JP2017198735A - Optical sheet, video source unit, and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet that can be suppressed from being deflected even when its thickness is reduced.SOLUTION: There is provided an optical sheet (30) that is arranged on an observer side of a light source (25), the optical sheet including a base material layer (31) and an optical functional layer (32) laminated in a thickness direction of the base material layer, wherein the optical functional layer includes: a plurality of light transmission parts (33) that include a predetermined cross section, extend in one direction, and arranged in a direction different from the extending direction at a predetermined interval; and light absorption parts (34) that are formed in the intervals between the plurality of light transmission parts, and the product of the tensile modulus of elasticity of the base material layer and the thickness of the base material layer is 500×10MPa μm or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical sheet disposed on an observer side of a light source, an image source unit using the optical sheet, and a liquid crystal display device.

  A liquid crystal display device such as an in-vehicle display or a liquid crystal television is provided with an optical sheet having various functions in order to control light emitted from a light source and provide high quality light to an observer.

  Patent Document 1 discloses a light control sheet having a layer in which prism portions and light absorbing portions are alternately arranged on one surface of a base film layer.

JP 2010-217871 A

  However, as described in Patent Document 1, in an optical sheet provided with a layer in which light transmitting portions and light absorbing portions are alternately arranged on one surface of a base material layer, when the optical sheet is thinned, In particular, the base material layer has a problem of insufficient rigidity and bending.

  Therefore, an object of the present invention is to provide an optical sheet that can suppress bending even if it is thin. In addition, an image source unit including the optical sheet and a liquid crystal display device are provided.

  The present invention will be described below. In order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated embodiment.

Invention of Claim 1 is an optical sheet (30) arrange | positioned at the observer side of a light source (25), Comprising: An optical sheet is a thickness direction of a base material layer (31) and a base material layer. An optical functional layer (32) to be laminated, and the optical functional layer has a predetermined cross section and extends in one direction, and a plurality of light transmission portions (arrayed at predetermined intervals in a direction different from the extending direction) 33) and a light absorbing portion (34) formed at intervals between the plurality of light transmitting portions, and the product of the tensile elastic modulus of the base material layer and the thickness of the base material layer is 500 × 10 ³ (MPa · μm) or more.

  According to a second aspect of the present invention, in the optical sheet according to the first aspect, the base material layer is mainly composed of polycarbonate.

  The invention according to claim 3 is the optical sheet according to claim 2, wherein the retardation of the base material layer is 15 nm or less.

  According to a fourth aspect of the present invention, in the optical sheet according to the first aspect, the base material layer contains polyethylene terephthalate as a main component.

  The invention according to claim 5 is the optical sheet according to claim 4, wherein the retardation of the base material layer is 4000 nm or more.

  The invention according to claim 6 is the light source (25), the optical sheet (30) according to any one of claims 1 to 5 disposed on the viewer side of the light source, and the viewer side of the optical sheet. A liquid crystal panel (15) disposed in the image source unit (10).

  According to a seventh aspect of the present invention, in the video source unit according to the sixth aspect, the optical sheet and the liquid crystal panel have at least a part that is not bonded.

  The invention according to claim 8 is a liquid crystal display device in which the video source unit according to claim 6 or 7 is housed in a casing.

  According to the present invention, even if the optical sheet is thinned, the optical sheet can be prevented from being bent. In addition, by suppressing the bending of the optical sheet, unevenness of light transmitted through the optical sheet can also be suppressed.

It is a disassembled perspective view explaining the image source unit 10 concerning one form. 4 is an exploded view showing a cross section of the video source unit 10. FIG. 4 is an exploded view showing another cross section of the video source unit 10. FIG. FIG. 3 is an enlarged view paying attention to a base material layer 31 and an optical function layer 32 in FIG. 2.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings. However, the present invention is not limited to these forms.

  FIG. 1 is a diagram illustrating one embodiment, and is an exploded perspective view illustrating an image source unit 10 including an optical sheet 30. 2 is a part of an exploded cross-sectional view of the image source unit 10 taken along the line II-II in FIG. 1, and cut along the line III-III in FIG. A part of the exploded cross-sectional view of the video source unit 10 is shown. Such a video source unit 10 operates as a video source unit 10 such as a power source that operates the video source unit 10 and an electronic circuit that controls the video source unit 10 in a housing (not shown), although the description is omitted. The liquid crystal display device is housed together with ordinary equipment required for the purpose. Hereinafter, the video source unit 10 will be described.

  The video source unit 10 includes a liquid crystal panel 15, a surface light source device 20, and a functional film 40. In FIG. 1, the upper side of the paper is the observer side.

