JP2011099931A - Optical sheet, backlight unit, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet capable of striking a balance between excellent brightness and excellent shielding performance, and to provide a backlight unit using the optical sheet, and a display device. <P>SOLUTION: In this optical sheet 1 used for illumination optical path control, for controlling an optical path of light entering from a light source 15 and emitting the light, an optical shape for condensing or diffusing light is formed on a light emission surface, and the optical shape is constituted of a combination of an approximately hemispherical microlens and a prism, and surface-roughening processing is applied to the surface of the optical shape. Hereby, high brightness and high shielding performance can be exhibited. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention illuminates, from the back side, a liquid crystal panel in which a transmission / non-transmission lens sheet and a display optical sheet in pixel units or a display element in which a display pattern is defined according to a transparent state / scattering state is arranged. The present invention relates to a backlight unit and a display device.

In recent years, display devices using TFT-type liquid crystal panels and STN-type liquid crystal panels have been commercialized mainly in color notebook PCs (personal computers) in the OA field.
In such a display device, a so-called backlight system is employed in which a light source is arranged on the back side of the liquid crystal panel (the side opposite to the observer) and the liquid crystal panel is illuminated with light from the light source.

  The backlight units used in this type of backlight system can be broadly divided into multiple light sources such as cold cathode fluorescent lamps (CCFL) within a flat light guide plate made of acrylic resin with excellent light transmission. There are two types of methods: a “light guide plate light guide method” (so-called edge light method) and a “direct type method” that does not use a light guide plate.

As a display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 6 is generally known.
In this type of display device, a liquid crystal panel 72 having both front and back surfaces sandwiched between polarizing plates 71 and 73 is disposed at the top, and a substantially rectangular plate shape is formed on the lower surface side of the liquid crystal panel 72. A light guide plate 79 made of a transparent base material such as PMMA (polymethyl methacrylate) or acrylic is disposed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate 79. . Further, on the lower surface of the light guide plate 79, a scattering reflection pattern portion (not shown) is printed so that the light introduced into the light guide plate 79 is efficiently scattered and reflected toward the liquid crystal panel 72. And a reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion.

Further, the light guide plate 79 is provided with a light source lamp 76 at the side end, and further covers the back side of the light source lamp 76 so that the light from the light source lamp 76 is efficiently incident on the light guide plate 79. Thus, a high-reflectance lamp reflector 81 is provided. The scattering reflection pattern portion is formed by printing, drying, and forming a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern. The light incident on the light plate 79 is imparted with directivity and guided to the light exit surface side, which is a device for increasing the brightness.

  Further, recently, in order to improve the light utilization efficiency and increase the brightness, for example, as shown in FIG. 7, a prism film (prism) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 is used. It is proposed to provide layers 74, 75. The prism films 74 and 75 are used to collect light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

On the other hand, direct type backlights are used in display devices such as large liquid crystal TVs where it is difficult to use light guide plates.
A liquid crystal display device shown in FIG. 8 is generally known as a direct backlight type display device. In this liquid crystal display device, a liquid crystal panel 72 having both front and back surfaces sandwiched between polarizing plates 71 and 73 is disposed at the upper portion, and a light source 51 made of a fluorescent tube or the like is disposed on the lower surface side of the liquid crystal panel 72. Further, an optical sheet such as a diffusion film 82 is provided on the upper surface side of the light source 51. In addition, a reflector 52 that reflects light traveling from the light source 51 in the direction opposite to the liquid crystal panel 72 toward the liquid crystal panel 72 is disposed on the back surface of the light source 51. Therefore, the light emitted from the light source 51 is diffused by the diffusion film 82, and the diffused light is condensed on the effective display area of the liquid crystal panel 72 with high efficiency.

  However, in the display device shown in FIGS. 6 and 8, since the control of the viewing angle depends only on the diffusibility of the diffusing film 182, the control is difficult, the central portion in the front direction of the display is bright and goes to the peripheral portion. The phenomenon of darkening is inevitable. For this reason, there is a problem that the luminance is greatly lowered when the liquid crystal screen is viewed from the side, and the light use efficiency is lowered.

