TWI524096B - An optical sheet for a liquid crystal display device, and a backlight unit using the same - Google Patents

Description

Optical sheet for liquid crystal display device and backlight unit using the same

The present invention relates to an optical sheet having a function of collecting light, diffusing light, refracting light in a normal direction, and particularly, an optical sheet suitable for a backlight unit for a liquid crystal display device, and a backlight unit using the same.

In the liquid crystal display device, a backlight method in which a liquid crystal layer is irradiated from the back surface is generally used, and a backlight unit such as a side light type (side light type) or a direct type is mounted on the lower side of the liquid crystal layer. As shown in FIG. 9(a), the edge type backlight unit 40 is generally provided with a rod-shaped light source 41 as a light source and a square plate shape in which the end portions are arranged along the light source 41. The light guide plate 42 and a plurality of optical sheets 43 laminated on the surface side of the light guide plate 42. The optical sheet 43 has specific optical functions such as refraction and light diffusion, and specifically includes the following elements: (1) The lenticular sheet 44 is disposed on the surface side of the light guide plate 42 and mainly has light diffusion. The function and the concentrating function; (2) the cymbal 45 is disposed on the surface side of the lenticular sheet 44, and mainly has a function of refracting toward the normal side.

Hereinafter, the function of the backlight unit 40 will be described. First, the light incident from the light source 41 to the light guide plate 42 is reflected by the reflection point or the reflection sheet (not shown) on the back surface of the light guide plate 42 and the side surfaces. The surface of the light plate 42 is emitted. The light emitted from the light guide plate 42 is incident on the lenticular sheet 44, and is diffused and emitted at the microlens interface provided on the surface. Then, the light emitted from the lenticular sheet 44 is incident on the cymbal sheet 45, and is emitted as a light beam showing a distribution of peaks in a substantially upper direction by the dam portion 46 formed on the surface. As described above, the backlight unit 40 diffuses the light emitted from the light source 41 by the optical sheet 43 and refracts the peak in a substantially normal direction, and illuminates the entire surface of the liquid crystal layer (not shown). .

Further, although not shown, the light guide characteristics of the light guide plate 42 and the optical function of the optical sheet 43 are considered, and a backlight unit in which a plurality of optical sheets 43 such as a lenticular sheet and a cymbal sheet are disposed is also provided.

As shown in FIG. 9(b), the conventional microlens sheet 44 is generally provided with a microlens array 47 composed of a plurality of microlenses on the surface, and has a planar shape on the back surface (for example, refer to Japanese Patent Application) Japanese Patent Publication No. 2004-191611, etc.). In the microlens interface disposed on the surface of the lenticular sheet, the light emitted from the light source is concentrated toward the front side, diffused, and angled toward the normal side.

However, the optical functions such as condensing, light diffusing, and variable angle of the lenticular sheet are determined by the surface shape and the refractive index, and thus have a certain limit on the lifting function. In particular, in the direct type backlight, when the light diffusing function of the optical sheet is insufficient, the erasing effect of the light source image is small, so that the light source image appears on the surface of the liquid crystal screen. Therefore, in the conventional backlight unit 40, although it is expensive and difficult to operate, it is necessary to have a plurality of optical sheets. In the case of the optical sheet having a plurality of sheets as described above, in addition to the disadvantage that the brightness of the liquid crystal display device is lowered, the thickness of the backlight unit is hindered.

Prior technical literature

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2004-191611

The present invention has an object to provide an optical sheet for a liquid crystal display device and a backlight unit using the same, and an optical sheet for the liquid crystal display device, which is particularly excellent in optical function, particularly a light diffusing device; It improves the quality of the viewing angle, the removal of the light source image, and the thinning.

The invention for solving the above problems is an optical sheet for a liquid crystal display device comprising: a transparent base material layer; and a microlens array comprising a plurality of microlenses formed on the surface and the back surface of the base material layer.

Since the optical sheet for a liquid crystal display device includes a microlens array on the back surface not only on the surface, it is possible to refract or diffuse light from the backlight even at the interface of the back surface of the optical sheet for a liquid crystal display device. 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 can further improve the optical function of the light diffusing function or the like. Further, according to the optical sheet for a liquid crystal display device, light is refracted and diffused by the refraction of the interface between the front and back surfaces, so that the loss of light in the optical sheet for a liquid crystal display device can be minimized, and the light transmittance can be improved. .

The microlens on the back can be a concave lens. Since the microlens on the back side is a concave lens, the light from the backlight will refract and diffuse in the direction of dispersion when the light is incident on the back side of the optical sheet. Therefore, with the optical sheet for a liquid crystal display device, optical functions such as a light diffusing function can be further improved.