  The liquid crystal panel 15 includes an upper polarizing plate 13 disposed on the viewer side, a lower polarizing plate 14 disposed on the surface light source device 20 side, and a liquid crystal disposed between the upper polarizing plate 13 and the lower polarizing plate 14. Layer 12. The upper polarizing plate 13 and the lower polarizing plate 14 decompose the incident light into two orthogonal polarization components (P wave and S wave), and the polarization component in one direction (direction parallel to the transmission axis) (for example, P And has a function of absorbing a polarization component (for example, S wave) in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

  In the liquid crystal layer 12, a plurality of pixels are arranged vertically and horizontally in a direction along the layer surface, and an electric field can be applied to each region where one pixel is formed. Then, the orientation of the pixel to which an electric field is applied changes. As a result, the polarization component (for example, P wave) parallel to the transmission axis transmitted through the lower polarizing plate 14 disposed on the surface light source device 20 side (that is, the light incident side) The polarization direction is rotated by 90 °, while the polarization direction is maintained when passing through a pixel to which no electric field is applied. Therefore, depending on whether or not an electric field is applied to the pixel, the polarization component (for example, P wave) transmitted through the lower polarizing plate 14 further passes through the upper polarizing plate 13 disposed on the light output side, or the upper polarizing plate 13 It is possible to control whether or not it is absorbed and blocked.

  In this way, the liquid crystal panel 15 has a structure for expressing an image by controlling transmission or blocking of light from the surface light source device 20 for each pixel.

The liquid crystal panel is configured to be able to provide an image to the observer based on such a principle. Therefore, when illuminating from the back side of the liquid crystal panel, it is possible to transmit light having a polarization component parallel to the transmission axis of the lower polarizing plate so as to transmit the lower polarizing plate and increase the light use efficiency. .
Furthermore, the liquid crystal panel is excellent in contrast and efficiency (transmittance) of the emitted light with respect to incident light from the normal direction of the liquid crystal panel due to its properties. However, with respect to the incident light obliquely with respect to the normal direction of the liquid crystal panel and the observation by the observer from the oblique direction, there are problems of a decrease in contrast and a low efficiency (transmittance). That is, increasing the incident light from the normal direction of the liquid crystal panel is also effective in increasing the light utilization efficiency.

  The kind of liquid crystal panel is not particularly limited, and examples thereof include known types of liquid crystal panels. These include, for example, TN, STN, VA, MVA, IPS, OCB, and the like.

Next, the surface light source device 20 will be described.
The surface light source device 20 is an illuminating device that is disposed on the side opposite to the observer side with respect to the liquid crystal panel 15 and emits planar light to the liquid crystal panel 15. As can be seen from FIGS. 1 to 3, the surface light source device 20 of the present embodiment is configured as an edge light type surface light source device, and includes a light guide plate 21, a light source 25, a light diffusion layer 26, a prism layer 27, and a reflective polarizing plate. 28, an optical sheet 30 and a reflection sheet 39.

  As can be seen from FIGS. 1 to 3, the light guide plate 21 includes a base portion 22 and a back optical element 23. The light guide plate 21 is a plate-like member as a whole formed of a light-transmitting material. In this embodiment, one plate surface side that is an observer side of the light guide plate 21 is a smooth surface, and the other plate surface side opposite to this is a back surface, and a plurality of back optical elements 23 are provided on the back surface. Are arranged.

  Various materials can be used as the material forming the base 22 and the back optical element 23. However, a material that is widely used as a material for an optical sheet incorporated in a display device and has excellent mechanical characteristics, optical characteristics, stability, workability, and the like, and can be obtained at low cost can be used. For example, a polymer resin having an alicyclic structure, a methacrylic resin, a polycarbonate resin, a polystyrene resin, an acrylonitrile-styrene copolymer, a methyl methacrylate-styrene copolymer, an ABS resin, a polyethersulfone, or the like. And epoxy acrylate and urethane acrylate-based reactive resins (such as ionizing radiation curable resins).

  The base portion 22 is a plate having a predetermined thickness at a portion that serves as a base of the back surface optical element 23 while light is guided therein.

The back optical element 23 is a protruding element formed on the back side of the base 22 (the side opposite to the side on which the reflective polarizing plate 28 is disposed), and in this embodiment, has a triangular prism shape. The back optical element 23 has a columnar shape in which the protruding top ridge line extends in the left-right direction in FIG. 1, and a plurality of back optical elements 23 are arranged side by side at a predetermined pitch in a direction orthogonal to the extending direction. The back optical element 23 of this embodiment has a triangular cross section, but is not limited to this, and may be a cross section of any shape such as a polygon, a hemisphere, a part of a sphere, or a lens shape.
The arrangement direction of the plurality of back surface optical elements 23 is preferably the light guide direction. That is, the ridge lines of the respective back surface optical elements 23 extend in parallel to the direction in which the light sources 25 are arranged, or in the direction in which the light sources 25 extend if they are one long light source.

