JP2010054995A - Lens sheet, backlight unit and display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens sheet in which diffused light to be emitted from a light diffusion plate is collected efficiently to improve the luminance on the side of an observer, which hardly generates a side lobe and the luminance distribution of which is changed smoothly and to provide a backlight unit using the lens sheet, and a display apparatus. <P>SOLUTION: The lens sheet 1 is constituted so that a plurality of first lenses 4 extending in straight lines are arranged in parallel to one another on the light emission surface 17a side of an almost sheet-shaped light-transmissive base material 17 to form a first lens array 3, a plurality of second lenses 6 extending along the directions, each of which and each of the extending directions of the first lenses 4 are made to cross each other, over the tops of the plurality of first lenses 4 are arranged in parallel to one another on the first lens array 3 to form a second lens array 5, and a plurality of third lenses 8 extending in straight lines are arranged in parallel to one another on the light entrance surface side of the light-transmissive base material 17 to form a third lens array 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lens sheet used for illumination optical path control, and a backlight knit and display device using the same, and more particularly to a lens sheet and backlight used for illumination optical path control in an image display device typified by a flat panel display. The present invention relates to a knit and display device.

In recent large-sized liquid crystal televisions, direct type backlights in which a plurality of cold cathode tubes and LEDs (Light Emitting Diodes) are arranged are employed.
In this direct type backlight, a light diffusion plate made of a synthetic resin plate having a high light scattering property is arranged between the image display element and the light source, so that a cold cathode tube or LED as a light source is a lamp image. As is not visible.

  This light diffusing plate usually requires a thickness of about 1 to 5 mm in order to support the optical film disposed on the light diffusing plate. Therefore, there is a considerable amount of light absorption due to the thickness, and there is a problem that the amount of light from the light source decreases and the liquid crystal screen display becomes dark.

  In order to cope with such a problem, conventionally, in a direct type backlight, a single or a plurality of lens sheets are arranged on a light diffusion plate in order to improve the luminance in the viewer side direction.

As an example of this lens sheet, a brightness enhancement film (BEF), which is a registered trademark of 3M USA, is widely used.
FIG. 10 is a schematic cross-sectional view showing an example of the BEF arrangement, and FIG. 11 is a perspective view of the BEF. As shown in FIGS. 10 and 11, the BEF 185 is an optical film in which unit prisms 187 having a triangular cross section are periodically arranged in one direction on a member 186. The unit prism 187 has a size (pitch) larger than the wavelength of light.

  Such a BEF 185 collects light from “off-axis” and redirects it “on-axis” or “recycle” toward the viewer. recycle) ". That is, the BEF 185 can increase the on-axis brightness by reducing the off-axis brightness when the display is used (observation). Here, “on the axis” means a direction that coincides with the viewing direction F ′ of the viewer, and is generally on the normal direction side with respect to the display screen.

  When a lens sheet represented by this BEF185 is used, generally, a light diffusion film having both diffusion and condensing functions is disposed between the light diffusion plate and the lens sheet. In addition, this light-diffusion film is comprised by apply | coating a diffusion filler on a transparent base material. Thereby, the diffused light emitted from the light diffusing plate can be efficiently collected, and the visibility of the light source that cannot be erased by the light diffusing plate alone can be suppressed.

  It is also effective to dispose the light diffusion film between the lens sheet and the liquid crystal panel. As a result, side lobes can be reduced, and moire interference fringes generated between regularly arranged lenses and liquid crystal pixels can be prevented.

When the above-described BEF is used as a brightness control member, light from the light source can be emitted from the film at a controlled angle by refraction, and the intensity of light in the viewer's visual direction is increased. Can be controlled. This allows the display designer to achieve the desired on-axis brightness while reducing power consumption.
In addition, as patent documents disclosing that a luminance control member having a repetitive array structure of prisms represented by BEF is adopted for a display, many are known as exemplified in Patent Documents 1 to 3. It has been.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

However, when BEF 185 is used, a light component due to reflection or refraction may simultaneously be emitted in the lateral direction without proceeding to the viewer's visual direction F ′.
The broken line B in FIG. 12 shows the characteristics of BEF. The light intensity is highest when the angle with respect to the light intensity and the viewing direction F ′ is 0 ° (on-axis direction), while the angle with respect to F ′ is ± A small light intensity peak (side lobe) occurs in the vicinity of 90 °. This indicates that the amount of light emitted from the lateral direction is increased.
A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution as shown by a solid line A in FIG. 12 having no light intensity peak around ± 90 ° is more desirable.

  Further, if only the on-axis brightness is excessively improved by adopting BEF, the peak width of the curve of the brightness distribution becomes remarkably narrow, and the viewing area is extremely limited. Therefore, in order to increase the peak width appropriately, it is necessary to newly use a light diffusing film of another member, and there is a problem that the number of members increases and the cost increases.

  Furthermore, when a light diffusion film is placed on the BEF, the side lobe is reduced and the luminance distribution can be smoothed, but on the other hand, the front luminance peak is reduced. Therefore, it is desirable that the haze degree of the light diffusion film is low from the viewpoint of increasing the brightness. However, in this case, since the change in the luminance distribution becomes large, the image display suddenly becomes dark when the line of sight is changed from the front direction to the oblique direction, which is not preferable in terms of image quality.

