JP2007279146A - Viewing angle control filter and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a viewing angle control film capable of controlling a viewing angle while satisfactorily keeping display quality when viewing a screen of a display device from the front. <P>SOLUTION: The viewing angle control film 1 is made by stacking a polarizing plate 2 which converts transmitting light into linearly polarized light, and a liquid crystal film 3 in which liquid crystal molecules are oriented. Alignment direction of the liquid crystal molecules 5, when viewed from the normal direction of the liquid crystal film 3, is parallel or vertical to the linearly polarized light direction of light transmitted through the polarizing plate 2; and the major axis of the liquid crystal molecules 5 is inclined from the normal direction when viewed from the normal direction and the direction vertical to a flat plane which contains the alignment direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a viewing angle control filter capable of controlling a viewing angle and a display device including the viewing angle control filter.

  There are many opportunities to use electronic devices having displays such as mobile phones and mobile personal computers in public places. In this case, there has been a problem that confidential documents and information that the user wants to browse personally can be seen by surrounding people.

  In response to this problem, a display device that can normally be set to a wide viewing angle display mode and can be switched to the narrow viewing angle display mode when being taken out to a public place is realized. The narrow viewing angle mode is a mode in which a normal display image can be viewed from the front direction of the display and a plain image or another image can be viewed from an oblique direction.

  As the viewing angle control means in such a display device capable of controlling the viewing angle, for example, a viewing angle control element described in Patent Document 1 can be cited.

  However, in the configuration in which the viewing angle is controlled by using a viewing angle control element such as a liquid crystal molecule, there is a problem that the thickness of the display device increases and a mechanism for driving the panel including the viewing angle control element is complicated. Thus, there arises a problem that productivity is lowered and a light shielding performance is low.

  Therefore, a method of controlling the viewing angle by sticking a film on the screen of a display device has been developed. This film is generally called a privacy filter, and examples thereof include those described in Patent Document 2 and those commercially available from Sumitomo 3M Limited.

  Since the privacy filter described in Patent Document 2 transmits only light in a direction perpendicular to the privacy filter, the privacy filter cannot be seen from the lateral direction when the privacy filter is attached to the screen of the display device.

  The privacy filter manufactured by Sumitomo 3M Co. has a structure in which a micro louver film is laminated with a film such as PET, and is a louver film that controls the direction and visible angle of transmitted light.

  FIG. 6 shows a configuration of a louver film 50 manufactured by Sumitomo 3M, wherein (a) is a cross-sectional view of the louver film 50, and (b) is a plan view of the louver film 50. As shown in FIG. 6A, the louver film 50 has louver shading portions 51 arranged at a constant interval. The light emitted from the display device passes through the transmission part 52 that is a space between the louver light shielding parts 51. At this time, the transmission angle of transmitted light (α in FIG. 6A) is limited by the louver shading unit 51, and thus the viewing angle is limited.

  In an in-vehicle liquid crystal display device, in order to prevent a display from being reflected on a windshield when mounted on an actual vehicle, such a louver film is used to limit the light emission direction.

A method for manufacturing an optical anisotropic element used for improving the viewing angle characteristics of the display color of a twisted nematic liquid crystal display element is disclosed in Patent Document 3.
JP 2005-221756 (Publication date: August 18, 2005) JP 2005-173571 (release date: June 30, 2005) JP-A-6-222213 (release date: August 12, 1994)

  However, in the conventional louver film, since the transmitted light is limited by the louver light shielding part 51, light that is blocked by the louver light shielding part 51 and cannot be transmitted is generated, and the luminance of the screen viewed from the front is reduced. There arises a problem that the image quality deteriorates due to the problem or the streaks of the louver shading part 51.

  In addition, there is a problem that the left and right (or vertical) symmetrical viewing angles cannot be controlled in order to prevent interference between the louver shading part 51 and the TFT (Thin Film Transistor) panel. As shown in FIG. 6B, the extending direction of the louver shading unit 51 is not parallel to the vertical direction (or horizontal direction) of the screen of the display device but is arranged in an inclined state. This is because if the extending direction of the louver shading unit 51 is parallel to the vertical direction (or horizontal direction) of the screen of the display device, the moire fringes are generated at a specific period due to interference with the color filter of the liquid crystal display device. This is because.

