λ is preferably set to 550 nm, which has high visibility in the wavelength range of visible light. When the liquid crystal display panel is viewed in plan, the slow axis of the λ / 4 retardation layer has an angle of 45 ° with respect to the absorption axis of the front polarizer, so that the light that has been linearly polarized by the front polarizer Can be converted into circularly polarized light, and when light incident on the reflective display region from the front polarizer side is reflected and emitted in a liquid crystal display panel in which liquid crystal molecules in the liquid crystal layer are vertically aligned, Circularly polarized light can be converted to linearly polarized light. As described above, when the λ / 4 retardation layer is arranged in the reflective display region and the liquid crystal molecules in the liquid crystal layer are vertically aligned, the λ / 4 position is obtained when the light is incident and emitted. By passing through the phase difference layer, black display can be performed in a normally black mode. Further, the λ / 4 retardation layer is disposed between the back substrate or the front substrate and the liquid crystal layer, thereby forming a structure (for example, a color filter, a TFT element, etc.) formed inside the liquid crystal display panel. Λ / 4 retardation layer can be formed in conjunction with the patterning, and patterning can be performed by accurately dividing into a transmissive display area and a reflective display area. If a retardation layer other than the liquid crystal layer is disposed inside the panel in the transmissive display area, the contrast display ratio is increased because the black display of the transmissive display becomes brighter to add a phase difference to the light incident from the back substrate side. Decreases. In the present invention, since the transmissive display area between the back substrate and the front substrate does not have a retardation layer other than the liquid crystal layer, display can be performed without reducing the contrast ratio of the transmissive display area. . In the present specification, the “retardation layer” refers to a layer having a retardation of 20 nm or more at least in the substrate in-plane direction or the substrate normal direction. In addition, the λ / 4 retardation layer may be disposed on one of the liquid crystal layer on the front substrate side or the back substrate side, but is disposed on the back substrate side, and the reflective layer or the reflective electrode is disposed on the back substrate. In this case, the liquid crystal layer is preferably disposed closer to the liquid crystal layer than the reflective electrode. The reflective layer is not particularly limited as long as it can reflect light, and may have conductivity or may not have conductivity.

In the first liquid crystal display device, in the transmission display region between the back substrate and the back polarizer, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the back polarizer, and the normal direction of the substrate Have a back biaxial retardation layer having a minimum main refractive index. The back biaxial retardation layer has a minimum main refractive index in the normal direction of the substrate, so that when the absorption axes of the two polarizing plates facing each other are arranged in a crossed Nicol arrangement, the liquid crystal display device can be viewed from an oblique direction. Since it is possible to simultaneously prevent light leakage caused by an apparent change in the angle between the absorption axes when observed, and phase compensation of the liquid crystal layer, the back substrate and back polarizer The liquid crystal molecules in the liquid crystal layer are aligned perpendicularly to the substrate in-plane direction by arranging the slow axis in the substrate in-plane direction parallel or orthogonal to the absorption axis of the back polarizer in the transmissive display area When the black display is performed, the oblique phase difference of the liquid crystal layer in the transmissive display region can be compensated. In addition, since the back biaxial retardation layer is disposed between the back substrate and the back polarizer, it can be attached to the back substrate in the same process as the back polarizer, thereby improving productivity. Can be planned. Further, by disposing the liquid crystal layer between the back polarizer and the back substrate, it is possible to make optical contact with the liquid crystal layer, so that an oblique phase difference of the liquid crystal layer in the transmissive display region can be compensated. Therefore, the viewing angle of transmissive display can be expanded as compared with the case where no biaxial retardation layer is disposed. Note that the back biaxial retardation layer only needs to be formed in the transmissive display region, and may or may not be formed in the reflective display region. From the viewpoint of productivity, since the number of manufacturing steps can be simplified, it is preferable to be provided in both the reflective display area and the transmissive display area. Further, in this specification, “parallel” is generated not only in the case of being completely parallel but also in light that has passed through the liquid crystal layer in which the liquid crystal molecules are aligned perpendicularly to the in-plane direction of the substrate in an oblique direction. This includes those that can be regarded as parallel to the extent that the phase difference can be compensated. Further, in the present specification, the term “orthogonal” refers to not only the case of being completely orthogonal, but also to light that has passed through an oblique direction through a liquid crystal layer in which liquid crystal molecules are aligned perpendicular to the in-plane direction of the substrate This includes those that can be viewed as orthogonal to the extent that the phase difference can be compensated. In this specification, “optically contacting” means that a member that imparts a phase difference is not disposed between two members.

The biaxial retardation layer having the minimum main refractive index in the substrate normal direction is smaller in the main refractive index in the substrate normal direction than the main refractive index in the substrate in-plane direction. It is a retardation layer having a slow axis and a fast axis having different main refractive indexes. The biaxial retardation layer having the minimum principal refractive index in the substrate normal direction is arranged in the in-plane direction of the substrate in the three-dimensional orthogonal coordinate system having the x, y, and z axes. The case where the z-axis is arranged in the normal direction of the substrate will be described as an example. The biaxial retardation layer having the smallest main refractive index in the substrate normal direction is aligned with the x axis in the in-plane direction of the substrate when the slow axis coincides with the y axis and the fast axis coincides with the y axis. Negative biaxial phase difference in which the main refractive index (nx) is greater than the main refractive index (ny) in the y-axis direction and the main refractive index (nz) in the z-axis direction is smaller than nx and ny It is called a layer.

As long as the first liquid crystal display device of the present invention has a back polarizer, a back substrate, a liquid crystal layer, a front substrate, a front polarizer, a λ / 4 retardation layer and a negative biaxial retardation layer as constituent elements, Other components may or may not be included, and there is no particular limitation. For example, the first liquid crystal display device of the present invention preferably has a backlight on the side opposite to the liquid crystal layer of the back polarizer in order to perform transmissive display, and the front light in front polarization for performing reflective display. You may have on the opposite side to the liquid crystal layer of a child.