Furthermore, in liquid crystal display devices such as display devices, light weight, low power consumption, high brightness, and thinning are strongly demanded as market needs, and accordingly, a backlight unit mounted on the liquid crystal display device. Similarly, it is required to be lightweight, low power consumption, and high brightness.
In particular, in a color liquid crystal display device that has made remarkable progress in recent years, the panel transmittance of the liquid crystal panel is remarkably lower than that of a monochrome-compatible liquid crystal panel. It is essential to obtain low power consumption.
However, as described above, it is difficult to say that the conventional apparatus sufficiently satisfies the demand for high luminance and low power consumption, and the user has low price, high luminance, high display quality, and low power consumption. Development of a backlight unit and a display device that can realize a liquid crystal display device with electric power is awaited.

  The present invention has been made in view of such problems, and by efficiently condensing the diffused light emitted from the light diffusion plate, the luminance on the viewer side is improved, and the side lobe is An object of the present invention is to provide a lens sheet that hardly changes and the luminance distribution changes smoothly depending on the viewing angle, a backlight unit using the same, and a display device.

In order to solve the above problems, the following means are proposed.
That is, the lens sheet according to the present invention includes a first lens array in which a plurality of linearly extending first lenses are arranged in parallel to each other on the light exit surface side of a substantially sheet-like translucent substrate. A second lens array comprising a plurality of second lenses arranged on the first lens array along a direction intersecting the first lens across the tops of the plurality of first lenses; The light transmitting surface side of the translucent substrate is provided with a third lens array in which a plurality of third lenses extending linearly are arranged in parallel to each other.

  According to the lens sheet having such a feature, since the light collecting effect in two directions can be obtained by the first lens array and the second lens array, it is possible to improve the luminance on the observer side and to generate side lobes. And the change of the viewing angle distribution can be smoothed by the third lens array.

  In the lens sheet according to the present invention, it is preferable that the top of the second lens coincides with the top of the first lens.

  In the lens sheet according to the present invention, an angle at which the first lens and the second lens intersect is approximately 90 °, and the third lens is any of the first lens and the second lens. It is preferable to extend substantially parallel to either of them.

  Furthermore, in the lens sheet according to the present invention, it is preferable that the shape of the third lens is a triangular prism.

In the lens sheet according to the present invention, the shape of the first lens is a trapezoidal prism having an isosceles trapezoidal cross section, and the shape of the second lens is a triangular prism having an apex angle of 70 to 110 °. It is preferable that
In this case, it is preferable that the angle formed by the extension lines of the pair of hypotenuses having an isosceles trapezoidal shape in the first lens is set to 70 to 110 °.

  Furthermore, in the lens sheet according to the present invention, it is preferable that an aspect ratio that is a ratio of a height of the third lens to a pitch of the third lens is 1 to 10%.

  A backlight unit according to the present invention includes any one of the lens sheets described above, a light source that is disposed on the light incident surface side of the lens sheet and that emits light, and is disposed between the lens sheet and the light source. And a light diffusion plate that diffuses light from the light source.

  A display device according to the present invention includes the backlight unit and an image display element that displays an image by light irradiation from the backlight unit.

  According to the backlight unit and the display device having such a feature, the use of the lens sheet makes it possible to obtain a condensing effect in two directions by the first lens array and the second lens array. The side luminance can be improved and the occurrence of side lobes can be suppressed, and the change in the viewing angle distribution can be smoothed by the third lens array.

  According to the lens sheet, the backlight unit, and the display according to the present invention, the luminance on the viewer side can be improved by the two-way condensing effect, and the occurrence of side lobes can be suppressed. It is possible to make the change in the luminance distribution due to the smooth.

  Hereinafter, embodiments of a lens sheet, a backlight unit, and a display device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of a display device employing the lens sheet and the backlight unit of the present embodiment.

The display device 70 according to the embodiment includes an image display element 35 and a backlight unit 55. In the backlight unit 55 according to the embodiment of the present invention, a plurality of light sources 41 are arranged in a lamp house (reflecting plate) 43, and light incident from the light sources 41 is diffused thereon (observer side direction F). The light diffusing plate 25 and the lens sheet 1 that are emitted are arranged and configured.
Under such a configuration, the light H emitted from the light source 41 is diffused by the light diffusion plate 25 and collected by the lens sheet 1 disposed thereon. Then, the light K emitted from the backlight unit 55 enters the image display element 35 and is emitted to the observer side F.

The light source 41 that is a constituent element of the backlight unit 55 supplies light to the image display element 35 through the light diffusion plate 25 and the lens sheet 1.
As the light source 41, for example, a plurality of linear light sources or point light sources can be used. Examples of the linear light source include a lamp light source such as a fluorescent lamp, a cold cathode fluorescent lamp (CCFL), or an EEFL, and examples of the point light source include an LED.

  The reflection plate 43 is disposed on the opposite side of the plurality of light sources 41 from the observer side F, and reflects the light emitted in the direction opposite to the observer side F out of the light emitted from the light source 41 in all directions. Then, the light is emitted to the observer side F. Thereby, the utilization efficiency of the light radiate | emitted from the light source 41 can be improved. The reflection plate 43 may be any member that reflects light with high efficiency. For example, a general reflection film, a reflection plate, or the like can be used.

  Next, the light diffusion plate 25 will be described. The light diffusion plate 25 is formed in a substantially plate shape with a light diffusion region dispersed in a transparent resin.