  The “triangular shape” in the present specification includes not only a triangular shape in a strict sense but also a substantially triangular shape including limitations in manufacturing technology, errors in molding, and the like. Similarly, terms used in the present specification to specify other shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, “ellipse”, “circle”, etc. are bound to the strict meaning. Therefore, it should be interpreted including an error to the extent that a similar optical function can be expected.

  The light guide plate 21 having such a configuration can be manufactured by extrusion molding or by molding the back optical element 23 on the base 22. In the light guide plate 21 manufactured by extrusion molding, the base portion 22 and the back surface optical element 23 can be integrally formed. Moreover, when manufacturing the light-guide plate 21 by shaping | molding, the back surface optical element 23 may be the same resin material as the base 22, or a different material.

Returning to FIGS. 1 to 3, the light source 25 will be described. The light source 25 is arrange | positioned among the side surfaces which the base 22 of the light-guide plate 21 has on the one side surface of the direction where the several back surface optical element 23 is arranged. The type of the light source is not particularly limited, but can be configured in various forms such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), or an incandescent bulb. In this embodiment, the light source 25 is composed of a plurality of LEDs, and is configured to be able to individually and independently adjust the lighting and extinction of each LED and / or the lighting brightness of each LED by a control device (not shown). Yes.
In this embodiment, the light source 25 is disposed on the side surface on one side as described above. However, the light source may be disposed on the side surface opposite to the side surface. In this case, the shape of the back optical element is also formed following a known example.

Next, the light diffusion layer 26 will be described. The light diffusion layer 26 is a layer that is disposed on the light output side of the light guide plate 21 and has a function of diffusing and emitting light incident thereon. Thereby, the uniformity of the light emitted from the light guide plate 21 can be further improved, and the scratches existing on the light guide plate 21 can be made inconspicuous.
As a specific embodiment of the light diffusion layer, a known light diffusion layer can be used, and examples thereof include a form in which a light diffusion agent is dispersed in a base material.

As can be seen from FIGS. 1 to 3, the prism layer 27 is a layer provided with a unit prism 27 a that is provided closer to the liquid crystal panel 15 than the light diffusion layer 26 and is convex toward the liquid crystal panel 15. The unit prism 27 a has a predetermined cross section and extends in the light guide direction of the light guide plate 21. The plurality of unit prisms 27a are arranged in a direction different from the light guide direction (in this embodiment, a direction orthogonal to the light guide direction in plan view).
As the cross-sectional shape of the unit prism of such a prism layer, a known shape can be applied according to a required function. Depending on the shape, light can be further diffused or condensed.

  Next, the reflective polarizing plate 28 will be described. The reflective polarizing plate 28 decomposes incident light into two orthogonal polarization components (P wave and S wave) and transmits a polarization component (for example, P wave) in one direction (direction parallel to the transmission axis). And has a function of reflecting a polarization component (for example, S wave) in the other direction (direction parallel to the reflection axis) orthogonal to the one direction. As the structure of such a reflective polarizing plate, a known structure can be applied.

  Next, the optical sheet 30 will be described. As can be seen from FIG. 1 to FIG. 3, the optical sheet 30 is provided on the base material layer 31 formed in a sheet shape and one surface of the base material layer 31 (the surface on the light guide plate 21 side in this embodiment). An optical function layer 32.

  As will be described later, the optical sheet 30 changes the traveling direction of the light incident from the light incident side and emits the light from the light outgoing side, thereby intensively improving the luminance in the front direction (normal direction) (light collection). Function). In this case, the change of the polarization component is suppressed, and the light use efficiency can be enhanced by these functions. Furthermore, it has a function (light absorption function) for absorbing light traveling at a large angle with respect to the front direction.

As shown in FIGS. 1 to 3, the base material layer 31 is a flat sheet-like member that supports the optical function layer 32.
In the base material layer 31, the product of the tensile elastic modulus of the base material layer and the thickness of the base material layer is preferably 500 × 10 ³ (MPa · μm) or more. Thereby, even if the optical sheet is thinned, the optical sheet can be provided with rigidity, so that the optical sheet can be prevented from being bent. This also means that even if the optical sheet is placed at a high temperature (for example, 105 ° C.) for a predetermined period (for example, 500 hours), the optical sheet can be prevented from being bent. Moreover, it is preferable that the product of the tensile elasticity modulus of a base material layer and the thickness of a base material layer is 1000 * 10 < ³ > (MPa * micrometer) or less. When the product of the tensile modulus of elasticity of the base material layer and the thickness of the base material layer exceeds 1000 × 10 ³ (MPa · μm), the base material layer becomes too thick, making it difficult to reduce the thickness of the optical sheet.
The thickness of the base material layer is not particularly limited as long as the product of the tensile elastic modulus of the base material layer and the thickness of the base material layer is within the above range, but is preferably 50 μm or more and 300 μm or less.