Further, in the display device using the prism films 74 and 75 illustrated in FIG. 7, two prism films 74 and 75 are required. The increase also caused the cost to rise.
Furthermore, in the prism films 74 and 75 excited in FIG. 8, if the distance between the light sources 51 is too wide, uneven brightness tends to occur on the screen. Therefore, the number of the light sources 51 cannot be reduced, and the increase in power consumption and cost. It was the cause that caused the increase.

  Here, in the display device as described above, light weight, low power consumption, high luminance, and thinning are strongly demanded as market needs, and accordingly, a backlight unit mounted on the display device is also included. Light weight, low power consumption, and high brightness are required.

In particular, in color display devices that have recently made remarkable progress, the panel transmittance of the liquid crystal panel is much lower than that of a monochrome-compatible liquid crystal panel. Therefore, it is possible to improve the brightness of the backlight unit installed in the liquid crystal panel. It is essential to obtain low power consumption of the display itself.
However, it is difficult to say that the above-described conventional backlight unit sufficiently satisfies the demand for high brightness and low power consumption, and the user has low price, high brightness, high display quality, and low power consumption. The development of a backlight unit capable of realizing a power liquid crystal display device is awaited.

In addition, there is an example as shown in Patent Document 1 as an attempt to impart other functions in addition to the optical function to the optical sheet, but it is limited to the case where the optical sheet is wound into a roll shape, and various processes are performed. It cannot be applied to.
On the other hand, for the purpose of improving the performance of the optical sheet, there are proposals for various optical shapes as shown in the following patent document besides the conventionally used prisms, lenticular lenses, microlenses, and polygonal pyramids. The shape is thought to increase.

JP 2008-203776 A Special table 2008-515026 gazette JP 2007-3571 A JP 2007-304565 A JP 2008-102497 A

  By the way, in the optical sheet used for the backlight unit of the display device, the optical performance greatly affects the appearance of the display device, that is, the commercial value. In general, high brightness is desired, but diffusion performance is also required to hide minute defects and to eliminate the shadow of the light source. However, since this diffusion performance also causes a decrease in luminance, it is very difficult to achieve both.

  The present invention has been made in view of such problems, and provides an optical sheet capable of achieving both good luminance and concealment performance, and a backlight unit and a display device using the optical sheet. Objective.

In order to solve the above problems, the present invention proposes the following means.
In other words, the optical sheet according to the present invention is an optical sheet used for illumination light path control that emits light by controlling the light path of light incident from a light source, and is an optical sheet that collects or diffuses light on a light exit surface. The optical shape is a combination of a substantially hemispherical microlens and a cylindrical lens or a prism, and the surface of the optical shape is roughened.

  According to such a configuration, since the optical shape is a combination of a microlens and a cylindrical lens or a prism, it is possible to have both a condensing and diffusing function with a single lens. Further, since the surface of the optical shape is roughened, it is possible to improve the concealment performance of defects and light source shadows. Further, when the cylindrical lens sheet or the prism sheet is subjected to a roughening process, the brightness is significantly reduced. However, in the present invention, the optical sheet has a microlens that is unlikely to cause a brightness decrease due to the roughening process. As a whole, both good luminance and concealment performance can be achieved.

In the optical sheet according to the present invention, the height difference of the unevenness formed by the roughening treatment is set in a range of 0.01 μm to 5 μm.
Thereby, it is possible to realize an optical sheet with improved concealment performance while minimizing luminance reduction.

The optical sheet according to the present invention is characterized in that the roughening treatment is applied to a top portion of the microlens and a trough portion of the optical shape.
Thus, k that achieves high luminance and high diffusion can be achieved by balancing luminance and concealment performance.

  In the optical sheet according to the present invention, it is preferable that a light incident surface of the optical sheet has a substantially flat surface shape.

