JP2011247947A - Optical sheet, surface light source device, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet which reduces a side lobe so as to enlarge a view angle, while keeping front luminance, reduces a Newton ring, and is hardly flawed or makes the flow inconspicuous even when flawed, and also to provide a surface light source device and a display device, where the sheet is used.SOLUTION: An optical sheet 15 is used for a surface light source device, where a plurality of convex shape unit optical shapes 151 are aligned on one surface and light is made incident from arc tubes 13, which are arranged on the side of the other surface, to the other surface. Valley bottom parts 152 having prescribed widths are arranged between the adjacent unit optical shapes 151 in the alignment direction of the unit optical shapes 151. At least the valley bottom parts 152 have rough surfaces with irregular and delicate rugged shapes.

Description

  The present invention relates to an optical sheet, a surface light source device using the optical sheet, and a display device.

Conventionally, various surface light source devices have been proposed and put to practical use as surface light sources for illuminating a liquid crystal display or the like from the back. Surface light source devices are classified into edge light type and direct type by mainly converting light sources that are not surface light sources into surface light sources.
For example, in the direct type, for example, a plurality of cold cathode fluorescent lamps (CCFLs) arranged mainly in parallel as light emitting sources are used, and an LCD (Liquid Crystal Display) is used by using the cold cathode fluorescent lamps. Light is introduced from the back of a transmissive display unit such as a panel. And, a distance between the cold cathode fluorescent lamp and the transmissive display unit is appropriately set, and a plurality of optical sheets in which a plurality of lens shapes and prism shapes having a light diffusion effect, a light collecting effect, and the like are arranged are arranged in combination therebetween. Therefore, improvement of front luminance and uniformity of luminance as a surface light source device are achieved (for example, Patent Document 1).
In addition, the optical sheet used in the surface light source device is devised in various ways to obtain desired optical characteristics such as widening the viewing angle regardless of the edge light type or the direct type (for example, Patent Document 2). ).

JP 2006-337797 A Japanese Patent No. 2705868

Depending on the lens shape or prism shape of such an optical sheet, the light is totally reflected or refracted at the interface of the lens shape, etc. There is light (hereinafter referred to as a side lobe) that is emitted in a direction greatly deviating from the viewing angle range. Such side lobes cause significant luminance unevenness when the optical sheet is bent due to long-term use or usage environment.
In addition, when such an optical sheet is arranged so as to be substantially in contact with another optical sheet, an LCD panel, or the like, Newton's ring or the like may be observed, and the image quality may deteriorate.

Furthermore, in an optical sheet having a lens shape or the like, the lens shape or the like may be damaged during assembly or transportation, and handling is not easy. Further, in order to prevent the lens shape from being damaged, the lens shape is usually protected by a masking film or the like, resulting in an increase in work process and cost. Further, when the optical sheet is used in a display device, if the optical sheet is scratched, the image quality may be deteriorated, for example, the scratched portion is observed through the transmission display unit.
In Patent Document 1 and Patent Document 2, no specific measures are disclosed regarding realizing both side lobe reduction and Newton's ring reduction, and it is difficult to scratch or scratches when scratches occur. No consideration is given to visibility.

  An object of the present invention is to reduce the side lobe, widen the viewing angle, reduce the Newton ring, maintain the front brightness, reduce the Newton's ring, and the optical sheet that is hard to be scratched and difficult to see even when scratched, and It is to provide a surface light source device and a display device using the same.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.
According to the first aspect of the present invention, a plurality of convex unit optical shapes (151, 251) are arranged on one surface, and a surface light source so that light is incident on the other surface from a light source arranged on the other surface side. An optical sheet used in the apparatus, wherein a valley bottom (152, 252) having a predetermined width (d) is provided between adjacent unit optical shapes in the arrangement direction of the unit optical shapes, and at least the The valley bottom is an optical sheet (15, 25) characterized in that it is a rough surface having irregular and fine irregularities.
According to a second aspect of the present invention, in the optical sheet of the first aspect, the unit optical shape (151, 251) is a rough surface having an irregular and fine irregular shape on the surface, and the valley bottom (152 , 252) is an optical sheet (15, 25) characterized in that the concavo-convex shape of the unit optical shape (151, 251) is larger than that of the unit optical shape (151, 251).

The invention according to claim 3 is the optical sheet according to claim 1 or 2, wherein the arithmetic average roughness Ra of the concave-convex shape of the valley bottom (152, 252) of the unit optical shape is the top (151t, 251t). A value R1 divided by the arithmetic average roughness Ra of the concavo-convex shape is an optical sheet (15, 25) characterized by satisfying 1 <R1 <50.
According to a fourth aspect of the present invention, in the optical sheet according to any one of the first to third aspects, the maximum height Rz of the concave-convex shape of the valley bottom portion (152, 252) of the unit optical shape is a top portion. A value R2 divided by the maximum height Rz of the uneven shape of (151t, 251t) is an optical sheet (15, 25) characterized by satisfying 1 <R2 <50.
According to a fifth aspect of the present invention, in the optical sheet according to any one of the first to fourth aspects, the width of the valley bottom portion (152, 252) in the arrangement direction of the unit optical shapes (151, 251). d is an optical sheet (15, 25) characterized by satisfying a relationship of 0 <d / w ≦ 0.15 with respect to the width w of the unit optical shapes in the arrangement direction of the unit optical shapes. .
According to a sixth aspect of the present invention, in the optical sheet according to any one of the first to fifth aspects, the unit optical shapes (151, 251) are arranged in one direction along the sheet surface. This is an optical sheet (15, 25).

A surface light source device (10) comprising the optical sheet (15, 25) according to any one of claims 1 to 6 and a light source part (13) that emits light. It is.
The invention of claim 8 is a display device (1) comprising the surface light source device (10) according to claim 7 and a transmissive display unit (11) illuminated from the back by the surface light source device.

According to the present invention, the following effects can be obtained.
(1) The optical sheet of the present invention is used in a surface light source device so that a plurality of convex unit optical shapes are arranged on one surface and light is incident on the other surface from a light source disposed on the other surface side. In the optical sheet, a valley bottom having a predetermined width is provided between adjacent unit optical shapes in the arrangement direction of the unit optical shapes, and at least the valley bottom is a rough surface having an irregular and fine uneven shape. Surface. Therefore, the light emitted from the valley bottom in a direction that makes a large angle with the normal direction of the sheet surface can be diffused to reduce the side lobe, and when the optical sheet is bent, the luminance unevenness caused by the side lobe can be reduced. Can be reduced. Moreover, the light emitted from the bottom of the valley is diffused by the uneven shape of the bottom of the valley, the change in luminance due to the emission angle becomes gradual, and the viewing angle is widened. In addition, since the change in luminance depending on the emission angle becomes gradual, even when the optical sheet is scratched, the scratch is difficult to see when used as a surface light source device. Furthermore, a masking film or the like for preventing scratches is not necessary, and effects such as shortening of work steps, reduction of costs, and improvement of handling are obtained.

(2) The unit optical shape is a rough surface having an irregular and fine concavo-convex shape on the surface, and the concavo-convex shape of the valley bottom is larger than the concavo-convex shape of the unit optical shape. The effects such as reduction, improvement in viewing angle, reduction in luminance unevenness caused when the optical sheet is bent, reduction in Newton's ring, improvement in the visibility of scratches when scratches occur can be further enhanced. In addition, it reduces the occurrence of Newton rings when it is built into a surface light source device and other optical sheets are stacked on this optical sheet, or when an LCD panel is placed on this optical sheet. can do. Moreover, it is hard to be damaged.

(3) Since the value R1 obtained by dividing the arithmetic average roughness Ra of the concave-convex shape at the bottom of the unit optical shape by the arithmetic average roughness Ra of the concave-convex shape at the top satisfies 1 <R1 <50, side lobe reduction, Effects such as an improvement in viewing angle, a reduction in luminance unevenness caused when the optical sheet is bent, a reduction in Newton's ring, and an improvement in the invisibility of a scratch when a scratch occurs can be effectively achieved.

