JP6611002B2 - Surface light source device and image display device - Google Patents

Description

  The present invention relates to a surface light source device including a light source device and an optical sheet, and an image display device including such a surface light source device.

  An image display device typified by a liquid crystal display or the like includes an image display panel such as a liquid crystal panel and a surface light source device that functions as a backlight. By controlling transmission and blocking of light from the surface light source device in units of pixels by the image display panel, a desired image is created by a set of pixel lights transmitted through the image display panel.

  For example, Patent Literatures 1 to 3 disclose a liquid crystal display device including a liquid crystal panel and a surface light source device. Patent Document 4 discloses a display in which a light source, a light guide assembly, and a light guide film are incorporated.

JP 2012-047912 A JP 2009-026554 A JP, 2015-060173, A JP 2014-150077 A

  The surface light source device as described above generally includes a light source device that guides light from a light source to emit light and an optical sheet such as a prism sheet provided on the light emitting surface of the light source device. In the surface light source device having such a configuration, the light source device and the optical sheet are pressed against each other inside the image display device, or are attracted to each other by electrostatic attraction by charging, and the optical sheet enters the light emitting surface of the light source device. The light surface sticks and a non-uniformity pattern in the surface of the light emission luminance called “wet-out” may appear. Since this wet-out affects optical characteristics and causes problems such as uneven transmission of light in the optical sheet, it is desirable not to cause wet-out in an actual product.

  Wet-out occurs prominently when the sheet-like members are in close contact with each other, but a plurality of convex ridge lines are formed on the contact surface of the sheet-like member, and the sheet-like members are connected via the plurality of ridge lines. It can also occur when closely contacting. Therefore, the surface light source device (the surface light source device is a mainstream) in which the prism sheet is placed on the light source device so that the ridges of the plurality of convex unit prisms constituting the prism sheet are in contact with the light emitting surface of the light source device. In contrast to the configuration in which the ridge line portion is arranged facing the image display panel side, the wet-out may occur even in the case of being referred to as an “inverted prism type surface light source device”. Further, in order to improve damage resistance, the light emitting surface of the light source device may be composed of a plurality of convex unit optical elements (for example, unit optical elements having flat or curved tops). Even when the ridge portion of such a unit optical element comes into contact with the light incident surface of the prism sheet, wet-out can occur.

  Therefore, a new technique capable of preventing wet-out is desired, and in particular, a proposal of a technique that can be effectively applied to an inverted prism type surface light source device is desired. However, the conventional technique is not always effective in preventing the occurrence of wet-out in the inverted prism type surface light source device.

  For example, in the apparatuses of Patent Documents 1 and 4, the occurrence of wet-out is prevented by making the height of the ridge line of each unit prism (light guide optical film) non-uniform in the extending direction. However, when such a structure is applied to an inverted prism type surface light source device (particularly, an optical sheet such as a prism sheet), the image quality deteriorates and the control of the viewing angle becomes difficult.

  Further, in the apparatus of Patent Document 2, in the unit prism of the surface light source sheet, the top of the unit prisms in one of the two to eight rows is formed higher than the top of the other rows, thereby reducing display unevenness. Is planned. However, the application of such a structure to an inverted prism type surface light source device (especially an optical sheet such as a prism sheet) cannot necessarily prevent the occurrence of wet-out. In particular, the technique disclosed in Patent Document 2 is intended for a case in which the top of each unit prism has a flat portion with a width of 100 nm to 400 nm, and does not necessarily work effectively in other cases.

  In the apparatus of Patent Document 3, the change in optical characteristics is prevented by optimizing the pitch of the unit prism and the tensile elastic modulus of the material constituting the unit prism. However, “change in optical characteristics” described in Patent Document 3 refers to a phenomenon caused by deformation (lens collapse) caused by contact of a unit prism with another member. The generation mechanism and optical characteristics are completely different from the above-described wet-out in the case where adhesion occurs. Therefore, even if the technique of Patent Document 3 is applied to an inverted prism type surface light source device, it is difficult to effectively prevent the wet-out described above.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an inverted prism type surface light source device capable of effectively preventing wet-out and an image display device to which such a surface light source device is applied. And

  One aspect of the present invention is a surface light source device including a light source device and an optical sheet stacked on the light source device, and the light source device has a light source unit that emits light and a convex shape that is arranged in parallel to each other. A plurality of light source side unit optical elements that emit light from the light source unit, and a light guide unit that has a plurality of light source side unit optical elements on the emission side, and the optical sheets are arranged side by side A plurality of convex sheet-side unit optical elements having a plurality of sheet-side unit optical elements that are in contact with at least some of the plurality of light source-side unit optical elements and into which light from the light guide portion is incident The tops of the plurality of light source side unit optical elements are not located on the same plane, and the tops of the plurality of sheet side unit optical elements are related to a surface light source device that is not located on the same plane.

  By arranging both the tops of the plurality of light source side unit optical elements and the tops of the plurality of sheet side unit optical elements as in this embodiment, wet-out can be effectively prevented.

  The plurality of light source side unit optical elements are different from the first position in the stacking direction with respect to at least one first light source side unit optical element in which the top is disposed at the first position in the stacking direction of the optical sheet and the light source device. At least one second light source unit optical element whose top is arranged at the second position, and the plurality of sheet side unit optical elements are at least one first unit whose top is arranged at the third position with respect to the stacking direction. One sheet-side unit optical element and at least one second sheet-side unit optical element whose top is arranged at a fourth position different from the third position in the stacking direction may be included.

  By configuring the plurality of light source side unit optical elements and the plurality of sheet side unit optical elements as in this embodiment, wet-out can be effectively prevented.

  At least some of the plurality of light source side unit optical elements constitute a plurality of light source side groups constituted by two or more light source side unit optical elements arranged adjacent to each other, and each of the plurality of light source side groups is At least one first light source side unit optical element and at least one second light source side unit optical element may be included.

  According to this aspect, wet-out can be effectively prevented in a range where at least a plurality of light source side groups are provided.

  The plurality of light source side groups may be periodically arranged.

  According to this aspect, wet-out can be effectively prevented while simply configuring the plurality of light source side unit optical elements.

  At least some of the plurality of sheet side unit optical elements constitute a plurality of sheet side groups constituted by two or more sheet side unit optical elements arranged adjacent to each other, and each of the plurality of sheet side unit optical elements includes: It may include at least one first sheet side unit optical element and at least one second sheet side unit optical element.

  According to this aspect, wet-out can be effectively prevented in a range where at least a plurality of sheet-side groups are provided.

  The plurality of sheet side groups may be periodically arranged.

  According to this aspect, wet-out can be effectively prevented while simply configuring the plurality of sheet-side unit optical elements.

  The distance between the tops of the plurality of light source side unit optical elements in the stacking direction of the optical sheet and the light source device may be 0.38 μm or more and 2 μm or less.

  According to this aspect, it is possible to effectively prevent wet-out while ensuring good image quality.

  The distance between the tops of the plurality of sheet-side unit optical elements in the stacking direction of the optical sheet and the light source device may be 0.38 μm or more and 2 μm or less.

  According to this aspect, it is possible to effectively prevent wet-out while ensuring good image quality.

  The top part of at least a part of the plurality of light source side unit optical elements may have a flat part or a curved part.

  According to this aspect, the light source side unit optical element can have good damage resistance.

  At least a part of the plurality of light source side unit optical elements may be a curved surface.

  According to this aspect, the light source side unit optical element can have good damage resistance.

  The plurality of light source side unit optical elements may be made of a thermoplastic resin.

  Another aspect of the present invention relates to an image display device comprising the above surface light source device and an image display panel on which light is incident from the surface light source device.

