JP2009086031A - Optical sheet, backlight unit, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet capable of suppressing warpage of the optical sheet caused by a temperature change upon lighting of a backlight and further reducing thickness of a backlight unit and a display device, and to provide the backlight unit and the display device. <P>SOLUTION: The optical sheet 3 is formed by laminating a light diffusing member 11 that diffuses incident light and a lens sheet 13 having a lens array 15 that condenses the diffused light from the light diffusing member 1, disposed on the light exit face side of a lens sheet base 14, wherein either the light diffusing member 11 or the lens sheet base 14 is made a thin film layer B with low rigidity and the other is made a substrate layer A with high rigidity. The thin film layer B is formed by extrusion molding, while the substrate layer A is formed by one of extrusion molding, cast molding, combination of extrusion molding and cast molding, or injection molding. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to, for example, an optical sheet suitable for controlling an illumination optical path to a liquid crystal display element, a backlight unit using the optical sheet, and a display device.

  In recent years, liquid crystal display devices (LCDs) using liquid crystal panels have been used in notebook personal computers, personal computer displays, image display means for information terminal equipment, image display means for information appliances such as large-screen TVs, mobile phones and personal use. 2. Description of the Related Art It has been used in various fields as an image display means of a personal digital assistant (PDA: Personal Digital Assistance). In a display device represented by a liquid crystal display device, a type having a built-in light source necessary for recognizing provided information is remarkably widespread. Such a liquid crystal display device is, for example, a light transmission type, and a so-called backlight is used as a surface light source device in which a light source is disposed on the back side of the liquid crystal panel, and light from the light source is converted into surface light emission to irradiate the liquid crystal panel. Unit is adopted.

  As an optical sheet mounted on such a backlight unit, for example, brightness enhancement films (BEF; DBEF; EBEF: registered trademark) shown in Patent Documents 1 to 3 are widely used. The brightness enhancement film is a film in which roof-shaped unit prisms having a triangular cross section are arranged in one direction on a sheet-like member. When a brightness enhancement film is used in a display device, the light from “off-axis” is collected and redirected to “on-axis” toward the viewer. ) Or “recycle”, the brightness in the normal direction relative to the display screen can be increased.

  In general, the optical sheet is provided with a light diffusing member, which can diffuse the light emitted from the light source unit to the display screen side to eliminate luminance unevenness due to the arrangement of the light source. Yes. Further, such an optical sheet is provided with a light-transmitting substrate having rigidity, thereby ensuring rigidity in the optical sheet and suppressing display image unevenness due to wrinkles and sagging.

As described above, as an optical sheet having a light collecting function, a light diffusing function, and rigidity, for example, as shown in Patent Document 4, components such as a lens sheet and a light diffusing member are integrated to reduce the number of parts. In addition, a product that aims to reduce costs is disclosed. By adopting a configuration in which the functions are integrated in this way, it is possible to promote the simplification of the manufacturing process and the thinning of the optical sheet itself.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2006-106197 A

  By the way, the integrated optical sheet as described above is formed by laminating components of different materials and manufacturing methods. Therefore, the optical sheet is formed by the difference in expansion / contraction of each layer due to temperature change when the backlight is turned on. Warp shape occurs. This becomes more prominent as the difference in dimensions of each layer due to expansion / contraction increases. Such a warped shape has no effect on the display image if it is a convex shape toward the light source without pressing the liquid crystal panel of the display device, but when trying to further reduce the thickness of the display device, Accordingly, if the case for storing the optical sheet is thinned, for example, as shown in FIG. 6, the optical sheet 41 is bent in a wavy shape due to warpage in the narrow case 40, thereby causing a defect in the display image. Therefore, when designing the display device, there is a problem that it is difficult to further reduce the thickness because it is necessary to consider the influence of the warp shape of the optical sheet.

  The present invention has been made in view of such a problem, and can suppress warpage of the optical sheet due to a temperature change when the backlight is turned on, and further reduce the thickness of the backlight unit and the display device. It is an object of the present invention to provide an optical sheet, a backlight unit, and a display device that can be used.

In order to solve the above problems, the present invention proposes the following means.
That is, an optical sheet according to the present invention includes a light diffusing member that diffuses incident light, and a lens sheet in which a lens array that condenses the diffused light of the light diffusing member is disposed on the exit surface side of the lens sheet substrate. The light diffusing member and the lens sheet base material are either a thin film layer having a low rigidity and the other is a substrate layer having a high rigidity, and the thin film layer is formed by extrusion molding. The substrate layer is formed by any one of extrusion molding, cast molding, combined use of extrusion molding and cast molding, and injection molding.

