JP2012003259A - Surface light source device and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device for improving luminance properties by enhancing use efficiency of the light of a light source.SOLUTION: A display device 10 comprises a transmission type display section 15 having a lower polarization plate 16, and a surface light source device 20 illuminating the transmission type display section from the side of the lower polarization plate. An optical anisotropic film 50 is provided closer to the incident side than the lower polarization plate. When observed from the front direction, the optical film is positioned so that an orientation axis of the optical anisotropic film with respect to an in-plane phase difference Re at the wavelength of 550 nm intersects a transmission axis Aa of the lower polarization plate.

Description

  The present invention relates to a display device and a surface light source device that can improve luminance characteristics by improving the utilization efficiency of light source light.

  A surface light source device used for a transmissive display device includes a light source and one or more optical sheets (optical films) for changing the traveling direction of light from the light source. The light source is typically composed of a linear cold cathode tube or a two-dimensionally arranged light emitting diode. In general surface light source devices, a light diffusion sheet that diffuses light from a light source to make the luminance distribution uniform according to the configuration of the light source (makes the light source image inconspicuous), and the light traveling direction to the front direction And a condensing sheet for improving the brightness in the front direction.

  As the condensing sheet, an optical sheet in which columnar unit-shaped elements (unit optical elements) extending linearly are arranged in a direction perpendicular to the longitudinal direction (so-called linear array or linear array) is widely used. (For example, Patent Document 1). The light-condensing sheet | seat which has the unit shape element extended linearly can be produced by shape | molding a unit shape element on a base film. As the base film, a stretched resin film (for example, a biaxially stretched PET film) having a stable quality and available at a low cost is used.

JP 2001-166116 A

  By the way, although a transmissive display device using a surface light source device, typically a liquid crystal display device using a liquid crystal display panel, has been rapidly spread so far, one of the important issues for further spread is cost reduction. Has been mentioned. Further, improving the utilization efficiency of light source light has been taken up as a big problem with respect to a transmissive display device (typically a liquid crystal display device). Particularly in recent years, as a part of countermeasures for environmental problems, there is a strong demand for an improvement in energy utilization efficiency for electrical appliances.

  The display device disclosed in Patent Document 1 incorporates a condensing sheet having a base material having birefringence and a plurality of linear prisms formed on the base material. In Patent Document 1, for the purpose of improving the utilization efficiency of the light source light, the base material is placed so that the polarization direction of the polarized light that has passed through the base material is substantially the same as the polarization direction of the lower polarizing plate of the liquid crystal panel. It has been proposed to position with respect to the liquid crystal panel. Similarly, Patent Document 1 proposes that the polarization axis direction of the base material forms a predetermined angle with respect to the ridge line direction of the prism.

  The inventors of the present invention have found that the configuration proposed in Patent Document 1 can be improved and further embodied by further earnest research, and the utilization efficiency of light source light can be further improved. That is, an object of the present invention is to provide a display device and a surface light source device that can improve luminance characteristics by improving the utilization efficiency of light source light.

A first display device according to the present invention includes:
A transmissive display unit having a lower polarizing plate and an upper polarizing plate;
A surface light source device that illuminates the transmissive display unit from the side of the lower polarizing plate,
An optically anisotropic film disposed on the light incident side with respect to the lower polarizing plate is provided, and this optically anisotropic film is a surface at a wavelength of 550 nm of the optically anisotropic film in the observation from the front direction. The alignment axis related to the inner phase difference Re is positioned so as to intersect the transmission axis of the lower polarizing plate.

A second display device according to the present invention includes:
A transmissive display unit having a lower polarizing plate and an upper polarizing plate;
A surface light source device that illuminates the transmissive display unit from the side of the lower polarizing plate,
An optically anisotropic film is provided on the light incident side with respect to the lower polarizing plate. This optically anisotropic film has a thickness direction position at a wavelength of 550 nm with respect to the optically anisotropic film in the observation from the front direction. The smaller angle formed by the principal axis related to the phase difference Rth and the transmission axis of the lower polarizing plate is the fast axis related to the in-plane retardation Re at the wavelength 550 nm of the optical anisotropic film and the lower polarization. It is positioned so as to be smaller than the smaller angle formed by the transmission axis of the plate.

  In the first or second display device according to the present invention, the optically anisotropic film has a fast axis related to an in-plane retardation Re at a wavelength of 550 nm with respect to the optically anisotropic film when observed from the front direction. The lower polarizing plate may be positioned so that the smaller angle formed by the transmission axis of the lower polarizing plate is 10 ° or more and 50 ° or less.

  In the first or second display device according to the present invention, the optical anisotropic film is disposed at a position closest to the lower polarizing plate from the light incident side in the optical anisotropic film included in the display device. It may be an optically anisotropic film.

  In the first or second display device according to the present invention, the in-plane retardation Re at a wavelength of 550 nm of the optically anisotropic film may be 500 nm or more and 5000 nm or less.

  In the first or second display device according to the present invention, the optically anisotropic film may be a stretched film.

  In the first or second display device according to the present invention, the surface light source device includes an optical sheet including a main body portion and a plurality of unit optical elements arranged on the main body portion, and the main body portion includes: The optically anisotropic film may be included. In the first or second display device according to the present invention, the plurality of unit optical elements are arranged in a certain direction on the main body, and each unit optical element intersects the arrangement direction. The optical sheet extends linearly in the upper direction, and the optical sheet has a smaller angle of 0 ° formed by the longitudinal direction of the unit optical element and the transmission axis of the lower polarizing plate in the observation from the front direction. It may be positioned so that it may be 45 degrees or less.

  Alternatively, in the first or second display device according to the present invention, the optically anisotropic film may be disposed so as to overlap the lower polarizing plate.

A first surface light source device according to the present invention includes:
A light source;
A reflective polarization separation sheet,
An optically anisotropic film is provided on the light incident side of the polarization separation sheet, and this optically anisotropic film has an in-plane retardation at a wavelength of 550 nm with respect to the optically anisotropic film when observed from the front direction. The alignment axis related to Re is positioned so as to intersect the transmission axis of the polarization separation sheet.

A second display device according to the present invention includes:
A light source;
A reflective polarization separation sheet,
An optically anisotropic film is provided on the light incident side of the polarized light separating sheet, and the optically anisotropic film has a thickness direction position at a wavelength of 550 nm with respect to the optically anisotropic film in the observation from the front direction. The smaller angle formed by the principal axis relating to the phase difference Rth and the transmission axis of the polarization separation sheet is the fast axis relating to the in-plane retardation Re at the wavelength of 550 nm for the optically anisotropic film and the polarization separation. You may position so that it may become smaller than the magnitude | size of the smaller angle made | formed with the said permeation | transmission axis | shaft of a sheet | seat.

  In the first or second surface light source device according to the present invention, the optically anisotropic film has a fast axis relating to an in-plane retardation Re at a wavelength of 550 nm with respect to the optically anisotropic film when observed from the front direction. And the small angle formed by the transmission axis of the polarization separation sheet may be positioned so as to be 10 ° or more and 50 ° or less.

  In the first or second surface light source device according to the present invention, the optically anisotropic film is a position closest to the polarization separation sheet from the light incident side in the optically anisotropic film included in the surface light source device. It may be an optically anisotropic film disposed on the surface.

  In the first or second surface light source device according to the present invention, the in-plane retardation Re at a wavelength of 550 nm of the optically anisotropic film may be 500 nm or more and 5000 nm or less.

  In the first or second surface light source device according to the present invention, the optically anisotropic film may be a stretched film.

  The first or second surface light source device according to the present invention further includes an optical sheet including a main body portion and a plurality of unit optical elements arranged on the main body portion, and the main body portion includes the optically anisotropic material. It may be configured to include an adhesive film. In the first or second surface light source device according to the present invention, the plurality of unit optical elements are arranged in a certain direction on the main body, and each unit optical element intersects the arrangement direction. The optical sheet extends linearly in the direction of the part, and the optical sheet has a smaller angle of 0 formed by the longitudinal direction of the unit optical element and the transmission axis of the polarization separation sheet in the observation from the front direction. It may be positioned so as to be at least 45 ° and at most 45 °.

A third display device according to the present invention includes:
One of the first and second surface light source devices according to the present invention described above;
A transmissive display unit disposed to face the surface light source device.

  According to the present invention, the luminance characteristics can be improved by improving the utilization efficiency of the light source light.

