JP2008020859A - Viewing angle control sheet and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To give a viewing angle restricting function comparable to an already available louver film to a viewing angle control sheet, and to prevent occurrence of moire. <P>SOLUTION: A liquid crystal display device 1 includes a liquid crystal panel 10 for display and the viewing angle control sheet 20. The viewing angle control sheet 20 includes a retardation plate 21 between an upper polarizing plate 22 of the control sheet and a lower polarizing plate 23 of the control sheet. The retardation plate 21 is formed by laminating a plurality of kinds of retardation plates with mutually different refractive indexes. In the viewing angle control sheet 20, either one of a retardation value Re of a white display region of the display device and a retardation value Re of a black display region satisfies nλ/2-λ/4<Re<nλ/2+λ/4 and the other one satisfies nλ-λ/4<Re<nλ+λ/4 (wherein n is an integer of ≥1) by combining the polarizing plates 22, 23 and the retardation plate 21. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a viewing angle control sheet that narrows the viewing angle of a display device, and a display device including the viewing angle control sheet.

  In general, a display device is required to have a viewing angle as wide as possible so that a clear image can be seen from any viewing angle.

  However, depending on the usage environment, it may be more convenient for the viewing angle to be narrow so that only the user himself can view the display content. In particular, a notebook personal computer, a portable information terminal (PDA: Personal Data Assistant), a mobile phone, or the like is highly likely to be used in a place where an unspecified number of people can exist, such as in a train or an airplane. In such a use environment, it is desirable that the viewing angle of the display device is narrow because it is not desirable to look into the display contents from other people in the vicinity from the viewpoint of maintaining confidentiality and protecting privacy.

  In response to such a demand, for example, as described in Patent Document 1, a visual field control sheet in which a louver-like light absorption wall array is formed inside a transparent substrate and the transmittance is changed depending on the incident angle of light. (Generally called a louver film) has been proposed.

As shown in FIG. 7, the visual field control sheet disclosed in Patent Document 1 is formed by laminating a louver-like film 102 on the upper side of a liquid crystal panel 101 having a liquid crystal cell 111 made of TN liquid crystal. As shown in FIG. 8, the louver-like film 102 includes a base 121 made of a light-transmitting material and a louver-like light-absorbing wall row 122 made of a light-absorbing material, and the louver-like light made of the light-absorbing material. The absorption wall row 122 has a refractive index lower than that of the base member 121 made of the light transmissive material. In the louvered film 102, the emission of light having a specific incident angle or more is prevented. Therefore, a visual field control sheet that exhibits a peeping prevention effect can be realized. Therefore, if such a louver film is used, it is possible to prevent a display content from being peeped by another person on a cellular phone or a bank ATM.
JP 2000-137294 A (published May 16, 2000) “Nitto Denko Technical Report” 84 (Vol.41), 26-29, 2003

  However, when the viewing angle of the display device is limited by using the louver film as described in the above-mentioned conventional patent document 1, light interference occurs due to the picture element arrangement of the display panel and the louver film periodic structure, and In other words, interference fringes, so-called moire, are generated, and the quality of the displayed image is deteriorated. Moreover, in order to prevent visual recognition from more directions, it is possible to use a plurality of louver films as described above. However, if a plurality of louver films are stacked, the generation of moire becomes even worse. The quality of the is greatly impaired.

  The present invention has been made in view of the above-described problems, and its object is to have a viewing angle limiting function equivalent to that of an existing louver film and to prevent the occurrence of moire. And providing a display device using the same.

  In order to solve the above problems, at least one display device according to the present invention is disposed on at least one of a display panel for displaying an image and a front surface or a back surface of the display panel, and has a viewing angle of the display panel. A viewing angle control sheet that is narrower than a viewing angle of the display device, the viewing angle control sheet including at least one polarizing plate and at least one retardation plate, Either one of the retardation value Re of the display unit and the retardation value Re of the black display unit is nλ / 2−λ / 4 <Re <nλ / 2 + λ / 4 (n is an integer of 1 or more), The other is characterized in that nλ−λ / 4 <Re <nλ + λ / 4 (n is an integer of 1 or more).

  In the display device of the present invention, as described above, one of the retardation value Re of the white display portion and the retardation value Re of the black display portion is nλ / 2−λ / 4 <Re <nλ / 2 + λ / 4. (N is an integer of 1 or more) and the other is nλ−λ / 4 <Re <nλ + λ / 4 (n is an integer of 1 or more), and the polarizing plate and the retardation plate in the viewing angle control sheet Is set. Thereby, a good white display is obtained in the white display portion that is a visible region, while a good black display is obtained in the black display portion that is a non-visible region and the display cannot be peeked. It becomes. That is, by using the viewing angle control sheet as described above, it is possible to have a viewing angle limiting function equivalent to that of an existing louver film and to prevent the occurrence of moire.

  Therefore, according to the display device of the present invention provided with the viewing angle control sheet as described above, visual recognition from a predetermined direction can be surely prevented, and a good image can be viewed from the visible direction. Can do.

