JP2005141070A - Viewing angle compensating plate and liquid crystal display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a viewing angle compensating plate which can expand a viewing angle of a transmission mode in a semi-transmission type liquid crystal display and a liquid crystal display device using it. <P>SOLUTION: The viewing angle compensating plate for a liquid crystal display having discotic liquid crystal aligned in a hybrid state is characterized in that it has a discotic liquid crystal layer whose discotic liquid crystal is aligned in the hybrid state so that the tilt angle of a director of the discotic liquid crystal becomes larger at the boundary of the side of a liquid crystal display device than at the boundary of the other side and also the inclined direction of the director of the discotic liquid crystal becomes roughly parallel with that of the director of liquid crystal for display in the liquid crystal display device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a viewing angle compensator for enlarging a viewing angle in a transmissive mode (when a backlight is lit) in a transflective liquid crystal display device, and a liquid crystal display device using the same.

  The transflective liquid crystal display device is configured such that a reflective portion that performs display in a reflective mode (when the backlight is not lit) and a transmissive portion that performs display in a transmissive mode (when the backlight is lit) exist in one pixel. It has been done.

  As shown in FIG. 5, a general configuration of a transflective liquid crystal display device conventionally used includes a liquid crystal panel 34 in which a liquid crystal 33 is sealed between a pair of transparent substrates 31 and 32, and the liquid crystal A first retardation plate 35 and a second retardation plate 36 disposed on both front and rear sides of the panel 34, a pair of polarizing plates 37 and 38 disposed on both front and rear sides of the pair of retardation plates 35 and 36, and the rear A reflective film 42 is formed on a part of the transparent substrate 32 so that a part of the liquid crystal panel 34 becomes a reflection part 40. The remaining part where the film 42 is not formed is configured to be the transmission part 41.

  A reflective film 42 that serves as a reflecting mirror is usually provided in the liquid crystal panel 34 at the reflecting portion 40. In some cases, the reflective film is disposed outside the liquid crystal panel 34 (for example, between the liquid crystal panel 34 and the second retardation film 36).

  The retardation plates 35 and 36 are obtained by bonding at least one, usually two retardation plates.

  In the transflective liquid crystal display device configured as described above, a special so-called viewing angle compensator is provided at the position of the second retardation plate 36 on the backlight 39 side in order to further widen the viewing angle of the transmission mode. A method of installing a kind of retardation plate is common.

  For example, in such a transflective liquid crystal panel, it has been proposed to install a viewing angle compensator with a refractive index main axis inclined from the normal direction of the panel on the backlight side (see, for example, Patent Document 1).

  In the normally white mode, a voltage is applied to the liquid crystal layer to display black. At this time, since the liquid crystal molecules rise from the substrate surface, the change in retardation of the liquid crystal layer when the viewing direction is tilted away from the panel normal is large. Therefore, if the line of sight is tilted, light leaks even when black is displayed, and the viewing angle is narrow (in the case of the semi-transmissive type, the viewing angle is generally defined by the viewing angle at which the contrast ratio is 5). Is).

  The compensation plate described in Patent Document 1 as described above works (compensates) to cancel the rise of the retardation of the liquid crystal molecules, so that the change in retardation when the line of sight is tilted is reduced and black light leakage occurs. Improves and widens the viewing angle.

  In the transmissive liquid crystal panel, a viewing angle compensator (product name: WV film: Fuji) is a hybrid type (an orientation in which the rising angle (tilt angle) of the discotic liquid crystal molecules for compensation differs between the front side and the back side of the compensator). A wide viewing angle can be obtained by attaching Photo Film Co., Ltd.) to both sides of the panel.

  When a voltage is applied, the liquid crystal molecules do not rise uniformly, but at the interface of the substrate, they are almost parallel to the substrate surface and rise gradually from there toward the inside of the panel (most up near the center of the panel). By using a hybrid type in which the tilt angle of the discotic liquid crystal for compensation is changed so as to correspond to the change in the rising angle of the liquid crystal molecules, and further sticking to both sides of the panel, the compensation effect can be increased (for example, Non-patent document 1).