A preferred embodiment of the first liquid crystal display device of the present invention will be described in detail below.
The first liquid crystal display device preferably does not have a biaxial retardation layer having a minimum main refractive index in the substrate normal direction in the reflective display region between the front substrate and the front polarizer. The first liquid crystal display device preferably has no retardation layer in the reflective display region between the front substrate and the front polarizer. According to this, since light incident on the reflective display region does not cause phase modulation other than phase modulation by the λ / 4 retardation layer, when the liquid crystal layer is vertically aligned, the light is incident on the absorption axis of the front polarizer. On the other hand, since the linearly polarized light is orthogonal to the contrast, the contrast ratio can be improved.

The back biaxial retardation layer has a phase difference in the in-plane direction of the substrate of 45 nm or more and 55 nm or less, a retardation of the substrate normal direction of −250 nm or more and −230 nm or less, and the liquid crystal layer contains liquid crystal molecules. It is preferable that the phase difference in the substrate normal direction in the transmissive display region is 300 nm or more and 390 nm or less when vertically aligned with respect to the substrate surface. Further, according to this, when the black display is performed in the transmissive part, the luminance change is small depending on the viewing angle direction, and the black display can be stably performed in a wide viewing angle range. Since there is no phase difference layer for compensation, stable reflective display can be performed. The liquid crystal layer more preferably has a phase difference of 150 nm or more and 195 nm or less in the reflective display region in the normal direction of the substrate when the liquid crystal molecules are vertically aligned with respect to the substrate surface. In other words, the thickness of the liquid crystal layer in the reflective display region is more preferably ½ of the thickness of the liquid crystal layer in the transmissive display region. According to this, since the optical path lengths of the transmissive display area and the reflective display area are equal, it is possible to align the increasing tendency of the transmittance when a voltage is applied to the liquid crystal layer in the reflective display area and the transmissive display area. it can. If the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region exceeds 390 nm, red (R), green (G), blue (B), etc. are displayed when a sufficient voltage is applied to perform bright display. Since there is a large difference in the retardation (retardation) of the liquid crystal layer for each color, the luminance of blue may be reduced and the white display may be yellowish. If the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region is less than 300 nm, the brightness of white display may not be ensured. Compensate for the phase difference of the liquid crystal layer if the phase difference in the substrate normal direction of the back biaxial retardation layer is −250 nm to −230 nm and the phase difference in the substrate in-plane direction is 45 nm to 55 nm. In addition, it is possible to prevent light leakage caused by an apparent change in the angle formed between the absorption axis of the back polarizing plate and the absorption axis of the front polarizing plate when the liquid crystal display device is observed from an oblique direction. Further, even when the phase difference in the substrate normal direction of the liquid crystal layer in the reflective display region exceeds 195 nm, the same phenomenon as in the case where the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region exceeds 390 nm may occur. There is. Even when the phase difference in the substrate normal direction of the liquid crystal layer in the reflective display region is less than 150 nm, the same phenomenon as in the case where the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region is less than 300 nm may occur. There is.

In a three-dimensional orthogonal coordinate system having x, y, and z axes, the x axis and y axis are arranged in the in-plane direction of the substrate, and the z axis is arranged in the normal direction of the substrate. When the slow axis coincides with the x axis in the in-plane direction of the negative biaxial retardation layer and the fast axis coincides with the y axis, the substrate surface of the negative biaxial retardation layer The phase difference (Re) in the inward direction can be calculated by the following formula (1), and the phase difference (Rth) in the substrate normal direction can be calculated by the following formula (2).
Re = (nx−ny) × d (1)
Rth = {nz− (nx + ny) / 2} × d (2)
Note that nx and ny are the main refractive indexes in the direction parallel to the surface of the retardation layer and perpendicular to each other (the in-plane direction of the substrate), and the slow axis or the fast axis coincided with the x-axis direction. It's time. nz is the main refractive index at a wavelength λ in the thickness direction (substrate normal direction) of the retardation layer, and d is the thickness of the retardation layer.

The first liquid crystal display device may further include a negative uniaxial retardation layer having an optical axis in the substrate normal direction in a reflective display region between the λ / 4 retardation layer and the liquid crystal layer. preferable. According to this, since the negative uniaxial retardation layer having an optical axis in the normal direction of the substrate is disposed at a position in optical contact with the liquid crystal layer, light incident from an oblique direction in the reflective display region It is possible to compensate for the phase difference imparted by the incident on the liquid crystal layer. Therefore, the viewing angle can be enlarged also in the reflective display region. A negative uniaxial retardation layer having an optical axis in the substrate normal direction has a smaller main refractive index in the substrate normal direction than the main refractive index in the substrate in-plane direction, and the main refraction in the substrate in-plane direction. It is a phase difference layer having the same rate. At this time, the phase difference in the in-plane direction of the substrate is 0 nm. In the present specification, “equal” includes not only the case of being completely equal, but also includes those that can be regarded as being equal in view of the operational effects of the present invention. In addition to the case of 0 nm, in addition to the effects of the present invention, those that can be equated with 0 nm are also included. Further, the negative uniaxial retardation layer having the optical axis in the substrate normal direction can also be referred to as a negative C plate, and can cancel the retardation of the liquid crystal layer in the oblique direction which is the positive C plate. The viewing angle can be enlarged.

In the three-dimensional orthogonal coordinate system in which the negative uniaxial retardation layer has x, y, and z axes, the x axis and y axis are arranged in the substrate in-plane direction, and the substrate normal direction is set. A case where the z axis is arranged will be described as an example. In the negative uniaxial retardation layer, the main refractive index (nx) in the x-axis direction is equal to the main refractive index (ny) in the y-axis direction, and the main refractive index (nz) in the z-axis direction is nx and ny. The smaller one is called a negative uniaxial retardation layer.