The microlens array on the back side is preferably composed of a plurality of microlenses having a random diameter. The optical sheet for a liquid crystal display device having a random diameter on the back side of the microlens, in the back surface of the optical sheet, the direction and angle of refraction and diffusion of light from the backlight are randomly distributed, so that the light diffusing device can be further improved. , to improve the uniformity of brightness, the removal of the light source image.

The average radius of the surface microlens may be 3 μm or more and 90 μm or less; and the microlens of the back surface may have an average radius of 2 μm or more and 60 μm or less. According to the optical sheet for a liquid crystal display device, since the microlens on the front surface and the back surface have an average radius in the above range, the optical function such as light diffusion can be further improved, and the optical function can be easily and surely adjusted.

The average radius of the microlenses on the back surface may be 1/12 or more and 1 or less of the average radius of the microlenses on the surface. The optical sheet for a liquid crystal display device having an average radius ratio of the microlens on the back surface and the surface is in the above range, and the light diffusion effect can be further enhanced by the multiplication effect of the microlenses on both sides.

The base material layer and the microlens array of the surface of the base material layer and the back surface may be integrally formed. By integrally molding the optical sheet as described above, light is not refracted or scattered inside the sheet, and light loss is suppressed to a minimum, so that light transmittance and brightness can be improved.

The arrangement pattern of the microlenses in at least the surface microlens array is preferably an equilateral triangle lattice pattern or a random pattern. In the regular triangular lattice pattern, since the microlenses can be more closely arranged, the lens filling rate of the optical sheet for a liquid crystal display device can be easily improved, and optical functions such as condensing and light diffusion can be particularly improved. Further, by arranging the microlenses in a random pattern, the occurrence of the moiré can be reduced when the optical sheet for the liquid crystal display device overlaps with other optical members.

The optical sheet for a liquid crystal display device can be formed by an extrusion sheet forming method using an embossing roll having an inverted shape of the microlens array having the surface, and the embossing roll An embossing roll arranged in parallel and having an inverted shape of the microlens array of the back surface). By this means, an optical sheet having a specific microlens array on both sides can be formed simply and accurately, and can be integrally formed by simply using the same material.

Therefore, the optical unit for a liquid crystal display device which is excellent in the optical function, particularly the light diffusing function and the control function thereof, is provided by the backlight unit for the liquid crystal display device which is guided by the light source from the light source. Quality can be improved by the uniformity and height of brightness.

Here, the "surface" and the "back surface" of the optical sheet for a liquid crystal display device mean that the surface of the backlight unit of the liquid crystal display device is provided on the front side (the liquid crystal layer side) when the optical sheet for a liquid crystal display device is provided. As the "surface", the surface on the opposite side (light guide plate side) serves as the "back surface". The term "microlens" means the concept of a convex lens and a concave lens. The "triangular lattice pattern" means an equilateral triangle whose surface is divided into the same shape, and a pattern of microlenses 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 diffusing device, can be exceptionally excellent, and the optical function can be controlled simply and surely. Further, by using the backlight of the optical sheet for a liquid crystal display device, it is possible to improve the quality of the viewing angle, to remove the light source image, to reduce the thickness, and to reduce the cost.

Hereinafter, embodiments of the present invention will be described in detail with reference to the appropriate drawings.

The optical sheet 1 for a liquid crystal display device of 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.

Since the base material layer 2 is required to transmit light, it is formed of a transparent, particularly colorless, transparent synthetic resin. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, and acetic acid. Cellulose, weather resistant vinyl chloride, radiation curable resin, and the like. Among them, a radiation curable resin such as an ultraviolet curable resin or an electron beam curable resin which is excellent in moldability of the microlens arrays 3 and 4, or a thermoplastic resin such as polycarbonate or polyolefin is preferable.

The thickness (average thickness) of the base material layer 2 is not particularly limited, and 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, the backlight unit or the like is likely to be bent when exposed to heat, which causes disadvantages such as difficulty in use. On the other hand, when the thickness of the base material layer 2 is outside the above range, the brightness of the liquid crystal display device may be lowered, and the thickness of the backlight unit may become large, which does not meet the demand for thinning of the liquid crystal display device.