FIG. 1 is a perspective view showing a schematic configuration of a display device for explaining an embodiment according to the present invention. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1, showing the optical sheet incorporated in the display device in FIG. FIG. 3 is a diagram showing the lower polarizing plate and the optically anisotropic film incorporated in the display device of FIG. 1 from the front direction, and shows the transmission axis of the lower polarizing plate and the fast axis of the optically anisotropic film. It is a figure for demonstrating a relationship. FIG. 4 is a diagram showing a refractive index ellipsoid for the optically anisotropic film. FIG. 5 is a schematic diagram for explaining an example of a method for manufacturing an optical sheet. FIG. 6 is a diagram corresponding to FIG. 1 for explaining a modification of the display device. FIG. 7 is a diagram corresponding to FIG. 1 and illustrating a modification of the surface light source device. FIG. 8 shows an angle formed by the fast axis related to the in-plane retardation Re of the optically anisotropic film included in the main body of the optical sheet and the transmission axis of the lower polarizing plate in the display device according to Investigation 1. It is a graph which shows the relationship with front direction brightness | luminance. FIG. 9 shows an angle formed by the fast axis relating to the in-plane retardation Re of the optically anisotropic film included in the main body of the optical sheet and the transmission axis of the lower polarizing plate in the display device according to Investigation 2. It is a graph which shows the relationship with front direction brightness | luminance.

  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 5 are diagrams for explaining an embodiment according to the present invention. Among these, FIG. 1 is a perspective view showing a schematic configuration of a transmissive display device and a surface light source device, and FIG. 2 is a cross-sectional view of an optical sheet.

  The display device 10 illustrated in FIG. 1 includes a transmissive display unit 15 and a surface light source device 20 that is disposed on the back side of the transmissive display unit 15 and illuminates the transmissive display unit 15 in a planar shape from the back side. ing. The transmissive display unit 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel, and forms an image in the display region Z1.

  In the present embodiment, the transmissive display unit 15 includes a liquid crystal display panel. That is, the transmissive display device 10 functions as a liquid crystal display device. The liquid crystal display panel (transmissive display unit) 15 has a pair of polarizing plates 16 and 17 and a liquid crystal layer 18 disposed between the pair of polarizing plates. The polarizing plates 16 and 17 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. is doing.

  An electric field can be applied to the liquid crystal layer 18 for each region where one pixel is formed. Then, the orientation of the liquid crystal layer 18 applied with an electric field changes. As an example, the polarization component in a specific direction (direction parallel to the transmission axis) transmitted through the lower polarizing plate 16 disposed on the light incident side has a polarization direction of 90 when passing through the liquid crystal layer 18 to which an electric field is applied. Rotate and maintain the polarization direction when passing through the liquid crystal layer 18 where no electric field is applied. For this reason, depending on whether or not an electric field is applied to the liquid crystal layer 18, the polarized light component in a specific direction transmitted through the lower polarizing plate 16 further passes through the upper polarizing plate 17 disposed on the light output side of the lower polarizing plate 16, or It is possible to control whether the light is absorbed and blocked by the upper polarizing plate 17. In this specification, “upper and lower” in the “upper polarizing plate 17” and the “lower polarizing plate 16” means “upper” on the light emission side, that is, the image observer side with respect to the liquid crystal layer 18. Call the incoming side “down”. It does not necessarily correspond to up and down in the direction of gravity (vertical direction).

  In this way, the liquid crystal panel (transmission type display unit) 15 can control transmission or blocking of light from the surface light source device 20 for each pixel. The configuration of the liquid crystal panel (liquid crystal cell) can be configured in the same manner as a device (member) incorporated in a conventional liquid crystal display device, and detailed description thereof is omitted here.

  By the way, in this specification, the “light-emitting side” means the downstream side (observer side, in FIG. 2) in the traveling direction of light from the light source 25 to the observer through the transmissive display unit 15 without turning back the traveling direction. Is the upstream side in the traveling direction of light from the light source 25 to the viewer through the transmissive display unit 15 without being folded back (light source side, This is the lower side of the drawing in FIG.

  In addition, terms used in this specification for specifying shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, and “symmetric” are not limited to strict meanings, Interpretation will be made including errors to the extent that an expected function can be expected.

  As shown in FIG. 1, the surface light source device 20 includes a light source 25 and an optical sheet 40 that receives light from the light source 25. The optical sheet 40 deflects the traveling direction of light from the light source 25 by refraction and / or reflection, and transmits at least a part of the light. In the example shown in FIG. 1, a light diffusion sheet (lower diffusion plate) 30 that diffuses light is further provided on the light incident side of the optical sheet 40, that is, between the optical sheet 40 and the light source 25. Yes.

  The surface light source device 20 may be configured in various forms such as an edge light (side light) type, but is configured as a direct type backlight unit in the present embodiment. Therefore, the light source 25 is disposed so as to face the optical sheet 40 on the light incident side of the optical sheet 40. Further, the light source 25 is covered from the back side by the reflecting plate 28. The reflection plate 28 is formed in a box shape having an opening (window) on the optical sheet 40 side.

  In the present specification, the terms “sheet”, “film”, and “plate” are not distinguished from each other only based on the difference in names. Therefore, for example, a “sheet” is a concept including a member that can also be called a film or a plate. As one specific example, “optically anisotropic film” includes members called “optically anisotropic sheet” and “optically anisotropic plate”.

  Further, in this specification, the “sheet surface (film surface, plate surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed globally and globally. Refers to the surface. In the present embodiment, the sheet surface of the optical sheet 40, the sheet surface of the light diffusion sheet 30, the sheet surface of the main body 45 described later of the optical sheet 40, and the optical anisotropic film described later constituting the main body 45. The film surface 50, the light emitting surface 20a of the surface light source device 20, the display surface 10a of the transmissive display device 10 and the like are parallel to each other.

  The light source 25 can be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube, a spot LED (light emitting diode), an incandescent lamp, and a planar EL (electroluminescent element). In the present embodiment, as shown in FIG. 1, the light source 25 has a light emitting section 25a composed of a plurality of cold cathode tubes extending in a straight line. The reflecting plate 28 is a member for directing light from the light source 25 toward the transmissive display unit 15, and at least the inner surface of the reflecting plate 28 is a material having a high reflectance such as a metal or a dielectric multilayer film. It is made up of.

  The light diffusing sheet 30 diffuses incident light, preferably isotropically diffuses incident light, and brightness unevenness corresponding to the configuration of the light source 25 (brightness intensity pattern corresponding to the arrangement position of the light-emitting portion 25a. Is a sheet-like member for making the in-plane distribution of luminance uniform and making the image of the light source 25 inconspicuous. As such a light diffusion sheet 30, a sheet including a base and light diffusing particles dispersed in the base and having a light diffusion function may be used. As an example, by configuring the light diffusing particles from a material having a high reflectance, or by configuring the light diffusing particles from a material having a refractive index different from the material forming the base, A light diffusion function can be imparted.

  Next, the optical sheet 40 will be described. The optical sheet 40 in the present embodiment mainly exhibits a function (condensing function) that changes the traveling direction of light incident from the light incident side and emits the light from the light output side to intensively improve the luminance in the front direction. It is configured to do so. In the present specification, the “front direction” is a normal direction nd (see FIG. 2) with respect to the light emitting surface 20a of the surface light source device 20, and is also in a normal direction of the display surface 10a of the display device 10 or the like. Also match.

  As shown in FIG. 2, the optical sheet 40 includes a sheet-like main body 45 and a large number of unit optical elements (also referred to as unit shape elements) 42 arranged on the light exit side surface 45 a of the main body 45. Have. In the embodiment shown in FIG. 1, the optical sheet 40 is disposed on the most light-emitting side of the surface light source device 20, and the unit optical element 42 of the optical sheet 40 is transmitted through the transmissive display unit 15 (particularly, in the illustrated example, transmission Adjacent to the lower polarizing plate 16) of the mold display section 15.

  As shown in FIG. 2, the main body 45 includes an optical anisotropic film 50 and a resin layer 47 laminated on the light output side of the optical anisotropic film 50. The resin layer 47 is a layer formed of the same resin material as that of the unit optical element 42 due to the manufacturing method of the optical sheet 40 described later, and may be omitted. As shown in FIG. 2, in the present embodiment, the main body 45 is a smooth light that forms the light incident side surface 40 b of the optical sheet 40 as the light incident side surface 45 b that faces the light output side surface 45 a on which the unit optical element 42 is formed. Has a surface. This smooth surface is formed by the optical anisotropic film 50.

