JP6146637B2 - Display device - Google Patents

Description

  The present invention relates to a display device capable of switching a viewing angle or a viewing direction in which an image can be viewed.

Display devices such as liquid crystal display devices are used in various electronic devices. In such an electronic device, in order to provide an additional function, it is preferable that a viewing angle or a viewing direction in which an image can be viewed can be changed. For example, in an electronic device such as a tablet PC, by changing the viewing angle, it is possible to cope with a case where it is desired to prevent the display content from being known to others and a case where a display content is desired to be observed by a plurality of people.
In order to control the viewing angle of the display device, a detachable louver sheet is used (see, for example, Patent Document 1).

JP 2003-58066 A

  However, when the conventional louver sheet is used, the viewing angle cannot be easily changed because it takes time to attach and detach the louver sheet. Moreover, even if it uses the said conventional louver sheet | seat, a visual recognition direction cannot be set to directions other than a front.

  The present invention has been made in consideration of such points, and an object thereof is to provide a display device that can easily change the viewing angle or the viewing direction.

A display device according to the present invention comprises:
A display device capable of switching a viewing angle or a viewing direction in which an image can be viewed,
A first layer having optical anisotropy, and a second layer that is laminated on the first layer and that forms an optical interface between the first layer and that changes the traveling direction of light of one polarization component. The optical interface has a plurality of unit optical interfaces arranged in one direction, and each unit optical interface extends in a direction non-parallel to the one direction, and the light proceeds according to the polarization state of the light. An optical sheet for controlling the direction;
An image display unit that is arranged facing the optical sheet and can switch and emit the light of the one polarization component and the light of the other polarization component in order to switch the viewing angle or the viewing direction. Is provided.

In the display device according to the present invention,
The image display unit emits light of the one polarization component when the viewing angle is set to the first viewing angle or the viewing direction is set to the first direction, and the viewing angle is set to the first viewing angle. When the second viewing angle is narrower than the viewing angle, or when the viewing direction is a second direction different from the first direction, the light of the other polarization component may be emitted.

  In the display device according to the present invention, the first layer may include a thermoplastic resin.

  In the display device according to the present invention, a glass transition temperature of the material forming the first layer may be 100 ° C. or higher.

  In the display device according to the present invention, the thermoplastic resin may be a polyethylene naphthalate resin.

  In the display device according to the present invention, the in-plane birefringence Δn of the first layer may be 0.13 or more.

  In the display device according to the present invention, the light of the other polarization component traveling in the normal direction to the optical sheet is transmitted through the optical sheet and then forms an angle of 2 ° or less with respect to the normal direction to the optical sheet. You may make it go to.

  In the display device according to the present invention, the dimensional stability of the optical sheet measured at 30 ° C. for 30 minutes and measured according to JIS C2151 may be 2% or less.

  In the display device according to the present invention, the second layer may be optically isotropic.

  In the display device according to the present invention, the magnitude of the electric dipole moment of the first layer may be larger than the magnitude of the electric dipole moment of the second layer.

  According to the present invention, the viewing angle or the viewing direction can be easily changed.

FIG. 1 is a perspective view schematically illustrating a display device for explaining an embodiment of the present invention. 2 is a view for explaining an optical path of light forming an image when displaying an image with a wide viewing angle on the display device of FIG. 1, and is a longitudinal sectional view of the display device of FIG. 3 is a view for explaining an optical path of light forming an image when the image is displayed with a narrow viewing angle in the display device of FIG. 1, and is a longitudinal sectional view of the display device of FIG. FIG. 4 is a perspective view showing refractive index ellipsoids of the first layer and the second layer of the optical sheet incorporated in the display device of FIG. FIG. 5 is a diagram showing a modification of the refractive index distribution in the plane of the first layer and the second layer. FIG. 6 is a diagram showing another modification of the refractive index distribution in the plane of the first layer and the second layer. FIG. 7 is a diagram showing still another modified example of the refractive index distribution in the planes of the first layer and the second layer. FIG. 8 is a diagram showing still another modified example of the refractive index distribution in the planes of the first layer and the second layer. FIG. 9 is a diagram for explaining an example of a method for manufacturing an optical sheet. FIG. 10 is a diagram for explaining another example of a method for manufacturing an optical sheet. 11 is a diagram for explaining an optical path of light forming an image when an image is displayed in a direction other than the front in a modification of the display device in FIG. 1, and is a longitudinal section of the modification of the display device in FIG. 1. FIG. 12 is a view for explaining an optical path of light forming an image when an image is displayed in the front direction in a modification of the display device of FIG. 1, and is a longitudinal sectional view of the modification of the display device of FIG. It is.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product.

  1 to 4 are diagrams for explaining an embodiment of the present invention. Among these, FIG. 1 is a perspective view showing a display device. 2 and 3 are diagrams for explaining the operation of the display device when displaying an image with a wide viewing angle or a narrow viewing angle, respectively. FIG. 4 is a perspective view showing refractive index ellipsoids of the first layer and the second layer of the optical sheet.

  Display device 10 in the present embodiment can display an image by switching the viewing angle. The display device 10 can be used for electronic devices such as a tablet PC, a car navigation system, and a television, for example. As illustrated in FIG. 1, the display device 10 includes an image display unit 15 and an optical sheet 40 disposed to face the image display unit 15. The image display unit 15 receives light of one linearly polarized light component for displaying an image with a wide viewing angle (first viewing angle) and a narrow viewing angle (from the first viewing angle) according to control from the outside. The other linearly polarized light component for displaying an image with a narrow second viewing angle) is switched and emitted. The optical sheet 40 controls the traveling direction of the light according to the polarization state of the light. More specifically, the optical sheet 40 controls the traveling direction of one linearly polarized light component for displaying an image with a wide viewing angle, and vibrates in a direction orthogonal to the vibrating direction of the one linearly polarized light component. The light traveling direction of the other linearly polarized light component is maintained.

