JP2017227790A - Liquid crystal display device and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device and a method for manufacturing the liquid crystal display device including a liquid crystal cell in a horizontal alignment mode, which can decrease the luminance observed in a frontal direction during a black display mode and the luminance observed in an oblique direction during the black display mode.SOLUTION: The liquid crystal display device includes a first polarizing plate, a retardation film (I), a retardation film (II), a liquid crystal cell in a horizontal alignment mode, and a second polarizing plate having a polarization transmission axis substantially perpendicular to the polarization transmission axis of the first polarizing plate, in this order from a viewing side with regard to a specific optical axis. Each of the retardation film (I) and the retardation film (II) is a co-stretched film including a resin layer (A1) made of a resin A1 having a positive intrinsic birefringence index, a resin layer (B) made of a resin B having a negative intrinsic birefringence index, and a resin layer (A2) made of a resin A2 having a positive intrinsic birefringence index, in this order from the viewing side. A method for manufacturing the above liquid crystal display device is also provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid crystal display device and a manufacturing method thereof.

  In a liquid crystal cell in a horizontal alignment mode such as an in-plane switching mode (IPS), liquid crystal molecules are aligned in parallel to the substrate surface of the liquid crystal cell, and the characteristics such as viewing angle characteristics are excellent. Therefore, in recent years, various studies have been made on liquid crystal display devices including such a liquid crystal cell in a horizontal alignment mode. Further, in a liquid crystal display device including such a liquid crystal cell and a liquid crystal cell of another mode, for example, a layer for optical compensation is provided at various positions such as between the liquid crystal cell and the viewing side polarizing plate. (For example, refer to Patent Documents 1 to 6).

JP 2010-217870 A JP 2012-514222 A JP 2008-180961 A JP 2009-192844 A JP 2011-39338 A JP 2014-149508 A

  In the liquid crystal display device, from the viewpoint of improving the image quality, it is required to reduce the luminance at the time of black display in which light transmission is blocked. Hereinafter, the luminance at the time of black display may be referred to as “black luminance” as appropriate. The black luminance is required to be low not only when the liquid crystal display device is observed from the front but also when observed from the tilt direction. However, in a liquid crystal display device including a liquid crystal cell in a horizontal alignment mode, the black luminance observed from the tilt direction may be high even when the black luminance observed from the front direction is low.

  Accordingly, an object of the present invention is to provide a liquid crystal display device including a liquid crystal cell in a horizontal alignment mode, which can reduce the luminance observed from the front direction during black display and the luminance observed from the tilt direction during black display, and its manufacture. It is to provide a method.

As a result of studying to solve the above-mentioned problems, the present inventor has provided a plurality of specific retardation films between a viewing-side polarizing plate and a liquid crystal cell of a liquid crystal display device including a liquid crystal cell in a horizontal alignment mode. The present inventors have found that the luminance observed from not only the front direction but also the tilt direction can be lowered during black display, and the present invention has been completed.
That is, the present invention is as follows.

[1] First polarizing plate, retardation film (I), retardation film (II), liquid crystal cell in horizontal alignment mode, and second having a polarization transmission axis substantially perpendicular to the polarization transmission axis of the first polarizing plate A liquid crystal display device comprising a polarizing plate in this order from the viewing side,
Each of the retardation film (I) and the retardation film (II)
A resin layer (A1) made of resin A1 having a positive intrinsic birefringence, a resin layer (B) made of resin B having a negative intrinsic birefringence, and a resin A2 having a positive intrinsic birefringence The resin layer (A2) is provided in this order from the viewing side, and the resin layer (A1) and the resin layer (B), and the resin layer (B) and the resin layer (A2) are in direct contact with each other. Is a co-stretched film,
The slow axis in the plane of the retardation film (I) and the slow axis in the plane of the retardation film (II) are substantially parallel,
The slow axis in the plane of the retardation film (I) and the slow axis in the plane of the liquid crystal cell during black display are substantially parallel,
The in-plane slow axis of the retardation film (I) and the polarization transmission axis of the first polarizing plate are substantially parallel.
The liquid crystal display device.
[2] The retardation film (I) and the retardation film (II) are both
In-plane retardation ReA1 of the resin layer (A1), retardation RthA1 in the thickness direction of the resin layer (A1), in-plane retardation ReB of the resin layer (B), measured at a wavelength of 550 nm, The retardation RthB in the thickness direction of B), the in-plane retardation ReA2 of the resin layer (A2), and the retardation RthA2 in the thickness direction of the resin layer (A2) are represented by the following formulas (1) to (6):
20 nm ≦ ReA1 ≦ 100 nm (1)
40 nm ≦ RthA1 ≦ 180 nm (2)
60 nm ≦ ReB ≦ 200 nm (3)
−180 nm ≦ RthB ≦ −40 nm (4)
0 nm ≦ ReA2 ≦ 20 nm (5)
0 nm ≦ RthA2 ≦ 20 nm (6)
The liquid crystal display device according to [1], wherein
[3] A method for manufacturing a liquid crystal display device according to [1] or [2],
A step of preparing a resin laminate, wherein the resin laminate comprises a layer a1 made of a resin A1 having a positive intrinsic birefringence, a layer b made of a resin B having a negative intrinsic birefringence, and an intrinsic A preparation step in which a layer a2 made of a resin A2 having a positive birefringence is provided in this order, the layer a1 and the layer b are in direct contact with each other, and the layer b and the layer a2 are in direct contact with each other. ;
Stretching the resin laminate to obtain the retardation film (I), stretching step (I),
The resin laminate is stretched to obtain the retardation film (II), the stretching step (II), and the first polarizing plate, the retardation film (I), the retardation film (II), and the liquid crystal cell. And the second polarizing plate is assembled so as to be provided in this order from the viewing side.
[4] The manufacturing method according to [3], wherein the preparation step includes a co-extrusion step of the resin A1, the resin B, and the resin A2.

  The liquid crystal display device of the present invention can reduce the luminance observed from the front direction during black display and the luminance observed from the tilt direction during black display. In the manufacturing method of the liquid crystal display device of the present invention, such liquid crystal A display device can be easily manufactured.

FIG. 1 is a perspective view schematically showing a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is an exploded perspective view schematically showing the liquid crystal display device 100 shown in FIG. 1 in an exploded manner. FIG. 3 is an exploded perspective view schematically showing the retardation film (I) 120 in FIGS. 1 and 2 in an exploded manner. FIG. 4 is an exploded perspective view schematically showing the retardation film (II) 130 in FIGS. 1 and 2 in an exploded manner. FIG. 5 is a contour diagram showing the luminance at the time of black display of the liquid crystal display device calculated by the simulation in Example 1 of the present invention. FIG. 6 is a contour diagram showing the luminance at the time of black display of the liquid crystal display device calculated by the simulation in the second embodiment of the present invention. FIG. 7 is a contour diagram showing the luminance at the time of black display of the liquid crystal display device calculated by the simulation in Example 3 of the present invention. FIG. 8 is a contour diagram showing the luminance at the time of black display of the liquid crystal display device calculated by the simulation in Comparative Example 1. FIG. 9 is a contour diagram showing the luminance at the time of black display of the liquid crystal display device calculated by the simulation in Comparative Example 2. FIG. 10 is a graph showing the relationship between the azimuth angle at the polar angle of 60 ° and the luminance at the time of black display, which is calculated by the simulation in the first embodiment of the present invention. FIG. 11 is a graph showing the relationship between the azimuth angle at the polar angle of 60 ° and the luminance at the time of black display, which is calculated by the simulation in the second embodiment of the present invention. FIG. 12 is a graph showing the relationship between the azimuth angle at a polar angle of 60 ° and the luminance at the time of black display, which is calculated by simulation in Example 3 of the present invention. FIG. 13 is a graph showing the relationship between the azimuth angle at a polar angle of 60 ° and the luminance at the time of black display, calculated by the simulation in Comparative Example 1. FIG. 14 is a graph showing the relationship between the azimuth angle at a polar angle of 60 ° and the luminance at the time of black display calculated by the simulation in Comparative Example 2. FIG. 15 is a schematic diagram showing an example of a change in the polarization state of light when the liquid crystal display device shown in Comparative Example 1 of the present application is observed from an oblique direction. FIG. 16 is a schematic diagram showing an example of a change in the polarization state of light when the liquid crystal display device shown in Comparative Example 1 of the present application is observed from an oblique direction. FIG. 17 is a schematic diagram illustrating an example of a change in the polarization state of light when the liquid crystal display device 100 illustrated in FIGS. 1 to 4 is observed from an oblique direction. FIG. 18 is a schematic diagram illustrating an example of a change in the polarization state of light when the liquid crystal display device 100 illustrated in FIGS. 1 to 4 is observed from an oblique direction. FIG. 19 is a schematic diagram illustrating an example of a change in the polarization state of light when the liquid crystal display device 100 illustrated in FIGS. 1 to 4 is observed from an oblique direction. FIG. 20 is a schematic diagram illustrating an example of a change in the polarization state of light when the liquid crystal display device 100 illustrated in FIGS. 1 to 4 is observed from an oblique direction.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and exemplifications, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

  In the present application, the in-plane retardation of a flat component such as a film is a value represented by (nx−ny) × d unless otherwise specified. Further, the retardation in the thickness direction of the constituent element is a value represented by {(nx + ny) / 2−nz} × d unless otherwise specified. Further, the NZ coefficient of the component is a value represented by (nx−nz) / (nx−ny) unless otherwise specified. Here, nx represents a refractive index in a direction (in-plane direction) perpendicular to the thickness direction of the component and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the component and in a direction perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the component. d represents the film thickness of the component. Unless otherwise stated, the retardation measurement wavelength in this application is 550 nm. The retardation can be measured using a commercially available retardation measuring device (for example, “M-2000U” manufactured by JA Woollam) or the Senarmon method.

  In the present application, a material having a positive intrinsic birefringence value means a material in which the refractive index in the stretching direction is larger than the refractive index in the direction perpendicular thereto unless otherwise specified. Further, a material having a negative intrinsic birefringence value means a material having a refractive index in the stretching direction that is smaller than a refractive index in a direction perpendicular to the stretching direction unless otherwise specified. The intrinsic birefringence value of the material can be calculated from the dielectric constant distribution.

  In the following description, the front direction of the liquid crystal display device means the normal direction of the display surface of the liquid crystal display device unless otherwise specified. Specifically, the polar angle of the display surface is 0 ° and the azimuth angle is 0. Point in the direction of °.

  In the following description, the tilt direction with respect to the liquid crystal display device means a direction that is neither parallel nor perpendicular to the display surface of the liquid crystal display device unless specifically stated otherwise. Specifically, the polar angle of the display surface is 0. It refers to the direction in the range greater than ° and less than 90 °.

  In the following description, the “long” film means a film having a length of 5 times or more, preferably 10 times or more, and specifically a roll. A film having such a length that it can be wound up and stored or transported. The upper limit of the length of the long film is not particularly limited, and can be, for example, 100,000 times or less with respect to the width.

  In the following description, the “polarizing plate” includes not only a rigid member but also a flexible member such as a resin film, unless otherwise specified.

  In the following description, the angle formed by the optical axis (polarization transmission axis, slow axis, etc.) of the optical member represents the angle when the optical member is viewed from the thickness direction unless otherwise specified.

  In the following description, the slow axis of the film represents the slow axis in the plane of the film unless otherwise specified.

[1. Embodiment of liquid crystal display device]
The liquid crystal display device of the present invention includes a first polarizing plate, a retardation film (I), a retardation film (II), a liquid crystal cell, and a second polarizing plate in this order from the viewing side. The liquid crystal display device of the present invention may further include a light source device as an optional component at a position farther from the viewing side than the second polarizing plate.