  The optically anisotropic film 50 is a film having at least an in-plane retardation Re that exhibits different values of refractive indexes in two axial directions that are parallel to the film surface of the film and orthogonal to each other. As the optical anisotropic film 50, for example, a film obtained by stretching (stretching) a polymer film by applying a force in one or more specific directions can be used. Such stretched films are used in various fields, such as packaging films, and are generally available at low cost while having stable mechanical and chemical properties. In many stretched films, the arrangement of the polymers has regularity due to the stretching process during production, and the axial directions of two light distribution axes that are parallel to the film surface of the film and perpendicular to each other ( The refractive indexes in the fast axis Ab direction and the slow axis direction orthogonal to this in FIG. 4 come to have different values (birefringence). Furthermore, in many biaxially stretched films adopted in this embodiment, as shown in FIG. 4, the major axis Ac of the refractive index ellipsoid is in the thickness direction (front direction, Z direction in FIG. 4). Inclined from.

  In the present embodiment, as an example, the optically anisotropic film 50 is made of biaxially stretched polyethylene terephthalate. As shown in FIG. 3, in the observation from the front direction, the orientation axis related to the in-plane retardation Re at the wavelength of 550 nm for the optical anisotropic film 50, that is, both the fast axis Ab and the slow axis are lower. The transmissive display unit 15 including the lower polarizing plate 16 and the optical sheet 40 including the optical anisotropic film 50 are positioned with respect to each other so as to intersect the transmission axis Aa of the polarizing plate 16. In particular, according to the present embodiment, in the observation from the front direction, by the fast axis Ab with respect to the in-plane retardation Re at the wavelength 550 nm for the optical anisotropic film 50 and the transmission axis Aa of the lower polarizing plate 16. Of the angles formed, the minor angle, that is, the magnitude (absolute value) of the smaller angle θ1 is 10 ° or more and 50 ° or less. When the present inventors have conducted extensive experiments, the brightness of the image displayed by the display device 10 is determined by inclining the orientation axis related to the in-plane retardation Re with respect to the transmission axis Aa in the observation from the front direction nd. Was able to brighten. In particular, the magnitude (absolute value) of the smaller angle θ1 among the angles formed by the fast axis Ab and the transmission axis Aa related to the in-plane phase difference Re in the observation from the front direction is 10 ° to 50 °. If so, a film (for example, a TAC film) having no in-plane retardation is used as compared with the case where any of the orientation axes related to the in-plane retardation Re is parallel to the transmission axis Aa. Compared with the case where it was, the brightness of the image | video displayed by the display apparatus 10 was able to be raised to such an extent that it could distinguish visually.

  Furthermore, in the present embodiment, as shown in FIG. 3, in the observation from the front direction, the main axis Ac regarding the thickness direction retardation Rth of the optical anisotropic film 50 at the wavelength of 550 nm and the transmission axis of the lower polarizing plate 16. The magnitude (absolute value) of the smaller angle θ2 of the angles formed by Aa is the fast axis Ab with respect to the in-plane retardation Re at the wavelength 550 nm for the optical anisotropic film 50 and the lower polarizing plate 16. A transmission type display unit 15 including the lower polarizing plate 16 and an optically anisotropic film so as to be smaller than the size (absolute value) of the smaller angle θ1 among the angles formed by the transmission axis Aa The optical sheet 40 including 50 is positioned with respect to each other. As a result of repeated experiments by the present inventors, the magnitude (absolute value) of the angle θ2 formed by the main axis Ac and the transmission axis Aa related to the thickness direction phase difference Rth in the observation from the front direction is If it is smaller than the magnitude (absolute value) of the angle θ1 formed by the fast axis Ab and the transmission axis Aa with respect to the in-plane phase difference Re in the observation, the magnitude (absolute value) of the angle θ2 is the above-mentioned. Compared with the case where the angle θ1 is greater than or equal to the magnitude (absolute value), the brightness of the image displayed by the display device 10 can be increased to a level that can be visually discriminated.

  Further, in order to increase the brightness of the display image by positioning the optically anisotropic film 50 with respect to the lower polarizing plate 16, the in-plane retardation Re at a wavelength of 550 nm for the optically anisotropic film 50 is 500 nm or more. It is preferable that it is 5000 nm or less. This is because when the in-plane retardation Re of the optically anisotropic film 50 is within this range, the brightness of the displayed image can be effectively increased.

  The phase advance axis Ab related to the in-plane retardation Re of the optically anisotropic film 50 is an axis extending in the direction in which the refractive index is the smallest of the directions parallel to the film surface of the optically anisotropic film 50. . On the other hand, the main axis Ac with respect to the thickness direction retardation Rth is an axis in a direction parallel to the major axis of the refractive index ellipsoid of the optically anisotropic film 50 as shown in FIG. The angle θ2 formed by the principal axis Ac with respect to the thickness direction retardation Rth and the transmission axis Aa in the observation from the front direction is the film surface of the optical anisotropic film 50 with respect to the principal axis Ac with respect to the thickness direction retardation Rth. This corresponds to the angle formed by the axis Ac ′ projected through the orthogonal projection and the transmission axis Aa. The fast axis Ab related to the in-plane phase difference Re and the main axis Ac related to the thickness direction phase difference Rth are “Ellipsometer M150” manufactured by JASCO Corporation or an automatic birefringence meter manufactured by Oji Scientific Instruments Co., Ltd. It can be specified using “KOBRA21ADH”. The slow axis related to the in-plane retardation Re is an axis extending on the film surface (XY plane) of the optical anisotropic film 50 in a direction orthogonal to the fast axis Ab related to the in-plane retardation Re. The slow axis related to the in-plane phase difference Re can be specified using the same device as the fast axis Ab related to the in-plane phase difference Re.

  Further, the in-plane phase difference Re, the fast axis Ab related to the in-plane phase difference Re, the thickness direction phase difference Rth, the main axis Ac related to the thickness direction phase difference Rth, the transmission axis Aa of the lower polarizing plate 16, and the like are used for measurement. It depends on the wavelength used. In the above description, as an example, the fast axis Ab and the thickness with respect to the in-plane phase difference Re at a wavelength of 550 nm of green light that is one of the three primary colors of light that is located at the center of the visible light wavelength range. Although it has been described that the main axis Ac with respect to the direction phase difference Rth and the transmission axis Aa of the lower polarizing plate 16 satisfy the predetermined condition, the present invention is not limited to this, and the above-described condition may be satisfied in the entire wavelength range of visible light. Good.

  By the way, when the optically anisotropic film 50 is formed by biaxial stretching, strictly speaking, the shape of the refractive index ellipsoid changes at each position in the optically anisotropic film 50. That is, the aforementioned angles θ1 and θ2 of the optically anisotropic film 50 included in the optical sheet 40 with respect to the fast axis Ab and the main axis Ac with respect to the transmission axis Aa also change at each position in the optically anisotropic film 50. However, in general, a change in brightness at the center of the display area Z1 is easily perceived by the observer, and conversely, a change in brightness at the edge of the display area Z1 is not easily perceived by the observer. That is, in order to expect the above-described effects, it is important to evaluate the angles θ1 and θ2 of the fast axis Ab and the main axis Ac with respect to the transmission axis Aa at the center of the display region Z1, and in the present invention, the fast axis Ab and the main axis Ac are specified at the center of the display area. For example, if the display area is formed in a rectangular shape, the fast axis Ab and the main axis Ac are specified at the intersection of a pair of diagonal lines related to the rectangular shape.

  Next, the unit optical element (unit shape element, unit prism, unit lens) 42 will be described. As shown in FIG. 2, in the present embodiment, the unit optical elements 42 are arranged side by side on the light output side surface 45 a of the main body 45 without leaving a gap. As a result, the light exit surface 40 a of the optical sheet 40 is constituted only by the light exit surface 42 a of the unit optical element 42.

  As shown in FIG. 1, a large number of unit optical elements 42 are arranged in a certain arrangement direction on the light exit side surface 45 a of the main body 45. Each unit optical element 42 extends linearly in a direction intersecting with the arrangement direction. In particular, in the present embodiment, the unit optical element 42 extends linearly. The longitudinal direction of the unit optical elements 42 is orthogonal to the arrangement direction of the unit optical elements 42 on a plane parallel to the sheet surface of the main body 45. As can be understood from FIG. 1, in the observation from the front direction, the arrangement direction of the unit optical elements 42 of the optical sheet 40 is parallel to the arrangement direction of the elongated light emitting portions (cold cathode tubes) 25a forming the light source 25. It has become.