As described above, since the optical sheet 30 is suppressed from being bent by having the predetermined base material layer, at least a part of the optical sheet 30 and the liquid crystal panel 15 is not bonded in this embodiment. It may have a site | part and does not need to adhere | attach the whole surface.
In addition, the intensity of the light transmitted through the optical sheet 30 is greatly affected by the incident angle and the output angle with respect to the optical sheet 30, so that the deflection of the optical sheet 30 is suppressed, thereby causing unevenness of the light transmitted through the optical sheet 30. In particular, light and dark unevenness can be suppressed.

  Various materials can be used as the material forming the base material layer 31. However, a material that is widely used as a material for an optical sheet incorporated in a display device and has excellent mechanical characteristics, optical characteristics, stability, workability, and the like, and can be obtained at low cost can be used. Examples thereof include polyethylene terephthalate resin (PET), triacetyl cellulose resin (TAC), methacrylic resin, and polycarbonate resin. Among these, in consideration of the combination of the surface light source device 20 and the lower polarizing plate 14, it is preferable to use TAC, methacrylic resin, and polycarbonate resin with little birefringence (retardation). Furthermore, a polycarbonate resin having a high glass transition point is desirable in applications that require high heat resistance such as in-vehicle applications. Specifically, the glass transition point of the polycarbonate resin is 143 ° C., which is generally suitable for in-vehicle applications that require durability at 105 ° C.

  From such a viewpoint, regarding the retardation, the retardation Re in the planar direction of the base material layer 31 is preferably 15 nm or less or 4000 nm or more at a wavelength of 400 nm to 700 nm. Here, the retardation Re is represented by Re = (Nx−Ny) × d. Nx is the maximum refractive index in the surface of the base material layer 31, and Ny is the minimum refractive index in the surface of the base material layer 31. D (nm) is the thickness of the base material layer 31.

  When the retardation Re is increased, color unevenness is likely to occur in the image in combination with the polarizing plate of the LCD and the polarizing property of the liquid crystal panel, and the reflection type polarizing plate for improving the luminance used in the case of the liquid crystal image display device. Details are as follows. That is, when birefringence (retardation) occurs in the layer, light travels in a plurality of directions. Then, when the light that has traveled separately travels out of the layer, it interferes with other light that travels separately. This is observed as so-called color unevenness. This is particularly remarkable when a layer having a large retardation is included between the polarizers. For example, in a liquid crystal display device, having a layer having a large retardation between a reflective polarizing sheet used for the purpose of improving luminance and a polarizing plate of a liquid crystal panel is one cause of color unevenness.

Therefore, the retardation Re of the base material layer 31 is preferably 15 nm or less. Thereby, it is possible to suppress color unevenness. In order to set the retardation Re to 15 nm or less, a material mainly composed of a polycarbonate resin is preferably used for the base material layer 31.
“Containing as a main component” means that a specific material is contained in an amount of 50% by mass or more when the mass of the entire base material layer is 100% by mass. The same applies to the following.

  On the other hand, the present inventors have found that color unevenness can be suppressed only in the case where the retardation Re is 4000 nm or more in the base material layer 31. Therefore, when increasing retardation Re of the base material layer 31, it is preferable that it is 4000 nm or more, and it is more preferable that it is 8000 nm or more. In addition, the upper limit of the retardation Re when the retardation Re is increased is not particularly limited, but is preferably 12000 nm or less from the viewpoint of manufacturing the base material layer. In order to set the retardation Re to 4000 nm or more, a material mainly composed of a highly stretched polyethylene terephthalate resin is preferably used for the base material layer 31.

  The optical functional layer 32 is a layer laminated on one surface of the base material layer 31 (the surface on the light guide plate 21 side in this embodiment), and light transmitting portions 33 and light absorbing portions 34 are alternately arranged along the layer surface. ing. FIG. 4 is an enlarged view of a part of FIG. 2 focusing on the base material layer 31 and the optical function layer 32.

  The optical functional layer 32 has a cross section shown in FIG. 4 and a shape extending to the back / front side of the paper. That is, in the cross section shown in FIG. 4, the light transmission part 33 having a substantially trapezoidal shape and the light absorption part 34 having a substantially trapezoidal cross section formed between two adjacent light transmission parts 33 are provided.

