JP2004309802A - Optical unit and back light unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical unit whose functions such as a light condensing function, a function of refracting toward the normal direction side and a light diffusing function are markedly high and wherein the aforesaid optical functions can be easily and reliably controlled, and also damages on another overlapped members can be suppressed, and to provide a backlight unit which acquires high brightness in the frontward direction and the uniform brightness, etc., by using the optical unit. <P>SOLUTION: An optical unit 1 is provided with a plurality of optical sheets in an overlapped state, and a microlens sheet 2 as well as a light diffusion sheet 3 etc., are used as the optical sheet. The microlens sheet 2 is provided with a microlens array 5 constituted of a plurality of microlenses 6 on the surface. The microlens 6 is partly formed to an ellipsoid whose major axis lies in the normal direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical unit having various functions such as light collection, diffusion, and refraction to a normal direction side, and particularly suitable for a backlight unit of a liquid crystal display device, and a backlight unit using the same. .
[0002]
[Prior art]
2. Description of the Related Art As a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back has become widespread, and a backlight unit such as an edge light type (side light type) or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 7A, the edge light type backlight unit 30 generally has a rod-shaped lamp 31 as a light source, and a rectangular plate-shaped lamp 31 whose end is arranged along the lamp 31. And an optical unit 33 laminated on the surface side of the light guide plate 32. The optical unit 33 includes a plurality of optical sheets in a superimposed manner, and has optical functions such as focusing, diffusing, and refracting transmitted light. The optical sheets provided in the optical unit 33 include (1) a light diffusion sheet 34 which is provided on the surface side of the light guide plate 32 and mainly has a light diffusion function, and (2) a light diffusion sheet which is provided on the surface side of the light diffusion sheet 34. For example, a prism sheet 35 having a function of refracting in the normal direction is used.
[0003]
The function of the backlight unit 30 will be described. First, a light beam incident on the light guide plate 32 from the lamp 31 is reflected by a reflection dot or a reflection sheet (not shown) on the back surface of the light guide plate 32 and each side surface. Emitted from the surface. Light emitted from the light guide plate 32 enters the light diffusion sheet 34, is diffused, and is emitted from the surface. Thereafter, the light beam emitted from the surface of the light diffusion sheet 34 enters the prism sheet 35, and is emitted as a light beam having a distribution showing a peak almost directly above by the plurality of ridge prism portions 35a formed on the surface. In this way, the light beam emitted from the lamp 31 is diffused by the optical unit 33, refracted so as to show a peak almost directly above, and illuminates the entire liquid crystal layer (not shown) further above.
[0004]
Although not shown, in consideration of the light guide characteristics of the light guide plate 32 and the optical function of the optical sheet provided in the optical unit 33, more optical sheets such as a light diffusion sheet and a prism sheet are provided. There is also an optical unit 33.
[0005]
As shown in FIG. 7B, the conventional light diffusion sheet 34 generally includes a base layer 36 made of a transparent synthetic resin and a light diffusion layer 37 laminated on the surface of the base layer 36. (For example, refer to JP-A-2000-89007). This light diffusion layer 37 generally contains resin beads 39 in a binder 38. Due to the presence of the resin beads 39, lens-shaped fine irregularities are formed on the surface of the light diffusion sheet. Optical functions such as diffusion and light collection of the light diffusion sheet 34 are exerted by the lens-shaped fine irregularities and refraction and reflection at the interface of the resin beads 39.
[0006]
[Patent Document 1]
JP 2000-89007 A
[0007]
[Problems to be solved by the invention]
In the light diffusion sheet 34 provided in the above-mentioned conventional optical unit 33, since the surface of the resin beads 39 is covered with the binder 38, the resin beads 39 are unlikely to protrude sufficiently, it is difficult to form the intended lens-like fine irregularities, and the light is condensed. There are certain limitations in improving optical functions such as diffusion and the like. Therefore, the conventional backlight unit 30 needs to include one or two prism sheets 35 in spite of being expensive and difficult to handle.
[0008]
Further, the prism sheet 35 generally has a predetermined inclination of the incident light beam that is optimal for refracting the outgoing light beam to the normal direction side since the protruding ridge prism portion 35a has a right-angled triangular cross-sectional shape. It has a corner (about 75 °). On the other hand, the light diffusion sheet 34 can control the optical functions such as light condensing by changing the particle diameter, the compounding amount, and the coating amount of the resin beads 39, but the uniform dispersion of the resin beads 39 and the uniform coating can be achieved. Since the processing is difficult due to aggregation or the like, accurate control of the optical function is impossible. For this reason, it is difficult for the light diffusion sheet 34 to control the light incident on the prism sheet 35 to an optimum tilt angle for refraction toward the normal direction, and as a result, it is difficult to improve the front luminance of the backlight unit 30. Has become.
[0009]
Further, since it is difficult to adjust the height of the fine unevenness formed on the surface of the light diffusion sheet 34, the light diffusion sheet 34 may be damaged by stress concentration on other optical members (for example, the prism sheet 35) to be superimposed. There is a risk of attaching.
[0010]
The present invention has been made in view of these inconveniences, and condensed light, refraction to the normal direction side, optical functions such as diffusion are extremely high, and the optical functions can be easily and reliably controlled. It is an object of the present invention to provide an optical unit capable of suppressing damage to another member to be superimposed and further improving the quality such as high luminance in a front direction and uniform luminance by using the optical unit. Is what you do.
[0011]
[Means for Solving the Problems]
The invention made in order to solve the above-mentioned problem has a plurality of optical sheets to be superimposed, a microlens sheet is used as the optical sheet, and the microlens sheet is composed of a plurality of microlenses. An optical unit having an array on its surface, wherein the microlens has an elliptical partial shape with its long axis oriented in the normal direction.
[0012]
The optical unit has excellent optical functions (a function of condensing transmitted light to the front side, a function of diffusing the transmitted light, a function of changing the angle to the normal direction side, etc.) by the microlens array provided on the surface of the microlens sheet. ing. Further, in the optical unit, since the microlens on the surface of the microlens sheet has a partial shape of an elliptical surface with its long axis directed in the normal direction, the spherical aberration of the microlens is reduced, and the optical function is reduced. Has been significantly increased. Further, the optical unit has a height ratio (H / R) of the microlenses of the microlens sheet. _L ), Aspect ratio (R _L / R _S ), Filling rate, major axis radius (R _L The optical function can be easily and reliably controlled by adjusting the surface roughness (Ra), the arrangement pattern and the like. Further, in the optical unit, by adjusting the height of the microlenses of the microlens sheet to be constant, stress concentration is suppressed, and damage to other superimposed members (for example, a prism sheet) is prevented.