In the optical sheet according to the present invention, the light incident surface is preferably subjected to a roughening treatment.
Thereby, light can be diffused on the light incident surface, and the concealment performance can be improved.

In the optical sheet according to the present invention, the ten-point average roughness Rz of the light incident surface subjected to the roughening treatment in the previous period is set within a range of 0.1 μm to 5 μm.
As a result, the light diffusion effect by the incident surface can be imparted within a range balanced with the light luminance.

The optical sheet according to the present invention is characterized in that a protrusion shape is formed on the light incident surface.
Thereby, the scratch resistance on the light incident surface side of the optical sheet can be improved.

In the optical sheet according to the present invention, the height of the protrusion shape is set in a range of 10 μm to 100 μm from the light incident surface.
Thereby, the scratch resistance on the light incident surface can be surely exhibited.

The backlight unit according to the present invention includes any one of the optical sheets described above and the light source that irradiates the optical sheet with light.
According to such a backlight unit, since the optical sheet is used, both high luminance and high concealment performance can be achieved.

A display device according to the present invention includes the backlight unit, and an image display unit that defines a display image according to transmission / shielding in pixel units and displays an image by light irradiation from the backlight unit. It is characterized by that.
According to such a display device, since the backlight unit is provided, it is possible to provide an image that achieves both high luminance and high concealment performance.

  According to the optical sheet, the backlight unit, and the display device according to the present invention, a roughening process is performed on an optical shape that is a combination of a microlens and a cylindrical lens or a prism, thereby achieving both good luminance and concealment performance. be able to. Therefore, it is possible to emit good outgoing light that achieves both high luminance and diffusion performance.

It is a longitudinal cross-sectional view of the display apparatus which concerns on embodiment. 2A is a perspective view of an optical sheet, and FIG. (A) is A-A 'sectional drawing of FIG.2 (b), (b) is B-B' sectional drawing of FIG.2 (b). It is a longitudinal cross-sectional view explaining the light-incidence surface of an optical sheet. It is a longitudinal cross-sectional view which shows the other structure of the display apparatus which concerns on embodiment. It is a longitudinal cross-sectional view which shows an example of the display apparatus of an edge light system. It is a longitudinal cross-sectional view which shows an example of the display apparatus of an edge light system provided with the prism film. It is a longitudinal cross-sectional view which shows an example of a direct type backlight type display apparatus. It is a figure explaining the roughening shape of a micro lens and a prism.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a longitudinal sectional view of the display device of this embodiment. In FIG. 1, the reduced scale of each component does not match the actual one.

  As shown in FIG. 1, the display device 27 according to the embodiment of the present invention is configured by providing a display unit (screen display unit) 20 on a backlight unit 13 that irradiates light to an observer side. The liquid crystal display device is configured to display a planar image by emitting display light S whose display is controlled by an image signal from the display unit 20 toward the viewer. In the following, the upper direction in FIG. 1 is referred to as the observer side or the front side, and the lower direction is referred to as the back side.

The display unit 20 includes two polarizing plates (polarizing films) 21 and 21 and a liquid crystal panel 19 sandwiched therebetween. The liquid crystal panel 19 is configured, for example, by filling a liquid crystal layer between two glass substrates.
The light L emitted from the backlight unit 13 is incident on the liquid crystal panel 19 through the polarizing plate 19 on the back side, and is emitted to the viewer side through the polarizing plate 21 on the viewer side.

  The display unit 20 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 optical sheet 1 improves the luminance toward the viewer side and reduces the viewing angle dependency of the light intensity. It is possible to display an image with high image quality by effectively using the light with reduced image quality.

  The display unit 20 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.

  Although the display device 27 is a liquid crystal display device including the display unit 20 as described above, as long as it includes at least the backlight unit 13, a projection screen device, a plasma display, an EL display, etc. The type of the image display unit that displays an image using the light from the backlight unit 13 as display light is not limited.