  According to the present invention, “the tops of the plurality of light source side unit optical elements are not located on the same plane” and “the tops of the plurality of sheet side unit optical elements are not located on the same plane”. Wet out can be effectively prevented in the prism type surface light source device.

FIG. 1 is an exploded perspective view conceptually showing an example of an image display device. 2 is a cross-sectional view of the image display panel and the surface light source device in the image display apparatus of FIG. 1 taken along line II-II in FIG. 3 is a cross-sectional view of the image display panel and the surface light source device in the image display apparatus of FIG. 1 taken along line III-III in FIG. FIG. 4 is an enlarged cross-sectional view illustrating a part of the unit optical element portion of the light source device. FIG. 5 is a cross-sectional view illustrating an enlarged part of a unit prism portion of a prism sheet which is one form of the optical sheet. FIG. 6 is a table showing the characteristics and evaluation results of each sample. FIG. 7 is a partial cross-sectional view showing a modification of the unit optical element. FIG. 8 is a schematic view schematically showing a damage resistance test method in the present invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that, in the drawings attached to the present specification, for convenience of illustration and understanding, the scale and vertical / horizontal dimension ratios are appropriately changed and exaggerated from those of the actual ones.

  In addition, the shape and geometric conditions used in this specification and the degree thereof are specified. For example, terms such as “parallel”, “orthogonal” and “identical”, and values of length and angle, etc. have a strict meaning. Without being bound, it should be interpreted including the extent to which similar functions can be expected. Thus, for example, terms representing geometric shapes such as “triangles”, “polygons”, “hemispheres”, “parts of spheres” and “lens shapes” are not only shapes in the strict sense, but also manufacturing. It can also mean a shape that takes into account technical limitations and manufacturing errors.

  FIG. 1 is an exploded perspective view conceptually showing an example of the image display device 10. The image display device 10 of the present embodiment includes the surface light source device 20, the image display panel 15, and the functional sheet 41, and the light emitted from the surface light source device 20 and transmitted through the image display panel 15 and the functional sheet 41 is It is provided to the observer as image information. When the image display device 10 is used in an actual product such as a liquid crystal display device, the surface light source device 20, the image display panel 15, and the functional sheet 41 are accommodated in a housing (not shown) and emitted from the functional sheet 41. Light (this constitutes image information) is delivered to the observer through an opening provided in the housing.

  The image display panel 15 of the present embodiment is configured as a liquid crystal panel, and includes an upper polarizing plate 13 disposed on the viewer side, a lower polarizing plate 14 disposed on the surface light source device 20 side, an upper polarizing plate 13 and a lower plate. It has the liquid crystal cell 12 arrange | positioned between the polarizing plates 14. The upper polarizing plate 13 and the lower polarizing plate 14 are optical elements that transmit only light polarized in a specific direction, and the specific polarization direction of the light transmitted by each of the upper polarizing plate 13 and the lower polarizing plate 14 is a liquid crystal cell. The selection may be made as appropriate depending on the 12 image forming methods and the design concept of the image display apparatus 10, and is not particularly limited. For example, an arrangement called crossed Nicols in which the light transmission axis directions of the upper polarizing plate 13 and the lower polarizing plate 14 are orthogonal to each other, or parallel Nicols in which the light transmission axis directions of the upper polarizing plate 13 and the lower polarizing plate 14 are parallel to each other. The upper polarizing plate 13 and the lower polarizing plate 14 can be provided in an arrangement called

  In the liquid crystal cell 12, an electric field can be applied to each region where one pixel is formed, and the orientation changes according to the applied electric field. The alignment method of the liquid crystal cell 12 is not particularly limited. For example, the TN (twisted nematic) liquid crystal cell 12 emits from the liquid crystal cell 12 with the polarization direction of incident light rotated by 90 degrees when no electric field is applied. On the other hand, in the state where an electric field is applied, the liquid crystal cell 12 can emit light while maintaining the polarization direction of incident light without changing it. By controlling the orientation of the liquid crystal cell 12 in units of pixels and changing the polarization direction of the light passing through the liquid crystal cell 12, light is emitted from the upper polarizing plate 13 or blocked by the upper polarizing plate 13 for each pixel. I can do it.

  In this way, the image display panel 15 transmits and blocks light from the surface light source device 20 for each pixel, so that desired image light constituting characters, pictures, and the like is emitted toward the functional sheet 41. There are various types of specific configurations and drive control methods of the image display panel 15 typified by a liquid crystal panel, and any type of image display panel 15 is used in the image display device 10 without any particular limitation. be able to.

  On the other hand, the functional sheet 41 on which the light emitted from the image display panel 15 is incident can be configured by, for example, sheets having various functions used in a normal liquid crystal display device. For example, a sheet having a color tone correction function such as a coloring filter, a sheet having an antiglare function, a sheet having an antireflection function, a sheet having a scratch resistance function such as a hard coat sheet, and / or a touch panel position detection. The functional sheet 41 can be configured by a sheet having a function of inputting contact position coordinates on the screen such as an electrode sheet. In the image display device 10 of the present embodiment, the functional sheet 41 is provided on the viewer side with respect to the image display panel 15, but in addition to the functional sheet 41 or instead of the functional sheet 41, it is necessary. A functional sheet that exhibits various functions may be provided at any location. For example, a functional sheet such as a reflective polarizer (trade name DBEF (Dual Brightness Enhancement Film), APF (Advanced Polarization Control Film)) of 3M, etc. is provided between the surface light source device 20 and the image display panel 15. A layer may be disposed.

  Next, the surface light source device 20 will be described.

  2 is a cross-sectional view of the image display panel 15 and the surface light source device 20 along the line II-II in FIG. 3 is a cross-sectional view of the image display panel 15 and the surface light source device 20 taken along line III-III in FIG. That is, the cross-sectional view of FIG. 2 and the cross-sectional view of FIG.

  The surface light source device 20 is an illumination device that emits light toward the image display panel 15, and light from the surface light source device 20 is incident on the image display panel 15. The surface light source device 20 of the present embodiment is configured as an edge light type surface light source device and includes an optical sheet 30 typified by a light source device 28, a reflection sheet 40, and a prism sheet. Hereinafter, in the present embodiment, a description will be mainly given of an embodiment in which the optical sheet is a prism sheet.

  The light source device 28 includes a plurality of light source units 26 that emit light, and a light guide unit 21 that guides the light emitted from each light source unit 26 to convert it into surface light emission and then emits the light toward the prism sheet 30.

  The plurality of light source units 26 can be configured by an arbitrary light source such as a cold cathode fluorescent lamp (CCFL) or an LED (Light Emitting Diode). In the present embodiment, a plurality of light source units 26 are arranged in a specific direction (see arrow “X” in the drawing) so as to face the side surface of the base 22 of the light guide unit 21, and emit light from each light source unit 26. The emitted light enters the light guide 21 from the side surface of the base 22 facing the light source 26.

  The light guide section 21 includes a back prism section 23 provided on the reflection sheet 40 side, a unit optical element section 24 provided on the prism sheet 30 side, and a base section provided between the back prism section 23 and the unit optical element section 24. 22.

  The base portion 22 is an element serving as a base that supports the back prism portion 23 and the unit optical element portion 24, and is a plate-like member having a predetermined thickness.

