JP2010176029A - Optical sheet for liquid crystal display device, and backlight unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet for a liquid crystal display device having optical functions, especially, a markedly high optical diffusion functions, and to provide a backlight unit, wherein improvement in quality including optimized angle of view, erasure of lump images, thin profile and the like is promoted using the optical sheet. <P>SOLUTION: The optical sheet for the liquid crystal display device includes a transparent base material layer and microlens arrays formed on the surface and rear surface of the base material layer and made of a plurality of microlenses. The microlenses of the rear surface are preferably concave lenses. The microlens array of the rear surface preferably consist of a plurality of microlenses having random diameters. Microlenses of the surface preferably have average radius of 3 to 90 μm. Microlenses of the rear surface have average radius of 2 to 24 μm and have average radius 1/12 to 1 times as large as the average radius of the microlenses of the surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical sheet suitable for a backlight unit for a liquid crystal display device, and a backlight unit using the same, having various functions such as light collection, light diffusion, and refraction in the normal direction of light rays. Is.

  In the liquid crystal display device, a backlight system that illuminates a liquid crystal layer from the back is 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. 9A, the edge light type backlight unit 40 generally has a rod-like lamp 41 as a light source, and a rectangular plate shape disposed so that an end thereof is along the lamp 41. The light guide plate 42 and a plurality of optical sheets 43 stacked on the surface side of the light guide plate 42 are provided. The optical sheet 43 has specific optical functions such as refraction and light diffusion. Specifically, (1) the optical sheet 43 is disposed on the surface side of the light guide plate 42 and mainly has a light diffusion function and a light collecting function. (2) a prism sheet 45 that is disposed on the surface side of the microlens sheet 44 and mainly has a refractive function toward the normal direction side.

  The function of the backlight unit 40 will be described. First, a light beam incident on the light guide plate 42 from the lamp 41 is reflected by a reflective dot or a reflection sheet (not shown) on the back surface of the light guide plate 42 and each side surface. Emitted from the surface. The light beam emitted from the light guide plate 42 enters the microlens sheet 44 and is diffused and emitted at the microlens interface provided on the surface. Thereafter, the light beam emitted from the microlens sheet 44 enters the prism sheet 45 and is emitted as a light beam having a distribution having a peak in a substantially upward direction by the prism portion 46 formed on the surface. In the backlight unit 40, the light emitted from the lamp 41 is diffused by the optical sheet 43 and refracted so as to have a peak in a substantially upward direction, and further illuminates the entire liquid crystal layer (not shown) above. To do.

  Although not shown, a backlight unit in which more optical sheets 43 such as microlens sheets and prism sheets are arranged in consideration of the light guide characteristics of the light guide plate 42 and the optical functions of the optical sheet 43 is also provided. is there.

  As the conventional microlens sheet 44, generally, as shown in FIG. 9B, a microlens array 47 composed of a plurality of microlenses is provided on the surface, and the back surface has a planar shape. (For example, refer to Japanese Patent Application Laid-Open No. 2004-191611, etc.). In this microlens interface provided on the surface of the microlens sheet as described above, the light emitted from the lamp is condensed on the front side, diffused, and changed in angle to the normal direction.

  However, since the optical functions such as light collection, light diffusion, and deflection of the microlens sheet are determined by the surface shape and the refractive index, there is a certain limit to improving the functions. In particular, in the direct type backlight, when the light diffusing function of the optical sheet is not sufficient, there is an inconvenience that the effect of erasing the lamp image is small and the lamp image appears on the surface of the liquid crystal screen. Therefore, the conventional backlight unit 40 needs to include a plurality of optical sheets, although it is expensive and difficult to handle. When a plurality of optical sheets are provided in this manner, there is a disadvantage that the luminance as a liquid crystal display device is lowered, and the backlight unit is prevented from being thinned.

JP 2004-191611 A

  The present invention has been made in view of these disadvantages. An optical sheet for a liquid crystal display device having a remarkably high optical function, in particular, a light diffusion function, and optimization of a viewing angle, erasing of a lamp image, and thinness using the optical sheet. An object of the present invention is to provide a backlight unit in which improvement in quality such as conversion is promoted.

The invention made to solve the above problems is
A transparent substrate layer;
An optical sheet for a liquid crystal display device comprising a microlens array comprising a plurality of microlenses formed on the front and back surfaces of the base material layer.

  Since the optical sheet for a liquid crystal display device includes a microlens array on the back surface as well as the front surface, the light beam from the backlight can be refracted and diffused at the interface on the back surface of the optical sheet for the liquid crystal display device. Can do. Therefore, the optical sheet for a liquid crystal display device can refract and diffuse light from the backlight at the interface between the front and back surfaces, and optical functions such as a light diffusion function are remarkably enhanced. In addition, according to the optical sheet for liquid crystal display device, the light beam is refracted and diffused by refraction at the interface between the front and back surfaces, so that the loss of the light beam in the optical sheet for liquid crystal display device is minimized and light is transmitted. The rate can be increased.