FIG. 1 is a perspective view schematically showing a liquid crystal display device 100 according to an embodiment of the present invention. FIG. 2 is an exploded perspective view schematically showing the liquid crystal display device 100 shown in FIG.
1 and 2, the liquid crystal display device 100 includes a first polarizing plate 110 that is a viewing side polarizing plate, a retardation film (I) 120, a retardation film (II) 130, a liquid crystal cell 140, and a light source side. A second polarizing plate 150 as a polarizing plate and a backlight unit 160 as a light source device are provided in this order from the viewing side. In the liquid crystal display device 100, the light emitted from the backlight unit 160 passes through the second polarizing plate 150 to become linearly polarized light, and the linearly polarized light becomes the liquid crystal cell 140, the retardation film (II) 130, the retardation film. (I) By passing through 120 and the first polarizing plate 110 in this order, an image is displayed on the display surface on the viewing side of the first polarizing plate 110. Here, the visual recognition side refers to the side close to the observer who observes the liquid crystal display device, and usually refers to the side close to the display surface of the liquid crystal display device. Further, in FIG. 1, arrow A _N indicates the normal direction of the display surface, an arrow A _C shows a tilt direction with respect to the display surface.

[1.1. First polarizing plate]
The first polarizing plate has a function of transmitting linearly polarized light having a vibration direction parallel to the polarization transmission axis and absorbing other polarized light. Here, the vibration direction of linearly polarized light means the vibration direction of the electric field of linearly polarized light. In the example shown in FIGS. 1 and 2, the first polarizing plate 110 on the viewing side is a polarizing plate having a polarization transmission axis in the direction perpendicular to the long side direction of the rectangular display surface, that is, the direction indicated by the arrow A _110. .

[1.2. Liquid crystal cell)
The liquid crystal cell is an element including a liquid crystalline compound whose molecular orientation can be changed according to a voltage applied from an electrode (not shown), and is transmitted through the second polarizing plate according to the applied voltage. The linearly polarized light incident on the light can be rotated and emitted to the first polarizing plate side. Such a liquid crystal cell usually has a pair of substrates and a liquid crystal compound inserted between the substrates. In the liquid crystal display device of the present invention, the liquid crystal cell is a horizontal alignment mode cell. Normally, in a liquid crystal cell in a horizontal alignment mode, the liquid crystal compound molecules change in alignment according to the applied voltage while keeping parallel to the substrate of the liquid crystal cell. Specific examples of the horizontal alignment mode include an in-plane switching (IPS) mode, a fringe field switching (FFS) mode, and a ferroelectric liquid crystal (FLC) mode.

In the liquid crystal cell in the horizontal alignment mode, the alignment direction of the liquid crystal compound is different between black display and white display, and therefore the in-plane slow axis is different between black display and white display. The liquid crystal cell in the horizontal alignment mode is usually provided so as to display black when no voltage is applied. In the example shown in FIGS. 1 and 2, the in-plane slow axis of the liquid crystal cell 140 during black display is the direction perpendicular to the long side direction of the rectangular display surface, that is, the direction of the arrow _A140 .

[1.3. Second polarizing plate]
Similar to the first polarizing plate, the second polarizing plate has a function of transmitting linearly polarized light having a vibration direction parallel to the polarization transmission axis and absorbing other polarized light. The second polarizing plate has a polarization transmission axis substantially perpendicular to the polarization transmission axis of the first polarizing plate. The polarization transmission axis of the first polarizing plate and the polarization transmission axis of the second polarizing plate are substantially perpendicular, the angle formed by them is usually 85 ° or more, preferably 88 ° or more, more preferably 89 ° or more, In addition, it means usually 95 ° or less, preferably 92 ° or less, more preferably 91 ° or less. Since the polarized light transmission axis of the first polarizing plate and the polarized light transmission axis of the second polarizing plate are substantially perpendicular, the liquid crystal display device can control light transmission and blocking by the liquid crystal cell.

In the example shown in FIGS. 1 and 2, the second polarizing plate 150 on the light source side is a polarizing plate having a polarization transmission axis in the direction parallel to the long side direction of the rectangular display surface, that is, the direction indicated by the arrow A _150. .

[1.4. (Backlight unit)
The backlight unit 160 is not particularly limited, and any light source that can be employed in a liquid crystal display device can be used. Specific examples of the backlight unit 160 include a backlight unit including a cold cathode tube, a light emitting diode, an organic electroluminescence element, and the like.

[1.5. Retardation films (I) and (II)]
In the liquid crystal display device of the present invention, each of the retardation films (I) and (II) includes a resin layer (A1), a resin layer (B), and a resin layer (A2) in this order from the viewing side. The resin layer (A1) and the resin layer (B) are in direct contact, and the resin layer (B) and the resin layer (A2) are in direct contact. That is, there is no other layer between the resin layer (A1) and the resin layer (B), and there is no other layer between the resin layer (B) and the resin layer (A2).

  The resin layer (A1) is a layer made of the resin A1 having a positive intrinsic birefringence. The resin layer (B) is a layer made of the resin B having a negative intrinsic birefringence. The resin layer (A2) is a layer made of the resin A2 having a positive intrinsic birefringence.

  FIG. 3 is an exploded perspective view schematically showing the retardation film (I) 120 in FIGS. 1 and 2 in an exploded manner. In FIG. 3, the retardation film (I) 120 has a resin layer (A1) 121, a resin layer (B) 122, and a resin layer (A2) 123 in this order from the viewing side. On the other hand, FIG. 4 is an exploded perspective view schematically showing the retardation film (II) 130 in FIGS. 1 and 2 in an exploded manner. In FIG. 4, the retardation film (II) 130 has a resin layer (A1) 131, a resin layer (B) 132, and a resin layer (A2) 133 in this order from the viewing side.

  In the liquid crystal display device of the present invention, the in-plane slow axis of the retardation film (I) and the in-plane slow axis of the retardation film (II) are substantially parallel, and the retardation film (I) The in-plane slow axis and the in-plane slow axis of the liquid crystal cell in the black display state are substantially parallel, and the in-plane slow axis of the retardation film (I) and the polarization transmission axis of the first polarizing plate Are substantially parallel.

  When the in-plane slow axis of the retardation film (I) and the in-plane slow axis of the retardation film (II) are substantially parallel, the angle formed by them is usually −0.5 ° or more. , Preferably −0.3 ° or more, more preferably −0.1 ° or more, and usually 0.5 ° or less, preferably 0.3 ° or less, more preferably 0.1 ° or less. .

  When the slow axis in the plane of the retardation film (I) and the slow axis in the plane of the liquid crystal cell in the black display state are substantially parallel, the angle formed by them is usually −0.5 ° or more. , Preferably −0.3 ° or more, more preferably −0.1 ° or more, and usually 0.5 ° or less, preferably 0.3 ° or less, more preferably 0.1 ° or less. .

  When the slow axis in the plane of the retardation film (I) and the slow axis in the plane of the liquid crystal cell in the black display state are substantially parallel, the angle formed by them is usually −0.5 ° or more. , Preferably −0.3 ° or more, more preferably −0.1 ° or more, and usually 0.5 ° or less, preferably 0.3 ° or less, more preferably 0.1 ° or less. .

1 to 4, the slow axis A ₁₂₁ of the resin layer (A1) 121, the slow axis A _{122 of} the resin layer (B) ₁₂₂ , and the slow axis A ₁₂₃ of the resin layer (A2) ₁₂₃ are: Both are directions perpendicular to the long side direction of the rectangular display surface. Thus, the slow axis A ₁₂₀ of the retardation film (I) 120 is also a direction perpendicular to the longitudinal direction of the rectangular display surface. Similarly, the slow axis A ₁₃₁ of the resin layer (A1) 131, the slow axis A 132 of the resin layer (B) ₁₃₂ , and the slow axis A ₁₃₃ of the resin layer (A2) ₁₃₃ are all rectangular displays. The direction perpendicular to the long side direction of the surface. Thus, the slow axis _{A 130} of the retardation film (II) 130 also becomes perpendicular to the longitudinal direction of the rectangular display surface. Thus, parallel to the slow axis _{A 130} in the plane of the slow axis _{A 120} and the retardation film (II) 130 in a plane of the retardation film (I) 120, a surface of the retardation film (I) 120 The slow axis A ₁₂₀ is parallel to the slow axis A ₁₄₀ in the plane of the liquid crystal cell 140 in the black display state, and the slow axis A ₁₂₀ in the plane of the retardation film (I) ₁₂₀ is the first polarizing plate. 110 is parallel to the polarization transmission axis A ₁₁₀ .

  The retardation films (I) and (II) are both co-stretched films. A co-stretched film means what is a film formed by extending | stretching the resin laminated body which has several layers which consist of multiple types of resin.

  In the liquid crystal display device of the present invention, by adopting the above configuration, not only the luminance observed from the front direction during black display, but also the luminance observed from the tilt direction during black display can be reduced. Has a remarkable effect.

  Specifically, by providing two retardation films (I) and (II) as a retardation film between the liquid crystal cell and the first polarizing plate, a similar retardation film is provided. Compared to the case, the black luminance when observed from various azimuth angles and polar angles can be made low and nearly uniform. This is shown, for example, by comparing the simulation results of Examples 1 to 3 and Comparative Examples 1 and 2 of the present application.

  However, each of the retardation films (I) and (II) is composed of a number of layers including a resin layer made of a resin having a positive intrinsic birefringence and a resin layer made of a resin having a negative intrinsic birefringence. . When such a structure consisting of a large number of layers is taken, there is a possibility that problems such as light leakage may occur based on a slight shift of the slow axis of each layer, compared with the case where there is only one retardation film. In some cases, the effects assumed in the simulation cannot be obtained in the implementation evaluation. For example, although Comparative Example 3 of the present application has an optical configuration substantially equivalent to that of Example 1 of the present application, the result of the mounting evaluation is poor.

  Here, when a co-stretched film is adopted as the retardation films (I) and (II), it is possible to easily obtain a shift of the slow axis of each component in the layer of less than 1 °. On the other hand, since the retardation film (I) and the retardation film (II) are separate co-stretched films, these optical characteristics can be easily adjusted to a mode in which a reduction in black luminance can be effectively obtained. Thus, the liquid crystal display device of the present invention balances the degree of freedom in which an optical aspect capable of effectively reducing the black luminance can be easily obtained and the advantage that each component can be easily mounted with high accuracy. As a result, not only the luminance observed from the front direction during black display but also the luminance observed from the tilt direction during black display can be reduced. .

  The example of the specific aspect in which the effect of this invention expresses is demonstrated with reference to FIGS. 17 to 20 are schematic diagrams illustrating examples of changes in the polarization state of light when the liquid crystal display device 100 illustrated in FIGS. 1 to 4 is observed from an oblique direction. 15 and 16 are schematic diagrams illustrating examples of changes in the polarization state of light when the liquid crystal display device shown in Comparative Example 1 of the present application is observed from an oblique direction.

  As will be described in more detail later, the liquid crystal display device shown in Comparative Example 1 of the present application is a tablet device in which a viewing side polarizing plate, an optical laminate, a liquid crystal cell, a light source side polarizing plate, and a backlight unit are arranged from the viewing side. This optical laminate is provided with a retardation film on the light source side and a retardation film on the viewing side, and the retardation film on the light source side is composed of a material having a negative intrinsic birefringence index Nz coefficient − The retardation film on the viewing side is a retardation film having an Nz coefficient of about 1.4 and made of a material having a positive intrinsic birefringence.

