JP2009075549A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transverse electric field mode liquid crystal display device capable of improving the viewing angle characteristic in black display at an oblique viewing angle with a simple structure. <P>SOLUTION: In the liquid crystal display device 100 controlling light transmittance of a liquid crystal layer 6 by a transverse electric field formed between a pixel electrode 32 and a common electrode 31, (a) the product Δn×d of the liquid crystal layer 6 is made within the range of 320 nm±20 nm, (b) polarizing plates 10 and 20 are composed of polarizers 11 and 21 and transparent protective films 12 and 22 holding the polarizers therebetween, and any new retardation plate or optical compensation layer are not arranged between the polarizing plates 10 and 20 and an array substrate 3 and a counter substrate 4, (c); the delay phase axes 52 and 62 of the transparent protective films 12a and 22a at the liquid crystal layer 6 sides are made nearly parallel with the absorption axes of the polarizers 11 and 21 of respective side, and (d) the in-plane retardation Re is defined as ≤10 nm, and the retardation Rth in thickness direction is defined as ≥30 nm and ≤40 nm for the transparent protective films 12a and 22a that protect the faces of the liquid crystal layer 6 sides. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a horizontal electric field type liquid crystal display device. In particular, it relates to improvement of black display at an oblique viewing angle.

  The liquid crystal display panel adjusts the light transmittance by applying a voltage to the liquid crystal to control the alignment of the liquid crystal. The liquid crystal display modes are classified according to the type of alignment change of the liquid crystal. At present, TN (Twisted Nematic) mode, VA (Vertical Alignment) mode, and IPS (In-Plane Switching) mode are mainstream. .

  In the TN mode, a vertical electric field perpendicular to the substrate is applied, and the display state is changed by causing the liquid crystal molecules to rise or fall with respect to the substrate surface according to the voltage application state. Also in the VA mode, the display state is changed by moving the liquid crystal molecules in the same manner with respect to the substrate surface.

  In the IPS mode, liquid crystal molecules are moved by applying a horizontal electric field parallel to the substrate. As a mode for moving liquid crystal molecules by a lateral electric field, an FFS (Fringe Field Switching) mode which is a kind of IPS mode can be cited in addition to the IPS mode. In the lateral electric field method such as the IPS mode and the FFS mode, the display state of ON and OFF is changed by moving the liquid crystal molecules in a plane parallel to the substrate. Δn · d) is characterized by small changes and wide viewing angle characteristics. Here, the retardation (Δn · d) is the product of the refractive index anisotropy Δn of the liquid crystal molecules and the liquid crystal layer thickness d.

  The viewing angle characteristics of the IPS mode are much better than those of the TN mode and VA mode. In general, the viewing angle characteristic of an IPS mode liquid crystal display device without a viewing angle compensation film is more than the viewing angle characteristic of a TN mode or VA mode liquid crystal display device with an optimum viewing angle compensation film. It is good.

  As described above, the viewing angle characteristics of the liquid crystal display device can be improved by reducing the viewing angle dependence of the liquid crystal layer itself. However, in addition to the viewing angle dependency of the liquid crystal layer itself, there are factors that determine viewing angle characteristics. That is the viewing angle dependence of a pair of orthogonal (crossed Nicols) polarizing plates. Even with only a pair of orthogonal polarizing plates, the orthogonality is lost in the oblique field of view. As a result, even if there is no liquid crystal layer, there is a problem that light leakage occurs in black display at an oblique viewing angle and the viewing angle characteristics are deteriorated.

  The light leakage level at the time of black display of the polarizing plate itself is smaller than the light leakage due to the change in retardation of the liquid crystal layer. For this reason, it has not been regarded as a problem in a mode in which light leakage from the liquid crystal layer such as the TN mode is large. However, in the IPS mode and FFS mode in which the viewing angle characteristics of the liquid crystal layer are excellent, light leakage due to the polarizing plate has become a problem.

  In the oblique viewing field at the time of black display, light leakage occurs due to the collapse of the orthogonality between the pair of polarizing plates. A method for arranging an optical compensation layer is proposed (for example, Patent Documents 1 to 4).