  The micro lens on the back surface may be a concave lens. Since the micro lens on the back surface is a concave lens, when the light beam from the backlight enters the back surface of the optical sheet, it is refracted and diffused in the direction in which the light beam is dispersed at the interface. Therefore, according to the optical sheet for a liquid crystal display device, optical functions such as a light diffusion function are further enhanced.

  The back microlens array is preferably composed of a plurality of microlenses having random diameters. According to the optical sheet for a liquid crystal display device in which the micro lens on the back surface has a random diameter, the direction and angle at which the light rays from the backlight are refracted and diffused are random on the back surface of the optical sheet. The function is further enhanced, and the uniformity of brightness and the erasability of the lamp image are promoted.

  The average radius of the front microlenses is preferably 3 μm to 90 μm, and the average radius of the back microlenses is preferably 2 μm to 60 μm. According to the optical sheet for a liquid crystal display device, since the front and back microlenses have an average radius in the above range, the optical functions such as light diffusion are further enhanced, and the optical functions are controlled. Easy and reliable.

  The average radius of the back microlenses is preferably 1/12 or more and 1 or less than the average radius of the front microlenses. According to the optical sheet for a liquid crystal display device in which the average radius ratio of the back and front microlenses is in the above range, the light diffusion effect can be further enhanced by the synergistic effect of the microlenses on both sides.

  The base material layer and the microlens arrays on the front surface and the back surface of the base material layer are preferably integrally formed. Since the optical sheet is integrally formed in this way, light is not refracted or scattered inside the sheet, and light transmittance and brightness can be increased by minimizing the loss of light. it can.

  The arrangement pattern of the microlens in at least the surface microlens array is preferably an equilateral triangular lattice pattern or a random pattern. Since this equilateral triangular lattice pattern can arrange microlenses more densely, the lens filling rate of the optical sheet for the liquid crystal infant device can be easily increased, and optical functions such as light collection and light diffusion are remarkably improved. To be improved. In addition, by arranging the microlenses in a random pattern, the occurrence of moire is reduced when the optical sheet for liquid crystal display device is overlapped with another optical member.

  The liquid crystal display device by an extrusion sheet forming method using an embossing roll having a reversal shape of the microlens array on the front surface and an embossing roll disposed in parallel with the embossing roll and having a reversal shape of the microlens array on the back surface An optical sheet for use is preferably formed. According to this means, an optical sheet having a predetermined microlens array on both sides can be easily and accurately molded, and can be easily integrally formed of the same material.

  Accordingly, in the backlight unit for a liquid crystal display device that guides the light beam emitted from the lamp and diffuses it to the surface side, the liquid crystal display device having a remarkably high optical function, particularly a light diffusion function and its control function By providing the optical sheet for use, the quality can be improved by unifying and enhancing the brightness.

  Here, the “front surface” and “back surface” of the optical sheet for liquid crystal display devices are the surfaces facing the front side (liquid crystal layer side) when the optical sheet for liquid crystal display devices is usually provided in the backlight unit of the liquid crystal display device. The “front surface” and the opposite surface (light guide plate side) are defined as “back surface”. The “micro lens” is a concept including a convex lens and a concave lens. The “regular triangle lattice pattern” means a pattern in which the surface is divided into equilateral triangles having the same shape and a microlens is arranged at each vertex of the equilateral triangle.

  As described above, according to the optical sheet for liquid crystal display of the present invention, the optical function, particularly the light diffusion function, is remarkably high, and the control of the optical function is easy and reliable. Further, the backlight using the optical sheet for a liquid crystal display device promotes improvement in quality and cost reduction such as optimization of viewing angle, erasing of a lamp image, and reduction in thickness.

1 is a schematic partial cross-sectional view showing an optical sheet for a liquid crystal display device according to an embodiment of the present invention. Typical sectional drawing which shows a backlight unit provided with the optical sheet for liquid crystal display devices of FIG. The typical fragmentary sectional view which shows the optical sheet for liquid crystal display devices which concerns on the form different from the optical sheet for liquid crystal display devices of FIG. Schematic partial sectional view showing an optical sheet for a liquid crystal display device different from the optical sheet for a liquid crystal display device of FIGS. Schematic partial sectional view showing an optical sheet for a liquid crystal display device different from the optical sheet for a liquid crystal display device in FIGS. Lamp image photograph when the optical sheet for the liquid crystal display device of the comparative example is incorporated in a direct type backlight unit Lamp image photograph when the optical sheet for the liquid crystal display device of Example 2 was incorporated into a direct type backlight unit Lamp image photograph when the optical sheet for the liquid crystal display device of Example 4 was incorporated in a direct type backlight unit (A) And (b) Typical perspective view which shows a general backlight unit, and typical sectional drawing which shows the conventional general micro lens sheet | seat

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic partial sectional view showing an optical sheet for a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a schematic sectional view showing a backlight unit including the optical sheet for a liquid crystal display device of FIG. 3 is a schematic partial sectional view showing an optical sheet for a liquid crystal display device according to a different form from the optical sheet for a liquid crystal display device of FIG. 1, and FIG. 4 is different from the optical sheet for a liquid crystal display device of FIGS. It is a typical fragmentary sectional view which shows the optical sheet for liquid crystal display devices. FIG. 5 is a schematic partial cross-sectional view showing an optical sheet for a liquid crystal display device different from the optical sheet for a liquid crystal display device shown in FIGS. 1, 3, and 4.