The substrate layer is formed by any one of extrusion molding, cast molding, a combination of extrusion molding and cast molding, and injection molding, and expands slightly at high temperatures.
In addition, for example, when the thin film layer is formed by stretch molding that is stretched under pressure at a high temperature state, the thin film layer in the optical sheet of the present invention is formed by extrusion molding. Therefore, although it expands slightly at high temperatures, it does not shrink as in the case of stretch molding.
Therefore, when the thin film layer and the substrate layer formed by such a method are laminated, both of them expand slightly when brought to a high temperature state, so that the difference in dimensions due to temperature change can be minimized. Therefore, according to the optical sheet of the present invention, although it is an integrated optical sheet having a light collecting function, a diffusing function, and rigidity, the warpage caused by the difference between expansion and contraction of each layer is minimized. be able to.

  In the optical sheet according to the present invention, the thickness of the thin film layer is 12 μm or more and 400 μm or less. When the thickness of the thin film layer is smaller than 12 μm, wrinkles are likely to occur when the optical sheet is formed. When the thickness of the thin film layer is larger than 400 μm, it is not possible to flexibly follow the warp of the substrate layer, and the warp shape of the optical sheet cannot be controlled. Therefore, it is preferable to set the thickness of the thin film layer to 12 μm or more and 400 μm or less.

  Furthermore, in the optical sheet according to the present invention, the thickness of the substrate layer is 1 mm or more and 5 mm or less. When the thickness of the substrate layer is smaller than 1 mm, the function of imparting rigidity to the optical sheet is insufficient. On the other hand, if it is thicker than 5 mm, it will hinder the thinning of the optical sheet. Therefore, it is preferable to set the thickness of the substrate layer to 1 mm or more and 5 mm or less.

  Further, the thin film layer and the substrate layer are formed of any one of polycarbonate, acrylic-styrene copolymer polystyrene, and cycloolefin polymer.

  Further, in the optical sheet according to the present invention, a bonding layer is formed by bonding the thin film layer and the substrate layer by a bonding member, and a ratio of an area occupied by the bonding member to an area of a bonding surface of the bonding layer is It is characterized by being 5% or more.

  As a result, the thin film layer and the substrate layer can be reliably bonded to each other, and even when warping occurs due to a high temperature state, the bonding does not loosen or separate from each other, and the warping shape is strong. Can be maintained.

  In the optical sheet according to the present invention, the lens sheet is formed of at least one of a prism lens array, a cylindrical lens array, and a microlens array.

  A backlight unit according to the present invention includes any one of the optical sheets described above and a light source unit that is disposed on the opposite side of the optical sheet and that emits light. Since the occurrence of warpage can be suppressed by using the above-described optical sheet, the reduction in thickness can be promoted.

  In the backlight unit according to the present invention, a distance between the optical sheet and the light source unit is 10 mm or less. Since the warpage of the optical sheet can be suppressed as described above, it is possible to reduce the thickness without causing a problem even if the distance between the optical sheet and the light source unit is 10 mm or less.

  A display device according to the present invention includes any one of the backlight units described above and a liquid crystal display unit that displays an image by irradiating light from the backlight unit. Thinning can be promoted by using the above-described backlight unit.

  The display device according to the present invention is characterized in that a distance between the liquid crystal display unit and the optical sheet is 10 mm or less. Since the warpage of the optical sheet can be suppressed as described above, it is possible to reduce the thickness without causing a problem even if the distance between the optical sheet and the liquid crystal display unit is 10 mm or less.

  According to the optical sheet, the backlight unit, and the display device according to the present invention, it is possible to suppress warpage of the optical sheet due to a temperature change when the backlight is turned on, and to further reduce the thickness of the backlight unit and the display device. Is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, about the optical sheet which concerns on this embodiment, it demonstrates with the backlight unit and display apparatus using the same.

  FIG. 1 is a schematic cross-sectional view showing a schematic configuration of the display device according to the present embodiment. In the display device 1 according to the present embodiment, as shown in FIG. 1, a light source unit 2, an optical sheet 3, and a liquid crystal display unit 4 are stacked in this order, and display control is performed by image signals from the liquid crystal display unit 4 toward the upper side in the figure. By emitting display light, for example, a planar rectangular image is displayed. The light source unit 2 and the optical sheet 3 constitute a backlight unit 5. Hereinafter, based on such an arrangement, the upper direction in FIG. 1 is simply referred to as the display screen side or the emission side, and the lower direction is simply referred to as the back side or the incident side.

  In FIG. 1, the light source unit 2 displays a plurality of light sources 7 in which linear light emitting units extending in the depth direction on the paper surface are spaced apart at a constant pitch in the horizontal direction in the figure, and covers the light sources 7 from the back side. A direct type system composed of a reflecting plate 8 opened on the screen side is adopted.

  As the light source 7, a cold cathode tube having a function of emitting white light is used. However, an LED light source in which a plurality of LED elements are arranged in a line along the depth direction of the paper surface, a cold cathode fluorescent lamp, an EL sheet, a semiconductor, and the like Etc. may be adopted.

  The light source unit 2 is not limited to such a configuration as long as white light can be emitted to the back side of the optical sheet 3, and any well-known light source may be employed. For example, an edge light type surface light source in which a line light source is disposed on the side surface of the light guide surface, or the like may be employed.

