JP2005077546A - Optical element equipped with microlens array, liquid crystal display equipped with the optical element, and manufacturing method of the optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate such failures where light loss due to unwanted light is large and front luminance is not satisfactory in the case of using a conventional prism sheet in a liquid crystal display. <P>SOLUTION: By using a two-layer constitution microlens element provided with a densely-arranged 1st microlens array and a 2nd microlens array positioned at a prescribed position to the 1st microlens array, and constituted so that light made incident on the 1st microlens array at a prescribed angle is emitted from the 2nd microlens array at an angle smaller than the incident angle, the light utilization efficiency is improved and the front luminance is improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element including a microlens array having a two-layer structure, a manufacturing method thereof, and a liquid crystal display device.

  The number of products equipped with liquid crystal display devices such as mobile phones, portable notebook computers, TVs, and digital cameras is increasing. In such products, it is necessary to increase the directivity of the backlight, that is, to increase the front luminance, which greatly affects the visibility of the display device, in order to reduce power consumption and extend the battery driving time. is there.

  As means for realizing this, as shown in FIG. 19, a backlight is proposed in which a prism sheet 101 in which a prism row is formed on one side is placed on the exit surface side of the light guide 102. Reference numeral 103 denotes a light source, 104 denotes a diffusion plate, and 105 denotes a liquid crystal panel. The mechanism of increase in front luminance by this prism sheet is as follows.

In the backlight, light emitted from the light guide 102 enters the prism sheet 101, a part of the incident light is refracted and transmitted by the prism sheet 101, and the rest is reflected back to the light guide 102. Such an edge light type generally has a directivity characteristic in which the front luminance is relatively low and the luminance seen from an oblique direction is high. The directional characteristics are improved so as to increase. Further, the reflected light from the prism sheet 101 is diffusely reflected by the diffusion plate 104 placed on the light exit surface of the light guide, and the brightness of the light exit surface can be increased, and the front brightness is also increased accordingly. To do.
JP-A-8-190806 (publication date 1996.7.23) JP-A-8-166582 (Publication Date 1996.6.25) Japanese Patent Laid-Open No. 10-161096 (publication date: 1998.6.19)

  FIG. 20 shows a cross section 106 of such a prism sheet 101. The light ray incident on the prism sheet 101 is a light ray A that is directly transmitted through the prism slope according to the incident angle, and is reflected once by one prism slope, and then reflected again by the other prism slope and returned to the incident side. B. After being reflected once by one prism slope, it is divided into rays C that are transmitted through the other prism slope and emitted. In this case, depending on the selection of the prism apex angle, there may be a component that causes multiple reflection, but the ratio is usually small. Among these, the light ray A is emitted in the front direction, that is, the observation direction, and is actually used. In addition, the light beam B is an effective light beam that is diffusely reflected by the diffusion plate 104 on the exit surface of the light guide 102 and increases the brightness of the exit surface. On the other hand, the light ray C is a light ray that is emitted at a wide angle outside the effective viewing angle of the liquid crystal display device, and is a light ray that does not contribute to an increase in front luminance.

  As a result, the light emitted from the prism sheet 101 is distributed in a range of a viewing angle of about ± 40 ° from the front (when the apex angle is 90 ° to 100 ° and the refractive index is about 1.5 to 1.59). When the viewing angle is larger than this, the luminance rapidly decreases, and once it becomes almost zero, the luminance increases again at a larger viewing angle. Therefore, as a result, the emission range of the emitted light is narrowed to increase the luminance.

  However, as described above, the viewing angle is as large as ± 40 °, and not only the front luminance is sufficiently increased, but also unnecessary light such as the light ray C is generated, resulting in a loss of light amount.

  In order to solve the above problems, the present invention has the following configuration.

  The optical element of the present invention includes a first microlens array arranged densely and a second microlens array positioned at a predetermined position with respect to the first microlens array. When the light beam incident at a predetermined angle is emitted from the second microlens array, the light beam is emitted at an angle smaller than the incident angle.

  Further, the second microlens array is arranged in the vicinity of the focal position of the first microlens array.

  The focal length of the first microlens array and the focal length of the second microlens array are equal to each other.

  Further, the first microlens array is flattened, and the incident surface is substantially flat.

  The first microlens array may be a prism array. The first microlens array may be a cylindrical lens array.

  The liquid crystal display device of the present invention includes any one of the above optical elements.

  An optical element manufacturing method according to the present invention includes a first microlens array that is densely arranged and a second microlens array that is positioned at a predetermined position with respect to the first microlens array. A step of forming a first microlens array; a step of applying a photosensitive resin material in the vicinity of a second microlens array formation region; and entering substantially parallel light into the first microlens array, The method includes a step of patterning the photosensitive resin material using light focused by the microlens array.

  In the method for manufacturing an optical element, the step of forming the first microlens array is molding using a transfer mold.

  In the method of manufacturing the optical element, in the step of causing the substantially parallel light to be incident on the first microlens array and patterning the photosensitive resin material, the incident angle of the substantially parallel light incident on the first microlens array is set. The shape of the second microlens array is formed while changing and changing the intensity of the parallel light with respect to the incident angle.