In the example of FIGS. 15 to 20, the Poincare sphere having the orthogonal coordinate axes S1, S2, and S3 is observed from the coordinate axis S2 side. In general, in the Poincare sphere, the position corresponding to the north pole of the polar coordinates (coordinate axis S3) represents circularly polarized light, the position corresponding to the south pole represents circularly polarized light in the reverse direction, and the position corresponding to the equator represents linearly polarized light. Positions other than represent elliptically polarized light. In the examples of FIGS. 15 to 20, the direction of the coordinate axis S2 corresponds to the transmission axis direction of the light source side polarizing plate (the direction indicated by the arrow A ₁₅₀ in the examples of FIGS. 1 to 2).

  In the examples of FIGS. 15 to 20, the polarization state of light when observed from the azimuth angle 45 ° and polar angle 60 ° directions with respect to the transmission axis direction of the viewing side polarizing plate is shown. In such observation, the polarization state of the light transmitted through the transmission axis of the light source side polarizing plate is indicated by a coordinate T150, which is a position slightly shifted from the coordinate axis S2. On the other hand, the absorption axis of the viewing side polarizing plate is indicated by coordinates AB110 shifted from the coordinate axes S2 to T150 in the opposite direction. Therefore, if the polarization state of the light emitted from the light source side polarizing plate is converted from the polarization state indicated by the coordinate T150 to the polarization state indicated by the coordinate AB110 by the retardation film, the black state when observed from the direction is displayed. Light leakage during display can be completely eliminated.

  In the liquid crystal display device shown in Comparative Example 1 of the present application, the light emitted from the light source and transmitted through the light source side polarizing plate and the liquid crystal cell is incident on the light source side retardation film. FIG. 15 shows how the polarization state of light incident on the light source side retardation film is converted by passing through and exiting the retardation film. Generally, since the retardation film has wavelength dispersion, the conversion of the polarization state is not uniform in the wavelength region of incident light. Therefore, as in this example, the light emitted from the retardation film on the light source side has a different polarization state for each wavelength. In this example, red (wavelength 650 nm), green (wavelength 550 nm), and blue (wavelength 450 nm) light emitted from the retardation film on the light source side is in the polarization state indicated by coordinates R1, G1, and B1, respectively. Is the polarization state distribution indicated by line V1.

  The light emitted from the retardation film on the light source side enters the retardation film on the viewing side, and is further converted by transmitting through the retardation film on the viewing side. FIG. 16 shows how the polarization state of the light emitted from the light source side retardation film and incident on the viewing side retardation film is converted by transmitting through the retardation film and exiting. ing. Incident light having the polarization state indicated by the coordinates R1, G1 and B1 and the line V1 is converted into the polarization state indicated by the coordinates R2, G2 and B2 and the line V2 by the conversion, and then emitted. The emitted light reaches the viewing side polarizing plate in this polarization state.

  In the example of FIGS. 15 to 16, the green light that is the central wavelength of visible light among the light that has reached the viewing side polarizing plate is in the polarization state indicated by the coordinate G <b> 2, and thus in the polarization state indicated by the coordinate AB <b> 110. It becomes very close. As a result, light leakage during black display is reduced at the wavelength. However, as a result of the chromatic dispersion, the polarization state of the light having a wavelength away from the green color is greatly separated from the polarization state indicated by the coordinate AB110. As a result, the entire visible light leaks a lot during black display.

  On the other hand, in the liquid crystal display device shown in FIGS. 1 to 4, light emitted from the light source and transmitted through the second polarizing plate (light source side polarizing plate), the liquid crystal cell, and the resin layer (A2) of the retardation film (II). Enters the resin layer (B). In the liquid crystal display device shown in FIGS. 1 to 4, FIG. 17 shows that the polarization state of the light incident on the resin layer (B) of the retardation film (II) is transmitted through the resin layer (B) and emitted. It shows how it is converted. In this example, the resin layer (A2) has an optically negligible phase difference, so that the polarization state of incident light is substantially the same as that in FIG. Light incident on the resin layer (B) undergoes non-uniform conversion in the wavelength region, and red, green, and blue light emitted from the resin layer (B) are polarized states indicated by coordinates R3, G3, and B3, respectively. Thus, the entire visible light has a polarization state distribution indicated by a line V3.

  The light emitted from the resin layer (B) of the retardation film (II) enters the resin layer (A1) of the retardation film (II) and is further converted by transmitting through the resin layer (A1). . In FIG. 18, the polarization state of the light emitted from the resin layer (B) of the retardation film (II) and incident on the resin layer (A1) of the retardation film (II) is transmitted through the resin layer (A1). It shows how it is converted by exiting. Incident light having the polarization state indicated by the coordinates R3, G3 and B3 and the line V3 is converted into the polarization state indicated by the coordinates R4, G4 and B4 and the line V4 by the conversion, and is emitted.

  The light emitted from the resin layer (A1) of the retardation film (II) passes through the resin layer (A2) of the retardation film (I), and enters the resin layer (B) of the retardation film (I). It further transforms by passing through the resin layer (B). In FIG. 19, the polarization state of the light emitted from the resin layer (A1) of the retardation film (II) and incident on the resin layer (B) of the retardation film (I) is transmitted through the resin layer (B). It shows how it is converted by exiting. Incident light having the polarization state indicated by the coordinates R4, G4 and B5 and the line V4 is converted into the polarization state indicated by the coordinates R5, G5 and B5 and the line V5 by the conversion, and is emitted.

  The light emitted from the resin layer (B) of the retardation film (I) is further converted by being incident on the resin layer (A1) of the retardation film (I) and transmitting through the resin layer (A1). . In FIG. 20, the polarization state of the light emitted from the resin layer (B) of the retardation film (I) and incident on the resin layer (A1) of the retardation film (I) is transmitted through the resin layer (A1). It shows how it is converted by exiting. Incident light having the polarization state indicated by the coordinates R5, G5 and B5 and the line V5 is converted into the polarization state indicated by the coordinates R6, G6 and B6 and the line V6 by the conversion, and is emitted. The emitted light reaches the first polarizing plate (viewing-side polarizing plate) in this polarization state.

  In the examples of FIGS. 17 to 20, the conversion by the retardation film (I) is performed so as to be in an elliptical polarization state far from the coordinate AB110, and then the polarization state is further converted by the retardation film (II) and close to the coordinate AB110. It is said. Thereby, the wavelength dispersion generated in the retardation film (I) can be canceled by the wavelength dispersion generated in the retardation film (II). As a result, not only the light having the green wavelength among the light reaching the first polarizing plate, but also the polarization state of the light having a wavelength away from the green is indicated by coordinates AB110 as compared to the examples of FIGS. It becomes possible to converge to a state close to the polarization state.

  Thus, when the retardation films (I) and (II) are combined, the polarization state of the transmitted light when observed from an oblique direction during black display in the wide wavelength region is set to the absorption axis of the polarizing plate on the viewing side. It becomes possible to converge to a state close to the corresponding polarization state. Therefore, according to the liquid crystal display device of the present invention having the retardation films (I) and (II), not only the luminance observed from the front direction during black display, but also the luminance observed from the tilt direction during black display. It has a remarkable effect that it can be lowered.

[1.6. Optical properties of retardation films (I) and (II)]
It is preferable that the retardation of the retardation film (I) and the retardation film (II) satisfy the following requirements. That is, in each of the retardation film (I) and the retardation film (II), the in-plane retardation ReA1 of the resin layer (A1), the retardation RthA1 in the thickness direction of the resin layer (A1), and the resin layer (B) In-plane retardation ReB, retardation RthB in the thickness direction of the resin layer (B), in-plane retardation ReA2 of the resin layer (A2), and retardation RthA2 in the thickness direction of the resin layer (A2) are represented by the following formula ( It is preferable to satisfy 1) to (6).
20 nm ≦ ReA1 ≦ 100 nm (1)
40 nm ≦ RthA1 ≦ 180 nm (2)
60 nm ≦ ReB ≦ 200 nm (3)
−180 nm ≦ RthB ≦ −40 nm (4)
0 nm ≦ ReA2 ≦ 20 nm (5)
0 nm ≦ RthA2 ≦ 20 nm (6)

  When the retardations of the retardation films (I) and (II) satisfy the formulas (1) to (6), the luminance observed from the front direction and the luminance observed from the tilt direction during black display are less uneven. It can be further lowered.

Further, the retardation film (I) preferably satisfies the following formulas (1-I) to (4-I), and the retardation film (II) has the following formulas (1-II) to (4-II). It is preferable to satisfy. By satisfying these, the luminance observed from the front direction and the luminance observed from the tilt direction during black display can be further reduced with less unevenness.
25 nm ≦ ReA1 ≦ 50 nm (1-I)
50 nm ≦ RthA1 ≦ 70 nm (2-I)
150 nm ≦ ReB ≦ 200 nm (3-I)
−180 nm ≦ RthB ≦ −100 nm (4-I)
50 nm ≦ ReA1 ≦ 100 nm (1-II)
70 nm ≦ RthA1 ≦ 150 nm (2-II)
60 nm ≦ ReB ≦ 100 nm (3-II)
−80 nm ≦ RthB ≦ −50 nm (4-II)

On the other hand, in the retardation films (I) and (II), it is preferable that the resin layer (A2) has an optically negligible retardation, and therefore the retardation films (I) and (I) (II) more preferably satisfies the following formulas (5 ′) and (6 ′).
0 nm ≦ ReA2 ≦ 10 nm (5 ′)
0 nm ≦ RthA2 ≦ 10 nm (6 ′)

  Thus, the resin layer (A2) having a retardation that is optically negligible does not contribute to optical compensation, but contributes to the strength and durability of the retardation films (I) and (II). sell. Specifically, the resin B having a negative intrinsic birefringence is often inferior in strength to the resin A1, but at the time of production, the resin layers (A1) and (A2) are provided on both sides of the resin B. And deterioration of the retardation film at the time of use can be reduced. In addition, the retardation film can be prevented from bending and warping.

  In each of the retardation film (I) and the retardation film (II), the in-plane slow axis of the resin layer (A1) and the in-plane slow axis of the resin layer (B) are parallel. Is preferred. More preferably, the in-plane slow axis of the resin layer (A1) and the in-plane slow axis of the resin layer (A2) are also preferably parallel. When the slow axis in the plane of the resin layer (A1) and the slow axis in the plane of the resin layer (B) or (A2) are parallel, the angle formed by them is usually −0.05 °. Or more, preferably −0.03 ° or more, more preferably −0.01 ° or more, and usually 0.05 ° or less, preferably 0.03 ° or less, more preferably 0.01 ° or less. Say.

The in-plane retardation Re (I) of the retardation film (I) is preferably 50 nm or more, more preferably 100 nm or more, and preferably 400 nm or less, more preferably 300 nm or less.
The retardation Rth (I) in the thickness direction of the retardation film (I) is preferably −100 nm or more, more preferably −80 nm or more, and preferably 200 nm or less, more preferably 100 nm or less.
The in-plane retardation Re (II) of the retardation film (II) is preferably 50 nm or more, more preferably 100 nm or more, and preferably 400 nm or less, more preferably 300 nm or less.
The retardation Rth (II) in the thickness direction of the retardation film (II) is preferably −50 nm or more, more preferably −40 nm or more, and preferably 200 nm or less, more preferably 100 nm or less.
By setting the in-plane retardation and the thickness direction retardation of the retardation films (I) and (II) within the above ranges, the luminance observed from the front direction and the luminance observed from the tilt direction during black display, It can be further reduced with less unevenness.