  The optical sheet 3 collects a part of the light emitted from the light source unit 2 to the display screen side, transmits the light to the display screen side, reflects the other light to the light source unit 2 side, and retransmits the light to the light source unit 2. As shown in FIG. 1, a light diffusing member 11 located on the back side and a lens sheet 13 located on the display screen side are laminated via a bonding layer 12 as shown in FIG. Moreover, in this embodiment, the distance of this optical sheet 3 and the light source part 2 is set to 10 mm or less.

  The light diffusion member 11 is a member provided at a position covering the display screen side of the light source unit 2 so as to diffuse light emitted from the light source unit 2 to the display screen side. Thereby, the uneven illuminance in the horizontal direction of the figure due to the plurality of light sources 7 is suppressed, and an appropriate viewing angle can be given to the display light. In the first embodiment, the light diffusing member 11 is a substrate layer A having a large thickness and high rigidity as compared with a lens sheet base material 14 described later in the lens sheet 13. Thereby, the rigidity of the optical sheet 3 is ensured.

  The light diffusing member 11 is formed by any one of extrusion molding, cast molding, extrusion molding and cast molding, and injection molding. The thickness of the light diffusing member 11 is 1 mm or more and 5 mm or less. If the thickness is less than 1 mm, the light diffusing member 11 is thin and does not have a strain, so that the light diffusing member 11 is easily bent and the optical sheet 3 has a function of giving rigidity. On the other hand, if it exceeds 5 mm, the transmittance of light from the light source unit 2 is deteriorated, and the optical sheet 3 is reduced in thickness.

  Further, the light diffusing member 11 includes a transparent resin and transparent particles dispersed in the transparent resin. The difference between the refractive index of the transparent resin and the refractive index of the transparent particles is 0. It is desirable that it is 02 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. In addition, it is preferable that this refractive index difference is 0.5 or less. Further, the light diffusing member 11 needs to be transmitted to the display screen side while scattering the light incident on the light diffusing member 11. For this reason, it is desirable that the average particle diameter of the transparent particles contained in the light diffusing member 11 is 0.5 μm to 10.0 μm. In addition, the structure by which the fine cavity containing air was formed instead of this transparent particle | grain may be sufficient, and light scattering performance can be obtained by the difference in the refractive index of the air of transparent resin in this case.

The transparent resin of the light diffusing member 11 is molded from any of polycarbonate, acrylic-styrene copolymer polystyrene, and cycloolefin polymer.
Moreover, as the transparent particles of the light diffusing member 11, transparent particles made of an inorganic oxide or transparent particles made of a resin can be used. For example, examples of the transparent particles made of an inorganic oxide include particles made of silica, alumina or the like. The transparent particles made of resin include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof; melamine-formalin condensate particles; PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetra Fluoropolymer particles such as fluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer); silicone resin particles and the like. Two or more kinds of these transparent particles may be mixed and used.

  The light diffusing member 11 may have a fine unevenness on at least one of the light incident surface 11a and the light emitting surface 11b, and the light diffusing member 11 may have a light diffusing function. As a specific example, an unevenness extending in one direction is formed only on the exit surface 11b side (see FIG. 2A), and an unevenness extending in one direction parallel to each other is formed on the entrance surface 11a and the exit surface 11b. And the like (see FIG. 2B), and the like where the incident surface 11a and the exit surface 11b are formed with irregularities extending in directions orthogonal to each other (see FIG. 2C). Here, examples of the fine irregularities include a cylindrical shape and a prism shape, but are not limited to these, and other shapes may be used as long as the irregular shape improves the light diffusion function.

  Further, the light diffusion function may be improved by providing a fine particle layer on at least one of the light incident surface 11a and the light emitting surface 11b of the light diffusing member 11 (see FIG. 2D). Examples of the fine particle layer include transparent ink containing beads, spacers, and the like, but other fine particles may be used as long as the light diffusion function can be improved.

  The lens sheet 13 is emitted from the light source unit 2 to the display screen side and collects a part of the light diffused by the light diffusion member 11 and transmits it to the display surface side. The lens array 15 is formed on the surface 14a side by arranging a plurality of unit lenses extending in the illustrated depth direction in the same direction as the light source 7 in a direction orthogonal to the illustrated depth direction. . In the first embodiment, the lens sheet base material 14 is a thin film layer B that is much thinner and less rigid than the light diffusing member 11.

  The lens sheet base material 14 is formed by, for example, extrusion molding, and has a very thin thickness of 12 μm to 400 μm. If the thickness is smaller than 12 μm, wrinkles are likely to occur when the optical sheet 3 is molded. On the other hand, if the thickness is larger than 400 μm, a certain degree of rigidity is provided, so that the warp of the light diffusion member 11 is increased. Can't be flexible.

  Further, the lens sheet base material 14 may be formed from any one of carbonate, acrylic-styrene copolymer polystyrene, and cycloolefin polymer, and the lens array 15 may be integrally formed. The lens array 15 may be a prism lens array, a cylindrical lens array, a microlens array, or the like. For example, the lens array 15 has a composite shape, that is, the prism array or the cylindrical lens array is alternately arranged in parallel. May be arranged in a direction orthogonal to each other. Further, the unit lens itself may be a composite shape of these, that is, a lens of another type formed on a part of the unit lens. Further, in order to obtain a desired luminance distribution, it may be formed by mixing the above-mentioned transparent particles until the haze becomes about 50%.