  The light transmission part 33 is a part whose main function is to transmit light. In this embodiment, in the cross section shown in FIGS. 2 and 4, the base layer 31 side has a long lower bottom, and the opposite side (light guide plate side). ) Having a substantially trapezoidal cross-sectional shape having a short upper base. The light transmissive portions 33 maintain the cross section along the layer surface of the base material layer 31 and extend in the above-described direction, and are arranged at a predetermined interval in a direction different from the extending direction. An interval having a substantially trapezoidal cross section is formed between the adjacent light transmission portions 33. Therefore, the interval has a trapezoidal cross section having a long lower base on the upper base side (light guide plate 21 side) of the light transmission part 33 and a short upper base on the lower base side (liquid crystal panel side) of the light transmission part 33. The light absorbing portion 34 is formed by filling a necessary material described later. In this embodiment, the adjacent light transmission parts 33 are connected on the long bottom side.

  The light transmission part 33 has a refractive index of Nt. Such a light transmission part 33 can be formed by hardening a transmission part constituent composition. Details will be described later. Although the value of the refractive index Nt is not particularly limited, as will be described later, the refractive index is from the viewpoint of appropriately reflecting light (including total reflection) at the interface with the light absorbing portion 34 on the slope of the trapezoidal cross section. It is preferable that it is 1.55 or more. However, since a material with a refractive index that is too high is likely to break, the refractive index is preferably 1.61 or less. More preferably, it is 1.56 or less.

The light absorption part 34 functions as an intermediate part formed at the above-described interval formed between the adjacent light transmission parts 33 and has a cross-sectional shape similar to the cross-sectional shape of the interval. Therefore, the short upper base faces the liquid crystal panel 15 side, and the long lower base becomes the light guide plate 21 side. And the light absorption part 34 is comprised so that a refractive index may be Nr and it can absorb light. Specifically, light absorbing particles are dispersed in a binder having a refractive index of Nr. The refractive index Nr is a refractive index lower than the refractive index Nt of the light transmission part 33. Thus, by making the refractive index of the light absorbing portion 34 smaller than the refractive index of the light transmitting portion 33, the light incident on the light transmitting portion 33 under a predetermined condition is appropriately totally reflected at the interface with the light absorbing portion 34. Can be made. Even when the total reflection condition is not satisfied, some light is reflected at the interface.
The value of the refractive index Nr is not particularly limited, but is preferably 1.50 or less from the viewpoint of appropriately performing the total reflection, and more preferably 1.47 or more from the viewpoint of availability. More preferably, it is 1.49 or more.

  The difference in refractive index between the refractive index Nt of the light transmitting portion 33 and the refractive index Nr of the light absorbing portion 34 is not particularly limited, but is preferably 0.05 or more and 0.14 or less. By increasing the refractive index difference, more light can be totally reflected.

The optical function layer 32 is not particularly limited, but for example, the light transmission part 33 and the light absorption part 34 are formed as follows. That is, the pitch between the light transmission part 33 and the light absorption part 34 represented by _Pk in FIG. 4 is preferably 20 μm or more and 100 μm or less, and more preferably 30 μm or more and 100 μm or less. Further, the angle formed by the interface on the hypotenuse between the light absorbing portion 34 and the light transmitting portion 33 indicated by θ _k in FIG. 4 and the normal of the layer surface of the optical functional layer 32 is 1 ° or more and 10 ° or less. Is preferred. And the thickness of the light absorption part 34 shown by _Dk in FIG. 4 is preferably 50 μm or more and 150 μm or less, and more preferably 60 μm or more and 150 μm or less. By being within these ranges, the balance between light transmission and light absorption is often appropriate.

  In this embodiment, an example in which the interface between the light transmitting portion 33 and the light absorbing portion 34 is straight in the cross section is shown. However, the present invention is not limited to this, and may be a polygonal line shape, a convex curved surface shape, a concave curved surface shape, etc. Also good. Moreover, the cross-sectional shape may be the same in the some light transmissive part 33 and the light absorption part 34, and a different cross-sectional shape may have predetermined regularity.

In this embodiment, a protective layer for protecting the optical functional layer 32 may be further laminated on the surface of the optical functional layer 32 opposite to the base material layer. By laminating the protective layer, it is possible to impart an effect of protecting the optical functional layer 32 from external damage and the like, and an effect of suppressing warpage when the optical sheet 30 is manufactured. As a material used for the protective layer, a known material such as an ultraviolet curable urethane acrylate can be used. The protective layer may be subjected to treatments such as antireflection treatment, antiglare treatment, antistatic treatment, and hard coat treatment.
The thickness of the protective layer is preferably 5 μm or more and 30 μm or less. If the thickness of the protective layer is less than 5 μm, it is difficult to apply stably, and if it is thicker than 30 μm, the cost of the material used increases. The haze of the protective layer is preferably 5% or more and 50% or less. If the haze of the protective layer is less than 5%, there is a risk of sticking to a film (for example, the reflective polarizing film 28 in FIGS. 1 to 3) disposed on the surface of the protective layer. On the other hand, if the haze of the protective layer exceeds 50%, the light transmitted through the protective layer is excessively diffused, and thus the front luminance tends to decrease.