  The backlight unit 13 includes an illumination optical path control optical sheet 1, a reflective polarization separation sheet 2, a diffusion sheet 3, and a light source unit 4 that are arranged facing the light incident side of the display unit 20. The light source unit 4, the diffusion sheet 3, the optical sheet 1, and the reflective polarization separation sheet 2 are laminated in order.

  The light source unit 4 emits light toward the front side, and an edge light system is adopted in this embodiment. The light source section 4 includes a light guide plate 5 having a flat plate shape formed from a transparent material, and a pair of light sources 15 and 15 disposed on the sides of the light guide plate 5. Thereby, the light emitted from the light sources 15 and 15 is repeatedly reflected in the light guide plate 5 and emitted as parallel light toward the front direction.

  The diffusion sheet 3 is a substantially plate-like member formed by dispersing a light diffusion region in a transparent resin, and imparts a diffusion effect to the light from the light source unit 4 and emits it to the front side. .

Hereinafter, the configuration of the optical sheet 1 of the present embodiment will be described with reference to FIG. 2A is a perspective view of the optical sheet 1, and FIG. 2B is a partially enlarged view of FIG. 2A.
As shown in FIG. 2A, the optical sheet 1 has a sheet shape, and the shape in plan view is adjusted in size and shape so as to be incorporated into a predetermined backlight.

  As shown in FIG. 2B, the light emission surface of the optical sheet 1 has an optical shape formed by combining a substantially hemispherical microlens 32 and a prism 33. That is, the microlenses 32 are discretely arranged in the arrangement of the prisms 33. In addition, the optical sheet 1 includes a base material 31 having a predetermined thickness. The surface on the viewer side of the base material 31 is a light emitting surface on which the surface formation is configured, and the opposite surface is the surface. The light incident surface 31a is used. In addition, the base material 31, the microlens 32, and the prism 33 may be comprised with a different material, and may be comprised integrally with the same material.

  The optical sheet 1 may include a cylindrical lens instead of the prism 33. Hereinafter, only the case where the prism 33 is provided will be described. However, even if the cylindrical lens is provided, the same effects as those provided when the prism 33 is provided are produced.

  The diameter of the microlens 32 is preferably set in the range of 10 μm to 200 μm. This is because if the diameter is smaller than 10 μm, the manufacture becomes difficult, and if it is larger than 200 μm, the microlens 32 itself is visually recognized as a point defect. The arrangement of the microlenses 32 may be regular or irregular.

  It is preferable that the pitch of the prisms 33 is set in a range of 10 μm to 200 μm. This is because if the pitch is smaller than 10 μm, the diffraction of incident light increases and the luminance is lowered, and if it is larger than 200 μm, the prism 33 interferes with the liquid crystal panel and moire occurs. The apex angle θ of the prism 33 is preferably set in the range of 60 ° to 150 °. If it is less than 60 °, the production is difficult, and if it is more than 150 °, the luminance cannot be obtained.

  In the present embodiment, the optical shape of the optical sheet 1 is subjected to a roughening process. This roughening treatment may be performed on the entire optical shape or may be performed partially.

  FIG. 3A shows a cross-sectional view taken along the line A-A ′ of FIG. As an example of the partial roughening process performed on the optical shape of the optical sheet 1, a roughening process is performed on the top of the microlens 32 and the valleys (optical valleys) of the microlens 32 and the prism 33. The aspect by which it roughens and the roughened part 34 is formed is mentioned. Although details will be described later, this method is highly effective in preventing luminance reduction and obtaining concealment performance.

  FIG. 3B shows a B-B ′ cross-sectional view of FIG. FIG. 3B shows a cross section of the valley portion of the prism 33. The roughness of the rough surface formed by the roughening treatment is usually measured and numerically measured by a predetermined method such as Ra, Rz, etc. In the normal method, the height of the microlens 32 and the prism 33 is also determined. It will be perceived as roughness.