  An optical sheet 1 for a liquid crystal display device in FIG. 1 includes a base material layer 2, a microlens array 3 formed on the surface of the base material layer 2, and a microlens array 4 formed on the back surface of the base material layer 2. It has.

  Since the base material layer 2 needs to transmit light, it is made of a synthetic resin that is transparent, particularly colorless and transparent. The synthetic resin used for the base material layer 2 is not particularly limited. For example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather resistant vinyl chloride, radiation curable resin. Etc. Among these, radiation curable resins such as ultraviolet curable resins and electron beam curable resins excellent in moldability of the microlens arrays 3 and 4 and thermoplastic resins such as polycarbonate and polyolefin are preferable.

  The thickness (average thickness) of the base material layer 2 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 2 is less than the above range, inconveniences such as curling tends to occur when exposed to heat in a backlight unit or the like, and handling becomes difficult. On the contrary, if the thickness of the base material layer 2 exceeds the above range, the luminance of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which is contrary to the demand for thinning of the liquid crystal display device. It will also be.

  A fine inorganic filler may be contained in the polymer resin forming the base material layer 2. Thus, the heat resistance of the base material layer 2 and by extension, the optical sheet 1 for liquid crystal display devices is improved by containing the fine inorganic filler in the base material layer 2. The inorganic material constituting the fine inorganic filler is not particularly limited, but 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 bonds with oxygen atoms. As the metal element constituting the inorganic oxide, for example, an element selected from Groups 2 to 6 of the Periodic Table of Elements is preferable, and an element selected from Groups 3 to 5 of the Periodic Table of Elements is more preferable. In particular, an element selected from Si, Al, Ti and Zr is preferable, and b colloidal silica in which the metal element is Si is most preferable as a fine inorganic filler in terms of heat resistance improvement effect and uniform dispersibility. The shape of the fine inorganic filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scale shape, and a crushed shape, and is not particularly limited.

  The lower limit of the average particle size of the fine inorganic filler is preferably 5 nm, and particularly preferably 10 nm. On the other hand, the upper limit of the average particle size of the fine inorganic filler is preferably 50 nm, particularly preferably 25 nm. This is because if the average particle size of the fine inorganic filler is less than the above range, the surface energy of the fine inorganic filler becomes high and aggregation or the like is likely to occur. Conversely, if the average particle size exceeds the above range, This is because it becomes cloudy under the influence of a short wavelength, the transparency of the base material layer 2 is lowered, and the transmittance is affected.

  Furthermore, the base material layer 2 may contain an antistatic agent. By forming the base material layer 2 from the polymer resin kneaded with the antistatic agent in this way, the antistatic effect is expressed in the optical sheet 1 for the liquid crystal display device, and dust is sucked or other optical sheets or the like are used. It is possible to prevent inconveniences caused by electrostatic charging, such as difficulty in superimposing the images. Further, when the antistatic agent is coated on the surface, the surface becomes sticky or contaminated. However, such an adverse effect is reduced by kneading the antistatic agent in the base material layer 2 in this way. The antistatic agent is not particularly limited. For example, anionic antistatic agents such as alkyl sulfates and alkyl phosphates, cationic antistatic agents such as quaternary ammonium salts and imidazoline compounds, polyethylene glycol-based compounds, Nonionic antistatic agents such as polyoxyethylene sorbitan monostearic acid ester and ethanolamides, and high molecular antistatic agents such as polyacrylic acid are used. Among these, a cationic antistatic agent having a relatively large antistatic effect is preferable, and an antistatic effect is exhibited by addition of a small amount.

  Further, the base material layer 2 may contain an ultraviolet absorber. By forming the base material layer 2 containing the ultraviolet absorber in this manner, the optical sheet 1 for liquid crystal display device is provided with an ultraviolet cut function, and a trace amount of ultraviolet light emitted from the lamp of the backlight unit is cut. The destruction of the liquid crystal layer due to ultraviolet rays can be prevented.

  It is also possible to use an ultraviolet stabilizer (including a base polymer in which an ultraviolet stabilizing group is bonded to a molecular chain) instead of the ultraviolet absorbent or together with the ultraviolet absorbent. By this ultraviolet stabilizer, radicals generated by ultraviolet rays, active oxygen and the like are inactivated, and ultraviolet stability, weather resistance and the like can be improved. As this ultraviolet stabilizer, a hindered amine ultraviolet stabilizer having high stability against ultraviolet rays is preferably used. In addition, the combined use of an ultraviolet absorber and an ultraviolet stabilizer significantly improves deterioration prevention and weather resistance due to ultraviolet rays.

  The microlens array 3 is composed of a large number of microlenses 5 having substantially the same diameter.