In the liquid crystal layer, the phase difference in the substrate normal direction in the reflective display region when the liquid crystal molecules are vertically aligned with respect to the substrate surface is the phase difference in the substrate normal direction of the negative uniaxial retardation layer. Preferably, the liquid crystal layer has a negative uniaxial retardation layer in which the phase difference in the substrate normal direction in the reflective display region when the liquid crystal molecules are vertically aligned with respect to the substrate surface. By canceling out the phase difference in the linear direction, the phase difference imparted by the liquid crystal layer to the light incident from the oblique direction can be more effectively compensated in the reflective display region. In the present specification, “cancelled” includes not only a case where it is completely canceled but also a thing that can be regarded as being canceled in view of the operational effects of the present invention.

The liquid crystal layer has a phase difference of 150 nm or more and 195 nm or less in the substrate normal direction in the reflective display region when the liquid crystal molecules are vertically aligned with respect to the substrate surface, and the negative uniaxial retardation layer is The phase difference in the normal direction of the substrate is preferably from −195 nm to −150 nm. According to this, since the optical path lengths of the transmissive display area and the reflective display area are equal, the display of the reflective display area and the transmissive display area can be made uniform. Furthermore, in both the transmissive display area and the reflective display area, it is possible to more effectively compensate for the phase difference imparted by the liquid crystal layer to light incident from an oblique direction. When the phase difference in the substrate normal direction of the liquid crystal layer in the reflective display region exceeds 195 nm, red (R), green (G), blue (B), etc. are displayed when a sufficient voltage is applied to perform bright display. Since there is a large difference in the retardation of the liquid crystal layer for each color, the luminance of blue may be reduced and the white display may be yellowish. Further, if the phase difference in the substrate normal direction of the liquid crystal layer in the reflective display region is less than 150 nm, it may be impossible to ensure the brightness of white display. When the phase difference in the substrate normal direction of the negative uniaxial retardation layer is −195 nm or more and −150 nm or less, the retardation of the liquid crystal layer can be compensated.

In the first liquid crystal display device, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the front polarizer in the transmissive display region and the reflective display region between the front substrate and the front polarizer. And a front biaxial retardation layer having a minimum main refractive index in the substrate normal direction, and the λ / 4 retardation layer is disposed in a reflective display region between the back substrate and the liquid crystal layer. It is preferable. By having the front biaxial retardation layer, in the transmissive display area, symmetry is improved between the back side and the front side of the first liquid crystal display device, so that display with a wider viewing angle can be performed. it can. In addition, in the reflective display area, the phase difference caused by the liquid crystal layer of light incident from an oblique direction can be compensated both before and after the light is reflected by the reflective layer. The corner can be enlarged.

The first liquid crystal display device has a transmissive display area and a reflective display area between the front substrate and the front polarizer, and a slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the front polarizer, and A front biaxial retardation layer having a minimum principal refractive index in the normal direction of the substrate, and the λ / 4 retardation layer is disposed in a reflective display region between the back substrate and the liquid crystal layer The back biaxial retardation layer and the front biaxial retardation layer have a retardation in the in-plane direction of the substrate of 50 nm to 60 nm and a retardation in the substrate normal direction of −140 nm to −110 nm. The liquid crystal layer preferably has a phase difference in the normal direction of the substrate in the transmissive display region of 300 nm or more and 390 nm or less when the liquid crystal molecules are aligned vertically to the substrate surface. By adopting such a structure, when the black display is performed in the transmissive display region, the luminance change is small depending on the viewing angle direction, and the black display can be stably performed in a wide viewing angle range. Moreover, it is more preferable that the phase difference of the reflective display region in the substrate normal direction is 150 nm or more and 195 nm or less. In other words, the thickness of the liquid crystal layer in the reflective display region is more preferably ½ of the thickness of the liquid crystal layer in the transmissive display region. According to this, since the optical path lengths of the transmissive display area and the reflective display area are equal, it is possible to align the increasing tendency of the transmittance when a voltage is applied to the liquid crystal layer in the reflective display area and the transmissive display area. it can. Further, the front biaxial retardation layer on the front substrate side and the liquid crystal layer are in optical contact with each other, so that the light incident from the observation surface side is reciprocally equivalent to the transmission optical system, and the viewing angle can be compensated. If the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region exceeds 390 nm, red (R), green (G), blue (B), etc. are displayed when a sufficient voltage is applied to perform bright display. Since there is a large difference in the phase difference of the liquid crystal layer for each color, there is a possibility that the luminance of blue will decrease and the white display will turn yellow. If the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region is less than 300 nm, the brightness of white display may not be ensured. The retardation of the liquid crystal layer is compensated if the phase difference in the substrate normal direction of the back biaxial retardation layer is −140 nm or more and −110 nm or less and the phase difference in the substrate in-plane direction is 50 nm or more and 60 nm or less. In addition, it is possible to prevent light leakage caused by an apparent change in the angle formed between the absorption axis of the back polarizing plate and the absorption axis of the front polarizing plate when the liquid crystal display device is observed from an oblique direction. Further, even when the phase difference in the substrate normal direction of the liquid crystal layer in the reflective display region exceeds 195 nm, the same phenomenon as in the case where the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region exceeds 390 nm may occur. There is. Even when the phase difference in the substrate normal direction of the liquid crystal layer in the reflective display region is less than 150 nm, the same phenomenon as in the case where the phase difference in the substrate normal direction of the liquid crystal layer in the transmissive display region is less than 300 nm may occur. There is.

The present invention is also a vertical alignment mode liquid crystal display device in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display area and a reflective display area are provided. The liquid crystal display device has a λ / 4 retardation layer in the reflective display region between the back substrate or the front substrate and the liquid crystal layer, and the transmissive display region between the back substrate or the front substrate and the liquid crystal layer. A layer that does not have a retardation layer other than the liquid crystal layer and expands the viewing angle of transmissive display in the transmissive display region between the back substrate and the back polarizer (hereinafter also referred to as a first viewing angle widening layer). A liquid crystal display device (hereinafter also referred to as a second liquid crystal display device).