(4) The value R2 obtained by dividing the maximum height Rz of the concave-convex shape at the bottom of the unit optical shape by the maximum height Rz of the concave-convex shape at the top satisfies 1 <R2 <50. It is possible to more effectively achieve such effects as improvement in brightness, reduction in luminance unevenness caused when the optical sheet is bent, reduction in Newton's ring, and improvement in the invisibility of scratches.

(5) The width d of the valley bottom in the arrangement direction of the unit optical shapes satisfies the relationship of 0 <d / w ≦ 0.15 with respect to the width w of the unit optical shapes in the arrangement direction of the unit optical shapes. The brightness is not greatly reduced. Moreover, since it is easy to manufacture a mold for shaping the unit optical shape, the production cost can be reduced.

(6) Since the unit optical shapes are arranged in one direction along the sheet surface, the light beam can be controlled in the arrangement direction. Moreover, an optical sheet can be easily produced by extrusion molding or the like.

(7) Since it is a surface light source device and a display device including the optical sheet of the present invention and a light source unit that emits light, the front luminance is high, there are few optical defects such as side lobes and Newton rings, and the viewing angle is wide, Good illumination with little unevenness in luminance can be performed.

It is a figure which shows the display apparatus and surface light source device of 1st Embodiment. It is the perspective view which expanded and looked at a part of optical sheet of a 1st embodiment. It is the figure which expanded a part of section of the optical sheet of a 1st embodiment. It is the perspective view which expanded and looked at a part of optical sheet of a 2nd embodiment. It is a figure which expands and shows a part of cross section of the optical sheet of 2nd Embodiment. It is a graph which shows the luminance distribution of the direction orthogonal to the arrangement direction of a unit optical shape of the optical sheet of the measurement examples 1-3, and a unit optical shape. It is a graph which shows the luminance distribution of the direction orthogonal to the arrangement direction of the unit optical shape of the optical sheet of the measurement examples 4 and 5 and the unit optical shape. It is a graph which shows the measurement result of the side lobe of the optical sheet of the measurement examples 1-5.

Embodiments of the present invention will be described below with reference to the drawings. In addition, each figure shown below is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
In addition, the terms “plate”, “sheet”, “film” and the like are used, but these are generally used in the order of thickness, “plate”, “sheet”, “film”. I am using it. However, since there is no technical meaning in such proper use, the description in the claims is used in the unified description of the sheet. Accordingly, the terms “sheet”, “plate”, and “film” can be appropriately replaced. For example, the optical sheet may be an optical film or an optical plate.
Furthermore, numerical values such as dimensions and material names of each member described in the present specification are examples of the embodiment, and the present invention is not limited thereto, and may be appropriately selected and used.

(First embodiment)
FIG. 1 is a diagram illustrating a display device 1 and a surface light source device 10 according to the first embodiment.
The display device 1 is a transmissive liquid crystal display device that includes an LCD panel 11, a reflecting plate 12, an arc tube 13, a milky white plate 14, an optical sheet 15, and the like. The display device 1 illuminates and displays an image displayed on the LCD panel 11 from the back. In addition, as the surface light source device (backlight) 10 that illuminates the LCD panel 11 from the back, a reflecting plate 12, an arc tube 13, a milky white plate 14, and an optical sheet 15 are applicable.
The LCD panel 11 is a transmissive display unit formed by a transmissive liquid crystal display element. The LCD panel 11 of this embodiment is 32 inches diagonal (740 mm × 420 mm), and can display a resolution of 1280 × 768 dots.

The arc tube 13 constitutes a light source unit of the surface light source device 10 and is a linear light source that emits light. In the present embodiment, a cold cathode tube (CCFL: Cold Cathode Fluorescent Lamp) is used as the arc tube 13.
In FIG. 1, six arc tubes 13 are schematically shown as being arranged, but in reality, 18 arc tubes are arranged in parallel at regular intervals of approximately 20 mm. A reflection plate 12 is provided on the back surface of the arc tube 13.
In the present embodiment, the direction parallel to the longitudinal direction of the arc tube 13 is the horizontal screen direction (the horizontal direction of the screen) when the surface light source device 10 and the display device 1 are used, and the direction in which the arc tubes 13 are arranged is This is the screen vertical direction (screen up-down direction) in the usage state of the surface light source device 10 and the display device 1. In the following description, unless otherwise specified, the screen vertical direction and the screen horizontal direction are the screen vertical direction and the screen horizontal direction when the surface light source device 10 and the display device 1 are used.

The reflector 12 is provided over the entire back side of the arc tube 13 (opposite to the milky plate 14), and diffuses and reflects the illumination light traveling toward the backside toward the milky plate 14 (outgoing direction). , Has the function of making the incident light illuminance uniform.
The milky white plate 14 is a diffusing plate having non-directional light diffusing characteristics, and is disposed on the LCD panel 11 side of the arc tube 13.

  The optical sheet 15 has a plurality of convex unit optical shapes 151 that are convex on the emission side on the emission side (LCD panel 11 side) in one direction along the sheet surface. In addition, the incident surface 154 on the opposite side of the surface on which the unit optical shape 151 and the valley bottom 152 of the optical sheet 15 are formed, and the incident surface 154 on which the light emitted from the arc tube 13 is incident, is a substantially smooth surface. . The optical sheet 15 has an action of diffusing and collecting light.

FIG. 2 is an enlarged perspective view of a part of the optical sheet 15 according to the first embodiment. FIG. 2 shows a state in which the end of the optical sheet 15 is observed from an obliquely upward direction on the emission side with an electron microscope.
FIG. 3 is an enlarged view of a part of the cross section of the optical sheet 15. The cross section shown in FIG. 3 is a cross section of the optical sheet 15 taken along arrows S1-S2 in FIG. 1, and is a cross section orthogonal to the sheet surface and parallel to the arrangement direction (vertical direction of the screen) of the unit optical shapes 151. is there.
Here, the sheet surface indicates a surface that is a planar direction of the sheet when viewed as the entire sheet in each sheet, and the same definition also in the present specification and claims. It is used as For example, in the optical sheet 15, the sheet surface is a surface in the planar direction of the optical sheet 15 when viewed as the entire optical sheet 15, and is parallel to the incident surface (surface on the arc tube 13) 154 of the optical sheet 15. This is a serious aspect.

The optical sheet 15 is formed by arranging a plurality of unit optical shapes 151 in the direction perpendicular to the screen along the sheet surface on the surface on the emission side (LCD panel 11 side). The unit optical shape 151 has a substantially triangular prism shape. As shown in FIG. 3, the cross-sectional shape in a cross section parallel to the normal direction of the sheet surface and parallel to the arrangement direction of the unit optical shapes 151 is a substantially isosceles triangle shape having a base angle α. The unit optical shape 151 has a top portion 151t formed of a curved surface having a radius of curvature R, and the side surface 151s and the top portion 151t are smoothly connected.
Further, a valley bottom 152 is formed between the unit optical shapes 151 with a predetermined width (interval) d.

  The height of the unit optical shape 151 (the dimension from the vertex t of the unit optical shape 151 in the normal direction of the sheet surface to the bottom of the valley bottom 152) is h, and the width of the unit optical shape 151 (unit in the arrangement direction). The dimension between the points v1 and v2 closest to the valley bottom 152 side of the side surface 151s of the optical shape 151) is w, and the arrangement pitch of the unit optical shapes 151 is P, and this arrangement pitch P is P = d + w Meet. The total thickness of the optical sheet 15 is T.

The interval between the unit optical shapes 151 (the width of the valley bottom portion 152) d is larger than 0% and less than 15% with respect to the width w of the unit optical shapes 151, and the relationship 0 <d / w ≦ 0.15 is satisfied. Satisfies. This is because when d / w = 0 (that is, d = 0), the diffusion effect due to the uneven shape of the valley bottom 152 cannot be obtained. When d / w> 0.15 (that is, d is greater than 15% with respect to w), the ratio of the area occupied by the valley bottom 152 in the sheet surface becomes too large, and the entire optical sheet 15 This is because the light collecting action of the unit optical shape 151 is reduced, and the effect of increasing the luminance cannot be obtained.
In order to obtain the diffusion effect due to the uneven shape of the valley bottom portion 152, it is preferable to satisfy the relationship of 0 <d / w ≦ 0.15. In order to further improve the optical characteristics such as reduction, it is more preferable that 0.02 ≦ d / w ≦ 0.15 (that is, the ratio of d to w is 2% or more and 15% or less).

