JP2012194397A - Optical sheet, surface light source device, transmissive display device and method for manufacturing optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet capable of improving luminance irregularity induced depending on the distance to a light source part to enhance uniformity in the luminance within the plane and reducing luminance irregularity caused by thermal distortion in the light source part in an edge light type surface light source device, and to provide a surface light source device and a transmissive display device using the optical sheet, and a method for manufacturing the optical sheet.SOLUTION: An optical sheet 15 is used in a surface light source device 10 and a transmissive display device 1 having a light source part 12 in one end of a light guide plate 13; and the optical sheet includes a prism film, a substrate film and a joint layer that integrally join the films. The joint layer has a thickness gradually decreasing from one end to the other end in a cross section along one direction perpendicular to the sheet plane. The optical sheet 15 prior to curing the joint layer is pressurized by use of a pair of nip rolls comprising a roll in a substantially truncated cone shape and a roll in a substantially cylindrical shape, to change the thickness of the joint layer.

Description

  The present invention relates to an optical sheet in which a plurality of unit optical shapes are arranged on at least one surface, a surface light source device including the optical sheet, a transmissive display device, and an optical sheet manufacturing method.

  In recent years, transmission-type display devices such as liquid crystal televisions have become larger and thinner. In order to reduce the thickness of a transmissive liquid crystal display device, an edge light type surface light source device is used as a backlight, or in order to improve luminance and reduce the thickness, an LED (Light Emitting Diode) is used as a light source. (For example, refer to Patent Document 1 and Patent Document 2).

JP 2009-301805 A JP 2008-96889 A

Here, in the edge light type surface light source device, the light source unit is arranged at the end of the light guide plate, and the luminance near the light source unit is high, but the luminance decreases as the distance from the light source unit increases. Luminance unevenness due to the distance to the portion is likely to occur, and the uniformity of in-plane luminance is reduced.
In addition, due to heat generated by the light source unit, a lens sheet, a prism sheet, or the like that is thinner than the light guide plate may bend or warp. In particular, when an LED or the like is used for the light source unit, since a plurality of LEDs are arranged and used, the heat generated is increased. In addition, with the increase in screen size and thickness of the transmissive display device, the position of the light source unit cannot be separated. For this reason, there is a problem that the light source part side of the optical sheet is deformed such as bending or warping due to the heat generated by the light source part, and local luminance unevenness occurs due to such deformation such as bending.

  None of Patent Documents 1 and 2 discloses an improvement for such luminance unevenness and measures for reducing deformation such as bending due to heat from the light source unit.

  An object of the present invention is to improve luminance unevenness caused by the distance to a light source unit in an edge light type surface light source device, improve uniformity of in-plane luminance, and reduce luminance unevenness due to heat deflection of the light source unit. An optical sheet, a surface light source device using the optical sheet, and a transmissive display device are provided.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.
The invention of claim 1 is an optical sheet that is used in an edge light type surface light source device, and in which a plurality of unit optical shapes (152) are arranged on at least a light-exiting surface, and the unit optical shapes are formed. Provided between the first layer (151,251,351,651), the second layer (156) facing the first layer, the first layer and the second layer; A bonding layer (155, 455) for bonding the first layer and the second layer, and the bonding layer continuously changes in thickness in a cross section in one direction orthogonal to the sheet surface. And an optical sheet (15, 25) having a region in which the thickness gradually decreases from at least one end of the optical sheet in the one direction toward the other end. , 35, 45, 55, 65).
According to a second aspect of the present invention, in the optical sheet according to the first aspect, the bonding layer (155) has the largest thickness of one end (15a, 25a, 35a) of the optical sheet in the one direction. The optical sheet characterized in that the other end (15b, 25b, 35b) is the thinnest and the thickness gradually decreases from the one end toward the other end. 15, 25, 35).
According to a third aspect of the present invention, in the optical sheet according to the first aspect, the bonding layer (455) includes both end portions (45a, 45b, 55a, 55b, 65a, 65b) of the optical sheet in the one direction. ) Is the thickest, the thickness of the central portion (45c, 55c, 65c) is the thinnest, and the thickness gradually decreases from both ends toward the central portion. It is a sheet (45, 55, 65).

According to a fourth aspect of the present invention, in the optical sheet according to any one of the first to third aspects, the thickness at the point where the total thickness of the optical sheet is the thickest is a, When the thickness is b, the optical sheet (15, 25, 35, 45, 55) is characterized in that the thickness ratio a / b satisfies the relationship of 1.0 <a / b <1.6. , 65).
The invention according to claim 5 is the optical sheet according to any one of claims 1 to 4, wherein the unit optical shape (152) is a substantially triangular prism shape. 15, 25, 35, 45, 55, 65).
The invention according to claim 6 is the optical sheet according to any one of claims 1 to 5, wherein the unit optical shape (152) is arranged with respect to the one direction on the sheet surface. It is an optical sheet (15, 25, 35, 45, 55, 65) characterized by making an angle of 0 ° to 90 °.
According to a seventh aspect of the present invention, in the optical sheet according to any one of the first to sixth aspects, the bonding layer (155, 455) is formed of a thermosetting resin or an ionizing radiation curable resin. This is an optical sheet (15, 25, 35, 45, 55, 65).

The invention according to claim 8 is a light source part that emits light, a light guide plate (13) in which the light source part (12, 12A, 12B) is disposed on one end face or two opposite end faces, and an emission side of the light guide plate The optical sheet (15, 25, 35, 45, 55, 65) according to any one of claims 1 to 7, wherein the portion where the thickness of the bonding layer is thick is The surface light source device (10, 40) is characterized by being arranged to be on the light source unit side.
The invention of claim 9 is a transmissive display device (1) comprising: the surface light source device (10.40) according to claim 8; and a transmissive display unit (11) illuminated from the back by the surface light source device. 4).

The invention of claim 10 is the method for producing an optical sheet (15, 25, 35, 45, 55, 65) according to any one of claims 1 to 7, wherein the second layer A resin layer forming step of forming an uncured resin layer (155R, 455R) for forming the bonding layer on the surface of (156), and after the resin layer forming step, on the resin layer (155R, 455R) A laminating step for laminating the first layers (151, 251, 351, 651), a pressurizing step for changing the thickness of the resin layer by applying pressure after the laminating step, and And a curing step of curing the resin layer to form the bonding layer (155, 455) later.
The invention of claim 11 is the method for producing an optical sheet according to claim 10, wherein, in the pressing step, the diameter of one end (92b) in the direction of the axis (92c) is the same as that of the other end (92a). A method for producing an optical sheet, characterized in that pressurization is performed using a substantially frustoconical roll (92) larger than the diameter.
According to a twelfth aspect of the present invention, in the optical sheet manufacturing method according to the tenth aspect, in the pressurizing step, the central diameter (93d) in the direction of the axis (93c) is larger than the diameters of both end portions (93a, 93b). It is a manufacturing method of an optical sheet characterized by pressurizing using a big crown roll (93).

According to the present invention, the following effects can be obtained.
(1) In the optical sheet according to the present invention, a plurality of unit optical shapes are arranged on at least a surface on the emission side, and a first layer on which the unit optical shapes are formed and a second layer facing the first layer. And a bonding layer that is provided between the first layer and the second layer, and bonds the first layer and the second layer, and the bonding layer is in one direction orthogonal to the sheet surface. In the cross section, the thickness continuously changes, and has a region where the thickness gradually decreases from at least one end of the optical sheet in one direction toward the other end. ing. Accordingly, the optical sheet has a form in which the thickness gradually decreases from at least one end portion toward the other end portion, and the thick portion has low light transmittance and is deformed by heat. Is unlikely to occur. Therefore, by using this optical sheet in an edge-light type surface light source device with the thick part located on the light source side, the brightness unevenness due to the distance from the light source part is reduced and the in-plane brightness is reduced. The uniformity of the light source can be improved, and deformation such as bending due to heat of the light source part and luminance unevenness caused by this can be reduced as much as possible.

(2) The thickness of one end of the optical sheet in one direction is the thickest, the thickness of the other end is the thinnest, and the bonding layer has a thickness from one end to the other end. It is getting thinner gradually. Therefore, this optical sheet has the largest thickness at one end of the optical sheet in one direction, the smallest thickness at the other end, and the thickness from one end toward the other end. When the light source unit is used in a surface light source device provided at one end of the light guide plate, the luminance unevenness due to the distance from the light source unit is reduced and the in-plane luminance is uniform. It is possible to effectively reduce deformation such as bending due to heat of the light source section and luminance unevenness caused by the deformation.

(3) The joining layer has the thickest thickness at both ends of the optical sheet in one direction, the thinnest thickness at the center, and the thickness gradually decreases from both ends toward the center. ing. Therefore, in this optical sheet, the thickness of both ends of the optical sheet in one direction is the thickest, the thickness of the center is the thinnest, and the thickness gradually decreases from both ends toward the center. When the light source unit is used in a surface light source device provided at two opposite ends of the light guide plate, the luminance unevenness due to the distance from the light source unit is reduced and the uniformity of in-plane luminance is increased. In addition, it is possible to effectively reduce deformation such as bending due to heat of the light source unit and luminance unevenness caused by the deformation.