  As the transparent resin constituting the light diffusion plate 25, a thermoplastic resin, a thermosetting resin, or the like can be used. For example, a polycarbonate resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, an epoxy acrylate resin, Polystyrene resin, cycloolefin polymer, methylstyrene resin, fluorene resin, polyethylene terephthalate (PET), polypropylene, acrylonitrile styrene copolymer, acrylonitrile polystyrene copolymer, and the like can be used.

The light diffusing region is preferably made of light diffusing particles because suitable diffusing performance can be easily obtained. As the light diffusing particles, transparent particles made of an inorganic oxide or a resin are used.
As the transparent particles made of an inorganic oxide, for example, silica, alumina or the like can be used.
The transparent particles made of resin include acrylic particles, acrylonitrile polystyrene copolymer particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine / formalin condensate particles, PTFE (polytetrafluoroethylene), PFA. Fluoropolymer particles such as (perfluoroalkoxy resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene / tetrafluoroethylene copolymer), silicone resin particles, etc. Can be used.
The size and shape of the transparent particles are not particularly defined, and two or more types of transparent particles may be used in combination from the above-described transparent particles.

Further, the light diffusing plate 25 may have a concavo-convex shape formed on its entrance surface or exit surface. As a method of forming this uneven shape, when forming the light diffusion plate 25, it is brought into close contact by applying pressure to a mold for shaping the uneven shape by a coextrusion forming method or an emission molding method. The method of transferring is mentioned.
Furthermore, as a method for forming the uneven shape, a method of forming a radiation curable resin such as a UV curable resin on the incident surface or the exit surface of the light diffusing plate 25 may be mentioned. More specifically, after the light diffusing plate 25 is formed as a plate-like member by a coextrusion method, the concavo-convex shape can be formed by UV-molding the concavo-convex shape on the incident surface or the exit surface of the light diffusing plate 25. .
Furthermore, it may be a method in which a film having a concavo-convex shape is formed as a separate body and molded by pasting the diffusion plate 25 through a bonding layer made of an adhesive material or an adhesive material.

  Here, when the light diffusion particles are used as the light diffusion region, the thickness of the light diffusion plate 25 is preferably 0.1 to 5 mm. When the thickness of the light diffusion plate 25 is 0.1 to 5 mm, optimum diffusion performance and brightness can be obtained, which is preferable in terms of optical characteristics. On the other hand, when the thickness is less than 0.1 mm, the desired diffusion performance cannot be exhibited. When the thickness exceeds 5 mm, the amount of resin is large, and the luminance decreases due to absorption, which is not preferable.

In the case where a thermoplastic resin is used as the transparent resin, air bubbles may be used as the light diffusion region.
The internal surface of the bubble formed inside the thermoplastic resin causes diffused reflection of light, and a light diffusing function equivalent to or higher than that when light diffusing particles are dispersed can be expressed. Therefore, it becomes possible to make the film thickness of the light diffusing plate 25 thinner.
Examples of such a light diffusion plate 25 include white PET and white PP. White PET is obtained by dispersing fillers such as resin incompatible with PET, titanium oxide (TiO2), barium sulfate (BaSO4), and calcium carbonate in PET, and then stretching the PET by a biaxial stretching method. Thus, bubbles are generated around the filler.

  Note that the light diffusion plate 25 made of thermoplastic resin only needs to be stretched in at least one axial direction. This is because bubbles can be generated around the filler by stretching in at least one axial direction.

  Examples of the thermoplastic resin include acrylonitrile polystyrene copolymer, polyethylene terephthalate (PET), polyethylene-2, 6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, cyclohexanedimethanol copolymer polyester resin, isophthalic acid copolymer polyester resin, Polyester resins such as sporoglycol copolymer polyester resin and fluorene copolymer polyester resin, polyolefin resins such as polyethylene, polypropylene, polymethylpentene, and alicyclic olefin copolymer resins, acrylic resins such as polymethyl methacrylate, polycarbonate, Polystyrene, polyamide, polyether, polyesteramide, polyetherester, polyvinyl chloride, cycloolefin polymer, And copolymers and these ingredients, also it can be used like a mixture of these resins are not particularly limited.

When bubbles are used as the light diffusion region, the thickness of the light diffusion plate 25 is preferably 25 to 500 μm.
When the thickness of the light diffusing plate 25 is less than 25 μm, it is not preferable because the sheet is insufficiently squeezed and wrinkles are easily generated in the manufacturing process and display. In addition, when the thickness of the light diffusion plate 25 exceeds 500 μm, there is no particular problem in optical performance, but since the rigidity increases, it is difficult to process into a roll shape, and the slit cannot be easily formed. Since the advantage of the thinness obtained by comparison becomes small, it is not preferable.

Next, the lens sheet 1 according to the present embodiment will be described in detail with reference to FIGS.
The lens sheet 1 collects a part of the light emitted from the light source 41 and diffused by the light diffusing plate 25 and transmits it to the image display element 35 side. As shown in FIG. Alternatively, a translucent substrate 17 having a substantially sheet shape and three lens arrays of the first lens array 3, the second lens array 5, and the third lens array 7 are provided.

  The first lens array 3 extends along one direction of the light exit surface 17a of the translucent substrate 17 (the depth direction in the drawing of FIG. 3), as shown in FIG. The plurality of first lenses 4, 4... Are arranged in an array along a direction orthogonal to the one direction so as to be parallel to each other.