  As shown in FIG. 1, the bonding layer 12 is a layer provided to stack and integrate the light diffusing member 11 and the lens sheet 13, and is appropriately provided between the light diffusing member 11 and the lens sheet 13. It is comprised from the joining member 16 and the air layer 17 formed using this joining member 16 as a spacer.

  The ratio of the area occupied by the bonding member 16 to the area of the bonding surface of the bonding layer 12 is set to 5% or more. When the value is less than this value, the light diffusing member 11 and the lens sheet 13 cannot be firmly bonded, and there is a problem that wrinkles are generated or both are separated when warping occurs. Examples of the bonding member 16 include a light-transmitting contact adhesive and a rib that can form a certain gap by bonding the light diffusion member 11 and the lens sheet 13.

  When a contact adhesive is used as the bonding member 16, for example, an acrylic, urethane, rubber, or silicone contact adhesive can be used. In either case, since the light source 7 is used in a high temperature environment, it is desirable that the storage elastic modulus G ′ at 100 ° C. is 1.0E + 04 Pa or more. If the value is lower than this, the light diffusing member 11 and the lens sheet 13 may be displaced in a high temperature state. Further, transparent fine particles such as beads may be mixed in the contact adhesive.

  The position where such a contact adhesive is applied to the light emitting surface 11b of the light diffusing member 11 which is the bonding surface as the bonding member 16 will be described with reference to FIG. Here, in the present embodiment, the areas of the emission surface 11 b of the light diffusing member 11 and the incident surface 13 a of the lens sheet 13 indicate the area of the bonding surface of the bonding layer 12. FIG. 3A shows a case where an adhesive or adhesive material is applied to the entire outer peripheral edge of the light-diffusing member 11 and the lens sheet 13, that is, the outer peripheral edge of the light-emitting surface 11 b of the light-diffusing member 11. is there. FIG. 3B and FIG. 3C show a case where the coating is applied only to a pair of opposite sides of the joint surface. FIG. 3 (d) shows a case where the coating is applied to the four corners of the joint surface. FIG. 4 (e) shows a case where the entire joint surface is applied in the form of dots. In addition, also in the case of FIG.4 (b) and FIG.4 (c), it is also possible to apply | coat to dot shape as needed. In addition, when the contact adhesive is applied as the joining member 16 in this way, it is necessary to suppress light absorption within 1% of the total light amount. Therefore, a large amount of colored additives should not be used. When it exceeds 1%, the integrated light quantity emitted from the optical sheet 3 decreases, and the front luminance decreases.

  In addition, as a method of apply | coating a contact adhesive, various coating apparatuses, such as a comma coater, a printing system, the method using a dispenser and a spray, or the coating by the manual work using a brush etc. may be sufficient.

  Next, the case where a rib is used as the joining member 16 will be described. When ribs are used, the air layer 17 can be uniformly formed with a constant thickness, so that appearance characteristics such as optical adhesion, unevenness, and Newton rings can be improved.

  The rib as the joining member 16 may be formed separately from the light diffusing member 11 or the lens sheet 13 or may be integrally formed. Examples of the rib material include polyester resins, acrylic resins, polycarbonate resins, polystyrene resins, methylstyrene resins, polymethylpentene resins, and thermoplastic resins such as cycloolefin polymers, or polyester acrylate, urethane acrylate, and epoxy acrylate. A radiation curable resin made of an oligomer such as acrylate or the like can be used, but a resin or the like that can exhibit rib characteristics can also be used other than this. Further, such a material may contain inorganic, organic particles, bubbles, or the like to have other effects such as diffusion and coloring. Even when the light diffusing member 11 and the lens sheet 13 are integrally formed, only the ribs may be made of another material different from these.

  In addition, as inorganic and organic particles dispersed in the rib material, inorganic materials such as silica, alumina, titanium oxide, carbon black, and glass beads, and organic materials such as various resin beads can be used. Various particles dispersed in the transparent rib can be locally disposed, for example, by giving the rib surface a reflection characteristic. Further, bubbles can be dispersed in the resin and used instead of the particles. The particles and bubbles dispersed in these main materials can be used as appropriate by combining a plurality of types according to the intended use.

  In addition, the thickness of the air layer 17, i.e., the height of the rib, needs to be maintained at 200 nm or more in order to prevent optical adhesion to the light diffusion member 11 due to distortion of the lens sheet base material 14 of the lens sheet 13 having no rigidity. On the other hand, if the rib thickness exceeds 2 mm, the visibility of the rib is increased, resulting in unevenness, and light leakage is liable to occur from the side. For example, even if the bonding area of the rib as the bonding member 16 is different on both surfaces, the area occupied by the rib with respect to the area of the bonding surface of the bonding layer 12 needs to be 5% or more.