(4) When the thickness at the point where the total thickness of the optical sheet is the thickest is a and the thickness at the thinnest point is b, the relationship 1.0 <a / b <1.6 is satisfied. It is possible to enhance the effect of reducing luminance unevenness due to the distance from the light source unit, deformation such as bending of the light source unit due to heat, and luminance unevenness due to this.

(5) Since the unit optical shape is a substantially triangular prism shape, the light condensing action can be exhibited. In addition, the unit optical shape can be easily designed in accordance with the desired optical characteristics.

(6) Since the arrangement direction of the unit optical shapes forms an angle of 0 ° to 90 ° with respect to the one direction on the sheet surface, the moiré that is likely to occur when other optical sheets are laminated is reduced as much as possible. it can.

(7) Since the bonding layer is formed of a thermosetting resin or an ionizing radiation curable resin, it is easy to form and can be manufactured at low cost.

(8) A light-emitting unit that emits light, a light guide plate that arranges the light source unit on one end face or two opposite end faces, and the optical sheet of the present invention that is arranged on the light exit side of the light guide plate, and a bonding layer Since the surface light source device is arranged so that the thick part is on the light source unit side, the luminance unevenness due to the distance from the light source unit is reduced, the uniformity of in-plane luminance is increased, and the heat of the light source unit is increased. It is possible to reduce as much as possible the deformation such as the bending due to the light and the luminance unevenness caused by this.

(9) Since the transmissive display device includes the surface light source device according to the present invention and a transmissive display unit illuminated from the back by the surface light source device, the in-plane luminance is high and luminance unevenness is suppressed as much as possible. Can display good images.

(10) The method for producing an optical sheet of the present invention comprises: a resin layer forming step of forming an uncured resin layer for forming a bonding layer on the surface of the second layer; and a resin layer forming step after the resin layer forming step. A laminating step of laminating the first layer, a pressurizing step of applying pressure to change the thickness of the resin layer after the laminating step, and after the pressurizing step, curing the resin layer, A curing step to be formed. Therefore, manufacturing is easy, mass production can be easily performed, and an optical sheet can be provided at low cost. Moreover, since the both sides of the resin layer are laminated on the first layer and the second layer in an uncured state, the uncured resin adheres to a jig or the like during the pressing process. It is difficult to improve productivity.

(11) The optical sheet manufacturing method is easy to manufacture because, in the pressing step, pressing is performed using a substantially truncated cone-shaped roll in which the diameter of one end in the axial direction is larger than the diameter of the other end. Can be done. Further, mass production can be easily performed, and an optical sheet can be provided at a low cost.

(12) In the pressurizing step, the optical sheet is manufactured by using a crown roll having a central diameter in the axial direction larger than the diameters at both ends, and therefore can be manufactured easily. Further, mass production can be easily performed, and an optical sheet can be provided at a low cost.

It is a figure which shows the transmissive display apparatus of 1st Embodiment. It is a figure which shows the optical sheet of 1st Embodiment. It is a figure which shows the optical sheet of another form of 1st Embodiment. It is a figure which shows the optical sheet which is another form of 1st Embodiment. It is a graph which shows the thickness of an optical sheet, and the relationship of a brightness | luminance. It is a figure explaining an example of the manufacturing method of the optical sheet of a 1st embodiment. It is a figure which shows the transmissive display apparatus of 2nd Embodiment. It is a figure which shows the optical sheet of 2nd Embodiment. It is a figure which shows the optical sheet of another form of 2nd Embodiment. It is a figure which shows the optical sheet which is another form of 2nd Embodiment. It is a figure explaining an example of the manufacturing method of the optical sheet of 2nd Embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
In addition, the terms “plate”, “sheet”, “film” and the like are used, but these are generally used in the order of thickness, “plate”, “sheet”, “film”. I am using it. However, since there is no technical meaning in such proper use, the description in the claims is used in the unified description of the sheet. Accordingly, the terms “sheet”, “plate”, and “film” can be appropriately replaced. For example, the optical sheet may be an optical film or an optical plate.
Furthermore, numerical values such as dimensions and material names of each member described in the present specification are examples of the embodiment, and the present invention is not limited thereto, and may be appropriately selected and used.

(First embodiment)
FIG. 1 is a diagram illustrating a transmissive display device according to a first embodiment.
The transmissive display device 1 is a liquid crystal transmissive display device including an LCD (Liquid Crystal Display) panel 11 and a surface light source device 10 that illuminates the LCD panel 11 from the back side.
The surface light source device 10 is an edge light type surface light source device (backlight) including a light source unit 12, a light guide plate 13, a reflection plate 14, an optical sheet 15, and the like.
The LCD panel 11 is a liquid crystal transmission display unit that displays an image. This LCD panel is a substantially rectangular member having a substantially rectangular shape, and for example, a screen having a diagonal size of 32 inches (diagonal 32 inches (740 mm × 420 mm) and a resolution of 1280 × 768 dots can be used.

The observation screen of the transmissive display device 1 (LCD panel 11) has a horizontally long rectangular shape when the transmissive display device 1 is used.
In the following description, the direction parallel to the short side of the observation screen (LCD panel 11) in the usage state of the transmissive display device 1 is the screen vertical direction (screen vertical direction) in the usage state, and the direction parallel to the long side is The left and right direction of the screen in the use state (the horizontal direction of the screen). In the following description, unless otherwise specified, it is assumed that the screen horizontal direction and the screen vertical direction are the screen horizontal direction and the screen vertical direction in the usage state of the transmissive display device 1 and the surface light source device 10.

  The light source unit 12 is a part that emits light that illuminates the LCD panel 11 from the back. The light source unit 12 of the present embodiment is provided at a position facing one end surface (light incident surface) 13 a of the light guide plate 13 in the vertical direction of the screen. The light source unit 12 uses LED (not shown) that is a point light source as a light source, and a plurality of LEDs are arranged at equal intervals in the horizontal direction of the screen along the light incident surface 13a.

The light guide plate 13 is a substantially flat member that propagates light. The light guide plate 13 allows light emitted from the light source unit 12 to be incident from the light incident surface 13a, is totally reflected by the light output surface 13c and the back surface 13d, and propagates to the other surface 13b side while appropriately transmitting from the light output surface 13c to the optical sheet 15. The light is emitted to the side.
The light guide plate 13 of the present embodiment is made of acrylic resin, and dots (not shown) and the like are formed on the back surface on the reflective plate 14 side by printing or the like.
In addition, although the light guide plate 13 of this embodiment has shown the example which is substantially flat form which has substantially equal thickness as shown in FIG. 1, it is not restricted to this, For example, in the screen up-down direction, the light source part 12 is shown. The light incident surface 13a side that is the side may be thick and the other surface 13b side may be thin.
The reflection plate 14 is a plate-like member that can reflect light, and is disposed on the back side (the side opposite to the optical sheet 15) from the light guide plate 13. The reflecting plate 14 has a function of reflecting light that is reflected by the optical sheet 15 or the like and travels toward the back side, and directs the light toward the optical sheet 15 again.

The optical sheet 15 is arranged on the emission side (LCD panel 11 side) from the light guide plate 13 and has an action of controlling the emission direction by condensing light emitted from the light guide plate.
FIG. 2 is a diagram illustrating the optical sheet 15 of the first embodiment. FIG. 2A is a perspective view of the optical sheet 15, and FIG. 2B schematically shows a cross section orthogonal to the sheet surface of the optical sheet 15 and parallel to the vertical direction of the screen. In FIG. 2B, in order to show the arrangement of the optical sheet 15 in the surface light source device 10, the light source unit 12 and the light guide plate 13 are also shown.

The optical sheet 15 includes a prism film 151, a bonding layer 155, and a base film 156, and these are integrally laminated.
As shown in FIG. 2, the optical sheet 15 is thickest at the end 15a on the light source 12 side in the vertical direction of the screen, and gradually decreases from the end 15a to the other side. The other end 15b is the thinnest. That is, the thickness of the optical sheet 15 changes in a cross section orthogonal to the sheet surface and parallel to the arrangement direction (the vertical direction of the screen) of the unit prisms 152.

  Here, the sheet surface indicates a surface that is a planar direction of the sheet when the sheet such as the optical sheet 15 is viewed as a whole sheet, and in the present specification and in the claims. Are also used as the same definition. The sheet surface of the optical sheet 15 is a plane that is a planar direction of the optical sheet 15 when viewed as the entire optical sheet 15, and is parallel to the observation surface of the LCD panel 11. The sheet surface of the optical sheet 15 is parallel to a plane passing through each vertex t of the unit prism 152. Further, the sheet surface of the optical sheet 15 is orthogonal to the thickness direction of the optical sheet 15.