  Here, the “white display portion” means an area where light can be transmitted and the display can be visually recognized, and the “black display portion” means an area where light is shielded and the display cannot be visually recognized. Therefore, the “white display portion” can be rephrased as a “viewing region”, and the “black display portion” can be restated as a “non-viewing region”. Further, here, the retardation value is a phase shift that occurs in the light that has passed through the viewing angle control sheet (more specifically, a phase that includes the phase of light traveling in the plane including the slow axis and the surface including the fast axis). It means the phase shift of the light traveling inside.

  In the display device of the present invention, one of the retardation value Re of the white display portion and the retardation value Re of the black display portion is nλ / 2 (n is an integer of 1 or more), and the other one is Nλ (n is an integer of 1 or more).

  According to said structure, the black display part of a display apparatus can be shielded more reliably, and the visual recognition from a predetermined direction can be prevented more reliably.

  In the display device of the present invention, the polarizing plate includes a first polarizing plate and a second polarizing plate, and at least one retardation plate is provided between the first polarizing plate and the second polarizing plate. Is preferably arranged.

  According to said structure, the display apparatus which becomes the above retardation values can be provided by changing the kind of phase difference plate.

  In the display device of the present invention, the polarization transmission axes of the first polarizing plate and the second polarizing plate are orthogonal to each other, and the retardation value Re1 of the white display portion is nλ / 2−λ / 4 < Re1 <nλ / 2 + λ / 4 (n is an integer of 1 or more), and the retardation value Re2 of the black display portion is nλ−λ / 4 <Re2 <nλ + λ / 4 (n is an integer of 1 or more). preferable.

  According to the above configuration, when the polarization transmission axes of the first polarizing plate and the second polarizing plate are orthogonal to each other, the black display portion of the display device is more reliably shielded from a predetermined direction. Can be more reliably prevented.

  In the display device of the present invention, the polarization transmission axes of the first polarizing plate and the second polarizing plate are parallel to each other, and the retardation value Re1 of the white display portion is nλ−λ / 4 <Re1 <. nλ + λ / 4 (n is an integer of 1 or more), and the retardation value Re2 of the black display portion is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4 (n is an integer of 1 or more). preferable.

  According to said structure, when each polarization transmission axis of a 1st polarizing plate and a 2nd polarizing plate is mutually parallel, the black display part of a display apparatus is shielded more reliably, from a predetermined direction. Can be more reliably prevented.

  In the display device of the present invention, it is preferable that a plurality of the retardation plates are provided so as to be stacked, and the retardation plates laminated to each other include those having different refractive indexes.

  According to said structure, the display apparatus which becomes the above retardation values can be provided using the existing phase difference plate.

  The display device of the present invention has, as the retardation plate, a positive A plate, a plurality of λ / 4 plates, three main refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other, nx > Nz> ny and a plurality of biaxial phase difference plates having a relationship of (nx−nz) /|nx−ny|=0.1, and 3 in the x, y, and z axis directions orthogonal to each other. A plurality of TAC plates having two main refractive indexes nx, ny, nz and a relationship of nx = ny> nz, and the TAC is between the first polarizing plate and the second polarizing plate. The plate, the biaxial retardation plate, the λ / 4 plate, the TAC plate, the positive A plate, the TAC plate, the λ / 4 plate, the biaxial retardation plate, and the TAC plate are laminated in this order. It is preferable.

  According to the above configuration, the two viewing angle areas of the display panel that are opposed to each other can be displayed in black, and a viewpoint that looks into these two areas (that is, two viewpoints that are opposed to the display panel (for example, Visual recognition from the right and left viewpoint)) can be reliably prevented.

  The viewing angle control sheet of the present invention is a viewing angle control sheet that is disposed on at least one of the back surface and the front surface of the display device and makes the viewing angle of the display device narrower than the original viewing angle. And a second polarizing plate, and a phase difference plate between the first polarizing plate and the second polarizing plate 3 in the x, y, and z axis directions orthogonal to each other. TAC plate having two main refractive indexes nx, ny, nz, and having a relationship of nx = ny> nz, having three main refractive indexes nx, ny, nz in the x, y, z axis directions orthogonal to each other, a plurality of biaxial retardation plates having a relationship of nx> nz> ny and (nx−nz) /|nx−ny|=0.1, the λ / 4 plate, the TAC plate, the positive A plate, The TAC plate, λ / 4 plate, biaxial retardation plate, and TAC plate are stacked in this order. And it is characterized in that they are.

  According to said structure, it has a viewing angle restriction | limiting function equivalent to the existing louver film, and generation | occurrence | production of a moire can be prevented. Furthermore, if the viewing angle control sheet of the present invention is used in a display device, two viewing angle regions on the display panel can be displayed in black, and a viewpoint (ie, a display panel) for peeking at these two regions. Can be reliably prevented from being viewed from two viewpoints facing each other (for example, a viewpoint in the left-right direction), and a good image can be seen from the visible direction.

  As described above, the display device of the present invention is a display device including a viewing angle control sheet that narrows the viewing angle of the display device from the original viewing angle, and the viewing angle control sheet includes at least one polarized light. And a retardation value Re of the white display part and a retardation value Re of the black display part of the display device, wherein nλ / 2−λ / 4 <Re < nλ / 2 + λ / 4 (n is an integer of 1 or more), and the other is nλ−λ / 4 <Re <nλ + λ / 4 (n is an integer of 1 or more).