  In FIG. 2, a cross section parallel to both the normal direction nd (see FIG. 1) of the sheet surface of the main body 45 of the optical sheet 40 and the arrangement direction of the unit optical elements 42 (also referred to as “main cutting surface of the optical sheet”). The optical sheet 40 is shown in FIG. In the present embodiment, as shown in FIG. 2, each unit optical element 42 has a triangular shape that protrudes toward the light exit side on the main cut surface of the optical sheet. From the viewpoint of intensively improving the brightness in the front direction, the cross-sectional shape is particularly an isosceles triangle shape, and the apex angle located between the equilateral sides protrudes from the light exit side surface 45a of the main body 45 to the light exit side. As described above, each unit optical element 42 is configured.

  Further, in the present embodiment, the cross-sectional shape of each unit optical element 42 on the main cut surface of the optical sheet is a right-angled isosceles triangle shape with a 90 ° apex angle projecting to the light exit surface side, and the unit optical element 42 It is constant along the longitudinal direction (direction extending linearly). The plurality of unit optical elements 42 included in the optical sheet 40 are all configured in the same manner.

  As a specific example of the unit optical element 42 having the above-described configuration, the arrangement pitch P of the unit optical elements 42 along the arrangement direction of the unit optical elements 42 (see FIG. 2: in the present embodiment, the unit optical elements 42 Can be 5 μm to 200 μm. Further, the protrusion height H (see FIG. 2) of the second unit optical element 42 from the light exit side surface 45a of the main body 45 along the normal direction nd to the sheet surface of the optical sheet 40 may be 1 μm to 150 μm. it can. Furthermore, when the cross-sectional shape of the unit optical element 42 is an isosceles triangle, from the viewpoint of intensively improving the luminance in the front direction, the apex angle θt ( 2) is preferably 80 ° or more and 120 ° or less, and more preferably 90 °.

  Next, an example of a method for manufacturing the optical sheet 40 having the above configuration will be described. In the following example, the unit optical element 42 can be formed on the optically anisotropic film 50 together with the resin layer 47 by molding using a molding apparatus 60 as shown in FIG. As a material used for forming the unit optical element 42 and the resin layer 47, a resin having good moldability and being easily available and having excellent light transmittance (for example, a refractive index of a cured product of 1.57). A transparent cured product of a composition of a transparent polyfunctional urethane acrylate oligomer and a dipentaerythritol hexaacrylate monomer) is preferably used.

  First, the molding apparatus 60 will be described. As shown in FIG. 5, the molding apparatus 60 has a molding die 70 having a substantially cylindrical outer contour. A cylindrical mold surface (uneven surface) 72 is formed in a portion corresponding to the outer peripheral surface (side surface) of the column of the molding die 70. The molding die 70 having a cylindrical shape has a central axis CA that passes through the center of the outer peripheral surface of the cylinder, in other words, a central axis CA that passes through the center of the cross section of the cylinder. On the mold surface 72, a recess (not shown) corresponding to the unit optical element 42 of the optical sheet 40 is formed. That is, the molding die 70 is configured as a roll die that molds the optical sheet 40 as a molded product while rotating around the central axis CA as a rotation axis (see FIG. 5).

  As shown in FIG. 5, the molding device 60 includes a molding base material supply device 62 that supplies an optical anisotropic film (molding base material sheet) 50 extending in a strip shape, and the supplied optical anisotropic film 50. A material supply device 64 that supplies a fluid material 43 between the molding surface 70 and the mold surface 72 of the molding die 70, and a material 43 between the optically anisotropic film 50 and the irregular surface 72 of the molding die 70. And a curing device 66 for curing. The curing device 66 can be appropriately configured according to the curing characteristics of the material 43 to be cured.

  Next, a method for producing the optical sheet 40 using such a molding apparatus 60 will be described. First, the optically anisotropic film 50 extending in a belt shape is supplied from a molding substrate supply device 62. In the present embodiment, for example, the supplied optical anisotropic film 50 has good mechanical properties (such as strength), chemical properties (such as stability), and optical properties (such as transparency). It is made of biaxially stretched polyethylene terephthalate that is available at low cost. As shown in FIG. 5, the supplied optically anisotropic film 50 is fed into a molding die 70, and is opposed to the uneven surface 72 of the die 70 by the molding die 70 and a pair of rollers 68. Will be held.

  Further, as shown in FIG. 5, as the optical anisotropic film 50 is supplied, a material having fluidity from the material supply device 64 between the optical anisotropic film 50 and the mold surface 72 of the molding die 70. 43 is supplied. This material 43 forms the unit optical element 42 and the resin layer 47 of the main body 45. Here, “having fluidity” means that the material 43 supplied to the mold surface 72 of the mold 70 has such fluidity that it can enter into a recess (not shown) of the mold surface 72. means.

  As the material 43 to be supplied, various known materials that can be used for molding (for example, the composition of a transparent polyfunctional urethane acrylate oligomer having a refractive index of 1.57 as described above and a dipentaerythritol hexaacrylate monomer). Ionizing radiation curable resin comprising a crosslinked cured product of the product. In the example shown below, an example in which ionizing radiation curable resin is supplied from the material supply device 64 will be described. As the ionizing radiation curable resin, for example, a UV curable resin that is cured by being irradiated with ultraviolet rays (UV) or an EB curable resin that is cured by being irradiated with an electron beam (EB) may be selected. it can.

  Thereafter, the optically anisotropic film 50 as a molding substrate passes through a position facing the curing device 66 in a state where the space between the mold 60 and the mold surface 72 is filled with an ionizing radiation curable resin. At this time, ionizing radiation corresponding to the curing characteristics of the ionizing radiation curable resin 43 is emitted from the curing device 66, and the ionizing radiation is transmitted through the optical anisotropic film 50 and irradiated to the ionizing radiation curable resin 43. Is done. When the ionizing radiation curable resin 43 is an ultraviolet curable resin, the curing device 66 is, for example, an ultraviolet irradiation device such as a high-pressure mercury lamp. As a result, the ionizing radiation curable resin 43 filled between the mold surface 72 and the optically anisotropic film 50 is cured, and the unit optical element 42 and the main body 45 made of the cured ionizing radiation curable resin are cured. The resin layer 47 is formed on the optical anisotropic film 50.

  Thereafter, as shown in FIG. 5, the optical anisotropic film 50 is separated from the mold 70, and accordingly, the unit optical element 42 molded in the concave portion of the mold surface 72 is formed on the optical anisotropic film 50. Together with the joined resin layer 47, it is pulled away from the mold 60 at the roller 68 on the right side in the figure. In this way, the optical sheet 40 described above is obtained.

  In the manufacturing method described above, the optically anisotropic film 50 is not in contact with the surface 72 of the mold 70. For this reason, as described above, the main body 45 of the produced optical sheet 40 includes the optical anisotropic film 50, the resin layer 47 that is surface-bonded to the optical anisotropic film 50 and cured into a sheet, It will be composed of. According to such a method, it is possible to effectively prevent the molded unit optical element 42 from partially remaining in the recess of the mold 70 at the time of mold release.

  As described above, while the molding die 70 configured as a roll die is rotated about its central axis CA, the material 43 having fluidity is supplied into the die 70; The process of curing the material 43 supplied into the mold 70 in the mold 70 and the process of removing the cured material 43 from the mold 70 are sequentially performed on the mold surface 72 of the mold 70, whereby the optical sheet 40 is obtained. It is done.

  Next, the operation of the display device 10 as described above will be described.

  In FIG. 1, the light emitted from the light source 25 travels to the viewer side either directly or after being reflected by the reflecting plate 28. The light traveling toward the viewer side is isotropically diffused by the light diffusion sheet 30 and then enters the optical sheet 40. The incident light passes through the main body 45, reaches the unit optical element 42 of the optical sheet 40, and then exits from the unit optical element 42.