  Hereinafter, each component will be further described in detail. In the following description, one linearly polarized light component that forms an image with a wide viewing angle is a first polarized light component that vibrates in the x-axis direction (see FIG. 1) parallel to the sheet surface of the optical sheet 40. The other linearly polarized light component that forms an image with a narrow viewing angle is a second polarized light component that vibrates in the y-axis direction (see FIG. 1) that is orthogonal to the x-axis direction and parallel to the sheet surface of the optical sheet 40.

  In the present specification, the terms “sheet”, “film”, and “plate” are not distinguished from each other only based on the difference in names. For example, “film” is a concept that includes members that can be referred to as sheets and plates. Therefore, “optical sheet” is distinguished only from the members that are referred to as “optical films” and “optical plates”. I don't get it.

  The “sheet surface (film surface, plate surface, panel surface)” is a target when the target sheet-like (film shape, plate shape, panel shape) member is viewed as a whole and globally. It refers to the surface that matches the planar direction of the sheet-like member (film-like member, plate-like member, panel-like member). In the present embodiment, the image forming surface 20a of the image forming device 20, the panel surface of the liquid crystal display panel 25, the panel surface of the polarization control device 30, the sheet surface of the optical sheet 40, and the display surface 10a of the display device 10 are as follows. It is parallel. Further, the front direction refers to the normal direction to the sheet surface of the optical sheet 40.

  Furthermore, terms specifying the shape and geometric conditions used in the present specification, for example, terms such as “parallel” and “orthogonal” can be expected to have the same optical function without being bound to a strict meaning. Interpretation will be made including a margin of error.

  First, the image display unit 15 includes an image forming apparatus 20 and a polarization controller 30 that transmits light from the image forming apparatus 20. The polarization controller 30 is disposed between the image forming apparatus 20 and the optical sheet 40. The image forming apparatus 20 includes a large number of pixels 21 arranged in a plane parallel to the image forming surface 20a. In the illustrated example, the large number of pixels 21 are arranged in stripes. Hereinafter, an example in which the image forming apparatus 20 forms an image with light of the first polarization component will be described. In this example, the polarization control device 30 maintains the polarization state of the light projected from the image forming device 20 as the first polarization component when displaying an image with a wide viewing angle, and displays the image with a narrow viewing angle. In some cases, the state is converted to the second polarization state. However, the present invention is not limited to this example, and the polarization of the light projected from the image forming apparatus 20 when the image forming apparatus 20 emits light of the second polarization component and the polarization control apparatus 30 displays an image with a wide viewing angle. When the state is converted to the first polarization component and an image is displayed with a narrow viewing angle, the second polarization state may be maintained.

  In the illustrated example, the image forming apparatus 20 is formed as a liquid crystal display device. That is, the image forming apparatus 20 includes a liquid crystal display panel 25 and a backlight 24 disposed on the back surface of the liquid crystal display panel 25. The backlight 24 may be formed using a known configuration such as an edge light type or a direct type.

  On the other hand, the liquid crystal display panel 25 includes a pair of polarizing plates 26 and 28 and a liquid crystal cell 27 disposed between the pair of polarizing plates 26 and 28. The polarizing plates 26 and 28 have a function of decomposing incident light into two orthogonal polarization components, transmitting the polarization component in one direction, and absorbing the polarization component in the other direction orthogonal to the one direction. It has a polarizer. In one specific example described here, the lower polarizing plate 26 disposed on the backlight 24 side transmits light of the second polarization component, and the upper polarizing plate 28 disposed on the polarization control device 30 side includes the first polarizing plate 26. The light of the polarization component is transmitted.

  The liquid crystal cell 27 has a pair of support plates and liquid crystal molecules (liquid crystal material) disposed between the pair of support plates. The liquid crystal cell 27 can be applied with an electric field for each region where one pixel is formed. Then, the orientation of the liquid crystal in the liquid crystal cell 27 applied with an electric field changes. As an example, when the light of the second polarization component transmitted through the lower polarizing plate 26 passes through a liquid crystal cell 27 to which an electric field is not applied, its vibration direction is rotated by 90 ° and passes through the liquid crystal cell 27 to which an electric field is applied. The polarization state is maintained. For this reason, depending on whether or not an electric field is applied to the liquid crystal cell 27, whether the light of the second polarization component transmitted through the lower polarizing plate 26 further passes through the upper polarizing plate 28 disposed on the light output side of the lower polarizing plate 26, Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 28. In this manner, an image is formed by the light of the first polarization component from each pixel 21 selectively transmitted through the upper polarizing plate 28.

  Next, the polarization controller 30 will be described. As a basic configuration, the polarization controller 30 includes a first electrode 34 and a second electrode 36, and a medium layer 35 disposed between the first electrode 34 and the second electrode 36. The medium layer 35 generates anisotropy of the refractive index when a voltage is applied between the pair of electrodes 34 and 36. In the illustrated example, the first electrode 34, the liquid crystal layer 35, and the second electrode 36 are disposed between the first support film 33 and the second support film 37. The first electrode 34, the medium layer 35, and the second electrode 36 are supported and protected by a pair of support films 33 and 37. Hereinafter, an example in which the medium layer is configured as the liquid crystal layer 35 will be described.

  The pair of electrodes 34 and 36 and the liquid crystal layer 35 are wide enough to face the entire region of the image forming surface 20 a of the image forming apparatus 20. As shown in FIGS. 2 and 3, the liquid crystal layer 35 is configured as a layer including liquid crystal molecules 31. The pair of electrodes 34 and 36 are electrically connected to a voltage applying means (not shown). The pair of electrodes 34 and 36 is kept at a predetermined interval by a spacer (not shown) or the like.

  When the liquid crystal molecules 31 included in the liquid crystal layer 35 are TN type liquid crystal molecules as a typical example, when a voltage is applied between the pair of electrodes 34 and 36, the liquid crystal molecules 31 are aligned as shown in FIG. . In this case, the polarization state of the light from the image forming apparatus 20 is maintained as the first polarization component. On the other hand, when no voltage is applied between the pair of electrodes 34 and 36, as shown in FIG. 3, the liquid crystal molecules 31 rotate 90 ° in a twisted manner. In this case, the polarization state of the light from the image forming apparatus 20 is converted from the vibration direction from the x-axis direction to the y-axis direction, that is, from the first polarization component to the second polarization component.