As with the first liquid crystal display device, the second liquid crystal display device of the present invention can enlarge the viewing angle of the transmissive display region and not cause a reduction in contrast ratio and luminance. As the first viewing angle widening layer of the transmissive display, when the liquid crystal molecules of the liquid crystal layer are aligned perpendicular to the in-plane direction of the substrate, the liquid crystal layer passes through the liquid crystal layer in an oblique direction with respect to the normal direction of the substrate. It is preferable that the phase difference generated in the light can be compensated, more preferably a layer formed by controlling the orientation of liquid crystal molecules, and the slow axis is orthogonal or parallel to the absorption axis of the back polarizer. And negative biaxial retardation layer. In the present specification, the “viewing angle” is an angle at which a contrast ratio of 10: 1 can be secured.
A preferred embodiment of the second liquid crystal display device of the present invention will be described in detail below.

The second liquid crystal display device preferably does not have a biaxial retardation layer having a minimum main refractive index in the normal direction of the substrate in the reflective display region between the front substrate and the front polarizer.
When the second liquid crystal display device does not have a biaxial retardation layer having a minimum main refractive index in the normal direction of the substrate in the transmissive display region between the front substrate and the front polarizer, One viewing angle expansion layer has a phase difference in the in-plane direction of the substrate of 45 nm or more and 55 nm or less, a phase difference in the normal direction of the substrate of −250 nm or more and −230 nm or less. It is preferable that the phase difference in the substrate normal direction in the transmissive display region is 300 nm or more and 390 nm or less when it is vertically aligned. Moreover, it is more preferable that the phase difference of the reflective display region in the substrate normal direction is −195 nm or more and −150 nm or less.
The second liquid crystal display device may further include a negative uniaxial retardation layer having an optical axis in the substrate normal direction in a reflective display region between the λ / 4 retardation layer and the liquid crystal layer. preferable.
In the liquid crystal layer, the phase difference in the substrate normal direction in the reflective display region when the liquid crystal molecules are vertically aligned with respect to the substrate surface is the phase difference in the substrate normal direction of the negative uniaxial retardation layer. It is preferable to cancel out.
The liquid crystal layer has a phase difference of 150 nm or more and 195 nm or less in the substrate normal direction in the reflective display region when the liquid crystal molecules are vertically aligned with respect to the substrate surface, and the negative uniaxial retardation layer is The phase difference in the normal direction of the substrate is preferably from −195 nm to −150 nm.
In the second liquid crystal display device, in the transmissive display area and the reflective display area between the front substrate and the front polarizer, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the front polarizer. It is preferable that the λ / 4 retardation layer is disposed in a reflective display region between the back substrate and the liquid crystal layer.
In the second liquid crystal display device, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the front polarizer in the transmission display region and the reflection display region between the front substrate and the front polarizer. When the λ / 4 retardation layer is disposed in the reflective display region between the back substrate and the liquid crystal layer, the second viewing angle expanding layer is provided. The one viewing angle widening layer and the second viewing angle widening layer have a phase difference in the in-plane direction of the substrate of 50 nm or more and 60 nm or less, a phase difference of the substrate normal direction of −140 nm or more and −110 nm or less, and the liquid crystal The layer preferably has a phase difference in the normal direction of the substrate in the transmissive display region of 300 nm or more and 390 nm or less when the liquid crystal molecules are vertically aligned with respect to the substrate surface.
According to these, the second liquid crystal display device of the present invention can obtain the same effects as the preferred embodiment of the first liquid crystal display device of the present invention.

According to the liquid crystal display device of the present invention, in the transmissive display region, when the liquid crystal molecules of the liquid crystal layer are vertically aligned with respect to the substrate surface, the luminance change is small depending on the viewing angle direction, and the contrast ratio and the luminance are prevented from being lowered. Therefore, stable display can be performed in a wide viewing angle range.

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.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view of a vertical alignment mode transflective liquid crystal display device according to the first embodiment.
FIG. 2 is a schematic plan view of the liquid crystal display device according to Embodiment 1 disassembled and displayed. In FIG. 2, members that do not modulate the phase difference other than the reflective electrode and the transparent electrode are omitted.
In the liquid crystal display device according to the first embodiment, the back polarizer 115, the back substrate 111, the liquid crystal layer 131, the front substrate 121, and the front polarizer 125 are stacked in this order, and the negative electrode is interposed between the back substrate 121 and the front substrate 111. A liquid crystal layer 131 including liquid crystal molecules having a dielectric constant of n is sandwiched.

First, the configuration on the back substrate side will be described.
A TFT element (not shown) is provided on the liquid crystal layer 131 side of the back substrate 111. The TFT element is provided at each intersection of a plurality of gate lines (not shown) and source lines (not shown) provided so as to extend in parallel to each other in an orthogonal direction. The drain electrode of the TFT element is connected to the transparent electrode 113 provided in the transmissive display region 160 and the reflective electrode 112 provided in the reflective display region 150. A back polarizer 115 is provided on the opposite side of the back substrate 111 from the liquid crystal layer 131, and the substrate normal direction is provided between the back polarizer 115 and the TFT substrate 111 in order to increase the viewing angle. The back biaxial retardation layer 116 having the smallest main refractive index is disposed.

The back biaxial retardation layer 116 can be formed by stretching a polycarbonate or norbornene film in two directions in two directions. The transparent electrode 113 can be made of a transparent conductive material such as indium tin oxide (ITO), and the reflective electrode 112 can be made of a material having a relatively high reflection efficiency such as aluminum. The surface of 112 preferably has an uneven shape, but may be flat. The back substrate 111 is preferably a colorless and transparent substrate, and more preferably a glass substrate, a plastic substrate, or the like from the viewpoint of cost reduction.