  Therefore, the meaning of the roughness of the roughening process of the present embodiment will be described in detail. The roughness of the roughening process in the present embodiment is a roughening process compared to the optical shape before the roughening process. It means how uneven the later shape is. However, in the case of this definition, it becomes very difficult to understand how much the roughness of the partial roughening of the microlens 32 is. Therefore, it is easy to measure the roughness at the valley of the prism 33, the ridgeline of the mountain, and the flat part.

  An example will be described with reference to FIG. 3B. The roughness Δh of the unevenness height of the valleys of the prism 33 is defined as the roughness of the optical sheet. In the present embodiment, it is preferable that Δh is set in the range of 0.01 μm to 5 μm. If it is smaller than 0.01 μm, the concealment performance is not observed at all, and if it is larger than 5 μm, the luminance is lowered.

  Here, the roughening of the microlens 32 and the prism 33 will be described in more detail. As shown in FIG. 9A, the roughened shape of the microlens 32 has a shape in which a part of the spherical surface is gently continuous. As an index of the gentleness, there is an unevenness that is 1/10 or less of the height of the microlens 32 and the spherical shape of the microlens 32 before the roughening is maintained. On the other hand, the roughened shape of the valley of the prism 33 has a shape in which the corners of the valley are crushed as shown in FIG. The width of the collapsed valley portion is preferably 1 mm or more.

  A case where such microlenses 32 and prisms 33 are mixed on the same surface will be described with reference to FIG. First, the incident light is strongly diffused in the prism 33 valley. Next, the diffused light is incident on the microlens 33 located higher than the valley of the prism 33, and the light distribution is adjusted by the gentle diffusion and condensing function of the microlens 32. That is, light diffusion (mixing) and light collection are effectively performed, and both excellent concealability and luminance can be achieved. In addition, the light diffused to the incident surface side in FIG. 9C is reflected by the incident surface, other members, a lamp house, etc., and is reused as incident light again.

4A to 4D are sectional views showing the shape of the light incident surface 31 a of the optical sheet 1. In each drawing of FIG. 5, the roughening of the optical shape is omitted in the drawing.
FIG. 4A shows a case where the light incident surface 31a is substantially flat. FIG. 4C shows a case where the light incident surface 31a has a protrusion 35. The protrusions 35 are provided for the purpose of preventing scratches, and the shapes thereof include various shapes such as a substantially hemispherical shape and a trapezoidal shape. It is desirable that the height of the protrusion 35 is set in the range of 10 μm to 100 μm. If the thickness is smaller than 10 μm, the effect of preventing scratches is hardly obtained, and if it is larger than 100 μm, the optical sheet is bent, which is not preferable. Further, it is desirable that the maximum diameter of the protrusion 35 is set in a range of 10 μm to 300 μm. This is because if it is smaller than 10 μm, production becomes difficult, and if it is larger than 300 μm, it is visually recognized as a point defect. However, since the light incident surface is less visible than the optical shape of the light exit surface, a shape larger than the optical shape can be selected.

  4B and 4D show a case where the light incident surface 31a is roughened. Since the light incident surface 31a is basically formed in a flat surface shape, if this portion is measured, it can be expressed with normal roughness. The roughness is preferably set in the range of Rz 0.1 μm to 10 μm. If it is smaller than 0.1 μm, the concealing performance is not exhibited, and if it is larger than 10 μm, the luminance is remarkably lowered. Further, when a roughness larger than 10 μm is required, it is preferable to provide a protrusion partially.

  Examples of the main material of the optical sheet 1 include polycarbonate, acrylic-styrene copolymer, polystyrene, styrene / butadiene / acrylonitrile copolymer, and cycloolefin polymer. Further, transparent particles may be dispersed in the main material. In this case, it is desirable that the refractive index of the main material and the refractive index of the transparent particles are different, and the difference between the refractive index of the main material and the refractive index of the transparent particles is 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, it is sufficient that the difference in refractive index is 0.5 or less. Furthermore, the average particle size of the transparent particles is desirably 0.5 to 30.0 μm.