[0013]
It is preferable to use a light diffusion sheet further including a base layer and a light diffusion layer containing a light diffusion agent in a binder as the optical sheet. As described above, by superimposing the light diffusion sheet in addition to the microlens sheet, the light diffusion function of the optical unit is significantly improved, and moire, glare, luminance unevenness, and the like due to overlapping geometric shapes are reduced. Occurrence is reduced and quality is improved.
[0014]
Preferably, a microlens sheet is superimposed on the surface side of the light diffusion sheet. The excellent optical function of the microlens sheet superimposed on the surface side is effectively exhibited, and the optical functions such as light collection, refraction toward the normal direction, and diffusion are further improved.
[0015]
Further, it is preferable to use a prism sheet having a plurality of ridge prism portions in a stripe shape on the surface as the optical sheet. As described above, by superimposing the prism sheet in addition to the microlens sheet, the function of refracting the optical unit in the normal direction is significantly improved.
[0016]
Preferably, a prism sheet is superimposed on the front side of the microlens sheet. Since the optical function of the microlens sheet can be easily and reliably controlled as described above, by superimposing the microlens sheet on the back side of the prism sheet, the peak direction of the light beam incident on the prism sheet is normal. The tilt angle can be controlled to be optimal for refraction in the direction side, and as a result, the emitted light beam can be more effectively guided to the normal direction side.
[0017]
In the optical unit, the major axis radius of the microlens (R _L ) Minor axis radius (R _S ) To the flat ratio (R _L / R _S ) Is preferably 1.05 or more and 1.7 or less. Flatness ratio (R _L / R _S ) Is in the above range, the spherical aberration of the microlens is significantly reduced, and the optical function of the optical unit is significantly improved.
[0018]
In addition, the major axis radius (R) of the height (H) of the microlens (R) _L ) To the height ratio (H / R) _L ) Is 3/4 or more and 1 or less, and the major axis radius (R _L ) Is 10 μm or more and 1000 μm or less, the filling ratio of the microlens is 40% or more, the surface roughness (Ra) of the microlens is 2 μm or less, and the refractive index of the material constituting the microlens array is 1.3 or more and 1 or more. .8 or less is preferred. Thus, the height ratio of the microlens (H / R _L ), Major axis radius (R _L ), The filling factor, the surface roughness (Ra), and the refractive index of the material within the above ranges, the optical function of the optical unit is further enhanced.
[0019]
It is preferable that the two minor axes on the elliptical surface of the microlens have substantially the same length. By making the two short axes of the microlenses approximately the same length in this way, the optical function of the optical unit is provided isotropically.
[0020]
The arrangement pattern of the micro lenses in the micro lens array is preferably a regular triangular lattice pattern or a random pattern. Since the equilateral triangular lattice pattern allows the microlenses to be arranged more densely, the filling rate of the microlens sheet is easily increased, and the optical functions such as light collection and diffusion are remarkably improved. In addition, by disposing the microlenses in a random pattern, the occurrence of moire in the optical unit is reduced.
[0021]
It is preferable to use a radiation curable resin or a thermoplastic resin as a material constituting the microlens array. According to the radiation-curable resin or the thermoplastic resin, a microlens array including the microlenses having the above-described shape can be easily and reliably formed.
[0022]
The optical sheet may have a sticking prevention layer in which beads are dispersed in a binder on the back surface. By providing the anti-sticking layer on the back surface, sticking between the optical sheet and the light guide plate, the prism sheet, and the like disposed on the back surface side is prevented.
[0023]
Therefore, in a backlight unit for a liquid crystal display device, which disperses light rays emitted from a lamp and guides the light rays to the front surface side, when the optical sheet having high optical functions such as condensing, diffusing, and changing angles is provided, energy efficiency is improved. In addition, the quality is improved by increasing the brightness in the front direction, making the brightness uniform, optimizing the viewing angle, and the like, and further reducing the number of optical sheets to promote thinning.
[0024]
Here, the “micro lens” is a concept including a convex lens and a concave lens. The “height (H)” is a vertical distance from the base surface of the micro lens to the top when the micro lens is a convex lens, and a vertical distance from the opening surface of the micro lens to the bottom when the micro lens is a concave lens. Means distance. “Filling rate” means the occupation ratio of microlenses per unit area in the surface projection shape of the microlens sheet. The “regular triangular lattice pattern” refers to a pattern in which the surface is divided into equilateral triangles having the same shape, and a microlens is provided at each vertex of the equilateral triangle. The cross-sectional shape of the “projecting prism portion” is not particularly limited, and includes, for example, various polygons such as a triangle, a quadrangle, and a pentagon, a waveform, and the like, in addition to a general right triangle.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic cross-sectional view showing an optical unit according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view showing an optical unit having a form different from that of FIG. 1, and FIGS. ) Is a schematic partial plan view and a schematic partial cross-sectional view showing a microlens sheet provided in the optical unit shown in FIGS. 1 and 2, and FIG. 4 is a schematic cross-sectional view showing a backlight unit provided with the optical unit shown in FIG. 5 is a schematic cross-sectional view showing a backlight unit including the optical unit of FIG. 2, and FIG. 6 is a schematic cross-sectional view showing an optical sheet having a different form from the optical sheet provided in the optical units of FIGS.
[0026]
The optical unit 1 of FIG. 1 includes a plurality of optical sheets to be superimposed. Specifically, the light diffusion sheet 3 and the light diffusion sheet 3 disposed on the back side (the light guide plate side of the backlight unit) are provided. And a microlens sheet 2 superposed on the front side of the microlens.
[0027]
As shown in FIGS. 3A and 3B, the microlens sheet 2 includes a sheet-shaped base layer 4 and a microlens array 5 provided on the surface of the base layer 4. The microlens sheet 2 has excellent optical functions such as light condensing, refraction to the normal direction side, and diffusion by the microlens array 5 on the surface.
[0028]
The base material layer 4 is formed of a transparent, particularly colorless and transparent synthetic resin because it is necessary to transmit light. The synthetic resin used for the base layer 4 is not particularly limited, and may be, for example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weatherable vinyl chloride, radiation-curable resin. And the like. Above all, a radiation curable resin such as an ultraviolet curable resin and an electron beam curable resin, and a thermoplastic resin such as polycarbonate and polyolefin, which are excellent in moldability of the microlens array 5, are preferable. Alternatively, a polyethylene terephthalate film, a polyethylene naphthalate film, or a polycarbonate film may be used as the base material layer 4, and the microlenses 6 may be formed thereon with an ultraviolet curable resin or the like.
[0029]
The thickness (average thickness) of the base layer 4 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 35 μm or more and 250 μm or less, and particularly preferably 50 μm or more and 188 μm or less. When the thickness of the base material layer 4 is less than the above range, inconveniences such as curling easily occurring when exposed to heat in a backlight unit and the like and difficulty in handling occur. Conversely, if the thickness of the base material layer 4 exceeds the above range, the brightness of the liquid crystal display device may decrease, and the thickness of the backlight unit increases, which is contrary to the demand for thinning the liquid crystal display device. It will be.