  However, the description of the image display unit 15, the image forming apparatus 20, and the polarization control apparatus 30 described above is merely a specific example, and known means can be used.

  Next, the optical sheet 40 will be described. As shown in FIGS. 1 to 3, the optical sheet 40 includes a first layer 51 and a second layer 52 provided adjacent to the first layer 51. In the illustrated example, the optical sheet 40 further includes a film layer 43 provided on the second layer 52.

  The film layer 43 is formed as a single layer or a plurality of stacked layers. The film layer 43 is a layer expected to exhibit a specific function, and forms the outermost light emitting side surface of the display device 10, that is, the display surface 10 a of the display device 10. As an example, the film layer 43 includes an antireflection layer (AR layer) having an antireflection function, an antiglare layer (AG layer) having an antiglare function, a hard coat layer (HC layer) having scratch resistance, It may be configured to include one or more antistatic layers (AS layers) having an antistatic function.

  The boundary surface between the first layer 51 and the second layer 52 is formed as an uneven surface. This boundary surface forms an optical interface 55 that changes the traveling direction of light of at least the first polarization component. In the illustrated example, the optical interface 55 that forms the boundary between the first layer 51 and the second layer 52 is configured as a surface including a plurality of unit optical interfaces 55a. As shown in FIG. 1, the unit optical interfaces 55a are arranged along a certain arrangement direction. Each unit optical interface 55a extends in a direction non-parallel to the arrangement direction. In particular, in the illustrated example, the unit optical interfaces 55a are arranged without gaps in the x-axis direction, and each unit optical interface 55a extends linearly in the y-axis direction. One unit optical interface 55a has the same shape at each position along the y-axis direction. The plurality of unit optical interfaces 55a are configured identically to each other.

  The unit optical interface 55a is appropriately designed so that light emitted from each pixel 21 is directed to a predetermined position. In the illustrated example, the unit optical interface 55a has a convex lens-like outline in a cross section parallel to both the front direction and the arrangement direction of the unit optical interfaces 55a, and a divergent light beam from each pixel 21 is set at a preset position. To collect light. The optical interface 55 as an aggregate of a plurality of unit optical interfaces 55a forms a lenticular lens.

  However, the illustrated unit optical interface 55a and the optical interface 55 are merely examples, and various modifications can be made. For example, as described in detail later, the cross-sectional contour of the unit optical interface 55a can be changed as appropriate. The plurality of unit optical interfaces 55a may have different shapes. As an example, the optical interface 55 may constitute a Fresnel lens. Further, although the example in which the unit optical interface 55a is composed of elongated elements arranged one-dimensionally is shown, the present invention is not limited to this, and the unit optical interface 55a may be arranged two-dimensionally.

Next, the refractive indexes of the first layer 51 and the second layer 52 will be described. The first layer 51 is optically anisotropic and has at least in-plane birefringence. That is, the refractive index n _1x of the first layer 51 in the x-axis direction is different from the refractive index n _{1y of} the first layer 51 in the y-axis direction. In addition, the optical sheet 40 will be described herein, the refractive index in the x-axis direction of the first layer 51 _{n 1x,} the refractive index in the x-axis direction of the second layer 52 _{n 2x,} y-axis direction of the first layer 51 refractive index _{n 1y} in, and the refractive index of the y-axis direction of the second layer 52 _{n 2y} satisfies the following relationship.
| N _1x −n _2x | ≠ | n _1y −n _2y |
Accordingly, the optical sheet 40 exhibits different optical functions for the light of the first polarization component that vibrates in the x-axis direction and the light of the second polarization component that vibrates in the y-axis direction. More specifically, when the light of the first polarization component and the light of the second polarization component traveling in the same direction pass through the optical interface 55 of the optical sheet 40, the light travels in different directions.

In particular, in the example described here, the following relationship is satisfied.
| N _1x −n _2x |> | n _1y −n _2y | = 0
In this case, the optical interface 55 of the optical sheet 40 no longer forms an optical interface having a refractive index difference with respect to the light of the second polarization component that vibrates in the y-axis direction. Accordingly, the light of the first polarization component is subjected to an optical function (for example, a lens function) from the optical interface 55 of the optical sheet 40, but the light of the second polarization component passes through the optical interface 55 of the optical sheet 40. The direction of travel is not changed. In this specification, the value of the refractive index is handled as a numerical value up to the second decimal place by rounding off the third decimal place.

However, in application to the display device 10, setting | n _1y −n _2y | = 0 is not an indispensable condition for practical use, but | n _1x −n _2x |> | n _1y −n _2y | and | It is sufficient if n _1y −n _2y | ≦ 0.02 is satisfied. In this case, the traveling direction of the light of the second polarization component is not changed at the optical interface 55 of the optical sheet 40 to such an extent that troubles such as ghost and crosstalk occur.

Further, in application to the display device 10, the degree of optical action exerted on the light of the second polarization component is not only the magnitude of | n _1y −n _2y | Other configurations such as the shape of the interface 55 are also affected. From such a viewpoint, after the light of the polarization component (second polarization component) oscillating in the y-axis direction traveling in the direction orthogonal to the sheet surface of the optical sheet 40 (ie, the front direction) is transmitted through the optical sheet 40, The optical sheet 40 may be configured to proceed in a direction that forms an angle of 2 ° or less with respect to the front direction. In this case, it is possible to effectively prevent the optical action that may cause defects, for example, image quality deterioration due to generation of a ghost when displaying an image, from being exerted on the light of the second polarization component transmitted through the optical sheet 40. can do.