The optical sheet 30 can be manufactured as follows, for example.
First, the light transmission part 33 is formed in the base material layer 31. This inserts the base material sheet used as the base material layer 31 between the mold roll which has the shape which can transfer the shape of the light transmission part 33 on the surface, and the nip roll arrange | positioned so as to oppose this. At this time, the mold roll and the nip roll are rotated while supplying the composition constituting the light transmitting portion between the base sheet and the mold roll. As a result, a groove corresponding to the light transmitting portion formed on the surface of the mold roll (a shape obtained by reversing the shape of the light transmitting portion) is filled with the composition that constitutes the light transmitting portion, and the composition becomes the surface of the mold roll. It will be along the shape.

  Here, examples of the composition constituting the light transmission part include ionizing radiation curable resins such as epoxy acrylate, urethane acrylate, polyether acrylate, polyester acrylate, and polythiol.

  Light for curing with a light irradiation device is irradiated from the substrate sheet side to the composition constituting the light transmission portion sandwiched between the mold roll and the substrate sheet and filled therein. Thereby, a composition can be hardened and the shape can be fixed. And the base material layer 31 and the shape | molded light transmission part 33 are released from a metal mold | die roll with a mold release roll.

  Next, the light absorption part 34 is formed. In order to form the light absorption part 34, first, the composition constituting the light absorption part is filled in the interval between the light transmission parts 33 formed above. Thereafter, the surplus composition is scraped off with a doctor blade or the like. Then, the remaining composition can be cured by irradiating with ultraviolet rays from the light transmitting portion 33 side to form the light absorbing portion 34.

  The material used as the light absorbing portion is not particularly limited, but for example, it is colored in a photocurable resin such as urethane (meth) acrylate, polyester (meth) acrylate, epoxy (meth) acrylate, and butadiene (meth) acrylate. And a composition in which the light absorbing particles are dispersed.

Further, instead of dispersing the light absorbing particles, the entire light absorbing portion can be colored with a pigment or a dye.
When using light-absorbing particles, light-absorbing colored particles such as carbon black are preferably used. However, the present invention is not limited to these, and selectively absorbs a specific wavelength according to the characteristics of image light. Colored particles may be used. Specific examples include organic fine particles colored with metal salts such as carbon black, graphite, and black iron oxide, dyes, pigments, colored glass beads, and the like. In particular, colored organic fine particles are preferably used from the viewpoints of cost, quality, availability, and the like. The average particle diameter of the colored particles is preferably 1.0 μm or more and 20 μm or less.
Here, the “average particle diameter” means an arithmetic average diameter obtained by observing 100 light absorbing particles with an electron microscope and measuring the diameter.

  Further, in the case where the protective layer described above is provided on the surface opposite to the base material layer 31 in the optical function layer 32, it can be laminated using a roll, a UV adhesive or the like.

  Thereby, the optical sheet 30 in which the optical functional layer 32 is laminated on one surface of the base material layer 31 is produced.

  Returning to FIGS. 1 to 3, the reflection sheet 39 of the surface light source device 20 will be described. The reflection sheet 39 is a member that reflects the light emitted from the back surface of the light guide plate 21 and makes the light enter the light guide plate 21 again. The reflection sheet 39 is a sheet that is capable of so-called specular reflection, such as a sheet made of a material having a high reflectance such as a metal, a sheet including a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, It can be preferably applied.

  The functional film 40 is a layer that is disposed on the light output side of the liquid crystal panel 15 and has functions of improving the quality of the video light and protecting the video source unit 10. Examples thereof include an antireflection film, an antiglare film, a hard coat film, a color tone correction film, a light diffusion film, and the like, and these are constituted by combining them alone or in combination.

  Next, the operation of the video source unit 10 having the above configuration will be described with an example of an optical path. However, the optical path example is conceptual for explanation, and does not strictly represent the degree of reflection or refraction.

  First, as shown in FIG. 2, the light emitted from the light source 25 enters the light guide plate 21 through the light incident surface on the side surface of the light guide plate 21. FIG. 2 shows an example of an optical path of the light L21 and L22 incident on the light guide plate 21 from the light source 25 as an example.