  Patent Document 2 discloses a viewing angle compensator using a rod-like nematic liquid crystal aligned in a hybrid orientation as a compensating liquid crystal, and a transflective liquid crystal panel using the viewing angle compensator. Retardation compensation is performed by reversing the rising direction of liquid crystal molecules in the panel and the rising direction of liquid crystal molecules for compensation.

JP 2000-258769 A JP 2003-156622 A H. Mori, Y. Ito, Y. Nishiura, T. Nakamura and Y. "SID'97 digest" co-authored by Shinagawa (Publisher: Society for Information Display, May 1997, 941-944)

  In the case of a transmissive liquid crystal display device, a viewing angle compensator that can clearly define the refractive index principal axis as in Patent Document 1 has insufficient compensation effect, and a hybrid alignment type viewing angle compensator is necessary. "SID'03 digest" by H. Mori, H. Nagai, H. Nakayama, Y. Ito, K. Kameda, K. Arakawa, and K. Kawata (publisher: Society for Information Display (Society for Information) Display), published in May 2003, pages 1058-1061)).

  As a hybrid alignment type viewing angle compensator, a WV film (Fuji Photo Film Co., Ltd.) using a discotic liquid crystal as a compensation liquid crystal, and an NH film (Nippon Mitsubishi Corp.) using a rod-like nematic liquid crystal are used. ) However, since the uniformity of retardation in the film surface is inferior to that of the WV film, the NH film has a problem that it is visually recognized as display unevenness especially when the screen size is large. On the other hand, the WV film is originally intended for a large transmissive liquid crystal monitor, and there is no such problem. Therefore, a WV film using a hybrid aligned discotic liquid crystal is preferable as the viewing angle compensator.

  However, in the case of a transflective type, if a compensation plate is arranged on the user side like a transmissive liquid crystal panel, this compensation plate affects the polarization state even in the reflection mode. Not possible, only on the backlight side. Further, a phase difference plate is installed on the user side for the reflection mode, and the optical design is different from that of the transmission side display device. For this reason, the method of installing the compensation plate that maximizes the compensation effect differs between the transflective type and the transmissive type.

  The present invention has been made to solve such a problem, and provides a viewing angle compensator capable of expanding the viewing angle of a transmission mode in a transflective liquid crystal display device and a liquid crystal display device using the same. With the goal.

  In the present invention, the hybrid type viewing angle compensator has a tilt angle of the discotic liquid crystal for compensation (the angle between the normal direction of the “dish” of the discotic liquid crystal and the substrate surface) at the interface on the panel side. It arrange | positions so that it may become small at the board side interface.

That is, the viewing angle compensator of the present invention is a viewing angle compensator for a liquid crystal display device having a discotic liquid crystal in a hybrid orientation,
Having a discotic liquid crystal layer that is hybrid-aligned so that the tilt angle of the director of the discotic liquid crystal is larger at the interface on the liquid crystal display device side than the other interface;
In addition, the tilt direction of the director of the discotic liquid crystal is substantially parallel to the tilt direction of the director of the display liquid crystal in the liquid crystal display device.

The liquid crystal display device of the present invention comprises a pair of substrates and a display liquid crystal layer sandwiched between the pair of substrates and oriented substantially parallel to and substantially parallel to the substrate surface. A liquid crystal panel having a reflective portion;
A pair of polarizing plates disposed on both sides of the liquid crystal panel;
At least one phase difference plate disposed between the polarizing plate and the liquid crystal panel;
The viewing angle compensator according to claim 1, wherein the viewing angle compensator is disposed between a polarizing plate on a back surface of the liquid crystal panel and the liquid crystal panel.