Next, the configuration on the front substrate side will be described.
A red, green and blue colored layer 122 is disposed on the liquid crystal layer 131 side of the front substrate 121, and a λ / 4 retardation layer 123 made of a liquid crystalline polymer or the like is disposed in the reflective display region 150. A common electrode 124 is disposed on the entire surface of the front substrate 121 thereon. A front polarizer 125 is provided on the opposite side of the front substrate 121 from the liquid crystal layer 131.

The λ / 4 retardation layer 123 can be formed by applying a liquid crystalline monomer on the colored layer 122, polymerizing and curing the film while controlling the alignment by ultraviolet irradiation or the like, and patterning. Red, blue and green photosensitive resins can be used for the colored layer 122, and a transparent conductive material made of indium tin oxide (ITO) or the like can be used for the common electrode 124. Like the back substrate 111, the front substrate 121 is preferably a colorless and transparent substrate, and more preferably a glass substrate, a plastic substrate, or the like from the viewpoint of cost reduction.

The λ / 4 retardation layer 123 is disposed in a region facing the reflective electrode 112 disposed on the back substrate 111 and is not disposed in a portion facing the transparent electrode 113. In the first embodiment, the thickness of the λ / 4 retardation layer 123 is approximately 2 μm, so that the liquid crystal layer thickness of the reflective display region 150 is approximately ½ of the liquid crystal layer thickness of the transmissive display region 160. By setting it to approximately ½, the optical path length of the liquid crystal layer 131 can be made uniform in the reflective display region 150 and the transmissive display region 160. Note that it is not necessary to control the thickness of the liquid crystal layer 131 in the reflective display region 150 only by the λ / 4 retardation layer 123, and a transparent resin is disposed in the reflective display region 150, and the λ / 4 retardation layer is formed thereon. The thickness of the liquid crystal layer 131 in the reflective display region 150 and the transmissive display region 160 may be controlled by disposing 123.

Note that the back polarizer and the front polarizer included in the back polarizer 115 and the front polarizer 125 may be formed by adsorbing iodine on a polyvinyl alcohol (PVA) film and stretching.

Next, the principle of optical compensation (expansion of viewing angle of transmissive display) according to the first embodiment will be described with reference to FIG.
The white arrows on the front polarizer 125 and the back polarizer 115 indicate the transmission axes of the respective polarizers. The front polarizer 125 and the back polarizer 115 absorb the front polarizer 125. The crossed Nicols arrangement is such that the axis and the absorption axis of the back polarizer 115 are orthogonal to each other. An arrow written in the λ / 4 retardation layer 123 indicates a slow axis. In the cross arrow described in the back biaxial retardation layer 116, a short arrow indicates a slow axis and a long arrow indicates a fast axis. Light is incident on the system combining these optical members from the vertical direction on the back polarizer 125 side using a backlight.

In the reflective display region 150, light incident from the front polarizer 125 side is converted into linearly polarized light by the front polarizer 125. Then, it passes through the λ / 4 retardation layer 123 having a slow axis inclined by 45 ° in the in-plane direction with respect to the polarization axis of the front polarizer, and becomes circularly polarized light. At this time, since the liquid crystal molecules in the liquid crystal layer 131 are vertically aligned, the circularly polarized light reaches the reflective electrode 112 without being subjected to phase modulation. The light reflected by the reflective electrode 112 becomes inversely circularly polarized light and again passes through the λ / 4 retardation layer 123 to become linearly polarized light orthogonal to the polarization axis of the front polarizer. Therefore, black display can be achieved.

In the transmissive display area 160, light from the back polarizer side passes through the back polarizer 115 and becomes linearly polarized light. The light that has become linearly polarized light passes through the back biaxial retardation layer 116. Thereafter, the light passes through the liquid crystal layer 131, but the light from the vertical direction is phase-modulated because the fast axis of the back biaxial retardation layer 116 is provided in parallel with the polarization axis of the back polarizer. However, the light from the oblique direction is phase-modulated and compensates for the phase of the linearly polarized light incident on the liquid crystal layer 131 from the oblique direction. For this reason, when the light is emitted from the front polarizer 125, the liquid crystal display device has an improved viewing angle in which gradation modulation does not occur even when observed from an oblique direction. The back biaxial retardation layer 116 is a biaxial retardation layer having a minimum main refractive index in the substrate normal direction, and has an in-plane retardation (Re) of 50 nm. (Rth) is -245 nm. Further, the slow axis of the back biaxial retardation layer 116 is arranged in a direction orthogonal to the transmission axis of the back polarizer 115, and the retardation value (Rth) in the thickness direction of the liquid crystal layer 131 is 320 nm. . In this way, by performing optical design, a liquid crystal display device can be provided in which the viewing angle of transmissive display is expanded and the luminance or the like of transmissive display is not reduced. In addition, about the phase difference of a back surface biaxial retardation layer and a liquid crystal layer, a main refractive index is measured with an ellipsometer, and it calculates | requires from the value of a main refractive index. Here, the main refractive index in the slow axis direction of the back biaxial retardation layer is 1.50010, the main refractive index in the fast axis direction is 1.49960, and the main refractive index in the substrate normal direction is 1.49740. The layer thickness of the back biaxial retardation layer is 100 μm.

In the first embodiment, an active matrix liquid crystal display device that performs display using TFT elements is used. However, the liquid crystal display device of the present invention is not limited to the active matrix method, and may be, for example, a passive matrix liquid crystal display device. Can also be applied. The present invention also has an advantage in that the manufacturing process is not complicated as compared with the case where a negative biaxial retardation layer is disposed in the liquid crystal display panel as in the case of the λ / 4 plate.

(Embodiment 2)
FIG. 3 is a schematic cross-sectional view illustrating a configuration of a vertical alignment mode transflective liquid crystal display device according to the second embodiment.
FIG. 4 is a schematic plan view of the liquid crystal display device according to Embodiment 2 disassembled and displayed. In FIG. 4, members other than the reflective electrode and the transparent electrode that do not modulate the phase difference are omitted.
In Embodiment 2 of the present invention, a back polarizer 215, a back substrate 211, a liquid crystal layer 231, a front substrate 221 and a front polarizer 225 are stacked in this order, and a negative dielectric is provided between the front substrate 221 and the back substrate 211. A liquid crystal layer 231 including liquid crystal molecules having a ratio is sandwiched.