In the present embodiment, the first lens 4 that is a constituent element of the first lens array 3 is a trapezoidal prism whose section perpendicular to the extending direction of the first lens 4 forms an isosceles trapezoid. Further, the angle θ1 formed by the extension lines of the pair of oblique sides of the isosceles trapezoid in the cross section of the first lens 4 is set in the range of 70 ° to 110 °, more preferably in the range of 80 ° to 110 °. .
The first lens 4 as such a trapezoidal prism exhibits an effect equivalent to that of a triangular prism because the inclined surfaces 4b and 4b constituting the hypotenuse in the cross section are substantially linear. Therefore, since the light condensing effect on the observer side F is increased, the luminance can be improved.

As shown in FIG. 4 which is a view in the B direction of FIG. 2, the second lens array 5 is arrayed along the extending direction of the first lens 4 so as to be parallel to each other. It is constituted by being arranged in. The second lens 6 is formed on the top 4a of the first lens. Specifically, as shown in FIGS. 2 and 5, the second lens 6 extends in a direction orthogonal to the first lens 4 over the plurality of first lenses 4, 4. It extends along the straight line.
That is, the second lens array 5 including the second lens 5 orthogonal to the first lens 4 is formed on the first lens array 3 including the first lens 4. The arrangement direction with the second lens array 6 is configured to be orthogonal.

The second lens 6, which is a component of the second lens array 5, has a triangular prism shape in which the top 6 a coincides with the top 4 a of the first lens 4. Thereby, the 2nd lens 6 can exhibit the high condensing effect to the observer side F. FIG.
In addition, it is preferable that apex angle (theta) 2 of the 2nd lens 6 which makes a triangular prism shape is set to the range of 70 degrees-110 degrees, More preferably, it is 80 degrees-100 degrees.

  The third lens array 8 extends along one direction of the incident surface 17b of the translucent substrate 17 (the depth direction in the drawing of FIG. 3), as shown in FIG. The plurality of first lenses 4, 4... Are arranged along a direction orthogonal to the one direction so as to be parallel to each other. In the present embodiment, the third lens 8 extends parallel to the first lens 4. However, the present invention is not limited to this, and the third lens 8 extends parallel to the second lens 6. It may be.

The third lens 8 that is a component of the third lens array 7 has a triangular prism shape. Further, in order to reduce the influence on the light collection effect by the first lens array 3 and the second lens array 5, the apex angle θ3 of the triangular prism of the third lens 8 is 160 ° to 178 °, particularly 170 ° to 175 °. It is preferable that the range is set.
Further, the aspect ratio of the third lens 8 in the present embodiment, that is, the ratio of the height t to the pitch R of the third lens 8 is set in the range of 1% to 10%.

The lens sheet 1 having such a configuration can be easily manufactured using molds 10 and 13 as shown in FIGS.
That is, the shape of the lens sheet 1 on the exit surface side is such that the first lens 4 is formed by the first lens forming portion 11 of the mold 10 shown in FIG. 6 and the second lens 6 is formed by the second lens forming portion 12. Thereby, the first lens array 3 and the second lens array 5 are simultaneously molded.
Further, the shape of the lens sheet 1 on the incident surface side is such that the third lens 8 is formed by the third lens forming portion 14 of the mold 13 shown in FIG. 7, and thereby the third lens array 7 is formed.

  Next, the image display element 35 will be described. As shown in FIG. 1, the image display element 35 includes two polarizing plates (polarizing films) 31 and 33 and a liquid crystal panel 32 sandwiched therebetween. The liquid crystal panel 32 is configured, for example, by filling a liquid crystal layer between two glass substrates. Then, the light K emitted from the backlight unit 55 is incident on the liquid crystal unit 32 through one polarizing filter 33 and is emitted to the viewer side F through the other polarizing filter 31.

The image display element 35 is preferably an element that displays an image by transmitting / blocking light in pixel units. If the image is displayed by transmitting / blocking light in pixel units, the luminance toward the observer side F through the lens sheet 1 is improved, and the viewing angle dependency of the light intensity is reduced. It is possible to display an image with high image quality by effectively using the light whose lamp image is reduced.
The image display element 35 is preferably a liquid crystal display element. A liquid crystal display element is a typical element that transmits / shields light in pixel units and displays an image, and can improve image quality and reduce manufacturing cost compared to other display elements. Can do.

Hereinafter, the operation of the display device 70 will be described.
A part of the light emitted from the light source 41 is emitted directly from the light source 41 toward the light diffusion plate 25, and the other light is reflected by the reflection plate 43 and then emitted toward the light diffusion plate 25. Is done. At this time, the illuminance unevenness corresponding to the arrangement pitch of the light sources 41 is mitigated by the action of the reflector 43, but remains to some extent. The light traveling to the light diffusing plate 25 is scattered by the light scattering region in the transparent resin of the light diffusing plate 25 and proceeds as diffused light, which eliminates unevenness in luminance of the light source 41 and has a spread angle in an appropriate angle range. The light reaches the exit surface of the light diffusion plate 25 as light.

  The light that has reached the exit surface of the light diffusing plate 25 is incident on the lens sheet 1, and the front luminance is increased by the light collecting effect in the process of passing through the lens sheet 1. The light emitted from the lens sheet 1 passes through the polarizing plate 33, the liquid crystal panel 32, and the polarizing plate 31 of the image display element 35, and the light is transmitted as display light from the predetermined pixel region, so that the image has a viewing angle. Is displayed.