  According to the present invention, the viewing angle in the transmission mode can be expanded by attaching the viewing angle compensation plate to the transflective liquid crystal panel.

  Next, the viewing angle compensator of the present invention and the liquid crystal display device using the same will be described in more detail with reference to the drawings.

In this embodiment, a brief explanation of the compensation effect by the hybrid aligned discotic liquid crystal is displayed in a semi-transmissive and mainstream homogeneous alignment (uniformly aligned within the panel and substantially parallel to the substrate surface). For example, the liquid crystal layer is used (see Non-Patent Document 1). FIG. 3 shows a schematic diagram of the orientation of the liquid crystal molecules M ₁ in the liquid crystal panel and the orientation of the compensating discotic liquid crystal M ₂ in a state where black is displayed by applying a voltage.

Consider the case where light travels in the paper. The rod-shaped liquid crystal for display in the panel has the main refractive index ne in the director direction (the main vector of the refractive index main axis that faces the main axis direction where the main refractive index is the extraordinary light refractive index ne is called the director). The compensation discotic liquid crystal has a main refractive index ne in the director direction smaller than the other main refractive index no. Therefore, as shown in FIG. 3, the direction of inclination of the director of the display-like liquid crystal M ₁ (the direction of projection of the director onto the substrate surface is defined as the direction of inclination), and the inclination of the discotic liquid crystal M ₂ for compensation. When the discotic liquid crystal layer is arranged so that the direction is parallel, the retardation of the discotic liquid crystal (the product of the difference in refractive index with respect to the intrinsic polarization and the distance through which light passes) works to cancel the retardation of the rod-like liquid crystal. In practice, complete cancellation is not achieved, but the overall retardation of the system is smaller than when no compensating discotic liquid crystal is provided. Therefore, the retardation change when the line of sight is tilted is reduced, the light leakage when displaying black is improved, and the viewing angle is widened.

  The change in the polarization state due to the liquid crystal can be expressed mathematically by a matrix (called the Jones matrix). In the case of FIG. 3, since one of the main refractive index directions of the liquid crystal (both rod-shaped and discotic) is always oriented in the direction perpendicular to the paper surface, the intrinsic polarization state is linearly polarized light in the same direction everywhere in the system. Therefore, if this linearly polarized light is taken as a basis, the Jones matrix becomes a diagonal matrix everywhere in the system. Since the diagonal matrix is commutative, the result will not change even if it is replaced. In other words, even if the discotic liquid crystal layer for compensation is reversed, the compensation effect does not change (however, in the case of the twisted-nematic (TN) orientation, which is the mainstream of transmissive liquid crystal display elements) Since the direction of the director of the rod-shaped liquid crystal for the use is twisted between the upper and lower substrates, the direction of the intrinsic polarization changes. Therefore, if the discotic liquid crystal layer for compensation is reversed, the compensation effect also changes).

  Usually, the compensating discotic liquid crystal layer is used by being attached to a support such as a thin resin film. As this support, a film having a small retardation such as triacetylcellulose (TAC) is used. However, since the retardation is not completely zero, it functions as a retardation plate and affects the viewing angle. However, if the support is installed so that one of the principal axes of the refractive index is perpendicular to the paper surface, the influence on the viewing angle is the same regardless of the location selected.

In summary, the following three conclusions can be drawn.
-A viewing angle is widened by forming a pair of a rod-shaped liquid crystal and a compensating discotic liquid crystal that are raised by applying a voltage to compensate for retardation.
・ The way of pairing does not depend on the order.
-The support of the discotic liquid crystal layer for compensation affects the viewing angle, but it does not matter where the support is.

  The above description is a case where the liquid crystal panel is viewed from the rising direction of the liquid crystal (the direction in the drawing in FIG. 3). Next, consider a case where light travels in a plane perpendicular to the rising direction, that is, in a plane perpendicular to the paper surface in FIG. A schematic diagram of the orientation of the liquid crystal molecules in the panel and the orientation of the compensating discotic liquid crystal in this case is shown in FIG. 4 (light travels in the paper in FIG. 4).