  In FIG. 1, light L <b> 21 and L <b> 22 emitted from the unit optical element 42 is refracted on the light exit side surface (prism surface) 42 a of the unit optical element (unit prism) 40. Due to this refraction, the traveling direction (outgoing direction) of the light L21 and L22 traveling in the direction inclined from the front direction nd is mainly compared with the traveling direction of the light just before entering the optical sheet 40. Bending is performed so that the angle with respect to the normal direction nd to the surface is small (see FIG. 2). By such an action of the optical sheet 40, the unit optical element 42 can narrow the traveling direction of the transmitted light to the front direction nd side. That is, the unit optical element 42 condenses the transmitted light and changes the angular distribution of the luminance so that the luminance in the front direction is intensively increased.

  Note that the light condensing action of the unit optical element 42 is more effectively exerted on the light traveling with a large inclination from the front direction nd. For this reason, although depending on the degree of diffusion by the light diffusion sheet 30 disposed on the light source side relative to the optical sheet 40, the light source 25 moves away from the light source 25 that tends to be incident at a large incident angle. In this area, the luminance in the front direction can be effectively increased (see the light L21 in FIG. 4).

  On the other hand, as shown in FIG. 2, the light L23 having a small inclination angle in the traveling direction with respect to the front direction nd repeats total reflection on the light exit side surface (lens surface) of the unit optical element 42, and the traveling direction is set to the light incident side. It may change to (light source side). For this reason, although depending on the degree of diffusion by the light diffusion sheet 30 disposed on the light source side relative to the optical sheet 40, a large amount of light tends to be incident from the light source 25 at a small incident angle. It is possible to prevent the luminance from becoming too high at the position.

  Thus, depending on the distance from the light source 25 in the direction parallel to the light emitting surface 20a of the surface light source device 20, the optical action mainly exerted from the unit lens 40 on the transmitted light is different. Thereby, the luminance unevenness (tube unevenness) generated according to the arrangement of the light emitting portions 25a of the light source 25 can be effectively reduced, and the light source image (light image) can be made inconspicuous. That is, the optical sheet 40 also exerts a light diffusing action on the transmitted light, and functions to make the in-plane variation in luminance uniform.

  As described above, the emission angle of the light emitted from the optical sheet 40 can be narrowed down to a narrow angle range centering on the front direction while eliminating the in-plane variation in luminance caused by the configuration of the light source 25. .

  The light emitted from the optical sheet 40 is then incident on the transmissive display unit 15. The transmissive display unit 15 selectively transmits the light from the surface light source device 20 for each pixel. Thereby, the observer of the transmissive display apparatus 10 can observe an image.

  By the way, the lower polarizing plate 16 of the transmissive display unit 15 transmits the polarization component in the direction parallel to the transmission axis Aa and absorbs the polarization component in the direction parallel to the absorption axis orthogonal to the transmission axis Aa. That is, a part of the light traveling from the optical sheet 40 to the transmissive display unit 15 is absorbed by the lower polarizing plate 16. Further, as described above, the main body portion 45 of the optical sheet 40 disposed on the light incident side of the lower polarizing plate 16 is configured using the optical anisotropic film 50. The refractive index of the optically anisotropic film 50 is different between the fast axis direction and the slow axis direction. For this reason, the light transmitted through the optically anisotropic film 50 causes a phase difference in the transmitted light between the polarized component whose electric field vibrates in the fast axis direction and the polarized component whose electric field vibrates in the slow axis direction. As a result, when linearly polarized light having different electric field strength in the fast axis direction and different electric field strength in the slow axis direction is transmitted, the polarization direction (vibration direction of the electric field) before and after transmission is the leading phase of the film 50. It has the property of rotating by an angle corresponding to the difference in refractive index and thickness between the axial direction and the slow axis direction.

  Further, in the display device as shown in FIG. 1, in the light beam path from the light source 25 to the transmissive display unit 15, there is a tendency to be polarized by various existing members, particularly the unit optical element 42. When assembling a display device as shown in FIG. 1 by a normal optical design, as a result of securing constraints on the manufacturing process and various performances required by the display device, for example, vertical and horizontal viewing angles for an observer, image contrast, The polarization direction generated by the unit optical element 42 and the like is different from the transmission axis of the lower polarizing plate 16 of the transmissive display unit 15. For example, in the display device having the configuration shown in FIG. 1, as a result of such overall design, the extending direction of the unit optical element 42 represented by a triangular prism and the lower polarizing plate 16 mainly by the polarization action of the unit optical element 42. The transmission axes are aligned with each other.

  Therefore, as described above, the fast axis Ab and the slow axis related to the in-plane retardation Re of the optically anisotropic film 50 intersect the transmission axis Aa of the lower polarizing plate 16 when observed from the front direction. . More specifically, the fast axis Ab related to the in-plane retardation Re of the optically anisotropic film 50 is 10 ° or more and 50 ° or less with respect to the transmission axis Aa of the lower polarizing plate 16 when observed from the front direction. It is inclined at an angle of the size of. Thus, when the fast axis Ab related to the in-plane retardation Re of the optical anisotropic film 50 is positioned with respect to the transmission axis Aa of the lower polarizing plate 16, the light of the linearly polarized light component generated by the unit optical element 42 On the other hand, the optically anisotropic film 50 can rotate the vibration direction of the light of the linearly polarized light component to reduce the deviation between the vibration direction and the transmission axis of the lower polarizing plate 16. In fact, it has been confirmed that the luminance of light (image light) emitted from the transmissive display portion 15 is increased by such a configuration.

  However, if only the mechanism as described above is used, the configuration in which the optically anisotropic film 50 is disposed on the light output side of the unit optical element 42 can reasonably explain the brightness enhancement effect. In the case of the configuration in which the optical anisotropic film 50 is disposed on the light incident side of the unit optical element 42 as shown in FIG.

  However, when the inventors repeated diligent experiments, contrary to such an expectation, the optical anisotropic film 50 is arranged on the light incident side of the unit optical element 42 as shown in FIG. In some cases, it was confirmed that the display device 10 can display a bright image. Although the details of the reason why such a phenomenon occurs are unknown, in the optically anisotropic film 50 employed in the present invention, in fact, the light transmittance transmitted through the film 50 and the polarization state of the transmitted light are: It is estimated that not only the orientation axis related to the in-plane retardation Re but also the principal axis Ac related to the thickness direction retardation Rth.

  As a result of repeating the diligent experiments, the inventors of the present invention have observed that the main axis Ac related to the thickness direction phase difference Rth is closer to the transmission axis Aa than the fast axis Ab related to the in-plane phase difference Re in the observation from the front direction. 3, that is, when the magnitude (absolute value) of the angle θ2 in FIG. 3 is smaller than the magnitude (absolute value) of the angle θ1, the magnitude (absolute value) of the angle θ2 is the magnitude (absolute value) of the angle θ1. It was also confirmed that the display device 10 can brightly display an image as compared with the case described above. The confirmation result agrees with the estimation that the light transmittance transmitted through the optical anisotropic film 50 and the polarization state of the transmitted light are also greatly influenced by the principal axis Ac with respect to the thickness direction retardation Rth. is there.

  According to the present embodiment as described above, an image can be displayed brighter on the display device 10 by effectively using the light from the light source 25 without increasing the light emission amount from the light source 25. That is, according to the present embodiment, it is possible to improve the luminance characteristics of the surface light source device 20 and the display device 10 by improving the utilization efficiency of light from the light source 25.

  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 as appropriate. In FIGS. 6 and 7 to be referred to in the following modifications, the same reference numerals as those used for the corresponding parts in the above-described embodiment are attached to the parts that can be configured in the same manner as the above-described embodiment. is doing.

  For example, in the above-described embodiment, the unit optical element (unit prism) 42 having a cross section of a right isosceles triangle is formed on the main section 45 including the optically anisotropic film 50. However, the present invention is not limited to this. For example, the cross-sectional shape at the main cutting surface of the unit optical element 42 may be a shape obtained by modulating and deforming a triangular shape for the purpose of imparting various characteristics. As a specific example, in order to adjust the optical function appropriately, the cross-sectional shape of the unit optical element 42 is a shape in which any one or more sides of the triangle are bent (bent), or a shape in which any one or more sides of the triangle are curved. (So-called fan shape), a shape in which the vicinity of the apex of the triangle is curved and rounded, or a shape in which minute irregularities are provided on one or more sides of the triangle may be used. Further, the cross-sectional shape of the unit optical element 42 at the main cut surface may have a shape other than the triangular shape, for example, various polygonal shapes such as a quadrangle such as a trapezoid, a pentagon, or a hexagon. Further, as shown in FIG. 6, the cross-sectional shape of the unit optical element 42 at the main cut surface may have a shape corresponding to a part of a circle, an ellipse, a fence line, a hyperbola, or a sinusoidal curve.