  The prism film 151 is a first layer provided on the emission side (LCD panel 11 side) of the optical sheet 15, and includes a prism layer 153 on which the unit prism 152 is formed and a prism base layer 154. Yes. The total thickness of the prism film 151 (the dimension from the apex t of the unit prism 152 to the surface on the bonding layer 155 side of the prism base material layer 154 in the direction orthogonal to the sheet surface) depends on the position on the sheet surface. It is constant or substantially constant.

In the prism layer 153, a plurality of unit prisms 152 are arranged in the vertical direction of the screen on the exit side surface.
The unit prism 152 is a unit optical shape having a substantially isosceles triangular prism shape with a base angle α. The height of the unit prism 152 (the dimension from the vertex t of the unit prism 152 in the direction orthogonal to the sheet surface to the point v serving as the valley bottom) is h, and the top of the unit prism 152 is a curved surface having a curvature radius R. ing. The arrangement pitch (corresponding to the lens width) of the unit prisms 152 is P. The unit prism 152 has a constant shape regardless of the position in the arrangement direction, and the arrangement pitch P is also constant.
The unit prism of this embodiment has a base angle α = 45 °, an arrangement pitch P = 50 μm, a height h = 25 μm, and a radius of curvature R = 1 μm.
The prism layer 153 is made of an ultraviolet curable resin. The prism layer 153 may be formed using another ionizing radiation curable resin such as an electron beam curable resin, a photocurable resin, or the like.

The prism base material layer 154 is a layer that becomes a base material for forming the prism layer 153. The prism base material layer 154 is a resinous film-like member having optical transparency, and the thickness thereof is constant or substantially constant. The prism base layer 154 of the present embodiment is a sheet-like member made of PET (polyethylene terephthalate) resin and has a thickness of 250 μm.
In this prism film 151, the prism layer 153 is formed by, for example, applying an ultraviolet curable resin to one surface of the prism base material layer 154 and pressing the surface to which the ultraviolet curable resin has been applied against a mold. Or the like. A method for creating the prism film 151 can be freely selected as appropriate.

The base film 156 is a second layer provided on the incident side (light guide plate 13 side) of the optical sheet 15. The base film 156 is a resinous film-like member having light permeability, and the thickness thereof is uniform or substantially uniform. The surface 156a of the base film 156 on the light guide plate 13 side is a light incident surface from the light guide plate 13, does not have an optical shape such as a unit lens, and has a substantially flat shape.
The base film 156 of this embodiment is made of PET resin and has a thickness of 188 μm.
The base film 156 is not limited to a PET resin, and for example, a PC (polycarbonate) resin, an AS (acrylonitrile / styrene) resin, an ABS (acrylonitrile / butadiene / styrene) resin, a PMMA (methyl methacrylate) resin, a cyclo An olefin resin, an MS (methyl methacrylate / styrene) resin, an MBS (methyl methacrylate / butadiene / styrene) resin, or the like may be used.

The bonding layer 155 is a layer that bonds the prism film 151 and the base film 156, and is formed of a resin having light transmittance or the like. The bonding layer 155 of the present embodiment is made of a thermosetting resin, but is not limited thereto, and for example, an ionizing radiation curable resin such as an ultraviolet curable resin may be used.
As shown in FIG. 2, the bonding layer 155 has a thickest end 15a in the cross section parallel to the screen vertical direction (the arrangement direction of the unit prisms 152) orthogonal to the sheet surface, and toward the other end 15b. It is getting thinner and the other end 15b is the thinnest.

  The optical sheet 15 has the thickness (maximum thickness) of the point (the end 15a on the light source unit 12 side) where the thickness (total thickness) of the optical sheet including the unit prism 152 (prism layer 153) is the thickest. When a is the thickness (minimum thickness) at the thinnest point (the other end 15b) is b, the thickness ratio a / b is 1.0 <a / b <. Meet 1.6. When the thickness ratio a / b satisfies this range, the optical sheet 15 has a uniform brightness within the screen as the surface light source device 10 and deformation such as bending caused by heat generated by the light source unit 12. The resulting luminance unevenness can be reduced.

  As shown in FIG. 2B, when the extreme end is displaced from the position of the apex t of the unit prism 152, the maximum thickness value a passes through a point v that is a valley between the unit prisms 152. This is a value obtained by adding the dimension d1 at the thickest point (end 15a) from the plane S parallel to the sheet surface to the incident surface 156a of the optical sheet 15 and the height h of the unit prism 152 (a = d1 + h). ), The minimum value b of the thickness is the point (end 15 b) where the dimension is the thinnest from the plane S parallel to the sheet surface through the point v that is the valley bottom between the unit prisms 152 to the incident surface 156 a of the optical sheet 15. A value obtained by adding the dimension d2 and the height h of the unit prism 152 (b = d2 + h).

The optical sheet 15 is not limited to the unit prisms 152 arranged in the vertical direction of the screen, but is arranged in the horizontal direction of the screen or the angle β (0 ° <β on the sheet surface with respect to the vertical direction of the screen). <90 °) may be adopted.
FIG. 3 is a diagram showing an optical sheet 25 of another form of the first embodiment. FIG. 3A is a perspective view of the optical sheet 25, and FIG. 3B shows the optical sheet 25 passing through the apex t of the unit prism 152 and perpendicular to the sheet surface of the optical sheet 25 in the vertical direction of the screen. It is a figure which shows typically the cross section cut | disconnected by the parallel cross section. In FIG. 3B, in order to show the arrangement of the optical sheet 25 in the surface light source device 10, the light source unit 12 and the light guide plate 13 are also shown.

The optical sheet 25 has substantially the same configuration as the optical sheet 15 described above except that the unit prisms 152 are arranged in the horizontal direction of the screen except that the optical sheet 25 is different from the optical sheet 15 described above.
The optical sheet 25 includes a prism film 251, a bonding layer 155, and a base film 156, which are laminated together. The prism film 251 includes a prism layer 153 and a prism base material layer 154. Similar to the optical sheet 15, the thickness of the optical sheet 25 changes in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, the end 25a side being the thickest, and the other end 25b It gradually becomes thinner, and the other end 25b side is the thinnest.

In the optical sheet 25, the thickness (maximum value of the thickness) of the point (end portion 25a) having the largest total thickness is defined as a, and the thickness (minimum value of the thickness) of the thinnest point (end portion 25b) is defined. When b is set, the thickness ratio a / b satisfies 1.0 <a / b <1.6.
A plurality of unit prisms 152 formed in the prism layer 153 are arranged in the horizontal direction of the screen. Further, as described above, the thickness of the bonding layer 155 changes in a cross section perpendicular to the sheet surface and parallel to the vertical direction of the screen, and is thickest on the end 25a side and gradually toward the other end 25b. The other end 25b is thinnest. Therefore, in the optical sheet 25, the arrangement direction of the unit prisms 152 is relative to the cross-sectional direction (up and down direction of the screen) in which the total thickness of the optical sheet 25 (the thickness of the bonding layer 155) is changed on the sheet surface. Orthogonal.
By adopting a configuration like the optical sheet 25, it is possible to exert a light beam control function mainly in the horizontal direction of the screen.

FIG. 4 is a diagram showing an optical sheet 35 according to another form of the first embodiment. FIG. 4A is a perspective view of the optical sheet 35, and FIG. 4B shows a state in which the prism film 351 side of the optical sheet 35 is observed from a direction orthogonal to the sheet surface.
This optical sheet 35 is different from the optical sheet 15 described above in that the arrangement direction of the unit prisms 152 forms an angle β (0 ° <β <90 °) with respect to the vertical direction of the screen on the sheet surface. Are substantially the same as the optical sheet 15 described above, except for the above.
The optical sheet 35 includes a prism film 351, a bonding layer 155, and a base film 156, which are laminated together. The prism film 351 includes a prism layer 153 and a prism base material layer 154. Similar to the optical sheet 15 described above, the thickness of the optical sheet 35 changes in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, with the end 35a side being the thickest and facing the other end 35b. The other end 35b is thinnest.
The optical sheet 35 has a thickness ratio a, where a is the thickness of the thickest point (maximum value of thickness) and b is the thickness of the thinnest point (minimum value of thickness). / B satisfies 1.0 <a / b <1.6.

As shown in FIGS. 4A and 4B, a plurality of unit prisms 152 in the prism layer 153 are arranged in a direction that forms an angle β (0 ° <β <90 °) with respect to the vertical direction of the screen on the sheet surface. It is arranged. Further, as described above, the thickness of the bonding layer 155 changes in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, and is thickest at the end 35a side and gradually toward the other end 35b. The other end 35b is thinnest. Therefore, in the optical sheet 35, the arrangement direction of the unit prisms 152 is relative to the cross-sectional direction (the vertical direction of the screen) in which the total thickness of the optical sheet 35 (the thickness of the bonding layer 155) is changed on the sheet surface. An angle β is formed. Regarding the angle β, when β = 0 ° corresponds to the optical sheet 15 described above, and when β = 90 ° corresponds to the optical sheet 25 described above.
By adopting a configuration like the optical sheet 35, moire due to interference between the pixels of the LCD panel 11 and unit lenses of other lens sheets stacked on the optical sheet 35 and the unit prism 152 of the optical sheet 35 is greatly reduced. can do.
In the case of a configuration like the optical sheet 35, the arrangement direction of the unit prisms 152 is about 2 to 10 degrees with respect to the screen vertical direction, or about 2 to 10 degrees with respect to the screen horizontal direction. It is effective to reduce the moire.