  The Nz coefficient of the retardation film (I) is preferably −0.5 or more, more preferably −0.3 or more, and is preferably 1.0 or less, more preferably 0.8 or less. The Nz coefficient of the retardation film (II) is preferably −0.5 or more, more preferably −0.3 or more, and is preferably 1.0 or less, more preferably 0.8 or less. By setting the Nz coefficient of the retardation films (I) and (II) within the above range, the luminance observed from the front direction and the luminance observed from the tilt direction during black display are further reduced with less unevenness. be able to.

[1.7. (Optional component)
The liquid crystal display device of the present invention may include arbitrary constituent elements in addition to the constituent elements described above. As an arbitrary component, the adhesive layer which bonds each layer, a reflecting plate, a diffusion plate, a brightness enhancement film, a protective film etc. are mentioned, for example.

[2. Manufacturing method of liquid crystal display device]
The liquid crystal display device of the present invention is manufactured by a manufacturing method in which a first polarizing plate, a retardation film (I), a retardation film (II), a liquid crystal cell, and a second polarizing plate are assembled in this order from the viewing side. sell. The assembly may be performed by simply superimposing these components, or may be performed by bonding these components with an appropriate adhesive. In the method for producing a liquid crystal display device of the present invention, each of the retardation film (I) and the retardation film (II) is produced by a preparation step for preparing a specific resin laminate and a stretching step for stretching the resin laminate. Yes. The preparation step and the stretching step can be performed by the method specifically described below.

[3. Specific examples of each component and preparation method]
Next, a preferable example of each component in the liquid crystal display device described above will be described more specifically.

[3.1. Retardation film: Resin A1]
The resin A1 constituting the resin layer (A1) of the retardation film usually contains a polymer having a positive intrinsic birefringence. Examples of this polymer include olefin polymers such as polyethylene and polypropylene; polyester polymers such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfide polymers such as polyphenylene sulfide; polyvinyl alcohol polymers, polycarbonate polymers, poly Examples include arylate polymers, cellulose ester polymers, polyethersulfone polymers, polysulfone polymers, polyallylsulfone polymers, polyvinyl chloride polymers, norbornene polymers, and rod-like liquid crystal polymers. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The polymer may be a homopolymer or a copolymer. Among these, a polycarbonate polymer is preferable from the viewpoints of expression of retardation, stretchability at low temperature, and adhesiveness between the resin layer (A1) and a layer other than the resin layer (A1).

  As the polycarbonate polymer, any polymer having a structural unit containing a carbonate bond (—O—C (═O) —O—) can be used. Examples of the polycarbonate polymer include bisphenol A polycarbonate, branched bisphenol A polycarbonate, o, o, o ', o'-tetramethylbisphenol A polycarbonate, and the like.

  Resin A1 may contain a compounding agent. Examples of compounding agents include: lubricants; layered crystal compounds; inorganic fine particles; stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, near infrared absorbers; plasticizers; dyes And coloring agents such as pigments; antistatic agents; and the like. Among these, a lubricant and an ultraviolet absorber are preferable because they can improve flexibility and weather resistance. Moreover, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the lubricant include inorganic particles such as silicon dioxide, titanium dioxide, magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, strontium sulfate; polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, cellulose acetate, cellulose acetate pro Organic particles such as pionate; Among these, organic particles are preferable as the lubricant.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, acrylonitrile ultraviolet absorbers, triazine compounds, nickel complex compounds. And inorganic powders. Specific examples of suitable UV absorbers include 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) ) Phenol, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone and the like. Particularly suitable is 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol).

  The amount of the compounding agent can be appropriately determined as long as the effects of the present invention are not significantly impaired. For example, the total light transmittance in terms of 1 mm thickness of the retardation film can be in a range where 80% or more can be maintained.

  The weight average molecular weight of the resin A1 is preferably adjusted to a range in which a method such as a melt extrusion method or a solution casting method can be performed with the resin A1.

The glass transition temperature _{Tg A1} of the resin A1 is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, more preferably 100 ° C. or more and especially preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher. Since the glass transition temperature Tg _A1 is high as described above, orientation relaxation of the resin A1 can be reduced. Moreover, although there is no restriction | limiting in particular in the upper limit of glass transition temperature Tg _A1 , Usually, it is 200 degrees C or less.

The breaking elongation of the resin A1 at the glass transition temperature Tg _B of the resin _B is preferably 50% or more, more preferably 80% or more. When the elongation at break is within this range, a retardation film can be stably produced by stretching. Here, the breaking elongation can be obtained at a pulling rate of 100 mm / min using a test piece type 1B test piece described in JISK7127. Moreover, although there is no restriction | limiting in particular in the upper limit of the said breaking elongation of resin A1, Usually, it is 200% or less.

[3.2. Retardation film: Resin B]
The resin B constituting the resin layer (B) of the retardation film usually contains a polymer having a negative intrinsic birefringence. Examples of this polymer include styrene or a homopolymer of a styrene derivative, and a polystyrene polymer including a copolymer of styrene or a styrene derivative and any other monomer; a polyacrylonitrile polymer; a polymethyl methacrylate A polymer; or a multi-component copolymer thereof. Moreover, as said arbitrary monomer which can be copolymerized with styrene or a styrene derivative, acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene are mentioned as a preferable thing, for example. Moreover, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, a polystyrene polymer is preferable from the viewpoint of high retardation development, and a copolymer of styrene or a styrene derivative and maleic anhydride is particularly preferable from the viewpoint of high heat resistance. In this case, the amount of the structural unit (maleic anhydride unit) having a structure formed by polymerizing maleic anhydride with respect to 100 parts by weight of the polystyrene-based polymer is preferably 5 parts by weight or more, more preferably 10 parts. Part by weight or more, particularly preferably 15 parts by weight or more, preferably 30 parts by weight or less, more preferably 28 parts by weight or less, particularly preferably 26 parts by weight or less.

Resin B may contain a compounding agent. As an example of a compounding agent, the thing similar to the compounding agent which resin A1 may contain is mentioned. Moreover, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
The amount of the compounding agent can be appropriately determined within a range that does not significantly impair the effects of the present invention. For example, the total light transmittance in terms of 1 mm thickness of the retardation film can be maintained within 80% or more.

  The weight average molecular weight of the resin B is preferably adjusted to a range in which the resin B can be subjected to a method such as a melt extrusion method or a solution casting method.

The glass transition temperature Tg _B of the resin B is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, more preferably 100 ° C. or more and especially preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher. With such a high glass transition temperature Tg _{B, the} relaxation of orientation of the resin B can be reduced. Although not particularly limited to the upper limit of the glass transition temperature Tg _B, usually it is 200 ° C. or less.

The breaking elongation of the resin B at the glass transition temperature Tg _A1 of the resin _A1 is preferably 50% or more, more preferably 80% or more. When the elongation at break is within this range, a retardation film can be stably produced by stretching. Here, although there is no restriction | limiting in particular in the upper limit of the breaking elongation of resin B, Usually, it is 200% or less.

The absolute value of the difference between the glass transition temperature Tg _A1 of the resin _A1 and the glass transition temperature Tg _B of the resin B is preferably greater than 5 ° C, more preferably 8 ° C or more, preferably 40 ° C or less, more preferably It is 20 degrees C or less. By making the absolute value of the difference between the glass transition temperatures larger than the lower limit value of the range, the temperature dependency of the expression of retardation can be increased. On the other hand, by setting it to the upper limit value or less, it is possible to facilitate the stretching of the resin having a higher glass transition temperature and improve the planarity of the retardation film.
Here, the glass transition temperature Tg _B of the resin _B is preferably lower than the glass transition temperature Tg _A1 of the resin A1. Therefore, the resin A1 and the resin _B, it is preferable to satisfy the relationship of _{Tg A1> Tg B + 5 ℃} .

[3.3. Retardation film: Resin A2]
As the resin A2, a resin different from the resin A1 may be selected from materials in the same range as the resin A1. Therefore, for example, the resin A2 may contain a different type of polymer from the polymer contained in the resin A1. In addition, for example, the resin A2 may include the same type of polymer as the polymer included in the resin A1, and may include a different type of compounding agent from the compounding agent included in the resin A1. Further, for example, the resin A2 may include the same type of polymer and compounding agent as the polymer and compounding agent included in the resin A1, and the amount of the polymer and compounding agent may be different from that of the resin A1. However, it is particularly preferable to use the same resin as the resin A1 as the resin A2. When the resin A1 and the resin A2 are the same resin, bending and warpage can be prevented in the retardation film. In the retardation film, the in-plane slow axis of the resin layer (A1) and the in-plane slow axis of the resin layer (A2) can be easily made parallel.

[3.4. Retardation Film: Outline of Manufacturing Method]
The retardation film can be produced by producing a specific resin laminate and co-stretching it. At this time, the resin laminate is stretched by a first stretching step in which the resin laminate is stretched in the first direction at a temperature T1; and the resin laminate stretched in the first stretching step at a temperature T2 lower than the temperature T1. It is preferable to perform a second stretching step in which a retardation film is obtained by stretching in a second direction orthogonal to the first direction. Hereinafter, this manufacturing method will be described.

[3.5. Retardation film: resin laminate]
The resin laminate includes a layer a1 made of the resin A1, a layer b made of the resin B, and a layer a2 made of the resin A2. The layer a1 and the layer b are in direct contact with each other, and the layer b and the layer a2 are in direct contact with each other. That is, there is no other layer between the layer a1 and the layer b, and there is no other layer between the layer b and the layer a2.

  The resin laminate is stretched in different directions orthogonal to each other at different temperatures of T1 and T2, so that in each of the layers a1, b, and a2, depending on the temperatures T1 and T2, the stretching ratio, and the stretching direction, respectively. It has the property that it can cause retardation. Using this property, a retardation film can be produced. Specifically, in the retardation film obtained by stretching this resin laminate, the retardation generated in the layer a1, the retardation generated in the layer b, and the retardation generated in the layer a2 are synthesized. The retardation film as a whole can obtain desired in-plane retardation and retardation in the thickness direction.

  The size of the retardation generated in the layers a1, b, and a2 by stretching depends on conditions such as the configuration of the resin laminate (for example, the number and thickness of each layer), the stretching temperature, and the stretching ratio. Therefore, the configuration of the resin laminate is preferably determined according to an optical function such as an optical compensation function to be developed.

Among them, the resin laminate has a stretching direction in one direction (that is, a uniaxial stretching direction) as an X axis, a direction orthogonal to the uniaxial stretching direction in the film plane as a Y axis, and a film thickness direction as a Z axis. The linearly polarized light (hereinafter referred to as “XZ-polarized light” where appropriate) that is incident perpendicularly to the film surface and whose electric vector vibration surface is in the XZ plane is incident perpendicularly to the film surface and the electric vector vibration surface. Is a phase with respect to linearly polarized light (hereinafter referred to as “YZ polarized light” where appropriate) in the YZ plane,
When one axis is stretched in the X-axis direction at one of the temperatures T1 and T2 (usually the temperature T1),
When the other of the temperatures T1 and T2 (usually the temperature T2) is uniaxially stretched in the X-axis direction,
(Hereinafter also referred to as “requirement P” as appropriate).

  The requirement P is satisfied when at least one of the various directions in the plane of the resin laminate is the X axis. Usually, since the resin laminate is an isotropic (that is, has no anisotropy) raw film, if any one direction in the plane is taken as the X axis, if any of the other directions is satisfied, The requirement P can also be satisfied when the X axis is used.

  In general, in a film in which an in-plane slow axis appears on the X axis by uniaxial stretching, the phase of XZ polarized light is delayed from that of YZ polarized light. Conversely, in a film in which a fast axis appears on the X axis by uniaxial stretching, the phase of XZ polarized light advances with respect to YZ polarized light. The resin laminate satisfying the above requirement P is a laminate utilizing these properties, and is usually a film whose in-plane slow axis or fast axis appears depending on the stretching temperature. The temperature dependence of the expression of such retardation can be adjusted, for example, by adjusting the relationship between the photoelastic coefficients of the resin A1, the resin B, and the resin A2, the thickness ratio of each layer, and the like.