[0030]
The microlens array 5 includes a large number of microlenses 6 protruding from the surface of the base layer 4. The microlens array 5 may be formed integrally with the base layer 4 or may be formed separately from the base layer 4. The microlens array 5 is formed of a transparent, particularly colorless and transparent synthetic resin because it is necessary to transmit light rays. Specifically, the same synthetic resin as the base layer 4 is used.
[0031]
The base layer 4 and the microlens 6 may contain, for example, a filler, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like, in addition to the synthetic resin.
[0032]
The micro lens 6 has a partial shape of the elliptical surface 7. In the elliptical surface 7, the major axis 8 is located parallel to the normal direction of the microlens sheet 2, and the minor axis 9 and the minor axis 10 are located parallel to the plane direction of the microlens sheet 2. As described above, by forming the microlens 6 into an upper part shape of the elliptical surface 7 whose major axis 8 is parallel to the normal direction, the spherical aberration of the microlens 6 is reduced, and the light collecting function of the microlens sheet 2 is improved. Optical functions such as a diffusion function and a deflection function are enhanced.
[0033]
The microlenses 6 are disposed relatively densely and geometrically on the surface of the base material layer 4. Specifically, the microlenses 6 are arranged on the surface of the base material layer 4 in a regular triangular lattice pattern. Therefore, the pitch of the microlenses 6 and the distance between the lenses are all constant. With this arrangement pattern, the microlenses 6 can be arranged most densely, and the optical functions of the microlens sheet 2 such as the condensing function, the diffusing function, and the angle changing function can be improved.
[0034]
The major axis radius (R) of the elliptical surface 7 at the height (H) of the microlens 6 _L ) To the height ratio (H / R) _L ) Is preferably 以上 or more and 1 or less. Height ratio of micro lens 6 (H / R _L ) Within the above range, the lens-like refraction effect of the microlens 6 is effectively exerted, and the optical function of the microlens sheet 2 such as condensing, diffusing, and changing the angle is combined with the reduction of the spherical aberration. Is significantly improved.
[0035]
The major axis radius (R _L ) Minor axis radius (R _S ) To the flat ratio (R _L / R _S The lower limit of () is preferably 1.05. On the other hand, the flattening ratio (R _L / R _S The upper limit of () is preferably 1.7, and particularly preferably 1.5. Here, "the minor axis radius (R _S ) "Means the radius (R _S1 ) And the radius of the short axis 10 (R _S2 ) And the average value. The microlens 6 has an aspect ratio (R _L / R _S ) Is in the above range, the spherical aberration is remarkably reduced, and the optical functions of the microlens sheet 2 such as condensing, diffusing, and changing the angle are remarkably improved.
[0036]
The major axis radius (R _L The lower limit of ()) is preferably 10 μm, particularly preferably 30 μm. On the other hand, the major axis radius (R _L The upper limit of ()) is preferably 1000 μm, particularly preferably 400 μm. The major axis radius (R) of the elliptical surface 7 constituting the microlens 6 _L If) is smaller than the above range, the influence of diffraction becomes large, and optical performance and color separation are liable to occur, resulting in quality deterioration. On the other hand, the major axis radius (R _L When the value (1) exceeds the above range, luminance unevenness is apt to occur, and similarly, the quality is lowered.
[0037]
The lower limit of the filling rate of the microlenses 6 is preferably 40%, particularly preferably 60%, and particularly preferably 70%. By setting the filling ratio of the microlenses 6 to the lower limit or more as described above, the area occupied by the microlenses 6 on the surface of the microlens sheet 2 is increased, and the optical functions of the microlens sheet 2 such as light collection and diffusion are improved. It is greatly improved.
[0038]
The upper limit of the surface roughness (Ra) of the microlens 6 is preferably 2 μm, particularly 0.5 μm, and more preferably 0.1 μm. On the other hand, the lower limit of the surface roughness (Ra) of the microlens 6 is preferably 0.005 μm, particularly preferably 0.01 μm. By setting the surface roughness (Ra) of the microlens 6 in the above range, a reduction in lens-like optical action due to irregular reflection or irregular refraction on the surface of the microlens 6 is reduced, and light collection, diffusion, An optical function such as a deflection angle is effectively exerted. If the surface roughness (Ra) of the microlens 6 is made relatively small within the above range, the optical functions of the microlens sheet 2 such as condensing and changing the angle become large. On the other hand, when the surface roughness (Ra) of the microlens 6 is increased within the above range, the light diffusion function of the microlens sheet 2 increases.
[0039]
The lower limit of the refractive index of the material constituting the microlens array 5 is preferably 1.3, and particularly preferably 1.45. On the other hand, the upper limit of the refractive index of this material is preferably 1.8, and particularly preferably 1.6. Within this range, the refractive index of the material constituting the microlens array 5 is most preferably 1.5. By setting the refractive index of the material constituting the microlens array 5 in the above range, the lens-like refraction effect of the microlens 6 is effectively exerted, and the microlens sheet 2 is focused on light such as condensing and diffusing. Objective function is further enhanced.
[0040]
The radius (R) of the short axis 9 on the elliptical surface 7 of the microlens 6 _S1 ) And the radius of the short axis 10 (R _S2 ) Should be approximately the same length. By forming the microlens 6 from the elliptical surface 7 having the two minor axes having substantially the same length, the optical sheet has an isotropic optical function such as light collection.
[0041]
The microlens sheet 2 has excellent optical functions such as condensing, diffusing, and changing angles due to the microlenses 6 having a small spherical aberration as described above. The microlens sheet 2 has a height ratio (H / R) of the microlenses 6 constituting the microlens array 5. _L ), Aspect ratio (R _L / R _S ), Major axis radius (R _L ), The optical function is easily and reliably controlled by adjusting the filling rate and the like. Further, in the microlens sheet 2, by adjusting the height (H) of the microlenses 6 to be constant, stress concentration is suppressed, and damage to other members to be stacked is prevented.
[0042]
The method for manufacturing the microlens sheet 2 is not particularly limited as long as the above structure can be formed, and various methods are adopted. As a method of manufacturing the microlens sheet 2, a method of separately forming the microlens array 5 after forming the base layer 4 and a method of integrally forming the base layer 4 and the microlens array 5 are possible. ,In particular,
(A) a method of forming a microlens sheet 2 by laminating a synthetic resin on a sheet mold having an inverted shape of the surface of the microlens array 5 and peeling off the sheet mold;
(B) an injection molding method of injecting a molten resin into a mold having an inverted shape on the surface of the microlens array 5;
(C) a method of transferring the shape by reheating the sheeted resin, pressing between a mold and a metal plate as described above, and pressing the same;
(D) an extruded sheet molding method in which a molten resin is passed through a nip between a roll mold having a reverse shape of the surface of the microlens array 5 on the peripheral surface and another roll, and the shape is transferred.