  The microlens array 4 is composed of a large number of microlenses 6 having random diameters. In the microlens array 4, a large number of microlenses 6 are formed relatively densely in a random pattern.

  The microlens arrays 3 and 4 may be formed integrally with the base material layer 2 or may be formed separately from the base material layer 2. Since the microlens arrays 3 and 4 need to transmit light, they are formed of a transparent, particularly colorless and transparent synthetic resin. Specifically, the same synthetic resin as that of the base material layer 2 is used. Moreover, as the base material layer 2, a polyethylene terephthalate film, a polyethylene naphthalate film or a polycarbonate film can be used, and the microlenses 5 and 6 can be formed thereon using an ultraviolet curable resin or the like.

  In addition to the above synthetic resin, for example, a filler, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like may be blended in the base material layer 2 and the microlenses 5 and 6.

  The microlens 5 is a so-called convex lens having a convex partial substantially spherical shape. The average radius of the microlens 5 is preferably 3 μm or more and 90 μm or less, particularly preferably 10 μm or more and 75 μm or less. If the average radius of the microlens 5 is less than the above range, a diffraction phenomenon may occur due to the relationship with the wavelength of light emitted from the light. Conversely, if the average radius exceeds the above range, sufficient light diffusibility is provided at the interface. Absent.

  The microlenses 5 are relatively densely and geometrically arranged on the surface of the base material layer 2. The microlenses 5 are arranged in a regular triangular lattice pattern on the surface of the base material layer 2. Accordingly, the pitch of the microlenses 5 and the distance between the lenses are all constant. In this arrangement pattern, the microlenses 5 can be arranged most densely, and the optical functions such as the light condensing function, the light diffusing function, and the angle changing function of the optical sheet 1 for the liquid crystal display device can be improved. it can.

  The lower limit of the filling rate of the microlens 5 is preferably 40%, particularly 60%, and more particularly 70%. Thus, by setting the filling rate of the microlenses 5 to be equal to or higher than the lower limit, the area occupied by the microlenses 5 on the surface of the optical sheet 1 for the liquid crystal display device is increased. Optical functions such as diffusion are significantly improved.

  The lower limit of the height ratio (H / R) of the lens height (H) of the microlens 5 to the radius of curvature (R) is preferably 5/8, and particularly preferably 3/4. On the other hand, the upper limit of the height ratio (H / R) is preferably 1. Here, “lens height” means a vertical distance from the base surface to the top of the microlens 5. Thus, by setting the height ratio (H / R) of the microlens 5 within the above range, the lens-like refraction action in the microlens 5 is effectively exerted, and the optical sheet 1 for the liquid crystal display device is condensed. Optical functions such as light diffusion are significantly improved.

  The upper limit of the distance ratio (S / D) to the diameter (D) of the inter-lens distance (S; PD) of the microlens 5 is preferably 1/2, and particularly preferably 1/5. Here, the “inter-lens distance” means the shortest distance between a pair of adjacent microlenses 5. Thus, by setting the inter-lens distance (S) of the microlens 5 to be equal to or less than the above upper limit, the flat portion that does not contribute to the optical function is reduced, and the optical sheet 1 for the liquid crystal display device 1 such as condensing, light diffusion, etc. The optical function is greatly improved.

  The average of the individual light emission angles of the microlens 5 is preferably ± 25 ° or more, particularly preferably ± 40 ° with respect to the normal to the plane of the optical sheet 1 for a liquid crystal display device. By forming the microlens array 3 from the microlenses 5 having such a light emission angle, it is possible to obtain viewing angle characteristics necessary as an optical sheet for a liquid crystal display device.

  The microlens 6 is a so-called concave lens having a partially substantially spherical inverted shape. Thus, when the microlens 6 of the microlens array 4 provided on the back surface of the base material layer 2 is a concave lens, the light diffusibility of the optical sheet 1 for a liquid crystal display device is remarkably improved. That is, according to the optical sheet 1 for a liquid crystal display device, when the light beam from the backlight is incident on the back surface of the optical sheet 1, the light beam is dispersed in the concave interface of the microlens 6 (the direction in which the light spreads). Therefore, the light diffusibility is improved.

  In this manner, by forming the microlens arrays 3 and 4 on both surfaces of the optical sheet 1 for the liquid crystal display device, it is possible to obtain a wide viewing angle by diffusing the light with the concave microlens 6 on the back surface where the light is incident. The front brightness can be maintained by raising the light in the normal direction by the convex microlens 5 on the surface from which the light is emitted. In particular, when the base material layer 2 and the microlens arrays 3 and 4 are integrally formed of the same material, these refractions are performed only at the front and back interfaces of the optical sheet 1 for liquid crystal display devices. Since light is not refracted or scattered inside the sheet 1, the loss of light inside the optical sheet 1 for a liquid crystal display device can be extremely reduced, and the light transmittance and front luminance can be increased.