  As shown in FIG. 2, the back prism portion 23 is formed on the back surface side of the base portion 22 (that is, the reflection sheet 40 side), and travels from the inside of the base portion 22 toward the back surface side (symbol “L” in FIG. 2). And the traveling direction (that is, the traveling angle) is changed. In the present embodiment, the concavo-convex back surface prism portion 23 is configured by a plurality of triangular prism-shaped unit back surface prisms 23a arranged continuously. Each unit back surface prism 23a is a columnar element extending in a direction in which a plurality of light source units 26 are arranged (see arrow “X” in the drawing), and a ridge line formed by the top of each unit back surface prism 23a extends. A plurality of unit back prisms 23a are continuously arranged in a direction perpendicular to the direction (see arrow “Y” in the figure). Each unit rear surface prism 23a has a cross-sectional shape (a cross-sectional shape along the YZ plane, hereinafter also referred to as a main cutting surface shape) in a direction orthogonal to the extending direction, which is constant with respect to the extending direction. . Therefore, the position of the top of each unit back prism 23a (that is, the position of the top with respect to the stacking direction of the prism sheet 30 and the light source device 28 (see the arrow “Z” direction in the figure)) is the extending direction (arrow “in the figure”). X ”). Each unit back prism 23a shown in FIG. 2 has a triangular main cut surface shape, but may have other main cut surface shapes, for example, a polygon such as a quadrangle, a pentagon, and a hexagon, a circle, and an ellipse. , A quadratic curve such as a fence line or a hyperbola, or an arbitrary main cutting plane shape such as a part thereof.

  In addition, regarding specific matters of the unit back surface prism 23a in the back surface side prism portion 23, for example, the shape, the values of the inner angles and the sides of the prism portion, etc., JP 2013-190778 A, JP What is necessary is just to follow the well-known design disclosed by 2013-190779 etc.

  The unit optical element unit 24 on the light emitting surface of the light guide unit 21 is composed of a plurality of convex light source unit optical elements 24a arranged side by side, and the light from the light source unit 26 is light source unit optical. The light is emitted from the element 24 a toward the prism sheet 30. That is, light incident from the light source unit 26 into the base unit 22 (light guide unit 21) is totally reflected on the surface (interface) of the light guide unit 21 formed by the back surface prism unit 23 and the unit optical element unit 24 and travels. Light that propagates in a direction orthogonal to the ridge line direction of the back-side unit prism 23a while changing the direction (traveling angle), and does not satisfy the total reflection condition on the surface (interface) formed by the unit optical element section 24 (from the critical angle). Light having a small incident angle) is emitted from each light source side unit optical element 24a (unit optical element portion 24).

  Each light source side unit optical element 24a is a columnar element extending in a direction (see arrow “Y” in the drawing) orthogonal to the direction in which each unit back prism 23a extends as shown in FIG. A plurality of light source side unit optical elements 24a are continuously arranged side by side in a direction (see arrow “X” in the figure) orthogonal to the direction in which the ridgeline formed by the top of the side unit optical element 24a extends. Each light source side unit optical element 24a extends in the shape of a cross section along the ZX plane orthogonal to the extending direction (see arrow “Y” in the drawing) (hereinafter also referred to as main cut surface shape). Constant with respect to direction. Therefore, each light source side unit optical element 24a has a constant top position (that is, a top position with respect to the stacking direction of the prism sheet 30 and the light source device 28 (see the arrow “Z” direction in the drawing)) in the extending direction. .

  A specific configuration example of the light source side unit optical element 24a will be described later.

  The light guide 21 (the base 22, the back prism 23, and the unit optical element 24) can be formed of various materials having translucency, and has mechanical characteristics, optical characteristics, stability, workability, and the like. It is preferable that it is made of a material that is excellent and inexpensively available. For example, polymer resin having alicyclic structure, methacrylic resin, polycarbonate resin, polystyrene, acrylonitrile-styrene copolymer, methyl methacrylate-styrene copolymer, ABS resin, polyethersulfone or other thermoplastic resin, or ionization The light guide part 21 (base part 22, back surface prism part 23, and unit optical element part 24) can be constituted by radiation curable resin or the like.

  Here, as the ionizing radiation curable resin, monomers (monomers) such as (meth) acrylates, polyesters, and epoxies that are cured by crosslinking or polymerization reaction upon irradiation with ionizing radiation, prepolymers (or oligomers). ). Here, the (meth) acrylate type includes both methacrylate type and acrylate type. Ionizing radiation is radiation having an energy quantum sufficient to cause a crosslinking or polymerization reaction in the molecule, and electromagnetic waves such as ultraviolet rays, visible rays, and X rays, or charged particle beams such as electron beams and α rays are used. Although it is possible to use normally, ultraviolet rays or electron beams are mainly used.

  Examples of (meth) acrylate ionizing radiation curable resins include monomers such as 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, and dipentaerythritol. Examples include penta (meth) acrylate and dipentaerythritol hexa (meth) acrylate.

  Examples of the prepolymer (or oligomer) include urethane (meth) acrylate, epoxy (meth) acrylate, polyester (meth) acrylate, and triazine (meth) acrylate.

  Usually, a liquid composition in which one or more of these monomers and one or more of these prepolymers are mixed and a diluent solvent is blended as necessary is used.

  When ultraviolet rays or visible rays are used as ionizing radiation, a photopolymerization initiator is added. As the photopolymerization initiator, for example, a thioxanthone-based, benzoin-based, acetophenone-based, benzophenone-based compound, or the like is used as the radical polymerizable compound. In the case of a cationic polymerization compound, compounds such as metallocene, aromatic sulfonium and aromatic iodonium are used. The addition amount of a photoinitiator is about 0.1-5 mass% of the whole ionizing-radiation-curable resin composition (except a volatile solvent).

  On the other hand, the reflection sheet 40 is a member that reflects light emitted from the back surface (back surface prism portion 23) of the light guide portion 21 and makes the light enter the light guide portion 21 (back surface prism portion 23) again. Accordingly, the reflection sheet 40 is preferably configured by a mirror-reflecting element. For example, a sheet made of a material having a high reflectivity such as a metal such as silver, aluminum, nickel, or chromium, or a thin film made of a material having a high reflectivity (for example, The reflection sheet 40 can be constituted by a sheet having the metal thin film as a surface layer.

  Next, the prism sheet 30 as an optical sheet laminated on the light source device 28 will be described. The prism sheet 30 of the present embodiment is a prism sheet for constituting a so-called reverse prism type surface light source device 20. That is, the ridge line part (top part) of the unit prism 32a which is a plurality of convex sheet side unit optical elements constituting the prism sheet 30 is the light emitting surface of the light source device 28 (in this embodiment, the unit optical element part 24 (light source side unit). The prism sheet 30 is placed on the light source device 28 in contact with the optical element 24a)).

  As shown in FIG. 2, the prism sheet 30 of this embodiment includes a unit prism portion 32 provided with a unit prism 32a facing the light source device 28, a light diffusion layer 33 provided on the image display panel 15 side, and a unit prism. A sheet-like main body 31 that is provided between the portion 32 and the light diffusion layer 33 and supports the unit prism portion 32 and the light diffusion layer 33.

  The prism sheet 30 changes the traveling direction of the light L incident from the light incident side (the light source device 28 side) and emits light from the light outgoing side (the image display panel 15 side). (See the arrow “Z” in the middle))). This light condensing function is mainly exhibited by the unit prism portion 32. The degree of light collection varies depending on the application and purpose, and can be changed by adjusting the shape of the unit prism portion 32 (particularly, the unit prism 32a described later). Further, the prism sheet 30 of the present embodiment has a function of preventing interference fringes between the image display panel 15 and hiding defects such as scratches, and further imparting appropriate light diffusibility, This function is mainly exhibited by the light diffusion layer 33.