  The shape of the rib includes a lenticular shape, a trapezoidal shape, a prism shape and the like extending in one direction, a polygonal cone, a cone (or a truncated cone, a truncated cone, etc.), a polygonal column, a cylindrical column, a rectangular parallelepiped, and a spherical shape. (Or hemispherical) or an ellipsoidal structure. Depending on the rib manufacturing method, the shape of the side surface may be an unspecified shape as long as the height of the rib is constant. The arrangement of these ribs may be periodic such as stripes or dotted lines, or random, and can be selected as appropriate according to the design.

Also, when joining the ribs, in order to reduce the visibility of unevenness due to the ribs at the time of image display, regarding the structure such as the lenticular shape, trapezoidal shape and prism shape extending in one direction, The line width is preferably 50 μm or less. In addition, when the rib shape is a cone (or polygonal frustum, truncated cone, etc.), a polygonal column, a column such as a cylinder, a rectangular parallelepiped, a sphere (or hemisphere), an ellipsoid, etc. Is preferably 2500 μm ² or less. In order to further improve the visibility, it is more preferable that the line width of each individual rib is 3 μm and the area is 900 μm ² or less.

 As a method for creating such ribs, in addition to integral molding with the light diffusing member 11 and the lens sheet 13, a UV curable resin is applied to the light diffusing member 11 and the lens sheet 13 on the corona treatment or easy adhesion treatment surface. It is also possible to create it. Moreover, when providing a rib in the light-diffusion member 11 or the lens sheet 13, it is also possible to adhere | attach a rib using the above contact adhesives.

  The contact adhesive and the rib as the joining member 16 as described above may contain a reflective material. Even when the reflective material is contained in this way, it is necessary to ensure the transmittance of all light rays to 40% or more. If the transmittance is less than this, the loss of light increases, and the minimum luminance cannot be ensured. Further, the adhesive containing the reflective material is prepared by applying metal particles or high refractive index transparent particles dispersed in the above-mentioned adhesive to the light diffusion member 11 or the lens sheet 13. Can do. The rib having a reflective surface can be prepared by mixing metal particles or high refractive index transparent particles in the rib material. It is also possible to form a metal such as silver, aluminum or nickel with high light reflectivity on the surface of the rib by dry film formation such as vapor deposition or sputtering. In addition, a method of applying an ink obtained by dispersing and mixing high refractive index transparent particles on the surface of a transparent rib, or an adhesive obtained by dispersing and mixing high refractive index transparent particles, metal particles, or a high refractive index. It can also be prepared by a method in which transparent particles are kneaded in a binder, formed by transfer, or a laminate of white foil or metal foil.

  Here, examples of the high refractive index transparent particles include titanium oxide, barium sulfate, magnesium carbonate, zinc oxide, clay, aluminum hydroxide, zinc sulfide, silica, and silicone. Examples of the metal particles or the metal foil include aluminum and silver. One kind of these high refractive index transparent particles, metal particles or metal foil may be used, or a plurality of kinds may be used in combination.

  Moreover, it is also possible to directly join the light diffusing member 11 and the lens sheet 13 without using the joining member 16 such as a contact adhesive or a rib. For example, as a method of joining the two by welding, a method using heat, ultrasonic waves, or laser can be mentioned. These methods are easy to process and are suitable for joining outside the display area. In addition, when using a method in which excimer UV is irradiated and bonding at room temperature is used, the bonding surface is irradiated with excimer UV having a wavelength of 172 nm and then laminated. Heat may be applied during lamination, or heat may be applied after lamination. Further, when the light diffusing member 11 and the lens sheet 13 are directly joined, a void formed by fine irregularities provided on these joining surfaces functions as the air layer 17.

  The liquid crystal display unit 4 includes, for example, a display element or panel 4a that controls a light transmission state according to an image signal for each of a plurality of pixel regions formed in a rectangular lattice shape, and light incident on the display element or panel 4a. The polarizing plate 4b controls the polarization direction of the light and the polarizing plate 4c controls the polarization direction of the emitted light. In the present embodiment, the distance between the liquid crystal display unit 4 and the optical sheet 3 is set to 10 mm or less.

Hereinafter, the operation of the display device 1 will be described focusing on the operation of the optical sheet 3.
A part of the light emitted from the light source 7 is emitted directly from the light source 7 toward the light diffusing member 11, and the other light is reflected by the reflecting plate 8 and then the light diffusing member 11 of the optical sheet 3. It is emitted toward At this time, the illuminance unevenness corresponding to the arrangement pitch of the light sources 7 is mitigated by the action of the reflector 8 but remains to some extent. The light traveling to the light diffusing member 11 is scattered by the transparent particles in the transparent resin of the light diffusing member 11 and proceeds as diffused light, which eliminates unevenness in luminance of the light source unit 2 and has a spread angle in an appropriate angle range. The light reaches the emission surface 11a of the light diffusing member 11 as light.