  In Patent Document 1, two biaxial optical compensation films having a retardation of 1/2 wavelength are disposed between a substrate and a polarizer, and the polarization state at oblique incidence is equal to the polarization state at perpendicular incidence. Thus, a method for compensating the viewing angle of the crossed Nicols polarizing plate has been proposed. Patent Document 2 proposes a method in which one biaxial optical compensation film having a retardation of 1/2 wavelength is disposed between a substrate and a polarizing plate. Patent Document 3 includes a first retardation region and a second retardation region having a retardation layer obtained by stretching an oil-based structure-containing polymer resin film between a substrate and a polarizing film (polarizer). A configuration to be arranged is disclosed. Patent Document 4 proposes a configuration in which an optical compensation layer having a compound containing a discotic structural unit and a protective film are disposed between a substrate and a polarizing film (polarizer).

Patent Document 4 also discloses a configuration in which viewing angle characteristics are improved by providing a polarizer sandwiched between a pair of protective films without providing an optical compensation layer having a compound containing the discotic structural unit. Has been.
JP 2001-350022 A (FIG. 5) JP-A-11-305217 (FIG. 3) JP-A-2005-321528 (FIG. 2, FIG. 3, paragraph numbers 0019 to 0021) Japanese Patent Laying-Open No. 2005-196119 (FIGS. 1 and 2)

  However, in order to further improve the viewing angle, it is understood from Patent Document 4 that it is preferable to dispose an optical compensation film having a compound containing the above-described discotic structural unit. The new arrangement of the compensation film complicates the structure and increases the cost.

  Needless to say, it is most preferable to improve the viewing angle characteristics with a simple configuration. In the case where an optical compensation layer is newly provided, in addition to an increase in cost, it is disadvantageous in reducing the thickness of the liquid crystal display device. In particular, when optical compensation is performed using a plurality of stretched films made of a birefringent polymer, not only the thickness of the optical compensation sheet increases, but also the adhesive layer used for lamination of the stretched films contracts due to changes in temperature and humidity. In some cases, a new problem occurs in which peeling or warping occurs. Further, the stretched birefringent polymer film is generally expensive, and there is a problem that further cost increase is unavoidable.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a horizontal electric field type liquid crystal display device capable of improving the viewing angle characteristics of black display at an oblique viewing angle with a simple configuration. Is to provide.

The liquid crystal display device according to the present invention includes a pair of transparent substrates, a liquid crystal layer sandwiched between the pair of transparent substrates, a pair of polarizing plates disposed opposite to the outside of the transparent substrate, and one of the transparent substrates. A pixel electrode and a common electrode that are spaced apart from each other, and the light transmittance of the liquid crystal layer can be controlled by an electric field formed between the pixel electrode and the common electrode. (A) to (d) are satisfied.
(A) The product Δn · d of the thickness d of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal layer is set within 320 nm ± 20 nm.
(B) Each of the pair of polarizing plates is composed of a polarizer and a transparent protective film that sandwiches the polarizer, and no new retardation plate or optical compensation layer is disposed between the polarizing plate and the transparent substrate. Attach directly.
(C) In each of the pair of polarizing plates, the transparent protective film that protects the liquid crystal layer side of the transparent protective film is substantially parallel to the slow axis of the transparent protective film and the absorption axis of the polarizer. And
(D) In each of the pair of polarizing plates, among the transparent protective films, the transparent protective film protecting the liquid crystal layer side is:
With the thickness direction as the Z axis, the refractive index in the axial direction is nz, and in the plane perpendicular to the Z axis, the maximum refractive index direction is the X axis, the refractive index is nx, and the direction perpendicular to the Z axis and the X axis is When the refractive index in the axial direction as the Y axis is ny and the thickness of the transparent protective film is df,
The in-plane retardation Re defined by Re = (nx−ny) × df is 10 nm or less, and the thickness direction retardation Rth defined by Rth = {(nx + ny) / 2−nz} × df is 30 nm or more, 40 nm or less.

  According to the present invention, there is an excellent effect that it is possible to provide a horizontal electric field type liquid crystal display device having a simple configuration and good viewing angle characteristics of black display at an oblique viewing angle.