  As shown in FIG. 2, the unit prism portion 32 has a plurality of convex unit prisms 32a arranged side by side. As will be described later, the plurality of unit prisms 32a are in contact with at least a part of the plurality of light source side unit optical elements 24a on the light exit surface of the light source device 28, and light from the light guide unit 21 enters. . More specifically, each unit prism 32a extends in a direction orthogonal to the direction in which each light source side unit optical element 24a extends (see arrow “X” in the drawing). In the present embodiment, the crossing angle between the direction in which each unit prism 32a extends and the direction in which each light source side unit optical element 24a extends (Y direction in the figure) is set to 90 degrees. The crossing angles in these two directions may be angles other than 90 degrees. For example, the deviation angle Δθ from the crossing angles in these two directions from 90 degrees exceeds 0 ° ± 10 degrees (that is, the crossing angle = 90 degrees). By setting + Δθ within a range of 80 degrees ≦ cross angle <90 degrees or 90 degrees <cross angle ≦ 110 degrees), it is also possible to effectively suppress the occurrence of moire.

  Also, a deviation angle between the extending direction of each unit prism 32a and the extending direction of each light source side unit optical element 24a is set, and −40 degrees <shift angle <−10 degrees or +10 degrees <shift angle <+40 degrees. By doing so, it is found that an inclination of a predetermined angle ΔΦ ≧ 10 ° is generated between the normal line N of the light exit surface 20a of the surface light source device 20 and the emitted light L from the surface light source device 20. Such a form is suitable mainly for an application in which an image observer located outside the normal line N direction of the image display apparatus 10 is inspected. Examples of such applications include display devices for car navigation systems, electronic signboards (also called electronic bulletin boards, electronic advertising boards, or digital signage).

  A specific configuration example of the unit prism 32a will be described later.

  The light diffusing layer 33 is a layer that diffuses and emits incident light isotropically. For example, a large number of light diffusing particles having a refractive index different from that of the light transmitting resin layer are contained in the light transmitting resin layer. It can be configured by containing. In this case, a part of the light diffusing particles protrudes from the surface of the light transmissive resin layer on the image display panel 15 side, whereby the “surface of the prism sheet 30 on the image display panel 15 side” is configured. The surface of the prism sheet 30 on the image display panel 15 side can be roughened. The light diffusion layer 33 may be omitted.

  The prism sheet 30 includes a main body 31, a unit prism 32, and a light diffusion layer 33 as shown in FIG. The materials constituting these are not particularly limited, and the main body 31, the unit prism 32, and the light diffusing layer 33 are configured by inexpensively available materials having excellent mechanical characteristics, optical characteristics, stability, workability, and the like. It is preferred that For example, a transparent resin mainly composed of at least one of styrene resin such as polystyrene, thermoplastic polyester resin such as polyethylene terephthalate, acrylic resin such as polymethyl methacrylate, polycarbonate resin, polyacrylonitrile, or the like, or the light guide unit 21 Various ionizing radiation curable resins and the like exemplified as the material can be used as the material of the main body portion 31 and the unit prism portion 32.

  In addition, the resin used for the light transmissive resin layer of the light diffusion layer 33 is not particularly limited, and a resin having light permeability that can be held in a state where the light diffusion particles are dispersed can be used for the light transmissive resin layer. Therefore, for example, by a thermoplastic resin such as polyamide resin, polyurethane resin, polyester resin or acrylic resin, epoxy resin, thermosetting polyester resin, thermosetting resin such as thermosetting urethane resin, or ionizing radiation curable resin, etc. The translucent resin layer of the light diffusion layer 33 can be configured. The light diffusing particles of the light diffusing layer 33 are, for example, organic fine particles composed of a thermoplastic resin such as acrylic-styrene copolymer, polymethyl methacrylate, polystyrene, or a crosslinked product such as polyurethane resin, benzoguanamine resin, or melamine resin, It can be composed of resin fine particles such as silicone, or inorganic fine particles such as silica, alumina or glass. It is found that the particle size of the light diffusing particles is about 1 to 10 μm as an average particle size. It is found that the amount of the light diffusing particles added is in the range of 1 to 30 parts by mass with respect to 100 parts by mass of the resin constituting the translucent resin layer. The light diffusing particles actually contained in the translucent resin layer may be one type or two or more types, and the shape of the light diffusing particles may be a sphere, a spheroid, a polyhedron, or an irregular shape. The particle size distribution of the light diffusing particles may be monodispersed or polydispersed.

  The manufacturing method of the above-mentioned light source device 28 (especially light guide part 21) and the prism sheet 30 is not specifically limited, For example, using arbitrary methods, such as the shaping | molding process using a metal mold | die, the cutting process using a bite, etc. The light source device 28 and the prism sheet 30 having a desired shape can be manufactured. For example, the light diffusion layer 33 is provided on one surface (the surface on the image display panel 15 side) of the plate-like base material constituting the main body 31 of the prism sheet 30, and then the other surface (light source) of the base material. The prism sheet 30 can be manufactured by providing the unit prism portion 32 on the device 28 side surface. The light diffusing layer 33 is formed by, for example, applying a light-transmitting resin layer before curing containing light diffusing particles on one surface of the substrate, and curing the light-transmitting resin layer on the substrate. it can. On the other hand, the unit prism portion 32 can be formed, for example, by pressing a mold against the other surface of the base material to mold the unit prism 32a.

<Light Source Side Unit Optical Element 24a and Unit Prism 32a as Sheet Side Unit Optical Element>
Next, specific configurations of the “light source side unit optical element 24a of the light source device 28” and the “unit prism 32a of the prism sheet 30” according to the present embodiment will be described.

  As a result of earnest research, the present inventor has made the height of the light source side unit optical element 24a constituting the unit optical element portion 24 which is the light source side unit optical element non-uniform, and the unit prism which is the sheet side unit optical element It has been newly found out that wet-out can be eliminated very effectively by making the height of the unit prisms 32a constituting the portion 32 non-uniform. That is, “the tops of the plurality of light source side unit optical elements 24 a are not located on the same plane” and “the tops of the plurality of unit prisms 32 a are not located on the same plane”, so that the occurrence of wet-out is remarkable. This inventor came to know and confirm that it can suppress.

  First, a specific configuration example of the light source side unit optical element 24a will be described.

  FIG. 4 is an enlarged cross-sectional view illustrating a part of the unit optical element portion 24 of the light source device 28. The plurality of light source side unit optical elements 24a constituting the unit optical element portion 24 of the present embodiment is “the stacking direction of the prism sheet 30 and the light source device 28 (see the direction of the arrow“ Z ”in the drawing. With respect to the prism sheet 30 (unit prism portion 32) relative to the prism sheet 30 (unit prism portion 32) with respect to the direction as “the height direction” (the first position or “from the surface of the light guide portion base 22 on the prism sheet 30 side” At least one first unit optical element (first light source side unit optical element) 24a-H (first light source side unit optical element) 24a-H (also referred to as “high position” in height) ”is arranged in the example shown in FIG. Light source side unit optical element 24a-H) and a position relatively far from the unit prism portion 32 of the prism sheet 30 with respect to the above-described stacking direction (see the arrow “Z” direction in the drawing) (the first position described above). Different from : At least one second unit optical element in which the top 24b is arranged at the second position or “the position where the“ height ”is low from the surface of the base portion 22 of the light guide portion on the prism sea 30 side” ” Second light source side unit optical element) 24a-L (in the example shown in FIG. 4, a plurality of second light source side unit optical elements 24a-L) ".

  At least a part of these light source side unit optical elements 24a constituting the unit optical element section 24 is an optical element group (light source side group) constituted by two or more light source side unit optical elements 24a arranged adjacent to each other. ) A plurality of Gf are configured, and the plurality of optical element groups Gf are periodically arranged. Each of the plurality of optical element groups Gf includes at least one first light source side unit optical element 24a-H and at least one second light source side unit optical element 24a-L. In the example illustrated in FIG. 4, one optical element group Gf is configured by the four light source side unit optical elements 24 a, and the two second light source side unit optical elements 24 a -H are sequentially arranged, and then the two second light source side unit optical elements 24 a -H are sequentially arranged. The light source side unit optical elements 24a-L are continuously arranged. This optical element group Gf composed of four light source side unit optical elements 24a (including two first light source side unit optical elements 24a-H and two second light source side unit optical elements 24a-L) is shown in the figure. The unit optical element portion 24 is configured by being repeatedly arranged in the direction indicated by the arrow “X”.