Here, the conditions to be satisfied by the resin laminate will be described by taking “in-plane retardation with reference to the stretching direction” as an example. The in-plane retardation with respect to the stretching direction is the difference between the refractive index nX in the X-axis direction which is the stretching direction and the refractive index nY in the Y-axis direction which is the direction perpendicular to the stretching direction in the plane (= nX−nY ) Multiplied by the thickness d. In this case, the in-plane retardation based on the stretching direction that can be expressed in the entire resin laminate when the resin laminate including the layer a1, the layer b, and the layer a2 is stretched is defined by the stretching direction expressed in the layer a1. It is synthesized from the in-plane retardation based on the reference, the in-plane retardation based on the stretching direction expressed in the layer b, and the in-plane retardation based on the stretching direction expressed in the layer a2. Therefore, the sign of the in-plane retardation based on the stretching direction developed when the resin laminate including the layer a1, the layer b, and the layer a2 is stretched is reversed between stretching at the high temperature T1 and stretching at the low temperature T2. Therefore, it is preferable to adjust the thicknesses of the layer a1, the layer b, and the layer a2 so as to satisfy the following conditions (i) and (ii).
(I) By stretching at a low temperature T2, the absolute value of retardation exhibited by a resin having a high glass transition temperature is smaller than the absolute value of retardation exhibited by a resin having a low glass transition temperature.
(Ii) By stretching at a high temperature T1, the absolute value of retardation exhibited by a resin having a low glass transition temperature is smaller than the absolute value of retardation exhibited by a resin having a high glass transition temperature.

  As described above, the difference between the refractive index nX in the X-axis direction and the refractive index nY in the Y-axis direction that is expressed in each of the layer a1, the layer b, and the layer a2 by stretching in one direction (that is, uniaxial stretching); By adjusting the total thickness of the layer a2 and the total thickness of the layer a2, the requirement P (ie, the phase of the XZ polarized light with respect to the YZ polarized light is in the X-axis direction at one of the temperatures T1 and T2). Thus, it is possible to obtain a resin laminate that satisfies the requirement that it is delayed when it is uniaxially stretched, and proceeds when it is uniaxially stretched in the X-axis direction at the other of the temperatures T1 and T2.

  For example, the first stretching step is performed at the temperature Ta, and the retardation based on the positive stretching direction in the layers a1 and a2 and the retardation based on the negative stretching direction in the layer b are developed. Next, the second stretching step is performed at a temperature Tb at a lower stretching ratio than the first stretching step in a direction orthogonal to the stretching direction in the first stretching step, and the layer a1 and the layer a2 in the positive first stretching step While maintaining the retardation based on the stretching direction, the in-plane retardation developed in the first stretching step in the layer b is offset. Thereby, a desired phase difference is imparted to both the resin layer (A1) and the resin layer (A2) obtained by stretching the layer a1 and the layer a2, and the resin layer (B) obtained by stretching the layer b. Thus, a desired retardation film can be obtained.

  Specific thicknesses of the layer a1, the layer b, and the layer a2 can be set according to the retardation of the retardation film to be manufactured so as to satisfy the requirement P described above. At this time, the ratio {(total thickness of layer a1 + total thickness of layer a2) / (total thickness of layer b)} of the total thickness of layers a1 and a2 and the total thickness of layer b is: The ratio is preferably 1/15 or more, more preferably 1/10 or more, and preferably 1/4 or less. Thereby, the temperature dependence of the retardation expression by extending | stretching process can be enlarged.

  The total thickness of the layers a1, b, and a2 is preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, preferably 500 μm or less, more preferably 200 μm or less, and particularly preferably 150 μm or less. . By setting the total thickness of the layer a1, the layer b, and the layer a2 to be equal to or greater than the lower limit of the above range, sufficient retardation can be exhibited. Further, the mechanical strength of the retardation film can be increased. Moreover, by making it into the upper limit value or less, the retardation film can have high flexibility and handling properties can be enhanced.

  Although there is no restriction | limiting in the manufacturing method of a resin laminated body, It is preferable to manufacture by the coextrusion method or the co-casting method using resin A1, resin B, and resin A2. Among these, the coextrusion method is preferable. The co-extrusion method is a method of extruding and molding a plurality of resins in a molten state. The coextrusion method is excellent in terms of production efficiency and in that a volatile component such as a solvent does not remain in the resin laminate.

  Examples of the coextrusion method include a coextrusion T-die method, a coextrusion inflation method, and a coextrusion lamination method. Among these, the coextrusion T-die method is preferable. The coextrusion T-die method includes a feed block method and a multi-manifold method. Among them, the multi-manifold method is particularly preferable in that variation in the thickness of the layer a1 and the layer a2 can be reduced.

  When the co-extrusion T-die method is employed, the melting temperature of the resin in the extruder having a T-die is preferably (Tg + 80) ° C. or higher, and (Tg + 100) ° C. or higher with respect to the glass transition temperature Tg of each resin. It is more preferable to set to (Tg + 180) ° C. or less, and (Tg + 150) ° C. or less is more preferable. By setting the melting temperature of the resin in the extruder to the lower limit value or more of the above range, the fluidity of the resin can be sufficiently enhanced. Moreover, deterioration of resin can be prevented by setting it as an upper limit or less.

The film-like molten resin extruded from the opening of the die is preferably brought into close contact with the cooling drum. Thereby, a molten resin can be hardened rapidly and a desired resin laminated body can be obtained efficiently.
The method for bringing the molten resin into close contact with the cooling drum is not particularly limited, and examples thereof include an air knife method, a vacuum box method, and an electrostatic contact method.
The number of cooling drums is not particularly limited, but is usually two or more. Examples of the arrangement method of the cooling drum include, but are not limited to, a linear type, a Z type, and an L type. Further, the way of passing the molten resin extruded from the opening of the die through the cooling drum is not particularly limited.

  The degree of adhesion of the extruded film-like resin to the cooling drum usually varies depending on the temperature of the cooling drum. Therefore, the temperature of the cooling drum is preferably (Tg + 30) ° C. or less, more preferably (Tg−5) ° C. to (Tg) with respect to the glass transition temperature Tg of the resin that is in contact with the drum out of the resin extruded from the die. -45) Set to a range of ° C. By setting the temperature of the cooling drum to be equal to or higher than the lower limit of the above range, it is possible to improve the adhesion of the resin to the cooling drum. Moreover, by setting it to the upper limit value or less, the film-like resin can be easily peeled off from the cooling drum. In addition, by keeping the temperature of the cooling drum within the above range, problems such as slipping and scratching can be prevented.

  Further, it is preferable to reduce the amount of residual solvent in the resin laminate. Means for that purpose include (1) reducing the residual solvent of the resin used as a raw material; and (2) pre-drying the resin before molding the resin laminate. For example, the preliminary drying is performed by a hot air dryer or the like in the form of pellets or the like. The drying temperature is preferably 100 ° C. or more, and the drying time is preferably 2 hours or more. By performing preliminary drying, the residual solvent in the resin laminate can be reduced, and foaming of the extruded film-like resin can be prevented.

[3.6. Retardation film: first stretching step]
In the first stretching step, the resin laminate is stretched in one direction at a temperature T1. That is, the resin laminate is uniaxially stretched at the temperature T1. At this time, the direction in which the resin laminate is stretched in the first stretching step is the first direction. By performing such a first stretching step, the layers a1, b, and a2 included in the resin laminate are co-stretched. When stretched at the temperature T1, retardation occurs in each of the layer a1, the layer b, and the layer a2 depending on the configuration of the resin laminate and the stretching conditions such as the stretching temperature T1 and the stretching ratio, and the layers a1, b, and Retardation also occurs in the entire resin laminate including the layer a2. At this time, for example, when the resin laminate satisfies the requirement P, the phase of the XZ polarized light with respect to the YZ polarized light is delayed or advanced.

The temperature T1 can be set to an appropriate temperature so that a desired retardation is obtained. For example, when the glass transition temperature Tg _A1 of the resin _A1 and the glass transition temperature Tg _A2 of the resin _A2 are higher than the glass transition temperature Tg _B of the resin B, the temperature T1 is preferably set as follows. That is, the temperature T1 is preferably higher than Tg _{B based} on the glass transition temperature Tg _{A1 of} the resin _A1 , the glass transition temperature Tg _{B of} the resin _B , and the glass transition temperature Tg _A2 of the resin A2, and higher than Tg _B + 5 ° C. More preferably Tg _B + 10 ° C., more preferably Tg _A1 and Tg _A2 whichever is higher + 20 ° C., Tg _A1 and Tg _A2 whichever is higher + 10 ° C. It is more preferable. When the temperature T1 is set higher than the lower limit of the temperature range, the in-plane retardation ReB and the thickness direction retardation RthB of the resin layer (B) can be stably stored in a desired range. When the temperature T1 is lower than the upper limit of the temperature range, the in-plane retardation ReA1 and the thickness direction retardation RthA1 of the resin layer (A1), and the in-plane retardation ReA2 and the thickness direction of the resin layer (A2). The retardation RthA2 can be stably contained in a desired range.

  The draw ratio in the first drawing step is preferably more than 2.0 times, preferably 4.0 times or less, more preferably 3.5 times or less, and particularly preferably 3.0 times or less. By setting the draw ratio in the first drawing step within the above range, a retardation film having a desired retardation can be produced.

  The stretching speed in the first stretching step is preferably 2.0 times / minute or more, preferably 4.0 times / minute or less, more preferably 3.5 times / minute or less, particularly preferably 3.0 times / minute. Is less than a minute. Productivity can be improved by making extending | stretching speed more than the lower limit of the said range. Moreover, the dispersion | variation in retardation can be reduced by making it below an upper limit.

  Uniaxial stretching can be performed by a conventionally known method. For example, a method of uniaxially stretching in the longitudinal direction (usually coincides with the MD direction) using a difference in peripheral speed between rolls; uniaxially stretching in the transverse direction (usually coincides with the TD direction) using a tenter. And the like. Examples of the method of uniaxially stretching in the machine direction include an IR heating method and a float method between rolls. Among them, the float method is preferable because a retardation film with high optical uniformity can be obtained. is there. On the other hand, as a method of uniaxially stretching in the transverse direction, a tenter method can be mentioned.

  Further, when stretching, in order to reduce stretching unevenness and thickness unevenness, a temperature difference may be created in the width direction of the resin laminate in the stretching zone. In order to create a temperature difference in the width direction in the stretching zone, for example, a known technique such as adjusting the opening degree of the hot air nozzle in the width direction or controlling the heating by arranging the IR heaters in the width direction can be used. Good.

  In the retardation film, the resin layer (A1) and the resin layer (A2) usually have an in-plane slow axis parallel to the first direction in which the resin laminate is stretched in the first stretching step. Therefore, the in-plane slow axis of the entire retardation film is usually parallel to the first direction. Therefore, the first direction is preferably set in parallel to the direction in which the in-plane slow axis is desired to be produced in the retardation film to be produced.

[3.7. Retardation film: second stretching step]
After the first stretching step, a second stretching step is performed. In the second stretching step, the resin laminate stretched in the first direction in the first stretching step is stretched in a second direction perpendicular to the first direction in the plane.