  As shown in FIGS. 2 and 3, the surface on the emission side of the optical sheet 15 including the valley bottom 152 and the unit optical shape 151 is a rough surface having irregular and fine irregularities. Then, in this fine uneven shape, the valley bottom 152 has a larger uneven shape and a larger surface roughness value than the unit optical shape 151. On the output side surface of the optical sheet 15 of the present embodiment, the unevenness of the top 151t is small and the value of the surface roughness is small, and the unevenness of the surface of the side surface 151s gradually increases from the top 151t to the valley bottom 152. The unevenness is large, the value of the surface roughness is also large, the unevenness of the uneven shape of the valley bottom 152 is the largest, and the value of the surface roughness is also the largest.

And it is preferable that the uneven | corrugated shaped surface roughness of the valley bottom part 152 and the uneven | corrugated shaped surface roughness of the top part 151t satisfy | fill the following relationships.
Regarding the arithmetic average roughness Ra (JIS B0601-2001), a value obtained by dividing the arithmetic average roughness Ra of the concave-convex shape of the valley bottom portion 152 by the arithmetic average roughness Ra of the concave-convex shape of the top portion 151t (that is, the concave-convex shape of the top portion 151t). (Ratio of the arithmetic average roughness Ra of the concave-convex shape of the valley bottom portion 152 to the arithmetic average roughness Ra) R1 preferably satisfies 1 <R1 <50, and more preferably satisfies 9 ≦ R1 ≦ 20.
Regarding the maximum height Rz (JIS B0601-2001), a value obtained by dividing the maximum height Rz of the concave-convex shape of the valley bottom portion 152 by the maximum height Rz of the concave-convex shape of the top portion 151t (that is, the concave-convex shape of the top portion 151t). The ratio of the maximum height Rz of the concave-convex shape of the valley bottom portion 152 to the maximum height Rz) preferably satisfies 1 <R2 <50, and more preferably satisfies 10 ≦ R2 ≦ 25.
The optical sheet 15 of the present embodiment satisfies a preferable range with respect to R1 and R2.

  The optical sheet 15 is formed by extrusion molding using a light-transmitting thermoplastic resin such as PC (polycarbonate) resin or AS (acrylonitrile / styrene) resin. As a mold (mold or the like) for shaping the shape of the unit optical shape 151 at the time of extrusion molding, an irregular and fine uneven shape is applied to substantially the entire surface by blasting or the like. The optical sheet 15 is not limited to the above example, but ABS (acrylonitrile butadiene styrene) resin, PMMA (methyl methacrylate) resin, PET (polyethylene terephthalate) resin, cycloolefin resin, MS (methyl methacrylate styrene) resin, You may form using MBS (methyl methacrylate * butadiene * styrene) resin etc.

In the mold used for the optical sheet 15 of the present embodiment, before the blasting process, the reverse shape of the unit optical shape 151 is adjacently arranged, and a predetermined width is provided between the reverse shapes of the unit optical shape 151. The flat surface etc. which have are not formed. That is, the mold used for the optical sheet 15 of the present embodiment is formed by blasting to form an inverted mold of the valley bottom 152 having a predetermined width d.
At the time of extrusion molding of the optical sheet 15, a large mold pressure is applied to the valley bottom 152 and the end of the side surface 151s on the valley bottom 152 side, but the mold pressure is applied to the portion that becomes the unit optical shape 151 (particularly the top 151t). small. Therefore, the transfer rate of the uneven shape on the surface of the unit optical shape 151 is lower than that of the valley bottom 152. Therefore, when the optical sheet 15 is formed by extrusion molding with a mold having a fine uneven shape on the entire surface, the valley bottom 152 has uneven surface irregularities on the surface compared to the unit optical shape 151. Large and rough surface.

  The optical sheet 15 is not limited to extrusion molding, and a unit optical shape or the like may be formed by ultraviolet molding using an ultraviolet curable resin or the like on one side of a sheet serving as a base material. In this case, the ultraviolet molding or the like has a higher shape transfer rate than the extrusion molding, and there is no difference in the transfer rate between the unit optical shape 151 and the valley bottom 152, so the portion corresponding to the valley bottom 152 is etched or the like, It is preferable to use a shaping mold or the like provided with an uneven shape rougher than the uneven shape of the unit optical shape 151.

(Second Embodiment)
FIG. 4 is an enlarged perspective view of a part of the optical sheet 25 of the second embodiment. FIG. 4 is a photomicrograph obtained by observing the end portion of the optical sheet 25 from an oblique upper side on the emission side with an electron microscope.
FIG. 5 is an enlarged view showing a part of the cross section of the optical sheet 25 of the second embodiment. The cross section shown in FIG. 5 is a cross section corresponding to the cross section taken along arrows S1-S2 of the optical sheet 15 of the first embodiment in FIG. 1, and is parallel to the arrangement direction (the screen vertical direction) of the unit optical shapes 251. A part of a cross section perpendicular to the sheet surface is shown enlarged.
The optical sheet 25 of the second embodiment has substantially the same form as the optical sheet 15 of the first embodiment described above except that the unit optical shape 251 has a different shape. Accordingly, parts having the same functions as those of the first embodiment described above are denoted by the same reference numerals or the same reference numerals at the end, and redundant description is omitted.
The optical sheet 25 of the second embodiment can be used in the surface light source device 10 and the display device 1 shown in FIG. 1 instead of the optical sheet 15 shown in the first embodiment. A plurality of unit optical shapes 251 are arranged on the surface of the optical sheet 25 on the LCD panel 11 side, and the incident surface 254 on the arc tube 13 side is a substantially smooth surface.

As shown in FIG. 5, the unit optical shape 251 has a base angle β (β> α) in a cross section that is parallel to the arrangement direction of the unit optical shapes 251 and orthogonal to the sheet surface. The shape is a curved surface. In the cross-sectional shape shown in FIG. 5, the top portion 251t of the unit optical shape 251 is formed of a substantially circular arc, and the top portion 251t and the side surface 251s are smoothly connected.
Between the unit optical shapes 251, valley bottom portions 252 are provided with a predetermined width (interval) d.
As shown in FIGS. 4 and 5, the surface on the emission side of the optical sheet 25 including the valley bottom 252 and the unit optical shape 251 has a rough surface shape having irregular and fine irregularities. And this fine uneven | corrugated shape has the uneven | corrugated shape of the uneven | corrugated shape of the valley bottom part 252 larger than the uneven | corrugated shape of the unit optical shape 251, and the value of the surface roughness is rough. In this embodiment, the top portion 251t has the smallest surface roughness value, the surface roughness value of the side surface 251s gradually increases from the top portion 251t toward the valley bottom portion 252, and the valley bottom portion 252 has the most surface roughness. The value of has increased.

Also in the optical sheet 25 of the present embodiment, regarding the arithmetic average roughness Ra (JIS B0601-2001), the ratio R1 of the arithmetic average roughness Ra of the concave and convex shape of the valley bottom portion 252 to the arithmetic average roughness Ra of the concave and convex shape of the top portion 251t. Preferably satisfies 1 <R1 <50, and more preferably satisfies 9 ≦ R1 ≦ 20. Further, regarding the maximum height Rz (JIS B0601-2001), the ratio R2 of the maximum height Rz of the concave / convex shape of the valley bottom portion 152 to the maximum height Rz of the concave / convex shape of the top portion 151t satisfies 1 <R2 <50. Is preferable, and it is more preferable to satisfy 10 ≦ R2 ≦ 25.
The optical sheet 25 of the present embodiment satisfies a preferable range with respect to R1 and R2.