The polymer resin forming the base material layer 2 may also contain a fine inorganic filler. As described above, the base material layer 2 and the optical sheet 1 for a liquid crystal display device can be improved in heat resistance by containing a fine inorganic filler in the base material layer 2. The inorganic substance constituting the micro inorganic filler is not particularly limited, and is preferably an inorganic oxide. The inorganic oxide is defined as various oxygen-containing metal compounds whose metal element is mainly bonded to an oxygen atom to form a three-dimensional network structure. The metal element constituting the inorganic oxide is preferably, for example, an element selected from Groups 2 to 6 of the periodic table, and more preferably an element selected from Groups 3 to 5 of the periodic table. In particular, a colloidal cerium oxide which is preferably an element selected from the group consisting of Si, Al, Ti, and Zr and a metal element of Si is most suitable as a fine inorganic filler for heat resistance improving effect and uniform dispersibility. Further, 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, or a crushed shape, and is not particularly limited.

The lower limit of the average particle diameter 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 diameter of the fine inorganic filler is preferably 50 nm, and particularly preferably 25 nm. When the average particle diameter 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 diameter exceeds the above range, it is short. When the wavelength is affected and white turbidity occurs, the transparency of the substrate layer 2 is lowered to affect the transmittance.

Further, the base material layer 2 may contain an antistatic agent. By forming the base material layer 2 by kneading a polymer resin having an antistatic agent as described above, the optical sheet 1 for a liquid crystal display device can exhibit an antistatic effect, and can prevent adsorption of impurities or hardly overlap with other optical sheets. Due to the shortcomings caused by static electricity. Further, when the antistatic agent is applied to the surface, the surface is sticky or dirty, but the antistatic agent can be reduced by the kneading of the antistatic agent in the substrate layer 2 as described above. The antistatic agent is not particularly limited, and examples thereof include an anionic antistatic agent such as an alkyl sulfate or an alkyl phosphate; a cationic antistatic agent such as a fourth ammonium salt or an imidazoline compound; and a polyethylene glycol system. A nonionic antistatic agent such as polyoxyethylene sorbitan monostearate or ethanolamine, or a polymer antistatic agent such as polyacrylic acid. Among them, a large cationic antistatic agent which is preferable in comparison with an antistatic effect is preferable, and an antistatic effect can be exhibited by adding 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, the optical film 1 for the liquid crystal display device can be shielded from ultraviolet rays, and a small amount of ultraviolet light emitted from the light source of the backlight unit can be blocked to prevent ultraviolet rays from being applied to the liquid crystal layer. damage.

It is also possible to use an ultraviolet stabilizer (the molecular chain contains a base polymer having a UV stabilizer) in place of or in addition to the ultraviolet absorber. The ultraviolet stabilizer can deactivate free radicals, active oxygen, and the like generated by ultraviolet rays to enhance ultraviolet stability, weather resistance, and the like. As the ultraviolet stabilizer, a hindered amine-based ultraviolet stabilizer which has high stability to ultraviolet rays can be preferably used. Further, by using an ultraviolet absorber and an ultraviolet stabilizer together, it is possible to prevent deterioration due to ultraviolet rays and to improve weather resistance.

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

The microlens array 4 is composed of a plurality of microlenses 6 having a random diameter. Further, a plurality of microlenses 6 in the microlens array 4 are formed in a random pattern and in a relatively dense manner.

The microlens arrays 3 and 4 may be integrally formed with the base material layer 2 or may be formed separately from the base material layer 2. Since the microlens arrays 3 and 4 are required to transmit light, they are formed of a transparent, particularly colorless, transparent synthetic resin. Specifically, the same synthetic resin as the above-mentioned base material layer 2 can be used. Further, 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 are formed thereon by an ultraviolet curable resin or the like.

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

The microlens 5 has a convex shape and a substantially spherical shape, that is, a convex lens. The average radius of the microlens 5 is preferably 3 μm or more and 90 μm or less, and particularly preferably 10 μm or more and 75 μm or less. If the average radius of the microlens 5 is lower than the above range, the diffraction phenomenon may occur due to the influence of the wavelength of the light emitted by the light source. Conversely, if the radius exceeds the above range, the light may not have sufficient light at the interface. Diffusion.

The microlens 5 is disposed on the surface of the substrate layer 2 in a relatively dense and geometric manner. The microlens 5 is disposed on the surface of the base material layer 2 in a regular triangular lattice pattern. Therefore, the pitch of the microlens 5 and the distance between the lenses are both fixed. By arranging the pattern, the microlens 5 can be disposed in the most dense manner, and the optical function such as the condensing function, the light diffusing function, and the variable angle function of the optical sheet 1 for a liquid crystal display device can be improved.

The lower limit of the filling ratio of the microlens 5 is preferably 40%, particularly preferably 60%, and most preferably 70%. By setting the filling ratio of the microlens 5 to the lower limit or more, the area occupied by the microlenses 5 on the surface of the optical sheet 1 for a liquid crystal display device can be increased, and the optical sheet 1 for the liquid crystal display device can be collected. Optical functions such as light diffusion are particularly improved.