(E) A UV curable resin is applied to the base material layer, pressed onto a sheet mold, a mold or a roll mold having the same inverted shape as above to transfer the shape to the uncured UV curable resin, Method to cure the ultraviolet curing resin
(F) A mold or roll mold having the same inverted shape as described above is filled and coated with an uncured UV-curable resin, pressed and leveled by a base material layer, and irradiated with UV rays to cure the UV-curable resin. Method,
(G) a method of injecting or discharging an uncured (liquid) ultraviolet curable resin or the like from a fine nozzle onto a sheet substrate and curing the resin;
(H) Method of using electron beam-curable resin instead of ultraviolet-curable resin
and so on.
[0043]
As a method of manufacturing a mold having a reverse shape of the microlens array 5, for example, a spot-shaped three-dimensional pattern is formed on a base material using a photoresist material, and the three-dimensional pattern is curved by heating and fluidizing. Then, a microlens array model is produced, a metal layer is laminated on the surface of the microlens array model by an electroforming method, and the metal layer is peeled off. In addition, as a method for manufacturing the microlens array model, the method described in (g) above can be employed.
[0044]
According to the above manufacturing method, the microlens array 5 having an arbitrary shape is easily and reliably formed. Therefore, the height ratio (H / R) of the microlenses 6 constituting the microlens array 5 _L ), Aspect ratio (R _L / R _S ), Major axis radius (R _L ), The filling rate, the arrangement pattern, and the like are easily and reliably adjusted, and as a result, the optical function of the microlens sheet 2 is easily and reliably controlled.
[0045]
The light diffusion sheet 3 includes a base layer 11 and a light diffusion layer 12 laminated on the surface of the base layer 11. The material, thickness, and the like of the base layer 11 are the same as those of the base layer 4 of the microlens sheet 2.
[0046]
The light diffusing layer 12 includes a binder 13 and a light diffusing agent 14 contained in the binder 13. The light diffusing agent 14 contained in the light diffusing layer 12 can uniformly diffuse the light transmitted through the light diffusing layer 12 from the back side to the front side. Further, fine irregularities are formed substantially uniformly on the surface of the light diffusion layer 12 by the light diffusion agent 14. The fine irregularities formed on the surface of the light diffusion sheet 3 can diffuse the light rays better. The thickness of the light diffusion layer 12 (meaning the thickness of the binder 13 excluding the light diffusion agent 14) is not particularly limited, but is, for example, about 1 μm or more and 30 μm or less. Further, since the binder 13 needs to transmit light, the binder 13 is transparent, and particularly preferably colorless and transparent.
[0047]
The light diffusing agent 14 is a particle having a property of diffusing light rays, and is roughly classified into an inorganic filler and an organic filler. Specifically, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or a mixture thereof can be used as the inorganic filler. Specific examples of the material of the organic filler include acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, and polyamide. Among them, acrylic resins having high transparency are preferable, and polymethyl methacrylate (PMMA) is particularly preferable.
[0048]
The shape of the light diffusing agent 14 is not particularly limited, and examples thereof include a sphere, a cube, a needle, a rod, a spindle, a plate, a scale, and a fiber. Are preferred.
[0049]
The lower limit of the average particle diameter of the light diffusing agent 14 is preferably 1 μm, particularly 2 μm, more preferably 5 μm, and the upper limit of the average particle diameter of the light diffusing agent 14 is preferably 50 μm, particularly 20 μm, and more preferably 15 μm. If the average particle diameter of the light diffusing agent 14 is less than the above range, the unevenness of the surface of the light diffusing layer 12 formed by the light diffusing agent 14 becomes small, and the light diffusing property required for the light diffusing sheet is not satisfied. Conversely, if the average particle diameter of the light diffusing agent 14 exceeds the above range, the thickness of the light diffusing sheet 3 increases, and uniform diffusion becomes difficult.
[0050]
The lower limit of the blending amount of the light diffusing agent 14 (the blending amount in terms of solid content with respect to 100 parts of the base polymer in the polymer composition as the material for forming the binder 13) is preferably 10 parts, particularly 20 parts, and more preferably 50 parts. . On the other hand, the upper limit of the amount is preferably 500 parts, particularly 300 parts, and more preferably 200 parts. If the amount of the light diffusing agent 14 is less than the above range, the light diffusing property becomes insufficient, while if the amount of the light diffusing agent 14 exceeds the above range, the light diffusing agent 14 is fixed. This is because the effect of doing so is reduced.
[0051]
The binder 13 is formed by crosslinking and curing a polymer composition containing a base polymer. The light diffusing agent 14 is arranged and fixed at substantially equal density over the entire surface of the base material layer 11 by the binder 13. The polymer composition for forming the binder 13 may further include, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, an ultraviolet absorber, an antioxidant, a viscosity modifier, A lubricant, a light stabilizer and the like may be appropriately compounded.
[0052]
The base polymer is not particularly limited, and examples thereof include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamide imides, epoxy resins, and ultraviolet curable resins. Can be used alone or in combination of two or more. In particular, as the base polymer, a polyol having high processability and capable of easily forming the light diffusion layer 12 by means such as coating is preferable. Further, the base polymer used for the binder 13 is transparent because it is necessary to transmit light, and is preferably colorless and transparent.
[0053]
Examples of the polyol include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, and a polyester polyol obtained under the condition of an excess of hydroxyl groups. These may be used alone or in combination of two or more. Can be used.
[0054]
Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, homoallyl alcohol, Hydroxyl group-containing unsaturated monomers such as cinnamon alcohol and crotonyl alcohol; (b) for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4-bis (hydroxymethyl) cyclohexane, phenyl A dihydric alcohol or an epoxy compound such as glycidyl ether, glycidyl decanoate, or Praxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.), for example, acrylic acid, methacrylic acid, maleic acid, or fumaric acid Crotonic acid, and the like react with the resulting hydroxyl group-containing unsaturated monomer with an unsaturated carboxylic acid such as itaconic acid. One or more selected from these hydroxyl-containing unsaturated monomers can be polymerized to produce a polyol.
[0055]
Also, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethylhexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-methacrylate Butyl, tert-butyl methacrylate, ethylhexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyl toluene, 1-methylstyrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, acetic acid Allyl, diallyl adipate, diallyl itaconate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylolacrylamide, N-butoxymethylacryl One or more ethylenically unsaturated monomers selected from amide, diacetone acrylamide, ethylene, propylene, isoprene and the like, and a hydroxyl-containing unsaturated monomer selected from the above (a) and (b) A polyol can also be produced by polymerizing the polymer.