  Here, in order to examine the relationship between the thickness (total thickness) of the optical sheet and the luminance, the optical prism has a light transmission property, and a unit prism is formed on one surface on the output side surface. Five types of measurement optical sheets having different (dimensions from the incident surface in the thickness direction to the apex of the unit prism) are prepared, and these measurement optical sheets are used to correspond to the surface light source device 10 of the present embodiment. A surface light source device was manufactured, and the front luminance at the center of the screen was measured. The total thickness of the five types of optical sheets for measurement is 250 μm, 350 μm, 435 μm, 535 μm, and 570 μm, respectively.

FIG. 5 is a graph showing the relationship between the thickness of the optical sheet and the luminance. In FIG. 5, the horizontal axis represents the total thickness of the optical sheet, and the vertical axis represents the relative luminance when the luminance of the optical sheet for measurement having a thickness of 570 μm is used as a reference (100%).
The optical sheet for each measurement has a constant total thickness (a dimension from the incident surface to the apex of the unit prism in the thickness direction). Each optical sheet for measurement has a prism film 151, a bonding layer 155, and a base film 156 in the same manner as the optical sheet of this embodiment. Each layer has a different thickness. The unit prism formed on the optical sheet for measurement has a substantially isosceles triangular prism shape with an arrangement pitch P = 50 μm, a prism height h = 25 μm, and a base angle α = 45 °, and a curvature radius R = It is 1 μm and is arranged in the vertical direction of the screen.
The surface light source devices using these optical sheets for measurement are actually turned on in the dark room environment, and the front luminance at the center of the screen in the dark room environment using a luminance meter (BM-9 manufactured by TOPCOM Co., Ltd.). Was measured, and the relative luminance based on the front luminance of the optical sheet for measurement having a thickness of 570 μm was calculated.
As shown in FIG. 5, the thinner the optical sheet, the higher the transmittance and the higher the brightness.

In general, in the edge light type surface light source device, the light source unit 12 is disposed at a position facing the light incident surface 13 a of the light guide plate 13 as shown in FIG. 1. Therefore, in the edge light type surface light source device, the light source part side is bright, the luminance gradually decreases as the distance from the light source part increases, and is slightly darker than the light source part side in the vicinity of the other end facing the light source part side end. It has a luminance distribution.
In addition, as described above, the optical sheet has a tendency that the luminance is higher when the total thickness is thinner, and the luminance is lower when the total thickness is thicker.
Therefore, the optical sheet 15 is laminated on the light emitting plate 13 having the luminance unevenness due to the distance from the light source unit as described above, with the light source unit 12 having a large thickness and a thickness decreasing with increasing distance from the light source unit 12. By doing so, the transmittance on the side far from the light source unit 12 can be increased as compared with the light source unit 12 side, the uniformity of in-plane luminance can be improved, and the luminance unevenness can be greatly improved.

In the transmissive display device 1 and the surface light source device 10, the light source unit 12 generates not only light but also heat. When the light source unit 12 is formed by arranging a large number of point light sources (LED light sources) as in the present embodiment, the vicinity of the light source unit 12 is considerably hot. Therefore, a portion near the light source unit 12 in the optical sheet is likely to be deformed such as bending or warping due to heat generated by the light source unit 12. Such deformation such as bending is unlikely to occur in a relatively thick light guide plate 13 having a thickness of about 3 to 5 mm, but is likely to occur in a relatively thin optical sheet having a thickness of several hundred μm.
In particular, when the screen is enlarged, the optical sheet needs to have higher rigidity than that used in a transmissive display device having a small screen size in order to maintain the flatness. For this reason, even in an optical sheet in which a problem such as bending does not occur in a transmission type display device with a small screen size, bending due to heat or the like is likely to occur.
Therefore, if the thickness of the optical sheet is increased uniformly, the luminance at a position far from the light source unit 12 is decreased due to an increase in production cost and a decrease in transmittance. In addition, in a transmissive display device and a surface light source device, a reduction in thickness is always a required issue.

As described above, the total thickness of the optical sheet 15 of the present embodiment is such that the thickness of the one end portion 15a is the largest, gradually decreases toward the other side, and the thickness of the other end portion 15b increases. The thickness is the thinnest.
The optical sheet 15 is arranged such that the thick end portion 15a is positioned on the light source section 12 side and the thin end section 15b is positioned on the other side, whereby the optical sheet 15 is heated by the heat generation of the light source section 12. Deformation such as bending can be reduced, luminance unevenness due to bending can be greatly reduced, and luminance unevenness due to distance from the light source unit 12 can be improved to increase in-plane luminance uniformity. it can.
Also, the stretching directions of the prism base layer 154 and the base film 156 are arranged so as to have a mirror image relationship when viewed from the normal direction of the sheet surface, or the thermal expansion coefficient of each layer constituting the optical sheet 15 is preferable. Can be appropriately selected and used, so that warping and bending due to heat can be more effectively reduced.
Further, a diffusion material or the like can be easily kneaded into the bonding layer 155 in accordance with the desired optical performance. Furthermore, the refractive index of each layer constituting the optical sheet 15 can be adjusted as appropriate, whereby the light emission direction can be controlled.

(Method for Manufacturing Optical Sheet of First Embodiment)
An example of the manufacturing method of the optical sheets 15, 25, and 35 of this embodiment will be described.
FIG. 6 is a diagram illustrating an example of a method for manufacturing an optical sheet according to the first embodiment. Here, in order to facilitate understanding, a description will be given of a method of manufacturing the optical sheet 15 using a prismatic film 151 and a base film 156 that are sheet-like.
The optical sheet of the first embodiment is formed by bonding the base film 156 and the prism film 151 by the bonding layer 155 by a method generally called a laminating method.
As shown in FIG. 6A, first, a sheet-like base film 156 cut into a predetermined size is placed on a table (not shown).
And as shown in FIG.6 (b), the resin layer 155R of thermosetting resin is formed in the predetermined thickness by the coater etc. which are not illustrated on the single side | surface of the base film 156 (resin layer formation process). At this time, the thermosetting resin forming the resin layer 155R has a viscosity in an uncured state of 2750 ± 600 mPa · s (25 ° C.) so that the shape formed in the pressurizing step described later can be maintained. It is preferable. More preferably, the viscosity in an uncured state satisfies about 2750 ± 600 mPa · s (25 ° C.) and about 1100 ± 300 mPa · s (40 ° C.).
Next, as shown in FIG. 6C, a sheet-like prism film 151 cut into a predetermined size is laminated on the thermosetting resin layer 155R (lamination step). At this time, the prism base layer 154 is laminated so as to be on the resin layer 155R side.

Next, as shown in FIG. 6 (d), a laminated body composed of the prism film 151, the uncured resin layer 155R, and the base film 156 is passed between a pair of nip rolls 91 and 92 to apply pressure (applying pressure). Pressure process). Of the pair of nip rolls 91 and 92, the roll 91 on the prism film 151 side has a substantially cylindrical shape and is driven to rotate about the shaft 91c. Further, as shown in FIGS. 6D and 6E, the roll 92 on the base film 156 side has a diameter of one end 92b larger than the diameter of the other end 92a in the direction of the axis 92c. It has a substantially frustoconical shape and is driven to rotate about the shaft 92c. The axes 91c and 92c are parallel.
By using such nip rolls 91 and 92 to press in the thickness direction, the thickness of the uncured resin layer 155R is such that one is thin and the other is thick in the direction parallel to the roll shafts 91c and 92c. It can be.
Further, since the base film 156 can prevent the resin of the resin layer 155R from adhering to the roll 92, the productivity can be improved, and the rigidity of the base film 156 can increase the thickness of the resin layer 155R after the pressing step. Can be prevented from returning to or deforming.

Next, as shown in FIG. 6 (f), the laminated body including the prism film 151, the thermosetting resin layer 155R, and the base film 156 is heated to cure the resin layer 155R to form the bonding layer 155. The prism film 151 and the base film 156 are joined (curing process).
Next, after cooling for a predetermined time, a process of cutting into a predetermined shape and size for incorporation into the surface light source device 10 is performed as necessary.
By the manufacturing method as described above, as shown in FIGS. 2 and 6 (g), one end 15a is the thickest, becomes thinner toward the other end 15b, and the other end 15b is the thinnest. The optical sheet 15 is obtained.
The optical sheets 25 and 35 can also be produced by the same manufacturing method by using the prism films 251 and 351, for example.