  As shown in FIG. 2, the light L21 and L22 incident on the light guide plate 21 repeats total reflection due to a difference in refractive index with air on the light exit side surface of the light guide plate 21 and the back surface on the opposite side, thereby guiding the light guide direction (FIG. Proceed to the right of page 2).

  However, the back optical element 23 is disposed on the back surface of the light guide plate 21. For this reason, as shown in FIG. 2, the light L21, L22 traveling in the light guide plate 21 has its traveling direction changed by the back surface optical element 23, and is incident on the light exit surface and the back surface at an incident angle less than the total reflection critical angle. There is also. In this case, the light can be emitted from the light exit surface of the light guide plate 21 and the back surface on the opposite side.

  Lights L21 and L22 emitted from the light exit surface are directed to the reflective polarizing plate 28 disposed on the light exit side of the light guide plate 21. On the other hand, the light emitted from the back surface is reflected by the reflection sheet 39 disposed on the back surface of the light guide plate 21, enters the light guide plate 21 again, and travels through the light guide plate 21.

  The light traveling in the light guide plate 21 and the light whose direction is changed by the back surface optical element 23 and reaching the light exit surface at an incident angle less than the total reflection critical angle are in each area along the light guide direction in the light guide plate 21. Arise. For this reason, the light traveling in the light guide plate 21 is gradually emitted from the light exit surface. Thereby, the light quantity distribution along the light guide direction of the light emitted from the light exit surface of the light guide plate 21 can be made uniform.

The light emitted from the light guide plate 21 then reaches the light diffusion layer 26 and the uniformity is improved. Then, the light diffused or condensed by the prism layer 27 as necessary and emitted from the prism layer 27 reaches the reflective polarizing plate 28 next. Here, the light in the polarization direction along the transmission axis of the reflective polarizing plate 28 passes through the reflective polarizing plate 28 and travels toward the optical sheet 30.
On the other hand, the light in the polarization direction along the reflection axis of the reflective polarizing plate 28 is reflected and returned to the light guide plate 21 side as shown by dotted arrows L21 ′ and L22 ′ in FIG. The returned light is reflected by the light guide plate 21, the back surface optical element 23, or the reflection sheet 39 and travels again toward the reflective polarizing plate 28. During this reflection, the polarization direction of a part of the light is changed, and a part of the light is transmitted through the reflective polarizing plate 28. Other light is returned to the light guide plate side again. Thus, the light reflected by the reflective polarizing plate 28 can be transmitted through the reflective polarizing plate 28 by repeating the reflection. Thereby, the utilization factor of the light from the light source 25 is increased.
Here, the light emitted from the reflective polarizing plate 28 has a polarization direction in a direction along the transmission axis of the lower polarizing plate 14, and is polarized light transmitted through the lower polarizing plate 14.

The light emitted from the reflective polarizing plate 28 enters the optical function layer 32. The light incident on the optical functional layer 32 is polarized light that passes through the lower polarizing plate 14 and travels with the following optical path. That is, for example, as indicated by L41 in FIG. 4, the light is transmitted through the light transmitting portion 33 without reaching the interface with the light absorbing portion 34. Alternatively, as indicated by L42 in FIG. 4, the light reaches the interface with the light absorbing portion 34 and is totally reflected and passes through the light transmitting portion 33. At this time, in this embodiment, the light reflected by the interface is brought closer to the direction parallel to the normal line of the liquid crystal panel 15 by the action of the inclination angle (θ _k ) of the interface. In addition, since the angle is smaller than the total reflection critical angle, some of the light that does not totally reflect is reflected at the interface. Such light also passes through the light transmitting portion 33 in the same manner.
As a result, it is possible to effectively provide the liquid crystal panel 15 with light that does not cause problems such as a decrease in contrast and color inversion when transmitted through the liquid crystal panel 15.

  On the other hand, as indicated by L43 in FIG. 4, the light incident on the optical function layer 32 at a large angle with respect to the normal to the sheet surface is absorbed by the light absorber 34 and is not provided to the liquid crystal panel 15. Accordingly, it is possible to absorb light that causes a problem such as a decrease in contrast and color inversion.

  With such an optical sheet 30, light from the light guide plate 21 is efficiently collected, and light that is not collected is absorbed by the light absorption unit, so that appropriate light can be efficiently provided to the liquid crystal panel. It is possible to greatly improve the light utilization efficiency.

  Further, the optical path will be described. The light emitted from the surface light source device 20 as described above enters the lower polarizing plate 14 of the liquid crystal panel 15. The lower polarizing plate 14 transmits one polarization component of incident light and absorbs the other polarization component. The light transmitted through the lower polarizing plate 14 selectively passes through the upper polarizing plate 13 according to the state of electric field application to each pixel. In this way, the liquid crystal panel 15 selectively transmits light from the surface light source device 20 for each pixel, so that an observer of the liquid crystal display device can observe an image. At that time, the image light is provided to the observer through the functional film 40, and the quality of the image is improved.