  Further, in the above-described embodiment, an example in which a large number of unit optical elements 42 extending linearly are formed on the main body portion 45 including the optical anisotropic film 50 is not limited thereto. I can't. Unit optical elements constituting a fly-eye lens (microlens) may be arranged on the main body 45 including the optically anisotropic film 50. As an example, unit optical elements consisting of a part of a spheroid or unit optical elements consisting of a part of a sphere such as a hemisphere may be arranged two-dimensionally on the main body 45.

  Furthermore, in the above-described embodiment, the example in which the unit shape elements 42 provided on the main body portion 45 including the optically anisotropic film 50 have the same configuration is shown. Two or more unit-shaped elements provided on the main body portion 45 including the optically anisotropic film 50 may have different shapes.

  Furthermore, in the above-described embodiment, among the optical anisotropic films incorporated in the display device 10, the optical anisotropic film 50 disposed at a position closest to the lower polarizing plate 16 from the light incident side, Although the example contained in the main-body part 45 of the optical sheet 40 was shown, it is not restricted to this. For example, as shown in FIG. 6, among the optical anisotropic films incorporated in the display device 10, the optical anisotropic film 51 disposed at the position closest to the lower polarizing plate 16 from the light incident side is It may be stacked adjacent to the lower polarizing plate 16 from the light incident side or via a separate layer (a mode shown in FIG. 6), or may be disposed facing the light incident side of the lower polarizing plate 16 with a gap. . As a specific example, the optical anisotropic film 51 may function as a film that protects the lower polarizing plate 16 from scratches or the like, or a base material that supports the lower polarizing plate 16.

In addition, when the inventors of the present invention repeatedly confirmed and confirmed that the unit-shaped element 42 formed on the main body 45 including the optically anisotropic film 50 was modified, the optical anisotropic Even in the above-described modification of changing the arrangement position of the conductive film 50, as described above,
-By making the orientation axis related to the in-plane retardation Re at the wavelength 550 nm for the optically anisotropic film 50 intersect the transmission axis Aa of the lower polarizing plate 16, By making the fast axis Ab related to the in-plane retardation Re at a wavelength of 550 nm intersect with the transmission axis Aa of the lower polarizing plate 16 at an angle of 10 ° to 50 ° (absolute value), And / or
In observation from the front direction, the magnitude of the smaller angle θ2 formed by the main axis Ac and the transmission axis Aa of the lower polarizing plate 16 with respect to the thickness direction retardation Rth at the wavelength of 550 nm for the optical anisotropic film 50 (Absolute value) is the size of the smaller angle θ1 formed by the fast axis Ab with respect to the in-plane retardation Re at the wavelength 550 nm and the transmission axis Aa of the lower polarizing plate 16 for the optically anisotropic film 50 ( By positioning so as to be smaller than the absolute value)
The brightness of the image displayed by the display device 10 can be improved.

  Further, in the above-described embodiment, the light emitting unit 25a of the light source 25 of the surface light source device 20 is formed of a cold cathode tube extending linearly, but is not limited thereto. As the light source 25, it is also possible to use a light-emitting unit made up of a spot-like LED (light-emitting diode), an incandescent light bulb, or the like, or a planar EL (electric field emitter). In the above-described embodiment, an example in which the optical sheet 40 is applied to the direct-type surface light source device 20 has been described, but the present invention is not limited thereto. It is also possible to apply the optical sheet 40 described above to, for example, an edge light type (also referred to as a side light type) surface light source device. In such a case as well, the optical sheet 40 is a direct type surface light source device 20. The effect similar to the case where it is applied to can be produced.

  Furthermore, in the above-described embodiment, an example of the overall configuration of the surface light source device 20 and the transmissive display device 10 in which the optical sheet 40 is incorporated has been described, but is not limited thereto. For example, the arrangement position may be changed as appropriate, or another sheet-like member may be added. As described above, the orientation axis (the fast axis Ab and the slow axis) related to the in-plane retardation Re of the optical anisotropic film 50 and the main axis Ac related to the thickness direction retardation Rth are transmitted through the lower polarizing plate 16. By maintaining the predetermined relationship described above with respect to the axis Aa, the brightness of the image displayed by the display device 10 can be increased. Therefore, a sheet that can affect the polarization state of light between the optically anisotropic film 50 and the lower polarizing plate 16 that are positioned with respect to each other in order to make it possible to enjoy such effects more remarkably. Is preferably not interposed.

  By the way, as shown in FIG. 7, a reflective polarization separation sheet 52 may be used for the surface light source device 20. The reflective polarization separation sheet 52 transmits the polarization component in the direction parallel to the transmission axis Ad, and reflects the polarization component in the direction parallel to the reflection axis orthogonal to the transmission axis Ad. Usually, in the observation from the front direction, the reflection type polarization separation sheet 52 of the surface light source device 20 is transmitted so that the transmission axis Ad of the reflection type polarization separation sheet 52 is parallel to the transmission axis Aa of the lower polarizing plate 16. The mold display unit 15 is positioned with respect to the lower polarizing plate 16. In general, in order to prevent the polarization state of light from being disturbed between the reflective polarization separation sheet 52 and the lower polarizing plate 16, the reflective polarization separation sheet 52 is the most light-emitting element of the surface light source device 20. The light emitting surface 20a of the surface light source device 20 is formed in many cases.

  In the display device 10 shown in FIG. 7, a part of the light traveling from the optical sheet 40 to the transmissive display unit 15 is transmitted through the polarization separation sheet 52, and the other light is reflected by the polarization separation sheet 52. The direction of travel is folded back toward the light incident side. After that, the light reflected by the polarization separation sheet 52 changes its polarization state by being repeatedly reflected and refracted, and can pass through the polarization separation sheet 52 again. That is, the reflective polarization separation sheet 52 recycles the light that should be absorbed by the lower polarizing plate 16, thereby contributing to improving the utilization efficiency of the light from the light source 25.

  As such a reflective polarization separation sheet 52, “DBEF” (registered trademark) available from 3M USA can be used. In addition to “DBEF”, a high-intensity polarizing sheet “WRPS” (registered trademark) available from Shinwha Intertek, Korea, a wire grid polarizer, or the like can also be used. Furthermore, for example, it has an optical rotation selection layer composed of a cholesteric liquid crystal layer having cholesteric regularity, and a quarter wavelength layer (λ / 4 retardation layer) laminated on the light output side of the optical rotation selection layer. The film member can be used as the reflective polarization separation sheet 52.

  In the surface light source device 20 including the polarization separation sheet 52, the inventors of the present invention have an orientation axis (fast axis Ab and slow axis) and a thickness direction retardation with respect to the in-plane retardation Re of the optically anisotropic film 50. The influence of the principal axis Ac on Rth on the transmission axis Ad of the polarization separation sheet 52 was also investigated. As a result, the orientation axis (the fast axis Ab and the slow axis) related to the in-plane retardation Re of the optical anisotropic film 50 and the main axis Ac related to the thickness direction retardation Rth are described above with respect to the transmission axis Aa of the lower polarization 16. In the same manner as the positioning, by positioning with respect to the transmission axis Ad of the polarization separation sheet 52, it was possible to obtain the same effect as the above-described embodiment.

  That is, in the observation from the front direction, the optically anisotropic film 50 and the reflective film are reflected so that the orientation axis related to the in-plane retardation Re of the optically anisotropic film 50 intersects the transmission axis Ad of the reflective polarization separation sheet 52. It is preferable that the polarizing plate 52 is positioned with respect to each other. In particular, in observation from the front direction, the fast axis Ab relating to the in-plane retardation Re of the optically anisotropic film 50 and the reflective polarizing separation Of the angles formed by the transmission axis Ad of the sheet 52, the smaller angle (absolute value) is preferably 10 ° to 50 °.

  As a result of repeated diligent experiments conducted by the present inventors, the brightness of the image displayed by the display device 10 is determined by inclining the orientation axis related to the in-plane retardation Re with respect to the transmission axis Ad in the observation from the front direction. I was able to brighten up. In particular, the smaller one of the angles formed by the fast axis Ab and the transmission axis Ad with respect to the in-plane phase difference Re in the observation from the front direction (absolute value) is 10 ° or more and 50 ° or less. If this is the case, a film (for example, a TAC film) having no in-plane retardation is used as compared with the case where the fast axis Ab and the transmission axis Aa are in parallel with respect to the in-plane retardation Re. Compared to the case, the brightness of the image displayed by the display device 10 could be increased to a level that can be visually discriminated.