  The light reaching the emission surface 11a of the light diffusing member 11 is subjected to a refracting action according to Snell's law according to the refractive index of the light diffusing member 11, the bonding layer 12, and the light diffusing member 11 and the air layer 17, Incident on the lens sheet 13. The light incident on the lens sheet 13 is refracted by the light incident surface 13a, then refracted by the lens array 15, and emitted to the display screen side. Then, the light emitted from the optical sheet 3 is transmitted as display light from a predetermined pixel region through the polarizing plate 4b, the display element or panel 4a, and the polarizing plate 4c of the liquid crystal display unit 4, and has a viewing angle. The image it has is displayed. At this time, the optical sheet 3 is exposed to a high temperature state by the light of the light source 7.

In the present embodiment, the light diffusion member 11 as the substrate layer A is formed by any one of extrusion molding, cast molding, combined use of extrusion molding and cast molding, and injection molding, and is heated by light from the light source 7. It expands slightly.
Moreover, when the lens sheet base material 14 as the thin film layer B is formed by, for example, stretch molding, that is, a method of stretching by applying pressure in a high temperature state, the lens sheet base material 14 is greatly contracted when exposed to a high temperature state again. On the other hand, in the present embodiment, the lens sheet base material 14 as the thin film layer B is formed by extrusion molding. Therefore, the lens sheet base material 14 expands slightly when exposed to a high temperature state, but shrinks as in the case of stretch molding. Never do.

Therefore, when the light diffusion member 11 as the substrate layer A and the lens sheet base material 14 as the thin film layer B formed by such a method are laminated, both of them expand slightly when the temperature is raised. Therefore, in the high temperature state, the difference between the two dimensions can be made as small as possible compared to the case where either one expands and the other contracts.
Therefore, according to the optical sheet 3 of the present embodiment, the light diffusing member 11 as the substrate layer A and the thin film layer B as the integrated optical sheet 3 having the light collecting function, the diffusing function, and the rigidity are provided. Warpage (for example, see FIG. 5) caused by a difference in dimensions due to a temperature change with the lens sheet substrate 14 can be suppressed to a minimum, for example, 10 mm or less, as will be described later in the embodiment. Thereby, even when the optical sheet 3 is exposed to a high temperature state when the backlight unit 5 is turned on, the optical sheet 3 is prevented from being bent, and thus the display image is not damaged. Therefore, the backlight unit 5 and the display device 1 can be further reduced in thickness.

  In addition, since the thickness of the lens sheet base material 14 as the thin film layer B is 12 μm or more and 400 μm or less, it is possible to prevent wrinkling when processing the optical sheet 3 and to form the light diffusion member 11 as the substrate layer A. Therefore, the warp shape of the optical sheet 3 can be controlled.

  Furthermore, since the thickness of the light diffusing member 11 as the substrate layer A is 1 mm or more and 5 mm or less, the optical sheet 3 can be properly given rigidity, and the optical sheet 3 can be made thinner. .

  Further, in the joining surface of the light emitting surface 11b and the light incident surface 13a facing each other between the light diffusing member 11 as the substrate layer A and the lens sheet base material 14 as the thin film layer B, the joining member 16 for joining them is used. Since the occupied area is 5% or more, both can be reliably bonded, and even when warping occurs due to a high temperature state, there is no loosening or separation between the two The warped shape can be maintained firmly.

  Further, by using such an optical sheet 3, it is possible to suppress the warpage of the optical sheet 3 itself as much as possible even when the backlight is turned on, so that the distance between the optical sheet 3 and the light source unit 2 is 10 mm. There is no problem even if the following. Similarly, in the display device 1 using the optical sheet 3, no problem occurs even when the distance between the optical sheet 3 and the liquid crystal display unit 4 is 10 mm or less. Therefore, the backlight unit 5 and the display device 1 can be further reduced in thickness.

  The optical sheet 3, the backlight unit 5, and the display device 1 according to the embodiment of the present invention have been described above. However, the present invention is not limited thereto, and may be appropriately selected without departing from the technical idea of the present invention. It can be changed. For example, as a modification, as shown in FIG. 4, while the diffusion member 11 is a substrate layer A having a thickness and high rigidity, the lens sheet base material 14 is a thin and non-rigid thin film layer B. The optical sheet 30 may be used. In this case as well, since the bending of the optical sheet 30 is suppressed as in the present embodiment, there is no problem with the display image, and further, the warp of the optical sheet 30 is reduced, so that the backlight unit 5 and the display device are reduced. 1 can be further reduced in thickness. In the case of this modification, the convex shape due to the warp of the optical sheet 3 is on the liquid crystal display unit 4 side, but since the warp is suppressed as described above, there is no particular problem.

  As a transparent member used as the material of the light diffusing member 11 and the lens sheet base material 14, the expansion / contraction ratio due to the temperature change of the samples manufactured by stretch molding and extrusion molding was compared. The sample of the transparent member formed by stretch molding was formed as a thin and thin thin film layer B, and PET and polystyrene were used as raw materials. A sample by extrusion molding uses polystyrene, polycarbonate, and an acrylic-copolymer as raw materials, and is formed as the above-described thin film layer B, and as a substrate layer A having thickness and rigidity. In addition, since the board | substrate layer B is not normally manufactured by extending | stretching shaping | molding, it excluded from the comparison object here.