FIG. 4 shows an example of a refractive index ellipsoid showing a refractive index distribution in each direction of the first layer 51 and the second layer 52. In this example,
(N _1x −n _2x )> | n _1y −n _2y | = 0
The relationship is satisfied. The refractive index n _1x of the first layer 51 in the x-axis direction is larger than the refractive index n _{1y of} the first layer 51 in the y-axis direction. In the example shown in FIG. 3, the second layer 52 is formed as an optically isotropic layer. That is, the refractive index n _2x of the second layer 52 in the x-axis direction is equal to the refractive index n _{2y of} the second layer 52 in the y-axis direction. Accordingly, the refractive index n _1x of the first layer 51 in the x-axis direction is larger than the refractive index n _{2x of} the second layer 51 in the x-axis direction. As a result, the optical interface 55 shown in FIG. 1 can exhibit the same lens function as a convex lens.

In the example shown in FIG. 1, the slow axis direction in which the refractive index is maximum in the plane of the first layer 51 coincides with the x-axis direction, and the refractive index is in the plane of the first layer 51. The fast axis direction in which the minimum value is the same as the y-axis direction. In addition, the refractive index n _2x in the y-axis direction (fast axis direction) in the plane of the first layer 51 and the refractive index n _2y in the y-axis direction in the plane of the second layer 52 are configured to coincide with each other. Therefore, the refractive index difference between the first layer 51 and the second layer 52 in the x-axis direction is set to 0 while the refractive index difference between the first layer 51 and the second layer 52 in the y-axis direction is set to zero. Can be set large. In addition, in application to a home display device, the birefringence index Δn (= n _1x −n _1y ) of the first layer 51 is set on condition that the optical interface 55 is manufactured in a shape that can be easily manufactured. It is preferable that it is 0.13 or more. On the other hand, when the optical anisotropy of the first layer 51 is imparted by stretching as will be described later, the birefringence Δn of the first layer 51 is set to 0. 0 in consideration of the in-plane uniformity in the stretching step. It is preferable to make it 22 or less.

  The refractive index of the first layer 51 and the second layer 52 is “KOBRA-WR” manufactured by Oji Scientific Instruments, “Ellipsometer M150” manufactured by JASCO Corporation, or Abbe refractometer (NAR- manufactured by Atago Co., Ltd.). 4T) can be used as the measured value.

  Such an optical sheet 40 can be manufactured as follows. First, as shown in FIG. 9, the resin film 71 is produced using a thermoplastic resin. Thereafter, the resin film 71 is stretched to produce the first layer 51 made of the stretched resin film 71. Then, the optical sheet 40 is obtained by forming the second layer 52 on the first layer 51.

  The resin film 71 can be produced by molding a resin material containing a thermoplastic resin as a main component, or the thermoplastic resin itself. As the molding process, injection molding or melt extrusion molding can be employed. According to these molding processes, the resin film 71 having the unevenness forming the optical interface 55 can be produced.

  For the molding of the resin film 71, a mold having a mold surface or a mold formed of a resin can be used. In particular, when using a mold made of resin, compared to using a metal mold surface, when applying a heated thermoplastic resin, suppresses rapid heat absorption from the thermoplastic resin to the mold surface. be able to. Thereby, the heated thermoplastic resin can extend and spread sufficiently on the mold surface, and the molding rate can be improved. Moreover, since the release property from the mold surface of the produced resin film 71 is good, it is possible to prevent defects during release. As the mold whose mold surface is made of resin, a long film mold can be used.

  The stretching of the resin film 71 is a process for imparting optical anisotropy to the resin film 71, and therefore, it is preferable that the stretching is uniaxial stretching. As shown in FIG. 9, the resin film 71 is stretched in a direction (y-axis direction) perpendicular to the arrangement direction of the convex portions of the resin film 71 that forms the unit optical interface 55 a of the optical interface 55.

  The stretching of the resin film 71 is performed in a state where the resin film 71 is heated to a temperature equal to or higher than the glass transition temperature of the thermoplastic resin forming the resin film 71. When the resin film 71 is produced by melt extrusion molding, the high-temperature resin film 71 just after extrusion may be stretched. That is, it is not necessary to separately provide a heat treatment for the resin film 71 for stretching. In addition, as shown in FIG. 9, the resin film 71 changes a shape by extending | stretching and comes to form the 1st layer 51. FIG. Therefore, in the molding process of the resin film 71 described above, the resin film 71 is manufactured in a shape that allows for deformation due to stretching.

Next, a second layer 52 is formed on the first layer 51 by applying a resin on the manufactured first layer 51 and curing the resin on the first layer 51. The second layer 52 formed on the first layer 51 has an unevenness corresponding to the unevenness of the first layer 51 as a surface facing the first layer 51, in other words, an unevenness complementary to the unevenness of the first layer 51. Will have. As another method, a separately formed second layer 52 may be laminated on the first layer 51. The resin that forms the second layer 52 may be a thermoplastic resin having no birefringence, that is, a refractive index isotropic (n _2x = n _2y ), a thermosetting resin, or an ionizing radiation curing. Mold resin may be used. The optical sheet 40 is obtained as described above. These resins such as thermoplastic resins having no birefringence constituting the second layer are usually solidified in an unstretched state.

  As another method, the optical sheet 40 can also be manufactured by the manufacturing method shown in FIG.

  In the manufacturing method shown in FIG. 10, first, the resin film 71 having the unevenness described above (see FIG. 9) and the unevenness corresponding to the unevenness of the resin film 71, in other words, complementary to the unevenness of the resin film 71. A second resin film 72 having irregularities is prepared. Next, the resin film 71 and the second resin film 72 are laminated through, for example, an adhesive or a pressure-sensitive adhesive so that the unevenness of each other meshes. Thereafter, the laminated resin film 71 and the second resin film 72 are stretched to obtain the optical sheet 40 having the first layer 51 made of the resin film 71 and the second layer 52 made of the second resin film 72. .