  The average radius of the microlens 6 is preferably 2 μm or more and 60 μm or less, particularly 6 μm or more and 40 μm or less. By setting the average radius of the microlens 6 within the above range, the microlens 6 is effective in the direction in which the light rays from the incident backlight are dispersed (the direction in which the light spreads) on the microlens array 4 on the back surface of the optical sheet 1 for liquid crystal display devices. Refracts and improves the light diffusibility. If the average radius of the microlenses 6 is less than the above range, a diffraction phenomenon may occur due to the relationship with the wavelength of light emitted from the light. If the average radius exceeds the above range, sufficient light diffusibility is not obtained.

  The average radius of the micro lens 6 is preferably 1/12 or more and 1 or less than the average radius of the micro lens 5. By providing the average radius ratio of the micro lens 6 on the back surface and the micro lens 5 on the front surface in this manner, light diffusibility can be improved while ensuring a certain front luminance. When the average radius of the microlens 6 is less than 1/12 of the average radius of the microlens 5, the front luminance is greatly reduced due to scattering and diffraction phenomenon. Conversely, when the average radius exceeds 1, sufficient light diffusibility is obtained. Not shown, brightness uniformity is reduced.

  The lower limit of the filling rate of the microlens 6 is preferably 50%, particularly 70%, and more particularly 80%. Thus, by setting the filling rate of the microlenses 6 to be equal to or higher than the lower limit, the area occupied by the microlenses 6 on the surface of the optical sheet 1 is increased, and the optical functions such as light diffusion of the optical sheet 1 for the liquid crystal display device are achieved. Greatly improved.

The method for producing the optical sheet 1 for a liquid crystal display device is not particularly limited as long as the above structure can be formed, and various methods are employed. As the manufacturing method of the optical sheet 1 for a liquid crystal display device, a method of separately forming the microlens array 3 and the microlens array 4 after forming the base material layer 2, a base material layer 2, the microlens array 3, and the microlens. A method of integrally molding the array 4 is possible. Specifically,
(A) A method of forming the optical sheet 1 for a liquid crystal display device by laminating a synthetic resin on a sheet mold having the inverted shape of the surface of the microlens arrays 3 and 4 and peeling the sheet mold;
(B) an injection molding method in which a molten resin is injected into a mold having an inverted shape of the surfaces of the microlens arrays 3 and 4;
(C) A method of transferring the shape by re-heating the sheeted resin and pressing between the same mold and metal plate as described above,
(D) an extrusion sheet molding method in which a molten resin is passed between two roll molds having the inverted shape of the surface of the microlens arrays 3 and 4 on the peripheral surface, and the shape is transferred;
(E) An ultraviolet curable resin is applied to the base material layer, and the shape is transferred to an uncured ultraviolet curable resin by pressing against a sheet mold, mold or roll mold having the same inverted shape as above, A method of curing an ultraviolet curable resin by application,
(F) An uncured ultraviolet curable resin is filled and applied to a mold or roll mold having the same inverted shape as described above, pressed by a base material layer, leveled, and irradiated with ultraviolet rays to cure the ultraviolet curable resin. Method,
(G) There is a method of using an electron beam curable resin instead of an ultraviolet curable resin.

  The method using the roll type in the above (d) to (f) will be described below. An embossing roll having a reversal shape of the microlens array 3 on the surface, and an embossing roll having a reversal shape of the microlens array 4 on the surface disposed in parallel with the embossing roll at a predetermined interval, the two embossing rolls By passing the film-like resin in between, the microlens array 3 is integrally formed on the front surface and the microlens array 4 is integrally formed on the back surface. According to this method, the optical sheet having the predetermined microlens arrays 3 and 4 can be formed easily and with high precision, and can be easily formed integrally with the same material. Furthermore, since it is formed with an embossing roll, a seamless optical sheet can be manufactured without causing discontinuous joint portions in the microlens arrays 3 and 4.

  The film-like resin that is passed between the two embossing rolls may be a molten resin or a sheet-like resin in which an uncured resin is laminated on both sides. It is preferable that it is extruded into a film. Thus, since the resin extruded in the melted state can be formed with an embossing roll by manufacturing by a so-called extrusion sheet forming method, the film forming and the microlens arrays 3 and 4 on the front and back surfaces are formed. Since it becomes possible to carry out simultaneously, the said optical sheet can be manufactured easily and efficiently.

  As a method for manufacturing a mold (mold, mold mold, etc.) having the inverted shape of the microlens arrays 3 and 4, for example, a spot-like three-dimensional pattern is formed on a substrate with a photoresist material, and this three-dimensional pattern is heated. A microlens array model can be produced by making the surface curved by fluidization, a metal layer is laminated on the surface of the microlens array model by electroforming, and the metal layer can be peeled off.

  According to the manufacturing method, the arbitrarily shaped microlens arrays 3 and 4 can be easily and reliably formed. Therefore, the size, filling rate, arrangement pattern, etc. of the microlenses 5 and 6 constituting the microlens arrays 3 and 4 are easily and reliably adjusted, and as a result, the optical function of the optical sheet 1 for the liquid crystal display device is easy. And it is controlled reliably.