  Therefore, according to the display device of the present invention, it is possible to reliably prevent visual recognition from a predetermined direction, and it is possible to see a good image in which the occurrence of moire is suppressed from the visible direction.

  The viewing angle control sheet of the present invention includes a first polarizing plate and a second polarizing plate, and a retardation plate is provided between the first polarizing plate and the second polarizing plate. The TAC plate, the biaxial retardation plate, the λ / 4 plate, the TAC plate, the positive A plate, the TAC plate, the λ / 4 plate, the biaxial retardation plate, and the TAC plate are laminated in this order. It is provided.

  Therefore, there is an effect that it has a viewing angle limiting function equivalent to that of an existing louver film and can prevent the occurrence of moire.

  Therefore, when the viewing angle control sheet of the present invention is used for a display device, it is possible to reliably prevent visual recognition from a predetermined direction, and it is possible to see a good image from a visible direction.

  An embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.

  First, the structure of the viewing angle control sheet 20 of this Embodiment is demonstrated based on FIG. The viewing angle control sheet 20 according to the present embodiment has a viewing angle of the display panel of the display device in order to prevent the display content from being viewed by others in the vicinity from the viewpoint of confidentiality protection and privacy protection. And the viewing angle (the viewing angle of the display device when the viewing angle control sheet is not provided). FIG. 1 is a cross-sectional view showing a schematic configuration of the viewing angle control sheet 20.

As shown in FIG. 1, the viewing angle control sheet 20 includes a retardation plate between a control sheet upper polarizing plate 22 (first polarizing plate) and a control sheet lower polarizing plate 23 (second polarizing plate). 21 is arranged. The control sheet polarizing plate 22 may be subjected to a diffusion treatment such as an AG treatment or an AR treatment on the surface thereof. The control sheet lower polarizing plate 23 is a so-called clear polarizing plate that is not subjected to surface treatment. In this embodiment, the polarized light transmission axis X ₂₂ of the control sheet on the polarizer 22, the polarized light transmission axis X ₂₃ of the control sheet under a polarizing plate 23 are orthogonal to each other. In the control sheet upper polarizing plate 22 and the control sheet lower polarizing plate 23, the configuration other than the above is not particularly limited, and a conventionally known polarizing plate used for a liquid crystal display panel or the like can be used.

  The phase difference plate 21 is formed by laminating a plurality of phase difference plates, and the types (that is, refractive indexes) of the laminated phase difference plates are different from each other.

  Specifically, the plurality of retardation plates are a positive A plate (positive A) 24, two λ / 4 plates 25a and 25b, two NEZs (trade name, refer to Non-Patent Document 1) 26a. 26b (biaxial retardation plate), these retardation plates are arranged in the order of NEZ26b, λ / 4 plate 25b, positive A24, λ / 4 plate 25a, NEZ26a from the lower polarizing plate 23 side of the control sheet. Has been.

  In addition to each of these phase difference plates, the phase difference plate 21 further includes four TAC films (TAC plates) 27a to 27d as phase difference plates. The TAC film 27a is between the positive A24 and the λ / 4 plate 25a, the TAC film 27b is between the positive A24 and the λ / 4 plate 25b, and the TAC film 27c is the control sheet upper polarizing plate 22 and the NEZ 26a. The TAC film 27d is provided between the control sheet lower polarizing plate 23 and the NEZ 26b.

  In other words, the viewing angle control sheet 20 of the present embodiment includes the control sheet lower polarizing plate 23, the TAC film 27d, the NEZ 26b, the λ / 4 plate 25b, the TAC film 27b, the positive A24, the TAC film 27a, and the λ / 4 plate 25a. , NEZ 26a, TAC film 27c, and polarizing plate 22 on the control sheet are stacked in this order. When the viewing angle control sheet 20 is provided in the liquid crystal display device, the control sheet upper polarizing plate 22 is disposed on the observer side, and the control sheet lower polarizing plate 23 is disposed on the backlight side in the liquid crystal display device. .

  Here, the characteristic of each said phase difference plate is demonstrated. In describing the characteristics of each phase difference plate, each phase difference plate has a thickness d as shown in FIG. 2A, and three main refractive indexes nx in the x, y, and z axis directions orthogonal to each other. , Ny, nz.

  2B shows the refractive index ellipsoids of NEZ 26a and 26b, FIG. 2C shows the refractive index ellipsoid of λ / 4 plates 25a and 25b, and FIG. 2D shows the positive A plate. (Positive A) A refractive index ellipsoid of 24 is shown.

  NEZ is a biaxial retardation plate having a relationship of nx> nz> ny and (nx−nz) /|nx−ny|=0.1. The λ / 4 plate is such that nx> nz> ny and the in-plane retardation value given by | nx−ny | · d is λ / 4 [nm] (380 nm <λ <780 nm). is there. The positive A plate has a relationship of nx> ny = nz. The TAC film has a relationship of nx = ny> nz, and generally has a retardation value given by | nx−nz | · d of 50 nm to 60 nm.