  As described above, the unit optical element section 24 according to the present embodiment includes a plurality of light source side unit optical elements 24a (first light source side units) having different positions of the top 24b with respect to the height direction (see the arrow “Z” direction in the drawing). It is constituted by a set of optical elements 24a-H and second light source side unit optical elements 24a-L). In addition, the structure of the optical element group Gf which forms the repeating unit of the light source side unit optical element 24a is not limited to the example shown in FIG. For example, each optical element group Gf is configured by two light source side unit optical elements 24a (including one first light source side unit optical element 24a-H and one second light source side unit optical element 24a-L). Alternatively, each optical element group Gf may be configured by three or more light source side unit optical elements 24a. Further, the arrangement of the plurality of light source side unit optical elements 24a constituting each optical element group Gf is not particularly limited, and a plurality of light source sides in which the positions of the top portions 24b with respect to the height direction (see the arrow “Z” direction in the drawing) are different. The unit optical elements 24a may be arranged in any way. Further, the positions of the top portions 24b of the plurality of light source side unit optical elements 24a constituting each optical element group Gf are not particularly limited, and the top portions are at three or more different positions in the height direction (see the arrow “Z” direction in the drawing). Each optical element group Gf may be constituted by a plurality of light source side unit optical elements 24a in which 24b is arranged.

  In the example shown in FIG. 4, “a valley between two adjacent first light source side unit optical elements 24a-H (hereinafter also referred to as“ unit optical element bottom ”) 36-H”, “adjacent first light source side”. Unit optical element bottom 36-M between unit optical element 24a-H and second light source side unit optical element 24a-L "and" unit optical element between two adjacent second light source side unit optical elements 24a-L " The positions of the bottom portions 36-L ”are different from each other with respect to the height direction (see the arrow“ Z ”direction in the drawing). That is, the unit optical element bottom portion 36-H is closest to the prism sheet 30 (unit prism portion 32), and then the unit optical element bottom portion 36-M is adjacent to the prism sheet 30 (unit prism portion 32). The unit optical element bottom portion 36-L is disposed at a position farthest from the prism sheet 30 (unit prism portion 32). However, the position of the unit optical element bottom portion 36 between the light source side unit optical elements 24a is not particularly limited, and each unit optical element bottom portion is located at a position different from FIG. 4 with respect to the height direction (see the arrow “Z” direction in the drawing). 36 may be disposed, or each unit optical element bottom 36 may be disposed at the same position (on the same plane) with respect to the stacking direction (see the arrow “Z” direction in the drawing).

  In addition, at least some of the top portions 24b among the plurality of light source side unit optical elements 24a constituting the unit optical element portion 24 may have a flat portion or a curved portion. Further, at least a part of the side surface 24c of each of the plurality of light source side unit optical elements 24a constituting the unit optical element portion 24 may be a curved surface. In the example shown in FIG. 4, the top part 24b of each unit optical element part 24 is comprised by the flat part, the side surface 24c of each unit optical element part 24 is a smooth curved surface, and each unit optical element bottom part 36 is an inflection. A smooth curved surface including points is formed. As described above, the unit optical element portion 24 has a side surface 24c formed with a smooth curved surface and each unit optical element bottom portion 36 forms a smooth curved surface including an inflection point. The shape is also called a so-called “reverse concavo-convex lenticular lens shape” in which a plurality of cylindrical concave lenses are arranged with their ridge lines parallel to each other. Each light source side unit optical element 24a is formed by making the shape of the top 24b of each light source side unit optical element 24a flat or curved, or making the shape of the side surface 24c of each light source side unit optical element 24a curved. Damage resistance is improved, and even when an external force such as an impact is applied, it is difficult to damage.

  However, when the shape of the apex 24b of each light source side unit optical element 24a is flat or curved, the adhesion of the unit optical element 24 to the unit prism 32 tends to increase, so that wet-out is likely to occur. . However, as in the present embodiment, “the positions of the tops of the plurality of light source side unit optical elements 24a are not made constant” and “the positions of the tops of the plurality of unit prisms 32a are not made constant”, each light source side unit optical element Even if the shape of the top 24b of the element 24a is flat or curved, the occurrence of wet-out can be effectively prevented. Therefore, while making the shape of the top 24b of each light source side unit optical element 24a flat or curved, “the positions of the tops of the plurality of light source side unit optical elements 24a are not constant” and “the tops of the plurality of unit prisms 32a” By making the position of “not constant”, it is possible to prevent the occurrence of wet-out while improving the damage resistance of the light source device 28 (unit optical element portion 24).

  In particular, the unit optical element portion 24 may be yellowed when light passes through the inside thereof when manufactured with an ultraviolet curable resin. In order to prevent yellowing, the plurality of light source sides that constitute the unit optical element portion 24 may be used. In many cases, the unit optical element 24a is made of a thermoplastic resin or the like. However, since the thermoplastic resin is generally soft and brittle, the damage resistance of each light source side unit optical element 24a made of thermoplastic resin is not necessarily high. Therefore, when each light source side unit optical element 24a is made of a thermoplastic resin, the top 24b of each light source side unit optical element 24a is made flat or curved in order to improve damage resistance. It is very effective to make the shape of the side surface 24c of the unit optical element 24a into a curved surface. Therefore, when each light source side unit optical element 24a is made of a thermoplastic resin, the shape of the top 24b of each light source side unit optical element 24a is made flat or curved, or the side surface of each light source side unit optical element 24a. The shape of the light source 24c is curved, and “the positions of the tops of the plurality of light source side unit optical elements 24a are not made constant” and “the positions of the tops of the plurality of unit prisms 32a are not made constant”. It is possible to prevent the occurrence of wet-out while improving the damage resistance of the side unit optical element 24a.

  Among the specific design items of the light source side unit optical element 24a in the light source side unit optical element section 24, matters other than the distance D1 in the height direction described below, for example, its shape, each internal angle, and each side About the value etc., what is necessary is just to follow the well-known design disclosed by Unexamined-Japanese-Patent No. 2013-190778, Unexamined-Japanese-Patent No. 2013-190779.

  However, the distance (the height of the prism sheet 30 and the light source device 28 between the top portions 24b of the plurality of light source side unit optical elements 24a constituting the unit optical element portion 24 (see the arrow “Z” direction in the figure)). The difference is also referred to as “height difference” (see reference sign “D1” in FIG. 4). This is a new design item unique to the present invention, and the distance D1 is emitted from each light source unit 26. Considering the shortest wavelength in the wavelength range of light (particularly visible light), it is preferably 0.38 μm (micrometer) or more. In addition, as a result of earnest research, the inventor of the present invention, as is clear from the following embodiments, considers the image quality, and between the top portions 24b of the plurality of light source side unit optical elements 24a constituting the unit optical element portion 24. Further, it has been newly found that the distance (see reference sign “D1” in FIG. 4) in the height direction (see the arrow “Z” direction in the drawing) is preferably 2 μm or less.

  Next, a specific configuration example of the unit prism 32a will be described.