The lower limit of the height ratio (H/R) of the lens height (H) to the radius of curvature (R) of the microlens 5 is preferably 5/8, particularly preferably 3/4. On the other hand, the upper limit of the height ratio (H/R) is preferably 1. The term "lens height" as used herein means the vertical distance from the base surface to the topmost portion of the microlens 5. By setting the height ratio (H/R) of the microlens 5 to the above range, the refractive action of the lens in the microlens 5 can be effectively exhibited, and the optical sheet 1 for the liquid crystal display device can be optically concentrated or diffused. The function is exceptionally improved.

The upper limit of the ratio (S/D) of the inter-lens distance (S; P-D) to the diameter (D) of the microlens 5 is preferably 1/2, particularly preferably 1/5. Here, the "inter-lens distance" means the shortest distance between one of the adjacent microlenses 5. By setting the inter-lens distance (S) of the microlens 5 to be equal to or less than the above-described upper limit, the flat portion that does not impart optical function can be reduced, and optical functions such as light collection and light diffusion of the optical sheet 1 for liquid crystal display device can be reduced. Extraordinarily improved.

The average of the light emission angles of the microlenses 5 is preferably ±25° or more, and 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 with the microlens 5 having the above-described light emission angle, the viewing angle characteristic required for the optical sheet for a liquid crystal display device can be obtained.

The microlens 6 has an inverted shape which is partially spherical in shape, that is, a concave lens. As described above, since 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 particularly improved. In other words, when the light from the backlight is incident on the back surface of the optical sheet 1 by the optical sheet 1 for a liquid crystal display device, the light is refracted toward the direction of dispersion (light diffusion direction) due to the concave interface of the microlens 6. Improve light diffusivity.

As described above, since the microlens arrays 3 and 4 are formed on both surfaces of the optical sheet 1 for a liquid crystal display device, a wide viewing angle can be obtained by diffusing the light by the concave microlens 6 on the back surface of the light incident; The surface to be emitted maintains the front luminance by the convex microlens 5 refracting the light toward the normal direction. In particular, when the base material layer 2 and the microlens arrays 3 and 4 are integrally formed of the same material, the refraction only occurs at the interface between the surface and the back surface of the optical sheet 1 for a liquid crystal display device, that is, an optical sheet for a liquid crystal display device. (1) Light refraction, scattering, and the like do not occur inside, so that loss of light inside the optical sheet 1 for liquid crystal display device can be minimized, and light transmittance and front luminance can be improved.

The average radius of the microlens 6 is preferably 2 μm or more and 60 μm or less, and particularly preferably 6 μm or more and 40 μm or less. By making the average radius of the microlens 6 within the above range, the microlens array 4 on the back surface of the optical sheet 1 for liquid crystal display device can effectively refract light entering the backlight from the dispersion direction (light diffusion direction) to enhance light diffusion. Sex. When the average radius of the microlens 6 is less than the above range, the diffraction phenomenon may occur due to the influence of the wavelength of the light emitted from the lamp source; if it exceeds the above range, it does not have sufficient light diffusibility.

The average radius of the microlens 6 is preferably 1/12 or more and 1 or less of the average radius of the microlens 5. By setting the average radius ratio of the microlens 6 on the back surface and the microlens 5 on the surface to the above range, it is possible to ensure a certain front luminance on the one hand and to improve light diffusibility on the other hand. 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, and conversely, if it exceeds 1, there is no sufficient light diffusibility and brightness. The uniformity will be reduced.

The lower limit of the filling ratio of the microlens 6 is preferably 50%, particularly preferably 70%, and most preferably 80%. By setting the filling ratio of the microlens 6 to the lower limit or more, the area occupied by the microlenses 6 on the surface of the optical sheet 1 can be increased, and the optical function such as light diffusion of the optical sheet 1 for a liquid crystal display device can be particularly improved. .