[0056]
The number average molecular weight of a polyol obtained by polymerizing a monomer component containing such a hydroxyl group-containing unsaturated monomer is from 1,000 to 500,000, preferably from 5,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 150 or less.
[0057]
Polyester polyols obtained under the condition of excess hydroxyl groups include (c), for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl Glycol, hexamethylene glycol, decamethylene glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, hexanetriol, glycerin, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis (hydroxymethyl) Polyhydric alcohols such as cyclohexane, hydroquinone bis (hydroxyethyl ether), tris (hydroxyethyl) isocinurate and xylylene glycol; and (d) maleic And polybasic acids such as fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimetic acid, terephthalic acid, phthalic acid, and isophthalic acid; and propanediol, hexanediol, polyethylene glycol, and trimethylolpropane. It can be produced by reacting under conditions where the number of hydroxyl groups in the polyhydric alcohol is larger than the number of carboxyl groups of the polybasic acid.
[0058]
The number average molecular weight of the polyester polyol obtained under such hydroxyl group excess conditions is from 500 to 300,000, preferably from 2,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 150 or less.
[0059]
The polyol used as the base polymer of the polymer composition is obtained by polymerizing the above-mentioned polyester polyol and a monomer component containing the above-mentioned hydroxyl group-containing unsaturated monomer, and (meth) acrylic unit. Is preferred. The binder 13 using such a polyester polyol or an acrylic polyol as a base polymer has high weather resistance and can suppress yellowing and the like of the light diffusion layer 12. Note that either one of the polyester polyol and the acrylic polyol may be used, or both may be used.
[0060]
The number of hydroxyl groups in the polyester polyol and acrylic polyol is not particularly limited as long as it is 2 or more per molecule, but when the hydroxyl value in the solid content is 10 or less, the number of crosslinking points decreases, and the solvent resistance is reduced. In addition, the coating properties such as water resistance, heat resistance, and surface hardness tend to decrease.
[0061]
The polymer composition may contain a fine inorganic filler. By containing the fine inorganic filler in the binder 13, the heat resistance of the light diffusion layer 12 and thus the light diffusion sheet 3 is improved. The inorganic substance constituting the fine inorganic filler is not particularly limited, and an inorganic oxide is preferable. This inorganic oxide is defined as various oxygen-containing metal compounds in which a metal element mainly forms a three-dimensional network through a bond with an oxygen atom. Further, as the metal element constituting the inorganic oxide, for example, an element selected from Groups II to VI of the Periodic Table of the Elements is preferable, and an element selected from Groups III to V of the Periodic Table of the Elements is more preferable. Among them, an element selected from Si, Al, Ti and Zr is particularly preferable, and colloidal silica in which the metal element is Si is most preferable as the fine inorganic filler in view of the heat resistance improving effect and the uniform dispersibility. The shape of the fine inorganic filler may be any particle shape such as a sphere, a needle, a plate, a scale, and a crushed shape, and is not particularly limited.
[0062]
The lower limit of the average particle size of the fine inorganic filler is preferably 5 nm, particularly preferably 10 nm. On the other hand, the upper limit of the average particle diameter of the fine inorganic filler is preferably 50 nm, particularly preferably 25 nm. This is because when the average particle diameter of the fine inorganic filler is less than the above range, the surface energy of the fine inorganic filler is increased, and aggregation or the like is likely to occur.Conversely, when the average particle diameter exceeds the above range, This is because the light diffusion sheet 3 becomes cloudy due to the influence of the short wavelength, and the transparency of the light diffusion sheet 3 cannot be completely maintained.
[0063]
The lower limit of the amount of the fine inorganic filler relative to 100 parts of the base polymer (the amount of the inorganic component alone) is preferably 5 parts in terms of solids, and particularly preferably 50 parts. On the other hand, the upper limit of the amount of the fine inorganic filler is preferably 500 parts, more preferably 200 parts, and particularly preferably 100 parts. If the amount of the fine inorganic filler is less than the above range, the heat resistance of the light diffusion sheet 3 may not be sufficiently exhibited, and conversely, the amount exceeds the above range. This is because compounding into the polymer composition becomes difficult, and the light transmittance of the light diffusion layer 12 may be reduced.
[0064]
As the fine inorganic filler, a material having an organic polymer fixed on its surface is preferably used. By using the organic polymer-fixed fine inorganic filler as described above, the dispersibility in the binder 13 and the affinity with the binder 13 are improved. This organic polymer is not particularly limited with respect to its molecular weight, shape, composition, presence or absence of a functional group and the like, and any organic polymer can be used. Regarding the shape of the organic polymer, any shape such as a linear, branched, or crosslinked structure can be used.
[0065]
Specific resins constituting such an organic polymer include, for example, (meth) acrylic resin, polystyrene, polyvinyl acetate, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyvinylidene chloride, polyesters such as polyethylene terephthalate and the like. Examples include copolymers and resins partially modified with functional groups such as amino groups, epoxy groups, hydroxyl groups, and carboxyl groups. Among them, those having an organic polymer containing a (meth) acrylic unit as an essential component such as a (meth) acrylic resin, a (meth) acryl-styrene resin, and a (meth) acryl-polyester resin have a film forming ability. It is suitable. On the other hand, a resin having compatibility with the base polymer of the polymer composition is preferable, and therefore, a resin having the same composition as the base polymer contained in the polymer composition is most preferable.
[0066]
In addition, the fine inorganic filler may include an organic polymer in the fine particles. This makes it possible to impart appropriate softness and toughness to the inorganic substance as the core of the fine inorganic filler.
[0067]
The organic polymer preferably contains an alkoxy group, and the content thereof is preferably 0.01 mmol or more and 50 mmol or less per 1 g of the fine inorganic filler to which the organic polymer is fixed. By such an alkoxy group, affinity with a matrix resin constituting the binder 13 and dispersibility in the binder 13 can be improved.
[0068]
Here, the alkoxy group refers to an RO group bonded to a metal element forming the skeleton of the fine particles. R is an alkyl group which may be substituted, and the RO groups in the fine particles may be the same or different. Specific examples of R include methyl, ethyl, n-propyl, isopropyl, n-butyl and the like. It is preferable to use the same metal alkoxy group as the metal constituting the fine inorganic filler. When the fine inorganic filler is colloidal silica, it is preferable to use an alkoxy group containing silicon as a metal.
[0069]
The content of the organic polymer in the fine inorganic filler to which the organic polymer is fixed is not particularly limited, but is preferably 0.5% by mass or more and 50% by mass or less based on the fine inorganic filler.