By using the manufacturing method as described above, an optical sheet in which one of the bonding layers 155 is thick in the vertical direction of the screen and the other is thin can be easily manufactured, and mass production can be easily performed. Furthermore, the extending direction of the base film 156 and the prism base layer 154 and the arrangement direction of the unit prisms 152 can be set as appropriate.
In addition, although the example manufactured using the sheet-like base film 156 and the prism film 151 was shown, you may manufacture using not only this but the web-like continuous base film 156 and the prism film 151. .

(Second Embodiment)
FIG. 7 is a diagram illustrating a transmissive display device according to the second embodiment.
In the transmissive display device 4 and the surface light source device 40 of the second embodiment, the light source portions 12A and 12B are provided at positions facing two opposite sides of the light guide plate 13, respectively, and include an optical sheet 45. Except for the difference between the transmissive display device 1 and the surface light source device 10 of the first embodiment, the configuration is substantially the same as that of the transmissive display device 1 and the surface light source device 10 of the first embodiment. Further, the optical sheet 45 of the second embodiment is that the central portion 45c (see FIG. 8) is thin and both ends are thick in the cross section in the vertical direction of the screen perpendicular to the sheet surface. Except for being different from 15, the configuration is substantially the same as the optical sheet 15 of the first embodiment. Therefore, parts having the same functions as those in the first embodiment described above are denoted by the same reference numerals or the same reference numerals at the end, and repeated description is appropriately omitted.

The transmissive display device 4 includes an LCD panel 11 and a surface light source device 40. The surface light source device 40 includes light source units 12A and 12B, a light guide plate 13, a reflection plate 14, and an optical sheet 45.
The light source parts 12A and 12B are arranged at positions facing the end faces 13a and 13b in the screen vertical direction of the light guide plate 13, respectively. Like the light source unit 12 shown in the first embodiment, the light source units 12A and 12B use LEDs (not shown) as light emission sources, and the light source units 12A and 12B have LEDs in the horizontal direction of the screen. Multiple arrays are arranged at intervals.
The transmissive display device 4 in which the surface light source device 40 of this embodiment is used often has a large screen as compared with the transmissive display device 1 shown in the first embodiment. The screen size of the LCD panel 11 of the present embodiment is, for example, 52 inches diagonal (1170 × 670 mm), and can display a resolution of 1920 × 1080 dots.

As shown in FIG. 7, the optical sheet 45 is arranged on the light exit side (LCD panel 11 side) from the light guide plate 13, and a plurality of unit prisms 152 are arranged along the vertical direction of the screen.
FIG. 8 is a diagram illustrating the optical sheet 45 of the second embodiment. FIG. 8A is a perspective view of the optical sheet 45, and FIG. 8B is a diagram schematically showing a cross section in the vertical direction of the screen, and the arrangement of the optical sheet 45 in the surface light source device 40. In order to show, the light source parts 12A and 12B and the light guide plate 13 are also shown.

The optical sheet 45 includes a prism film 151, a bonding layer 455, and a base film 156, which are laminated together.
The total thickness of the prism film 151 and the base film 156 is constant as shown in the first embodiment. On the other hand, the bonding layer 455 is formed so that the central portion 45c is the thinnest and the both end portions 45a and 45b are the thickest in a cross section orthogonal to the sheet surface of the optical sheet 45 and parallel to the arrangement direction of the unit prisms 152 (the vertical direction of the screen). Has been. As a result, the total thickness of the optical sheet 45 is perpendicular to the sheet surface and parallel to the arrangement direction of the unit prisms 152 (the vertical direction of the screen), the center portion 45c is the thinnest, and both end portions 45a and 45b are the thickest. ing.

The optical sheet 45 has a thickness ratio a / b, where a is the thickness of the thickest point (both ends 45a and 45b) and b is the thickness of the thinnest point (central portion 45c). However, 1.0 <a / b <1.6 is satisfied.
Further, the incident surface 156a of the optical sheet 45 (the surface of the base film 156 on the light guide plate 13 side) is a gentle concave curve or a central portion 45c in a cross section parallel to the screen vertical direction and perpendicular to the sheet surface. Is a concave curve and smoothly connects to the straight lines on both ends 45a and 45b.
As shown in FIG. 7, the optical sheet 45 is arranged in the surface light source device 40 so that the thicker end portions 45a and 45b are on the light source portions 12A and 12B side.

The optical sheet 45 of the second embodiment is not limited to the unit prisms 152 arranged in the vertical direction of the screen. The optical sheet 45 may be arranged in the horizontal direction of the screen or the vertical direction of the screen on the sheet surface. An angle β (0 ° <β <90 °) may be formed.
FIG. 9 is a diagram showing an optical sheet 55 of another form of the second embodiment. FIG. 9A is a perspective view of the optical sheet 55, and FIG. 9B is a cross section orthogonal to the sheet surface of the optical sheet 55 and parallel to the vertical direction of the screen and passing through the vertex t of the unit prism 152. In order to show the arrangement of the optical sheet 55 in the surface light source device 40, the light source units 12A and 12B and the light guide plate 13 are also shown.
The optical sheet 55 has a prism film 251, a bonding layer 455, and a base film 156, which are laminated together. The optical sheet 55 has substantially the same shape as the optical sheet 45 described above except that the unit prism 152 includes a prism film 251 arranged in the horizontal direction of the screen. Similar to the optical sheet 45 described above, the thickness of the optical sheet 55 changes in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, with the central portion 55c being the thinnest and facing both end portions 55a and 55b. The thickness gradually increases, and both end portions 55a and 55b are thickest.
In the optical sheet 55, the thickness (maximum value of the thickness) of the point (end portions 55a and 55b) having the largest total thickness is a, and the thickness (minimum value of the thickness) of the thinnest point (center portion 55c). Is b, the thickness ratio a / b satisfies 1.0 <a / b <1.6.

  A plurality of unit prisms 152 formed in the prism layer 153 are arranged in the horizontal direction of the screen. Further, as described above, the thickness of the bonding layer 455 changes in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, the central portion 55c is the thinnest, and gradually increases toward both end portions 55a and 55b. The both end portions 55a and 55b are the thickest. Therefore, in the optical sheet 55, the arrangement direction of the unit prisms 152 is relative to the cross-sectional direction (the screen vertical direction) in which the total thickness of the optical sheet 55 (the thickness of the bonding layer 455) changes on the sheet surface. Orthogonal.

FIG. 10 is a diagram showing an optical sheet 65 of another form of the second embodiment. FIG. 10A is a perspective view of the optical sheet 65, and FIG. 10B shows a state in which the prism film 651 side of the optical sheet 65 is observed from a direction orthogonal to the sheet surface.
The optical sheet 65 differs from the optical sheet 15 described above except that the arrangement direction of the unit prisms 152 is an angle β with respect to the vertical direction of the screen on the sheet surface. It is substantially the same form. Similar to the optical sheet 45 described above, the optical sheet 65 has a thickness that varies in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, the central portion 65c being the thinnest, and both end portions 65a and 65b. The thickness gradually increases toward the side, and both end portions 65a and 65b are the thickest.
In this optical sheet 65, the thickness (maximum value of the thickness) of the point having the largest total thickness (both ends 65a, 65b) is a, and the thickness (minimum value of the thickness) of the thinnest point (center portion 65c). ) Is b, the thickness ratio a / b satisfies 1.0 <a / b <1.6.

The optical sheet 65 includes a prism film 651, a bonding layer 455, and a base film 156, which are laminated together. The prism film 651 includes a prism layer 153 and a prism base material layer 154.
As shown in FIG. 10A, a plurality of unit prisms 152 of the prism layer 153 are arranged in a direction that forms an angle β (0 ° <β <90 °) with respect to the vertical direction of the screen. Further, as described above, the thickness of the bonding layer 455 changes in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen, the central portion 65c is the thinnest, and toward the both end portions 65a and 65b side. The both ends 65a and 65b are thickest gradually. Therefore, in the optical sheet 65, the arrangement direction of the unit prisms 152 is an angle β (0 ° <0 ° <0) with respect to the cross-sectional direction of the optical sheet 65 in which the total thickness of the optical sheet 65 (the thickness of the bonding layer 155) changes. β <90 °). Regarding the angle β, when β = 0 ° corresponds to the optical sheet 45 described above, and when β = 90 ° corresponds to the optical sheet 55 described above.

By adopting a configuration like the optical sheet 65, moire due to interference between the optical sheet 65 and the pixels of the LCD panel 11 can be greatly reduced.
As described in the first embodiment, in the case of a configuration like the optical sheet 65, the arrangement direction of the unit prisms 152 is a direction that forms about 2 to 10 degrees with respect to the vertical direction of the screen, or It is effective to reduce the moire when the direction is about 2 to 10 ° with respect to the horizontal direction of the screen.