The method for producing the optical sheet 1 for a liquid crystal display device is not particularly limited as long as the above-described structure can be formed, and various methods can be employed. As a method of manufacturing 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 the base layer 2 is formed; the base layer 2, the microlens array 3, and The method for integrally forming the microlens array 4 has, in particular, the following method:

(a) a method of laminating a synthetic resin on a sheet mold having inverted shapes of the surfaces of the microlens arrays 3 and 4, and then removing the sheet mold to form the optical sheet 1 for a liquid crystal display device;

(b) an injection molding method in which a molten metal is injected into a metal mold having inverted shapes of the surfaces of the microlens arrays 3 and 4;

(c) reheating the slab-formed resin, holding it between the same metal mold and the metal plate as described above, and performing a method of press-transferring the shape;

(d) passing the resin in a molten state between two roll molds having a reverse shape of the surface of the microlens arrays 3 and 4 on the circumferential surface to transfer the extruded sheet forming method of the above shape;

(e) applying an ultraviolet curable resin to the base material layer, pressing it against a sheet mold, a metal mold or a roll mold having the same reverse shape as described above, and transferring the shape to the uncured ultraviolet curable resin And then irradiating ultraviolet rays, and then curing the ultraviolet curable resin;

(f) a method of applying an uncured ultraviolet curable resin to a metal mold or a roll mold having the same reverse shape as described above, and uniformly pressing the base material layer, and then irradiating the ultraviolet ray to cure the ultraviolet curable resin ;

(g) A method of replacing an ultraviolet curable resin with an electron beam curing resin.

Hereinafter, a method of using a roll mold in the above (d) to (f) will be described. An embossing roll having an inverted shape of the microlens array 3 on the surface, and an embossing roll having a reversed shape of the microlens array 4 on the surface in parallel with the embossing roll at a predetermined interval, the film-like resin By passing between the above two embossing rolls, the microlens array 3 on the surface and the microlens array 4 on the back side can be integrally formed. According to this method, the optical sheets having the specific microlens arrays 3 and 4 can be formed simply and accurately, and can be integrally formed by simply using the same material. Further, since the embossing roll is used for molding, the microlens arrays 3 and 4 do not generate discontinuous portions, and a seamless optical sheet can be produced.

The film-like resin passing between the two embossing rolls may be a molten resin, or may be an unhardened resin in a two-layer layer of a sheet-like resin. Preferably, the molten thermoplastic resin is extruded into a film from a T-die. Shape. As described above, by the so-called extrusion sheet forming method, since the resin which can be extruded in a molten state is formed by the embossing roll, the surface and the back surface microlens arrays 3 and 4 can be simultaneously formed at the time of film formation. Thus, the optical sheet can be manufactured simply and efficiently.

The method for producing the mold (metal mold, mold, etc.) having the inverted shape of the microlens arrays 3 and 4 can be manufactured, for example, by forming a speckled three-dimensional pattern on a substrate by a photoresist material, and The three-dimensional pattern is heated and fluidized to be curved to form a microlens array model, and a metal layer is laminated on the surface of the microlens array model by electroplating, and then the metal layer is peeled off.

According to the above manufacturing method, the microlens arrays 3 and 4 of any shape can be formed simply and surely. Therefore, the size, the filling ratio, the arrangement pattern, and the like of the microlenses 5 and 6 constituting the microlens arrays 3 and 4 can be easily and surely adjusted, and as a result, the optical function of the optical sheet 1 for liquid crystal display device can be simply and surely Be controlled.

Another manufacturing method of the above-described mold (sheet mold or the like) having the inverted shape of the microlens array 3 and the microlens array 4 can be manufactured by using an optical sheet original having a microlens array shape on the surface, and an optical sheet. The surface of the original plate is laminated with a synthetic resin layer for the mold by an extrusion lamination method, and then the optical sheet original is peeled off from the synthetic resin layer for the mold. In the extrusion lamination method, a synthetic resin layer for a mold can be laminated between the optical sheet original sheet and the substrate sheet for a mold by a sandwich extrusion method.

According to the above-described manufacturing method, the surface shape of the optical sheet precursor having the shape of the microlens array on the surface can be faithfully transferred by the extrusion lamination method, so that the optical sheet having optical properties such as high light diffusion function can be produced with good productivity. . In particular, by the sandwich extrusion lamination method, the strength of the optical sheet forming mold can be ensured by the substrate sheet for a mold, and the transfer property of the surface shape of the optical sheet original, heat resistance, and the synthetic resin layer for the optical layer can be used. In order to select the synthetic resin constituting the synthetic resin layer for the mold, the precision of the surface shape of the optical sheet which is precisely calculated and the moldability of the optical sheet forming mold are increased.

Further, by the above-described manufacturing method of the extrusion lamination method, even if it is a mold having a reverse shape of the microlens array 4 on the back surface (the microlens array 4 is composed of a plurality of microlenses 6 having a random diameter), The light-diffusing sheet formed by coating beads having a plurality of diameters is simply used as a master and then transferred.