  Further, although not used in the retardation plate 21 according to the present embodiment, a negative C plate or the like can be cited as another retardation plate that can be used in the present invention. The negative C plate has a relationship of nx = ny> nz, and the retardation value given by | nx−nz | · d is generally 90 nm to 240 nm. Furthermore, as another phase difference plate, what is described in the nonpatent literature 1 is mentioned, for example.

  In the present invention, each retardation plate used for constituting the retardation plate 21 is not particularly limited as long as retardation values Re1 and Re2 described later can be obtained by combining a plurality of retardation plates. It is possible to use various retardation plates.

  Next, the arrangement direction of each retardation plate used in the viewing angle control sheet 20 will be described with reference to FIG. In describing the arrangement direction of each phase difference plate, first, the definition of the viewing angle with respect to the viewing angle control sheet 20 will be described. FIG. 4 is a schematic diagram illustrating the definition of the viewing angle with respect to the viewing angle control sheet 20 and explaining each viewpoint.

As shown in FIG. 4, the azimuth angle θ is a rotation angle of a line connecting a leg of a perpendicular line dropped from a viewpoint to a plane including the surface of the control sheet upper polarizing plate 22 and a center 22 c of the control sheet upper polarizing plate 22. It is. In FIG. 4, the azimuth angle θ increases counterclockwise when viewed from the upper side in the normal direction of the polarizing plate 22 on the control sheet with the azimuth angle in the direction of the viewpoint P ₁ (first viewpoint) as 0 °. Shall. In FIG. 4, the azimuth angle θ ₂ of the viewpoint P ₂ (second viewpoint) is 90 °, the azimuth angle θ ₃ of the viewpoint P ₃ (third viewpoint) is 180 °, and the viewpoint P ₄ (fourth viewpoint) is The azimuth angle θ ₄ is 270 °. The polar angle Φ is an angle formed by a straight line connecting the center 22c of the polarizing plate 22 on the control sheet and the viewpoint with the normal line of the polarizing plate 22 on the control sheet. Here, Φ _{1 to} Φ ₄ are all 45 °. To do. The viewpoint P ₅ (fifth viewpoint) is a viewpoint from the upper side in the normal direction of the upper polarizing plate 22 on the control sheet.

FIG. 3A is a schematic diagram showing the axial angles of each polarizing plate and each retardation plate. This axial angle coincides with the azimuth angle θ shown in FIG. In addition, since all the TAC films 27a to 27d constituting the retardation film 21 are arranged with an axis angle of 0 °, they are omitted in FIG. FIG. 3B is a table showing the in-plane retardation, thickness retardation, and axial angle of each polarizing plate and each retardation plate constituting the viewing angle control sheet 20. In the table shown in FIG. 3B, the in-plane phase difference is a phase difference (nm) (retardation) given by | nx−ny | · d, and the thickness phase difference is | nx−nz. The phase difference (nm) (retardation) given by | · d or | ny−nz | · d. The axis angle means the axis angle of the polarization transmission axes X ₂₂ and X ₂₃ in the case of a polarizing plate, and in the case of a phase difference plate, the nx axes X ₂₄ , X _25a , X _25b , The axis angle of _X26a and _X26b is meant.

Next, viewing angle characteristics when the viewing angle control sheet 20 having the above configuration is used by being attached to the front surface of a display panel of a display device that displays characters, images, and the like will be described. In addition, the structure which affixed the viewing angle control sheet | seat 20 on the front surface of the display panel of a display apparatus is contained in the display apparatus of this invention. FIGS. 5A and 5B show luminance distribution characteristics obtained when the liquid crystal display device is provided on the front surface of the display panel as an example of the display device. The polar angle (°) shown on the horizontal axis of the graph in FIG. 5B indicates the polar angle Φ toward the azimuth angle 0 ° direction by (+), and the polar angle Φ toward the azimuth angle 180 ° direction (− ). In FIG. 5A, L _{1 to} L ₈ have transmittances of 0.03, 0.07, 0.10, 0.14, 0.18, 0.21, 0.25, and It is an equipotential line showing the distribution of the viewing angle of 0.29.

As shown in FIGS. 5A and 5B, the viewing angle in the horizontal direction of the viewing angle control sheet 20 (directions where the azimuth angle θ is 0 ° and 180 °, also referred to as the left-right direction) is the conventional viewing angle. It can be seen that the viewing angle characteristics of the louver film are narrower than those of the viewing angle characteristics (for example, the viewing angle characteristics as shown in FIG. 1 of Patent Document 1). That is, it can be seen that visual recognition from the horizontal direction (in other words, visual recognition from two opposing viewpoints P ₁ and P ₃ ) can be limited to the same extent as compared with a conventional louver film. In this case, the Re values at the two viewpoints P ₁ and P ₃ are the retardation value Re2 of the black display portion (for example, nλ / 2−λ / 4 <Re2 <nλ / 2 + λ / 4 (n is an integer of 1 or more)). It becomes.