  Also in the manufacturing method shown in FIG. 10, the resin film 71 and the second resin film 72 can be manufactured by molding using a thermoplastic resin in the same manner as the above-described manufacturing method shown in FIG. Also in the manufacturing method shown in FIG. 10, birefringence is imparted to the resin film 71 in the plane by stretching the resin film 71. The second resin film 72 is also stretched together with the resin film 71, but it is not necessary to positively impart optical anisotropy to the second resin film 72. Therefore, in order to prevent in-plane birefringence from occurring in the second resin film 72, it is preferable that the magnitude of the electric dipole moment of the molecules constituting the second resin film 72 is small. In particular, the magnitude of the electric dipole moment of the molecules constituting the second resin film 72 is preferably smaller than at least the magnitude of the electric dipole moment of the molecules constituting the resin film 71. The electric dipole moment is measured by first measuring the dielectric constant using a test fixture HP16451B electrode of a precision LCR meter HP4284A manufactured by Yokogawa-Hewlett-Packard Co., and then using the measured dielectric constant. This can be done by specifying the electric dipole moment.

By selecting the magnitude of the electric dipole moment of the constituent molecules for the resin film 71 and the second resin film 72 as described above, the resin film 71 and the second resin film 72 are stretched in an equal amount, Even if molecular orientation occurs, the degree of birefringence (refractive index anisotropy) that appears in each film depends on the magnitude of the electric dipole moment of the constituent molecules.
When the birefringence index Δ _n1 of the resin film 71> the birefringence index Δ _n2 of the second resin film 72 or the respective refractive indexes in the x and y axis directions of both films,
It is found that n _1x −n _1y > n _2x −n _2y (ideally → 0).

  As described above, the optically anisotropic first layer 51 containing the thermoplastic resin, and the optical interface 55 that is laminated on the first layer 51 and changes the traveling direction of the light of the first polarization component are combined with the first layer 51. The optical sheet 40 having the second layer 52 formed therebetween can be manufactured.

  Note that polycarbonate resin, cycloolefin polymer resin, acrylic resin, polyester resin, or the like can be used as the thermoplastic resin included in the first layer 51. Of these, polyester resins are advantageous in terms of cost and mechanical strength. Specific examples of the polyester resin include polyethylene naphthalate, polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate), and polyethylene-2,6-naphthalate. Further, the polyester resin forming the first layer 50 may be a copolymer of these polyester resins, and the polyester is the main component (for example, a component of 80 mol% or more), and a small proportion (for example, 20 mol% or less). It may be blended with other types of resins. As the polyester resin, polyethylene naphthalate is preferable in that a large birefringence can be secured. As the polyester resin, polyethylene terephthalate or polyethylene-2,6-naphthalate is preferable because of a good balance between mechanical properties and optical properties. In addition, from the viewpoint of the stability of the optical sheet 40, the glass transition temperature of the material forming the first layer 51 is preferably 100 ° C. or higher.

  In the display device 10 including such an optical sheet 40, an image can be displayed with a narrow viewing angle or a wide viewing angle as follows. First, a case where an image is displayed with a narrow viewing angle will be described with reference mainly to FIG.

  The backlight 24 illuminates the liquid crystal display panel 25 in a planar shape from the back side. The liquid crystal display panel 25 selectively transmits the light from the backlight 24 for each pixel 21. The image lights L31 to L34 thus formed serve as a first polarization component that can pass through the lower polarizing plate 28 of the image forming apparatus 20 in a state where the image lights L31 to L34 are emitted from the image forming surface 20a of the image forming apparatus 20. . Thereafter, the image lights L31 to L34 enter the polarization controller 30. When an image is displayed with a narrow viewing angle, no voltage is applied between the pair of electrodes 34 and 36 of the polarization controller 30. For this reason, as shown in FIG. 3, the liquid crystal molecules 31 are turned 90 °. As a result, the image lights L31 to L34 transmitted through the polarization controller 30 change their polarization states. As a result, the image lights L <b> 31 to L <b> 34 become the second polarization component in a state where the image lights L <b> 31 to L <b> 34 are emitted from the image display unit 15.

The image lights L31 to L34 emitted from the image display unit 15 enter the optical sheet 40. The optical sheet 40 has an optical interface 55 formed as an uneven surface. The optical interface 55 is configured as a boundary surface between the optically anisotropic first layer 51 and the second layer 52. However, the refractive index n _1y of the first layer 51 in the y-axis direction, which is the vibration direction of the second polarization component forming the image light L31 to L34, and the refractive index n _2y of the second layer 52 in the y-axis direction are the same. Is set. Accordingly, the image lights L31 to L34 travel without being bent in the traveling direction at the optical interface 55 of the optical sheet 40. In this way, the image lights L31 to L34 are emitted from the display surface 10a of the display device 10 in the front direction. As a result, the observer can observe the image from the front direction.

  The light from the backlight 24 that illuminates the liquid crystal display panel 25 has an optical axis in the front direction (that is, has a brightness peak in the front direction) and a certain angle around the front direction. Proceed in the direction of the region. Therefore, the light that has passed through each pixel 21 is emitted from the display surface 10a of the display device 10 as divergent light toward a certain angle range. As a result, the observer can observe the image formed on the display surface 10a from a certain angle range. That is, the viewing angle in this case depends on the degree of light divergence from the backlight 24.

  Next, a case where an image is displayed with a wider viewing angle than the above description will be described. When displaying an image with a wide viewing angle, image light L21 to L25 is emitted from the image forming apparatus 20 in the same manner as when displaying an image with a narrow viewing angle. Next, the image lights L <b> 21 to L <b> 25 enter the polarization controller 30.

  As shown in FIG. 2, when displaying an image with a wide viewing angle, a voltage is applied between the pair of electrodes 34 and 36 of the polarization controller 30. For this reason, the image lights L21 to L25 are transmitted through the polarization controller 30 while maintaining the polarization state in the first state.