  Therefore, it is difficult to control the viewing angle symmetrically (or vertically symmetrical) with respect to the screen of the liquid crystal display device.

  Further, the fact that the extending direction of the louver shading unit 51 is inclined with respect to the vertical direction (or horizontal direction) of the screen of the display device is one of the factors that deteriorate the image quality viewed from the front.

  Moreover, since the privacy filter described in Patent Document 2 transmits only light from the front direction, there is a problem that it is difficult to set a predetermined viewing angle including an oblique direction. In addition, when a plurality of sheets are used to improve the light shielding property, problems such as coloring in the front direction, a decrease in luminance, and an increase in thickness occur.

  The present invention has been made to solve the above-described problems, and its object is to provide a viewing angle control film capable of controlling the viewing angle without deteriorating image quality (front quality) when viewed from the front. And providing a display device including the same.

  In order to solve the above problems, the viewing angle control filter according to the present invention is formed by laminating a polarizing layer that converts transmitted light into linearly polarized light and a retardation layer in which liquid crystal molecules are arranged. When viewed from the normal direction of the retardation layer, the alignment direction of the liquid crystal molecules and the linear polarization direction of light transmitted through the polarizing layer are parallel or perpendicular, and the major axis of the liquid crystal molecules is When viewed from a direction perpendicular to the plane including the normal direction and the alignment direction, the film is inclined from the normal direction.

  According to the above configuration, since the polarization direction of the linearly polarized light transmitted through the polarizing layer and the alignment direction of the liquid crystal molecules when viewed from the normal direction of the retardation layer are parallel or perpendicular, the normal direction When viewed from above, birefringence does not occur in the retardation layer. Therefore, when a viewing angle control filter is arranged in a display device having polarizing means so that the linear polarization direction of light transmitted through the polarizing layer and the linear polarization direction of light transmitted through the polarization means of the display device are parallel to each other. The screen of the display device can be visually recognized.

  On the other hand, since the major axis of the liquid crystal molecules when viewed from a direction perpendicular to the plane including the normal direction and the alignment direction is inclined from the normal direction, this inclination angle is referred to as a predetermined angle. When viewed from a direction inclined by a predetermined angle or more from the normal direction (hereinafter referred to as viewed from an oblique direction), the alignment direction of the liquid crystal molecules has a crossing angle with the polarization direction of the light transmitted through the polarizing layer. . Therefore, when viewed from an oblique direction, birefringence occurs in the liquid crystal molecules, and the polarization direction of the light transmitted through the retardation layer changes. As a result, when the viewing angle control filter is arranged in the display device having the polarizing means as described above, the light transmitted through the phase difference layer cannot be transmitted through the polarizing means when viewed from an oblique direction. The screen of the device cannot be seen.

  According to such a configuration, since the viewing angle is controlled by utilizing the birefringence of liquid crystal molecules, the viewing angle is maintained in a state in which the display quality when the screen of the display device is viewed from the front is kept good. Can be controlled.

  Moreover, it is preferable that the said phase difference layer is pinched | interposed into the two said polarizing layers, and the linearly polarized light directions of the light which permeate | transmits the said two polarizing layers are mutually parallel.

  According to said structure, since one of the polarizing layers of a viewing angle control filter can be functioned as one of the polarizing means of a display apparatus, the thickness of a display apparatus can be reduced.

  The retardation layer is preferably composed of two layers, and the orientation directions of the two retardation layers are preferably orthogonal to each other.

  According to said structure, the control direction of a viewing angle can be made into two directions (for example, the left-right direction and an up-down direction) orthogonal to each other.

  Further, the display device includes the viewing angle control filter and the polarization unit, and the retardation layer is positioned between the polarization layer and the polarization unit, and is a straight line of light transmitted through the polarization layer. A display device in which the polarization direction is parallel to the linear polarization direction of the light transmitted through the polarization means is also included in the technical scope of the present invention.