  More specifically, when the viewing angle control sheet 20 is used, as shown in FIGS. 5A and 5B, the azimuth angle θ is −60 ° to + 60 °, and the polar angle Φ is 45. The transmittance of the region where the angle is θ to 90 °, the azimuth angle θ is + 120 ° to + 240 °, and the polar angle Φ is 45 ° to 90 ° is 0.05 or less. Therefore, the display cannot be visually recognized in the above area.

  That is, the azimuth angle θ is −60 ° to + 60 ° (0 ° to 60 ° and 300 ° to 360 °), the polar angle Φ is 45 ° to 90 °, and the azimuth angle θ is + 120 ° to +240. In the region where the polar angle Φ is 45 ° to 90 °, the Re value is close to λ (that is, λ−λ / 4 to λ + λ / 4), and the display cannot be visually recognized “black display Part ". In other regions, the Re value is a value close to λ / 2 (that is, λ / 2−λ / 4 to λ / 2 + λ / 4). Become.

  The viewing angle characteristics shown in FIGS. 5A and 5B are those when the viewing angle control sheet 20 is used in a liquid crystal display device, but are almost the same when used in other display devices. Viewing angle characteristics can be obtained.

  As described above, according to the viewing angle control sheet 20 of the present embodiment, two opposing viewing angle regions of the display panel can be displayed in black, and a viewpoint that looks into these two regions (that is, a point of view) Visual recognition from two viewpoints facing the display panel (for example, viewpoints in the left-right direction) can be reliably prevented.

  Furthermore, since the viewing angle control sheet 20 performs narrow viewing angle control by combining a polarizing plate and a retardation plate instead of a louver film, it prevents moiré that occurs when a louver film is used. be able to.

  Some conventional louver films, such as a louver film manufactured by Sumitomo 3M Co., Ltd., have the louver shading plate shifted in the longitudinal direction in order to prevent the occurrence of moire. However, there is also a problem that a symmetrical viewing angle control effect cannot be obtained by shifting the longitudinal axis of the louver shading plate.

  In contrast, the viewing angle control sheet 20 of the present embodiment includes the retardation plate 21 having the above-described configuration between the control sheet upper polarizing plate 22 and the control sheet lower polarizing plate 23. As a result, as shown in FIGS. 5A and 5B, two opposing areas of the display panel can be displayed in black, and a symmetrical viewing angle control effect can be obtained.

In the viewing angle control sheet 20 according to the present embodiment, the polarization transmission axes X ₂₂ and X ₂₃ of the control sheet upper polarizing plate 22 and the control sheet lower polarizing plate 23 are orthogonal to each other. In this case, as described above, the retardation value Re1 of the white display portion of the display device is nλ / 2−λ / 4 <Re1 <nλ / 2 + λ / 4, and the retardation value Re2 of the black display portion is nλ−λ /. If 4 <Re2 <nλ + λ / 4, then shielding in the left-right direction can be realized. That is, Re1 only needs to be a value close to an integer multiple of λ / 2, and Re2 only needs to be a value close to an integer multiple of λ. Note that n is an integer of 1 or more (n = 1, 2, 3,...), And each n in Re1 and Re2 may be the same or different.

  In order to obtain better narrow viewing angle characteristics, the retardation values Re1 and Re2 are set to nλ / 2−λ / 8 <Re1 <nλ / 2 + λ / 8 and nλ−λ / 8 <Re2 <nλ + λ /, respectively. It is preferable that Re1 is set to nλ / 2, and Re2 is set to be as close as possible to nλ. Re1 = nλ / 2 and Re2 = nλ are further set. preferable. Here, all n are integers of 1 or more, and each n in Re1 and Re2 may be the same or different.

  In the present embodiment, the phase difference plate 21 is set so that each retardation value is as described above. Here, the “white display portion” means a portion where light can be transmitted and the display can be visually recognized, and the “black display portion” means a portion where light is shielded and the display cannot be visually recognized. To do. The retardation value means a phase shift between components of light that has passed through the phase difference plate. Further, the passing light here means light having a wavelength of 380 to 780 nm (visible light region) among light passing through the viewing angle control sheet.

  In the present invention, it is preferable to use a combination of a plurality of retardation plates having different refractive indexes. According to this, the viewing angle control sheet which has the above retardation values can be comprised using the existing phase difference plate.

  The retardation value as described above can be set by determining a region to be shielded and a region to be visually recognized at a narrow viewing angle, and simulating an optimal combination of a retardation plate and a polarizing plate.

Further, the viewing angle control sheet 20 of the present embodiment has a structure in which a retardation plate 21 having a configuration as shown in FIG. 1 is provided between a control sheet upper polarizing plate 22 and a control sheet lower polarizing plate 23. However, the present invention is not necessarily limited to such a configuration. However, in order to realize a state where a sufficient shielding effect is obtained at the viewpoints P ₁ and P ₃ shown in FIG. 4 (for example, a state having a transmittance distribution as shown in FIG. 5A), control is performed. Between the on-sheet polarizing plate 22 and the control-sheet lower polarizing plate 23, there is provided a retardation plate 21 including one or more types of retardation plates (retardation plates having different refractive indexes). Preferably it is. Here, the phase difference plate having different refractive indexes means a phase difference plate in which at least one of the three main refractive indexes nx, ny, and nz is different in the x, y, and z axis directions orthogonal to each other.