  As the transparent particles, transparent particles made of an inorganic oxide or transparent particles made of a resin can be used. For example, examples of the transparent particles made of an inorganic oxide include particles made of silica, alumina or the like. The transparent particles made of resin include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof; melamine-formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetra Examples thereof include fluorine-containing polymer particles such as fluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), and silicone resin particles. These transparent particles may be used as a mixture of two or more. Alternatively, the plate-like member has a structure in which a main material has a fine cavity containing air, and diffusion performance may be obtained by a difference in refractive index between the main material and air.

In the optical sheet 1, the substrate 31 may have a single layer structure or a multilayer structure, and may include a transparent layer.
Moreover, the optical sheet 1 can be manufactured by an extrusion method, a casting method, an injection method, etc., and the thickness can be 12 micrometers-1 mm. If the thickness is less than 12 μm, the rigidity that can withstand the processing is insufficient, and if it exceeds 1 mm, the flexibility that can withstand the processing is insufficient.

  In addition to the above method, the optical sheet 1 may be manufactured by a UV curing method. When prepared by the UV curing method, a UV curable resin is applied on the substrate, a mold having a desired shape is pressed, and UV irradiation is performed to obtain an optical layer. As the base material 31, a film of PET (polyethylene terephthalate), polycarbonate, acrylic, polypropylene, or the like well known in the art can be used.

  The reflective polarization separating sheet 2 has a configuration in which, for example, a polarizing layer and two or more optical layers are laminated, and a commercially available one can be used as appropriate.

Next, operations of the backlight unit 13 and the display device 27 including the optical sheet 1 having the above-described configuration will be described.
The light emitted from the light source 15 of the light source unit 4 passes through the light guide plate 5 and proceeds to the front side, and then enters the diffusion plate sheet 3. Then, after the light scattering effect is given by the diffusion sheet 3 and sufficiently diffused, the light is emitted to the front side. The light that has passed through the diffusion sheet 3 sheet passes through the optical sheet 1 and the reflective polarization separation sheet 2, and further passes through the display unit 20, so that it is visually recognized by the observer as an image display.

According to the optical sheet 1 described above, since the optical shape is a combination of the microlens 32 and the prism 33, a single sheet can have both the functions of condensing and diffusing. Further, since the surface of the optical shape is roughened, it is possible to improve the concealment performance of defects and light source shadows.
Further, for example, when the surface of the prism sheet is roughened, the luminance is significantly reduced. However, in the present embodiment, the optical sheet 1 has the microlens 32 that is less likely to be reduced in luminance due to the roughening. As a whole, both good luminance and concealment performance can be achieved.
Such a function and effect is the same even when a cylindrical lens is employed instead of the prism 33.

  In addition, since the backlight unit 13 and the display device 27 of the present embodiment use the optical sheet 1 having the above-described configuration, it is possible to realize emitted light and image display that achieve both good luminance and concealment performance.

As described above, the embodiment in the present embodiment has been described in detail. However, without departing from the technical idea of the present embodiment, the present invention is not limited thereto, and some design changes and the like are possible.
For example, a display device 28 as shown in FIG. 5 may be used as a modification. The display device 28 is different from the embodiment in the configuration of the backlight unit 14.

  That is, the backlight unit 14 includes a light source unit 4 including a plurality of light sources 15 arranged in parallel to the emission surface and a lamp house 17 that surrounds the back side and the side of the light sources 15. The diffusion sheet 3 and the optical sheet 1 are laminated on the front side of the light source unit 4. Also in this modified example, since the optical sheet 1 is used as in the embodiment, it is possible to realize emitted light and image display that achieve both good luminance and concealment performance.

(Optical sheet manufacturing method)
First, hemispherical microlenses that have been subjected to various roughening treatments and a die roll having a reverse shape of a prism, a mold roll having a reverse shape of the protrusion, and a reverse shape of the protrusion are not present A mold roll was prepared.
These mold rolls are placed close to the extruder, the thermoplastic polycarbonate resin sheet is melted and molded by the extruder, and the molded product is molded by the mold roll that is cooled and cured, so that the optical shape is formed on the surface. An optical sheet was obtained. The optical sheet had a thickness of 320 μm, and M1201 from Teijin Chemicals Ltd. was used as the thermoplastic polycarbonate.
For comparison, a prism sheet and a microlens sheet having an apex angle of 90 ° with or without a roughening treatment were prepared in the same manner.
These prepared sheets were cut into 730 mm × 310 mm squares and used for evaluation.