  FIG. 5 is an enlarged cross-sectional view illustrating a part of the unit prism portion 32 of the prism sheet 30 that is a sheet-side unit optical element. The plurality of unit prisms 32a constituting the unit prism portion 32 of the present embodiment are related to “the height direction (refer to the direction of the arrow“ Z ”in the drawing. Hereinafter, this will also be referred to as“ the height direction ””). A position relatively high from the light source device 28 (unit optical element part 24) (a third position or a position having a high "height" from the surface opposite to the "unit prism part 32" of the "prism sheet 30") And at least one first unit prism (first sheet side unit optical element) 32a-H (a plurality of first unit prisms 32a-H in the example shown in FIG. 5) ”. , “A position (a fourth position or a position different from the third position, which is relatively far from the light source device 28 (unit optical element portion 24) with respect to the height direction described above (see the arrow“ Z ”direction in the drawing)). “Prism sheet 30” At least one second unit prism (second sheet side unit optical element) 32a in which the top portion 32b is arranged at a position having a low height from the surface opposite to the position prism portion 32 ". -L (a plurality of second unit prisms 32a-L in the example shown in FIG. 5) ".

  Each unit prism 32a is a columnar element extending in a direction orthogonal to the direction in which each light source side unit optical element 24a extends (see arrow “X” in the figure), and the ridge line of each unit prism 32a extends. A plurality of unit prisms 32a are continuously arranged side by side in a direction orthogonal to the direction to be performed (see arrow “Y” in the figure). In each unit prism 32a, the shape of the main cut surface (the shape of the cross section along the YZ plane) in the direction orthogonal to the extending direction (see arrow “X” in the drawing) is constant with respect to the extending direction. Accordingly, each unit prism 32a has a constant position of the top portion 32b (that is, the position of the top portion 32b with respect to the height direction (see the arrow “Z” direction in the drawing)) in the extending direction.

  At least a part of the plurality of unit prisms 32a constitutes a plurality of prism groups (sheet side groups) Gp composed of two or more unit prisms 32a arranged adjacent to each other, and the plurality of prism groups. Gp is periodically arranged. Each of the plurality of prism groups Gp includes at least one first unit prism 32a-H and at least one second unit prism 32a-L. In the example shown in FIG. 5, one prism group Gp is constituted by two unit prisms 32a, and one first unit prism 32a-H and one second unit prism 32a-L are arranged adjacent to each other in succession. Has been. A prism group Gp constituted by two unit prisms 32a (including one first unit prism 32a-H and one second unit prism 32a-L) is formed in a direction indicated by an arrow “Y” in the drawing. The unit prism portion 32 shown in FIG. 5 is configured by being repeatedly arranged.

  As described above, the unit prism portion 32 according to the present embodiment has a plurality of different positions of the top portion 32b with respect to the “height direction” (see the arrow “Z” direction in the drawing) that is the stacking direction of the prism sheet 30 and the light source device 28. Of unit prisms 32a. The configuration of the prism group Gp that forms the repeating unit of the unit prism 32a is not limited to the example shown in FIG. For example, each prism group Gp may be configured by three or more unit prisms 32a. In addition, the arrangement of the plurality of unit prisms 32a constituting each prism group Gp is not particularly limited. What is the plurality of unit prisms 32a in which the positions of the top portions 32b in the height direction (see the arrow “Z” direction in the drawing) are different. You may line up. Further, the positions of the top portions 32b of the plurality of unit prisms 32a constituting each prism group Gp are not particularly limited, and the top portions 32b are arranged at three or more different positions in the height direction (see the arrow “Z” direction in the drawing). Each prism group Gp may be configured by a plurality of unit prisms 32a.

  In the example shown in FIG. 5, the “valley part (hereinafter also referred to as“ unit prism bottom part ”) 38” between the adjacent unit prisms 32a (the first unit prism 32a-H and the second unit prism 32a-L) is high. They are arranged at the same position (on the same plane) with respect to the vertical direction (see the arrow “Z” direction in the figure). However, the position of the unit prism bottom 38 between the unit prisms 32a is not particularly limited, and the unit prism bottoms 38 may be arranged at different positions with respect to the height direction (see the arrow “Z” direction in the drawing). Good.

  The specific shape, apex angle, size, etc. of each unit prism 32a constituting the unit prism portion 32 are appropriately selected within the range exemplified for each unit back prism 23a constituting the back prism portion 23, for example. The selection is not particularly limited. However, the distance (see reference numeral “D2” in FIG. 5) between the apexes 32b of the plurality of unit prisms 32a constituting the unit prism portion 32 in the height direction (see the arrow “Z” direction in the drawing) is the light source. Considering the shortest wavelength in the wavelength region of light (visible light) emitted from the portion 26, it is preferably 0.38 μm or more. Further, as a result of earnest research, the inventor of the present invention considers the image quality, and the height direction between the top portions 32b of the plurality of unit prisms 32a constituting the unit prism portion 32 is clear from the examples described below. It has been newly found that the distance (refer to the reference sign “D2” in FIG. 5) regarding the distance (see the arrow “Z” direction in the figure) is preferably 2 μm or less.

  The inventor has a plurality of light source devices 28 (particularly, the unit optical element part 24 to the light source side unit optical element 24a) and a prism sheet 30 (particularly, the unit prism part 32 to the unit prism 32a) having different characteristics. Prototypes (samples 1 to 15) of the image display device 10 were actually made to evaluate the occurrence of wet-out and the like. Each prototype of the image display device 10 basically has the configuration shown in FIGS. 1 to 3, but for the performance evaluation of the unit prism unit 32, the main body unit 31 and the unit prism unit 32 described above. However, the prism sheet 30 that does not include the light diffusion layer 33 is used.

  FIG. 6 is a table showing the characteristics and evaluation results of each sample. In FIG. 6, the item “sample” indicates the sample number (“1” to “15”), and the item “top width” of “light source device (unit optical element portion)” indicates the light source side unit optical element 24a. The width of the flat portion of the top 24b (the size in the direction perpendicular to the direction in which each light source side unit optical element 24a extends (see the direction of the arrow “X” in FIG. 4)) is shown. In Samples 11 and 15 in which the “top width” is “0.0 μm”, the top 24 b of each light source side unit optical element 24 a is formed in a non-flat shape and has a pointed shape.

  The item “height difference” of “light source device (unit optical element portion)” in FIG. 6 is between the top portions 24b of the plurality of light source side unit optical elements 24a constituting each optical element group Gf (see FIG. 4). , The maximum distance among the distances in the stacking direction of the prism sheet 30 and the light source device 28 (see reference numeral “D1” in FIG. 4). For example, with respect to samples 1 to 3 and 5 to 15, between a top 24 b of a light source side unit optical element 24 a represented by “high” and a top 24 b of a light source side unit optical element 24 a represented by “low” described later. The “height difference” is represented by the distance in the stacking direction of the prism sheet 30 and the light source device 28. On the other hand, in the sample 4, since the top portions 24b of all the light source side unit optical elements 24a constituting the unit optical element portion 24 exist at the same position in the height direction, the height difference is “0.0 μm”.

  The item “pattern” of “light source device (unit optical element section)” in FIG. 6 indicates an arrangement pattern of the plurality of light source side unit optical elements 24a constituting each optical element group Gf, and “high” indicates “high”. A light source side unit optical element 24a (see “first light source side unit optical element 24a-H” in FIG. 4) in which the top portion 24b is disposed at a position relatively close to the prism sheet 30 (unit prism portion 32) in the vertical direction. “Low” indicates “a light source side unit optical element 24a (the“ second light source side unit ”in FIG. 4) in which the top 24b is disposed at a position relatively far from the prism sheet 30 (unit prism portion 32) in the height direction. "Medium" means "the position of the top 24b of the light source side unit optical element 24a represented by" high "in the height direction and the light source side unit represented by" low "." Optical element 24a Shows a light source side unit optical elements 24a in which the top portion 24b is located "between the position of the top 24b. Therefore, for example, the unit optical element section 24 shown in FIG. 4 is represented by “high-high-low-low” in the “pattern” item of “light source device (unit optical element section)”.