  Hereinafter, an example of an embodiment to which the present invention is applied will be described. It goes without saying that other embodiments may also belong to the category of the present invention as long as they match the gist of the present invention. Moreover, the size and ratio of each member in the following drawings are for convenience of explanation, and are different from actual ones.

  The liquid crystal display device according to the present embodiment is a horizontal electric field type liquid crystal display device. Here, an IPS liquid crystal display device will be described as an example of a horizontal electric field liquid crystal display device. FIG. 1 is a schematic exploded perspective view showing the configuration of the liquid crystal display device 100 according to the first embodiment. 2A is a schematic cross-sectional view when a voltage is not applied to the liquid crystal display device 100, and FIG. 2B is a schematic cross-sectional view when a voltage is applied to the liquid crystal display device 100. Show.

  As shown in FIGS. 1 and 2, the liquid crystal display device 100 includes an array substrate 3 and a counter substrate 4. The pair of substrates are bonded to each other through a seal pattern formed using a seal material 5, and a liquid crystal layer 6 is filled in a space formed by these. The liquid crystal molecules 7 constituting the liquid crystal layer 6 are schematically enlarged and illustrated for convenience of explanation.

  The array substrate 3 includes a switching element (not shown), an insulating film (not shown), a common electrode 31 that is a comb-shaped electrode, and a pixel that is also a comb-shaped electrode on a transparent insulating substrate made of a substrate such as glass, polycarbonate, or acrylic resin. An electrode 32 and the like are formed. The pixel electrode 32 is formed in each pixel region on the liquid crystal layer 6 side of the array substrate 3, and a selected video signal is supplied through a video signal line (not shown). A common signal is supplied to the common electrode 31 disposed away from the pixel electrode 32 through a common signal line (not shown). A first alignment film 33a and the like are formed on these electrodes and wirings. The first alignment film 33a functions to align the liquid crystal molecules 7, and the comb-shaped electrode composed of the common electrode 31 and the pixel electrode 32 facing each other functions to twist and deform the liquid crystal layer 6 by applying a voltage parallel to the substrate. Bear. The light transmittance is controlled according to the degree of twist deformation of the liquid crystal layer 6. The switching element (not shown) is constituted by a TFT (Thin Film Transistor) or the like, and plays a role of supplying a voltage to the pixel electrode 32 on the insulating film. A first polarizing plate 10 is disposed on the outer main surface of the array substrate 3. In the present embodiment, the IPS mode in which both the common electrode 31 and the pixel electrode 32 are comb-shaped electrodes has been described. However, one of the common electrode 31 and the pixel electrode 32 is a comb-shaped electrode, and the other is a lower layer through an insulating film. The present invention can also be applied to an FFS mode or the like of an electrode configuration arranged on the entire surface.

  The first polarizing plate 10 has a structure in which a first polarizer 11 is sandwiched between two first transparent protective films 12 (12a, 12b). The polarizing plate is usually configured by laminating a transparent protective film on a polarizer. A polarizer passes two polarized components of incident light that are orthogonal to each other (one whose vibration direction is parallel to the transmission axis of the polarizer) and the other component (the vibration direction is parallel to the absorption axis of the polarizer). Optical component). Here, of the transparent protective film 12, the liquid crystal layer-first transparent protective film 12a is disposed on the liquid crystal layer 6 side, and the backlight side-first transparent is disposed on the backlight 8 side. It is set as the protective film 12b. The configuration of the transparent protective film 12 will be described in detail later.

  The counter substrate 4 includes a transparent insulating substrate, a light shielding layer (black matrix layer) (not shown), a color filter layer (not shown) functioning as a color material layer, a second alignment film 33b, and the like. The transparent insulating substrate can be composed of a transmissive substrate such as a glass substrate or a quartz substrate. A second polarizing plate 20 is disposed on the outer main surface of the counter substrate 4.

  The second polarizing plate 20 has a structure in which a second polarizer 21 is sandwiched between two second transparent protective films 22 (22a, 22b). Here, among the transparent protective films 22, the liquid crystal layer-second transparent protective film 22a is disposed on the liquid crystal layer 6 side, and the visual side-second transparent protective film 22b is disposed on the viewer side. And The first polarizer 11 and the second polarizer 21 are arranged with their transmission axes orthogonal to each other.