  These samples were heated from a normal temperature of 25 ° C. to a high temperature of 90 ° C., the dimensions of the samples at that time were measured, and an expansion / contraction ratio based on the dimensions at 25 ° C. was obtained. Table 1 shows the measurement results. In Table 1, MD represents the line traveling direction in stretch molding and extrusion molding, and TD represents the respective expansion / contraction ratio in the direction orthogonal to the line.

  As can be seen from Table 1, the sample prepared by stretch molding has a negative expansion / contraction rate at a high temperature, which indicates that the sample contracted at a high temperature. Moreover, the sample produced by extrusion molding has a positive value of expansion and contraction in a high temperature state and expands, and a large difference due to raw materials is not seen. Accordingly, when both the substrate layer A and the thin film layer B are manufactured by extrusion molding, since both expand at a high temperature state, a difference in dimensions due to a temperature change can be reduced. On the other hand, when the thin film layer B is manufactured by stretch molding, it expands and contracts in a high temperature state, so that a difference in size from the substrate layer A manufactured by extrusion molding becomes large. Therefore, it can be seen that manufacturing the substrate layer A and the thin film layer B together by extrusion as in the present embodiment is effective in reducing the warpage of the optical sheet 3.

  The reason why the transparent member produced by stretch molding shrinks in a high temperature state is that it is stretched by applying a high pressure in a high temperature state during production, so that when heated again, it repels the pressure during production. This is because a contracting force acts. Therefore, if it does not shrink at high temperatures, it is not limited to extrusion molding. For example, even those manufactured by cast molding, a combination of extrusion molding and cast molding, injection molding or the like exhibit the same effect.

The optical sheet 3 of the embodiment shown in FIG. 1 was actually created and incorporated into a liquid crystal television to confirm the quality of the image.
First, the production method of the lens sheet 13 provided with the lens sheet base material 14 as the thin film layer B will be described. A mold roll cut into a shape of a convex cylindrical lens having a pitch of 140 μm was placed in the vicinity of the extruder, and the thermoplastic polycarbonate resin sheet was melted and extruded by an extruder. And before this cooled and hardened | cured, it shape | molded with the 1st metal mold | roll, and the lens sheet 13 which has a lenticular lens was obtained. In addition, 30% by weight of styrene particles having a refractive index of 1.49 and a particle diameter of 2 μm was added to the thermoplastic polycarbonate resin to give a certain haze. The lens sheet 13 was formed to a thickness of 400 μm.

  A method for producing the light diffusing member 11 as the substrate layer A will be described. MS200 manufactured by Nippon Steel Chemical Co., Ltd. was used, and a mixture of commercially available silicone and resin filler was used as transparent particles. Moreover, the rib was directly formed at the time of extrusion molding. That is, the surface of the No. 1 cooling roll or the No. 2 cooling roll of the extruder was processed to form an uneven mold on the surface of the cooling roll. At the time of extrusion molding, the concavo-convex shape was transferred to the plate material using a mold on the surface of the cooling roll. The rib shape is a trapezoidal shape extending in one direction, the rib width is 60 μm, the height is 100 μm, and the pitch interval is 600 μm. The light diffusing member 11 was formed to a thickness of 1.5 mm.

  Alternatively, the lens sheet base material 14 may be the substrate layer A, and the light diffusion member 11 may be the thin film layer B.

  A method for joining the substrate layer A and the thin film layer B as described above will be described. Note that four types of bonding methods were used.

  In the case of a method using an adhesive as the first bonding method, each of the substrate layer A and the thin film layer B is cut into 600 mm × 1000 mm, and an adhesive mainly composed of an acrylic resin is applied to the light diffusion member 11 with a roll coater. It was applied (the amount applied was 5 g / m 2), the lens sheet substrate 14 was laminated, and the adhesive was cured by placing it in a drying oven at 80 ° C. and 50% for 30 minutes.

  In the case of the method using an adhesive as the second bonding method, each of the substrate layer A and the thin film layer B was cut into 600 mm × 1000 mm, the adhesive was applied to the substrate layer A, and the thin film layer was laminated.

  As a third joining method, in the case of using an adhesive mixed with fine particles, 20% polystyrene filler having a particle size of 15 um is added to a commercially available UV curable adhesive, and the thickness is applied to a plate-like member by a roll coater. 30 um was applied. It was cured once with UV until the tack remained. Thereafter, the thin film layer B was laminated, and UV was again irradiated to completely cure the adhesive.

  In the case of the method using excimer UV as the fourth bonding method, each of the substrate layer A and the thin film layer B is cut into 600 mm × 1000 mm, and the thin film layer B is irradiated with 172 nm excimer UV for 10 seconds to laminate the substrate layer A and the laminate. did. Thereafter, it was placed in an oven at 80 ° C. for 1 hour, taken out, and returned to room temperature.