[0070]
As described above, a polymer having a hydroxyl group is used as the organic polymer fixed to the fine inorganic filler, and a polyfunctional isocyanate compound having two or more functional groups that react with the hydroxyl group in the polymer composition constituting the binder 13, melamine It is preferable to contain at least one selected from a compound and an aminoplast resin. Thereby, the fine inorganic filler and the matrix resin of the binder 13 are bonded in a cross-linked structure, and the storage stability, stain resistance, flexibility, weather resistance, storage stability, and the like are improved, and the obtained coating film is further improved. It becomes glossy.
[0071]
Examples of the polyfunctional isocyanate compound include aliphatic, alicyclic, aromatic and other polyfunctional isocyanate compounds and modified compounds thereof. Specific examples of the polyfunctional isocyanate compound include, for example, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, 2,2,4-trimethylhexylmethane diisocyanate, methylcyclohexane diisocyanate, 1,6 A trimer such as a biuret or isocyanurate of hexamethylene diisocyanate; and 2 formed by the reaction of these polyfunctional isocyanates with polyhydric alcohols such as propanediol, hexanediol, polyethylene glycol and trimethylolpropane. Compounds in which at least two isocyanate groups remain; these polyfunctional isocyanate compounds are Choles, compounds having a phenolic hydroxyl group such as phenol and cresol, acetoximes, oximes such as methyl ethyl ketoxime, ε-caprolactam, blocked polyfunctional isocyanate compounds blocked with a lactam such as γ-caprolactam and the like. Can be mentioned. In addition, the said polyfunctional isocyanate compound can be used individually by 1 type or in mixture of 2 or more types. Among them, a non-yellowing polyfunctional isocyanate compound having no isocyanate group directly bonded to an aromatic ring is preferable in order to prevent yellowing of the coating.
[0072]
Examples of the melamine compound include dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine, isobutyl ether melamine, n-butyl ether melamine, and butylated benzoguanamine.
[0073]
Examples of the aminoplast resin include an alkyl etherified melamine resin, a urea resin, a benzoguanamine resin, and the like. These aminoplast resins can be used alone or as a mixture or cocondensate of two or more. The alkyl etherified melamine resin is obtained by methylolating an aminotriazine and alkyl etherifying it with cyclohexanol or an alkanol having 1 to 6 carbon atoms. Resin is a typical one. Further, a sulfonic acid-based catalyst for accelerating curing, for example, paratoluenesulfonic acid and its amine salt can be used.
[0074]
As the base polymer, a polyol having a cycloalkyl group is preferable. As described above, by introducing a cycloalkyl group into the base polymer (polyol) constituting the binder 13, the hydrophobicity such as the water repellency and the water resistance of the binder 13 is increased, and the binder 13 under the conditions of high temperature and high humidity is obtained. The deflection resistance, dimensional stability, and the like of the light diffusion sheet 3 are improved. In addition, the basic properties of the coating film such as the hardness, weather resistance, texture, and solvent resistance of the light diffusion layer 12 are improved. Further, the affinity with the fine inorganic filler having the organic polymer fixed on the surface and the uniform dispersibility of the fine inorganic filler are further improved.
[0075]
The cycloalkyl group is not particularly limited, for example, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, cycloundecyl group, cyclododecyl group, cyclotridecyl group, Examples include a cyclotetradecyl group, a cyclopentadecyl group, a cyclohexadecyl group, a cycloheptadecyl group, and a cyclooctadecyl group.
[0076]
The polyol having a cycloalkyl group is obtained by copolymerizing a polymerizable unsaturated monomer having a cycloalkyl group. The polymerizable unsaturated monomer having a cycloalkyl group is a polymerizable unsaturated monomer having at least one cycloalkyl group in a molecule. The polymerizable unsaturated monomer is not particularly limited, and includes, for example, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, and the like.
[0077]
Further, the polymer composition preferably contains an isocyanate as a curing agent. By including the isocyanate in the polymer composition in this manner, a stronger crosslinked structure is obtained, and the physical properties of the light diffusion layer 12 are further improved. As this isocyanate, the same substance as the above-mentioned polyfunctional isocyanate compound is used. Among them, aliphatic isocyanates that prevent yellowing of the coating film are preferred.
[0078]
In particular, when a polyol is used as the base polymer, one or more of hexamethylene diisocyanate, isofuron diisocyanate, and xylene diisocyanate may be used as a curing agent to be mixed into the polymer composition. When these curing agents are used, the curing reaction speed of the polymer composition increases, so that even if a cationic one that contributes to the dispersion stability of the fine inorganic filler is used as the antistatic agent, the cationic antistatic agent can be used. Can sufficiently compensate for the decrease in the curing reaction rate. Further, the improvement in the curing reaction rate of the polymer composition contributes to the uniform dispersibility of the fine inorganic filler in the binder. As a result, the light diffusion sheet can remarkably suppress bending and yellowing due to heat, ultraviolet light, and the like.
[0079]
Further, an antistatic agent may be kneaded in the polymer composition. By forming the binder 13 from the polymer composition in which the antistatic agent is kneaded in this manner, an antistatic effect is exerted on the light diffusion sheet 3, making it difficult to attract dust and to overlap with a prism sheet or the like. It is possible to prevent inconveniences caused by electrostatic charging such as becoming. In addition, when the surface is coated with an antistatic agent, stickiness and turbidity of the surface are caused, but such adverse effects are reduced by kneading the polymer composition in such a manner. The antistatic agent is not particularly limited. For example, anionic antistatic agents such as alkyl sulfates and alkyl phosphates, quaternary ammonium salts, cationic antistatic agents such as imidazoline compounds, polyethylene glycol-based Nonionic antistatic agents such as polyoxyethylene sorbitan monostearate and ethanolamide, and high molecular antistatic agents such as polyacrylic acid are used. Among them, a cationic antistatic agent having a relatively large antistatic effect is preferable, and an antistatic effect can be obtained by adding a small amount.
[0080]
Next, a method for manufacturing the light diffusion sheet 3 will be described. The method for manufacturing the light diffusion sheet 3 includes: (a) a step of manufacturing a coating solution for a light diffusion layer by mixing a light diffusion agent 14 with a polymer composition constituting the binder 13; Applying the layer coating liquid to the surface of the base material layer 11 to laminate the light diffusion layer 12.
[0081]
The light diffusing sheet 3 has a high light diffusing function due to reflection and refraction at the interface of the light diffusing agent 14 and refraction at fine irregularities formed on the surface of the light diffusing layer 12. It has a refracting function toward the normal direction.