  In the second stretching step, the resin laminate is stretched at a temperature T2 lower than the temperature T1. That is, the resin laminate is uniaxially stretched at a relatively low temperature T2. When stretched at the temperature T2, retardation occurs in each of the layers a1, b, and a2 depending on the configuration of the resin laminate and stretching conditions such as the stretching temperature T2 and the stretching ratio, and the layers a1, b, and Retardation also occurs in the entire resin laminate including the layer a2. At this time, for example, if the resin laminate satisfies the requirement P, if the phase of the XZ polarized light with respect to the YZ polarized light is delayed by the stretching in the first stretching step, the XZ polarized YZ polarized light is stretched by the stretching in the second stretching step. When the phase of the XZ polarized light with respect to the YZ polarized light is advanced by stretching in the first stretching step, the phase of the XZ polarized light with respect to the YZ polarized light is delayed by stretching in the second stretching step.

The temperature T2 can be set to an appropriate temperature so that a desired retardation is obtained. For example, when the glass transition temperature Tg _A1 of the resin _A1 and the glass transition temperature Tg _A2 of the resin _A2 are higher than the glass transition temperature Tg _B of the resin B, the temperature T2 is preferably set as follows. That is, the temperature T2, based on the glass transition temperature Tg _B of the resin _B, it is preferably higher than Tg B -20 ° _C., more preferably higher than Tg B -10 ° C., also lower than _Tg B + 5 ° C. Is preferable, and it is more preferable that it is lower than Tg _B. By making extending | stretching temperature T2 higher than the minimum of the said temperature range, a fracture | rupture and white turbidity of a resin laminated body can be prevented at the time of extending | stretching. Moreover, the retardation ReB and RthB of a resin layer (B) can be stably stored in a desired range by setting it to the upper limit value or less.

  The difference between the temperature T1 and the temperature T2 is preferably 5 ° C. or higher, more preferably 10 ° C. or higher. By increasing the difference between the temperature T1 and the temperature T2 as described above, the retardation film can stably exhibit the polarizing plate compensation function. Moreover, although there is no restriction | limiting in the upper limit of the difference of temperature T1 and temperature T2, it is 100 degrees C or less from a viewpoint of industrial productivity.

  The stretching ratio in the second stretching step is preferably smaller than the stretching ratio in the first stretching step. The specific draw ratio in the second drawing step is preferably 1.01 times or more, more preferably 1.02 times or more, particularly preferably 1.03 times or more, and preferably 1.15 times or less. More preferably, it is 1.12 times or less, and particularly preferably 1.10 times or less. By setting the stretching ratio in the second stretching step within the above range, a retardation film having a desired retardation can be produced.

  The stretching speed in the second stretching step is preferably 1.01 times / minute or more, more preferably 1.02 times / minute or more, particularly preferably 1.03 times / minute or more, preferably 1.15 times / minute. Min. Or less, more preferably 1.12 times / min or less, particularly preferably 1.10 times / min or less. Productivity can be improved by making extending | stretching speed more than the lower limit of the said range. Moreover, the dispersion | variation in retardation can be reduced by making it below an upper limit.

  As the stretching in the second stretching step, uniaxial stretching can be performed. As a specific method of this uniaxial stretching, a method similar to the method that can be adopted in the uniaxial stretching in the first stretching step can be used.

  A combination of stretching directions in the first stretching step and the second stretching step is arbitrary. For example, the film may be stretched in the longitudinal direction in the first stretching process and stretched in the transverse direction in the second stretching process. Further, for example, the film may be stretched in the transverse direction in the first stretching process and stretched in the longitudinal direction in the second stretching process. Furthermore, for example, the film may be stretched in an oblique direction in the first stretching process, and may be stretched in an oblique direction orthogonal to the oblique direction in the second stretching process. Here, the diagonal direction represents a direction not parallel to both the vertical direction and the horizontal direction. Especially, it is preferable to extend | stretch to a horizontal direction at a 1st extending | stretching process, and to extend | stretch to a vertical direction at a 2nd extending | stretching process. By performing stretching in the second stretching step with a small stretching ratio in the longitudinal direction, variation in the direction of the optical axis can be reduced over the entire width of the obtained retardation film.

  As described above, by performing the first stretching step and the second stretching step on the resin laminate, in each of the first stretching step and the second stretching step, the stretching temperature is applied to the layer a1, the layer b, and the layer a2. Retardation according to stretching conditions such as stretching direction and stretching ratio occurs. For this reason, in the retardation film obtained through the first stretching step and the second stretching step, the retardations generated in the layers a1, b, and a2 are synthesized in each of the first stretching step and the second stretching step. Accordingly, retardation sufficient to develop an optical function such as a polarizing plate compensation function is generated. Therefore, a retardation film having a desired retardation can be obtained by a production method including a first stretching step and a second stretching step.

  Moreover, since the manufacturing method by co-stretching has obtained the resin layer (A1), the resin layer (B), and the resin layer (A2) by extending | stretching the resin laminated body provided with the layer a1, the layer b, and the layer a2, separately. Since the resin layer (A1), the resin layer (B), and the resin layer (A2) are prepared and then bonded to each other, it is unnecessary to apply and cure the adhesive. The manufacturing process can be shortened and the manufacturing cost can be reduced. Furthermore, since adjustment of the bonding angle is unnecessary, it is easy to improve the direction accuracy of the in-plane slow axis, and high product quality can be expected.

  In the manufacturing method described above, for example, the resin layer (A1), the resin layer (B), and the resin layer (A2) of the retardation film are adjusted by adjusting the stretching ratio and the stretching temperature in the first stretching step and the second stretching step. ) In-plane retardation and retardation in the thickness direction can be adjusted.

[3.8. Retardation film: any process]
In the manufacturing method of the retardation film mentioned above, you may perform arbitrary processes other than the 1st extending process and the 2nd extending process which were mentioned above.
For example, a step of preheating the resin laminate (preheating step) may be provided before stretching the resin laminate. Examples of means for heating the resin laminate include an oven-type heating device, a radiation heating device, or immersion in a liquid. Of these, an oven-type heating device is preferable. The heating temperature in the preheating step is preferably a stretching temperature of −40 ° C. or more, more preferably a stretching temperature of −30 ° C. or more, preferably a stretching temperature of + 20 ° C. or less, more preferably a stretching temperature of + 15 ° C. or less. Here, the stretching temperature means a set temperature of the heating device.

  Further, for example, the stretched film may be fixed after the first stretching step, after the second stretching step, or both after the first stretching step and after the second stretching step. The temperature in the fixing treatment is preferably room temperature or higher, more preferably stretching temperature −40 ° C. or higher, preferably stretching temperature + 30 ° C. or lower, more preferably stretching temperature + 20 ° C. or lower.

  Furthermore, for example, a step of providing an arbitrary layer such as a mat layer, a hard coat layer, an antireflection layer, or an antifouling layer on the surface of the obtained retardation film may be performed.

[3.9. Polarizer〕
The polarizing plate usually includes a polarizer, and includes a protective film for protecting the polarizer as necessary.
As a polarizer, for example, a film of an appropriate vinyl alcohol polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol, a dyeing treatment with a dichroic substance such as iodine and a dichroic dye, a stretching treatment, a crosslinking treatment, etc. Can be used in a suitable order and manner. Usually, in the stretching process for producing a polarizer, a long film before stretching is stretched in the longitudinal direction, and therefore the obtained polarizer can exhibit an absorption axis parallel to the longitudinal direction of the polarizer. This polarizer is capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and is preferably excellent in polarization degree. The thickness of the polarizer is generally 5 μm to 80 μm, but is not limited thereto.

  Any transparent film can be used as a protective film for protecting the polarizer. Among these, a resin film excellent in transparency, mechanical strength, thermal stability, moisture shielding properties and the like is preferable. Examples of such resins include acetate resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, chain olefin resins, cyclic olefin resins, acrylic resins, methacrylic resins, And combinations thereof.

[3.10. Liquid crystal cell)
Examples of the horizontal alignment mode liquid crystal cell include the IPS mode, the FFS mode, and the FLC mode as described above. Examples of liquid crystals used in such a drive mode include nematic liquid crystals and smectic liquid crystals. Usually, nematic liquid crystal is used for the IPS mode and FFS mode, and smectic liquid crystal is used for the FLC mode.

  In the IPS mode, voltage-controlled birefringence (ECB) effect is used to generate liquid crystal molecules that are homogeneously aligned in the absence of an electric field, for example, between a counter electrode and a pixel electrode formed of metal. , And an electric field parallel to the substrate (also referred to as a transverse electric field). More specifically, for example, in the normally black mode, the alignment direction when no electric field is applied to the liquid crystal cell and the polarization absorption axis of the polarizer on one side are matched, and the upper and lower polarizing plates are arranged orthogonally, Black display with no electric field. When there is an electric field, the liquid crystal molecules rotate while keeping parallel to the substrate, whereby the transmittance according to the rotation angle can be obtained (Techno Times publication “Monthly Display July issue” p. 83-p. 88 (1997 version) and “Liquid Crystal vol.2 No. 4” p.303 to p.316 (1998 version) published by the Japanese Liquid Crystal Society. The IPS mode includes a super-in-plane switching (S-IPS) mode and an advanced super-in-plane switching (AS-IPS) mode using a V-shaped electrode or a zigzag electrode.

  The FFS mode uses a voltage-controlled birefringence effect, and a substrate in which liquid crystal molecules aligned in a homogeneous molecular arrangement in the absence of an electric field are generated by a counter electrode and a pixel electrode formed of, for example, a transparent conductor It is made to respond by an electric field (also called a transverse electric field) parallel to the. The lateral electric field in the FFS mode is also called a fringe electric field. This fringe electric field can be generated by setting the interval between the counter electrode formed of a transparent conductor and the pixel electrode to be narrower than the cell gap. More specifically, for example, in the normally black mode, the alignment direction when no electric field is applied to the liquid crystal cell coincides with the absorption axis of the polarizer on one side, and the upper and lower polarizing plates are arranged orthogonally, Displayed in black with no light. When there is an electric field, the liquid crystal molecules rotate while keeping parallel to the substrate, whereby a transmittance corresponding to the rotation angle can be obtained (SID (Society for Information Display) 2001 Digest, p. 484-p. 487, and JP 2002-031812 A). The FFS mode includes an advanced fringe field switching (A-FFS) mode and an ultra fringe field switching (U-FFS) mode in which a V-shaped electrode, a zigzag electrode, or the like is employed.

  The FLC mode utilizes the property that, for example, when a ferroelectric chiral smectic liquid crystal is sealed between electrode substrates having a thickness of about 1 μm to 2 μm, two stable molecular orientation states are exhibited. More specifically, the ferroelectric chiral smectic liquid crystal molecules are rotated in a plane parallel to the substrate by an applied voltage, and are caused to respond. In this FLC mode, black and white display can be obtained on the same principle as the IPS mode and FFS mode. In addition, the FLC mode has a faster response speed than other drive modes. The FLC mode includes a surface stabilization (SS-FLC) mode, an antiferroelectric (AFLC) mode, a polymer stabilization (PS-FLC) mode, and a V-shaped characteristic (V-FLC) mode. .

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
The operations described below were performed under normal temperature and atmospheric conditions unless otherwise specified.

〔Evaluation method〕
(Measurement method of thickness)
The thickness of the film was measured using a contact-type thickness meter.
In addition, the thickness of each layer included in the film is embedded using an epoxy resin, sliced using a microtome (“RUB-2100” manufactured by Yamato Koki Kogyo Co., Ltd.), and cross-sectioned using a scanning electron microscope. Observed and measured.

(Measurement method of retardation)
For the measurement of in-plane retardation and thickness direction retardation of the retardation film, each layer in the retardation film, and other components, a spectroscopic ellipsometer (“M-2000U” manufactured by JA Woollam) is used. I went. The measurement wavelength was 550 nm.