The operation of the lens sheet 1 having the light collecting effect as described above will be described in more detail.
Two lens arrays of a first lens array 3 and a second lens array 5 are formed on the exit surface side of the lens sheet 1 of the present embodiment.
Generally, in the case of a lens array in which unit lenses extending in one direction are arranged in a stripe shape, a light collecting effect is obtained only in the arrangement direction of the unit lenses. In this respect, since the lens sheet 1 is formed with the two lens arrays as described above, the light passing through the lens sheet 1 is directed in the arrangement directions of the first lens array 3 and the second lens array 5, respectively. A converging effect in two directions can be obtained. Thereby, it is possible to effectively improve the front luminance of the observer side F.

  In the present embodiment, since the extending directions of the first lens 4 and the second lens 6 are orthogonal to each other, in particular, the direction along the horizontal direction when the display device 70 is erected (hereinafter referred to as “the vertical direction”). A condensing effect in two directions, that is, a direction along the vertical direction (hereinafter referred to as a Ve direction) can be obtained.

Here, examples of the optical film having a light collecting function in two or more directions include a lens sheet provided with a polygonal pyramid lens represented by a square pyramid, in addition to the lens sheet 1 of the present embodiment. In order to adjust the light collection ratio in two directions in this lens sheet, it is necessary to change the vertex angle of the polygonal lens. Taking a quadrangular pyramid lens as an example, the configuration with the highest luminance is a quadrangular pyramid with an apex angle of 90 °. However, to change the viewing range in one direction, it is necessary to increase or decrease the apex angle. Arise. However, if the apex angle is changed from 90 ° to adjust the visual field range, there arises a problem that the luminance is lowered.
In this respect, in the lens sheet 1 of the present embodiment, the first lens 4 constituting the first lens array 3 has a trapezoidal prism shape, and the second lens 6 constituting the second lens array 5 has a triangular prism shape. And since the top part 4a of the 1st lens 4 and the top part 5a of the 2nd lens 5 correspond, by adjusting the width | variety L of the top part 4a of the 1st lens 4, the condensing ratio of two directions Can be adjusted without greatly changing the brightness.
In other words, according to the lens sheet 1 in the present embodiment, the brightness in the Ho direction is set higher than the Ve direction, the brightness in the two directions in the Ho direction and the Ve direction is set to the same level, and the brightness is maintained high. However, it is possible to arbitrarily set the visual field range.

However, although the visual field range can be adjusted by changing the light collection ratio in the two directions of the lens sheet 1 as described above, the degree of change in luminance, that is, the slope of the luminance distribution is the same in both directions. In this respect, in the lens sheet 1 of the present embodiment, since the third lens array 7 is formed on the incident surface, the inclination of the luminance distribution can be relaxed and the visual field can be smoothed.
In the present embodiment, the third lens 8 constituting the third lens array 7 extends in parallel with the first lens 4, and therefore, in particular, the inclination of the viewing angle distribution of the first lens array 1. Can be relaxed.
In this way, by reducing the inclination of the viewing angle distribution, it is possible to suppress the brightness and darkness of the image display due to the viewing angle.

Hereinafter, the operation of the first lens array 3, the second lens array 5, and the third lens array 7 will be described with a graph.
As a comparison object, FIG. 8A shows a luminance distribution diagram of a 90 ° triangular prism. Since the triangular prism condenses in the front direction, it has a maximum peak at 0 °, but a side lobe occurs and a valley Va is generated in the vicinity of 45 °. The side lobe is emitted light in a direction unnecessary for the display device 70, but the side lobe itself is not a problem in observing the display device 70, and the valley Va between the main peak at 0 ° and the side lobe There is a problem that there is a significant luminance difference between the two. This is because when the display device 70 is observed from the angle of the valley Va, the screen becomes dark. Therefore, if the luminance of the valley Va is too low even if the side lobes are reduced, it is not desirable for the display device 70.

FIG. 8B shows a lens sheet (Back Flat) that includes only the first lens array 3 and the second lens array 5 but does not include the third lens array 7, the first lens array 3, and the second lens array 5. The luminance distribution figure of the lens sheet 1 (Back Prism) of this embodiment provided with the 3rd lens array 7 is shown. Since both have a composite shape including the first lens array 3 and the second lens array 5, the valley Va as shown in FIG. 8A does not occur. Therefore, the brightness and darkness of the image display due to the viewing angle can be suppressed.
Further, the lens sheet 1 (Back Prism) of the present embodiment has a lower front luminance than the one without the third lens array 7 (Back Flat), but the visual field distribution is expanded to reduce the change in luminance. To do. Therefore, by forming the third lens array 7, it is possible to more effectively suppress the brightness and darkness of the image display depending on the viewing angle.

  Therefore, according to the lens sheet 1 of the present embodiment, the light collecting effect in two directions can be obtained by the first lens array 3 and the second lens array 5, so that the luminance on the observer side F is improved and the side lobe is increased. Since the change in the viewing angle distribution can be smoothed by the third lens array 7, it is possible to prevent the occurrence of brightness and darkness due to the viewing angle.

  Further, according to the backlight unit 25 and the display device 70 using such a lens sheet 1, as described above, the luminance on the observer side F is improved, the generation of side lobes is suppressed, and the viewing angle distribution is smoothed. Furthermore, the lamp image can be reduced by the contribution of the light diffusion plate 25.

  As described above, in the present embodiment, the aspect ratio of the third lens 8, that is, the ratio of the height t to the pitch R of the third lens 8 is set in the range of 1 to 10%. Hereinafter, this point will be described in detail.