In the present embodiment, as an example of the viewing angle control sheet of the present invention, the polarization transmission axes X ₂₂ and X ₂₃ of the control sheet upper polarizing plate 22 and the control sheet lower polarizing plate 23 are substantially orthogonal to each other. Although described by way of example, the present invention is not limited to this. That is, the polarization transmission axes X ₂₂ and X _{23 of} the control sheet upper polarizing plate 22 and the control sheet lower polarizing plate 23 may be substantially parallel to each other.

  In this case, the retardation value Re1 of the white display portion of the display device is nλ−λ / 4 <Re1 <nλ + λ / 4, and the retardation value Re2 of the black display portion is nλ / 2−λ / 4 <Re2 <nλ / 2 + λ. If it is / 4 (where n is an integer equal to or greater than 1), the shielding in the left-right direction can be realized. That is, Re1 only needs to be a value close to an integer multiple of λ, and Re2 only needs to be a value close to an integer multiple of λ / 2.

  As described above, the retardation value of the white display portion and the retardation value of the black display portion are switched according to the following principle when the polarization transmission axes of the two polarizing plates are orthogonal to each other and parallel. Here, it is assumed that the transmission axis and the absorption axis of the polarizing plate are orthogonal to each other.

  When the polarization transmission axes are orthogonal, and the retardation value is λ / 2, the vibration plane of the light that has passed through the lower polarizer rotates 90 °, matches the transmission axis of the upper polarizer, passes through the upper polarizer, and passes through the white plane. Display. On the other hand, if the retardation value is λ, the vibration plane of the light that has passed through the lower polarizing plate rotates 180 °, coincides with the absorption axis of the upper polarizing plate, does not pass through the upper polarizing plate, and becomes black.

  When the polarization transmission axis is parallel and the retardation value is λ / 2, the vibration plane of the light that has passed through the lower polarizing plate rotates 90 °, matches the absorption axis of the upper polarizing plate, and does not pass through the upper polarizing plate. Black display. On the other hand, if the retardation value is λ, the vibration plane of the light that has passed through the lower polarizing plate rotates 180 °, matches the transmission axis of the upper polarizing plate, passes through the upper polarizing plate, and becomes white display.

  As described above, the viewing angle control sheet of the present invention combines the polarizing plate and the retardation plate so that one of the retardation value Re of the white display portion of the display device and the retardation value Re of the black display portion is Nλ / 2−λ / 4 <Re <nλ / 2 + λ / 4, and the other one may be nλ−λ / 4 <Re <nλ + λ / 4 (n is an integer of 1 or more).

  Further, as another embodiment of the viewing angle control sheet of the present invention, a viewing angle control sheet having a configuration including a reflection plate in addition to a polarizing plate and a retardation plate is also included in the present invention. By providing a reflecting plate on the viewing angle control sheet of the present invention, the number of retardation plates and polarizing plates can be reduced, and a viewing angle control sheet that can achieve the same effect as the viewing angle control sheet 20 can be obtained. That is, by providing the reflector under the positive A 24 in FIG. 1, it is possible to omit the polarizer and each retardation plate from the control sheet lower polarizer 23 to the TAC film 27b.

  The viewing angle control sheet of the present invention is applicable to various display devices such as a liquid crystal display device, a cathode ray tube type display device, and a self-luminous display device using an organic EL element. The viewing angle control sheet of the present invention is linearly polarized as in a liquid crystal display device because the polarizing plate used in the sheet can be shared with the polarizing plate used in the display panel (that is, one polarizing plate can be omitted). It is preferably used for a display device that emits light.

  Subsequently, as an example of the display device of the present invention, a configuration of a liquid crystal display device including the viewing angle control sheet 20 will be described. FIG. 6 is a cross-sectional view showing a schematic configuration of the liquid crystal display device 1. For the convenience of explanation, FIG. 6 shows only the main members necessary for explaining the present invention in a simplified manner among the constituent members according to the embodiment of the present invention. Therefore, the liquid crystal display device of the present invention can include any constituent member not shown in FIG. Moreover, the dimension of the member in a figure does not represent the dimension of an actual structural member, the dimension ratio of each member, etc. faithfully.

  As shown in FIG. 6, the liquid crystal display device 1 includes a display liquid crystal panel 10 (display panel) as a display panel for displaying an image, and a field of view for narrowing the viewing angle of the display panel from the original viewing angle. And an angle control sheet 20. The display liquid crystal panel 10 is a transmissive type, and a backlight 30 is used as a light source.

  The viewing angle control sheet 20 is provided, for example, on the front side of the display liquid crystal panel 10 as shown in FIG. That is, the display liquid crystal panel 10 and the viewing angle control sheet 20 are arranged in this order from the backlight 30 side. However, the present invention is not limited to this, and the viewing angle control sheet 20 may be provided on the back side of the display liquid crystal panel 10 (that is, between the backlight 30 and the display liquid crystal panel 10).

  Since the liquid crystal display device 1 is provided with the viewing angle control sheet 20, the viewing angle of the display unit of the display liquid crystal panel 10 is narrower than that in the case where the sheet is not provided.