  In particular, the in-plane retardation and the retardation in the thickness direction of each layer included in the retardation film were measured as follows. First, the surface of the retardation film was polished with a plastic polishing cloth to form each layer as a single layer. In this state, the refractive index nx in the in-plane direction of each layer and giving the maximum refractive index, the refractive index ny in the in-plane direction of each layer and perpendicular to the nx direction, and the thickness direction of each layer The refractive index nz of was measured. From the values of these refractive indexes nx, ny and nz and the thickness d of each layer, the in-plane retardation Re and the thickness direction retardation Rth of each layer were calculated.

(Measurement method of slow axis direction)
The direction of the in-plane slow axis was measured by the spectroscopic ellipsometer.

(Visual inspection evaluation criteria for mounting evaluation)
Evaluation criteria for visual inspection in mounting evaluation of the liquid crystal display device were as follows.
A: When viewed from the top, bottom, left, and right sides, it looks beautiful with no light leakage.
○: When viewed from the top, bottom, left, right, or diagonal, there is some light leakage, but it looks beautiful.
Δ: When viewed from the top, bottom, left, right, or diagonal, there is a slight light leakage, and light and shade are visible.
X: When viewed from the top, bottom, left, and right, there is light leakage, and black display is difficult to see.

[Production Example 1]
A film forming apparatus for two-layer / three-layer co-extrusion molding (a type of forming a film composed of three layers with two kinds of resins) was prepared.

  As a resin having a positive intrinsic birefringence, a pellet of polycarbonate resin (“Wonderlite PC-115” manufactured by Asahi Kasei Co., Ltd., glass transition temperature 140 ° C.) was prepared. The pellets were put into one single screw extruder equipped with a double flight type screw and heated to melt.

  As a resin having a negative intrinsic birefringence, a pellet of a styrene-maleic anhydride copolymer resin (“Dylark D332” manufactured by Nova Chemicals, glass transition temperature: 130 ° C.) was prepared. The pellets were put into another single screw extruder equipped with a double flight type screw and heated to melt.

  The melted polycarbonate resin at 260 ° C. was supplied to one manifold of a multi-manifold die (die slip surface roughness Ra = 0.1 μm) through a leaf disk-shaped polymer filter having an opening of 10 μm. The molten 260 ° C. styrene-maleic anhydride copolymer resin was supplied to the other manifold through a leaf disk-shaped polymer filter having an opening of 10 μm.

  A polycarbonate resin and a styrene-maleic anhydride copolymer resin are simultaneously extruded from the multi-manifold die at 260 ° C., and a layer a made of polycarbonate resin a1 / a layer b made of styrene-maleic anhydride copolymer resin / from a polycarbonate resin A film-like molten resin having a three-layer structure including the layer a2 was obtained. This film-like molten resin was cast on a cooling roll adjusted to a surface temperature of 130 ° C., and then passed between two cooling rolls adjusted to a surface temperature of 50 ° C. to obtain a resin laminate. This resin laminate comprises a polycarbonate resin layer (layer a1: thickness 15 μm), a styrene-maleic anhydride copolymer resin layer (layer b: thickness 76 μm), and a polycarbonate resin layer (layer a2: thickness 4 μm). Prepared in order. The total thickness of the resin laminate was 95 μm. Both ends in the width direction of the obtained resin laminate were cut off to obtain a long resin laminate having a width of 500 mm.

  The resin laminate thus obtained was supplied to a tenter transverse uniaxial stretching machine, and stretched in the width direction of the film over 1 minute at a stretching temperature of 150 ° C. and a stretching ratio of 2.85 times (first stretching step). After stretching, both end portions in the width direction of the resin laminate were removed to make the width 1600 mm.

  Subsequently, this resin laminate was supplied to a longitudinal uniaxial stretching machine, and stretched in the longitudinal direction of the film over 1 minute at a stretching temperature of 124 ° C. and a stretching ratio of 1.05 to obtain a laminated retardation film (No. 1). Two stretching step). The width direction edge part of the obtained lamination | stacking phase difference film was cut off, and the width | variety was 1300 mm.

  The laminated retardation film was then heated to 110 ° C. for 1 minute to fix the orientation state (fixing process). At this time, by fixing both ends of the laminated retardation film in the width direction, the dimension in the width direction of the laminated retardation film is fixed to 0.99 times the dimension immediately after the second stretching step is completed. Oita. Then, the width direction both ends of the lamination | stacking phase difference film were cut off, and the width | variety was 1200 mm.

  Thus, the laminated phase difference film provided with the resin layer (A1), the resin layer (B), and the resin layer (A2) in this order was obtained. About the obtained laminated phase difference film, the thickness of each layer, Re, Rth, and the slow axis direction, and the total thickness, Re, and Rth of the laminated phase difference film were measured.

[Production Examples 2 to 7]
The resin layer (A1), the resin layer (B), and the resin layer (A2) were prepared in the same manner as in Production Example 1, except that the draw ratios of the first stretching step and the second stretching step were changed as shown in Table 1. A laminated retardation film provided in this order was obtained. About the obtained laminated phase difference film, the thickness of each layer, Re, Rth, and the slow axis direction, and the total thickness, Re, and Rth of the laminated phase difference film were measured.

  Table 1 summarizes the operation and the measurement results in the production examples. In Table 1, the slow axis direction is an angle in which the width direction of the long film is 0 °.

[Example 1]
(1-1. Evaluation by simulation)
Evaluation by simulation of the liquid crystal display device was performed using a simulator for liquid crystal display device (“LCD Master” manufactured by Shintech Co., Ltd.). The liquid crystal display device set in the evaluation is the liquid crystal display device 100 having the configuration shown in FIGS. The liquid crystal display device 100 includes a first polarizing plate 110, a retardation film (I) 120, a retardation film (II) 130, a liquid crystal cell 140, a second polarizing plate 150, and a backlight unit 160 in this order. Each of the retardation film (I) 120 and the retardation film (II) 130 has a resin layer (A1) (121 or 131) made of the resin A1 having a positive intrinsic birefringence index, and the intrinsic birefringence index is negative. The resin layer (B) (122 or 132) made of the resin B and the resin layer (A2) (123 or 133) made of the resin A2 having a positive intrinsic birefringence are provided in this order from the viewing side. A polarization transmission axis _{A 110} of the first polarizer 110, the polarization transmission axis _{A 150} of the second polarizing plate 150 and the vertical. The slow axis _{A 120} in a plane of the retardation film (I) 120, the slow axis _{A 130} in a plane of the retardation film (II) 130, and a parallel. It was parallel to the slow axis _{A 140} in a plane of the retardation film (I) 120 slow axis _{A 120} and the black display when the liquid crystal cell 140 in the plane of the. The in-plane slow axis A ₁₂₀ of the retardation film (I) 120 and the polarization transmission axis A _{110 of} the first polarizing plate 110 were parallel.

In such a liquid crystal display device 100, the following data is used as data of the retardation film (I) 120, the retardation film (II) 130, the liquid crystal cell 140, the polarizing plates 110 and 150, and the backlight unit 160. did.
(I) As the data of the retardation film (I) 120, the measurement result of the laminated retardation film obtained in Production Example 1 was used.
(Ii) As the data of the retardation film (II) 130, the measurement result of the laminated retardation film obtained in Production Example 5 was used.
(Iii) As data of the liquid crystal cell 140, the polarizing plates 110 and 150, and the backlight unit 160, a liquid crystal cell provided in a commercially available tablet device (manufactured by Apple, trade name “iPad3 (registered trademark)”, the same applies below). The data of the polarizing plate and the backlight unit were used. These data were obtained by disassembling the tablet device, taking out the liquid crystal cell, the polarizing plate and the backlight unit, and measuring them.

  This tablet device is provided with a viewing side polarizing plate, an optical laminate, a liquid crystal cell, a light source side polarizing plate, and a backlight unit in this order from the viewing side. The optical layered body of this tablet device had a retardation film on the light source side and a retardation film on the viewing side. The retardation film on the light source side was a retardation film composed of a material having a negative intrinsic birefringence, and Re was 60 nm and Rth was −90 nm. The retardation film on the viewing side is a retardation film made of a material having a positive intrinsic birefringence, and Re was 90 nm and Rth was 79 nm. The slow axis of the retardation film on the light source side and the retardation film on the viewing side were parallel, and were also parallel to the slow axis of the liquid crystal cell in the state where no voltage was applied. Therefore, the liquid crystal display device of this tablet device has the structure shown in FIGS. 1 to 2 except that the optical laminate is used instead of the retardation films (I) and (II).

  For the liquid crystal display device 100 set as described above, the luminance at the time of black display was calculated. The calculation was performed by optical simulation using a 2 × 2 matrix method. In addition, the calculation of luminance is performed in 5 ° increments in the polar angle range of 0 ° to 80 ° in the polar angle direction, and 5 ° in the range of azimuth angle of 0 ° to 360 ° in the azimuth angle direction. I went in steps. As a value of luminance at the time of black display, a relative luminance with respect to the luminance of the backlight was obtained. That is, the backlight unit 160 alone (that is, a state in which nothing is arranged on the viewing side of the backlight 160) is turned on, and a relative luminance value is obtained with the luminance when viewed from the front direction being 100.0. The measurement results were displayed as a contour diagram. The results are shown in FIG. In addition, FIG. 10 shows the relationship between the azimuth angle and the luminance for black display at a polar angle of 60 °. 5 to 9, thick contour lines in the contour diagrams indicate lines with luminance of 0.0001, and an angle (0 to 360 °) indicated by radiation is an angle corresponding to the azimuth angle φ in FIG. 1. The angle (0 to 80 °) indicated by the concentric circles is an angle corresponding to the polar angle θ in FIG. 10 to 14, the horizontal axis represents the azimuth angle φ, and the vertical axis represents the luminance at the time of black display. Further, Table 2 shows average values of transmission luminance at a polar angle of 60 °.

(1-2. Mounting evaluation)
The tablet device was disassembled, and the member closer to the viewing side than the liquid crystal cell was taken out. The retardation film (I), the retardation film (II), and the polarizing plate were bonded in this order to the surface on the viewing side of the liquid crystal cell.

  As the retardation film (I), the laminated retardation film obtained in Production Example 1 was used. As the retardation film (II), the laminated retardation film obtained in Production Example 5 was used. As the polarizing plate, the one originally used for the tablet device was used. The pasting was performed via an adhesive (polyether adhesive, “CS9621” manufactured by Nitto Denko Corporation, the same in the following).

  The bonding is performed by bonding the surface on the viewing side of the liquid crystal cell and the surface on the resin layer (A2) side of the retardation film (I) to the surface on the resin layer (A1) side of the retardation film (I). The surface of the phase difference film (II) on the resin layer (A2) side was bonded, and the surface of the phase difference film (II) on the resin layer (A1) side and the surface of the polarizing plate were bonded. Further, when laminating, the slow axis of the retardation film (I), the slow axis of the retardation film (II), and the slow axis of the liquid crystal cell at the time of black display are parallel, and the retardation film (I) These orientations were adjusted so that the slow axis of the polarizing plate was parallel to the polarization transmission axis of the polarizing plate on the viewing side. However, these were not completely parallel and vertical, but had errors within the ranges of approximately parallel and approximately vertical, respectively.

  Accordingly, the first polarizing plate 110, the retardation film (I) 120, the retardation film (II) 130, the liquid crystal cell 140, the second polarizing plate 150, and the backlight unit 160 having the configuration shown in FIGS. A liquid crystal display device 100 having the above in this order was obtained. This liquid crystal display device was driven, and the color and light leakage were visually evaluated. As a result, it was found that the color was the best among Examples 1 to 3 and Comparative Examples 1 to 3, and the light leakage was the smallest among Examples 1 to 3 and Comparative Examples 1 to 3. The evaluation results based on the visual inspection evaluation criteria are shown in Table 2.