FIG. 9A is a graph showing the relationship between the aspect ratio of the third lens array 7 and the luminance, and FIG. 9B is the relationship between the aspect ratio of the third lens array 7 and the half-value angles in the Ve direction and the Ho direction. FIG. 9C is a graph showing the relationship between the aspect ratio of the third lens array 7 and the luminance change amount.
The luminance is 1.0 when the third lens array 7 is not provided.
Here, the half-value angle represents a viewing angle at which the luminance is 50% when the luminance in the 0 ° direction (observer side F) is 100%.
In the measurement, the display device 70 is arranged such that the arrangement direction of the first lens array 3 is the Ve direction, the arrangement direction of the second lens array 5 is the _HO direction, and the arrangement direction of the third lens array 7 is the Ve direction. Arranged.
Further, the luminance change amount is a ratio between the luminance difference of 30 ° and 45 ° and the luminance of 0 °.
9A to 9C is the ratio of the height t of the third lens array 7 to the pitch R of the third lens 7, that is, the aspect ratio value.

  As shown in FIG. 9B, when the aspect ratio of the third lens array 7 is increased, the light condensing effect of the first lens array 3 is weakened, and the half-value angle in the Ve direction is increased. On the other hand, the condensing effect of the second lens array 5 is not affected, and the half-value angle in the Ho direction hardly changes. Conversely, when the aspect ratio of the third lens array 7 is reduced, the light condensing effect of the first lens array 3 is strengthened, so that the half-value angle in the Ve direction is narrowed, but the light condensing effect of the second lens array 5 is not affected. The half-value angle in the Ho direction hardly changes.

  As shown in FIG. 9C, when the aspect ratio of the third lens array 7 is increased, the light condensing effect of the first lens array 3 is weakened and the luminance change amount in the Ve direction is decreased. On the other hand, the condensing effect of the second lens array 5 is not affected, and the luminance change amount in the Ho direction does not change unless the aspect ratio becomes 10% or more. On the contrary, when the aspect ratio of the third lens array 7 is reduced, the light condensing effect of the first lens array 3 is strengthened, so that the amount of luminance change in the Ve direction is increased and the light condensing effect of the second lens array 5 is not affected. The amount of change in luminance in the Ho direction does not change.

  When the display device 70 of the present embodiment is used for television, it is desirable that the half-value angle in the Ho direction is large. This is because when observing the television, the observer observes the television from various positions in the Ho direction. However, when the display device 70 of the present embodiment is used for advertising billboards or the like, it may be desirable that the half-value angle in the Ve direction is large.

  In the lens sheet 1 of the present embodiment, the first lens array 3 may be arranged in the Ve direction, or may be arranged in the Ho direction. This is because the half-value angle in both the Ve direction and the Ho direction can be controlled by changing the width L of the top portion 4a of the first lens 4 constituting the first lens array 3 as described above. Therefore, the ratio between the width L of the top 4a of the first lens 4 and the pitch P of the first lens 4 can be arbitrarily selected.

  Further, in the lens sheet 1 of the present embodiment, the third lens array 7 may be arranged in the direction of the first lens array 3 or may be arranged in the direction of the second lens array 5. This is because the amount of change in luminance can be controlled by changing the direction of the third lens array 7 according to the Ve direction, the Ho direction, and the aspect ratio, as described above. Therefore, the ratio between the height t of the third lens 8 and the pitch R of the third lens 8 can be arbitrarily selected.

  Further, the third lens array 7 of the lens sheet 1 of the present embodiment does not require the relationship between the first lens array 3 and the second lens array 5, and the pitch, alignment, and direction that are parameters of the third lens array 7. Can be selected arbitrarily.

The pitch R of the third lens 8 constituting the third lens array 7 is equal to the pitch P of the first lens 4 and the third lens when the third lens 8 extends in parallel with the first lens 4. It is preferable that a relationship of 0.05 ≦ R / P ≦ 0.5 is satisfied with the pitch R of 8.
In the case of R / P> 0.5, the direction or the incident position of the light incident on the first lens 4 of the first lens array 3 is greatly different between the adjacent first lenses 4, and as a result, the first lens array 3 causes uneven brightness on the viewer side F, which is not preferable.
On the other hand, when R / P ≦ 0.5, substantially the same light is incident on each first lens 4 of the first lens array 3 and a uniform image display can be obtained. If R is extremely smaller than P, for example, 0.05> R / P, it is difficult to form the third lens array 7 and a diffraction phenomenon may occur. Since the effect is reduced, it is not preferable.

Further, when the aspect ratio of the third lens array 7 is changed, as shown in FIGS. 9A and 9C, the luminance and the luminance change amount greatly change. Here, in terms of the characteristics of the lens sheet 1, it is required that the front luminance is high and the luminance change amount is low, but both cannot be satisfied.
However, in the case of a liquid crystal television, it is important in terms of product characteristics that the amount of change in luminance is low. This is because even if the front brightness is very high, if the viewing angle distribution is narrow and the brightness changes depending on the viewing angle, it is not preferable as a display. Even if the front luminance is somewhat reduced, it can be said that it is desirable that the display image changes smoothly according to the viewing angle.
In view of the above, it is preferable that the aspect ratio of the third lens 8 constituting the third lens array 7 is set in the range of 1% to 10%, particularly 2% to 6%. If the aspect ratio exceeds 10%, the front luminance continues to decrease, but this is not desirable because the change in luminance change is small. Conversely, when the aspect ratio is less than 1%, it is not preferable because it is difficult to mold the third lens 8.