  The item “height difference” of “prism sheet (unit prism portion)” in FIG. 6 relates to the height direction between the top portions 32b of the plurality of unit prisms 32a constituting each prism group Gp (see FIG. 5). The maximum distance among the distances (see reference sign “D2” in FIG. 5) is shown. Therefore, with respect to Samples 1 to 7 and 9 to 15, the distance in the height direction between the top 32b of the unit prism 32a represented by “high” and the top 32b of the unit prism 32a represented by “low” described later. This “height difference” is expressed. In the sample 8, since the top portions 32b of all the unit prisms 32a constituting the unit prism portion 32 exist at the same position in the height direction, the height difference is “0.0 μm”.

  The item “pattern” of the “prism sheet (unit prism portion)” indicates an arrangement pattern of the plurality of unit prisms 32a constituting each prism group Gp, and “high” indicates “with respect to the height direction, the light source device 28 ( FIG. 5 shows a unit prism 32a (see “first unit prism 32a-H” in FIG. 5) in which the top portion 32b is disposed at a position relatively close to the unit optical element portion 24). , Shows a unit prism 32a (see “second unit prism 32a-L” in FIG. 5) in which the top portion 32b is arranged at a position relatively far from the light source device 28 (unit optical element portion 24). “In the height direction, the unit prism 3 in which the top portion 32b is disposed between the position of the top portion of the unit prism 32a represented by“ high ”and the position of the top portion of the unit prism 32a represented by“ low ”. It shows the a. " Therefore, for example, the unit prism portion 32 shown in FIG. 5 is represented by “high-low” in the “pattern” item of the “prism sheet (unit prism portion)”.

  The item “damage resistance” in FIG. 6 mainly indicates the ease of damage due to the external force of impact or friction of the unit optical element portion 24 (light source side unit optical element 24a) of the light source device 28. Evaluation of damage resistance is based on the following test method. After testing the light guide 21 and the prism sheet 30 as an optical sheet by the following damage resistance test method, the unit optical of the light guide 21 is visually observed. The scratch on the surface of the element part 24 was evaluated. As a result of the evaluation, “◯” indicates that no scratch was found on the surface of the unit optical element portion 24, and that the unit optical element portion 24 was evaluated as having excellent damage resistance and relatively difficult to damage. “X” indicates that scratches are observed on the surface of the unit optical element portion 24 and the unit optical element portion 24 is relatively easily damaged by an external force.

(Damage resistance test method)
FIG. 8 is a schematic view schematically showing a damage resistance test method in the present invention. As shown in FIG. 8, a prism sheet (optical sheet) 30 as a test piece is set on the movable platen 110 of the abrasion resistance tester so that the main body 31 side is positioned on the movable platen 110 side. A load of 2.45 N (250 gf) was applied to the load part 130 through the light guide part 21 of 12 cm ² . At that time, the unit optical element portion 24 of the light guide portion 21 and the unit prism portion 32 of the prism sheet 30 face each other. In that state, the movable platen 110 was moved in the direction of arrow 140 in FIG. 8 at a speed of 5 mm / s for 20 seconds. Thereafter, the light guide portion 21 was taken out, and the presence or absence of scratches on the surface of the unit optical element portion 24 was visually evaluated.

  A test piece obtained by cutting the obtained optical sheet into a length of 150 mm and a width of 40 mm was used.

  As a measuring device, a trade name AB-301 Gakushin type friction fastness tester manufactured by Tester Sangyo Co., Ltd. was used.

The light guide unit 21 was cut into an area of 12 cm ² .

  The microscope used the brand name digital microscope VHX-200N by Keyence Corporation.

The bottom surface of the load portion is a donut shape having an outer diameter of 20 mm and an inner diameter of 10 mm, and the bottom area is 2.36 cm ² .

  The item “image quality (light source device)” in FIG. 6 indicates the influence of the light source device 28 on the image quality, and “◯” indicates that the light emitted from the unit optical element section 24 is surface-emitted evenly visually. “×” indicates that the light emitted from the unit optical element section 24 is unevenly light that is visually nonuniformly emitted and is not allowed in practice, and “Δ” indicates unit optics. It shows that the light emitted from the element portion 24 is surface-emitted nonuniformly visually, but has light unevenness that is practically acceptable. The item “image quality (prism sheet)” in FIG. 6 indicates the influence of the prism sheet 30 on the image quality, and “◯” indicates that the luminance of light emitted from the prism sheet 30 (main body portion 31) is visually uniform. “×” indicates that the luminance of light emitted from the prism sheet 30 (main body portion 31) is visually non-uniform. In addition, the item “Wet-out” in FIG. 6 indicates whether or not the occurrence of wet-out has been visually confirmed, “O” indicates that the occurrence of wet-out has not been confirmed, and “X” indicates the occurrence of wet-out. Indicates that the occurrence of

  As is apparent from the table of FIG. 6, “when the top 24 b of the light source device 28 on the unit optical element light source side is disposed at the same position in the height direction (see samples 4 and 15)” or “prism sheet 30. In the case where the top 24b of the unit prism 32a is disposed at the same position in the stacking direction of the prism sheet 30 and the light source device 28 (see sample 8), occurrence of wet-out was confirmed. On the other hand, “the top 24b of the light source side unit optical element 24a of the light source device 28 is arranged at a different position with respect to the height direction” and “the top 24b of the unit prism 32a of the prism sheet 30 is arranged at a different position with respect to the height direction. In the case of “Yes” (see Samples 1 to 3, 5 to 7, and 9 to 14), the occurrence of wet-out was not confirmed. Therefore, from the viewpoint of preventing the occurrence of wet-out, “the top portions 24b of the plurality of light source side unit optical elements 24a are not located on the same plane” and “the top portions 32b of the plurality of unit prisms 32a that are sheet side unit optical elements. It is understood that the surface light source device 20 configured so that “they are not located on the same plane” is preferable.

  As apparent from the item of “damage resistance” in FIG. 6, in order to improve the damage resistance of the unit optical element portion 24 (light source side unit optical element 24 a), the top portion of each light source side unit optical element 24 a is used. It is preferable to provide a flat part in 24b (refer to the item of “top width” in samples 1 to 10 and 12 to 14).

  Further, as apparent from the item of “image quality (light source device)” in FIG. 6, in order to appropriately emit light from the light source device 28, a plurality of light source side unit optical elements 24 a constituting each optical element group Gf. It is preferable to reduce the maximum distance in the height direction between the top portions 24b of “the light source device (unit optical element portion)” of the samples 1 to 4, 6 to 11, and 13 to 15. reference). In particular, when the maximum distance in the height direction between the top portions 24b of the plurality of light source side unit optical elements 24a is about “2 μm”, the surface emission of the light source device 28 starts to be disturbed (see sample 3). It was found that the surface emission of the light source device 28 was disturbed and the image quality was adversely affected at 3 μm ”(see Sample 5). Further, if the flat portion formed on the top 24b of each light source side unit optical element 24a is too large, the surface light emission of the light source device 28 is disturbed, and the width of the top 24b of each light source side unit optical element 24a is about 2 [mu] m or less. For example, light is appropriately emitted from the light source device 28 (see Samples 1 to 2, 4, 6 to 11, and 13 to 15). However, when the width of the top 24b of each light source side unit optical element 24a becomes “3 μm”. It has been found that the surface emission of the light source device 28 is disturbed and adversely affects the image quality (see Sample 12).