  The liquid crystal display device 100 further includes a control board (not shown) that generates a drive signal, an FFC (Flexible Flat Cable) (not shown) that electrically connects the control board to a terminal (not shown), and a back that serves as a light source. Light 8 etc. are also provided. The backlight 8 is disposed on the non-viewing side (back side) of the liquid crystal display panel 1 and is configured to irradiate light to the viewing side via the liquid crystal display panel 1. As the backlight 8, the thing of the general structure provided with the light source, the light-guide plate, the reflective sheet, the diffusion sheet, the prism sheet, the reflective polarizing sheet etc. can be used, for example.

  For example, the liquid crystal display device 100 operates as follows to display an image. That is, when an electric signal is input from the control board, a driving voltage is applied to the common electrode 31 and the pixel electrode 32, and the direction of the molecules of the liquid crystal molecules 7 changes according to the driving voltage. For example, in the case of a p-type liquid crystal, the liquid crystal molecules 7 tend to move in the direction of the electric field, so that twist deformation is induced. The light transmittance is controlled by the degree of twist deformation of the liquid crystal molecules 7. Light is emitted from the backlight 8, and is transmitted or blocked outside through the array substrate 3, the liquid crystal molecules 7, and the counter substrate 4, whereby an image or the like is displayed on the liquid crystal display device 100.

  As a result of intensive studies by the present inventors to improve the viewing angle characteristics with a simple configuration, the liquid crystal display device 100 configured as described above satisfies the following (a) to (d): It has been found that the object can be achieved.

(A) The retardation of the liquid crystal layer 6 satisfies the formula <1>.
300 nm ≦ Δn · d ≦ 340 nm <1>
Here, d is the thickness of the liquid crystal layer 6, and Δn is the refractive index anisotropy of the liquid crystal molecules 7. That is, the retardation of the liquid crystal layer 6 is set within a range of 320 nm ± 20 nm. It has been found that by setting this range, light leakage during black display in the oblique viewing angle direction during black display can be effectively suppressed in combination with conditions (b) to (d) described later. In the horizontal electric field type liquid crystal display device 100, the retardation of the liquid crystal layer 6 is reduced to half that of green light (540 to 560 nm) with high visibility in order to suppress color tracking (voltage dependency of chromaticity). Generally, it is set to about the wavelength (λ / 2). That is, the retardation of the liquid crystal layer 6 is generally set to about 270 to 280 nm.

  (B) The polarizing plates 10 and 20 are composed of polarizers 11 and 21 and transparent protective films 12 and 22 that sandwich the polarizers 11 and 21. The first polarizing plate 10 and the array substrate 3 are directly attached without providing a new retardation plate or optical compensation film. Similarly, the second polarizing plate 20 and the counter substrate 4 are directly attached without providing an optical compensation layer such as a new retardation plate or an optical compensation film. As a result, the liquid crystal display device 100 can be thinned and reduced in cost with a simple configuration.

(C) The slow axes 52 and 62 of the transparent protective films 12a and 22a on the liquid crystal layer 6 side constituting the first and second polarizing plates 10 and 20, and the absorption axes 51 and 61 of the first and second polarizers 11 and 21. Are substantially parallel.
In the present embodiment, the absorption axis 51 of the first polarizer 11 constituting the first polarizing plate 10 and the slow axis of the two transparent protective films 12 (12a, 12b) sandwiching the first polarizer 11 are used. 52 is substantially parallel. Similarly, an absorption axis 61 of the second polarizer 21 constituting the second polarizing plate 20 and a slow axis 62 of the two transparent protective films 22 (22a, 22b) sandwiching the second polarizing property 21 are provided. It is almost parallel.

  (D) In-plane retardation Re of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a for protecting the first and second polarizers 11, 21 on the liquid crystal layer 6 side. The thickness direction retardation Rth is set to the following range.

When the in-plane retardation Re of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a is defined by the following formula <2>, the one satisfying the condition of the formula <3> is used. .
Re = (nx−ny) × df <2>
Here, nx is the maximum refractive index direction (X axis) in the plane perpendicular to the Z axis when the thickness direction of the first (second) transparent protective film 12 (22) is the Z axis. Ny represents the refractive index in the direction perpendicular to the Z axis and the X axis (Y axis). Moreover, df shows the thickness of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a.
Re ≦ 10 nm <3>
The in-plane retardation Re between the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a may be 10 nm or less, and Re may be zero.