The image lights L21 to L25 emitted from the image display unit 15 enter the optical sheet 40. The refractive index n _1x of the first layer 51 in the x-axis direction, which is the vibration direction of the first polarization component that forms the image light L21 to L25, is larger than the refractive index n _2x of the second layer 52 in the x-axis direction. It has become. Thereby, the optical interface 55 of the optical sheet 40 controls the traveling direction of the image light L21 to L25 from each pixel 21.

  Each unit optical interface 55a of the optical interface 55 exhibits a lens function and diverges light from each pixel 21. That is, the light is refracted by the difference in refractive index at the lens interface (optical interface 55) and the incident angle of the light, and the viewing angle is expanded. Each unit optical interface 55a is designed so that light diverges toward a wider angle range than when no voltage is applied between the pair of electrodes 34 and 36 described above. As a result, the observer can observe the image formed on the display surface 10a from a wider angle range. That is, the viewing angle can be widened.

  Thus, according to the present embodiment, the image display unit 15 has one linearly polarized light component for displaying an image with a wide viewing angle and the other linearly polarized light for displaying an image with a narrow viewing angle. The viewing angle can be easily changed by switching and emitting the component light.

  For example, if the observer can observe an image from near the front of the display device 10 and it is difficult to observe the image from other than the front, the viewing angle may be narrowed. In addition, when it is desired that a plurality of observers other than the front can observe the image, the viewing angle may be widened. When such a display device 10 is applied to a tablet PC, the viewing angle is narrowed when it is desired to prevent the display content from being known to others, and the viewing angle is widened when the display content is desired to be observed by a plurality of people. That's fine. When applied to a car navigation system, for example, the viewing angle may be narrowed when a driver located outside the front of the display device 10 is not allowed to observe an image.

  In addition, according to the present embodiment, the first layer 51 having the in-plane birefringence of the optical sheet 40 exhibits optical anisotropy by the stretched thermoplastic resin. Therefore, the first layer 51 can sufficiently have a glass transition temperature of 100 ° C. or higher. For this reason, the optical sheet 40 according to the present embodiment and the display device 10 including the optical sheet 40 exhibit excellent stability. As an example, the optical sheet 40 according to the present embodiment can be remarkably improved in dimensional stability measured in accordance with JIS C2151 by heating at 150 ° C. for 30 minutes. Specifically, according to the present embodiment, the dimensional stability of the optical sheet 40 measured at 30 ° C. for 30 minutes and measured according to JIS C2151 can be suppressed to 2% or less. As a result, the optical sheet 40 according to the present embodiment can be used without significant restrictions in a usage environment within the range of general applications such as a home television receiver, and according to the present embodiment. The optical sheet 40 can express the expected optical function.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above embodiment are used for the parts that can be configured in the same manner as in the above embodiment. A duplicate description is omitted.

  The optical sheet 40 is merely an example and can be changed as appropriate. First, the film layer 43 is not an essential layer and can be omitted from the optical sheet 40. In addition, a film layer that is expected to exhibit some function may be provided closer to the polarization control device 30 than the first layer 51 and the second layer 52. Furthermore, as described above, the configurations of the optical interface 55 and the unit optical interface 55a can be appropriately changed according to the expected optical function. Furthermore, the first layer 51 having optical anisotropy may be disposed closer to the observation side than the second layer 52.

  Here, modified examples of the optical interface 55 and the unit optical interface 55a will be described with reference to FIGS. In this modification, the display device 10 can switch the viewing direction in which an image can be viewed.

  11 is a diagram for explaining an optical path of light forming an image when an image is displayed in a direction other than the front in a modification of the display device in FIG. 1, and is a longitudinal section of the modification of the display device in FIG. 1. FIG. 12 is a view for explaining an optical path of light forming an image when an image is displayed in the front direction in a modification of the display device of FIG. 1, and is a longitudinal sectional view of the modification of the display device of FIG. It is.

  In the illustrated example, the unit optical interface 55a has a triangular (unit prism) -like outline in a cross section parallel to both the front direction and the arrangement direction of the unit optical interfaces 55a, and light from each pixel 21 is preset. Can be directed in directions other than the directed front direction. In the illustrated example, the contour of the unit optical interface 55a has an isosceles triangle shape arranged symmetrically about the front direction. What is necessary is just to set suitably the angle of the vertex angle of this isosceles triangle shape according to the direction which directs light. The optical interface 55 as an aggregate of the plurality of unit optical interfaces 55a forms a prism surface.

  In the display device 10 including such an optical sheet 40, the viewing direction can be switched to the front direction or a direction other than the front as follows. First, a case where an image is displayed with the viewing direction set to the front direction will be described with reference mainly to FIG.

  In this case, the basic operation principle is the same as when displaying an image with a narrow viewing angle in the above-described embodiment, and no voltage is applied between the pair of electrodes 34 and 36 of the polarization controller 30. . As a result, the image lights L <b> 31 to L <b> 34 become the second polarization component in a state where the image lights L <b> 31 to L <b> 34 are emitted from the image display unit 15.

  The image lights L31 to L34 emitted from the image display unit 15 travel without being bent in the traveling direction at the optical interface 55 of the optical sheet 40. In this way, the image lights L31 to L34 are emitted from the display surface 10a of the display device 10 in the front direction. As a result, the observer can observe the image from the front direction.

  Next, a case where an image is displayed with the viewing direction set to a direction other than the front will be described. As shown in FIG. 11, in this case, a voltage is applied between the pair of electrodes 34 and 36 of the polarization control device 30. For this reason, the image lights L21 to L24 are transmitted through the polarization controller 30 while maintaining the polarization state in the first state.

  The image lights L21 to L24 emitted from the image display unit 15 enter the optical sheet 40. The optical interface 55 of the optical sheet 40 controls the traveling direction of the image light L21 to L24 from each pixel 21.