(Method for Manufacturing Optical Sheet of Second Embodiment)
An example of a method for manufacturing the optical sheets 45, 55, 65 of the second embodiment will be described.
FIG. 11 is a diagram illustrating an example of a method for manufacturing an optical sheet according to the second embodiment. Here, in order to facilitate understanding, a description will be given of a method of manufacturing the optical sheet 45 using a prismatic film 151 and a base film 156 that are in the form of single sheets.
The optical sheet of the second embodiment is formed by bonding the base film 156 and the prism film 151 with the bonding layer 455 by a method generally called a laminating method.

As shown in FIG. 11A, first, a sheet-like substrate film 156 cut into a predetermined size is placed on a table (not shown).
And as shown in FIG.11 (b), the resin layer 455R of a thermosetting resin is formed in the single side | surface of the base film 156 by a coater etc. (not shown) (resin layer formation process). At this time, the thermosetting resin forming the resin layer 455R has a viscosity of about 2750 ± 600 mPa · s (25 ° C.) in an uncured state so that the shape formed in the pressurizing step described later can be maintained. Preferably there is. More preferably, the viscosity in an uncured state satisfies about 2750 ± 600 mPa · s (25 ° C.) and about 1100 ± 300 mPa · s (40 ° C.).
Next, as shown in FIG. 11C, a sheet-like prism film 151 cut into a predetermined size is laminated on the thermosetting resin layer 455R (lamination step). At this time, the prism base layer 154 is laminated so as to be on the resin layer 455R side.

Next, as shown in FIG. 11 (d), a laminate composed of the prism film 151, the uncured resin layer 455 R, and the base film 156 is passed between a pair of nip rolls 91 and 93 to apply pressure (applying). Pressure process).
Of the pair of nip rolls 91 and 93, the roll 91 on the prism film 151 side has a substantially cylindrical shape and is driven to rotate about the shaft 91c. Further, as shown in FIGS. 11D and 11E, the roll 93 on the base film 156 side has the same diameter in both end portions 93a and 93b in the axial direction, and the diameter of both end portions 93a and 93b. This is a crown roll having a large diameter at a point 93d which is the center in the direction of the shaft 93c. The roll 93 is driven to rotate about the shaft 93c. The axes 91c and 93c are parallel.
By applying pressure in the thickness direction using such nip rolls 91 and 93, the thickness of the resin layer 455R can be made thin in the direction of the roll shafts 91c and 93c and thick at both ends.
Further, since the base film 156 can prevent the resin of the uncured resin layer 155R from adhering to the roll 93, the productivity can be improved, and the rigidity of the base film 156 allows the resin layer 155R after the pressurizing step. It is possible to prevent the thickness of the base from returning to the base or from being deformed.

Next, as shown in FIG. 11 (f), the laminated body composed of the prism film 151, the thermosetting resin layer 455R, and the base film 156 is heated to cure the resin layer 455R to form a bonding layer 455. The prism film 151 and the base film 156 are joined (curing process).
Next, after cooling for a predetermined time, a process of cutting into a predetermined shape and size for incorporation into the surface light source device 40 is performed as necessary.
By the manufacturing method as described above, as shown in FIG. 9 and FIG. 11G, the central portion 45c is thin, becomes thicker toward the both end portions 45a and 45b, and both end portions 45a and 45b are the thickest optical sheet 45. Is obtained.
The optical sheets 55 and 65 can also be manufactured by the same manufacturing method by using the prism films 251 and 651, for example.
By using the manufacturing method as described above, an optical sheet having a shape in which the thickness of the bonding layer 455 is thin in the center and thin at both ends in the vertical direction of the screen can be easily manufactured, and mass production can be easily performed. Furthermore, the extending direction of the base film 156 and the prism base layer 154 and the arrangement direction of the unit prisms 152 can be set as appropriate.
In addition, although the example manufactured using the sheet-like base film 156 and the prism film 151 was shown, you may manufacture using not only this but the web-like continuous base film 156 and the prism film 151. .

According to the present embodiment, even in a two-lamp type surface light source device and a transmissive display device, luminance unevenness caused by whether or not the light source units 12A and 12B are close to each other is improved, and optical due to heat generation of the light source unit 12 is achieved. It is possible to reduce deformation such as bending of the sheet 15, greatly reduce luminance unevenness due to bending or the like, and improve uniformity of in-plane luminance.
Further, the two-lamp type surface light source device 40 and the transmissive display device 4 as in the present embodiment are one-lamp type devices such as the surface light source device 10 and the transmissive display device 1 of the first embodiment described above. Compared to a large screen in many cases, the uniformity of in-plane luminance can be improved even for a large screen where uniformity of in-plane luminance tends to be a problem.
Furthermore, the stretching direction of the prism base material layer 154 and the base film 156, the thermal expansion coefficient of each layer constituting the optical sheet 15 and the like can be selected as appropriate, and the warp and the deflection due to heat can be reduced more effectively. Can do.
Furthermore, a diffusion material can be easily kneaded into the bonding layer 455 in accordance with the desired optical performance. Furthermore, the light emission direction can be controlled by appropriately adjusting the refractive index of each layer constituting the optical sheet 15.

(Evaluation of examples and luminance unevenness of each embodiment)
Here, optical sheets of Examples 1 to 24 corresponding to Examples and Comparative Examples of the optical sheet of each embodiment were prepared, and the optical performance and deformation due to heat were examined.
In the optical sheets of Examples 1 to 24, the resin forming the bonding layer is a thermosetting resin.
The unit prisms 152 of the optical sheets of Examples 1 to 24 have substantially the same shape except that the arrangement directions thereof are different from each other. The arrangement pitch P = 50 μm, the unit prism height h = 25 μm, and the base angle α. = A substantially isosceles triangular prism shape of 45 °, and the radius of curvature R at the top is R = 1 μm. The prism base layer 154 is a PET resin member having a thickness of 250 μm, and the base film 156 is made of PET resin having a thickness of 188 μm.
The optical sheets of Examples 1 to 4, 13 to 16, and 21 to 24 have the same shape except that the thickness of the bonding layer is substantially uniform and the thicknesses (total thicknesses) are different.
The optical sheets of Examples 5 to 12 are optical sheets that are thick at both ends and thin at the center, and have the same shape except that the maximum value a and the minimum value b of the thickness are different.
The optical sheets of Examples 17 to 20 are optical sheets that are thick at one end and thin at the other end, and have the same shape except that the maximum value a and the minimum value b of the thickness are different.
The optical sheets of Examples 5 to 12 and 17 to 20 are arranged so that the thickness thereof continuously changes in the vertical direction of the screen in a state of being incorporated in the transmissive display device.

In the optical sheets of Examples 1, 5, 9, 13, 17, and 21, the arrangement direction of the unit prisms is the vertical direction of the screen, and the vertical direction of the screen (the cross-sectional direction in which the thickness of the optical sheet varies). The angle β = 0 °.
In the optical sheets of Examples 3, 7, 11, 15, 19, and 23, the arrangement direction of the unit prisms is the horizontal direction of the screen, and the vertical direction of the screen (the cross-sectional direction in which the thickness change of the optical sheet occurs). The angle β = 90 °.
In the optical sheets of Examples 2, 6, 10, 14, 18, and 22, the arrangement direction of unit prisms is an angle β with respect to the vertical direction of the screen (the cross-sectional direction in which the thickness of the optical sheet changes) on the sheet surface. = 7 °.
In the optical sheets of Examples 4, 8, 12, 16, 20, and 24, the arrangement direction of the unit prisms forms an angle of 7 ° with respect to the horizontal direction of the screen on the sheet surface, and the vertical direction of the screen (the thickness of the optical sheet) The angle β is equal to 83 ° with respect to the cross-sectional direction in which the change occurs.

The transmissive display devices incorporating the optical sheets of Examples 1 to 24 have screen sizes of 32 inches, 46 inches, 52 inches, and 60 inches diagonally. The transmissive display device having a screen size of 32 inches diagonal is a single lamp type having one light source unit, and the light source unit 12 is provided in the lower part of the screen in the vertical direction. A transmissive display device having a screen size of 46 inches, 52 inches, and 60 inches is a two-lamp type having two light source portions, and light source portions 12A and 12B are provided at both ends in the vertical direction of the screen.
Among the optical sheets of Examples 1 to 24, the optical sheets of Examples 5 to 12 and 17 to 20 have a thickness ratio a / b satisfying 1.0 <a / b <1.6. This corresponds to an example of the optical sheet of each embodiment. Examples 17 to 20 correspond to examples of the optical sheets 15, 25, and 35 of the first embodiment, and Examples 5 to 12 correspond to examples of the optical sheets 45, 55, and 65 of the second embodiment. .

(Evaluation of uniformity of in-plane brightness)
Each transmissive display device incorporating each of the optical sheets of Examples 1 to 24 is prepared, the light source is actually turned on to display white, and the front direction (normal direction of the observation surface) of the center of the screen is 100 cm, 200 cm, 300 cm. In each of the positions, the screen was observed from all directions around the position, and the presence or absence of luminance unevenness (such as luminance unevenness due to the distance from the light source unit 12 or 12A, 12B) was visually examined.
And, regardless of the distance from the screen to each observation position, luminance unevenness due to the distance from the light source unit is not observed, and those with high in-plane luminance uniformity are indicated by ○ in Table 1 described later as good. In Table 1, a luminance unevenness caused by the distance from the light source part is generated, the luminance uniformity in the surface is low, and those that are not suitable for use are shown as x in Table 1.