[0082]
In the optical unit 1, optical functions such as light condensing, refraction in the normal direction, and diffusion are significantly improved by the microlens sheet 2, and moire and glare are provided by the light diffusion sheet 3 having an excellent light diffusion function. In addition, the occurrence of uneven brightness and the like is reduced, and the quality is improved. The optical unit 1 has a height ratio (H / R) of the microlenses 6 of the microlens sheet 2. _L ), Aspect ratio (R _L / R _S ), Major axis radius (R _L The optical function is easily and reliably controlled by adjusting the filling rate, the arrangement pattern, and the like. Further, in the optical unit 1, by adjusting the height (H) of the microlenses 6 of the microlens sheet 2 to be constant, stress concentration is suppressed, and damage to other superimposed members is prevented.
[0083]
The edge light type backlight unit shown in FIG. 4 includes a light guide plate 15 and a pair of linear lamps 16 arranged on the opposite sides of the light guide plate 15. The optical units 1 are arranged in an overlapping manner. The light emitted from the lamp 16 and emitted from the surface of the light guide plate 15 has a relatively strong peak inclined at a predetermined angle with respect to the normal direction. The front luminance is remarkably enhanced by the optical unit 1 having a function, a function of changing the angle to the normal direction side, and the like, and has an appropriate viewing angle. Further, in the backlight unit, emitted light is more uniformly diffused by the light diffusion sheet, and unevenness of brightness, glare, and the like are prevented. Therefore, according to the backlight unit, the number of optical sheets conventionally required can be reduced, and the backlight unit can be made thinner, the brightness can be improved, and the cost can be reduced. The edge light type backlight unit may be equipped with four or six lamps 16.
[0084]
The optical unit 17 of FIG. 2 includes a plurality of optical sheets to be superimposed. Specifically, the micro lens sheet 2 and the micro lens sheet 2 disposed on the back side (the light guide plate side of the backlight unit) And a prism sheet 18 superimposed on the front side of the prism sheet. Since the microlens sheet 2 is the same as the optical sheet 1, the same reference numerals are given and the description is omitted.
[0085]
The prism sheet 18 includes a sheet-shaped base layer 19 and a plurality of ridged prism portions 20 formed in a stripe shape (parallel and at equal intervals) on the surface of the base layer 19. The prism sheet 18 has a high refraction function toward the normal direction due to a plurality of ridge prism portions 20 having a stripe shape on the surface. The base layer 19 is the same as the base layer 4 of the microlens sheet 2.
[0086]
The ridge prism section 20 is formed of a transparent, particularly colorless and transparent synthetic resin because it is necessary to transmit light rays. Specifically, the same synthetic resin as that of the base layer 4 is used. Further, similarly to the microlens array 5, the lower limit of the refractive index of the material constituting the ridge prism portion 20 is preferably 1.3, particularly 1.45, and the upper limit thereof is 1.8, particularly 1.6. Is preferred.
[0087]
The ridge prism portion 20 is a triangular prism having one side surface (bottom surface) in contact with the surface of the base material layer 19. The cross-sectional shape of the ridge prism section 20 is generally a right-angled isosceles triangle having a vertical angle α of 90 ° and a base angle β of 45 °.
[0088]
The lower limit of the width (W) of the bottom surface of the ridge prism portion 20 is preferably 10 μm, and particularly preferably 30 μm. On the other hand, the upper limit of the width (W) is preferably 1000 μm, particularly preferably 400 μm. This is because if the width (W) of the bottom surface of the ridge prism portion 20 is smaller than the lower limit, it is difficult to form the ridge prism portion 20, and conversely, the width (W) of the bottom surface of the ridge prism portion 20 is small. If the upper limit is exceeded, glare and uneven brightness may occur.
[0089]
The method of manufacturing the prism sheet 18 is not particularly limited as long as the prism sheet 18 can be formed as described above. And a method of integrally molding the stripe prism portion 20. Specifically,
(A) a method of forming a prism sheet 18 by laminating a synthetic resin on a sheet mold having an inverted shape of the surface of the prism sheet 18 and peeling off the sheet mold;
(B) an injection molding method of injecting a molten resin into a mold having an inverted shape on the surface of the prism sheet 18;
(C) a method of transferring the shape by reheating the sheeted resin, pressing between a mold and a metal plate as described above, and pressing the same;
(D) an extruded sheet molding method in which a molten resin is passed through a nip between a roll mold having an inverted shape of the surface of the prism sheet 18 on the peripheral surface and another roll to transfer the shape,
(E) A UV curable resin is applied to the base material layer, pressed onto a sheet mold, a mold or a roll mold having the same inverted shape as above to transfer the shape to the uncured UV curable resin, Method to cure the ultraviolet curing resin
(F) A mold or roll mold having the same inverted shape as described above is filled and coated with an uncured UV-curable resin, pressed and leveled by a base material layer, and irradiated with UV rays to cure the UV-curable resin. Method,
(G) Method of using electron beam-curable resin instead of ultraviolet-curable resin
and so on.
[0090]
In the optical unit 17, optical functions such as condensing, refraction to the normal direction, and diffusion are improved by the microlens sheet 2, and refraction to the normal direction is significantly improved by the prism sheet 18. . The optical unit 17 has a height ratio (H / R) of the microlens 6 similar to the optical unit 1. _L ), Aspect ratio (R _L / R _S ), Major axis radius (R _L ), Since the optical function can be easily and reliably controlled by adjusting the filling rate, the arrangement pattern, and the like, the peak direction of the incident light beam on the prism sheet 18 is set to an optimum tilt angle for refraction toward the normal direction. As a result, the emitted light can be more effectively guided toward the normal direction. Further, similarly to the optical unit 1, the optical unit 17 regulates the height (D) of the microlenses 6 of the microlens sheet 2 to be constant, thereby suppressing stress concentration and overlapping the prism sheet 18 to be superimposed. Is prevented from being scratched or from being hurt to another member to be stacked.
[0091]
The edge light type backlight unit shown in FIG. 5 includes a light guide plate 15 and a pair of linear lamps 16 arranged on the opposite sides of the light guide plate 15. The optical units 17 are arranged in an overlapping manner. The light emitted from the lamp 16 and emitted from the surface of the light guide plate 15 has a relatively strong peak inclined at a predetermined angle with respect to the normal direction. The front luminance is remarkably increased by the optical unit 17 having a function and the like, in particular, having a function of changing the angle to the high normal direction side. Therefore, according to the backlight unit, the number of optical sheets conventionally required can be reduced, and the backlight unit can be made thinner, the brightness can be improved, and the cost can be reduced. The edge light type backlight unit may be equipped with four or six lamps 16.
[0092]
The optical sheet 21 in FIG. 6 is a microlens sheet, a light diffusion sheet, a prism sheet, or the like, and includes an optical sheet main body 22 and a sticking prevention layer 23 laminated on the back surface of the optical sheet main body 22. The optical sheet main body 22 has the same structure as the micro lens sheet 2, the light diffusion sheet 3, the prism sheet 18, and the like.