(Measurement of brightness of optical sheet and evaluation of concealment)
The obtained optical sheet 1 was incorporated into a display, a white screen was displayed, and the center luminance was measured from a distance of 50 cm in the normal direction of the screen with SR-3A manufactured by Topcon. The configuration of the backlight unit was one using a Teijin Chemicals diffusion plate 65HLW and an optical sheet.
The hiding property was evaluated by evaluating the hiding property of the light source using a direct type backlight. The optical sheet was incorporated into the display with the same configuration as the luminance measurement, and a white screen was displayed for visual observation. Since this visual evaluation has individual differences, it was performed by three or more subjects.

  The results are shown in Table 1. In Table 1, (mountains) and (valleys) indicate roughened portions of the optical prism. The rough surface of the optical shape was also applied to the top of the microlens.

From Table 1, no. 0-No. 6 is compared, it can be seen that both the brightness and the hiding property are good when the surface roughness is from 0.01 μm to 5 μm. No. For 6, the luminance is below 0.95.
Furthermore, no. 2 and No. 7 shows that both the luminance and the concealment are good, but it is understood that the luminance reduction is suppressed when the roughened portion is arranged in the valley rather than the peak of the prism.
No. 2 and no. 8-No. In comparison of 10, the luminance and concealment were good regardless of the shape of the back surface (light incident surface).
Furthermore, no. 11 and no. 12, it was found that the prism sheet had high brightness but the concealability was poor, and the brightness was significantly lowered by roughening. On the other hand, it was found that the brightness of the microlens sheet was low regardless of whether or not the surface was roughened.
In the examples, for the simplest comparison, the backlight is configured using a Teijin Chemicals diffusion plate 65HLW and an optical sheet. However, the optical sheet of the present embodiment is combined with other optical sheets. Even if it is used, its performance is not impaired.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Reflection type polarization separation sheet 3 Diffusion sheet 4 Light source part 5 Light guide plate 15 Light source 20 Display part (image display part)
32 Micro lens 33 Prism 34 Roughened portion 35 Projection

Claims (10)

An optical sheet used for illumination optical path control for controlling and emitting an optical path of light incident from a light source,
The light exit surface has an optical shape for condensing or diffusing light,
The optical shape consists of a combination of a substantially hemispherical microlens and a cylindrical lens or prism,
An optical sheet, wherein the surface of the optical shape is roughened.   2. The optical sheet according to claim 1, wherein the unevenness formed by the roughening treatment is set in a range of 0.01 μm to 5 μm.   The optical sheet according to claim 1, wherein the roughening treatment is performed on a top portion of the microlens and a trough portion of the optical shape.   4. The optical sheet according to claim 1, wherein a light incident surface of the optical sheet has a substantially flat surface shape. 5.   The optical sheet according to any one of claims 1 to 4, wherein the light incident surface is subjected to a roughening treatment.   The optical sheet according to claim 5, wherein a ten-point average roughness Rz of the light incident surface that has been subjected to the roughening treatment in the previous period is set in a range of 0.1 μm to 5 μm.   The optical sheet according to claim 4, wherein a protrusion shape is formed on the light incident surface.   The optical sheet according to claim 7, wherein the height of the protrusion shape is set in a range of 10 μm to 100 μm from the light incident surface. The optical sheet according to any one of claims 1 to 8,
A backlight unit comprising the light source for irradiating the optical sheet with light. The backlight unit according to claim 9,
A display device comprising: an image display unit that defines a display image in accordance with transmission / shading in pixel units and displays an image by light irradiation from the backlight unit.

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