  As another manufacturing method of the mold (sheet mold or the like) having the inverted shape of the microlens array 3 and the microlens array 4 described above, an optical sheet master having a microlens array shape on the surface is used and extruded onto the surface of the optical sheet master. It can be manufactured by laminating a synthetic resin layer for a mold by a laminating method and peeling the optical sheet original plate from the synthetic resin layer for a mold. Among the extrusion laminating methods, a synthetic resin layer for a mold is preferably laminated between the optical sheet original plate and the mold base sheet, particularly by a sandwich extrusion laminating method.

  According to the above manufacturing method, the surface shape of the optical sheet precursor having a microlens array shape can be faithfully transferred to the surface by the extrusion laminating method, so that an optical sheet having high optical performance such as a light diffusion function is manufactured with high productivity. be able to. In particular, according to the sandwich extrusion laminating method, the strength of the optical sheet forming mold is ensured by the mold base sheet, the synthetic resin constituting the mold synthetic resin layer is transferred to the surface shape of the optical sheet original plate, and heat resistant. Therefore, it is possible to select the justification for separation from the synthetic resin layer for the optical layer as a main point, which contributes to the precise formability of the surface shape of the optical sheet material to be settled and the life extension of the optical sheet forming mold.

  Moreover, according to the manufacturing method by the extrusion laminating method, a mold having a reversed shape of the back microlens array 4 composed of a plurality of microlenses 6 having a random diameter is also coated with beads having a plurality of diameters. It can be easily manufactured by transferring the light diffusion sheet formed by the above as an original plate.

  The edge light type backlight unit shown in FIG. 2 is disposed so as to overlap the light guide plate 7, the pair of linear lamps 8 disposed on the opposite side of the light guide plate 7, and the surface side of the light guide plate 7. And an optical sheet 1 for a liquid crystal display device. A light beam emitted from the lamp 8 and emitted from the surface of the light guide plate 7 has a relatively strong peak inclined at a predetermined angle with respect to the normal direction. However, according to the backlight unit, the light beam is collected on the front side. The optical sheet 1 for a liquid crystal display device having a light function and a remarkably high light diffusion function while having a conventional function in the light function and the function of changing the angle toward the normal direction side, makes the luminance uniform and provides a wide viewing angle. It is converted into light. Therefore, the backlight unit can reduce the number of optical sheets (bead coated sheets and the like) required in the past, and promote the reduction in thickness, quality, and cost. Furthermore, the improvement in luminance is promoted by reducing the number of optical sheet equipment. The edge light type backlight unit may be equipped with four, six, etc. lamps 8.

  An optical sheet 11 for a liquid crystal display device in FIG. 3 includes a base material layer 2, a microlens array 3 formed on the surface of the base material layer 2, and a microlens array 12 formed on the back surface of the base material layer 2. And. The base material layer and the microlens array 3 are the same as the optical sheet 1 for a liquid crystal display device shown in FIG.

  The microlens array 12 includes a large number of microlenses 13 having substantially the same diameter.

  The micro lens 13 is a concave lens. The diameter of the microlens 13 is preferably the same as or smaller than the diameter of the microlens 5 constituting the microlens array 3 on the surface.

  The microlenses 13 are relatively densely and geometrically disposed on the back surface of the base material layer 2. The microlenses 13 are arranged in a regular triangular lattice pattern on the back surface of the base material layer 2. Accordingly, the pitch of the microlenses 13 and the distance between the lenses are all constant. With this arrangement pattern, the microlenses 13 can be arranged most closely, and the optical functions such as the light diffusion function of the optical sheet 1 for the liquid crystal display device can be improved. In particular, it is arranged so that the center of the microlens 13 on the back surface is located on the center of the microlens 5 on the front surface, or the back surface on the center of each triangle of the equilateral triangular lattice pattern constituting the microlens array 3 on the front surface. By arranging so that the center of the microlens 13 is positioned, the synergistic effect of the microlens arrays on both the front and back surfaces can be enhanced, and the optical functions such as the light diffusion function can be remarkably improved.

  An optical sheet 21 for a liquid crystal display device in FIG. 4 includes a base material layer 2, a microlens array 3 formed on the surface of the base material layer 2, and a microlens array 22 formed on the back surface of the base material layer 2. And. The base material layer and the microlens array 3 are the same as the optical sheet 1 for a liquid crystal display device shown in FIG.

  The microlens array 22 includes a large number of microlenses 23 having a random diameter.

  The micro lens 23 is a convex lens. The average radius of the microlens 23 is preferably 2 μm or more and 24 μm or less, particularly 6 μm or more and 18 μm or less, like the microlens 6 of the optical sheet 1 for a liquid crystal display device, and is 1 of the average radius of the microlens 5 provided on the surface. It is preferably / 12 or more and 1 or less. Further, the lower limit of the filling rate of the microlens 23 is preferably 50%, particularly 70%, and more particularly 80%.

  In addition, the average focal length of the microlens 23 is preferably less than or equal to ½ of the average thickness of the base material layer 2. According to the microlens 23 having such a focal length, the light incident from the back surface of the optical sheet 21 for a liquid crystal display device is refracted at the interface of the microlens array 22 on the back surface, and then the microlens array formed on the front surface. Therefore, the light diffusion function of the optical sheet 21 for a liquid crystal display device can be improved.

