JP2009223191A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To actualize a high performance of light condensation while preventing a moire phenomenon in an optical device having a micro-lens array. <P>SOLUTION: An optical sheet 1 has a light incident face 1a and a light emission face 1b. The micro-lens array 10 is formed on the reference face 12 of at least one of the light incident face 1a or light emission face 1b. The micro-lens array 10 has a plurality of micro-lenses 11 arranged in a cycle and in a matrix. Each of a plurality of micro-lenses 11 has a convex or concave shape. The reference face 12 has a wavy form. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical element.

  Conventionally, liquid crystal display devices are widely used for computer displays, television devices, and the like.

  Usually, in a liquid crystal display device, a light source device is disposed on the back of a liquid crystal display cell. In recent years, there has been a strong demand for high-definition display image quality in liquid crystal display devices and reduction in power consumption of liquid crystal display devices. Accordingly, higher light emission efficiency is also desired in light source devices.

  As means for improving the light emission efficiency of the light source device, conventionally, means for installing a sheet for improving luminance on the light emitting surface side of the planar light source is known. Here, as the sheet for improving the brightness, for example, a bead-coated light diffusion sheet in which a coating containing microbeads is applied, a prism array sheet in which a plurality of prisms having an isosceles cross section are arranged, and the like. Can be mentioned.

  However, the bead-coated light diffusion sheet has only a small light focusing performance. For this reason, even if a plurality of bead-coated light diffusion sheets are used in an overlapping manner, it is difficult to obtain a sufficient brightness enhancement effect.

  In the prism array sheet, there is a direction that does not emit light. For this reason, there exists a problem that the viewing angle of a liquid crystal display device is restrict | limited.

For example, Patent Documents 1 and 2 disclose so-called microlens array sheets as optical sheets that can solve such problems of conventional sheets.
JP 7-333406 A JP 2004-145328 A

  Usually, in the microlens array sheet, a plurality of microlens arrays are regularly arranged in a matrix. In the microlens array sheet, from the viewpoint of improving the light focusing performance, it is preferable to increase the microlens occupation ratio, which is the ratio of the area occupied by the microlens to the area of the light exit surface.

  However, when the microlens occupation ratio is increased, the moire phenomenon is likely to occur. For this reason, the conventional microlens array sheet has a problem that it is difficult to achieve both suppression of the occurrence of the moire phenomenon and sufficiently high light focusing performance.

  The present invention has been made in view of such a point, and an object thereof is to realize high light focusing performance while suppressing the occurrence of a moire phenomenon in an optical element having a microlens array.

  The optical element according to the present invention has a light incident surface and a light exit surface. A microlens array in which a plurality of microlenses are periodically arranged in a matrix is formed on at least one reference surface of the light incident surface and the light emitting surface. Each of the plurality of microlenses is formed in a convex shape or a concave shape. The reference surface is formed in a wavy shape.

  It is preferable that the reference surface has a undulation represented by 2 μm or more and 50 μm or less as an arithmetic average undulation Wa measured with a cutoff wavelength λc = 0.08 mm and a contour curve filter λf = 40 mm.

  In one specific aspect of the present invention, the plurality of microlenses are arranged in a triangular lattice shape.

  In another specific aspect of the present invention, the plurality of microlenses are arranged in an equilateral triangular lattice shape.

  In another specific aspect of the present invention, the diameter of each microlens is 2 μm or more and 100 μm or less.

  In still another specific aspect of the present invention, the plurality of microlenses are arranged such that the minimum value of the distance between the end portions of adjacent microlenses is 1 μm or more and 10 μm or less.

  In still another specific aspect of the present invention, each microlens is formed in a convex shape, and the microlens array is formed on a light exit surface.

  In still another specific aspect of the present invention, the optical element is substantially made of plastic and has an average thickness of 20 μm or more and 500 μm or less.