The edge light type backlight unit shown in FIG. 2 is provided with a light guide plate 7, a pair of paired side light sources 8 disposed on the light guide plate 7, and a liquid crystal display device which is disposed on the surface side of the light guide plate 7 in a superposed manner. Optical sheet 1. The light emitted from the light source 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, the backlight unit has a concentrating function toward the front side and toward the normal line. In addition to the conventional function, the optical sheet 1 for a liquid crystal display device having an excellent light diffusing function can be used to achieve a uniform viewing angle and a wide viewing angle. Light. Therefore, the number of the optical sheets (bead coated sheets, etc.) required for the conventional backlight unit can be reduced, and the thickness, the quality, and the cost can be reduced. Further, by reducing the number of optical sheets mounted, the brightness can be improved. In addition, the edge light type backlight unit can also be equipped with a light source 8 such as 4 tubes or 6 tubes.

The optical sheet 11 for a liquid crystal display device of 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. The base material layer and the microlens array 3 are the same as those of the optical sheet 1 for a liquid crystal display device of FIG. 1 described above, and the same reference numerals will be given thereto, and description thereof will be omitted.

The microlens array 12 is composed of a plurality of microlenses 13 having substantially the same diameter.

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

The microlens 13 is disposed on the back surface of the substrate layer 2 in a relatively dense and geometric manner. The microlens 13 is disposed on the back surface of the base material layer 2 in a regular triangular lattice pattern. Therefore, the pitch of the microlenses 13 and the distance between the lenses are both fixed. In this arrangement pattern, the microlenses 13 can be disposed in the most dense manner, and the optical function such as the light diffusing function of the optical sheet 1 for a liquid crystal display device can be improved. In particular, it is disposed such that the center of the microlens 5 on the surface is located at the center of the microlens 13 on the back side, or the microlens having the center of each triangle of the equilateral triangle lattice pattern constituting the surface of the microlens array 3 on the back side. The center position of the 13 is arranged to increase the multiplying effect of the microlens array on both sides of the watch, and the optical function such as the light diffusing function can be particularly improved.

The optical sheet 21 for a liquid crystal display device of 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. The base material layer and the microlens array 3 are the same as those of the optical sheet 1 for a liquid crystal display device of FIG. 1 described above, and the same reference numerals will be given thereto, and description thereof will be omitted.

The microlens array 22 is composed of a plurality of microlenses 23 having a random diameter.

The microlens 23 is a convex lens. The average radius of the microlens 23 is the same as that of the microlens 6 of the optical sheet 1 for a liquid crystal display device, and is preferably 2 μm or more and 24 μm or less, particularly preferably 6 μm or more and 18 μm or less, wherein the microlens 5 provided on the surface is further used. It is preferable that the average radius is 1/12 or more and 1 or less. Further, the lower limit of the filling ratio of the microlens 23 is preferably 50%, particularly preferably 70%, and most preferably 80%.

Further, the average focal length of the microlens 23 may be 1/2 or less of the average thickness of the base material layer 2. By the microlens 23 having the above focal length, the light incident from the back surface of the optical sheet 21 for liquid crystal display device is refracted through the interface of the microlens array 22 on the back surface, and is dispersed before the microlens array 3 formed on the surface is formed. Therefore, the light diffusing function of the optical sheet 21 for a liquid crystal display device can be improved.

The optical sheet 31 for a liquid crystal display device of 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. The base material layer and the microlens array 3 are the same as those of the optical sheet 1 for a liquid crystal display device of FIG. 1 described above, and the same reference numerals will be given thereto, and description thereof will be omitted.

The microlens array 32 is composed of a plurality of microlenses 33 having substantially the same diameter.

The microlens 33 is a convex lens. The diameter of the microlens 33 is preferably the same as or smaller than the diameter of the microlens 5 of the microlens array 3 constituting the surface. By making the diameter of the microlens 33 different from the size of the microlens 5 on the surface side, it is possible to adjust the focal length of the object, and the light diffusion and surface uniformity can be further improved by combining the microlenses on the surface and the back surface. .

The microlens 33 is disposed on the back surface of the substrate layer 2 in a relatively dense and geometric manner. The microlens 33 is disposed on the back surface of the base material layer 2 in a regular triangular lattice pattern. Therefore, the pitch of the microlens 33 and the distance between the lenses are both fixed. By arranging the pattern, the microlenses 33 can be arranged in the most dense manner, and the optical function such as the light diffusing function of the optical sheet 1 for a liquid crystal display device can be improved. In particular, it is disposed such that the center of the surface microlens 5 is located at the center of the microlens 33 on the back side, or the microlens having the center of each triangle of the equilateral triangle lattice pattern constituting the surface of the microlens array 3 is located at the back side. The center position of 33 is arranged to improve the multiplying effect of the microlens array on both sides of the watch, and the optical function such as the light diffusing function can be particularly improved.