  An optical sheet 31 for a liquid crystal display device in FIG. 5 includes a base material layer 2, a microlens array 3 formed on the surface of the base material layer 2, and a microlens array 32 formed on the back surface of the base material layer 2. And. The base material layer and the microlens array 3 are the same as the optical sheet 1 for a liquid crystal display device shown in FIG.

  The microlens array 32 includes a large number of microlenses 33 having substantially the same diameter.

  The micro lens 33 is a convex lens. The diameter of the micro lens 33 is preferably the same as or smaller than that of the micro lens 5 constituting the micro lens array 3 on the surface. By making the diameter of the microlens 33 different from that of the microlens 5 on the front surface side, the focal length can be adjusted according to the object, and the light diffusibility can be achieved by combining the front and back microlenses. In addition, the surface uniformity can be further improved.

  The microlenses 33 are disposed relatively densely and geometrically on the back surface of the base material layer 2. The microlenses 33 are arranged in a regular triangular lattice pattern on the back surface of the base material layer 2. Accordingly, the pitch of the micro lenses 33 and the distance between the lenses are all constant. In this arrangement pattern, the microlenses 33 can be arranged most closely, and the optical functions such as the light diffusion function of the optical sheet 1 for the liquid crystal display device can be improved. In particular, it is arranged so that the center of the microlens 33 on the back surface is located on the center of the microlens 5 on the front surface, or the back surface on the center of each triangle of the equilateral triangular lattice pattern constituting the microlens array 3 on the front surface. By arranging so that the center of the micro lens 33 is located, the synergistic effect of the micro lens array on both the front and back surfaces can be enhanced, and the optical function such as the light diffusion function can be remarkably improved.

  In addition, the average focal length of the microlens 33 is preferably 1/2 or less of the average thickness of the base material layer 2. According to the microlens 33 having such a focal length, the light incident from the back surface of the optical sheet 21 for the liquid crystal display device is refracted at the interface of the microlens array 32 on the back surface, and then reaches the microlens array 3 on the front surface. Therefore, the light diffusion function of the optical sheet 31 for liquid crystal display device can be improved.

  In any of the optical sheets 11, 21, and 31 for the liquid crystal display device, the microlens array is formed on both surfaces of the optical sheet for the liquid crystal display device, so that the microlenses 13, 23, or 33 are formed on the back surface where light enters. Light can be diffused to obtain uniform brightness and a wide viewing angle, and high front brightness can be maintained by raising the light in the normal direction by the convex microlenses 5 on the surface from which the light is emitted.

  The optical sheet for a liquid crystal display device of the present invention is not limited to the above embodiment, for example, the arrangement pattern of the microlenses on the surface is not limited to the regular triangular lattice pattern that can be densely packed, Square grid patterns and random patterns are also possible. According to the random pattern, the occurrence of moire is reduced when the optical sheet for a liquid crystal display device is overlapped with another optical member. It is also possible to provide a microlens array composed of concave microlenses on the surface. Even when a microlens array of concave lenses is provided on the surface, it has an optical function such as excellent light diffusivity as in the case of providing the microlens array of convex lenses. Further, the front microlens and the back microlens may be made of materials having different refractive indexes. Since the front and back surfaces are formed of microlenses made of different refractive index materials, light is refracted even when placed at the interface between the materials. Surface uniformity can be improved.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

[Comparative Example]
An optical sheet for a liquid crystal display device in which a microlens array composed of microlenses of convex lenses was provided on the surface of a transparent polyethylene terephthalate film having a thickness of 100 μm was used. The microlens sheet of the comparative example was molded with an average microlens diameter of 60 μm and a filling rate of 70%.

[Examples 1 to 4]
A microlens array composed of microlenses of convex lenses was provided on the surface of a transparent polyethylene terephthalate film having a thickness of 100 μm, and a microlens array having the following shape was provided on the back surface. An optical sheet for a liquid crystal display device of Example 1 was obtained by providing a microlens array composed of microlenses that are concave lenses having random diameters on the back surface. An optical sheet for a liquid crystal display device of Example 2 was obtained by providing a microlens array composed of microlenses that are concave lenses having substantially the same diameter on the back surface. An optical sheet for a liquid crystal display device of Example 3 was obtained by providing a microlens array consisting of microlenses that are convex lenses having random diameters on the back surface. An optical sheet for a liquid crystal display device of Example 4 was obtained by providing a microlens array composed of microlenses that are convex lenses having substantially the same diameter on the back surface.

  In the microlens array on the back surface, the microlenses having substantially the same diameter were molded with an average diameter of 60 μm, the microlenses with random diameters having an average diameter of 12 μm, and a filling rate of 70%.