  The optical element according to the present invention enables easy and accurate alignment of the two-layer microlens array, and can be converted into a light beam with less unnecessary light and good directivity. It is possible to improve the screen brightness of the display device and reduce power consumption.

  Examples of the present invention will be described below.

  FIG. 1 shows a configuration diagram of an optical element including a first microlens array and a second microlens array according to this embodiment.

  A first microlens array 2 is formed in advance on the resin sheet 1, and a second microlens array 3 is formed on the opposite side.

  The first microlens array 2 and the second microlens array 3 are made of an ultraviolet curable resin, and the resin sheet 1 is made of PET (polyethylene terephthalate) or PC (polycarbonate) and has a thickness of 100 μm. As shown in FIG. 2, the planar arrangement of the first microlens array 2 is a square dense arrangement, and the second microlens array 3 is the same arrangement. The first microlens array 2 and the second microlens array 3 are arranged so that the lens centers coincide with each other.

  The focal length of the first microlens array 2 is equal to the thickness of the resin sheet 1, 100 μm in the resin sheet, and the focal length of the second microlens array 3 is also 100 μm. Therefore, the first microlens array 2 focuses on the vicinity of the second microlens array 3 when a parallel light beam enters.

  Here, the pitch of the first microlens array depends on the pixel interval of the panel of the liquid crystal display device. The pixel interval of the liquid crystal panel is about 100 to 300 μm in the XGA or SXGA class of about 15 inches to 19 inches, and about 50 to 200 μm in the high-definition type for portable devices, so at least for one pixel. It is necessary for one microlens to correspond. Therefore, the pitch of the first microlens array needs to be at least 300 μm or less, preferably 100 μm or less. When the pitch of the first microlens array is 300 μm, for manufacturing reasons, the focal length is 300 μm or more, and when the refractive index of the resin sheet is 1.5, the resin sheet thickness is about 200 μm. Similarly, when the pitch of the first microlens array is 100 μm, the focal length is 100 μm or more and the resin sheet thickness is about 67 μm. If the refractive index of the resin sheet is 1.59, the resin sheet thickness is about 189 μm. Similarly, when the pitch of the first microlens array is 100 μm, the focal length is 100 μm or more and the resin sheet thickness is about 63 μm. From the above, the microlens array pitch is preferably about 50 to 300 μm, and the thickness of the lens resin sheet is preferably about 0.6 to 0.7 times the lens array pitch.

  FIG. 3A shows a light beam incident on the first microlens array 2 at 0 degrees. The light beam focused by the first microlens array 2 near the optical axis of each lens of the second microlens array 3 passes through the second microlens array 3 as it is. On the other hand, as shown in FIG. 3B, a light beam incident at a constant incident angle is focused at a position away from the optical axis of the second microlens array 3, and the focal position of the second microlens array 3 is Since it is in the first microlens array 2, the principal ray is emitted in a direction perpendicular to the resin sheet 1 by the second microlens array 3. That is, even if the direction of incidence on the first microlens array 2 varies, the principal ray obtains an emitted light beam substantially perpendicular to the resin sheet substrate by transmitting through the optical element of this embodiment. It is possible. As a comparative example, when the microlens array is formed on one surface of the substrate, the chief ray is not perpendicular to the resin sheet substrate but is inclined at an angle. Accordingly, since the spread angle becomes large, the directivity of the emitted light beam cannot be improved.

  At this time, the light distribution of the light beam transmitted through the optical element is determined by the NA of the first microlens array. If the spread angle of the light beam is 2δ, there is a relationship of NA = Sinδ. Therefore, in order to increase the directivity, 2δ may be reduced, that is, the NA may be reduced.

  Here, the viewing angle of the liquid crystal display device is determined by the NA of the first microlens through which light enters. The viewing angle in a high-definition type for mobile devices such as mobile phones and PDAs is preferably ± 15 to 25 degrees. Therefore, it is preferable that the NA of the first microlens to which light enters is made to be 0.25 to 0.42.

  Further, the planar arrangement 4 of the second microlens array 3 may be a dense arrangement of rectangles as shown in FIG. 4, and even if the light distribution in the vertical direction and the horizontal direction is different with respect to the incident light flux, By using a rectangular shape, the directivity of the emitted light beam can be improved.

Next, a method for manufacturing an optical element will be described. 5 to 11 are flowcharts of a method for manufacturing an optical element.
After the ultraviolet curable resin 5 is applied on the resin sheet 1 and the stamper 6 is pressed, the ultraviolet curable resin 8 is cured by irradiating the ultraviolet rays 7 (FIG. 5). When the stamper 6 is released, the first microlens array 2 can be formed (FIG. 6). An ultraviolet curable resin 8 is applied to the surface opposite to the surface on which the first microlens array 2 is formed (FIG. 7), and ultraviolet exposure light 9 is incident as a substantially parallel light beam from the first microlens array 2 side. The ultraviolet curable resin 8 is cured at the condensing point of the lens array 2 to form a cured portion A10 (FIG. 8). Further, the ultraviolet exposure light 11 is tilted and obliquely incident to form a cured portion B12 (FIG. 9). In this way, the shape of the second microlens array 3 is produced by tilting the exposure light (FIG. 10). Thereafter, the UV curable resin 13 in the uncured portion is removed by washing or the like, and the second microlens array 3 is formed (FIG. 11).