  Further, the smaller one of the angles (absolute value) of the angles formed by the main axis Ac and the transmission axis Ad of the reflective polarization separation sheet 52 with respect to the thickness direction retardation Rth of the optically anisotropic film 50. From the angle (absolute value) of the smaller one of the angles formed by the fast axis Ab related to the in-plane retardation Re of the optically anisotropic film 50 and the transmission axis Ad of the reflective polarization separation sheet 52. However, it is preferable that the optically anisotropic film 50 and the reflective polarization separation sheet 52 are positioned with respect to each other so as to be small. When the present inventors conducted extensive experiments, the magnitude (absolute value) of the angle formed by the main axis Ac and the transmission axis Ad with respect to the thickness direction phase difference Rth in the observation from the front direction is observed from the front direction. When the angle is smaller than the magnitude (absolute value) of the angle formed by the fast axis Ab and the transmission axis Ad with respect to the in-plane phase difference Re, the display device 10 displays the image as compared with the opposite case. It was possible to increase the brightness of the displayed image to such an extent that it can be visually discerned.

  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.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.

  A virtual display device composed of the surface light source device 20 and the lower polarizing plate 16 disposed on the surface light source device 20 was actually manufactured, and the front direction luminance of the manufactured virtual display device was evaluated.

[Display device]
(Display device according to Survey 1)
As schematically shown in FIG. 8, the surface light source device included in the virtual display device is a light source configured by a light emitting unit 25a composed of a plurality of cold cathode tubes extending in an elongated shape, as in the embodiment described above. 25, a reflection plate 28 disposed behind the light source, a light diffusion sheet (lower diffusion plate) 30 disposed on the light output side of the light source 25, an optical sheet 40 disposed on the light output side of the light diffusion sheet, It was made to have. Among the components of the virtual display device, the members of the surface light source device other than the optical sheet and the lower polarizing plate 16 are used by being incorporated in a commercially available liquid crystal television (LC-32GH3 manufactured by Sharp Corporation). The same virtual display devices were used for each virtual display device.

  As in the above-described embodiment, the optical sheet 40 includes a sheet-like main body 45, and a large number of linearly extending unit prisms 42 provided on the light output side surface 45a of the main body so as to be parallel to each other. It was made to have. As in the above-described embodiment, the unit prism is configured so that the cross-sectional shape at the main cutting plane is a right-angled isosceles triangle shape that is symmetrically arranged about the front direction. A number of unit prisms included in one optical sheet are configured identically, and the unit prisms are configured identically between the optical sheets. Further, in each optical sheet, the unit prisms were arranged on the main body portion at a pitch of 64 μm without any gap.

  Each optical sheet was manufactured by molding a unit prism on the optical anisotropic film 50 in substantially the same manner as the manufacturing method described with reference to FIG. 5 in the above-described embodiment. A biaxially stretched PET film was used as the optically anisotropic film 50 forming a part of the main body. The angle between the fast axis Ab related to the in-plane retardation Re of the biaxially stretched PET film and the direction of the ridgeline of the unit prism 42 (longitudinal direction of the unit prism) is varied between optical sheets incorporated in different virtual display devices. Changed. Further, in all virtual display devices, the lower polarizing plate 16 is used for the surface light source device including the optical sheet so that the direction of the ridge line of the unit prism of each optical sheet is parallel to the transmission axis Aa of the lower polarizing plate. Was positioned. That is, in the observation from the front direction, the angle formed by the transmission axis Aa of the lower polarizing plate and the longitudinal direction of the unit prism of the optical sheet is 0 ° between the virtual display devices, The angle θ1 formed by the transmission axis Aa of the lower polarizing plate 16 and the fast axis Ab related to the in-plane retardation Re of the biaxially stretched PET film 50 included in the main body 45 of the optical sheet 40 in the observation from the front direction is as follows. Various differences were made between virtual display devices.

The transmission axis Aa of the lower polarizing plate and the fast axis Ab related to the in-plane retardation Re of the optically anisotropic film 50 were specified using an automatic birefringence meter “KOBRA21ADH” manufactured by Oji Scientific Instruments. The wavelength for specifying each transmission axis was 550 nm.

(Display device according to Survey 2)
As schematically shown in FIG. 9, a reflective polarization separation sheet 52 is arranged between the optical sheet 40 of the display device according to Survey 1 and the lower polarizing plate 16 to produce a display device according to Survey 2. . That is, the display device according to Survey 2 is different from the display device according to Survey 1 in that the polarization separation sheet 52 is provided, and is otherwise the same as the display device according to Survey 1. The reflective polarization separation sheet 52 was positioned so that the transmission axis Ad thereof was parallel to the transmission axis Aa of the lower polarizing plate 16 when observed from the front direction. The transmission axis Ad of the reflective polarization separation sheet 52 was specified with light having a wavelength of 550 nm using an automatic birefringence meter “KOBRA21ADH” manufactured by Oji Scientific Instruments. As the reflective polarization separation sheet 52, “DBEF” (registered trademark) manufactured by 3M Corporation of the United States was used.

〔Evaluation methods〕
With the light source of each virtual display device turned on, the luminance in the front direction (cd / m ² ) on the light exit surface of the lower polarizing plate was measured. BM-7 manufactured by Topcon was used for the measurement of luminance. The brightness | luminance measurement result about the virtual display apparatus which concerns on the investigation 1 and the investigation 2 is shown in FIG. 8 and FIG. 9, respectively. 8 and 9, the vertical axis represents the measured luminance value as a ratio, and the horizontal axis represents the transmission axis Aa of the lower polarizing plate and the optically anisotropic film 50 when observed from the front direction. It represents the smaller angle θ1 of the angles formed by the fast axis Ab with respect to the in-plane phase difference Re.

  The orientation axis (the fast axis Ab and the slow axis) relating to the in-plane retardation Re of the optically anisotropic film 50 is the transmission axis Aa of the lower polarizing plate 16 (for the display device according to Investigation 2, the lower polarizing plate 16 By tilting with respect to the transmission axis Aa and the transmission axis Ad) of the reflective polarization separation sheet 52, the orientation axis (the fast axis Ab and the slow axis) with respect to the in-plane retardation Re of the optically anisotropic film 50 and below When the transmission axis Aa of the polarizing plate 16 is parallel (the absolute value of the angle formed by the fast axis Ab with respect to the in-plane retardation Re of the optically anisotropic film 50 and the transmission axis Aa of the lower polarizing plate 16) Is 0 ° and 90 °, and the luminance in the front direction can be improved as compared with the central portion and both end portions of the horizontal axis in FIGS. 8 and 9. In particular, the absolute value (size) of the smaller angle θ1 among the angles formed by the fast axis Ab with respect to the in-plane retardation Re of the optically anisotropic film 50 and the transmission axis Aa of the lower polarizing plate 16 is 5. When the angle is not less than 70 ° and not more than 70 °, particularly when the angle is not less than 10 ° and not more than 50 °, the alignment axis related to the in-plane retardation Re of the optically anisotropic film 50 and the transmission axis Aa of the lower polarizing plate 16 are parallel. Compared with the case where it becomes, it was able to confirm the raise of the brightness visually.

As a comparative survey, an optically anisotropic film made of the biaxially stretched polyethylene terephthalate of the display device according to Survey 1 is used as a biaxially stretched triacetylcellulose film having the same thickness (hereinafter referred to as a biaxially stretched TAC film). The front direction luminance of the display device according to the replaced comparative example was investigated. In the display device according to the comparative example, the front luminance was changed by rotating the biaxially stretched TAC film with respect to the lower polarizing plate. However, the amount of change in the luminance in the front direction for the display device according to the comparative example using the biaxially stretched TAC film was very small compared to the display device according to the survey committee 1 using the biaxially stretched PET. . In the display device of the example using the optically anisotropic film 50 made of biaxially stretched PET, the fast axis Ab related to the in-plane retardation Re of the optically anisotropic film 50 is the transmission axis of the lower polarizing plate 16. When the angle is 5 ° or more and 70 ° or less, particularly 10 ° or more and 50 ° or less with respect to Aa, it is judged visually by comparing with the brightness of the image displayed on the display device according to the comparative example. The brightness of the image could be increased to the extent possible.