  As described above, the viewing angle control filter according to the present invention is formed by laminating a polarizing layer that converts transmitted light into linearly polarized light and a retardation layer in which liquid crystal molecules are arranged. When viewed from the normal direction, the alignment direction of the liquid crystal molecules and the linear polarization direction of light transmitted through the polarizing layer are parallel or perpendicular, and the major axis of the liquid crystal molecules is the normal direction and When viewed from a direction perpendicular to a plane including the orientation direction, the structure is inclined from the normal direction.

  Therefore, by using the birefringence of the liquid crystal molecules, there is an effect that the viewing angle can be controlled in a state where the display quality when the screen of the display device is viewed from the front is kept good.

  One embodiment of the present invention will be described below with reference to FIGS.

(Basic configuration of viewing angle control film 1)
FIG. 1 is a cross-sectional view showing a basic configuration of a viewing angle control film 1 of the present embodiment. The viewing angle control film 1 has a configuration in which a polarizing plate 2 (polarizing layer) and a liquid crystal film 3 (retardation layer) are laminated.

  The viewing angle control film 1 is attached to the display screen via the adhesive 4 so that the liquid crystal film 3 side is adjacent to the display screen of the display device. In this configuration, the light emitted from the display device passes through the liquid crystal film 3 and then passes through the polarizing plate 2.

  Alternatively, the viewing angle control film 1 is disposed on the back side (side facing the direction opposite to the direction of light emitted from the display device) of the main liquid crystal display unit included in the liquid crystal display device.

  The liquid crystal film 3 is a film having liquid crystal molecules 5 oriented in a specific direction, and functions as an inclined retardation plate. The liquid crystal film 3 is, for example, an ultraviolet curable liquid crystal polymer. The alignment direction of the liquid crystal molecules 5 is uniaxial alignment (homogeneous), and when the liquid crystal film 3 is viewed from the front direction (the direction of the arrow 6 in FIG. 1, the z-axis direction), a certain direction (in FIG. 1). Oriented in the y-axis direction). The alignment direction of the liquid crystal molecules 5 is referred to as a liquid crystal alignment direction. In FIG. 1, the shape of the liquid crystal molecules 5 is a football type, but the shape of the liquid crystal molecules 5 is not limited to this.

  The front direction is a direction (normal direction) perpendicular to a plane including the viewing angle control film 1 (xy plane in FIG. 1).

  When viewed from the front direction, since the liquid crystal alignment direction of the liquid crystal molecules 5 is constant, the polarization state in the front direction is maintained as it is.

  Further, when the liquid crystal film 3 is viewed from a direction perpendicular to the plane including the front direction and the liquid crystal alignment direction (in FIG. 1, the direction of the arrow 10, the x-axis direction), the liquid crystal molecules 5 are in the front direction. The liquid crystal molecules 5 are arranged in a plurality of rows in parallel directions, and the angle of the liquid crystal molecules 5 with respect to the front direction (hereinafter referred to as an inclination angle θ) is about 45 °.

  Therefore, when the viewing angle control film 1 is viewed from an oblique direction inclined by an angle θ from the front direction, the liquid crystal film 3 functions as a ½λ plate (1/2 wavelength plate) and is viewed from an oblique direction. The polarization state is lost, and the screen of the display device is hardly visible. In other words, the liquid crystal film 3 functions as a retardation plate having a phase difference of (n · λ / 2: n = odd number) when viewed from an oblique direction. Here, λ means 550 nm to 589 nm. In addition, the above “approximately” means that a considerable effect is achieved within a range of ± 10%.

  When the tilt angle θ is set to 45 °, the polarization axis is twisted by 90 ° by the liquid crystal film 3. Therefore, when the transmission axis (or absorption axis) of the polarizing plate 2 described later is parallel to the liquid crystal alignment direction, a crossed Nicol state is obtained, and the shielding rate is maximized. In this case, when viewed from an angle inclined by 45 ° or more from the front direction of the viewing angle control film 1, the screen of the display device becomes completely dark. That is, the viewing angle of the viewing angle control film 1 is limited to a range tilted by 45 degrees in both directions perpendicular to the liquid crystal alignment direction (viewing angle control direction described later) with the front direction as the center.