  According to the present invention, in an optical element having a microlens array, high light focusing performance can be realized while suppressing the occurrence of a moire phenomenon.

  Hereinafter, an example of a preferable embodiment in which the present invention is implemented will be described in detail by taking the optical sheet 1 shown in FIG. 1 as an example. However, the optical sheet 1 shown in FIG. 1 is merely an example. The present invention is not limited to the optical sheet 1.

  FIG. 1 is a plan view of the optical sheet 1. FIG. 2 is a cross-sectional view of the optical sheet 1.

  The optical sheet 1 has light transmittance. In other words, the optical sheet 1 is formed of a light transmissive material. The transmission wavelength region of the optical sheet 1 is not particularly limited. It can set suitably according to the use of the optical sheet 1, etc. For example, when the optical sheet 1 is used in a liquid crystal display device, the transmission wavelength region of the optical sheet 1 is generally set to a visible light region having a wavelength of about 380 nm to 700 nm.

  The material of the optical sheet 1 is not particularly limited as long as it can secure the above-described light transmittance. Examples of the material of the optical sheet 1 include glass and plastic. Among these, the material of the optical sheet 1 is preferably plastic. That is, it is preferable that the optical sheet 1 is substantially made of plastic. This is because plastic is excellent in light weight, flexibility, and processability.

  Specific examples of the plastic include polymethyl methacrylate, polycarbonate, polyethylene terephthalate and polyacrylonitrile. Moreover, you may add a weathering agent, a processing aid, a filler, a reinforcing agent, etc. to the optical sheet 1 in the range which does not inhibit translucency.

  In addition, the thickness of the optical sheet 1 is not specifically limited. The thickness of the optical sheet 1 is set to, for example, an average thickness of about 20 μm or more and 500 μm or less.

  As shown in FIG. 2, the optical sheet 1 includes a light incident surface 1a and a light emitting surface 1b.

  In the present embodiment, the light incident surface 1a is formed as an optical mirror surface. For this reason, the high light beam focusing function of the optical sheet 1 is realized. However, the light incident surface 1a may not be formed on an optical mirror surface. The light incident surface 1a may be formed on a rough surface in order to reduce adhesion to other members, and one or a plurality of protrusions may be formed on the light incident surface 1a. The light incident surface 1a may be subjected to frosting, embossing, printing, or the like.

  In the present embodiment, the microlens array 10 is formed on the light emitting surface 1b. However, the microlens array may be formed on the light incident surface 1a. Further, a microlens array may be formed on both the light incident surface 1a and the light emitting surface 1b. However, from the viewpoint of improving the light focusing performance, it is preferable to form the microlens array 10 having a plurality of convex microlenses 11 on the light emitting surface 1b.

  As shown in FIG. 1, the microlens array 10 includes a plurality of microlenses 11. The microlens 11 is formed in a convex shape or a concave shape. Specifically, in the present embodiment, the microlens 11 is formed in a convex shape. The plurality of microlenses 11 are formed periodically and in a matrix. However, the microlens 11 may be formed in a concave shape, for example.

  In this specification, “matrix shape” means that the first direction and the first direction are periodically arranged in both the second direction forming an angle. Here, the first direction and the second direction may not be perpendicular to each other, and may be oblique.

  The microlens array 10 may have a plurality of types of microlenses 11. For example, the microlens array 10 may include a plurality of types of microlenses 11 having different sizes. More specifically, as shown in FIG. 7, the microlens array 10 may include a plurality of types of microlenses 11a and 11b having different diameters arranged alternately and in a matrix.

In the present embodiment, the plurality of microlenses 11 are specifically arranged in a triangular lattice shape. That is, as shown in FIG. 1, a plurality of micro lenses 11, figure T ₁ which is formed by connecting the centers C ₁ -C ₃ between the adjacent microlenses 11 are arranged so as to be triangular. More specifically, the plurality of microlenses 11 are arranged in an equilateral triangular lattice shape. That is, as shown in FIG. 1, a plurality of micro lenses 11, the center C ₁ -C ₃ figure T ₁ which is formed by connecting the adjacent microlenses 11 are arranged such that an equilateral triangle .