(Evaluation of uneven brightness due to bending)
After the evaluation of the uniformity of the in-plane luminance, the transmissive display devices each incorporating the optical sheets of Examples 1 to 24 are kept in a 60 ° C. environment with the light source portion turned on and white display. After being left for 24 hours, the light source part is turned on, and then left in a room temperature environment (about 25 ° C.) for 24 hours, and the occurrence of luminance unevenness due to deformation such as bending of the optical sheet of Examples 1 to 24 is the same. I investigated.
And, it is shown as good in Table 1 that the luminance unevenness due to the deflection of the optical sheet is not observed as good, and is indicated as Δ in Table 1 where the luminance unevenness due to the deflection is observed but within the allowable range. Brightness unevenness due to bending occurs, and those that are not suitable for use are shown as x in Table 1 as being unacceptable.

Table 1 is a table summarizing the evaluation results of unevenness of luminance due to in-plane luminance uniformity and deflection, the thicknesses of the optical sheets of Examples 1 to 24, and the like.
As shown in Table 1, the transmissive display device using the optical sheets of Examples 5 to 12 and 17 to 20 in which the thickness ratio a / b satisfies 1.0 <a / b <1.6. Also, there was no luminance unevenness due to the distance from the light source part, deformation such as bending due to heat, or luminance unevenness due to this deformation, and the evaluation result was good. The effect of reducing luminance unevenness due to the distance from the light source unit, deformation such as bending due to heat, and luminance unevenness due to this deformation was obtained regardless of the arrangement direction of the unit prisms 152.
On the other hand, the transmission type display device using the optical sheets of Examples 1 to 4, 13 to 16, and 21 to 24, in which the thickness ratio a / b does not satisfy 1.0 <a / b <1.6, Luminance unevenness due to the distance from the light source unit, deformation such as bending due to heat, and luminance unevenness due to this deformation have occurred.

In the optical sheets of Examples 9 to 12, the thickness ratio a / b satisfies 1.0 <a / b <1.6, and the screen size of the LCD panel is 46 inches diagonal and 52 inches diagonal. When used in a transmissive display device, brightness unevenness and unevenness due to bending did not occur, and it was good. However, when the optical sheets of Examples 9 to 12 were used in a transmissive display device in which the screen size of the LCD panel was 60 inches diagonal, luminance unevenness due to bending was observed.
Moreover, although not described in Table 1, it has a thickness ratio a / b similar to that of the optical sheets of Examples 17 to 20, and the central portion is thin as shown in the second embodiment, and the end portion in the vertical direction of the screen When a thick optical sheet is prepared and used in a transmissive display device with a screen size of 46 inches diagonally, the thickness ratio 1.0 <a / b <1.6 is satisfied, but due to bending Brightness unevenness was observed.
Therefore, the optical sheet generally has a thickness capable of exhibiting rigidity capable of maintaining flatness according to the screen size of the surface light source device and the transmissive display device, and the thickness ratio a / b is It is preferable to satisfy 1.0 <a / b <1.6 from the viewpoint of improving luminance unevenness and reducing luminance unevenness due to heat-induced deflection of the light source unit.

On the other hand, the thickness ratio is a / b ≦ 1.0, and the transmission type using the optical sheet whose thickness is larger than the screen size (for example, the optical sheets of Examples 1 to 4 and 13 to 16). In the case of the display device, the luminance unevenness due to the bending is reduced, but the luminance unevenness due to the distance from the light source unit is not improved, and the uniformity of the in-plane luminance is low. In the case of a transmissive display device using a thickness ratio a / b ≦ 1.0 and a thickness of the optical sheet that is thinner than the screen size (for example, the optical sheets of Examples 21 to 24). However, the luminance unevenness due to the distance from the light source unit is not improved, and the luminance unevenness due to the bending is not sufficiently improved.
Although not described in Table 1, for a transmissive display device using an optical sheet having a thickness ratio of a / b ≧ 1.6, the deflection of the light source unit due to heat can be reduced, and uneven brightness due to the deflection can be reduced. Although it was able to reduce, the brightness | luminance by the side of a light source part falls, the brightness nonuniformity resulting from the position from a light source part is not improved, and the uniformity of in-plane brightness | luminance is low.
From the above, the brightness unevenness due to the position from the light source part is improved to increase the uniformity in the screen, and the heat deflection from the light source part and the brightness unevenness due to such a flexure are reduced. In order to improve luminance uniformity, the thickness ratio a / b preferably satisfies 1.0 <a / b <1.6.

(Evaluation of moire)
Next, the moire evaluation will be described.
The optical sheets of Examples 9 to 12 and 17 to 20 in which the thickness ratio a / b satisfies 1.0 <a / b <1.6 were evaluated for the presence or absence of moire. First, transmissive display devices with screen sizes of 32 inches, 46 inches, and 52 inches each incorporating the optical sheets of Examples 9 to 12 and 17 to 20 were prepared, the light source section was actually turned on to display white, and the center of the screen At the position of 30 cm in the front direction (normal direction of the observation surface), the presence or absence of moiré was examined visually, and the results are shown in Table 2.

As shown in Table 2, the transmission type using the optical sheets of Examples 10, 12, 18, and 20 in which the arrangement direction of the unit prisms is a direction that forms an angle (7 °) with respect to the screen vertical direction or the screen horizontal direction. In the display device, moire does not occur.
On the other hand, in the transmissive display device using the optical sheets of Examples 9, 11, 17, and 19 in which the unit prisms are arranged in parallel with the screen up-down direction or the screen left-right direction, the moire is slightly within the allowable range. It has occurred.

Although not described in Table 2, the transmission type display device using the optical sheets of Examples 5 to 8 where the thickness ratio a / b satisfies 1.0 <a / b <1.6. In the transmission type display devices using the optical sheets of Examples 6 and 8, in which the unit prisms are arranged at an angle (7 °) with respect to the vertical direction of the screen or the horizontal direction of the screen, no moire is observed. However, in the transmissive display devices using the optical sheets of Examples 5 and 7 that are parallel to the screen vertical direction or the screen horizontal direction, moiré is slightly generated although it is within the allowable range.
This is because the pixels of the LCD panel (one set of three subpixels of R, G, B) are generally arranged along two directions, the screen vertical direction and the screen horizontal direction. I think that.
From the above, moire can be reduced by using the optical sheet in which the unit prisms 152 are arranged in a direction that makes an angle with respect to the screen vertical direction or the screen horizontal direction.

In the optical sheets corresponding to the examples of the first embodiment and the second embodiment described above, the thickness ratio a / b satisfies 1.0 <a / b <1.6.
Therefore, according to each embodiment, in the edge light type surface light source device, luminance unevenness due to whether or not it is close to the light source unit is improved to make the in-plane luminance uniform, and by the heat generated by the light source unit It is possible to provide a surface light source device and a transmissive display device that can reduce the deflection of the optical sheet and the resulting luminance unevenness and can display a good image with uniform brightness in the screen.

Moreover, according to each embodiment, it can manufacture without using a special shaping | molding die etc., manufacture is easy, mass production is possible, and it can provide at low cost. In addition, according to each embodiment, since the thickness of the optical sheet is not increased more than necessary, such as increasing the thickness of only the light source unit and increasing the overall thickness, the production cost is not hindered. Can also be suppressed.
Furthermore, in particular, according to the second embodiment, it is possible to easily cope with a large screen.
Furthermore, according to each embodiment, it is easy to produce an optical sheet in which the arrangement direction of the unit prisms is changed to a desired direction in accordance with the usage environment of the transmissive display device. And the optical sheet which can reduce the brightness nonuniformity produced by the distance from a light source part and the bending | flexion by a heat | fever irrespective of the arrangement direction of a unit prism can be provided. Moreover, by arranging the unit prisms 152 in a direction that makes an angle with respect to the vertical direction of the screen or the horizontal direction of the screen, a moire reduction effect can also be obtained.
In addition, according to each embodiment, the direction of stretching of the prism base material layer 154 and the base film 156 is made to be a mirror image, or by adjusting the thermal expansion coefficient of each member constituting the optical sheet, Warpage can be reduced more effectively.

(Deformation)
Without being limited to the embodiments described above, various modifications and changes are possible, and these are also within the scope of the present invention.
(1) In each embodiment, the prism films 151, 251, 351, and 651 are examples in which the prism layer 153 and the prism base material layer 154 made of ultraviolet curable resin are integrally laminated. For example, a single-layer prism film may be used.
Such a single-layer prism film can be formed by extrusion molding or the like and can be easily manufactured. In this case, the prism film can be formed using a light-transmitting thermoplastic resin such as PC resin, AS resin, ABS resin, PMMA resin, PET resin, cycloolefin resin, MS resin, or MBS resin.