First, the configuration on the back substrate side will be described.
A TFT element (not shown) is provided on the back substrate 211 on the liquid crystal layer 231 side. The TFT element is provided at each intersection of a plurality of gate lines (not shown) and source lines (not shown) provided so as to extend in parallel to each other in an orthogonal direction. The drain electrode of the TFT element is connected to the transparent electrode 213 provided in the transmissive display region 260 and the reflective electrode 212 provided in the reflective display region 250. A back polarizer 215 is provided on the opposite side of the back substrate 211 from the liquid crystal layer 231, and the substrate normal direction is provided between the back polarizer 215 and the TFT substrate 211 in order to increase the viewing angle. The back biaxial retardation layer 216 having the smallest main refractive index is disposed.

Next, the configuration on the front substrate side will be described.
A red, green, and blue colored layer 222 is disposed on the liquid crystal layer 231 side of the front substrate 221, and a λ / 4 retardation layer 223, a negative layer 223 is disposed on the reflective display region 250 on the liquid crystal layer 231 side of the colored layer 222. These uniaxial retardation layers 226 are arranged in this order. A common electrode 224 is disposed on the entire surface of the front substrate 221 on the liquid crystal layer 231 side of the coloring layer 222. A front polarizer 225 is provided on the opposite side of the substrate 221 from the liquid crystal layer 231.

The λ / 4 retardation layer 223 and the negative uniaxial retardation layer 226 are disposed in a region facing the reflective electrode 212 disposed on the back substrate 211 and are not disposed in a portion facing the transparent electrode 213. In the second embodiment, the thickness of the laminated λ / 4 retardation layer 223 and the negative uniaxial retardation layer 226 is set to 2 μm, so that the liquid crystal layer thickness in the reflective display region is changed to the liquid crystal layer thickness in the transmissive display region. On the other hand, it is set to 1/2. Note that it is not necessary to control the thickness of the liquid crystal layer in the reflective display region only with the λ / 4 retardation layer, and a transparent resin layer or the like is disposed between the λ / 4 retardation layer in the reflective display region and the front substrate 221. Accordingly, the liquid crystal layer thicknesses of the reflective display region 250 and the transmissive display region 260 may be controlled. The negative uniaxial retardation layer 226 can be formed by applying a thin film of a cholesteric liquid crystalline polymer on a transparent film.

Next, the principle of optical compensation (expanding the viewing angle of transmissive display) according to the second embodiment will be described with reference to FIG.
White arrows described on the front polarizer 225 and the back polarizer 215 indicate the transmission axis directions of the respective polarizers, and the front polarizer 225 and the back polarizer 215 correspond to the front polarizer 225. The absorption axis and the absorption axis of the back polarizer 215 are in a crossed Nicols arrangement orthogonal to each other. An arrow written in the λ / 4 retardation layer 223 indicates a slow axis. In the cross-shaped arrow described in the back biaxial retardation layer 216, a short arrow indicates a slow axis and a long arrow indicates a fast axis. Light is incident on the system combining these optical members from the back polarizer 215 side using a backlight.

In the reflective display region 250, light incident from the front polarizer 225 side is converted into linearly polarized light by the front polarizer 225. Then, it passes through the λ / 4 retardation layer 223 having a slow axis inclined by 45 ° in the in-plane direction with respect to the polarization axis of the front polarizer, and becomes circularly polarized light. The light that has been circularly polarized by the λ / 4 retardation layer 223 enters the liquid crystal layer 231 through the negative uniaxial retardation layer 226. At this time, since the liquid crystal molecules in the liquid crystal layer 231 are vertically aligned, the circularly polarized light reaches the reflective electrode 212 without being subjected to phase modulation. The light reflected by the reflective electrode 212 becomes reverse circularly polarized light and passes through the λ / 4 retardation layer 223 again, and becomes linearly polarized light orthogonal to the absorption axis of the front polarizer 225. Therefore, black display can be achieved. Further, the light incident from the oblique direction on the front substrate 221 side can compensate for the phase difference imparted by the liquid crystal layer 231 by the negative uniaxial retardation layer 226, so that the viewing angle can be expanded. it can.

In the transmissive display area 260, light from the back polarizer side passes through the back polarizer 215 and becomes linearly polarized light. The light that has become linearly polarized light passes through the back biaxial retardation layer 216. Thereafter, the light passes through the liquid crystal layer 231, but the light from the vertical direction is phase-modulated because the fast axis of the back biaxial retardation layer 216 is provided in parallel with the polarization axis of the back polarizer. However, the light from the oblique direction is phase-modulated and compensates for the phase of the linearly polarized light incident on the liquid crystal layer 231 from the oblique direction. For this reason, when the light is emitted from the front polarizer 225, the liquid crystal display device has an improved viewing angle in which gradation modulation or the like does not occur even when observed from an oblique direction. The back biaxial retardation layer 216 is a negative biaxial retardation layer having an in-plane retardation (Re) of 50 nm and a substrate normal direction retardation (Rth) of −245 nm. Used. Further, the slow axis of the back biaxial retardation layer 216 is arranged in a direction orthogonal to the transmission axis of the back polarizer 215, and the retardation value (Rth) in the thickness direction of the liquid crystal layer 231 is 320 nm. . Further, the retardation (Rth) in the substrate normal direction of the negative uniaxial retardation layer is set to −160 nm. Thus, by performing optical design, a liquid crystal display device can be provided in which the viewing angle is expanded and the luminance of transmissive display is not reduced. Here, the main refractive index in the slow axis direction of the back biaxial retardation layer is 1.50010, the main refractive index in the fast axis direction is 1.49960, and the main refractive index in the substrate normal direction is It was 1.49740. The main refractive index in the substrate normal direction of the negative uniaxial retardation layer is 1.55, and the main refractive index in the in-plane direction of the substrate is 1.50. The thickness of the back biaxial retardation layer is 100 μm, and the thickness of the negative uniaxial retardation layer is 3.2 μm.