  The inclination angle θ is not limited to 45 °, and may be any angle within the range of 0 ° to 90 °, but is preferably within the range of 30 to 45 °. For example, when the inclination angle θ is 30 °, the screen of the display device becomes completely dark when viewed from an angle inclined by 30 ° or more from the front direction of the viewing angle control film 1. The tilt angle θ may be set according to the application of the viewing angle control film 1.

  As the liquid crystal film 3, for example, the structure of a WV (wide view) film (trade name) made of Fuji Film or the structure of a film described in Patent Document 3 can be used as a basic structure.

  The polarizing plate 2 converts transmitted light into linearly polarized light. The polarization transmission axis (or absorption axis) of the polarizing plate 2 is parallel or perpendicular to the liquid crystal alignment direction of the liquid crystal molecules. That is. The polarization transmission axis of the polarizing plate 2 extends in the y-axis direction or the x-axis direction in FIG. In other words, the transmission axis of the polarizing plate 2 and the axis (slow axis or fast axis) of the liquid crystal film 3 as a phase difference plate are parallel or perpendicular.

  The transmission axis is an axis parallel to the linear polarization direction of the light transmitted through the polarizing plate 2.

(Viewing angle control direction of viewing angle control film 1)
The viewing angle control direction of the viewing angle control film 1 can be controlled in two directions if the liquid crystal film 3 is provided with one liquid crystal film 3.

  2 and 3 are schematic views showing the configuration of the viewing angle control film 1 and the viewing angle control direction. FIG. 2 shows a configuration including one liquid crystal film 3, and FIG. 3 shows a configuration including two liquid crystal films 3.

  As shown in FIG. 2 (a), when the viewing angle control film 1 includes one polarizing plate 2 and one liquid crystal film 3, as shown in FIG. 2 (b), the viewing angle control direction (arrow 7 direction) is one direction.

  The liquid crystal alignment direction of liquid crystal molecules 5 (the direction of arrow 8) and the transmission axis direction of polarizing plate 2 (the direction of arrow 9) are parallel to each other (parallel to the y-axis in FIG. 2B), and viewing angle control is performed. On the plane including the film 1, the viewing angle control direction is formed in a direction perpendicular to the liquid crystal alignment direction and the transmission axis direction (x-axis direction in FIG. 2B).

  As shown in FIG. 3A, when the viewing angle control film 1 includes one polarizing plate 2 and two liquid crystal films 3, the viewing angle control direction is set to 2 as shown in FIG. Direction (direction of arrows 7a and 7b). At this time, the first liquid crystal film 3a and the second liquid crystal film 3b are laminated between the polarizing plate 2 and the adhesive 4, and the liquid crystal alignment directions (arrows 8a and 8b) of the liquid crystal films 3a and 3b are aligned. They are arranged so as to be orthogonal to each other. The direction of the transmission axis of the polarizing plate 2 (the direction of the arrow 9) is parallel to the liquid crystal alignment direction of one liquid crystal film (the direction of the arrow 8a in FIG. 3B).

  In the viewing angle control film 1 having this configuration, directions perpendicular to the liquid crystal alignment directions of the two liquid crystal films 3 on the plane including the viewing angle control film 1 (the x-axis direction and the y-axis in FIG. 3B). Viewing angle control direction (arrows 7a and 7b).

(Effect of viewing angle control film 1)
Next, the effect of the viewing angle control film 1 will be described with reference to Table 1 below.

  Table 1 shows a result of comparison between a louver film (LCF) manufactured by Sumitomo 3M, a liquid crystal display device capable of controlling the viewing angle (bale view LCD), and a viewing angle control film 1 (present invention). In the table, Δ indicates that the performance is inferior, ○ indicates that the performance is excellent, and ◎ indicates that the performance is particularly excellent.