(2) In each embodiment, although the optical sheet 15, 25, 35, 45, 55, 65 showed the example which is not provided with the layer containing a diffusion material, not only this but diffusion of styrene beads etc., for example The material may be kneaded and molded into the bonding layers 155, 455, the base film 156, the prism base layer 154, and the like.

(3) In each embodiment, the optical sheets 15, 25, 35, 45, 55, and 65 are substantially isosceles whose unit optical shape is a curved surface whose top is convex on the exit side. Although an example in which a plurality of triangular prism unit prisms 152 are arranged has been shown, the present invention is not limited to this. For example, the unit optical shape may be a part of a substantially cylindrical shape or a part of an elliptical column, and the top part may be It may be a substantially triangular prism shape having a corner, a shape formed from a plurality of curved surfaces having different curvatures, or a shape formed by combining a plane and a curved surface.
The optical sheets 15, 25, 35, 45, 55, and 65 are not limited to the exit-side surface, but may be configured such that unit optical shapes are arranged on the entrance-side surface, and unit optics on the exit and entrance sides. It is good also as a form where a shape is arranged.
Furthermore, the unit optical shapes may be arranged in two directions (for example, the screen vertical direction and the screen horizontal direction) along the sheet surface. At this time, the unit optical shape may be a substantially hemispherical shape, a partial shape of a substantially spheroidal sphere, or a substantially quadrangular pyramid shape.
Furthermore, the unit optical shape is not limited to one type, and may be a combination of a plurality of types. For example, as disclosed in Japanese Patent Application Laid-Open No. 2010-043379, a first unit shape element having a partial shape of a hemisphere or an elliptical sphere arranged at intervals to form a fly-eye lens, and a first unit shape element In between, it is good also as an optical sheet provided with the triangular unit-like 2nd unit shape element arranged in one direction along a sheet surface, and the unit optical shape in which pitch, height, etc. change irregularly It may be a formed optical sheet.

(4) In the first embodiment, the incident surfaces 156a of the optical sheets 15, 25, and 35 are substantially in a cross section orthogonal to the sheet surface and parallel to the vertical direction of the screen (that is, a cross section in which the thickness changes). It may be a straight line or a concave curve.
In the second embodiment, the incident surface 156a of the optical sheet 45, 55, 65 is a central portion in a cross section perpendicular to the sheet surface and parallel to the vertical direction of the screen (that is, a cross section in which the thickness changes). May form a concave curve, and both sides may be substantially linear, or may be a gentle concave curve.
In the first embodiment, the optical sheets 15, 25, 35 are thickest at the end portions 15 a, 25 a, 35 a on the light source unit 12 side and gradually become thinner toward the other side, and end portions 15 b, If the thicknesses of 25b and 15b are the thinnest, the incident surfaces 156a of the optical sheets 15, 25, and 35 are cross sections orthogonal to the sheet surfaces and parallel to the vertical direction of the screen (that is, changes in thickness occur). It is good also as the gentle convex curve shape which becomes convex at the light-guide plate 13 side in a cross section.
Also in the second embodiment, if the central portions 45c, 55c, and 65c are the thinnest and gradually thicker toward both ends, and the both ends 45a, 45b, 55a, 55b, 65a, and 65b are the thickest, the optical sheet The incident surfaces 45, 55, and 65 are perpendicular to the sheet surface and parallel to the vertical direction of the screen (that is, the cross section in which the thickness changes), and the end portions 45a, 55a, and 65a and the central portions 45c and 55c. , 65c, and two gentle convex curves connecting the end portions 45b, 55b, 65b and the central portions 45c, 55c, 65c.

(5) In each embodiment, the surface light source device 10 and 40 shows an example provided with the light source parts 12, 12A and 12B, the light guide plate 13, the reflection plate 14, and the optical sheets 15, 25, 35, 45, 55 and 65. However, the present invention is not limited to this, and a diffusion sheet having a diffusing action or a lens sheet in which various lens shapes or prism shapes are formed on the incident side or the emission side of the optical sheets 15, 25, 35, 45, 55, 65. Or a prism sheet may be combined to obtain desired optical characteristics according to the usage environment.

(6) In each embodiment, the light guide plate 13 has dot printing on the back surface and has an example of a substantially flat plate shape. However, the present invention is not limited to this, and for example, the back surface of the light guide plate 13 (on the reflection plate 14 side). Surface) or a light emitting side (LCD panel 11 side) surface, prism shapes or the like may be arranged, or dot printing or the like may not be provided. The light guide plate 13 may have a form containing a diffusing material or the like. Further, in the first and second embodiments, the light guide plate 13 has a shape in which the thickness on the light source part side is thick, the thickness on the side facing the light source part 12 is thin, and the cross section in the thickness direction is substantially trapezoidal. Also good.

(7) The first embodiment shows the surface light source device 10 and the transmissive display device 1 in which the light source unit 12 is disposed at a position facing one end surface 13a of the light guide plate 13 in the vertical direction of the screen. In the embodiment, the surface light source device 40 and the transmissive display device 4 provided at the positions where the light source units 12A and 12B face both end surfaces 13a and 13b are shown. However, the present invention is not limited thereto. 13 may be provided at a position facing one end surface in the left-right direction of the screen or a position facing both end surfaces. At this time, a plurality of LEDs are arranged at equal intervals along the light incident surface in the vertical direction of the screen. In such a configuration, the surface light source device and the transmissive display device of each embodiment may be configured to be rotated by 90 ° about the normal passing through the center of the observation surface.

(8) In each embodiment, although the base film 156 and the light guide plate 13 are shown as separate examples, the present invention is not limited thereto. For example, the base film 156 may be the light guide plate 13. In other words, the bonding layer and the base film may be integrally laminated on the light guide plate 13. However, at this time, the refractive index of the bonding layer is preferably smaller than the refractive index of the light guide plate from the viewpoint of light propagation.

  In addition, although this embodiment and modification can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited by the embodiments described above.

DESCRIPTION OF SYMBOLS 1,4 Transmission type display device 10,40 Surface light source device 11 LCD panel 12,12A, 12B Light source part 13 Light guide plate 14 Reflection plate 15,25,35,45,55,65 Optical sheet 151,251,351,651 Prism Film 152 Unit prism 155,455 Bonding layer 156 Base film

Claims (12)

Used in an edge light type surface light source device, an optical sheet in which a plurality of unit optical shapes are arranged at least on the surface on the emission side,
A first layer in which the unit optical shape is formed;
A second layer facing the first layer;
A bonding layer that is provided between the first layer and the second layer, and bonds the first layer and the second layer;
The thickness of the bonding layer continuously changes in a cross-section in one direction orthogonal to the sheet surface, and extends from at least one end of the optical sheet to the other end in the one direction. Having an area where the thickness gradually decreases toward the
An optical sheet characterized by The optical sheet according to claim 1,
The bonding layer has the largest thickness at one end of the optical sheet in the one direction, the smallest thickness at the other end, and the thickness from the one end toward the other end. That it is getting thinner,
An optical sheet characterized by The optical sheet according to claim 1,
The bonding layer has the thickest thickness at both ends of the optical sheet in the one direction, the thinnest thickness at the central portion, and the thickness gradually decreases from both the end portions toward the central portion. That
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 3,
When the thickness at the point where the total thickness of the optical sheet is the thickest is a and the thickness at the thinnest point is b, the thickness ratio a / b is:
1.0 <a / b <1.6
Satisfying the relationship
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 4,
The unit optical shape is a substantially triangular prism shape,
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 5,
The arrangement direction of the unit optical shapes forms an angle of 0 ° to 90 ° with respect to the one direction on the sheet surface;
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 6,
The bonding layer is formed of a thermosetting resin or an ionizing radiation curable resin;
An optical sheet characterized by A light source that emits light;
A light guide plate in which the light source unit is disposed on one end face or two opposite end faces;
The optical sheet according to any one of claims 1 to 7, which is disposed on an emission side of the light guide plate;
With
Being arranged so that the thick portion of the bonding layer is on the light source side,
A surface light source device. A surface light source device according to claim 8,
A transmissive display unit illuminated from the back by the surface light source device;
A transmissive display device. It is a manufacturing method of the optical sheet according to any one of claims 1 to 7,
A resin layer forming step of forming an uncured resin layer for forming the bonding layer on the surface of the second layer;
After the resin layer forming step, a laminating step of laminating the first layer on the resin layer;
After the laminating step, applying a pressure to change the thickness of the resin layer,
After the pressing step, the resin layer is cured, and a curing step for forming the bonding layer;
Providing
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet according to claim 10,
In the pressurizing step, pressurization is performed using a substantially frustoconical roll in which the diameter of one end in the axial direction is larger than the diameter of the other end.
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet according to claim 10,
In the pressurizing step, pressurization is performed using a roll having a shape in which the central diameter in the axial direction is larger than the diameters at both ends,
An optical sheet manufacturing method characterized by the above.

Images