Further, it is preferable that a relationship of 0.05 ≦ Q / P ≦ 2.0 is established between the pitch Q of the second lenses 6 constituting the second lens array 5 and the pitch P of the first lenses 4.
Here, the second lens array 5 of the lens sheet 1 of the present embodiment is formed on the top 4a of the first lens 4 constituting the first lens array 3, and the first lens 4 is a trapezoidal prism. The second lens 5 is a triangular prism. Furthermore, since the optimum range of the apex angle is 70 ° to 110 °, the first lens 4 is a trapezoidal prism having an apex angle of 70 °, and the second lens 6 is a triangular prism having an apex angle of 110 °. When the pitch Q of the second lens 6 exceeds twice the pitch P of the first lens 4, the height of the second lens 6 becomes higher than the height of the first lens 4. In this case, the light condensing effect by the first lens array 3 disappears. Therefore, it is desirable that Q / P ≦ 2.0.
Further, when the pitch Q of the second lens 6 is smaller than the pitch P of the first lens 4, there is no problem in optical characteristics. For example, when the pitch Q of the second lens 6 is 20 μm, Q / P is 0. When it is 05, the pitch P of the first lens 4 is 400 μm. If the pitch P of the first lens 4 is too large, moire interference fringes are likely to occur between the periodic structure of the image display element 35 and the periodic structure of the first lens array 3, which is not desirable. On the other hand, if the pitch P of the first lens 4 is reduced, the pitch R of the second lens 6 becomes too small, which is not desirable. Therefore, it is desirable that 0.05 ≦ Q / P.

The lens sheet 1 described above emits light emitted from the light source 41 and passing through the light diffusion plate 25 as light K having an optical gain of 1 or more from the emission surface, as shown in FIG.
Here, the optical gain is one of indexes indicating the diffusibility of the optical diffusing member, and is expressed as a ratio to the luminance of the light, assuming that the luminance of the diffuser that completely diffuses is 1. When the diffusivity of the diffusing member to be measured is biased depending on the direction, the diffusion characteristic of the diffusing member can be shown by obtaining the optical gain for each direction.
Also, complete diffusion refers to an ideal diffuser that has zero absorption and a constant intensity in any direction. That is, an optical gain of 1 or more indicates that there is an effect of collecting light in the measurement direction, and that the larger the value, the stronger the light collection effect.

In setting the thickness of the lens sheet 1, the thickness is set in consideration of the manufacturing process of the lens sheet 1, the required physical characteristics, and the like, rather than considering the influence on the optical characteristics.
For example, when the first lens array 3 and the second lens array 5 are formed by UV molding, since the base material thickness of the supporting base film is 50 μm or less, wrinkles are generated, so the thickness exceeds 50 μm. Need to form.
Furthermore, the thickness of the substrate varies depending on the size of the backlight unit or display device used. For example, in a display device having a diagonal size of 37 inches or more, the substrate thickness is preferably set between 0.05 mm and 3 mm.

  Further, in general, many displays have a periodic pixel structure, and as a result, high-order moire such as moire between the respective periodic structures and secondary moire generated in three or more periodic structures is generated, and the appearance is impaired. Disadvantages. In order to avoid this, it is effective to shift the lenticular direction of the lens sheet 1 within a range of 30 ° or less from the direction of the periodic structure of the image display element 35. Thereby, it is possible to prevent moiré that occurs between the horizontal or vertical structure of the periodic pixel structure of the image display element 35.

Furthermore, as a method for preventing the above-described moire, a method of meandering the first lens array 3, the second lens array 5, and the third lens array 7 is also effective.
Furthermore, moire can also be prevented by making the lens pitch of the first lens array 3, the second lens array 5, and the third lens array 7 random. In this case, there are a method of changing the lens height and pitch to make it random, and a method of making only the pitch random without changing the lens height, but from the viewpoint of unevenness in appearance, a random method that does not change the lens height. In this case, the random rate (pitch increase / decrease rate with respect to the standard pitch) is preferably 20% or less, particularly 10% or less.

The embodiment of the present invention has been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the present invention.
For example, a diffusing film, a prism sheet, a polarization separating / reflecting sheet, or the like may be disposed on the display device 70. Thereby, the image quality can be further improved.

In the embodiment, the case where the first lens 4 constituting the first lens array 3 is a trapezoidal prism and the second lens 6 constituting the second lens array 5 is a triangular prism has been described. The shapes of the first lens 4 and the second lens 6 can be arbitrarily selected.
Here, for example, a convex lenticular can be mentioned. When the convex lenticular is formed only in one direction, a display device 70 having a wide visual field range can be obtained. On the other hand, since the light condensing effect on the observer side F is weak, it is difficult to obtain high luminance. However, when a convex lenticular lens is formed as the second lens 6 on the top of the convex lenticular, a condensing effect in two directions of the horizontal direction Xo and the vertical direction Ve can be obtained, and the display device 70 having a wide viewing range and high brightness can be obtained. Obtainable.

In the embodiment, the case where the third lens 8 constituting the third lens array 7 is a triangular prism has been described. However, the shape of the third lens 8 can be arbitrarily selected.
Here too, a convex lenticular can be cited as an example. When a convex lenticular lens is formed as the convex third lens 8, the same effect as a prism can be obtained because the aspect ratio is low. When light is incident on the prism, the light is split in two directions, but in the case of a lenticular lens, when the light is incident, the light is separated into a certain angle range, and finally a smoother viewing angle distribution is obtained. be able to.