  The second microlens array 3 is formed on the basis of the light condensing point of the first microlens array 2, so that there is no need for alignment, and the second microlens array 3 is easily and very accurately arranged.

  As another configuration, the first microlens array 14 may be flattened by a flat layer 15 as shown in FIG. At this time, the refractive index of the flat layer 15 needs to be smaller than the refractive index of the first microlens array 14. As a result, even when arranged overlapping with other members, the lens shape is not destroyed, and the light beam 16 is once refracted by the flat layer 15, so that it can be directed to a light beam having a larger incident angle. It becomes possible to improve the performance.

  Furthermore, as shown in FIG. 13, the second microlens array may be a microprism 17. As a result, all rays having an incident angle of + θ enter the slope A18, and all rays having an incident angle of −θ enter the slope B19. Therefore, total reflection is difficult to occur. There is no light.

  Further, the shape of the second microlens array 20 may be a shape as shown in FIG. As a result, the front luminance can be further improved. 11, 13, and 14 show a two-dimensional shape. However, for example, an anamorphic shape as shown in FIGS. 15 and 16 or a pyramid shape shown in FIG. 17 may be used. It may be a shape.

  FIG. 18 shows a liquid crystal display device 21 provided with the optical element of the present invention. It comprises a light source 22, a light guide plate 23, an optical element 24, and a liquid crystal panel 25. The light beam exiting the light guide plate has a constant light intensity with respect to the emission angle of the light guide plate, but the front luminance is relatively low, but the front luminance is improved by the optical element 24 and the directivity is increased. It becomes possible. Various optical sheets such as a diffusion plate may be added between the light guide plate 23 and the liquid crystal panel 25 as necessary.

It is sectional drawing of the optical element which shows the Example of this invention. It is a top view of the optical element which shows the Example of this invention. It is explanatory drawing of the optical element which shows the Example of this invention. It is a top view of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is a manufacturing flowchart of the optical element which shows the Example of this invention. It is explanatory drawing of the optical element which shows the Example of this invention. It is explanatory drawing of the optical element which shows the Example of this invention. It is sectional drawing of the optical element which shows another Example of this invention. It is a perspective view of the optical element which shows another Example of this invention. It is a perspective view of the optical element which shows another Example of this invention. It is a perspective view of the optical element which shows another Example of this invention. It is sectional drawing of the liquid crystal display device which shows the Example of this invention. It is sectional drawing of the liquid crystal display device which shows a prior art example. It is sectional drawing of the prism sheet which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resin sheet 2 1st micro lens array 3 2nd micro lens array 4 Planar arrangement | positioning 5 of a 2nd micro lens array 5 UV curable resin 6 Stamper 7 UV 8 UV curable resin 9 UV exposure light 10 Curing part A
11 UV exposure light 12 Curing part B
13 UV-cured resin in uncured portion 14 First microlens array 15 Flat layer 16 Light beam 17 Microprism 18 Slope A
19 Slope B
20 Second microlens array 21 Liquid crystal display device 22 Light source 23 Light guide plate 24 Optical element 25 Liquid crystal panel

Claims (10)

A first microlens array arranged densely and a second microlens array positioned at a predetermined position with respect to the first microlens array, and a light beam incident on the first microlens array at a predetermined angle However, when emitting from the second microlens array, the optical element emits at an angle smaller than the incident angle. 2. The optical element according to claim 1, wherein the second microlens array is disposed in the vicinity of the focal position of the first microlens array. 3. The optical element according to claim 1, wherein the focal length of the first microlens array and the focal length of the second microlens array are equal to each other. 4. The optical element according to claim 1, wherein the first microlens array is flattened and the incident surface is substantially flat. 5. The optical element according to claim 1, wherein the first microlens array is a prism array. 6. The optical element according to claim 1, wherein the first microlens array is a cylindrical lens array. A liquid crystal display device comprising the optical element according to claim 1. Forming a first microlens array in advance in an optical element having a densely arranged first microlens array and a second microlens array positioned at a predetermined position with respect to the first microlens array; A step of applying a photosensitive resin material in the vicinity of the second microlens array formation region, and substantially parallel light is incident on the first microlens array, and the light focused by the first microlens array is used. A method for producing an optical element, comprising a step of patterning the photosensitive resin material. 9. The method of manufacturing an optical element according to claim 8, wherein the step of forming the first microlens array is molding using a transfer mold. 10. The method of manufacturing an optical element according to claim 8, wherein substantially parallel light is incident on the first microlens array and the photosensitive resin material is patterned, and is substantially incident on the first microlens array. A method of manufacturing an optical element, wherein the shape of the second microlens array is formed while changing the incident angle of the parallel light and changing the intensity of the parallel light with respect to the incident angle.

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