  In the present invention, the arrangement of the plurality of microlenses 11 is not limited to the triangular lattice arrangement. The plurality of microlenses 11 may be arranged in a square lattice, for example. In other words, the plurality of microlenses 11 may be regularly arranged in both the first direction and the second direction perpendicular to the first direction.

  In the present embodiment, the microlens 11 is formed in a substantially hemispherical shape. However, in the present invention, the shape of the microlens is not limited to a substantially hemispherical shape. The microlens may be formed in, for example, a partially cut oval, parabolic rotator, cone, pyramid, truncated cone, or truncated pyramid. However, the shape of the microlens is preferably a true hemisphere. This is because the light focusing performance can be further increased.

  The diameter D of the microlens 11 is not particularly limited, but can be set to, for example, about 2 μm or more and 100 μm or less. A preferable diameter D of the microlens 11 is not less than 5 μm and not more than 75 μm. When the diameter D of the microlens 11 is less than 2 μm, the amount of diffracted light generated in the microlens array 10 tends to increase. When the diameter D of the microlens 11 exceeds 100 μm, the microlens 11 tends to be visually recognized. For this reason, for example, when an optical sheet having a microlens with a diameter D exceeding 100 μm is used in a display device, luminance unevenness tends to be visually recognized.

  In the present specification, the diameter of the microlens means the diameter when the microlens is viewed in plan. In addition, when the microlens has an oval shape with a part cut away, the diameter of the microlens is an average value of the major axis and the minor axis.

  Although the minimum value P of the distance between the edge part of the adjacent micro lens 11 is not specifically limited, For example, it can set to about 1 micrometer or more and 10 micrometers or less. The minimum distance P of the plurality of microlenses 11 is preferably 2 μm or more and 5 μm or less. When the distance minimum value P of the plurality of microlenses 11 is less than 1 μm, it is difficult for the area between adjacent microlenses 11 to function as an air layer. For this reason, the lens function of the microlens 11 tends to deteriorate. On the other hand, when the distance minimum value P of the plurality of microlenses 11 exceeds 10 μm, the occupation ratio of the microlenses 11 with respect to the light exit surface 1b decreases, and thus it tends to be difficult to suppress the vertically transmitted light.

  As shown in FIG. 2, the microlens array 10 is formed on the reference surface 12. The reference surface 12 is not a surface that actually exists in the manufactured optical sheet 1. The reference surface 12 is a virtual surface.

  In the present invention, the “reference surface” means a surface remaining after removing a substantially hemispherical portion in a state where the microlens is removed, for example, in the case of a substantially hemispherical microlens. In the microlens array, the reference surface is formed by complementing the cross section of the bottom of the microlens with a substantially flat surface, and the complemented plane and the surface of the portion where the microlens is not formed.

  In the optical sheet, the reference surface is, for example, a microscopic observation of an arbitrary vertical cut surface, and a portion where the microlens is not formed on the light exit surface is extracted, and a portion where the microlens is formed is represented by spline interpolation or the like Can be specified by performing interpolation.

  In the present embodiment, the reference surface 12 is formed in a wavy shape. In other words, the reference surface 12 is not a flat surface. For this reason, the optical regularity of the arrangement of the plurality of microlenses 11 is low. Therefore, the occurrence of moire phenomenon in the optical sheet 1 can be suppressed. Furthermore, generation of diffracted light in the microlens array 10 can be suppressed.

  Hereinafter, these effects will be described in more detail with reference mainly to FIGS. For example, as shown in FIG. 3, when the reference surface 112 is a flat surface, as shown in FIG. 4, the light main emission portion 113 that emits the largest amount of light in the microlens 11 is linearly highly regular. Will be arranged. For this reason, there exists a problem that a moire phenomenon and a diffraction phenomenon generate | occur | produce easily.