  Each unit optical interface 55a of the optical interface 55 directs light from each pixel 21 in a direction other than the front. In the illustrated example, at each unit optical interface 55a, the light refracted on one equilateral side of the isosceles triangle shape and the light refracted on the other equilateral side intersect after being emitted from the display surface 10a of the display device 10. Thus, each unit optical interface 55a is designed. That is, the light that has passed through each pixel 21 is emitted from the display surface 10a of the display device 10 in a direction other than the front direction. As a result, the observer can observe the image formed on the display surface 10a from a direction other than the front, and cannot observe from the front. That is, the viewing direction in which an image can be viewed can be changed without changing the orientation of the display device 10. For example, when the display device 10 of this modification is applied to a car navigation system, the seat where the image can be observed can be switched by switching the viewing direction.

  Thus, in this modification, the image display unit 15 emits light of the first polarization component when the viewing direction is set to a direction other than the front (first direction), and the viewing direction is set to the front direction (first direction). When the second direction is different from the first direction, light of the second polarization component is emitted. However, the second direction is not limited to the front direction.

In the above-described embodiment, the refractive index n _1x of the first layer 51 in the x-axis direction, the refractive index n _{1y of} the first layer 51 in the y-axis direction, and the refractive index n _{2x of} the second layer 52 in the x-axis direction. Although the relationship between the refractive index n _{2y in} the y-axis direction of the second layer 51 has been described, the above-described relationship between the refractive indexes n _1x , n _1y , n _2x , and n _2y is merely an example.

For example, in the above-described embodiment, the example in which the refractive index n _{1x in} the x-axis direction of the first layer 51 is larger than the refractive index n _{2x in} the x-axis direction of the second layer 52 is shown, but the present invention is not limited thereto. Instead, the refractive index n _{1x of} the first layer 51 in the x-axis direction may be smaller than the refractive index n _{2x of} the second layer 52 in the x-axis direction. In the example shown in FIG. 5 as an example, the following relationship is satisfied:
(N _2x −n _1x )> | n _1y −n _2y | = 0
When the relationship of FIG. 5 is established, for example, by configuring the unit optical interface 55a of the optical interface 55 as a concave lens, it is possible to obtain an optical function substantially similar to the optical sheet 40 of the above-described embodiment. As already described, the following two conditions may be satisfied instead of the refractive index relationship shown in FIG.
(N _2x −n _1x )> | n _1y −n _2y |
| N _1y −n _2y | ≦ 0.02
Further, (n _2x −n _1x )> | n _1y −n _2y | is satisfied, and light of the second polarization component traveling in the front direction is transmitted through the optical sheet 40 and then 2 ° or less with respect to the front direction. The optical sheet 40 may be configured to proceed in a direction that forms an angle of.

In the embodiment described above, the magnitude of the refractive index difference (| n _1x −n _2x |) between the first layer 51 and the second layer 52 in the x-axis direction is the first in the y-axis direction. Although an example in which the magnitude of the refractive index difference (| n _1y −n _2y |) between the layer 51 and the second layer 52 is larger is shown, the example in the x-axis direction is used instead of the above-described example. The difference in refractive index between the first layer 51 and the second layer 52 is smaller than the difference in refractive index between the first layer 51 and the second layer 52 in the y-axis direction. Also good.

As an example, the following relationship may be satisfied.
| N _1y −n _2y |> | n _1x −n _2x | = 0
In this case, the traveling direction of the light of the second polarization component that vibrates in the y-axis direction is controlled by the optical interface 55. On the other hand, the light of the first polarization component that vibrates in the x-axis direction passes through the optical interface 55 while maintaining the traveling direction. In this example, the image display unit 15 emits light for displaying an image with a wide viewing angle as light of the second polarization component by switching the polarization control device 30, for example, and displays an image with a narrow viewing angle. May be emitted as the light of the first polarization component. Also by such an example, the same effect as embodiment mentioned above can be anticipated. In this example, as shown in FIG. 6, the refractive index n _{1y in} the y-axis direction of the first layer 51 is larger than the refractive index n _{2y in} the y-axis direction of the second layer 52, and the following relationship is satisfied. You may be made to do.
(N _1y −n _2y )> | n _1x −n _2x | = 0
Alternatively, as shown in FIG. 7, the refractive index n _{1y in} the y-axis direction of the first layer 51 is smaller than the refractive index n _{2y in} the y-axis direction of the second layer 52 so that the following relationship is satisfied. Also good.
(N _2y −n _1y )> | n _1x −n _2x | = 0

As already described, the following two conditions may be satisfied instead of the refractive index relationship shown in FIG.
(N _1y −n _2y )> | n _1x −n _2x |
| N _1x −n _2x | ≦ 0.02
Further, (n _1y −n _2y )> | n _1x −n _2x | is satisfied, and the polarization component (first order) that vibrates in the x-axis direction that proceeds in the direction orthogonal to the sheet surface of the optical sheet 40 (that is, the front direction). The optical sheet 40 may be configured so that light of one polarization component) travels in a direction that forms an angle of 2 ° or less with respect to the front direction after passing through the optical sheet 40.

Similarly, the following two conditions may be satisfied instead of the refractive index relationship shown in FIG.
(N _2y −n _1y )> | n _1x −n _2x |
| N _1x −n _2x | ≦ 0.02
Further, (n _2y −n _1y )> | n _1x −n _2x | is satisfied, and after the light of the first polarization component traveling in the front direction is transmitted through the optical sheet 40, it is 2 ° or less with respect to the front direction. The optical sheet 40 may be configured so as to proceed in a direction that forms the angle.