As shown in FIG. 5, the height of the unit optical shape 251 (the dimension from the apex t of the unit optical shape 251 to the bottom of the valley bottom 252 in the normal direction of the sheet surface) is h, and the unit optical shape 251 The width (the dimension between points v1 and v2 that is closest to the valley bottom 252 side of the side surface 251s of the unit optical shape 251 in the arrangement direction) is w, and the arrangement pitch of the unit optical shapes 151 is P (P = d + w). It is. The total thickness of the optical sheet 25 is T.
Further, the interval between the unit optical shapes 251 (the width of the valley bottom 252) d satisfies the relationship of 0 <d / w ≦ 0.15 with respect to the width w of the unit optical shape 251. From the viewpoint of further enhancing the diffusion effect due to the uneven shape of the valley bottom 252, it is more preferable that 0.02 ≦ d / w ≦ 0.15 (that is, d is 2% or more and 15% or less with respect to w). .

Similar to the optical sheet 15 of the first embodiment, the optical sheet 25 is formed by extrusion molding using a light-transmitting thermoplastic resin such as PC resin or AS resin. As a mold (mold or the like) for shaping the shape of the unit optical shape 251 at the time of extrusion molding, an irregular and fine uneven shape is applied to almost the entire surface by blasting or the like. The mold of the optical sheet 25 is a state in which the reverse molds of the unit optical shapes 251 are arranged at a predetermined interval before the irregular shape is formed on the surface thereof by blasting or the like. The space between the inverted molds is a substantially smooth surface (corresponding to the valley bottom 252 before the formation of the uneven shape). Then, this smooth surface is formed into an uneven shape by blasting, and becomes a reverse type of the valley bottom 252.
The optical sheet 25 is not limited to the above example, and may be formed using ABS resin, PMMA resin, PET resin, cycloolefin resin, MS resin, MBS resin, or the like.
Further, the optical sheet 25 is not limited to extrusion molding, and the unit optical shape 251 and the like may be formed by ultraviolet molding using an ultraviolet curable resin.

(Regarding the ratio of surface roughness)
Here, the optical sheets of Measurement Examples 1 to 5 including the optical sheets which are examples of the first embodiment and the second embodiment are prepared, and the surface roughness between the top and bottom of the unit optical shape is measured. The ratio of the surface roughness of the valley bottom to the surface roughness of the top was determined.
The optical sheets of measurement examples 1 and 2 are optical sheets corresponding to the examples of the optical sheet 15 of the first embodiment. The optical sheets of measurement examples 1 and 2 have different blasting strengths for the mold, and the blasting of the mold used for molding the optical sheet of measurement example 1 is the blast used for molding the optical sheet of measurement example 2. Compared with processing, the strength of the blast is large. Therefore, the mold used for molding the optical sheet of Measurement Example 1 has larger irregularities formed on the surface than the mold used for molding the optical sheet of Measurement Example 2.
The optical sheet of measurement example 1 has a radius of curvature R = 25 μm at the top 151t, a height h = 58 μm of the unit optical shape 151, a width d = 4 μm of the valley bottom 152, a width w = 136 μm of the unit optical shape 151, and a unit. The arrangement pitch P of the optical shape 151 is 140 μm, and the total sheet thickness T is 350 μm. Further, the optical sheet of Measurement Example 1 satisfies d / w≈0.0294, and satisfies 0 <d / w ≦ 0.15 and 0.02 ≦ d / w ≦ 0.15.
The optical sheet of measurement example 2 has a radius of curvature R = 25 μm at the top 151t, a height h = 59 μm of the unit optical shape 151, a width d = 3 μm of the valley bottom 152, a width w = 137 μm of the unit optical shape 151, and a unit. The arrangement pitch P of the optical shape 151 is 140 μm, and the total sheet thickness T is 350 μm. The optical sheet of Measurement Example 2 satisfies d / w≈0.0219, and satisfies 0 <d / w ≦ 0.15 and 0.02 ≦ d / w ≦ 0.15.

The optical sheet of measurement example 3 is an optical sheet of a comparative example with respect to the optical sheet 15 of the first embodiment (optical sheets of measurement examples 1 and 2), and is the same as the mold for molding the optical sheet of measurement examples 1 and 2. Although it is a shaping | molding die, it is formed by the shaping | molding die which has not performed blasting etc. and is not provided with the irregular fine uneven | corrugated shape on the surface. In the optical sheet of Measurement Example 3, the width d of the valley bottom is approximately 0 μm, the concave and convex shapes are not formed on the unit optical shape and the valley bottom, and the surface roughness between the unit optical shape and the valley bottom is approximately equal. However, it is substantially the same form as the optical sheets of Measurement Examples 1 and 2 except that they are different from the optical sheets of Measurement Examples 1 and 2.
The optical sheet of measurement example 3 has a top radius of curvature R = 25 μm, a unit optical shape height h = 60 μm, and a total sheet thickness T = 350 μm. In the optical sheet of Measurement Example 3, the width d between the unit optical shapes is approximately 0 μm, and the width w and the arrangement pitch P of the unit optical shapes are w = P = 140 μm. In addition, the optical sheet of Measurement Example 3 satisfies d / w≈0 and does not satisfy 0 <d / w ≦ 0.15.

The optical sheet of measurement example 4 is an optical sheet corresponding to the example of the optical sheet 25 of the second embodiment.
The unit optical shape of the optical sheet of measurement example 4 is as follows: the radius of curvature R of the top 251t R = 31 μm, the base angle β = 70 °, the height h of the unit optical shape 251 = 40 μm, the width of the valley bottom 252 (the interval between the unit optical shapes) ) D = 8 μm, width w of unit optical shape 251 = 85 μm, and arrangement pitch P of unit optical shape 251 = 93 μm. The optical sheet of Measurement Example 4 has a total sheet thickness T = 450 μm. Further, the optical sheet of Measurement Example 4 satisfies d / w≈0.0941, and satisfies 0 <d / w ≦ 0.15 and 0.02 ≦ d / w ≦ 0.15.
On the other hand, the optical sheet of measurement example 5 is an optical sheet of a comparative example with respect to the optical sheet 25 of the second embodiment (optical sheet of measurement example 4). The optical sheet of Measurement Example 5 is the same mold as the mold for molding the optical sheet of Measurement Example 4, but is not subjected to blasting or the like, and has no irregular fine irregular shape on the surface. It is formed by a mold. The optical sheet of Measurement Example 5 is different from the optical sheet of Measurement Example 4 in that the unit optical shape and the surface of the valley bottom portion do not have irregular irregular shapes, and the valley bottom portion is a substantially flat surface. These are the forms substantially the same as the optical sheet of the measurement example 4.
The unit optical shape of the optical sheet of measurement example 5 has a radius of curvature R at the top portion of R = 31 μm, a base angle β = 70 °, a height of the unit optical shape h = 39 μm, a width of the unit optical shape w = 86 μm, and a unit optical shape. The arrangement pitch P is 93 μm, and the flat valley bottom width d between unit optical shapes is d = 7 μm. The optical sheet of Measurement Example 5 has a total sheet thickness T = 450 μm. In addition, the optical sheet of Measurement Example 5 satisfies d / w≈0.0814, and satisfies 0 <d / w ≦ 0.15 and 0.02 ≦ d / w ≦ 0.15.
In addition, all the optical sheets of the measurement examples 1 to 5 described above are formed by extruding AS resin.