  On the other hand, in this embodiment, as shown in FIG. 2, the reference surface 12 is formed in a wavy shape. For this reason, as shown in FIG. 5, the regularity of the arrangement | sequence of the light ray main emission part 13 is comparatively low. Therefore, the distance between the centers of the adjacent ray main emission portions 13 is also random. Thus, in this embodiment in which the reference surface 12 is formed in a wavy shape, the optical regularity is low with respect to the arrangement of the plurality of microlenses 11. Therefore, the occurrence of moire phenomenon and diffraction phenomenon is effectively suppressed.

  The degree of waviness of the reference surface 12 is not particularly limited. However, it is preferable that the reference surface 12 has a undulation represented by 2 μm or more and 50 μm or less as an arithmetic average undulation Wa measured with a cutoff wavelength λc = 0.08 mm and a contour curve filter λf = 40 mm.

  By setting the waviness of the reference surface 12 to 2 μm or more as the arithmetic average waviness Wa, the occurrence of moire phenomenon and diffraction phenomenon can be more effectively suppressed. However, when the waviness of the reference surface 12 exceeds 50 μm as the arithmetic average waviness Wa, the optical function of the microlens 11 tends to be lowered.

  The arithmetic average waviness Wa means an arithmetic average waviness defined by JIS B 0601: 2001.

  By the way, as another method for suppressing the occurrence of the moire phenomenon, it is conceivable to reduce the diameter of the microlenses and shorten the distance between adjacent microlenses. However, when this method is adopted, the ratio of the area occupied by the microlens to the light exit surface tends to be small. For this reason, it becomes difficult to realize high light convergence performance.

  On the other hand, in this embodiment, since the generation of the moire phenomenon is suppressed by making the reference surface 12 wavy, it is not necessary to increase the distance minimum value P of the microlens 11. In other words, as in this embodiment, by forming the reference surface 12 in a wavy shape, the minimum distance P of the microlens 11 is reduced, and the ratio of the area occupied by the microlens 11 to the light exit surface 1b. Even when the occupation ratio is high, it is possible to suppress the occurrence of moire phenomenon and diffraction phenomenon. That is, according to the present embodiment, high light focusing performance can be realized while suppressing the occurrence of moire phenomenon and diffraction phenomenon.

  In the present embodiment, the plurality of microlenses 11 are arranged in a triangular lattice shape. For this reason, the ratio which occupies for the light-projection surface 1b of the micro lens array 10 is enlarged. Accordingly, the vertically transmitted light is more effectively suppressed. At the same time, high light focusing performance is realized.

  In the present embodiment, in detail, the plurality of microlenses 11 are arranged in an equilateral triangular lattice shape. For this reason, the ratio of the microlens array 10 to the light emitting surface 1b is further increased. Accordingly, the vertically transmitted light is more effectively suppressed. At the same time, high light focusing performance is realized.

  In addition, the manufacturing method of the optical sheet 1 is not specifically limited, The manufacturing method of the optical element generally used conventionally is applied for manufacture of the optical sheet 1. FIG. Examples of the method for producing the optical sheet 1 include press molding using a molding die, UV polymerization molding method, and printing molding method using an ink jet method.

  Moreover, you may produce the optical sheet 1 by bonding another translucent sheet | seat in which the microlens array 10 was formed to a translucent sheet | seat.

  FIG. 5 is a schematic side view of a liquid crystal display device 2 using the optical sheet 1 of the present embodiment. As shown in FIG. 5, the liquid crystal display device 2 includes a light source device 21, the optical sheet 1, and a liquid crystal display cell 25. The light source device 21 and the optical sheet 1 constitute a light source unit 20.