Furthermore, in the above-described embodiment, an example in which only the first layer 51 is optically anisotropic and the second layer 51 is optically isotropic has been described, but both the first layer 51 and the second layer 52 are described. Both may be optically anisotropic. In the example shown in FIG. 8 as an example, the refractive index n _1x in the x-axis direction of the first layer 51, the refractive index n _1y in the y-axis direction of the first layer 51, and the refraction in the x-axis direction of the second layer 52. The index n _2x and the refractive index n _{2y in} the y-axis direction of the second layer 51 satisfy the following relationship.
(N _1x −n _2x )> | n _1y −n _2y | = 0
n _1x > n _1y
n _2x <n _2y
According to the example shown in FIG. 8, the first refractive index difference between the first layer 51 and the second layer 52 in the y-axis direction is small and typically kept at 0, while the first index in the x-axis direction is kept. The difference in refractive index between the layer 51 and the second layer 52 can be increased. Thereby, the optical interface 55 of the optical sheet 40 can exhibit a strong optical function only with respect to the light of the polarization component that vibrates in the x-axis direction. The example shown in FIG. 8 can be manufactured by the manufacturing method described with reference to FIG. 10 as an example. At this time, a resin film 71 is produced using a material (for example, polyethylene naphthalate resin) in which the stretching direction and the slow axis direction coincide with each other, and the stretching direction and the fast axis direction coincide with each other. For example, the second resin film 72 may be manufactured using (styrene resin).

As already described, the following four conditions may be satisfied instead of the refractive index relationship shown in FIG.
(N _1x −n _2x )> | n _1y −n _2y |
| N _1y −n _2y | ≦ 0.02
n _1x > n _1y
n _2x <n _2y
Further, (n _1x −n _2x )> | n _1y −n _2y |, n _1x > n _1y and n _2x <n _2y are satisfied, and the direction orthogonal to the sheet surface of the optical sheet 40 (ie, the front direction). The light of the polarization component (second polarization component) oscillating in the y-axis direction that travels to the optical sheet 40 passes through the optical sheet 40 and then travels in a direction that forms an angle of 2 ° or less with respect to the front direction. It may be configured.

  Furthermore, in the above-described embodiment, the example in which the difference in refractive index between the first layer 51 and the second layer 52 in any one of the x-axis direction and the y-axis direction has been described. However, the refractive index difference between the first layer 51 and the second layer 52 may not be zero in both the x-axis direction and the y-axis direction. Also in this example, the effects similar to those of the above-described embodiment can be obtained by appropriately designing the configuration of the optical interface 55 and the unit optical interface 55a.

Further, in the above-described embodiment, the main axis (slow axis and fast axis) in the plane of the first layer 51 is vibration of light that forms an image with a wide viewing angle and light that forms an image with a narrow viewing angle. Although an example in which the direction matches is shown, it does not have to match. Also in this example, the effects similar to those of the above-described embodiment can be obtained by appropriately adjusting the sizes of the refractive indexes n _1x , n _1y , n _2x , and n _2y .

  Furthermore, in the above-described embodiment and its modifications, by stretching a resin film containing a thermoplastic resin, the first layer 51 and the second layer 52 of the optical sheet 40 have optical anisotropy, in other words, in-plane. An example of imparting birefringence was shown. However, the first layer 51 and the second layer 52 of the optical sheet 40 are formed as layers containing liquid crystal (liquid crystal molecules, liquid crystal material), and are provided with optical anisotropy by the light distribution of the liquid crystal. Also good. The first layer 51 or the second layer 52 of the optical sheet 40 is typically an ultraviolet curable type containing liquid crystal (liquid crystal molecules, liquid crystal material) on a base material that has been subjected to alignment treatment such as rubbing. It can be made by curing the resin. Also in such a modification, the same effect as the embodiment described above can be obtained.

  In addition, although the some modification with respect to embodiment mentioned above was demonstrated above, naturally, it is also possible to apply combining several modifications suitably.

DESCRIPTION OF SYMBOLS 10 Display apparatus 10a Display surface 15 Image display unit 20 Image forming apparatus 20a Image forming surface 21 Pixel 24 Backlight 25 Liquid crystal display panel 26 Polarizing plate, lower polarizing plate 27 Liquid crystal cell 28 Polarizing plate, upper polarizing plate 30 Polarization control device 31 Liquid crystal Molecule, liquid crystal material, liquid crystal 33 first support film 34 first electrode 35 liquid crystal layer 36 second electrode 37 second support film 40 optical sheet 43 film layer 51 first layer 52 second layer 55 optical interface, birefringence interface, lens Surface 55a Unit optical surface, unit lens

Claims (7)

A display device capable of switching a viewing direction in which an image can be viewed ,
A first layer having optical anisotropy, and a second layer that is laminated on the first layer and that forms an optical interface between the first layer and that changes the traveling direction of light of one polarization component. The optical interface has a plurality of unit optical interfaces arranged in one direction, and each unit optical interface extends in a direction non-parallel to the one direction, and the light proceeds according to the polarization state of the light. An optical sheet for controlling the direction;
An image display unit that is arranged facing the optical sheet and can switch and emit the light of the one polarization component and the light of the other polarization component in order to switch the viewing direction ;
The optical sheet directs the traveling direction of the light of the other deflection component emitted from the image display unit in a second direction, and sets the traveling direction of the light of the one deflection component emitted from the image display unit to the first direction. A display device oriented in a first direction different from the direction of 2 .   The image display unit includes an image forming apparatus having a pixel array, and a polarization control device disposed between the image forming apparatus and the optical sheet,
  The image forming apparatus emits one light of the light of the one deflection component and the light of the other deflection component from each pixel,
  The polarization control device maintains the polarization state of the light emitted from the image forming apparatus, and changes the polarization state of the light emitted from the image forming apparatus to change the one light to the one deflection component. The display device according to claim 1, wherein the display device can convert light into the other of the light and the light of the other deflection component.   3. The display device according to claim 1, wherein the unit optical interface has a shape that forms two sides of a triangle in a cross section parallel to both the normal direction and the one direction of the optical sheet.   4. The unit optical interface has a shape forming two equal sides of an isosceles triangle in a cross section parallel to both the normal direction and the one direction of the optical sheet. The display device according to item. The image display unit, when the viewing direction to the first direction, when the emitted light of the polarization component of the one, to the viewing direction to a second direction different from the first direction, the injecting the other polarization of light components, the display device according to any one of claims 1-4. The first layer comprises a thermoplastic resin, a display device according to any one of claims 1 to 5. The birefringence Δn in the plane of the first layer is 0.13 or more, the display device according to any one of claims 1 to 6.

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