When the thickness direction retardation Rth of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a is defined by the following formula <4>, a film that satisfies the condition of the formula <5> is used. . Here, nz is the refractive index in the Z-axis direction (the thickness direction of the first and second transparent protective films 12 and 22).
Rth = {(nx + ny) / 2−nz} × df <4>
30 nm ≦ Rth ≦ 40 nm <5>

  In the backlight side-first transparent protective film 12b and the viewer side-second transparent protective film 22b, it is not particularly necessary to satisfy the above formulas <3> and <5>, and the function of protecting the polarizers 11, 21. If there is.

  In addition, as the 1st, 2nd transparent protective films 12 and 22 which protect the 1st and 2 polarizers 11 and 21, a triacetyl cellulose film (TAC) is generally used. The TAC has a slight in-plane retardation Re. In the present embodiment, the slow axes 52 and 62 of the in-plane retardation Re of the first and second transparent protective films 12 and 22 and the absorption axis directions of the first and second polarizers 11 and 21 are substantially parallel to each other. It is configured as follows. Moreover, there was also a phase difference in the thickness df direction, and the thickness df direction phase difference Rth was in the range of 50 nm to 60 nm.

  The first polarizing plate 10 is disposed so that the absorption axis 51 of the first polarizer 11 is substantially parallel to the rubbing direction of the first alignment film 33a, and the second polarizing plate 20 disposed on the viewing side is The absorption axis 61 of the two polarizers 21 was disposed so as to be substantially orthogonal to the rubbing direction of the second alignment film 33b. The rubbing process is performed so that the rubbing direction has an angle of θ1 with the long side direction of the comb-shaped electrode. The term “parallel” and “orthogonal” as used herein does not indicate completely parallel or orthogonal, but includes an error within ± 5 degrees. Here, it is described as substantially parallel and substantially orthogonal.

The liquid crystal molecules 7 in the off state to which no voltage is applied are in a uniaxial alignment state along the rubbing direction. In the ON state in which a voltage is applied, torsional deformation is induced in the liquid crystal layer 6 by a lateral electric field applied in a direction perpendicular to the long side direction of the comb-shaped electrode composed of the common electrode 31 and the pixel electrode 32 facing each other. Part or all of the light passes through the liquid crystal layer 6 due to the birefringence effect of the liquid crystal layer 6. The transmittance can be controlled by changing the twist of the liquid crystal molecules 7.
Regarding the rubbing direction, the absorption axis 51 of the first polarizer 11 is arranged so as to be substantially orthogonal to the rubbing direction of the liquid crystal layer 6, and the absorption axis 61 of the second polarizer 21 is arranged in the rubbing direction of the liquid crystal layer 6. The same effect can be obtained even if they are arranged substantially parallel to each other.
Also, the rubbing direction can be set in a predetermined direction according to the viewing angle characteristics required for the direction of the comb electrode.

  According to the present embodiment, the physical properties of the transparent protective films 12 and 22 that protect the first and second polarizers 11 and 21 constituting the first and second polarizing plates 10 and 20 and the liquid crystal layer 6 are optimized. Therefore, a lateral electric field such as an IPS mode or an FFS mode can be directly bonded between the first polarizing plate 10 and the array substrate 3 and the counter substrate 4 without arranging a new retardation plate or an optical compensation layer. The viewing angle characteristics of the system can be improved.

More specifically, the retardation value of the liquid crystal layer 6 and the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film of the first and second polarizing plates 10 and 20 disposed on the liquid crystal layer 6 side. By adjusting the thickness direction retardation Rth and the in-plane direction retardation Re of 22a, it is possible to reduce the light leakage of black display in the oblique viewing angle direction caused by the polarizing plate without adding a new optical compensation layer. . Thereby, the liquid crystal display device 100 having a simple configuration can be provided.
In addition, since no new optical compensation layer is added, the liquid crystal display device 100 can be reduced in thickness and cost.
Moreover, there is no need to laminate and bond the stretched films forming the optical compensation layer, and the problem of peeling or warping between the films due to shrinkage of the adhesive layer due to temperature and humidity changes does not occur.
Furthermore, by setting the retardation of the liquid crystal layer 6 within the range of the above formula <1>, the transmittance can be improved as compared with a case where the retardation is generally set to 270 to 280 nm.