  In general, the P wave (also referred to as P-polarized light) exhibits a higher transmittance than the S wave (also referred to as S-polarized light), and conversely, the S wave exhibits a higher reflectance than the P wave. It becomes like this. In particular, with respect to the light that is incident on the light exit side of the unit optical element from the angle that can be deflected in the front direction by refraction at the light exit side 42a of the unit optical element 42 in the main cutting plane, The transmittance of the P wave whose electric field oscillates in the direction of the main cutting plane is much higher than the transmittance of the S wave whose electric field oscillates in the ridge line direction of the unit optical element. That is, the optical sheet 40 formed by arranging the linear unit optical elements 42 is polarized light (separated) that selectively transmits P waves whose electric field vibrates in the arrangement direction (perpendicular to the ridge line) of the linear unit optical elements. ) It has a function. However, in reality, there is also some light that travels in the direction of the ridgeline in the unit optical element and exits from the slope of the unit optical element. For these lights, light whose electric field vibrates in the direction of the ridgeline is P-wave. Since the light exits and is mixed, the polarization direction of the light exiting from the linear unit optical element (vibration direction of the electric field) is not completely parallel to the arrangement direction, but is almost parallel. Therefore, from the viewpoint of utilizing the polarization (separation) function of the optical sheet and transmitting and utilizing the light incident on the lower polarizing plate as much as possible, the polarization direction of the light exiting the optical sheet 40 is the front. In observation from the direction, it preferably crosses the direction of the transmission axis Aa of the lower polarizing plate at an angle of 0 ° to less than 45 °, and the direction of the transmission axis Aa of the lower polarizing plate. It is particularly preferred that they are parallel. On the other hand, the light transmitted through the optical anisotropic film 50 having the in-plane retardation Re has an action of rotating the polarization direction with respect to the orientation axis related to the in-plane retardation. Therefore, in the embodiment, the optical sheet 40 and the optical anisotropic film 50 are arranged with a specific angular relationship between the orientation axis related to the in-plane retardation of the optical anisotropic film 50 and the transmission axis Aa of the lower polarizing plate. . As a result, in the present case, the optical anisotropic film 50 is obtained by crossing the transmission axis Aa of the lower polarizing plate 16 and the polarization direction of the outgoing light of the unit optical element 42 incident on the lower polarizing plate 16. The polarization direction of the light incident on the lower polarizing plate coincides with the transmission axis Aa of the lower polarizing plate 16 (or at least the crossing angle is reduced). This minimizes the light component that is absorbed by the lower polarizing plate 16 and becomes a loss.

  On the other hand, in the display devices according to Survey 1 and Survey 2 (see the schematic diagrams in FIGS. 8 and 9), the arrangement direction of the unit optical elements is from the front direction due to various design circumstances of the transmissive liquid crystal display device. In this observation, it is orthogonal to the direction of the transmission axis Aa of the lower polarizing plate. This form is often used in an actual liquid crystal display device, but the light component absorbed and lost by the lower polarizing plate 16 due to the polarization direction orthogonal to the transmission axis Aa of the lower polarizing plate 16 is present. Arise. Therefore, it can be said that it is the most disadvantageous arrangement from the viewpoint of effectively using the polarization separation function of the optical sheet itself. Nevertheless, as described above, the orientation axis (particularly, the fast axis Ab) related to the in-plane retardation Re of the optical anisotropic film 50, or the main axis Ac of the refractive index ellipsoid in the thickness direction is used as the lower polarizing plate 16. By positioning in a predetermined relationship with the transmission axis Aa, the brightness of the displayed image can be improved to the extent that it can be visually determined, and the luminance in the front direction can be increased by about 4 to 6%. The amount of increase in the brightness in the front direction due to the alignment axis (in particular, the fast axis Ab) relating to the in-plane retardation Re of the optically anisotropic film or the positioning of the principal axis Ac of the refractive index ellipsoid in the thickness direction is The amount of increase in luminance in the front direction due to the polarization separation function by the unit optical element of the optical sheet was larger.

DESCRIPTION OF SYMBOLS 10 Display apparatus 15 Transmission type display part 16 Lower polarizing plate 17 Upper polarizing plate 20 Surface light source device 25 Light source 25a Light emission part 30 Light diffusion sheet 40 Optical sheet 40a Light emission surface 40b Light incident surface 42 Unit optical element (unit shape element, unit prism) , Unit lens)
42a Light exit surface (prism surface, lens surface)
45 Main body 45a Light exit side surface 45b Light incident side surface 47 Resin layer 50 Optical anisotropic film 51 Optical anisotropic film 52 Polarized light separation sheet

Claims (12)

A transmissive display unit having a lower polarizing plate and an upper polarizing plate;
A surface light source device that illuminates the transmissive display unit from the side of the lower polarizing plate,
An optically anisotropic film disposed on the light incident side with respect to the lower polarizing plate is provided, and this optically anisotropic film is a surface at a wavelength of 550 nm of the optically anisotropic film in the observation from the front direction. The alignment axis related to the inner phase difference Re is positioned so as to intersect the transmission axis of the lower polarizing plate,
A display device characterized by that. A transmissive display unit having a lower polarizing plate and an upper polarizing plate;
A surface light source device that illuminates the transmissive display unit from the side of the lower polarizing plate,
An optically anisotropic film is provided on the light incident side with respect to the lower polarizing plate. This optically anisotropic film has a thickness direction position at a wavelength of 550 nm with respect to the optically anisotropic film in the observation from the front direction. The smaller angle formed by the principal axis related to the phase difference Rth and the transmission axis of the lower polarizing plate is the fast axis related to the in-plane retardation Re at the wavelength 550 nm of the optical anisotropic film and the lower polarization. Positioned to be smaller than the size of the smaller angle made by the transmission axis of the plate,
A display device characterized by that.   The optically anisotropic film is a small one formed by the fast axis relating to the in-plane retardation Re at a wavelength of 550 nm and the transmission axis of the lower polarizing plate in the observation from the front direction. The display device according to claim 1, wherein the display device is positioned so that a size of the angle is not less than 10 ° and not more than 50 °.   The said optically anisotropic film is an optically anisotropic film arrange | positioned in the position closest to the said lower polarizing plate from the light-incidence side among the optically anisotropic films contained in a display apparatus. The display apparatus as described in any one of -3.   The display device according to any one of claims 1 to 4, wherein an in-plane retardation Re at a wavelength of 550 nm of the optically anisotropic film is 500 nm or more and 5000 nm or less.   The display device according to claim 1, wherein the optically anisotropic film is a stretch-formed film. The surface light source device includes an optical sheet including a main body portion and a plurality of unit optical elements arranged on the main body portion,
The said main-body part is a display apparatus as described in any one of Claims 1-6 comprised including the said optically anisotropic film. The plurality of unit optical elements are arranged in a certain direction on the main body, and each unit optical element extends linearly in a direction on the main body that intersects the arrangement direction.
In the observation from the front direction, the optical sheet has a smaller angle of 0 ° or more and 45 ° or less formed by the longitudinal direction of the unit optical element and the transmission axis of the lower polarizing plate, The display device according to claim 7, wherein the display device is positioned.   The display device according to claim 1, wherein the optically anisotropic film is disposed so as to overlap the lower polarizing plate. A light source;
A reflective polarization separation sheet,
An optically anisotropic film is provided on the light incident side of the polarization separation sheet, and this optically anisotropic film has an in-plane retardation at a wavelength of 550 nm with respect to the optically anisotropic film when observed from the front direction. It is positioned so that the orientation axis related to Re intersects the transmission axis of the polarization separation sheet,
A surface light source device. A light source;
A reflective polarization separation sheet,
An optically anisotropic film is provided on the light incident side of the polarized light separating sheet, and the optically anisotropic film has a thickness direction position at a wavelength of 550 nm with respect to the optically anisotropic film in the observation from the front direction. The smaller angle formed by the principal axis relating to the phase difference Rth and the transmission axis of the polarization separation sheet is the fast axis relating to the in-plane retardation Re at the wavelength of 550 nm for the optically anisotropic film and the polarization separation. Positioned to be smaller than the size of the smaller angle formed by the transmission axis of the sheet,
A surface light source device. A surface light source device according to claim 10 or 11,
A transmissive display unit disposed to face the surface light source device,
A display device characterized by that.

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