Further, the average focal length of the microlens 33 may be 1/2 or less of the average thickness of the base material layer 2. By the microlens 33 having the above-described focal length, the light incident from the back surface of the optical sheet 31 for liquid crystal display device is refracted through the interface of the microlens array 32 on the back surface, and is dispersed before the microlens array 3 reaching the surface. The light diffusing function of the optical sheet 31 for a liquid crystal display device can be improved.

In any of the optical sheets 11, 21, and 31 for liquid crystal display devices, a microlens array is formed on both surfaces of an optical sheet for a liquid crystal display device, and light is incident on the back surface of the light by the microlenses 13, 23, or 33. Diffusion allows uniformity of brightness and wide viewing angle; on the surface where light is emitted, the convex microlens 5 refracts light in the normal direction to maintain a high frontal brightness.

Further, the optical sheet for a liquid crystal display device of the present invention is not limited to the above embodiment, and for example, the arrangement pattern of the microlenses on the surface is not limited to the above-mentioned equilateral triangular lattice pattern which can be densely filled, or Square grid pattern or random pattern. If it is a random pattern, the generation of the moiré can be reduced when the optical sheet for the liquid crystal display device is overlapped with other optical members. Further, a microlens array composed of microlenses of concave lenses may be provided on the surface. When a microlens array having a concave lens is provided on the surface, it also has an optical function such as light diffusibility which is excellent in comparison with a microlens array in which the above-mentioned convex lens is provided. Further, the microlens on the surface and the microlens on the back may be formed of materials having different refractive indices. Since the surface and the back surface are formed by microlenses having different refractive index materials as described above, light refraction or the like is also generated at the interface between the materials, so that the light diffusibility and surface of the liquid crystal display optical sheet can be improved. Uniformity.

Example

Hereinafter, the present invention will be described in detail based on the examples, but the present invention is limited by the description of the examples.

[Comparative example]

An optical sheet for a liquid crystal display device in which a microlens array composed of a microlens of a convex lens is provided on a surface of a transparent polyethylene terephthalate film having a thickness of 100 μm is used. The microlens of the microlens sheet of the comparative example was molded so that the average diameter of the microlenses was 60 μm and the filling ratio was 70%.

[Examples 1 to 4]

A microlens array composed of a microlens of a convex lens was provided on the surface of a film made of a transparent polyethylene terephthalate 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 a microlens having a concave lens having a random diameter 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 having 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 composed of microlenses having a convex lens having a random diameter 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 having convex lenses having substantially the same diameter on the back surface.

In the microlens array on the back surface, the average diameter of the microlenses having substantially the same diameter was 60 μm, the average diameter of the microlenses having a random diameter was 12 μm, and the filling ratio was 70%.

[Feature evaluation]

The optical sheets for liquid crystal display devices of Examples 1 to 4 and the optical sheets for liquid crystal display devices of Comparative Examples were used to measure the haze. The haze was measured by a haze tester of Suga Test Instruments Co., Ltd. in accordance with the measurement method specified in JIS-K7136. Further, using the optical sheets for liquid crystal display devices of Examples 2 and 4 and Comparative Examples described above, the half value angles of the luminances were measured. Further, using the optical sheets for liquid crystal display devices of the above-described Examples 2 and 4 and Comparative Examples, the optical sheets were actually incorporated in a direct type backlight unit, and the light diffusibility thereof was evaluated. The evaluation of the light diffusibility was performed by visually confirming the degree of erasure of the light source image on the surface side when the backlight was irradiated, and the evaluation was performed based on the following criteria.

(a) The situation where the light source image is almost invisible is ◎

(b) The case where the light source image is not easily seen is ○

(c) The situation where the light source image can be seen slightly is △

(d) The situation in which the light source image can be clearly seen is ×

The results are shown in Table 1. Further, the light source image of the liquid crystal display device for a liquid crystal display device of the comparative example is shown in FIG. 6, and the light for the liquid crystal display device of the second embodiment is incorporated in the direct type backlight unit. The source image photograph is shown in Fig. 7. The light source image of the liquid crystal display device of Example 4 is shown in Fig. 8 when it is incorporated in the direct type backlight unit.

As shown in the above Table 1, the optical sheets for liquid crystal display devices of Examples 1 to 4 exhibited higher haze than the optical sheets for liquid crystal display devices of Comparative Examples having no microlens array on the back surface, that is, Indicates high light diffusivity and a wide viewing angle. Further, if compared between Examples 1 to 4, the microlenses on the back side have a random diameter, and those having a concave lens shape exhibit a high haze, that is, a display having a high light diffusibility and a wide field of view. angle.