  The display liquid crystal panel 10 includes a liquid crystal cell 11 having a liquid crystal sandwiched between a pair of translucent substrates, and a liquid crystal panel upper polarizing plate 12 and a liquid crystal panel lower polarizing plate 13 provided on the front and back of the liquid crystal cell 11. ing. The liquid crystal mode and the cell structure of the liquid crystal cell 11 are arbitrary. Moreover, the drive mode of the display liquid crystal panel 10 is also arbitrary. That is, as the display liquid crystal panel 10, any liquid crystal panel that can display characters, images, or moving images can be used. Therefore, in FIG. 6, the detailed structure of the display liquid crystal panel 10 is not shown, and the description thereof is also omitted.

  The display liquid crystal panel 10 may be a panel capable of color display or a panel dedicated to monochrome display. Further, the configuration of the backlight 30 is not limited at all, and any known backlight can be used. Therefore, the detailed structure and illustration of the backlight 30 are also omitted.

  In addition, the said control sheet lower polarizing plate 23 is not necessarily required, and can be abbreviate | omitted. That is, it is sufficient that at least one polarizing plate exists between the viewing angle control sheet 20 and the display liquid crystal panel 10, so that the liquid crystal panel upper polarizing plate 12 of the display liquid crystal panel 10 is used as the control sheet lower polarizing plate 23. It is possible to share it. In this case, the polarizing plate 12 on the liquid crystal panel corresponds to the polarizing plate of the present invention.

  Since the liquid crystal display device 1 has the above-described configuration, the retardation values as described above are obtained in the black display portion and the white display portion, as shown in FIGS. 5A and 5B. It has transmittance characteristics, and can be reliably prevented from being visually recognized from the left-right direction. Further, since moire does not occur as in the case of using an existing louver film having a viewing angle limiting function, a good image can be seen from a visible direction.

  In the present embodiment, as an example of the display device of the present invention, a display device with a viewing angle control sheet in which a viewing angle control sheet is arranged on the front side of the display panel (that is, the viewer side) has been described. The present invention is not limited to this configuration. As another example of the display device of the present invention, a display device with a viewing angle control sheet in which a viewing angle control sheet is disposed on the back side (that is, the backlight side) of the display panel, the front side and the back side of the display panel Examples thereof include a display device with a viewing angle control sheet in which a viewing angle control sheet is disposed.

  As described above, the display device of the present invention includes not only one provided with one viewing angle control sheet but also one provided with a plurality of viewing angle control sheets. Further, by arranging two identical viewing angle control sheets in different directions and overlapping them on the front or back of the display panel, more multi-directional shielding (for example, shielding in the vertical direction as well as the horizontal direction) can be realized. be able to.

  In the conventional louver film, when two sheets are used in an overlapping manner, the generation of moire becomes more serious, and the quality of the displayed image is deteriorated. That is, when two louver films are used to achieve shielding in the vertical and horizontal directions (shielding in four directions), the longitudinal axis of the louver light shielding plate needs to be arranged in the vertical and horizontal directions, respectively. However, the display panel has periodic patterns such as source lines in the vertical direction and gate lines in the horizontal direction, and the louver film has periodic patterns of louver shading plates, which interfere with each other. More moire occurs. On the other hand, according to the viewing angle control sheet of the present invention, moire does not occur even when two or more sheets are used in an overlapping manner, and the quality of the display image is not impaired.

  In the liquid crystal display device 1 described above, a directional backlight using a lens sheet or the like can be used instead of the backlight 30. By setting it as such a structure, the right-and-left shielding effect can be improved more.

  In the liquid crystal display device 1 described above, a λ / 2 plate can be added to the lowermost layer of the viewing angle control sheet, for example. Since the shielding direction can be changed by this, the visual field in a desired direction can be limited.

  The present invention can be applied to a viewing angle control sheet that limits the viewing angle in order to prevent visual recognition from a predetermined direction. If the viewing angle control sheet of the present invention is used for a display device, a display device that takes privacy protection and security into consideration can be realized without deteriorating the image quality due to the occurrence of moire.

It is sectional drawing which shows the structure of the viewing angle control sheet concerning one Embodiment of this invention. (A) shows a schematic diagram of a retardation plate, (b) shows a refractive index ellipsoid of a NEZ plate constituting the retardation plate of the viewing angle control panel, and (c) shows a viewing angle control panel. A refractive index ellipsoid of a λ / 4 plate constituting the retardation plate is shown, and (d) shows a positive A refractive index ellipsoid constituting the retardation plate of the viewing angle control panel. (A) is a schematic diagram which shows the axial angle of the polarizing plate and phase difference plate which comprise the viewing angle control sheet | seat shown in FIG. 1, (b) is the polarizing plate which comprises the viewing angle control sheet | seat shown in FIG. 5 is a table showing in-plane retardation, thickness retardation, and axial angle of the retardation plate. FIG. 4 is a schematic diagram illustrating a visual definition for a viewing angle control sheet arranged in the same direction as that in FIG. (A) is a chart which shows the transmittance | permeability distribution at the time of affixing the viewing angle control sheet | seat shown in FIG. 1 on the display panel of a liquid crystal display device. (B) is a graph which shows the transmittance | permeability of the horizontal direction (direction angle (theta) direction of 0 degree and 180 degrees) at the time of affixing the viewing angle control sheet | seat shown in FIG. 1 on the display panel of a liquid crystal display device. It is sectional drawing which shows the structure of the display apparatus concerning one embodiment of this invention. It is a cross-sectional schematic diagram which shows the structure of the liquid crystal display device provided with the louver film for the conventional viewing angle control. It is sectional drawing of the louver film for showing the viewing angle control principle of the said louver film.