[Evaluation of properties]
Using the optical sheets for liquid crystal display devices of Examples 1 to 4 and the optical sheet for liquid crystal display devices of Comparative Examples, these haze values were measured. This haze value was measured with a haze meter manufactured by Suga Test Instruments Co., Ltd. according to the measurement method defined in JIS-K7136. Moreover, these brightness | luminance half-value angles were measured using the optical sheet for liquid crystal display devices of the said Examples 2 and 4 and a comparative example. Furthermore, using the optical sheets for liquid crystal display devices of Examples 2 and 4 and the comparative example, these sheets were actually incorporated into a direct type backlight unit, and the light diffusibility was evaluated. Evaluation of light diffusivity is visually confirmed about the degree of erasure of the lamp image from the surface side when the backlight is irradiated,
(A) When the lamp image is almost invisible ◎
(B) When the lamp image is difficult to see ○
(C) When the lamp image is somewhat visible
(D) When the lamp image is clearly visible x
As evaluated. The results are shown in Table 1 below. FIG. 6 shows a lamp image when the optical sheet for the liquid crystal display device of the comparative example is incorporated in the direct type backlight unit, and FIG. 7 shows the optical sheet for the liquid crystal display device of Example 2 incorporated in the direct type backlight unit. FIG. 8 shows a lamp image photograph when the optical sheet for the liquid crystal display device of Example 4 is incorporated in a direct type backlight unit.

  As shown in Table 1 above, the optical sheets for liquid crystal display devices of Examples 1 to 4 have a higher haze value than the optical sheet for liquid crystal display device of the comparative example not provided with the microlens array on the back surface, that is, It has been shown to have high light diffusivity and a wide viewing angle. Further, when compared in Examples 1 to 4, the microlenses on the back surface have a random diameter, and those having a concave lens shape exhibit a high haze value, that is, have a high light diffusibility and a wide viewing angle. It has been shown.

  In addition, as shown in Table 1, the optical sheets for liquid crystal display devices of Examples 2 and 4 have a wider half-value angle than the optical sheet for liquid crystal display device of the comparative example not provided with the microlens array on the back surface. Yes.

  Furthermore, as shown in Table 1 and FIGS. 7 to 9, the optical sheets for liquid crystal display devices of Examples 2 and 4 have a high degree of erasure of the lamp image. That is, the optical sheets for liquid crystal display devices of Examples 2 and 4 are shown to have high light diffusibility and a wide viewing angle. Further, from the lamp image erasure degree (comparison between FIG. 8 and FIG. 9), the optical sheet for liquid crystal display device having the concave lens-shaped microlens on the back surface has higher light diffusibility and wider viewing angle. It is shown.

  As described above, the optical sheet for a liquid crystal display device of the present invention is useful as a component of a backlight unit of a liquid crystal display device, and is particularly suitable for use in a transmissive liquid crystal display device.

DESCRIPTION OF SYMBOLS 1 Optical sheet for liquid crystal display devices 2 Base material layer 3 Micro lens array 4 Micro lens array 5 Micro lens 6 Micro lens 7 Light guide plate 8 Lamp 11 Optical sheet for liquid crystal display devices 12 Micro lens array 13 Micro lens 21 Optics for liquid crystal display devices Sheet 22 Micro lens array 23 Micro lens 31 Optical sheet for liquid crystal display device 32 Micro lens array 33 Micro lens 40 Backlight unit 41 Lamp 42 Light guide plate 43 Optical sheet 44 Micro lens sheet 45 Prism sheet 46 Prism unit 47 Micro lens array

Claims (10)

A transparent substrate layer;
An optical sheet for a liquid crystal display device, comprising: a microlens array comprising a plurality of microlenses formed on the front and back surfaces of the base material layer.   The optical sheet for a liquid crystal display device according to claim 1, wherein the micro lens on the back surface is a concave lens.   The optical sheet for a liquid crystal display device according to claim 1 or 2, wherein the back microlens array comprises a plurality of microlenses having random diameters.   4. The optical sheet for a liquid crystal display device according to claim 1, wherein an average radius of the microlenses on the surface is 3 μm or more and 90 μm or less. 5.   5. The optical sheet for a liquid crystal display device according to claim 1, wherein an average radius of the microlenses on the back surface is 2 μm or more and 60 μm or less.   6. The optical sheet for a liquid crystal display device according to claim 1, wherein an average radius of the back microlenses is 1/12 or more and 1 or less of an average radius of the front microlenses.   The optical sheet for a liquid crystal display device according to any one of claims 1 to 6, wherein the base material layer and the microlens arrays on the front surface and the back surface of the base material layer are integrally formed.   The optical sheet for a liquid crystal display device according to any one of claims 1 to 7, wherein an arrangement pattern of microlenses in at least the surface microlens array is an equilateral triangular lattice pattern or a random pattern.   It is formed by an extrusion sheet molding method using an embossing roll having a reverse shape of the microlens array on the front surface and an embossing roll disposed in parallel with the embossing roll and having a reverse shape of the microlens array on the back surface. The optical sheet for a liquid crystal display device according to any one of claims 1 to 8. In a backlight unit for a liquid crystal display device that guides light emitted from a lamp to the surface side by dispersing it,
A backlight unit for a liquid crystal display device, comprising the optical sheet for a liquid crystal display device according to any one of claims 1 to 9.