[0093]
The anti-sticking layer 23 includes a binder 24 and beads 25 dispersed in the binder 24. The binder 24 is formed by crosslinking and curing the same polymer composition as the binder 13 of the light diffusion layer 12. The same beads 25 as the light diffusing agent 14 of the light diffusing layer 12 are used. The thickness of the anti-sticking layer 23 (the thickness of the binder 24 excluding the beads 25) is not particularly limited, but is, for example, about 1 μm or more and 10 μm or less.
[0094]
The blending amount of the beads 25 is relatively small. The beads 25 are separated from each other and dispersed in the binder 24, and most of the beads 25 have their lower ends projecting a very small amount from the binder 24. Therefore, when the optical sheet 21 is laminated on the light guide plate, the lower ends of the protruding beads 25 contact the surface of the light guide plate or the like, and the entire back surface of the optical sheet 21 does not contact the light guide plate or the like. Thereby, sticking between the optical sheet 21 and the light guide plate or the like is prevented, and uneven brightness on the screen of the liquid crystal display device is suppressed.
[0095]
Note that the anti-sticking layer 23 is formed of an optical sheet (for example, the light diffusion sheet 3 in the case of the optical unit 1 in FIG. 1 and a microlens sheet in the case of the optical unit 17 in FIG. 2) superposed on the light guide plate in the backlight unit. It is good to laminate on the back surface of 2). Thereby, sticking between the optical sheet 21 and the light guide plate is prevented.
[0096]
The method of forming the anti-sticking layer 23 includes, for example, (a) a step of producing a coating solution for the anti-sticking layer by mixing beads 25 with a polymer composition constituting the binder 24; Applying a layer coating liquid to the back surface of the optical sheet body 22 to laminate the anti-sticking layer 23.
[0097]
The optical unit of the present invention is not limited to the above embodiment. For example, for example, (a) an optical unit in which a light diffusion sheet is superimposed on the front side of a microlens sheet, and (b) an optical unit in which the front side of a prism sheet is disposed An optical unit on which a microlens sheet is superimposed; (c) an optical unit including two or more optical sheets used in addition to the above embodiment; (d) an optical unit including another optical sheet in addition to the above embodiment; Is also possible. In the optical unit (a), the occurrence of moire, glare, uneven brightness and the like is reduced by the high light diffusion function of the light diffusion sheet on the front surface side, and the quality is improved. The optical unit (b) has a light-collecting function, a refracting function toward the normal direction, a diffusing function, and the like, with high and well-balanced by the microlens sheet on the front side. Further, the protruding ridge prism section is not limited to the above-described triangular prism having a right triangular cross-section, but may be, for example, various polygons such as a quadrangle or a pentagon or a waveform.
[0098]
【The invention's effect】
As described above, according to the optical unit of the present invention, light collection, refraction to the normal direction side, optical functions such as diffusion are extremely high, the control of the optical functions is easy and reliable, Damage to the optical sheet and damage to other members are suppressed. Further, according to the backlight unit using the optical unit, quality improvement such as higher luminance in the front direction and uniform luminance is promoted.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an optical unit according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing an optical unit according to a mode different from the optical unit of FIG.
FIGS. 3A and 3B are a schematic partial plan view and a schematic partial cross-sectional view showing a microlens sheet provided in the optical unit shown in FIGS. 1 and 2. FIG.
FIG. 4 is a schematic sectional view showing an edge light type backlight unit including the optical unit of FIG. 1;
FIG. 5 is a schematic sectional view showing an edge light type backlight unit including the optical unit of FIG. 2;
FIG. 6 is a schematic cross-sectional view showing an optical sheet different from the optical sheet provided in the optical unit shown in FIGS. 1 and 2;
FIG. 7A is a schematic perspective view showing a conventional general edge light type backlight unit. (B) is a schematic sectional view showing a conventional light diffusion sheet.
[Explanation of symbols]
1 Optical unit
2 Micro lens sheet
3 Light diffusion sheet
4 Base material layer
5 Micro lens array
6 micro lens
7 Ellipsoid
8 Long axis
9 short axis
10 short axis
11 Base material layer
12 Light diffusion layer
13 binder
14 Light diffuser
15 Light guide plate
16 lamps
17 Optical unit
18 Prism sheet
19 Base material layer
20 Prism section
21 Optical sheet
22 Optical sheet body
23 Sticking prevention layer
24 binder
25 beads

Claims (16)

It comprises a plurality of optical sheets to be superimposed, a microlens sheet is used as this optical sheet,
This microlens sheet has a microlens array composed of a plurality of microlenses on its surface,
An optical unit in which the microlens has a partial shape of an elliptical surface with its long axis directed in the normal direction. A light diffusion sheet is further used as the optical sheet,
The optical unit according to claim 1, wherein the light diffusion sheet includes a base layer and a light diffusion layer containing a light diffusion agent in a binder. The optical unit according to claim 2, wherein a microlens sheet is superimposed on a surface side of the light diffusion sheet. A prism sheet is further used as the optical sheet,
The optical unit according to claim 1, wherein the prism sheet includes a plurality of ridge prism portions in a stripe shape on a surface. The optical unit according to claim 4, wherein a prism sheet is superimposed on a front side of the microlens sheet. The height ratio (H / R _L ) to the major axis radius (R _L ) of the height (H) of the microlens is 3/4 or more and 1 or less. 6. Optical sheet. The flat ratio (R _L / R _S ) of the long axis radius (R _L ) to the short axis radius (R _S ) of the microlens is 1.05 or more and 1.7 or less. Item 2. The optical sheet according to item 1. The optical sheet according to claim 1, wherein a major axis radius (R _L ) of the microlens is 10 μm or more and 1000 μm or less. The optical sheet according to any one of claims 1 to 8, wherein a filling factor of the microlens is 40% or more. The optical sheet according to any one of claims 1 to 9, wherein the microlens has a surface roughness (Ra) of 2 µm or less. The optical sheet according to any one of claims 1 to 10, wherein a material constituting the microlens array has a refractive index of 1.3 or more and 1.8 or less. The optical sheet according to any one of claims 1 to 11, wherein an arrangement pattern of the micro lenses in the micro lens array is an equilateral triangular lattice pattern or a random pattern. The optical sheet according to any one of claims 1 to 12, wherein two minor axes on the elliptical surface of the microlens have substantially the same length. The optical sheet according to any one of claims 1 to 13, wherein a radiation curable resin or a thermoplastic resin is used as a material forming the microlens array. The optical sheet according to any one of claims 1 to 14, further comprising a sticking prevention layer in which beads are dispersed in a binder, on a back surface of the optical sheet. In a backlight unit for a liquid crystal display device, which disperses a light beam emitted from a lamp and guides the light to a surface side,
A backlight unit for a liquid crystal display device, comprising the optical sheet according to any one of claims 1 to 15.

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