Explanation of symbols

1 Liquid crystal display device (display device)
10 LCD panel for display (display panel)
DESCRIPTION OF SYMBOLS 11 Liquid crystal cell 12 Polarizing plate 13 on a liquid crystal panel Lower polarizing plate 20 on a liquid crystal panel Viewing angle control sheet 21 Phase difference plate 22 Polarizing plate on a control sheet (first polarizing plate)
23 Control sheet lower polarizing plate (second polarizing plate)
24 Positive A plate (retardation plate)
25a λ / 4 plate (retardation plate)
25b λ / 4 plate (retardation plate)
26a NEZ (retardation plate, biaxial retardation plate)
26b NEZ (retardation plate, biaxial retardation plate)
27a TAC film (retardation plate / TAC plate)
27b TAC film (retardation plate / TAC plate)
27c TAC film (retardation plate / TAC plate)
27d TAC film (retardation plate / TAC plate)
30 Backlight X ₂₂ Polarization transmission axis X ₂₃ Polarization transmission axis

Claims (8)

A display device comprising: a display panel that displays an image; and a viewing angle control sheet that is disposed on at least one of the front and back surfaces of the display panel and that narrows the viewing angle of the display panel from the original viewing angle Because
The viewing angle control sheet includes at least one polarizing plate and at least one retardation plate,
Any one of the retardation value Re of the white display part and the retardation value Re of the black display part of the display device is nλ / 2−λ / 4 <Re <nλ / 2 + λ / 4 (n is an integer of 1 or more) The other is nλ−λ / 4 <Re <nλ + λ / 4 (n is an integer of 1 or more).   Either one of the retardation value Re of the white display part and the retardation value Re of the black display part is nλ / 2 (n is an integer of 1 or more), and the other is nλ (n is 1 or more). The display device according to claim 1, wherein the display device is an integer. The polarizing plate comprises a first polarizing plate and a second polarizing plate,
The display device according to claim 1, wherein at least one retardation plate is disposed between the first polarizing plate and the second polarizing plate. The polarization transmission axes of the first polarizing plate and the second polarizing plate are orthogonal to each other,
The retardation value Re1 of the white display portion is nλ / 2−λ / 4 <Re1 <nλ / 2 + λ / 4 (n is an integer of 1 or more), and the retardation value Re2 of the black display portion is nλ−λ / 4 <. The display device according to claim 3, wherein Re2 <nλ + λ / 4 (n is an integer of 1 or more). The polarization transmission axes of the first polarizing plate and the second polarizing plate are parallel to each other,
The retardation value Re1 of the white display portion is nλ−λ / 4 <Re1 <nλ + λ / 4 (n is an integer of 1 or more), and the retardation value Re2 of the black display portion is nλ / 2−λ / 4 <Re2 <. The display device according to claim 3, wherein nλ / 2 + λ / 4 (n is an integer of 1 or more).   The display device according to claim 3, wherein a plurality of the retardation plates are provided so as to be laminated, and the retardation plates laminated to each other include those having different refractive indexes. . As the retardation plate, a positive A plate, a plurality of λ / 4 plates,
It has three main refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other, nx>nz> ny, and (nx−nz) /|nx−ny|=0.1 A plurality of biaxial retardation plates having the relationship:
A plurality of TAC plates having three principal refractive indexes nx, ny, nz in the x, y, z axis directions orthogonal to each other and having a relationship of nx = ny>nz;
Between the first polarizing plate and the second polarizing plate, the TAC plate, the biaxial retardation plate, the λ / 4 plate, the TAC plate, the positive A plate, the TAC plate, the The display device according to claim 6, wherein the λ / 4 plate, the biaxial retardation plate, and the TAC plate are laminated in this order. A viewing angle control sheet that is disposed on at least one of the back surface and the front surface of the display device, and makes the viewing angle of the display device narrower than the original viewing angle,
A first polarizing plate and a second polarizing plate;
Between the first polarizing plate and the second polarizing plate, as a retardation plate,
A TAC plate having three principal refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other and having a relationship of nx = ny>nz;
It has three main refractive indexes nx, ny, and nz in the x, y, and z axis directions orthogonal to each other, nx>nz> ny, and (nx−nz) /|nx−ny|=0.1 A plurality of biaxial retardation plates having the relationship:
A viewing angle, wherein the λ / 4 plate, the TAC plate, the positive A plate, the TAC plate, the λ / 4 plate, the biaxial retardation plate, and the TAC plate are stacked in this order. Control sheet.

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