  Regarding the productivity, the viewing angle control film 1 is superior to the louver film and the bale view LCD. The reason why the productivity of the viewing angle control film 1 is superior to the bail view LCD is as described above. Moreover, the productivity of the viewing angle control film 1 is superior to that of the louver film. In the louver film, the process of forming the louver shading portion is complicated, whereas in the viewing angle control film 1, the productivity is particularly high. This is because a complicated manufacturing process is not included.

  Regarding the thickness of the display device, the viewing angle control film 1 can make the thickness of the display device thinner than the bail-view LCD, like the louver film. Furthermore, since the viewing angle control film 1 has only the polarizing plate 2 and the liquid crystal film 3, the viewing angle control film 1 can be made thinner than the louver film.

  Regarding the luminance reduction rate when the screen of the display device is viewed from the front, the viewing angle control film 1 is 15 to 20%, 20 to 30% of the louver film, and 20% to 50% of the bale view LCD. In comparison, the luminance reduction rate is low.

  Regarding the image quality (front quality) when the screen of the display device is viewed from the front, the viewing angle control film 1 does not affect the front quality, like the veil view LCD, whereas in the louver film, The front quality is reduced by the streaks of the louver shading part.

  Regarding the viewing angle, in the bail view LCD, a viewing angle of ± 60 ° to 30 ° can be realized by changing the voltage applied to the liquid crystal panel, whereas in the viewing angle control film 1 and the louver film, different viewing angles are achieved. By manufacturing a plurality of filters having an angle, it is possible to cope with various uses.

  As for the light shielding performance, the viewing angle control film 1 is superior to the bail-view LCD like the louver film.

  As for the moiré countermeasure, the louver film needs to take the moiré countermeasure as described above, but the viewing angle control film 1 and the bale view LCD do not need to.

  Judging comprehensively based on the above comparison results, it can be said that the viewing angle control film 1 is superior to the louver film and the bale view LCD. That is, the viewing angle control film 1 can control the viewing angle without reducing the brightness and image quality of the screen viewed from the front, and can suppress an increase in the thickness of the display device, and the viewing angle is symmetrical (or up and down). And a predetermined viewing angle including an oblique direction can be set.

(Example of change in configuration of viewing angle control film 1)
FIG. 4A is a cross-sectional view showing another configuration of the viewing angle control film 1. As shown in FIG. 4A, the viewing angle control film 1 may have a configuration in which the liquid crystal film 3 is sandwiched between two polarizing plates 2a and 2b. In this configuration, the transmission axes of the polarizing plate 2a and the polarizing plate 2b are parallel. The viewing angle control film 1 having this configuration has good productivity.

  The viewing angle control film 1 is disposed so that one of the polarizing plates 2a and 2b is adjacent to the display screen of the display device, or is disposed on the back side of the main liquid crystal display unit.

  FIG. 4B is a cross-sectional view showing still another configuration of the viewing angle control film 1. As shown in FIG. 4B, the viewing angle control film 1 is provided with polarizing plates 11 and 12 (polarizing means) for compensating a liquid crystal panel on the side of the liquid crystal film 3 opposite to the side in contact with the polarizing plate 2. It may be. This configuration is obtained by replacing one of the two polarizing plates 2 with the polarizing plate provided in the liquid crystal display device in the configuration shown in FIG. With this configuration, the thickness of the liquid crystal display device can be further reduced.

(Example of changing liquid crystal film 3)
FIG. 5A is a schematic diagram showing the structure of the liquid crystal film 3 including the liquid crystal molecules 5 having different inclination angles θ. As shown in FIG. 5A, the liquid crystal film 3 may include liquid crystal molecules 5 having different inclination angles θ. That is, the liquid crystal film 3 may have a hybrid tilt angle θ.