  Further, as apparent from the item of “image quality (prism sheet)” in FIG. 6, in order to prevent uneven brightness of the light emitted from the prism sheet 30, the top portions 32 b of the plurality of unit prisms 32 a constituting each prism group Gp. It is preferable to reduce the maximum distance in the height direction (refer to the item of “height difference” of “prism sheet (unit prism portion)” of samples 1 to 8 and 10 to 15). In particular, if the maximum distance in the height direction between the apexes 32b of the plurality of unit prisms 32a is about 2 μm or less, light can be emitted from the prism sheet 30 without uneven brightness, but when the maximum distance becomes “3 μm”. It has been found that luminance unevenness occurs in the light emitted from the prism sheet 30 and adversely affects the image quality (see Sample 9).

  As described above, the unit prism portion 32 of the prism sheet 30 which is an optical sheet faces the unit optical element portion 24 of the light source device 28, and both are in contact with each other. The inverted prism type surface light source device 20 (image display device) 10), the height between the top portions 24b of the plurality of light source side unit optical elements 24a constituting the unit optical element portion 24 is made non-uniform, while the height between the top portions 32b of the plurality of unit prisms 32a constituting the unit prism portion 32 is set. Occurrence of wet-out can be effectively prevented by making the height non-uniform.

  In particular, while providing a flat portion or a curved portion on the top portion 24b of each single light source side optical element 24a of the light source device 28, "the position of the top portion 24b of the plurality of light source side unit optical elements 24a constituting the unit optical element portion 24" The light source device 28 has excellent resistance to resistance by suppressing the “variation in the height direction” and the “variation in the height direction of the positions of the top portions 32b of the plurality of unit prisms 32a constituting the unit prism portion 32” within a specific range. The prism sheet 30 can exhibit good image quality performance while exhibiting damage, and the light source device 28 and the prism sheet 30 as a whole can effectively prevent wet out.

<Modification>
The present invention is not limited to the above-described embodiments and examples, and various modifications may be added to these embodiments and examples.

  For example, the shape of each light source side unit optical element 24a is not particularly limited. FIG. 7 is a partial cross-sectional view showing a modification of the light source side unit optical element 24a. Each light source side unit optical element 24a has a reverse lenticular lens shape as shown in FIG. 7A, for example, and the top portion 24b may be pointed, or as shown in FIG. 7B, a reverse lenticular lens shape. The top portion 24b may have a curved shape (curved portion). Further, each light source side unit optical element 24a does not necessarily have an inverse lenticular lens shape, and the side surface 24c of each light source side unit optical element 24a may be a flat surface, or between the light source side unit optical elements 24a. The trough (unit optical element bottom 36) may not form a smooth curved surface.

  Further, “all the single light source side optical elements 24a constituting the unit optical element portion 24 of the light source device 28” and “all the unit prisms 32a constituting the unit prism portion 32 of the prism sheet 30” are referred to as “wet-out”. It is not necessary to satisfy the conditions for “preventing the occurrence”. It is sufficient that the “part of the plurality of light source unit optical elements 24a” and the “part of the plurality of unit prisms 32a” satisfy the above-mentioned “conditions for preventing the occurrence of wet-out”. In the range, the occurrence of wet-out can be effectively prevented.

  In the above-described embodiments and examples, the example in which the prism sheet 30 is used as the optical sheet laminated on the light source device 28 has been described. However, an optical sheet other than the prism sheet may be laminated on the light source device 28. For example, a unit optical element such as a lenticular lens having a ridge portion formed of a part of a cylinder or an elliptic cylinder instead of the unit prism 32a may be in contact with the light source side unit optical element 24a of the light source device 28. By satisfying the above-mentioned “conditions for preventing the occurrence of wet-out”, the occurrence of wet-out can be effectively prevented.

  The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, changes, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Image display apparatus 12 Liquid crystal cell 13 Upper polarizing plate 14 Lower polarizing plate 15 Image display panel 20 Surface light source device 21 Light guide part 22 Base part 23 Back surface prism part 23a Unit back surface prism 24 Unit optical element part 24a Light source side unit optical element 24b Top part 24c Side 26 Light source part 28 Light source device 30 Prism sheet 31 Main body part 32 Unit prism part 32a Unit prism 32b which is a sheet side unit optical element Top part 33 Light diffusion layer 36 Unit optical element bottom part 38 Unit prism bottom part 40 Reflective sheet 41 Functional sheet 110 Movable platen 130 Load section Gf Optical element group Gp Prism group

Claims (12)

A surface light source device comprising a light source device and an optical sheet laminated on the light source device,
The light source device includes a light source unit that emits light and a plurality of convex light source unit optical elements that are arranged side by side and that emit light from the light source unit. A light guide, and
The optical sheet is a plurality of convex sheet-side unit optical elements arranged side by side, in contact with at least a part of the plurality of light source-side unit optical elements, from the light guide unit A plurality of sheet side unit optical elements on which light is incident;
The tops of the plurality of light source side unit optical elements are not located on the same plane,
The tops of the plurality of sheet side unit optical elements are not located on the same plane ,
The surface light source device in which the distance between the top portions of the plurality of light source side unit optical elements in the stacking direction of the optical sheet and the light source device is 0.38 μm or more and 2 μm or less . 2. The surface light source device according to claim 1, wherein a distance between the top portions of the plurality of sheet-side unit optical elements in the stacking direction of the optical sheet and the light source device is 0.38 μm or more and 2 μm or less. A surface light source device comprising a light source device and an optical sheet laminated on the light source device,
The light source device includes a light source unit that emits light and a plurality of convex light source unit optical elements that are arranged side by side and that emit light from the light source unit. A light guide, and
The optical sheet is a plurality of convex sheet-side unit optical elements arranged side by side, in contact with at least a part of the plurality of light source-side unit optical elements, from the light guide unit A plurality of sheet side unit optical elements on which light is incident;
The tops of the plurality of light source side unit optical elements are not located on the same plane,
The tops of the plurality of sheet side unit optical elements are not located on the same plane,
The surface light source device in which the distance between the top portions of the plurality of sheet side unit optical elements in the stacking direction of the optical sheet and the light source device is 0.38 μm or more and 2 μm or less. The plurality of light source side unit optical elements include at least one first light source side unit optical element in which the top portion is disposed at a first position with respect to the stacking direction of the optical sheet and the light source device, and Including at least one second light source side unit optical element in which the top portion is disposed at a second position different from the first position;
The plurality of sheet-side unit optical elements are different from at least one first sheet-side unit optical element in which the top is disposed at a third position with respect to the stacking direction and the third position with respect to the stacking direction. the surface light source device according to any one of claims 1-3 and at least one second sheet side unit optical elements in the fourth position the top is arranged. At least some of the plurality of light source side unit optical elements constitute a plurality of light source side groups configured by two or more light source side unit optical elements arranged adjacent to each other,
5. The surface light source device according to claim 4 , wherein each of the plurality of light source side groups includes at least one first light source side unit optical element and at least one second light source side unit optical element. The surface light source device according to claim 5 , wherein the plurality of light source side groups are periodically arranged. At least some of the plurality of sheet side unit optical elements constitute a plurality of sheet side groups configured by two or more sheet side unit optical elements arranged adjacent to each other,
The surface according to any one of claims 4 to 6 , wherein each of the plurality of sheet side groups includes at least one first sheet side unit optical element and at least one second sheet side unit optical element. Light source device. The surface light source device according to claim 7 , wherein the plurality of sheet side groups are periodically arranged.   The surface light source device according to any one of claims 1 to 8, wherein the top part of at least a part of the plurality of light source side unit optical elements has a flat part or a curved part.   The surface light source device according to claim 1, wherein at least a part of at least a part of the plurality of light source side unit optical elements is a curved surface.   The surface light source device according to claim 1, wherein the plurality of light source side unit optical elements are made of a thermoplastic resin. A surface light source device according to any one of claims 1 to 11,
An image display device comprising: an image display panel on which light is incident from the surface light source device.

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