About the measurement and evaluation of the surface roughness of the optical sheet of each measurement example, (a) to (d) shown below using a non-contact three-dimensional surface expression / roughness measuring device (Zygo New View 6300 manufactured by Zygo). ) And measured / calculated.
(A) The sample piece of the optical sheet of each measurement example is fixed to the sample stage.
(B) Adjustment is made so that the top and valley bottoms of the unit optical shape enter the 1.07 mm × 1.07 mm field of view of the sample piece, and the top and valley bottoms are respectively focused, and the scan length is 0.100 mm. Measure the surface roughness with. Three measurement points are arbitrarily selected from the sample piece, and the arithmetic average roughness Ra (JIS B0601-2001) and the maximum height Rz (JIS B0601-2001) of each top and valley bottom are measured.
(C) The average values of the Ra and Rz values at the top obtained by the measurement are obtained. Similarly, average values of Ra and Rz values at the bottom of the valley obtained by measurement are obtained.
(D) Divide the average value of Ra at the bottom of the valley by the average value of Ra at the top to determine the ratio R1 of Ra at the bottom of the valley to Ra at the top. Similarly, the average value of Rz at the bottom of the valley is divided by the average value of Rz at the top, and the ratio R2 of Rz at the bottom of the valley with respect to Rz at the top is obtained.

Table 1 is a table | surface which shows the surface roughness of the top part of the optical sheet of the measurement examples 1-5, and a valley bottom part.
Non-contact three-dimensional surface expression / roughness measuring machine (Zygo NewView 6300, manufactured by Zygo) uses scanning white light interferometry, irradiates measurement light to the target, and measures the surface roughness using the reflected light. is doing. The bottoms of the measurement examples 3 and 5 do not have an uneven shape, and the width thereof is approximately 0 μm. Therefore, when measured with the above-described measuring instrument without performing a treatment such as sputtering, The intensity was strong and the reflected light was saturated, making measurement difficult. However, the unit optical shape and the valley bottom of the optical sheets of Measurement Examples 3 and 5 do not have a concavo-convex shape by blasting or the like on the surface, and are formed by a molding die having a substantially smooth surface. It becomes a substantially smooth surface. Therefore, it is presumed that the surface roughness of the valley bottom in the optical sheets of measurement examples 3 and 5 and the surface roughness of the unit optical shape are substantially equal. Therefore, as shown in Table 1, the ratios R1, R2 of the surface roughness between the valley bottom and the top in the optical sheets of Measurement Examples 3 and 5 are both assumed to be 1.00.
In addition, when the sputter process for forming the black platinum layer on the surface of the unit optical shape and valley bottom of measurement examples 3 and 5 is performed and the process for reducing the reflected light is performed, the measurement can be performed with the above-described measuring instrument. However, as described above, it is assumed that the surface roughness of the valley bottom in the optical sheets of measurement examples 3 and 5 is substantially equal to the surface roughness of the unit optical shape. Does not go.

As described above, the ratio R1 of the arithmetic average roughness Ra at the bottom to the arithmetic average roughness Ra at the top is preferably 1 <R1 <50, and more preferably 9 ≦ R1 ≦ 20. The ratio R2 of the maximum height Rz of the valley bottom to the maximum height Rz of the top is preferably 1 <R2 <50, and more preferably 10 ≦ R2 ≦ 25.
In the case of R1 ≦ 1 or R2 ≦ 1, the uneven shape at the top is the same size as the uneven shape at the bottom of the valley, or is larger than the uneven shape at the bottom of the valley. For this reason, the effect of reducing the side lobes cannot be obtained, and the light emitted from the top is diffused, resulting in a decrease in front luminance. In addition, the larger values of R1 and R2 are preferable in terms of optical characteristics because the effect of reducing side lobes is larger, but those having values of R1 and R2 of 50 or more are difficult to manufacture at present. R1 <50 and R2 <50.
In addition, although a more preferable range differs between R1 and R2, this is due to a difference in the way of defining the arithmetic average roughness Ra and the maximum height Rz.

As shown in Table 1, the optical sheet of Measurement Example 1 has R1 = 8.52 and R2 = 10.06, and the optical sheet of Measurement Example 2 has R1 = 4.28 and R2 = 7.53. The optical sheets of Measurement Examples 1 and 2 satisfy the preferable range or more preferable range of R1 and R2, respectively. However, the optical sheet of Measurement Example 3 has R1 = 1.00 and R2 = 1.00, and both R1 and R2 do not satisfy the preferred range.
Moreover, the optical sheet of the measurement example 4 has R1 = 18.35 and R2 = 23.26, and satisfies both the more preferable ranges of R1 and R2. However, the optical sheet of measurement example 5 has R1 = 1.00 and R2 = 1.00, and both R1 and R2 do not satisfy the preferred range.

(Regarding evaluation)
Here, the optical sheets of measurement examples 1 and 2 and the optical sheet of measurement example 3, and the optical sheet of measurement example 4 and the optical sheet of measurement example 5 are respectively compared to determine whether side lobes are generated and the viewing angle is widened. We investigated the optical performance and the ease of scratching.
First, the front luminance of the optical sheets of Measurement Examples 1 to 5 was measured and evaluated.
The method for measuring the front luminance is to prepare surface light source devices each incorporating the optical sheets of Measurement Examples 1 to 5, and using a luminance meter (BM-9 manufactured by TOPCOM Co., Ltd.) under dark room conditions, Front luminance at the center of the screen (luminance in the normal direction of the sheet surface) was measured.
For the optical sheets of Measurement Examples 1 to 3, the front brightness of the optical sheet of Measurement Example 3 is used as a reference (100%), and the front of the optical sheets of Measurement Examples 1 and 2 with respect to the front brightness of the optical sheet of Measurement Example 3 The ratio of luminance was calculated and the front luminance was evaluated. For the optical sheets of measurement examples 4 and 5, the front luminance of the optical sheet of measurement example 5 is used as a reference (100%), and the front luminance of the optical sheet of measurement example 4 with respect to the front luminance of the optical sheet of measurement example 5 is calculated. The ratio was calculated and the front luminance was evaluated.

Next, the viewing angle of the optical sheets of Measurement Examples 1 to 5 and the presence or absence of side lobes were measured and evaluated.
Regarding the viewing angle, using a viewing angle measuring device (Murakami Color Research Laboratory Co., Ltd. Screen Optical Characteristic Evaluation Device GP-500 type), completely diffused light was respectively received from the incident surface side of the optical sheets of Measurement Examples 1 to 5. The luminance distribution in the direction perpendicular to the arrangement direction and the arrangement direction of the unit optical shapes when irradiated was measured under dark room conditions. Further, from the measurement results, the half-value angle αV in the arrangement direction of the unit optical shapes of the optical sheets of Measurement Examples 1 to 5 and the half-value angle αH in the direction orthogonal to the arrangement direction of the unit optical shapes were obtained.

  Regarding the side lobes, the optical sheets of measurement examples 1 to 3 irradiate completely diffused light from the incident surface 154 side, and the optical sheets of measurement examples 4 and 5 from the incident surface 254 side to the normal direction of the sheet surface. Irradiate parallel, substantially parallel light, both measure the luminance distribution in the range of the emission angle of 50 ° to 80 ° with respect to the sheet surface in the arrangement direction of the unit optical shape using the aforementioned viewing angle measuring device, The presence or absence of occurrence of was investigated.

In addition, when the unit optical shape is a substantially prism shape as in Measurement Examples 1 to 3, no side lobe is generated even when substantially parallel light is irradiated. For the evaluation, completely diffused light was used. On the other hand, in the case of the unit optical shapes as in measurement examples 4 and 5, since the presence or absence of side lobes is more significantly observed when substantially parallel light is irradiated than completely diffused light, measurement examples 4 and 5 are observed. For the evaluation of the side lobe of the optical sheet, substantially parallel light was used.
In addition, in the ridge line direction (longitudinal direction) of the unit optical shape, side lobes hardly occur. Therefore, in this measurement, only the arrangement direction of the unit optical shapes was measured. Further, since the side lobe is generated in a region having a relatively large emission angle with respect to the sheet surface, the measurement was performed in the range of 50 to 80 ° of the emission angle in this measurement.

Next, Newton rings of the optical sheets of Measurement Examples 1 to 5 were examined.
Newton rings tend to occur when the top of a unit lens is stacked in contact with the surface of another lens sheet or stacked with a slight gap in a surface light source device, etc. This is not preferable.
Newton's ring is evaluated by measuring the screen at a position 50 cm away from the observation surface of the display device (corresponding to the liquid crystal transmission type display device 1 shown in FIG. 1) incorporating the optical sheets of Measurement Examples 1 to 5 respectively. Were observed in a dark room environment to determine whether Newton rings were observed.