Further, as shown in Table 1, the optical sheets for liquid crystal display devices of Examples 2 and 4 have a wide half angle of brightness compared to the optical sheets for liquid crystal display devices of Comparative Examples in which the back surface does not have a microlens array.

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

Production Industry availability

As described above, the optical sheet for a liquid crystal display device of the present invention can be used as a constituent element of a backlight unit of a liquid crystal display device, and is particularly suitable for use in a transmissive liquid crystal display device.

1. . . Optical sheet for liquid crystal display device

2. . . Substrate layer

3. . . Microlens array

4. . . Microlens array

5. . . Microlens

6. . . Microlens

7. . . Light guide

8. . . Light source

11. . . Optical sheet for liquid crystal display device

12. . . Microlens array

13. . . Microlens

twenty one. . . Optical sheet for liquid crystal display device

twenty two. . . Microlens array

twenty three. . . Microlens

31. . . Optical sheet for liquid crystal display device

32. . . Microlens array

33. . . Microlens

40. . . Backlight unit

41. . . Light source

42. . . Light guide

43. . . Optical sheet

44. . . Microlens sheet

45. . . Bract

46. . . Crotch

47. . . Microlens array

Fig. 1 is a schematic partial cross-sectional view showing an optical sheet for a liquid crystal display device according to a specific embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing a backlight unit including the optical sheet for a liquid crystal display device of Fig. 1.

Fig. 3 is a schematic partial cross-sectional view showing an optical sheet for a liquid crystal display device which is different from the optical sheet for a liquid crystal display device of Fig. 1.

4 is a schematic partial cross-sectional view showing an optical sheet for a liquid crystal display device which is different from the optical sheet for a liquid crystal display device of FIGS. 1 and 3.

Fig. 5 is a schematic partial cross-sectional view showing an optical sheet for a liquid crystal display device which is different from the optical sheets for liquid crystal display devices of Figs. 1, 3 and 4.

Fig. 6 is a photograph showing a light source image when an optical sheet for a liquid crystal display device of a comparative example is incorporated in a direct type backlight unit.

Fig. 7 is a view showing a light source image when the optical sheet for a liquid crystal display device of the second embodiment is incorporated in a direct type backlight unit.

Fig. 8 is a view showing a light source image when the optical sheet for a liquid crystal display device of the fourth embodiment is incorporated in a direct type backlight unit.

9(a) and 9(b) are schematic perspective views showing a general backlight unit, and a schematic cross-sectional view showing a conventional general lenticular sheet.

1. . . Optical sheet for liquid crystal display device

2. . . Substrate layer

3. . . Microlens array

4. . . Microlens array

5. . . Microlens

6. . . Microlens

D. . . Microlens diameter

H. . . Microlens height

P. . . Distance between microlenses

R. . . Microlens radius of curvature

S. . . Distance between microlenses

Claims (8)

An optical sheet for a liquid crystal display device, comprising: a transparent substrate layer; and a microlens array comprising a plurality of microlenses formed on a surface and a back surface of the substrate layer; the microlens array on the back surface is randomly The microlens of the back surface is a concave lens, and the microlens of the back surface has an average radius smaller than an average radius of the microlenses of the surface. The optical sheet for a liquid crystal display device according to claim 1, wherein the surface microlens has an average radius of 3 μm or more and 90 μm or less. The optical sheet for a liquid crystal display device according to claim 1, wherein the microlens on the back surface has an average radius of 2 μm or more and 60 μm or less. The optical sheet for a liquid crystal display device of claim 1, wherein the average radius of the microlenses on the back surface is 1/12 or more of the average radius of the surface microlenses and is less than 1. The optical sheet for a liquid crystal display device according to claim 1, wherein the substrate layer is integrally formed with the microlens array of the surface of the substrate layer and the back surface. The optical sheet for a liquid crystal display device of claim 1, wherein the arrangement pattern of the microlenses in at least the surface microlens array is an equilateral triangle lattice pattern or a random pattern. An optical sheet for a liquid crystal display device according to claim 1, which is formed by an extrusion sheet forming method; the extruded sheet forming method is used An embossing roll having an inverted shape of the microlens array of the surface, and an embossing roll disposed in parallel with the embossing roll and having an inverted shape of the microlens array of the back surface. A backlight unit for a liquid crystal display device that disperses and guides light emitted from a light source to a surface side, and is characterized by comprising the optical sheet for a liquid crystal display device of claim 1 of the patent application.