  In the above-described form, the optical functional layer 32 has a direction in which the short upper base of the light transmitting portion 33 is on the light guide plate 21 side and the long lower base is on the liquid crystal panel 15 side, but this may be reversed. In other words, the short upper base of the light transmission part may be oriented toward the liquid crystal panel and the long lower base toward the light guide plate. In this case, it does not have a light condensing function, but it can provide light to the lower polarizing plate while maintaining the polarization direction transmitted through the lower polarizing plate, and can suppress the light absorbed by the lower polarizing plate, It is possible to improve the light utilization efficiency (transmittance).

Example 1
As Example 1, an optical sheet having a protective layer laminated on the optical sheet as shown in FIG. 4 was prepared, and the relationship between the product of the tensile modulus of the base material layer and the thickness of the base material layer and the deflection was evaluated.
The specific shape of the optical sheet according to Example 1 is as follows. In addition, the protective layer is laminated | stacked on the surface on the opposite side to the base material layer of an optical function layer.

<Base material layer>
・ Material: Polyethylene terephthalate resin ・ Thickness: 130μm
<Optical function layer>
・ Pitch (see FIG. 4): P _k = 39 μm
· Light absorbing portion upper base width: 4 [mu] m _(W a in FIG. 4)
・ Light absorption part lower bottom width: 10 μm (W _{b in} FIG. 4)
-Thickness of the light absorbing portion (see FIG. 4): D _k = 102 μm
・ Thickness of optical functional layer: 127 μm
-Light transmitting material and refractive index: UV curable urethane acrylate with refractive index of 1.56-Light absorbing material and refractive index: UV curable urethane acrylate with refractive index of 1.49 and acrylic beads containing carbon black 25 mass% dispersion <Protective layer>
・ Material: UV curable urethane acrylate resin ・ Rough surface: Haze 30
・ Thickness: 25μm

(Example 2)
In the optical sheet according to Example 1, the material of the base material layer was changed to polycarbonate resin, the thickness of the base material layer was changed to 250 μm, and the optical sheet according to Example 2 was produced.

(Comparative Example 1)
In the optical sheet according to Example 2, the thickness of the base material layer was changed to 130 μm, and an optical sheet according to Comparative Example 1 was produced.

  The optical sheet as described above was cut into a size of 120 mm in width and 300 mm in length, and the four sides of the optical sheet were taped to glass and tested in the atmosphere at 105 ° C. for 500 hours. And the bending of the optical sheet after a test was judged visually. The results are shown in Table 1. In addition, the tensile elasticity modulus of each base material layer is measured in advance according to ASTM D638.

  The optical sheets according to Example 1 and Example 2 did not bend. On the other hand, the optical sheet according to Comparative Example 1 was bent.

DESCRIPTION OF SYMBOLS 10 Image source unit 15 Liquid crystal panel 20 Surface light source device 21 Light guide plate 25 Light source 26 Light diffusion layer 27 Prism layer 28 Reflective polarizing plate 30 Optical sheet 32 Optical function layer 33 Light transmission part 34 Light absorption part

Claims (8)

An optical sheet disposed on the observer side of the light source,
The optical sheet includes a base layer and an optical functional layer laminated in the thickness direction of the base layer,
The optical functional layer is
A light transmissive portion having a predetermined cross section and extending in one direction and arranged in a direction different from the extending direction at a predetermined interval;
A light absorbing portion formed at the interval between the plurality of light transmitting portions, and
The optical sheet whose product of the tensile elasticity modulus of the said base material layer and the thickness of a base material layer is 500 * 10 < ³ > (MPa * micrometer) or more.   The optical sheet according to claim 1, wherein the base material layer includes a polycarbonate resin as a main component.   The optical sheet according to claim 2, wherein the retardation of the base material layer is 15 nm or less.   The optical sheet according to claim 1, wherein the base material layer includes a polyethylene terephthalate resin as a main component.   The optical sheet according to claim 4, wherein the retardation of the base material layer is 4000 nm or more. A light source;
The optical sheet according to any one of claims 1 to 5, which is disposed on an observer side of the light source;
A liquid crystal panel disposed on the viewer side of the optical sheet;
A video source unit.   The video source unit according to claim 6, wherein the optical sheet and the liquid crystal panel have a portion that is not bonded to at least a part thereof.   A liquid crystal display device in which the video source unit according to claim 6 is housed in a casing.

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