  In the present embodiment, a liquid crystal display device including a so-called direct-type backlight will be described as an example. However, in the present invention, the liquid crystal display device may have, for example, a so-called edge light type backlight. The liquid crystal display device may be a reflective liquid crystal display device that does not have a backlight.

  The light source device 21 includes a casing 22, a plurality of linear light sources 23, and a light diffusing plate 24. The plurality of linear light sources 23 are accommodated in the casing 22. In the present embodiment, the linear light source 23 is constituted by a cold cathode ray tube. However, the type of the filament light source 23 is not particularly limited. Further, instead of the linear light source 23, a plurality of point light sources may be arranged in a matrix. The point light source can be configured by, for example, an LED (light-emitting diode).

  The optical sheet 1 is disposed above the light emission surface of the light source device 21. A liquid crystal display cell 25 is disposed on the light exit surface 1 b side of the optical sheet 1. In the present embodiment, the liquid crystal display cell 25 is disposed above the light emitting surface 1b. However, the liquid crystal display cell 25 may be disposed on the light emitting surface 1b.

  As described above, according to the optical sheet 1, high light focusing performance can be realized while suppressing the occurrence of moire phenomenon and diffraction phenomenon. Therefore, the liquid crystal display device 2 having high brightness and high display quality can be realized.

(Modification)
In the above embodiment, the example in which the microlens array 10 is formed on the surface of the optical sheet 1 has been described. However, in the present invention, the optical element on which the microlens array 10 is formed is not limited to this. The optical element on which the microlens array 10 is formed is not particularly limited as long as it has a light incident surface and a light output surface.

(Example)
The polyethylene terephthalate film was manufactured using a hot press molding method to produce a first sheet having a wavy shape formed on the surface. In the hot press molding method, a paired first mold and second mold were used. As the first mold, a mold having a surface having an undulation of 20 μm in arithmetic mean waviness Wa was used. The molding surface of the second mold was substantially a mirror surface. The average thickness of the obtained first sheet was 300 μm. Moreover, the surface of the obtained 1st sheet | seat had a 19 micrometer wave | undulation by arithmetic mean wave | undulation Wa.

  Next, the optical sheet 1 shown in FIGS. 1 and 2 was obtained by using the UV curable acrylic resin to produce the microlens array 10 on the surface having the undulation of the first sheet by the UV polymerization molding method. . The shape of the microlens 11 was a hemispherical shape with a radius of 45 μm. The arrangement of the plurality of microlenses 11 was an equilateral triangular lattice arrangement. The minimum distance P of the microlens 11 was 10 μm.

  A 20-inch size liquid crystal display device 2 shown in FIG. 6 was produced using the obtained optical sheet 1.

  About the obtained liquid crystal display device 2, the light focusing performance, the moire phenomenon occurrence situation, and the diffraction phenomenon occurrence situation were evaluated.

  Specifically, the light focusing performance was evaluated by measuring the luminance at the center of the screen in the normal direction of the screen in a state where white display was performed on the entire screen of the liquid crystal display device 2. Moreover, the relative brightness value was calculated by measuring the non-mounting luminance when the optical sheet 1 was not mounted and dividing the mounting luminance when the optical sheet 1 was mounted by the non-mounting luminance.

  The evaluation of the occurrence of the moire phenomenon was performed by displaying a radial test chart (Japanese Image Society Screen Gauge) on the liquid crystal display device 2 and visually confirming the presence or absence of the moire phenomenon.

  In addition, the evaluation of the state of occurrence of the diffraction phenomenon is performed by visually observing the range of −60 ° to + 60 ° in the horizontal direction and −45 ° to + 45 ° in the vertical direction with white display on the entire screen of the liquid crystal display device 2. This was done by observing the presence or absence of coloring.

  The results are shown in Table 1 below.

(Comparative Example 1)
A liquid crystal display device was produced in the same manner as in the above example except that the surface of the first mold was flattened, and the same evaluation was performed.

  The results are shown in Table 1 below.