  In the present embodiment, the IPS method has been described. However, the present invention can be applied to other horizontal electric field type liquid crystal display devices such as an FFS method.

[Example]
EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the following examples. The liquid crystal display device 100 according to the present embodiment employs the IPS mode shown in FIG. 2 and uses p-type liquid crystal. The liquid crystal display panel 1 was produced as follows.

The following was used as the liquid crystal layer 6.
Refractive index anisotropy: Δn = 0.089 (550 nm, 20 ° C.)
Dielectric anisotropy: Δε = + 7.8
-Thickness of the liquid crystal layer 6: d = 3.6 μm
Retardation of liquid crystal layer 6: Δn · d = 320 nm

  The in-plane retardation Re of the transparent protective films 12 (12a, 12b) and 22 (22a, 22b) was 10 nm or less. Further, the slow axis 52 and 62 direction of the in-plane retardation Re of the first and second transparent protective films 12 and 22 and the absorption axis direction of the polarizers 11 and 21 on each side are substantially parallel to each other. As the first and second transparent protective films 12 and 22, the same liquid crystal side-first transparent protective film 12a and liquid crystal side-second transparent protective film 22a were used as described above.

  The thickness d of the liquid crystal layer 6 is adjusted via a spacer. As the spacer, a spherical spacer, a columnar spacer, or the like can be used. As the alignment film 33 (33a, 33b), for example, a polyimide type or polyamic acid type is used, and an alignment process is performed by rubbing using a cloth such as rayon. The rubbing direction was performed at an angle of about 15 ° with respect to the long side direction of the comb-shaped electrode. The second alignment film 33 b disposed on the counter substrate 4 was rubbed in parallel with the rubbing direction of the first alignment film 33 a disposed on the array substrate 3.

  FIG. 3 shows black luminance at an oblique viewing angle (azimuth angle 60 °, polar angle 70 °) with respect to the thickness direction retardation Rth of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a. The result of calculating is shown. The polar angle is an inclination angle from the normal line of the display surface, and the azimuth angle is an angle within the display surface. It can be seen that by setting the retardation of the liquid crystal layer 6 to 320 nm, the value of the black luminance can be reduced as compared with a comparative example described later. Further, when the retardation of the liquid crystal layer 6 is set to 320 nm, the thickness direction retardation Rth of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a is 20 to 20 as shown in FIG. It can be seen that 50 nm is preferable. And the optimal range is 30-40 nm.

[Comparative example]
Next, a comparative example will be described. The following was used as the liquid crystal layer 6.
Refractive index anisotropy: Δn = 0.089 (550 nm, 20 ° C.)
Dielectric anisotropy: Δε = + 7.8
Liquid crystal layer 6 thickness: d = 3.14 μm
Retardation of liquid crystal layer 6: Δn · d = 280 nm

  The in-plane retardation Re of the transparent protective films 12 (12a, 12b) and 22 (22a, 22b) was 10 nm or less. Other member configurations were the same as in the above example. As the transparent protective films 12 and 22, the same liquid crystal side-first transparent protective film 12a and liquid crystal side-second transparent protective film 22a were used as described above.

  FIG. 4 shows black luminance at an oblique viewing angle (azimuth angle 60 °, polar angle 70 °) with respect to the thickness direction retardation Rth of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a. The result of calculating is shown. From FIG. 4, it can be seen that the loss of black luminance becomes smaller as the thickness direction retardation Rth of the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a is smaller. For this reason, when the retardation of the liquid crystal layer 6 is designed to be 280 nm, it is better not to have the liquid crystal side-first transparent protective film 12a and the liquid crystal side-second transparent protective film 22a. The polarizing plates 10 and 20 cannot be produced without using 12 and 22. Therefore, in order to reduce the black omission of the black display when viewed from the oblique viewing angle direction, a retardation plate and an optical compensation layer film for newly performing viewing angle compensation are required.