Further, regarding the optical sheets of Measurement Examples 4 and 5, flickering when used as a surface light source device or the like was also examined. The flicker described here is a phenomenon of brightness flicker observed when the screen is observed from a direction that makes an angle with respect to the front direction of the screen of a surface light source device or the like. This phenomenon occurs in a surface light source device or a display device using an optical sheet in which unit optical shapes are arranged at predetermined intervals and the unit optical shapes are flat surfaces (for example, the optical sheet of Measurement Example 5). It is likely to be generated by light that is emitted from the flat surface without receiving the light beam control action by the unit optical shape or the like and reaches the observer side. This flickering is undesirable because it causes a reduction in image quality. Therefore, only the measurement examples 4 and 5 were examined for flicker.
Regarding flickering, in the dark room environment, at the position 50 cm away from the observation surface of the surface light source device in which the optical sheets of Measurement Examples 4 and 5 are incorporated, the center of the screen is in the normal direction of the observation surface (the normal of the sheet surface). Direction), and in order to make an observation while visually observing while moving in a direction that makes a large angle with respect to the normal direction of the observation surface.

Next, the scratch resistance of the optical sheets of Measurement Examples 1 to 5 and the difficulty of seeing the scratches when the scratches occurred were examined. The scratch resistance was evaluated by a pencil hardness test. In addition, the difficulty of seeing the scratch when the scratch was generated was evaluated by a scratch test using a taper tester.
The pencil hardness test was performed according to JIS K5600-5-4, and was measured using the test equipment described in JIS K5600-5-4.
The procedure of the scratch test by the taper tester is as follows. First, a taper tester (TABER ABRASION TESTER manufactured by Toyo Seiki Co., Ltd.) is used for the surface (exit-side surface) on which the unit optical shape of the optical sheets of measurement examples 1, 3, 4, and 5 is formed, and the load is 250 g. Then, scratching is performed under the condition of one rotation. Next, as evaluation 1, the appearance of the optical sheet of each measurement example was visually observed in a bright room environment to evaluate the appearance of scratches, and as evaluation 2, a surface light source device provided with each optical sheet was created. The appearance of scratches when the arc tube was actually turned on was evaluated visually. In Table 2, when the surface of the optical sheet is not observed even when observed from any direction, the surface is marked with ◎, and when observed from the front direction (normal direction of the sheet surface), the surface is thinly scratched. Although it was recognized, the case where no scratches were observed when the optical sheet was observed from an oblique direction by changing the angle was indicated by ◯. Also, in addition to the front direction, the case where scratches are observed even when the optical sheet is observed obliquely at different angles is indicated as x, and the case where scratches are observed on the surface of the optical sheet is observed from any direction. It was shown as xx as impossible.

Table 2 is a table summarizing the above-described evaluation results of the optical sheets of Measurement Examples 1 to 5.
With the front brightness of the optical sheet of measurement example 3 as a reference (100%), the front brightness of the optical sheet of measurement example 1 is 99.4%, and the front brightness of the optical sheet of measurement example 2 is 99.8%. Compared to the optical sheet of Measurement Example 3, both are slightly lower. Further, the optical sheet of Measurement Example 4 has a front luminance of 98.9% with the optical sheet of Measurement Example 5 as a reference (100%), which is slightly lower than the optical sheet of Measurement Example 5. .
This is because, in the optical sheets of measurement examples 1, 2, and 4, light was diffused by the irregular and very fine irregularities formed on the surfaces of the unit optical shapes 151 and 251 and the valley bottoms 152 and 252. It is believed that there is. However, the optical sheets of Measurement Examples 1, 2, and 4 have sufficient brightness as the front luminance used as the surface light source device and the display device, and there is no problem in use.

FIG. 6 is a graph showing the luminance distribution in the arrangement direction of the unit optical shapes of the optical sheets of Measurement Examples 1 to 3 and the direction orthogonal to the arrangement direction. FIG. 7 is a graph showing the luminance distribution in the arrangement direction of the unit optical shapes of the optical sheets of measurement examples 4 and 5 and the direction orthogonal to the arrangement direction. 6 and 7, the arrangement direction of the unit optical shapes is a direction orthogonal to the longitudinal direction of the unit optical shapes, and corresponds to the screen vertical direction in the use state when used in the display device 1 shown in FIG. Further, the direction orthogonal to the arrangement direction of the unit optical shapes is a direction parallel to the longitudinal direction of the unit optical shapes, and corresponds to the horizontal direction of the screen when used in the display device 1 shown in FIG.
6A shows the luminance distribution in the arrangement direction of the unit optical shapes of the optical sheets of Measurement Examples 1 to 3, and FIG. 6B shows the arrangement direction of the unit optical shapes of the optical sheets of Measurement Examples 1 to 3. The luminance distribution in a direction orthogonal to the direction (longitudinal direction of the unit optical shape) is shown. FIG. 7A shows the luminance distribution of the optical sheet in the arrangement direction of the unit optical shapes of the optical sheets of Measurement Examples 4 and 5, and FIG. 7B shows the unit optical shape of the optical sheet of Measurement Examples 4 and 5. The luminance distribution in the direction (longitudinal direction of the unit optical shape) orthogonal to the arrangement direction of the. In each graph shown in FIG. 6 and FIG. 7, the vertical axis represents relative luminance when the luminance peak in each optical sheet is 1.0, the horizontal axis represents the emission angle with respect to the sheet surface, and the horizontal axis The positive direction indicates the upper side in the vertical direction of each optical sheet, and the negative direction indicates the lower side in the vertical direction.

  FIG. 8 is a graph showing the measurement results of the side lobes of the optical sheets of Measurement Examples 1 to 5. FIG. 8A shows the measurement results of the side lobes of the optical sheets of Measurement Examples 1 to 3 (luminance distribution at 50 ° to 80 ° in the arrangement direction of the unit optical shapes). FIG. 5 shows the measurement results of side lobes of the optical sheet No. 5 (brightness distribution at 50 ° to 80 ° in the arrangement direction of the unit optical shapes). In the graphs shown in FIGS. 8A and 8B, the vertical axis represents the relative luminance when the peak luminance is the reference value (1.0), and the horizontal axis represents the emission angle with respect to the sheet surface in the vertical direction. is there.

As shown in FIGS. 6A and 6B, the optical sheets of Measurement Examples 1 and 2 are orthogonal to the arrangement direction of the unit optical shapes and the arrangement direction of the unit optical shapes as compared to the optical sheet of Measurement Example 3. In any direction (longitudinal direction of the unit optical shape), the change in luminance with respect to the emission angle is gradual. Further, when the optical sheets of measurement examples 1 and 2 are compared, the change in luminance with respect to the emission angle is slower in the optical sheet of measurement example 1 than in the optical sheet of measurement example 2.
Next, as shown in FIG. 7A, the optical sheet of measurement example 4 has a gentler change in luminance with respect to the emission angle in the arrangement direction of the unit optical shapes than the optical sheet of measurement example 5. Yes.

Regarding the half-value angle, as shown in Table 2, the optical sheet of Measurement Example 3 has a half-value angle αV = 35.0 ° in the arrangement direction of the unit optical shape, and a direction orthogonal to the arrangement direction of the unit optical shape (unit optical The half-value angle αH of the longitudinal direction of the shape is 51.8 °. However, the optical sheet of measurement example 1 has a half-value angle αV = 36.7 ° and a half-value angle αH = 54.6 °, and the optical sheet of measurement example 2 has a half-value angle αV = 36.6 ° and a half-value angle αH. = 52.7 °, and each of the half-value angles is larger than that of the optical sheet of Measurement Example 3. Therefore, the viewing angles of the optical sheets of Measurement Examples 1 and 2 are wider than those of the optical sheet of Measurement Example 3. Further, when comparing the optical sheets of Measurement Examples 1 and 2, the optical sheet of Measurement Example 1 has a larger half-value angle than the optical sheet of Measurement Example 2, and a wide viewing angle can be obtained.
Next, in the optical sheet of Measurement Example 5, the half-value angle αV = 40.8 ° in the arrangement direction of the unit optical shape, and the half-value angle αH in the direction orthogonal to the arrangement direction of the unit optical shape (longitudinal direction of the unit optical shape) 61.8 °. However, the optical sheet of measurement example 4 has a half-value angle αV = 42.3 ° and a half-value angle αH = 63.3 °, and each half-value angle is larger than that of the optical sheet of measurement example 5. Therefore, the viewing angle of the optical sheet of measurement example 4 is wider than that of the optical sheet of measurement example 5.