(Embodiment 3)
FIG. 5 is a schematic cross-sectional view illustrating a configuration of a vertical alignment mode transflective liquid crystal display device according to a third embodiment.
FIG. 6 is a schematic plan view of the liquid crystal display device according to Embodiment 3 disassembled and displayed. In FIG. 6, members that do not modulate the phase difference other than the reflective electrode and the transparent electrode are omitted.
In Embodiment 3 of the present invention, a back polarizer 315, a back substrate 311, a liquid crystal layer 331, a front substrate 321 and a front polarizer 325 are stacked in this order, and a negative dielectric is provided between the front substrate 321 and the back substrate 311. A liquid crystal layer 331 configured to include liquid crystal molecules having a ratio is sandwiched.

First, the configuration of the back substrate will be described.
A TFT element (not shown) is provided on the back substrate 311 on the liquid crystal layer 331 side. The TFT element is provided at each intersection of a plurality of gate lines (not shown) and source lines (not shown) provided so as to extend in parallel to each other in an orthogonal direction. The drain electrode of the TFT element is connected to the transparent electrode 313 provided in the transmissive display region 360 and the reflective electrode 312 provided in the reflective display region 350. A back polarizer 315 is provided on the opposite side of the back substrate 311 from the liquid crystal layer 331. Between the back polarizer 315 and the TFT substrate 311, the normal direction of the substrate is used to increase the viewing angle. The back biaxial retardation layer 316 having the smallest main refractive index is disposed. A λ / 4 retardation layer 323 is disposed between the reflective electrode 312 and the liquid crystal layer 331 in the reflective display region 350.

Next, the configuration of the front substrate will be described.
A red, green, and blue colored layer 322 is disposed on the liquid crystal layer 331 side of the front substrate 321, and a λ / 4 retardation layer 323 made of a liquid crystalline polymer is disposed in the reflective display region 350. A common electrode 324 is disposed on the entire surface of the front substrate 321 thereon. Further, a front polarizer 325 is provided on the opposite side of the front substrate 321 from the liquid crystal layer 331, and the minimum main refractive index in the normal direction of the substrate is between the front substrate 321 and the front polarizer 325. A front biaxial retardation layer 326 having the following structure is disposed.

The λ / 4 retardation layer 323 is disposed on the liquid crystal layer 331 side of the reflective electrode 312 and is not disposed in the transmissive display region 360. In the third embodiment, the thickness of the λ / 4 retardation layer 323 is approximately 2 μm, so that the liquid crystal layer thickness in the reflective display region is approximately ½ of the liquid crystal layer thickness in the transmissive display region. Note that it is not necessary to control the thickness of the liquid crystal layer in the reflective display region only with the λ / 4 retardation layer, and the reflective resin is disposed in the reflective display region and the λ / 4 retardation layer is disposed thereon. You may control the liquid crystal layer thickness of a display area and a transmissive display area.

Next, the principle of optical compensation (expansion of viewing angle of transmissive display) according to the third embodiment will be described with reference to FIG.
The white arrows on the front polarizer 325 and the back polarizer 315 indicate the transmission axes of the respective polarizers. The front polarizer 325 and the back polarizer 315 are absorbed by the front polarizer 325. The axis and the absorption axis of the back polarizer 315 are in a crossed Nicols arrangement orthogonal to each other. An arrow written in the λ / 4 retardation layer 323 indicates a slow axis. In the cross-shaped arrow described in the back biaxial retardation layer 316, a short arrow indicates a slow axis and a long arrow indicates a fast axis. Light is incident on the system combining these optical members from the back polarizer 315 side using a backlight.

In the reflective display region 350, light incident from the front polarizer 325 side is converted into linearly polarized light by the front polarizer 325. Then, linearly polarized light is incident on the liquid crystal layer 331 via the front biaxial retardation layer 326. At this time, since the liquid crystal molecules in the liquid crystal layer 331 are vertically aligned, the circularly polarized light reaches the reflective electrode 312 without being subjected to phase modulation. Subsequently, when passing through a λ / 4 retardation layer 323 having a slow axis inclined by 45 ° in the in-plane direction with respect to the absorption axis of the front polarizer 325, circular polarization is obtained. Then, the light reflected by the reflective electrode 312 becomes reverse circularly polarized light and again passes through the λ / 4 phase difference layer 323, thereby becoming linearly polarized light orthogonal to the polarization axis of the front polarizer. In this way, black display can be achieved by reflection display. At this time, the phase difference given when the light incident from the oblique direction on the front substrate side passes through the liquid crystal layer and the phase difference given when it passes through the liquid crystal layer after being reflected by the reflective electrode are represented by the front surface 2. Compensation can be achieved by passing through the axial retardation layer 326 twice. For this reason, a viewing angle can be expanded also in a reflective display area.