[Example 2]
In the simulation, as the data of the retardation film (I), the data of the laminated retardation film obtained in Production Example 2 was used in place of the data of the laminated retardation film obtained in Production Example 1. Further, as the data of the retardation film (II), the data of the laminated retardation film obtained in Production Example 4 was used in place of the data of the laminated retardation film obtained in Production Example 5.
In mounting evaluation, the laminated retardation film obtained in Production Example 2 was used as the retardation film (I) instead of the laminated retardation film obtained in Production Example 1. Further, as the retardation film (II), the laminated retardation film obtained in Production Example 4 was used in place of the laminated retardation film obtained in Production Example 5.
Except for changing the above points, evaluation and mounting evaluation by simulation of the liquid crystal display device were performed by the same operation as in Example 1. The simulation results are shown in FIGS. Table 2 shows the average value of transmitted luminance at a polar angle of 60 °. Table 2 shows the evaluation results based on the visual inspection evaluation criteria.
As a result of visual evaluation, it was found that the color tone was the second highest after Example 1, and the light leakage was the second lowest after Example 1.

Example 3
In the simulation, as the data of the retardation film (I), the data of the laminated retardation film obtained in Production Example 3 was used in place of the data of the laminated retardation film obtained in Production Example 1. Further, as the data of the retardation film (II), the data of the laminated retardation film obtained in Production Example 6 was used in place of the data of the laminated retardation film obtained in Production Example 5.
In mounting evaluation, the laminated retardation film obtained in Production Example 3 was used in place of the laminated retardation film obtained in Production Example 1 as the retardation film (I). Instead of the laminated retardation film obtained in Production Example 5, the laminated retardation film obtained in Production Example 6 was used as the retardation film (II).
Except for changing the above points, evaluation and mounting evaluation by simulation of the liquid crystal display device were performed by the same operation as in Example 1. The simulation results are shown in FIGS. Table 2 shows the average value of transmitted luminance at a polar angle of 60 °. Table 2 shows the evaluation results based on the visual inspection evaluation criteria. As a result of visual evaluation, it was found that the color tone was the second highest after Example 2, and the light leakage was the second lowest after Example 2.

[Comparative Example 1]
The tablet device was evaluated. That is:
-The liquid crystal display device to be simulated does not have the retardation film (I) 120 and the retardation film (II) 130, but instead includes the optical laminate of the tablet device described above, The same simulation as (1-1) of Example 1 was performed.
-The tablet device itself was driven, and the color and light leakage were visually evaluated.
The simulation results are shown in FIGS. Table 2 shows the average value of transmitted luminance at a polar angle of 60 °. Table 2 shows the evaluation results based on the visual inspection evaluation criteria. As a result of visual evaluation, it was found that the color was the second best after Comparative Example 2, and the light leakage was the second smallest after Comparative Example 2.

[Comparative Example 2]
As a retardation film, the liquid crystal display device having only one retardation film obtained in Production Example 7 was evaluated. That is:
In the simulation, as the data of the retardation film (I), the data of the laminated retardation film obtained in Production Example 7 was used instead of the data of the laminated retardation film obtained in Production Example 1. The liquid crystal display device to be simulated is not provided with the retardation film (II).
In mounting evaluation, the laminated retardation film obtained in Production Example 7 was used in place of the laminated retardation film obtained in Production Example 1 as the retardation film (I). Moreover, retardation film (II) was not used.
Except for changing the above points, evaluation and mounting evaluation by simulation of the liquid crystal display device were performed by the same operation as in Example 1. The simulation results are shown in FIGS. Table 2 shows the average value of transmitted luminance at a polar angle of 60 °. Table 2 shows the evaluation results based on the visual inspection evaluation criteria. As a result of visual evaluation, it was found that the color was the second best after Example 3 and the light leakage was the second lowest after Example 3.

[Comparative Example 3]
(C3-1. Retardation films A11 and A12)
As a resin having a positive intrinsic birefringence, pellets of polycarbonate resin (manufactured by Asahi Kasei Corporation, trade name “Wonderlite PC-115”, glass transition temperature 140 ° C.) were prepared. The pellets were put into a single screw extruder equipped with a double flight type screw and melted. The film was extruded with a single-screw extruder and extruded from a film-forming die to obtain a rectangular unstretched film having a thickness of 30 μm.

  About this film before extending | stretching, using a biaxial stretching test apparatus (Brand name "EX10-B", the Toyo Seiki Seisakusho Co., Ltd. product, the same hereafter), two types of sequential biaxial stretching is performed, and two types of phase difference films are used. Got.

  In the first sequential biaxial stretching, the stretching temperature was 147 ° C., and the stretching ratio was 1.45 times in the width direction in the first stretch and 1.01 times in the longitudinal direction in the second stretch. This produced Re31nm, Rth69nm retardation film A11 of the same retardation as the resin layer (A1) of manufacture example 1.

  On the other hand, in the second sequential biaxial stretching, the stretching temperature was 145 ° C., and the stretching ratio was 1.85 times in the width direction in the first stretch and 1.01 times in the longitudinal direction in the second stretch. This produced Re67nm and Rth150nm retardation film A12 of the same retardation as the resin layer (A1) of manufacture example 5.

(C3-2. Retardation films B2 and B3)
As a resin having a negative intrinsic birefringence, a styrene-maleic anhydride copolymer resin (manufactured by Nova Chemicals, trade name “Dylark D332”, glass transition temperature 130 ° C.) is extruded with a single-screw extruder, and has a thickness of 30 μm. A rectangular unstretched film was obtained.

  About this film before extending | stretching, using a biaxial stretching test apparatus (Brand name "EX10-B", the Toyo Seiki Seisakusho Co., Ltd. product, the same hereafter), two types of sequential biaxial stretching is performed, and two types of phase difference films are used. Got.

  In the first sequential biaxial stretching, the stretching temperature was 118 ° C., and the stretching ratio was 1.35 times in the width direction in the first stretch and 1.01 times in the longitudinal direction in the second stretch. This produced Re 169 nm and Rth-134 nm retardation film B2 having the same retardation as that of the resin layer (B) of Production Example 1.

  On the other hand, in the second sequential biaxial stretching, the stretching temperature was 120 ° C., and the stretching ratio was 1.85 times in the width direction in the first stretch and 1.01 times in the longitudinal direction in the second stretch. This produced Re91nm and Rth-65nm retardation film A12 of the same retardation as the resin layer (B) of manufacture example 5.

(C3-2. Laminated retardation film (I ′) and (II ′))
The retardation films A11 and B2 were bonded with the slow axes aligned in the same direction to obtain a laminated retardation film (I ′). Further, the retardation films A12 and B3 were bonded with the slow axes aligned in the same direction to obtain a laminated retardation film (II ′).

(C3-3. Evaluation of mounting)
The same as (1-2) of Example 1 except that the laminated retardation film (I ′) was used as the retardation film (I) and the laminated retardation film (II ′) was used as the retardation film (II). Then, the mounting evaluation was performed. At the time of pasting, pasting was performed so that the A11 side surface of the laminated retardation film (I ′) and the A12 side surface of the laminated retardation film (II ′) were directed to the viewing side. The evaluation results based on the visual inspection evaluation criteria are shown in Table 2. In visual evaluation, it was found that the color was the worst among Examples 1 to 3 and Comparative Examples 1 to 3, and the light leakage was the highest among Examples 1 to 3 and Comparative Examples 1 to 3. .

100: Liquid crystal display device 110: First polarizing plate 120: Retardation film (I)
121: Resin layer (A1)
122: Resin layer (B)
123: Resin layer (A2)
130: Retardation film (II)
131: Resin layer (A1)
132: Resin layer (B)
133: Resin layer (A2)
140: Liquid crystal cell 150: Second polarizing plate 160: Backlight unit A ₁₁₀ : Polarization transmission axis of the first polarizing plate A ₁₂₀ : Slow axis of the retardation film (I) A ₁₂₁ : Slow phase of the resin layer (A1) Axis A ₁₂₂ : Slow axis of resin layer (B) A ₁₂₃ : Slow axis of resin layer (A2) A ₁₃₀ : Slow axis of retardation film (II) A ₁₃₁ : Slow axis of resin layer (A1) A ₁₃₂ : Slow axis of the resin layer (B) A ₁₃₃ : Slow axis of the resin layer (A 2) A ₁₄₀ : Slow axis in the plane of the liquid crystal cell in the black display state A ₁₅₀ : Polarized light transmission of the second polarizing plate Axis A _N : Normal direction of display surface A _C : Inclination direction with respect to display surface

Claims (4)

A first polarizing plate, a retardation film (I), a retardation film (II), a liquid crystal cell in a horizontal alignment mode, and a second polarizing plate having a polarization transmission axis substantially perpendicular to the polarization transmission axis of the first polarizing plate A liquid crystal display device provided in this order from the viewing side,
Each of the retardation film (I) and the retardation film (II)
A resin layer (A1) made of resin A1 having a positive intrinsic birefringence, a resin layer (B) made of resin B having a negative intrinsic birefringence, and a resin A2 having a positive intrinsic birefringence The resin layer (A2) is provided in this order from the viewing side, and the resin layer (A1) and the resin layer (B), and the resin layer (B) and the resin layer (A2) are in direct contact with each other. Is a co-stretched film,
The slow axis in the plane of the retardation film (I) and the slow axis in the plane of the retardation film (II) are substantially parallel,
The slow axis in the plane of the retardation film (I) and the slow axis in the plane of the liquid crystal cell during black display are substantially parallel,
The in-plane slow axis of the retardation film (I) and the polarization transmission axis of the first polarizing plate are substantially parallel.
Liquid crystal display device. The retardation film (I) and the retardation film (II) are both
In-plane retardation ReA1 of the resin layer (A1), retardation RthA1 in the thickness direction of the resin layer (A1), in-plane retardation ReB of the resin layer (B), measured at a wavelength of 550 nm, The retardation RthB in the thickness direction of B), the in-plane retardation ReA2 of the resin layer (A2), and the retardation RthA2 in the thickness direction of the resin layer (A2) are represented by the following formulas (1) to (6):
20 nm ≦ ReA1 ≦ 100 nm (1)
40 nm ≦ RthA1 ≦ 200 nm (2)
60 nm ≦ ReB ≦ 180 nm (3)
−180 nm ≦ RthB ≦ −40 nm (4)
0 nm ≦ ReA2 ≦ 20 nm (5)
0 nm ≦ RthA2 ≦ 20 nm (6)
The liquid crystal display device according to claim 1, wherein: It is a manufacturing method of the liquid crystal display device according to claim 1 or 2,
A step of preparing a resin laminate, wherein the resin laminate comprises a layer a1 made of a resin A1 having a positive intrinsic birefringence, a layer b made of a resin B having a negative intrinsic birefringence, and an intrinsic A preparation step in which a layer a2 made of a resin A2 having a positive birefringence is provided in this order, the layer a1 and the layer b are in direct contact with each other, and the layer b and the layer a2 are in direct contact with each other. ;
Stretching the resin laminate to obtain the retardation film (I), stretching step (I),
Stretching the resin laminate to obtain the retardation film (II), a stretching step (II), and the first polarizing plate, the retardation film (I), the retardation film (II), and the liquid crystal cell And the second polarizing plate is assembled so as to be provided in this order from the viewing side.   The manufacturing method according to claim 3, wherein the preparation step includes a co-extrusion step of the resin A1, the resin B, and the resin A2.