Further, as shown in FIG. 8A, in the optical sheet of measurement example 3, side lobes are generated at an emission angle of about 65 ° to 77 °. In the optical sheets of measurement examples 1 and 2, the measurement example The side lobe is reduced as compared with the optical sheet 3. When comparing the optical sheets of Measurement Examples 1 and 2, the optical sheet of Measurement Example 1 has a higher sidelobe reduction effect than the optical sheet of Measurement Example 2. The side lobe reduction effect of the optical sheets of Measurement Examples 1 and 2 is also apparent from FIG.
Next, as shown in FIG. 8B, in the optical sheet of Measurement Example 4, no side lobe is generated, and the luminance is smoothly reduced as the emission angle with respect to the sheet surface increases. On the other hand, in the optical sheet of Measurement Example 5, a side lobe having a peak at an emission angle of about 79 ° occurs at an emission angle of about 77 ° to 80 °.

From the above, the optical sheets of Measurement Examples 1, 2, and 4 are effective in reducing side lobes. The side lobe reduction effect in the optical sheets of the measurement examples 1, 2, and 4 is due to the minute and irregular uneven shape formed on the valley bottoms 152 and 252 and the side surfaces 151s and 251s of the measurement examples 1, 2, and 4. The unit optical shape molded by the mold without blasting is obtained by diffusing the cause light of the lobe, or by molding the unit optical shape of the measurement examples 1, 2, and 4 by the blasted molding die. Compared to measurement examples 3 and 5), it is assumed that the height of the unit optical shape is slightly reduced.
Further, by reducing such side lobes, the light forming the side lobes is emitted within the viewing angle range, and the optical sheets of measurement examples 1, 2, and 4 have the effect of improving the viewing angle. It has been.

When the optical sheet in which the side lobe is generated is incorporated in the display device 1 as shown in FIG. 1, the light emitted from the optical sheet as the side lobe is reflected in the housing of the display device 1. The amount of light emitted from the panel 11 is small. However, when the display device 1 is used for a long time, for example, when the optical sheet is bent, the sheet surface is bent, so that a light beam serving as a side lobe is emitted from the LCD panel 11, and the luminance due to the bending. In addition to unevenness, brightness unevenness due to side lobes also occurs, the image quality is greatly reduced, and the bending of the optical sheet is also observed significantly. Therefore, it is preferable to reduce the side lobes as much as possible.
Therefore, even if the optical sheets of the measurement examples 1, 2, and 4 are bent, the deterioration in image quality due to luminance unevenness caused by the side lobe can be suppressed as much as possible.

Regarding Newton rings, as shown in Table 2, almost no Newton rings were observed in the optical sheets of Measurement Examples 1, 2, and 4. However, in the optical sheets of Measurement Examples 3 and 5, the occurrence of Newton rings was observed, and the image quality was deteriorated.
This is because the tops 151t and 251t of the unit optical shapes 151 and 251 in the optical sheets of the measurement examples 1, 2, and 4 have a rough surface with fine unevenness, which causes the generation of Newton rings. This is probably because the contact area with a certain LCD panel 11 or the like has been reduced. Further, it is considered that the visibility of the Newton ring is lowered due to the light diffusion effect of the valley bottom portions 152 and 252 even when some Newton rings are generated.
Therefore, the optical sheets of measurement examples 1, 2, and 4 are effective in reducing Newton rings.

Regarding flickering, as shown in Table 2, the optical sheet of Measurement Example 4 can be observed from a direction that makes an angle with respect to the normal direction of the observation surface (parallel to the sheet surface of the optical sheet of Measurement Example 4). No flicker was observed, and a good image was observed. In addition, streaky bright and dark lines that deteriorate the image quality were not observed. However, the optical sheet of Measurement Example 5 was observed to flicker when observed from a direction of 45 ° to 50 ° with respect to the normal direction of the observation surface.
This is because, in the optical sheet of measurement example 5, the bottom of the valley between the unit optical shapes is a substantially smooth surface, whereas in the optical sheet of measurement example 4, the valley bottom 252 has an uneven shape, This is because light emitted from the portion is diffused.
Therefore, the optical sheet of measurement example 4 is effective in reducing flickering and streak-like bright and dark lines.

  Regarding scratch resistance, as shown in Table 2, in the arrangement direction of unit optical shapes (direction orthogonal to the longitudinal direction), the optical sheet of Measurement Example 1 has a pencil hardness of F, and the optical sheet of Measurement Example 2 is The pencil hardness was F. On the other hand, the optical sheet of measurement example 3 had a pencil hardness of HB in the arrangement direction of the unit optical shapes, and the pencil hardness was lower than the optical sheets of measurement examples 1 and 2. In addition, the optical sheet of measurement example 4 had a pencil hardness of F in the arrangement direction of the unit optical shape, whereas the optical sheet of measurement example 5 had a pencil hardness of B in the arrangement direction of the unit optical shape and was measured. The pencil hardness was lower than that of the optical sheet of Example 4. This is because, in the optical sheets of measurement examples 1, 2, and 4, the unit optical shapes 151 and 251 have irregular irregular shapes on the surface thereof, and in particular, the tops 151t and 251t are rough surfaces. It is considered that the effect is obtained.

In addition, regarding the invisibility of scratches, as shown in Table 2, the optical sheets of Measurement Examples 1, 2, and 4 have an evaluation of 1 and a favorable evaluation of 2. When only the optical sheet is observed, it is somewhat Although scratches are observed, no scratches were observed when the surface light source device was actually turned on. On the other hand, in the optical sheets of Measurement Examples 3 and 5, both Evaluation 1 and Evaluation 2 are unsuitable, both when only the optical sheet is observed and when it is actually turned on using the surface light source device. Scratches were recognized and not suitable for use. This is because, in the optical sheets of measurement examples 1, 2, and 4, when only the optical sheet is observed, scratches are difficult to see due to the minute and irregular uneven shape of the surface of the unit optical shape, and the surface light source device When it is actually turned on, the viewing angle is wide and the luminance distribution is gentle, so that the scratches are blurred and the effect is obtained.
From the above, the optical sheets of measurement examples 1, 2, and 4 are less likely to be scratched than the optical sheets of measurement examples 3 and 5, and even when scratched, the scratches are difficult to see.

As described above, the optical sheets of measurement examples 1, 2, and 4 that are rough surfaces having irregular irregular shapes at the bottom of the valley, and the measurement examples 3 and 5 that do not have a valley bottom or are flat at the bottom of the valley. Comparing the optical sheets, the front luminance is slightly higher in each of the optical sheets in measurement examples 3 and 5 than in the optical sheets in measurement examples 1, 2, and 4, but both have good front luminance for use. is doing.
However, the optical sheets of Measurement Examples 3 and 5 have side lobes as shown in FIG. In addition, in the optical sheets of measurement examples 3 and 5, the luminance change due to the emission angle with respect to the sheet surface is steep compared to the optical sheets of measurement examples 1, 2, and 4, and the half-value angles (αV, αH) are also large. Small and narrow viewing angle. Furthermore, Newton rings are observed in the optical sheets of Measurement Examples 3 and 5, and image quality is deteriorated. In addition, since the optical sheets of Measurement Examples 3 and 5 are easily scratched and require careful handling, they are difficult to handle during production. Further, when it is damaged, the scratch is conspicuous and causes a reduction in image quality.