  In the above examples and comparative examples, the second alignment film 33b disposed on the counter substrate 4 is parallel to the rubbing direction of the first alignment film 33a disposed on the array substrate 3, but the same is true even when rubbing antiparallel. It was the result.

1 is a schematic perspective view illustrating a configuration of a liquid crystal display device according to an embodiment. (A) is typical sectional drawing in case the voltage is not applied to the liquid crystal display device which concerns on this embodiment, (b) is typical sectional drawing when a voltage is applied to the liquid crystal display device which concerns on this embodiment. The figure which plotted black luminance with respect to thickness direction phase difference Rth of the transparent protective film which concerns on an Example. The figure which plotted black luminance with respect to the thickness direction phase difference Rth of the transparent protective film which concerns on a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 3 Array substrate 4 Counter substrate 5 Seal 6 Liquid crystal layer 7 Liquid crystal molecule 8 Backlight 10 1st polarizing plate 11 1st polarizer 12 1st transparent protective film 12a Liquid crystal side-1st transparent protective film 12b Backlight side -First transparent protective film 20 Second polarizing plate 21 Second polarizing 22 Second transparent protective film 22a Liquid crystal side-Second transparent protective film 22b Viewing side-Second transparent protective film 31 Common electrode (comb electrode)
32 Pixel electrode (comb electrode)
33a First alignment film 33b Second alignment film 51 Absorption axis 52 of the first polarizer 52 Slow axis 61 of the first transparent protective film Second absorption axis 62 Slow axis 100 of the second transparent protective film Liquid crystal display device

Claims (4)

A pair of transparent substrates;
A liquid crystal layer sandwiched between the pair of transparent substrates;
A pair of polarizing plates opposed to the outside of the transparent substrate;
On one of the transparent substrates, a pixel electrode and a common electrode disposed apart from each other,
A liquid crystal display device that controls light transmittance of the liquid crystal layer by an electric field formed between the pixel electrode and the common electrode, and satisfies the following (a) to (d).
(A) The product Δn · d of the thickness d of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal layer is set within 320 nm ± 20 nm.
(B) Each of the pair of polarizing plates includes a polarizer and a transparent protective film that sandwiches the polarizer, and the polarizing plate and the transparent substrate are directly bonded to each other.
(C) In each of the pair of polarizing plates, the transparent protective film that protects the liquid crystal layer side of the transparent protective film is substantially parallel to the slow axis of the transparent protective film and the absorption axis of the polarizer. And
(D) In each of the pair of polarizing plates, among the transparent protective films, the transparent protective film protecting the liquid crystal layer side is:
With the thickness direction as the Z axis, the refractive index in the axial direction is nz, and in the plane perpendicular to the Z axis, the maximum refractive index direction is the X axis, the refractive index is nx, and the direction perpendicular to the Z axis and the X axis is When the refractive index in the axial direction as the Y axis is ny and the thickness of the transparent protective film is df,
The in-plane retardation Re defined by Re = (nx−ny) × df is 10 nm or less, and the thickness direction retardation Rth defined by Rth = {(nx + ny) / 2−nz} × df is 30 nm or more, 40 nm or less.   The liquid crystal display device according to claim 1, wherein the liquid crystal layer is mainly composed of liquid crystal molecules that are twisted and deformed by an electric field formed between the pixel electrode and the common electrode. In the pair of transparent substrates, an alignment film for controlling the alignment of the liquid crystal molecules of the liquid crystal layer is disposed on a surface in contact with the liquid crystal layer,
Of the pair of polarizing plates, the absorption axis of one polarizer is substantially parallel to the rubbing direction of the alignment film on the polarizer side, and the absorption axis of the polarizer of the other polarizing plate is the rubbing direction of the alignment film. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is disposed so as to be substantially orthogonal to the vertical axis. In the pair of transparent substrates, an alignment film for controlling the alignment of the liquid crystal molecules of the liquid crystal layer is disposed on a surface in contact with the liquid crystal layer,
Of the pair of polarizing plates, the absorption axis of one polarizer is substantially perpendicular to the rubbing direction of the alignment film on the polarizer side, and the absorption axis of the polarizer of the other polarizing plate is the rubbing direction of the alignment film. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is disposed so as to be substantially parallel to the liquid crystal display.

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