Also in this case, retardation cancellation occurs in the pairs P _{1 to} P ₆ as shown in the figure, and the viewing angle is expanded as compared with the case where there is no compensation discotic liquid crystal layer.

  However, unlike when viewed from the rising direction of the liquid crystal, the main refractive index direction of the liquid crystal (both rod-shaped and discotic) is not oriented in the direction perpendicular to the paper surface, so that the intrinsic polarization state differs depending on the system location. Therefore, if the intrinsic polarization at a certain location is taken as a basis, the Jones matrix at other locations is not represented by a diagonal matrix. Since general matrices are non-commutative, changing the result will change the result. That is, when viewed from the direction perpendicular to the rising direction of the liquid crystal, the compensation effect changes when the compensating discotic liquid crystal layer is reversed.

When disposing the compensating discotic liquid crystal M ₂ on both sides of the display rod-shaped liquid crystal M ₁ as shown in FIG. 4, the pairs P _{1 to} P ₆ are not arranged in order from the discotic liquid crystal adjacent to the panel. And effective compensation can not be obtained.

  Table 1 shows the results of examining the effect of the arrangement of the compensating discotic liquid crystal on the viewing angle characteristics of the transmissive TN panel, which is the mainstream of the transmissive liquid crystal panel.

  In a transmissive liquid crystal panel, the viewing angle is generally defined by the angle from the panel normal in the viewing direction where the contrast ratio (the brightness of white display divided by the brightness of black display) is 10. This definition was adopted. The “direction” in the table is a direction in which the direction of the line of sight is tilted, and for example, “left” is a viewing angle when the panel is viewed from the left side.

  It can be seen that when the arrangement of the compensating discotic liquid crystal is properly arranged so as to form a pair of the display rod-like liquid crystal and the compensating discotic liquid crystal, the viewing angle is widened in the horizontal direction. This is because, as briefly discussed above, when the viewing angle compensator is arranged so as to form a pair of the display rod-like liquid crystal and the compensating discotic liquid crystal, compensation works effectively.

  In the case of the transflective type, the compensation plate cannot be attached to both sides of the panel as in the case of the transmissive type. Since compensation is performed only on the backlight side, the viewing angle compensation plate is attached to both sides of the display element. A beautiful pair cannot be made. In the transflective type, a phase difference plate is used separately from the viewing angle compensation plate. For this reason, the correct arrangement of the viewing angle compensators cannot be determined by simple considerations such as the transmission type.

  For the reasons described above, the orientation of the discotic liquid crystal layer needs to be examined when the transflective mode is widened. However, there have been no reports of such studies in the past.

In summary, the following three conclusions can be drawn.
The viewing angle is widened by forming a pair of a rod-like liquid crystal that has risen when a voltage is applied and a compensating discotic liquid crystal to compensate for retardation.
-Since the way of pairing depends on the arrangement order, it is necessary to consider the direction of the compensating discotic liquid crystal layer.
-Since the support of the discotic liquid crystal layer for compensation affects the viewing angle and depends on where the support is, it is necessary to consider where to place the support.

  In other words, when using a viewing angle compensator that uses a discotic liquid crystal that is hybrid-aligned in the compensation liquid crystal layer in order to increase the viewing angle of the transmission mode of the transflective liquid crystal panel, the viewing angle in the horizontal direction is These optimizations are necessary because they depend on the orientation of the compensating discotic liquid crystal layer and the location of the support.

  Currently, the only viewing angle compensator that uses a discotic liquid crystal hybrid-aligned with a compensation liquid crystal layer available as a commercial product is a WV film (trade name, manufactured by Fuji Photo Film Co., Ltd.). The WV film is a TAC film on the support layered with a hybrid alignment discotic liquid crystal layer, and the tilt angle of the discotic liquid crystal on the TAC side (the rising angle of the director from the substrate plane) is compensated for viewing angle. It is a board.