  For example, the liquid crystal molecules 5c near one surface of the liquid crystal film 3 are in a substantially parallel state (inclination angle θ is approximately 90 °) with respect to the xy plane, and the liquid crystal molecules 5a near the other surface of the liquid crystal film 3 are placed. Is inclined by approximately 30 ° with respect to the normal direction (z-axis direction) (the inclination angle θ is approximately 30 °), and the liquid crystal molecules 5b positioned between the liquid crystal molecules 5a and the liquid crystal molecules 5c are: It is good also as a state inclined in the range between 30 degrees and 90 degrees with respect to the normal line direction (state where inclination-angle (theta) is 30 degrees-90 degrees).

  In this case, the viewing angle of the viewing angle control film 1 is substantially determined by the average tilt angle of the liquid crystal molecules 5a, 5b, and 5c.

  FIG. 5B is a schematic view showing the structure of the liquid crystal film 3 including the liquid crystal molecules 5 having different shapes. As shown in FIG. 5B, the liquid crystal molecules 5 may be discotic liquid crystals 5d (liquid crystal molecules). That is, the liquid crystal molecules 5 may have a flat cylindrical shape. The tilt angles θ of the discotic liquid crystals 5d may be all aligned or the hybrid type described above.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in the embodiments are also included. It is included in the technical scope of the present invention.

  Since the viewing angle can be controlled by a thin and simple structure film, it can be applied to a display of a portable electronic device such as a portable communication terminal, a mobile personal computer, an AV device, a DVD player, and an in-vehicle LCD.

It is sectional drawing which shows the basic composition of the viewing angle control film of one Embodiment. The structure of a viewing angle control film provided with one liquid crystal film is shown, (a) is sectional drawing which shows the structure of a viewing angle control film, (b) is a top view which shows a viewing angle control direction. The structure of a viewing angle control film provided with two liquid crystal films 3 is shown, (a) is sectional drawing which shows the structure of a viewing angle control film, (b) is a top view which shows a viewing angle control direction. . (A) is sectional drawing which shows another structure of a viewing angle control film, (b) is sectional drawing which shows another structure of a viewing angle control film. (A) is schematic which shows the structure of the liquid crystal film containing the liquid crystal molecule which has different inclination | tilt angle (theta), (b) is schematic which shows the structure of the liquid crystal film containing the liquid crystal molecule which has a different shape. The structure of the conventional louver film is shown, (a) is sectional drawing of a louver film, (b) is a top view of a louver film.

Explanation of symbols

1 Viewing angle control film 2 Polarizing plate (polarizing layer)
2a Polarizing plate (polarizing layer)
2a Polarizing plate (polarizing layer)
2b Polarizing plate (polarizing layer)
3 Liquid crystal film (retardation layer)
3b Liquid crystal film (retardation layer)
5 Liquid crystal molecules 5a Liquid crystal molecules 5b Liquid crystal molecules 5c Liquid crystal molecules 5d Discotic liquid crystals (liquid crystal molecules)
11 Polarizing plate (polarizing means)
12 Polarizing plate (polarizing means)

Claims (4)

A polarizing layer that converts transmitted light into linearly polarized light;
A phase difference layer in which liquid crystal molecules are arranged is laminated,
The alignment direction of the liquid crystal molecules when viewed from the normal direction of the retardation layer and the linear polarization direction of light transmitted through the polarizing layer are parallel or perpendicular,
The viewing angle control filter, wherein the major axis of the liquid crystal molecule is inclined from the normal direction when viewed from a direction perpendicular to a plane including the normal direction and the alignment direction.   2. The viewing angle control filter according to claim 1, wherein the retardation layer is sandwiched between the two polarizing layers, and linear polarization directions of light transmitted through the two polarizing layers are parallel to each other. .   The viewing angle control filter according to claim 1, wherein the retardation layer includes two layers, and the orientation directions of the two retardation layers are orthogonal to each other. A display device comprising the viewing angle control filter according to claim 1 and polarizing means,
The retardation layer is located between the polarizing layer and the polarizing means,
A display device, wherein a linear polarization direction of light transmitted through the polarizing layer and a linear polarization direction of light transmitted through the polarizing means are parallel to each other.

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