  In these bondings, the ratio of the bonding area in the bonding layer 12 is 1 (100%, that is, applied to the entire bonding surface of the bonding layer 12), 0.1 (10 %), 0.05 (5%), 0.02 (2%), and 0.1 (10%), 0.05 (5%), 0.02 in the case of the other three joining methods. A plurality of optical sheets 3 (2%) were prepared.

  In addition, as a comparative example, two types are formed by molding a lens sheet 13 as a thin film layer B using PET manufactured by stretch molding and bonding the light diffusion member 11 as the above-described substrate layer A with an adhesive or an adhesive. An optical sheet was prepared.

  The optical sheet 3 produced as described above was incorporated in a liquid crystal TV, the backlight was turned on in an environment of 60 ° C. and left for 2 hours, and then a white screen and a black screen were displayed to check for any abnormality. The temperature of the optical sheet after standing for 2 hours reached 80 ° C. Thereafter, the backlight of the liquid crystal television was turned off and returned to an environment of 25 ° C. After 10 hours, the backlight was turned on and immediately a white screen and a black screen were displayed to check whether there was any abnormality. As the backlight unit 5, a light source having a distance of 10 mm between the light source 7 and the optical sheet 3 and a distance of 5 mm between the optical sheet 3 and the liquid crystal display unit 4 was used.

  Further, only the optical sheet 3 was placed flat on a flat table in an environment of 80 ° C., and the amount of warpage was measured after 2 hours. As shown in FIG. 5, the average amount of warpage h at the four corners of the optical sheet 3 was used as the amount of warpage. Table 2 shows the relationship between the bonding area and the amount of warpage of the optical sheet 3 produced by each bonding method and the quality of the image on the liquid crystal television. Table 3 shows the relationship between the bonding area and the amount of warpage of the optical sheet as a comparative example, and the quality of the image on the liquid crystal television.

  From Table 2, in the optical sheet 3 according to the embodiment, when any bonding method is used, the ratio of the bonding area in the bonding layer 12 is set to 0.05 or more, that is, 5% or more. It has been found that a good image can be displayed without causing a defect in the image of the liquid crystal television, and further, the amount of warpage can be suppressed to 10 mm or less. On the other hand, in the optical sheet as a comparative example, even when the bonding area is large, a problem occurs in the image of the liquid crystal television and the amount of warpage is large. From the above, it was found that when the optical sheet 3 according to the embodiment is used, it is possible to effectively suppress warping and to perform image display well.

It is typical sectional drawing which shows schematic structure of the display apparatus by embodiment of this invention. It is a figure explaining the unevenness | corrugation formed in the light-diffusion member. It is a figure explaining the position which applies a contact adhesive. It is typical sectional drawing which shows schematic structure of the optical sheet of a modification. It is a figure which shows the curvature shape of an optical sheet. It is a figure explaining the state which the optical sheet bent in the case.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Light source part 3 Optical sheet 5 Backlight unit 7 Light source 12 Bonding layer 13 Lens sheet
14 Lens sheet base material 15 Lens array 16 Joining member 17 Air layer A Substrate layer B Thin film layer

Claims (10)

A light diffusing member for diffusing incident light;
A lens array that condenses the diffused light of the light diffusing member is laminated with a lens sheet that is arranged on the exit surface side of the lens sheet substrate,
Either one of the light diffusion member and the lens sheet base material is a thin film layer having low rigidity, and the other is a substrate layer having high rigidity,
The optical sheet, wherein the thin film layer is formed by extrusion molding, and the substrate layer is formed by any of extrusion molding, cast molding, a combination of extrusion molding and cast molding, or injection molding.   The optical sheet according to claim 1, wherein the thin film layer has a thickness of 12 μm to 400 μm.   The optical sheet according to claim 1 or 2, wherein the thickness of the substrate layer is 1 mm or more and 5 mm or less.   The optical film according to any one of claims 1 to 3, wherein the thin film layer and the substrate layer are molded from any one of polycarbonate, acrylic-styrene copolymer polystyrene, and cycloolefin polymer. Sheet. A bonding layer is formed by bonding the thin film layer and the substrate layer by a bonding member,
5. The optical sheet according to claim 1, wherein the ratio of the area occupied by the bonding member to the area of the bonding surface of the bonding layer is 5% or more.   The optical sheet according to any one of claims 1 to 5, wherein the lens sheet is formed of at least one of a prism lens array, a cylindrical lens array, and a microlens array. The optical sheet according to claim 1,
A backlight unit provided with a light source unit disposed on the opposite side of the lens sheet to irradiate light.   The backlight unit according to claim 7, wherein a distance between the optical sheet and the light source unit is 10 mm or less. The backlight unit according to claim 7 or 8,
And a liquid crystal display unit configured to display an image by light irradiation from the backlight unit.   The display device according to claim 9, wherein a distance between the liquid crystal display unit and the optical sheet is 10 mm or less.

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