When the orientation of the discotic liquid crystal layer is changed, the position of the TAC as the support automatically changes. Therefore, there are the following two combinations of the orientation of the discotic liquid crystal layer and the position of the TAC to be examined.
-The tilt angle of the discotic liquid crystal is larger on the liquid crystal panel side than on the polarizing plate side. At this time, the TAC is located between the discotic liquid layer and the panel. The tilt angle of the discotic liquid crystal is smaller on the liquid crystal panel side than on the polarizing plate side. At this time, the TAC is located between the discotic liquid layer and the polarizing plate.

Embodiment 1
The panel configuration of the transflective liquid crystal display device according to the present embodiment shown in FIG. 1 includes a liquid crystal panel 4 in which liquid crystal 3 is sealed between a pair of transparent substrates 1 and 2, and both front and rear sides of the liquid crystal panel 4. The four phase plates arranged, that is, the first phase plate 5, the second phase plate 6, the third phase plate 7 and the fourth phase plate 8, and the four phase plates 5-8. A pair of polarizing plates 9 and 10 disposed on both front and rear sides, and a backlight 11 disposed on the rear side of the polarizing plate 10 on the rear side, and the inner surface of the transparent substrate 2 with a part of the liquid crystal panel 4 as a reflecting portion A reflection film (not shown) is formed on the side, and the remaining portion where the reflection film is not formed is configured as a transmission part. Further, between the liquid crystal panel 4 and the third retardation plate 7 on the rear side. Is provided with a viewing angle compensator 14 comprising a support 12 and a compensating discotic liquid crystal layer 13. It is.

For the viewing angle compensation plate 14, a commercially available WV film (trade name, manufactured by Fuji Photo Film Co., Ltd.) for transmissive TN panels is used. As shown in FIG. 1, the WV film was placed so that the support 12 made of a TAC film was on the liquid crystal panel 4 side. In this case, as shown in FIG. 2, the tilt angle θ _c of the compensating discotic liquid crystal 13 is larger on the liquid crystal panel 4 side than on the polarizing plate 10 side.

  The front (inside the compensation plate) retardation Re of the WV film was about -35 nm, the retardation Rth in the thickness direction was about 156 nm, and the average tilt angle was about 19 °. The value of Re is negative because the discotic liquid crystal of the WV film generates retardation in a direction orthogonal to the tilt direction of the discotic liquid crystal.

  Two user-side phase difference plates, the first and second phase difference plates 5 and 6, are used for the following reason. Retardation depends on the wavelength (called dispersion), but the dispersion is different between the retardation plate (transparent resin such as polycarbonate is generally used) and the liquid crystal material, so when there is only one retardation plate, If the optical properties are optimized at a certain wavelength, it will deviate from the optimum conditions at other wavelengths. Therefore, the contrast ratio is reduced due to white display coloring and black display light leakage. It is known that by combining two retardation plates, optical properties can be optimized in a wide wavelength range by bringing the dispersion of retardation of the combined retardation plates close to the dispersion of the liquid crystal material (Japanese Patent Laid-open No. Hei. 10-68816). Usually, the first retardation plate 5 is 200 to 300 nm, and the second retardation plate 6 is 80 to 140 nm.

  The reason why two retardation plates on the backlight side are used as the third and fourth retardation plates 7 and 8 is the same reason. However, since the viewing angle compensation plate 14 (WV film) also has retardation Re, the total retardation with the retardation plate 7 is set to 80 to 140 nm.

  The retardation values of the respective retardation plates 5 to 8 (manufactured by Sumitomo Chemical Co., Ltd.) are as shown in Table 2.