(Lens sheet of Example)
As a lens sheet corresponding to the embodiment, a lens sheet using a polycarbonate and having a light-transmitting substrate thickness of 250 μm was prepared by an extrusion method.
The first lens array was a trapezoid prism, the angle (vertical angle) formed by the extension lines of the pair of hypotenuses of the trapezoid was 90 °, the pitch P was 100 μm, and the width L of the top of the trapezoid was 20 μm.
The second lens array was a triangular prism having an apex angle of 90 ° and a pitch Q of 25 μm, and the angle formed by the first lens array and the second lens array was 90 °.
The third lens array was a triangular prism having an apex angle of 170 ° and a pitch R of 30 μm, and was arranged in the same direction as the first lens array.

(Comparative lens sheet)
A lens sheet having a light-transmitting substrate thickness of 250 μm was prepared by extrusion molding using polycarbonate.
The first lens array was a trapezoid prism, the angle (vertical angle) formed by the extension lines of the pair of hypotenuses of the trapezoid was 90 °, the pitch P was 100 μm, and the width L of the top of the trapezoid was 20 μm.
The second lens array was a triangular prism having an apex angle of 90 ° and a pitch Q of 25 μm, and the angle formed by the first lens array and the second lens array was 90 °.
Moreover, the back surface of the translucent base material was made into a planar shape, and the 3rd lens array was not formed.

(Backlight unit)
A backlight unit was produced using the lens sheets of the above examples and comparative examples. In the configuration of the backlight unit, a CCFL was arranged as a light source on the observer side F of the reflector, and a light diffusion plate and a lens sheet were arranged in this order on the observer side F (observer side F).
In the lens sheets of the example and the comparative example, the arrangement direction of the first lens array was arranged as the Ve direction (direction along the vertical direction).

(Measurement / Evaluation)
The luminance distribution of the two backlight units was measured. The measurement result is as shown in FIG. When both were compared, almost the same brightness was confirmed from the front. On the other hand, when the field of view was changed from the front, the brightness of both decreased, but it was confirmed that the brightness of the lens sheet of the example was higher in the vicinity of ± 44 ° than the lens sheet of the comparative example.
From this, it was found that the lens sheet with the third lens array has a slower luminance change amount than the lens sheet without the third lens array.

It is a longitudinal cross-sectional view of the display apparatus which concerns on embodiment. It is a perspective view of a lens sheet concerning an embodiment. It is an A direction arrow directional view in FIG. It is a B direction arrow line view in FIG. It is a C direction arrow directional view in FIG. It is a perspective view of the metal mold | die which shape | molds a 1st lens array and a 2nd lens array. It is a perspective view of the metal mold | die which shape | molds a 3rd lens array. (A) is a luminance distribution diagram of light passing through a triangular prism, (b) is a lens sheet or first lens array according to an embodiment including a first lens array, a second lens array, and a third lens array, and a second lens array. It is a luminance distribution figure of the light which passes through the lens sheet provided with only a lens array. (A) is a graph showing the relationship between the aspect ratio of the third lens array and the luminance, (b) is a graph showing the relationship between the aspect ratio of the third lens array and the half-value angle in the Ve direction and the Ho direction, c) is a graph showing the relationship between the aspect ratio of the third lens array and the amount of change in luminance. It is a cross-sectional schematic diagram which shows an example of arrangement | positioning of BEF. It is a perspective view of BEF. It is a graph which shows the relationship between light intensity and the angle with respect to a visual field direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens sheet 3 1st lens array 4 1st lens 5 2nd lens array 6 2nd lens 7 3rd lens array 8 3rd lens 17 Translucent base material 17a Light output surface 17b Light incident surface 25 Light diffusing plate 35 Image Display element 55 Backlight unit 70 Display device

Claims (9)

A light emitting surface side of a light-transmitting base material having a substantially sheet shape is provided with a first lens array in which a plurality of linearly extending first lenses are arranged in parallel with each other,
On the first lens array, a second lens array in which a plurality of second lenses extending along a direction intersecting the first lens over the tops of the plurality of first lenses is arranged in parallel with each other,
The lens sheet further comprising a third lens array in which a plurality of linearly extending third lenses are arranged in parallel to each other on the light incident surface side of the translucent substrate.   The lens sheet according to claim 1, wherein a top portion of the second lens coincides with a top portion of the first lens. The angle at which the first lens and the second lens intersect is approximately 90 °,
3. The lens sheet according to claim 1, wherein the third lens extends substantially parallel to one of the first lens and the second lens.   The lens sheet according to any one of claims 1 to 3, wherein the third lens is a triangular prism. The first lens is a trapezoidal prism having an isosceles trapezoidal cross section, and
The lens sheet according to claim 1, wherein the second lens is a triangular prism having an apex angle of 70 ° to 110 °.   6. The lens sheet according to claim 5, wherein an angle formed by a pair of hypotenuse extension lines having an isosceles trapezoidal shape in the first lens is set to 70 ° to 110 °.   The lens sheet according to any one of claims 1 to 6, wherein an aspect ratio, which is a ratio of a height of the third lens to a pitch of the third lens, is 1% to 10%. The lens sheet according to any one of claims 1 to 7,
A light source that is disposed on the light incident surface side of the lens sheet and emits light;
A backlight unit comprising a light diffusing plate disposed between the lens sheet and the light source and diffusing light from the light source. A backlight unit according to claim 8;
A display device comprising: an image display element that displays an image by irradiating light from the backlight unit.

Images