(Comparative Example 2)
A liquid crystal display device was produced and evaluated in the same manner as in Comparative Example 1 except that a plurality of microlenses were irregularly arranged with fluctuations within a range of ± 20 μm from the equilateral triangular lattice arrangement.

  The results are shown in Table 1 below.

(Comparative Example 3)
The liquid crystal display device was the same as Comparative Example 1 except that the microlens array was a hemispherical microlens having a radius of 45 μm and a hemispherical microlens having a radius of 35 μm alternately arranged in an equilateral triangular lattice. A similar evaluation was made.

  The results are shown in Table 1 below.

  As shown in Table 1, also in the example in which the reference surface 12 has a wavy shape, high light focusing performance was confirmed as in Example 1 in which the reference surface 12 was flat. In Comparative Example 1, the moire phenomenon and the diffraction phenomenon were observed, whereas in the example, the moire phenomenon and the diffraction phenomenon were not observed.

Further, in Comparative Example 2 in which the microlens array was fluctuated, the moire phenomenon and the diffraction phenomenon were not observed as in the example. However, the light focusing performance in the example is 455 cd / m ² and the relative value is 1.45, whereas the light focusing performance in the comparative example 2 is 383 cd / m ² and the relative value is 1.22. Low.

In Comparative Example 3 in which two types of microlenses were arranged, the diffraction phenomenon was not observed, but the moire phenomenon was observed. The light focusing performance in the example is 455 cd / m ² and the relative value is 1.45, whereas the light focusing performance in the comparative example 3 is 411 cd / m ² and the relative value is 1.31. Low.

  From the above results, it can be seen that by making the reference surface 12 wavy, high light focusing performance can be realized while suppressing the occurrence of moire and diffraction phenomena.

It is a top view showing a part of optical sheet concerning an embodiment. It is the II-II arrow line view in FIG. It is the III-III arrow line view in FIG. It is a top view of the optical sheet whose reference plane is flat. It is a top view of the optical sheet in an embodiment for explaining the arrangement of the main ray emitting part. It is a schematic sectional drawing of a liquid crystal display device. It is a top view showing a part of optical sheet concerning a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical sheet 1a ... Light-incidence surface 1b ... Light-projection surface 2 ... Liquid crystal display device 10 ... Micro lens array 11 ... Micro lens 12 ... Reference surface 13 ... Light beam main emission part 20 ... Light source unit 21 ... Light source device 22 ... Casing 23 ... Line light source 24 ... Light diffusion plate 25 ... Liquid crystal display cell

Claims (8)

  A microlens array having a light incident surface and a light exit surface, each having a plurality of microlenses formed in a convex shape or a concave shape, arranged periodically and in a matrix, includes a light entrance surface and a light exit surface. The optical element is formed on at least one of the reference surfaces, and the reference surface is formed in a wavy shape.   2. The optical element according to claim 1, wherein the reference surface has a waviness represented by 2 μm or more and 50 μm or less as an arithmetic average waviness Wa measured with a cutoff wavelength λc = 0.08 mm and a contour curve filter λf = 40 mm. .   The optical element according to claim 1, wherein the plurality of microlenses are arranged in a triangular lattice shape.   The optical element according to claim 1, wherein the plurality of microlenses are arranged in an equilateral triangular lattice shape.   The diameter of each said micro lens is an optical element as described in any one of Claims 1-4 which are 2 micrometers or more and 100 micrometers or less.   The optical device according to any one of claims 1 to 5, wherein the plurality of microlenses are arranged such that a minimum value of a distance between end portions of adjacent microlenses is 1 µm or more and 10 µm or less. element. Each of the microlenses is formed in a convex shape,
The optical element according to claim 1, wherein the microlens array is formed on the light emitting surface.   The optical element according to any one of claims 1 to 7, which is substantially made of plastic and has an average thickness of 20 µm or more and 500 µm or less.

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