  The retardation of the liquid crystal layer of the liquid crystal panel was 320 nm, and the liquid crystal layer was homogeneously aligned (aligned uniformly in the panel and substantially parallel to the substrate surface). The tilt direction of the director of the liquid crystal for display was made parallel to the tilt direction of the director of the discotic liquid crystal for compensation, and this direction was set as the downward direction of the panel.

Comparative Example 1
In the configuration of the first embodiment, the direction of application of the WV film was set upside down so that the TAC side came to the polarizing plate side. In this case, the tilt angle of the compensating discotic liquid crystal is smaller on the liquid crystal panel side than on the polarizing plate side.

Table of Viewing Angle Comparison Table 3 shows the viewing angles of Embodiment 1 and Comparative Example 1. In the case of a transflective liquid crystal display element, since the viewing angle is generally defined by the angle from the panel normal in the viewing direction where the contrast ratio is 5, this definition is also adopted in Table 3. The “direction” in Table 3 is the direction in which the direction of the line of sight is tilted, and for example, “left” is the viewing angle when the panel is viewed from the left side.

  As described above, the viewing angle compensator of the present invention, i.e., the discotic liquid crystal layer in which the tilt angle of the director of the discotic liquid crystal is hybrid-aligned so that the interface on the liquid crystal display device side is larger than the other interface. A liquid crystal for display having a viewing angle compensator having a homogeneous orientation with a viewing angle compensator characterized in that the direction of inclination of the director of the discotic liquid crystal is substantially parallel to the direction of inclination of the director of the liquid crystal for display in the liquid crystal display device By arranging the transflective liquid crystal display element having a layer between the polarizing plate on the back of the panel (opposite to the user) and the liquid crystal panel, the viewing angle is widened in the left-right direction.

It is a section explanatory view showing one embodiment of a liquid crystal display provided with a viewing angle compensator of the present invention. It is explanatory drawing for demonstrating the tilt angle of the discotic liquid crystal for compensation of FIG. It is explanatory drawing for demonstrating typically the orientation of the liquid crystal molecule of a liquid crystal panel in a general transmissive liquid crystal panel, and the orientation of a discotic liquid crystal molecule for compensation, and it looked at the panel from the rising direction of the liquid crystal molecule It is explanatory drawing in the case. It is explanatory drawing for demonstrating typically the orientation of the liquid crystal molecule of a liquid crystal panel and the orientation of a discotic liquid crystal molecule for compensation in a general transmission type liquid crystal panel, Comprising: From the direction perpendicular to the rising direction of a liquid crystal molecule It is explanatory drawing at the time of seeing a panel. It is sectional explanatory drawing of a general transflective liquid crystal display device.

Explanation of symbols

4 LCD panel
5 First retardation plate
6 Second retardation plate
7 Third retardation plate
8 Fourth retardation plate 9, 10 Polarizing plate 11 Backlight 12 Support 13 Compensating discotic liquid crystal 14 Viewing angle compensation plate

Claims (2)

A viewing angle compensator for a liquid crystal display device having a discotic liquid crystal in a hybrid orientation,
Having a discotic liquid crystal layer that is hybrid-aligned so that the tilt angle of the director of the discotic liquid crystal is larger at the interface on the liquid crystal display device side than the other interface;
A viewing angle compensator, wherein the direction of inclination of the director of the discotic liquid crystal is substantially parallel to the direction of inclination of the director of the liquid crystal for display in the liquid crystal display device. A pair of substrates and a liquid crystal panel that is sandwiched between the pair of substrates, and is composed of a display liquid crystal layer that is aligned substantially parallel to the substrate surface and uniformly, and has a transmissive portion and a reflective portion in one pixel;
A pair of polarizing plates disposed on both sides of the liquid crystal panel;
At least one phase difference plate disposed between the polarizing plate and the liquid crystal panel;
2. A liquid crystal display device comprising: a viewing angle compensation plate according to claim 1, which is disposed between a polarizing plate on a back surface of the liquid crystal panel and the liquid crystal panel.

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