In the transmissive display area 360, light from the back polarizer 315 side passes through the back polarizer 315 and becomes linearly polarized light. The light that has become linearly polarized light passes through the back biaxial retardation layer 316. Thereafter, the light passes through the liquid crystal layer 331, the front biaxial retardation layer 326, and the front polarizer 325, and is emitted. At this time, the liquid crystal layer 331 is vertically aligned, the fast axis of the back biaxial retardation layer 316 is provided in parallel with the polarization axis of the back polarizer, and the fast phase of the front biaxial retardation layer 326 is set. Since the axis is provided in parallel with the absorption axis of the front polarizer 325, the light from the vertical direction does not undergo phase modulation. Light from an oblique direction is phase-modulated when passing through the liquid crystal layer 331, but the phase difference is compensated for by the back biaxial retardation layer 316 and the front biaxial retardation layer 326. Therefore, a liquid crystal display device with an improved viewing angle in which gradation modulation or the like does not occur even when observed from an oblique direction can be obtained. The back biaxial retardation layer 316 and the front biaxial retardation layer 326 have an in-plane retardation (Re) of 55 nm and a substrate normal direction retardation (Rth) of −125 nm. ing. The retardation value (Rth) in the thickness direction of the liquid crystal layer 331 is set to 320 nm. Here, the main refractive index in the slow axis direction of the back biaxial retardation layer 316 and the front biaxial retardation layer 326 is 1.50010, and the main refractive index in the fast axis direction is 1.49955. The main refractive index in the substrate normal direction is 1.49858. The layer thickness of the back biaxial retardation layer and the front biaxial retardation layer is 100 μm. Thus, by performing optical design, it is possible to obtain a liquid crystal display device that further expands the viewing angle and does not lower the luminance and contrast ratio of transmissive display.

1 is a schematic cross-sectional view illustrating a configuration of a liquid crystal display device according to Embodiment 1. FIG. It is the plane schematic diagram decomposed | disassembled and displayed about the liquid crystal display device which concerns on Embodiment 1. FIG. 6 is a schematic cross-sectional view illustrating a configuration of a liquid crystal display device of Embodiment 2. FIG. It is the plane schematic diagram decomposed | disassembled and displayed about the liquid crystal display device which concerns on Embodiment 2. FIG. 6 is a schematic cross-sectional view illustrating a configuration of a liquid crystal display device of Embodiment 3. FIG. It is the plane schematic diagram decomposed | disassembled and displayed about the liquid crystal display device which concerns on Embodiment 3. FIG.

Explanation of symbols

111, 211, 311: Back substrate 112, 212, 312: Reflective electrode 113, 213, 313: Transparent electrode 115, 215, 315: Back polarizer 116, 216, 316: Back biaxial retardation layer 121, 221; 321: Front substrates 122, 222, 322: Colored layers 123, 223, 323: λ / 4 retardation layers 124, 224, 324: Common electrodes 131, 231, 331: Liquid crystal layer 226: Negative uniaxial retardation layer 326: Front biaxial retardation layer

Claims (9)

A vertical alignment mode liquid crystal display device in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display region and a reflective display region are provided,
The liquid crystal display device has a λ / 4 retardation layer in a reflective display region between a back substrate or a front substrate and a liquid crystal layer, and a liquid crystal display in a transmissive display region between the back substrate or the front substrate and the liquid crystal layer. There is no retardation layer other than the layer,
In the transmissive display region between the back substrate and the back polarizer, the slow axis in the in-plane direction of the substrate is parallel or orthogonal to the absorption axis of the back polarizer and has the smallest main refractive index in the substrate normal direction. A liquid crystal display device comprising a biaxial retardation layer. The liquid crystal display device does not have a biaxial retardation layer having a minimum main refractive index in a substrate normal direction in a reflective display region between a front substrate and a front polarizer. 1. A liquid crystal display device according to 1. The back biaxial retardation layer has a retardation in the substrate in-plane direction of 45 nm or more and 55 nm or less, and a retardation in the substrate normal direction of −250 nm or more and −230 nm or less,
3. The liquid crystal display according to claim 2, wherein the liquid crystal layer has a phase difference in a substrate normal direction in a transmissive display region of 300 nm or more and 390 nm or less when liquid crystal molecules are vertically aligned with respect to the substrate surface. apparatus. The liquid crystal display device further includes a negative uniaxial retardation layer having an optical axis in the normal direction of the substrate in a reflective display region between the λ / 4 retardation layer and the liquid crystal layer. The liquid crystal display device according to claim 1. In the liquid crystal layer, the phase difference in the substrate normal direction in the reflective display region when the liquid crystal molecules are aligned vertically with respect to the substrate surface is the phase difference in the substrate normal direction of the negative uniaxial retardation layer. 5. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is canceled out. The liquid crystal layer has a phase difference of 150 nm or more and 195 nm or less in the normal direction of the substrate in the reflective display region when the liquid crystal molecules are vertically aligned with respect to the substrate surface.
The liquid crystal display device according to claim 5, wherein the negative uniaxial retardation layer has a retardation in a substrate normal direction of not less than −195 nm and not more than −150 nm. The liquid crystal display device further includes a transmissive display area and a reflective display area between the front substrate and the front polarizer, the slow axis in the in-plane direction of the substrate being parallel or orthogonal to the absorption axis of the front polarizer, and the substrate A front biaxial retardation layer having a minimum main refractive index in the normal direction;
The liquid crystal display device according to claim 1, wherein the λ / 4 retardation layer is disposed in a reflective display region between the back substrate and the liquid crystal layer. The back biaxial retardation layer and the front biaxial retardation layer have a phase difference in the in-plane direction of the substrate of 50 nm or more and 60 nm or less, and a phase difference of the substrate normal direction of −140 nm or more and −110 nm or less,
8. The liquid crystal display according to claim 7, wherein the liquid crystal layer has a phase difference in the normal direction of the substrate in the transmissive display region of 300 nm or more and 390 nm or less when liquid crystal molecules are vertically aligned with respect to the substrate surface. apparatus. A vertical alignment mode liquid crystal display device in which a back polarizer, a back substrate, a liquid crystal layer, a front substrate, and a front polarizer are arranged in this order, and a transmissive display region and a reflective display region are provided,
The liquid crystal display device has a λ / 4 retardation layer in a reflective display region between a back substrate or a front substrate and a liquid crystal layer, and a liquid crystal display in a transmissive display region between the back substrate or the front substrate and the liquid crystal layer. There is no retardation layer other than the layer,
A liquid crystal display device comprising a layer for enlarging a viewing angle of transmissive display in a transmissive display region between a back substrate and a back polarizer.

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