  On the other hand, the optical sheets of measurement examples 1, 2, and 4 have reduced side lobes, and the change in luminance due to the emission angle with respect to the sheet surface is gentler than the optical sheets of measurement examples 3 and 5, The half-value angles (αV, αH) are large, and the viewing angles in the vertical and horizontal directions are wide, indicating good optical characteristics. In addition, in the optical sheets of Measurement Examples 1, 2, and 4, no Newton ring is observed, and the image quality is good. Furthermore, the optical sheets of measurement examples 1, 2, and 4 are less likely to be scratched, are easy to handle, and even if scratches occur, the scratches are difficult to see, and deterioration in image quality can be suppressed. In addition, the flickering of the optical sheet of Measurement Example 4 is effectively reduced.

Therefore, according to each embodiment of the present invention, an optical sheet with high front luminance, reduced side lobes, good viewing angle, and good optical performance with reduced Newton rings can be obtained. As a result, the surface light source device 10 and the display device 1 are made to have good front luminance and viewing angle, no unpleasant Newton ring is generated, and the surface light source device 10 and the display device 1 can display good images. Can do. In addition, according to each embodiment of the present invention, the side lobes are reduced, and therefore, when the optical sheet is bent due to the use environment or the like, it is possible to suppress the occurrence of luminance unevenness caused by the side lobes as much as possible. .
Further, according to each embodiment of the present invention, the surface on which the unit optical shapes 151 and 251 and the valley bottom portions 152 and 252 of the optical sheets 15 and 25 are formed is not easily scratched and is easy to handle. Even when the surface on which the unit optical shapes 151 and 251 and the valley bottom portions 152 and 252 are formed at the time of manufacturing or the like, the scratches are not conspicuous and the deterioration of the image quality due to the scratches can be greatly reduced. In addition, a masking process for preventing scratches is not required, and the work process can be shortened and the production cost can be reduced.
Furthermore, according to the second embodiment of the present invention, it is possible to reduce flicker that is likely to occur when the optical sheets are arranged with a predetermined interval between the unit optical shapes 251.

  Furthermore, according to the present invention, light is diffused by the concave and convex shapes of the valley bottoms 152 and 252, which is effective in reducing luminance unevenness. In particular, as shown in the first and second embodiments, when the arc tube 13 is used as a light source, the arrangement direction of the unit optical shapes 151 is parallel to the arrangement direction of the arc tube 13. This is effective in reducing luminance unevenness (so-called tube unevenness) due to the position of the arc tube 13.

(Deformation)
Without being limited to the embodiments described above, various modifications and changes are possible, and these are also within the scope of the present invention.
(1) In 1st Embodiment, the unit optical shape 151 shows the example which is the substantially isosceles triangular prism shape in which the top part 151t is formed with a curved surface, and in 2nd Embodiment, the unit optical shape 251 has the top part 251t with a curved surface. However, the present invention is not limited to this, and the unit optical shape may be, for example, a partial shape of a substantially elliptical cylinder shape. Further, it may be a partial shape of a cylinder such as a semi-cylindrical shape, or may be a polygonal prism shape such as a triangular prism shape. Moreover, it is good also as a shape where the angle | corner which consists of two planes instead of a curved surface is formed.
Moreover, the cross-sectional shape of the unit optical shape may be a shape formed of a plurality of curved surfaces having different curvatures, or a shape formed by combining a flat surface and a curved surface.

(2) In each embodiment, the side surfaces 151 s and 251 s of the unit optical shapes 151 and 251 show an example in which the unevenness of the uneven shape increases as it becomes closer to the valley bottoms 152 and 252, and the surface roughness value increases. However, the present invention is not limited to this, and may have a certain uneven shape and surface roughness.

(3) In each embodiment, the example in which the optical sheets 15 and 25 are positioned closest to the emission side as the surface light source device 10 has been shown, but the present invention is not limited thereto, and the microlens sheet, the prism sheet, and other lens shapes are used. A lens sheet or a diffusing sheet formed by kneading a diffusing material or the like into a light-transmitting resin may be appropriately disposed on the incident side or the emitting side of the optical sheets 15 and 25.
Thus, when arranging a prism sheet, a lenticular lens sheet, etc., if the arrangement direction of the prism or the like is orthogonal to the arrangement direction of the unit lenses of the optical sheets 15 and 25, the effect of improving the viewing angle can be enhanced. it can. In addition, the second optical sheet having the same shape as the optical sheets 15 and 25 is arranged such that the arrangement direction of the unit optical shapes is perpendicular to the optical sheets 15 and 25, and the incident side and the outgoing side of the optical sheets 15 and 25. You may arrange in the side. As described above, other optical sheets to be combined with the optical sheets 15 and 25 may be freely selected as appropriate in accordance with desired optical characteristics and the like.

(4) In each embodiment, although the optical sheet 15 and 25 showed the example which does not contain a diffusing material, even if it shape | molds using resin which knead | mixed diffusing materials, such as not only this but a styrene bead. Alternatively, a multilayer structure in which layers having different refractive indexes of resins, presence or absence of a diffusing material, and the like are stacked may be used.

(5) In each embodiment, the unit optical shapes 151 and 251 have been illustrated as being arranged in the screen vertical direction of the display device 1 along the sheet surface. Alternatively, the arrangement direction may be appropriately selected according to the desired optical characteristics and the like.

(6) In each embodiment, the example in which the unit optical shapes 151 and 251 are arranged in one direction along the sheet surface is not limited to this. For example, the unit optical shapes 151 and 251 are, for example, substantially hemispherical shapes or substantially spheroidal spheres. It may have a part shape or a substantially quadrangular pyramid shape, and may be arranged in two directions (for example, a vertical direction and a horizontal direction) along the sheet surface.

(7) In each embodiment, although the example which uses the arc tube 13 which is a line light source as a light emission source which comprises the light source part of the surface light source device 10 was shown, it is not restricted to this, For example, LED (Light Emitting Diode) A point light source such as an organic EL (Electro Luminescence) or an inorganic EL may be used.

  In addition, although this embodiment and modification can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited to the embodiment described above.

DESCRIPTION OF SYMBOLS 1 Display apparatus 10 Surface light source device 11 LCD panel 12 Reflector plate 13 Light emission tube 14 Milky white board 15,25 Lens sheet 151,251 Unit optical shape

Claims (8)

A plurality of convex unit optical shapes are arranged on one surface, and an optical sheet used for a surface light source device so that light is incident on the other surface from a light source disposed on the other surface side,
Between the unit optical shapes adjacent in the arrangement direction of the unit optical shapes, a valley bottom having a predetermined width is provided,
At least the valley bottom is a rough surface having irregular and fine irregularities;
An optical sheet characterized by The optical sheet according to claim 1,
The unit optical shape is a rough surface having an irregular and fine irregular shape on the surface,
The uneven shape of the bottom of the valley is larger than the uneven shape of the unit optical shape,
An optical sheet characterized by In the optical sheet according to claim 1 or 2,
A value R1 obtained by dividing the arithmetic average roughness Ra of the concave-convex shape of the valley bottom portion of the unit optical shape by the arithmetic average roughness Ra of the concave-convex shape of the top portion,
Satisfy 1 <R1 <50,
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 3,
A value R2 obtained by dividing the maximum height Rz of the concave-convex shape at the bottom of the unit optical shape by the maximum height Rz of the concave-convex shape at the top is:
Satisfy 1 <R2 <50,
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 4,
The width d of the valley bottom in the arrangement direction of the unit optical shapes is relative to the lens width w of the unit optical shapes in the arrangement direction of the unit optical shapes.
0 <d / w ≦ 0.15
Satisfying the relationship
An optical sheet characterized by In the optical sheet according to any one of claims 1 to 5,
The unit optical shapes are arranged in one direction along the sheet surface;
An optical sheet characterized by The optical sheet according to any one of claims 1 to 6,
A light source that emits light;
A surface light source device comprising: A surface light source device according to claim 7;
A transmissive display unit illuminated from the back by the surface light source device;
A display device comprising: