JP5640366B2 - Optical sheet, backlight unit and display device - Google Patents

Description

  The present invention relates to a backlight unit that illuminates from the back side a liquid crystal panel in which an image display element that displays an image by controlling transmission / non-transmission of light or a transparent state / scattering state in units of pixels, The present invention relates to a display device and a display optical sheet used therefor.

  In recent years, display devices using TFT-type liquid crystal panels and STN-type liquid crystal panels have been commercialized mainly for color notebook PCs (personal computers) in the OA field.

  Such a display device employs a so-called backlight method in which a light source is disposed on the back side (opposite to the observer) of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source.

  As a backlight unit employed in this type of backlight system, a light source lamp such as a cold cathode fluorescent lamp (CCFT) is roughly divided into a flat light guide plate made of acrylic resin having excellent light transmittance. There are a “light guide plate light guide method” for reflecting (a 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. 8 is generally known.

  This is provided with a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 at the top, and a light guide plate 79 made of a transparent base material such as a substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic on the lower surface side. Is installed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate.

  Further, on the lower surface of the light guide plate 79, a scattering reflection pattern portion for efficiently scattering and reflecting the light introduced into the light guide plate 79 in the direction of the liquid crystal panel 72 is provided by printing or the like ( 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 can be 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.

  Furthermore, recently, in order to improve the light utilization efficiency and increase the brightness, as shown in FIG. 9, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 is used. ) 74 and 75 are proposed. The prism films 74 and 75 are configured 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.

However, in the apparatus illustrated in FIG. 8, the control of the viewing angle is left only to the diffusibility of the diffusion film 78, which is difficult to control, and the center in the front direction of the display is bright and becomes darker toward the periphery. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.
Furthermore, in the apparatus using the prism film illustrated in FIG. 9, two prism films are required, which not only greatly reduces the amount of light due to the absorption of the film but also increases the cost due to the increase in the number of members. It was also.

  On the other hand, in the direct type, a display device such as a large liquid crystal TV in which the light guide plate is difficult to use is used.

  As a direct type display device, a device illustrated in FIG. 10 is generally known. In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and is emitted from a light source 51 made of a fluorescent tube or the like on the lower surface side thereof and diffused by an optical sheet such as a diffusion film 82. The light is condensed on the effective display area of the liquid crystal panel 72 with high efficiency. In order to efficiently use the light from the light source 51 as illumination light, a reflector 52 is disposed on the back surface of the light source 51.

  However, even in the apparatus illustrated in FIG. 10, the control of the viewing angle is left only to the diffusibility of the diffusion film 82, and the control is difficult. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced. Furthermore, in the case of using a prism film, since the number of prism films is two, not only the light amount is greatly decreased due to absorption of the film but also the cost is increased due to an increase in the number of members.

  If the distance between the light sources 51 is too wide, uneven brightness tends to occur on the screen, and the number of light sources 51 cannot be reduced, leading to an increase in power consumption and an increase in cost.

  By the way, in such a liquid crystal display device, light weight, low power consumption, high luminance, and thinning are strongly demanded as market needs, and accordingly, a backlight unit mounted on the liquid crystal display device is also light. In addition, low power consumption and high brightness are required.

  In particular, in a color liquid crystal display device that has recently made remarkable progress, the panel transmittance of the liquid crystal panel is remarkably lower than that of a monochrome-compatible liquid crystal panel. It is essential to obtain power consumption.

  However, as described above, it is difficult to say that the conventional apparatus sufficiently satisfies the demand for high luminance and low power consumption, and the user has low price, high luminance, high display quality, and low power consumption. The development of a backlight unit capable of realizing a power liquid crystal display device is awaited.

  As an attempt to give other functions in addition to optical functions to the optical sheet, there is an example as shown in Patent Document 1, but it is limited to a case where it is wound in a roll shape, and can be applied to various processes. It is not possible.

  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.

JP2008-203776 JP2007-3571 JP2007-304565A JP2008-102497

The optical sheet used for the backlight unit of the display has a great influence on the appearance of the display, that is, the commercial value, depending on the optical performance. In general, high brightness is desired, but diffusion performance is also required to hide minute defects or to eliminate the shadow of the light source. Since the diffusion performance also causes a decrease in luminance, it is very difficult to manufacture an optical sheet that achieves both good luminance performance and good diffusion performance.
Accordingly, an object of the present invention is to provide an optical sheet free from unevenness defects that can achieve both good luminance performance and diffusion performance.

In order to solve the above-described problems, the present invention provides an optical sheet that collects and / or diffuses incident light, and transmits light that is transmitted through and emitted from a planar plate-like substrate having translucency. the exit surface, and a plurality of micro lenses convex hemispherical shape, and a plurality of ridges shape extending in one direction formed while projected, the height of the aspect to diameter of the light exit plane of the microlens the ratio is 50%, in the range ratio of surface on which the microlenses are formed for the light exit plane entire surface of 40% to 60% in a plan view, the ridge shape prism shape or It is a lenticular lens shape, the heights of the plurality of microlenses are constant, the heights of the plurality of ridge shapes vary with a swing width, and a plurality of heights based on the light emitting surface The ridge shape of The value obtained by dividing the nominal height, which is the height to the center of the fluctuation width, by the height of the microlens is in the range of 10% or more and 90% or less, and is based on the light exit surface The height fluctuation width of the plurality of ridge shapes is within a range of ± 20% or more and ± 40% or less of the nominal height, and the flat portion on the back surface of the light emitting surface is roughened. The surface roughness is in the range of 0.5 μm to 1.5 μm.

  In the present invention, the optical sheet has a surface shape composed of a combination of a substantially hemispherical microlens and a ridge shape, and has a function of condensing and diffusing by one sheet. Furthermore, since the actual height of the ridge shape varies with a width relative to the nominal height, the height of the boundary between the microlens and the ridge shape is not constant. Thereby, when the microlens and the ridge shape are simply combined, it is possible to suppress the mura defect that occurs at the boundary between the two. With the above points as the excellent points of the present invention, it is possible to provide an optical sheet free from uneven defects, which has both good luminance performance and diffusion performance.

Explanatory drawing which shows the cross section of the example of a display apparatus structure using the optical sheet of this invention. Explanatory drawing which shows the cross section of the example of a display apparatus structure using the optical sheet of this invention. The figure which shows partial expansion of the optical sheet of this invention, and an optical sheet. (A) The figure which shows the A-A 'cross section of FIG. 3, (b) The figure which shows the B-B' cross section. Explanatory drawing which shows the roughening of the lower surface of the optical sheet of this invention. The top view which shows the generation | occurrence | production location of a nonuniformity defect. Explanatory drawing which shows other embodiment of the optical sheet of this invention. Explanatory drawing which shows the example of a display apparatus structure by a prior art. Explanatory drawing which shows the example of a display apparatus structure by a prior art. Explanatory drawing which shows the example of a display apparatus structure by a prior art.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a cross section of a configuration example of a display device using the optical sheet of the present invention. Hereinafter, the upper side in FIGS. 1 and 2 is referred to as the upper side, the lower side is referred to as the lower side, the surface facing the upper side is represented as the front surface, and the surface facing the lower side is represented as the back surface. FIG. 1 shows a configuration example of a display device 22 including an edge light type backlight unit 21. Light K from the light source 15 enters the light guide plate 5. Thereafter, the diffusion sheet 3, the optical sheet 1 of the present invention, and the reflective polarization separation sheet 2 are transmitted from the exit surface of the light guide plate 5. Finally, light is emitted as L from the exit surface of the reflective polarization separation sheet 2. L reaches the liquid crystal panel 19 sandwiched between the polarizing plates 20. The light transmitted through it is emitted to S and is visually recognized by an observer. In addition, you may increase / decrease an optical sheet suitably not only what was mention | raise | lifted to the structural example.
FIG. 2 shows a configuration example of the display device 24 including the direct type backlight unit 23. Light K from the light source 15 enters the diffusion plate 6. Thereafter, the light reaches the optical sheet 1 of the present invention from the exit surface of the diffusion plate 6, and finally light is emitted as L from the exit surface of the optical sheet 1. L reaches the liquid crystal panel 19 sandwiched between the polarizing plates 20. The liquid crystal panel 19 displays an image by controlling transmission / non-transmission of light in pixel units. The light transmitted through the liquid crystal panel 19 is emitted to S and is visually recognized by an observer. In addition, you may increase / decrease an optical sheet suitably not only what was mention | raise | lifted to the structural example.

3A and 3B are views showing the optical sheet of the present invention and partial enlargement of the optical sheet. As shown in FIG. 3B, the optical sheet 1 is adjusted in size and shape so that it can be incorporated into a predetermined backlight unit. When a part of one side of the optical sheet 1 is enlarged, as shown in FIG. 3A, a substantially hemispherical microlens 32 (hereinafter referred to as a microlens 32) and a convex shape 33 (in the figure, a prism is formed). Are).
The convex shape is a cylindrical lens or a prism, or a combination of these, and is formed by arranging convex shapes extending in one direction in a substantially semicircular or substantially triangular shape in parallel with each other.
The optical sheet 1 has a thickness, and the thickness portion is shown as a base material 31 in the figure. That is, the substrate when the microlens 32 and the ridge shape 33 are absent is referred to as a base material 31. A surface on which incident light is incident on the substrate 31 is referred to as a light incident surface 31a, and a surface exiting from the substrate is referred to as a light emitting surface 31b. These show the base material, the light incident surface, and the light emitting surface in the claims.
The base material 31, the micro lens 32, and the ridge shape 33 that constitute the optical sheet 1 may be made of different materials, or may be made of the same material.

  The diameter of the microlens 32 is preferably 10 μm to 200 μm. If it is smaller than 10 μm, it is difficult to manufacture, and if it is larger than 200 μm, the microlens 32 itself looks like a point defect. The arrangement of the microlenses 32 may be regular or irregular. Also, the aspect ratio of the height to the diameter on the exit surface is set to 40% or more and 70% or less. If the aspect ratio is small, luminance cannot be obtained, and even if the aspect ratio is high, luminance cannot be obtained. The ratio of the microlens 32 to the exit surface is preferably 35% to 60% in plan view. If it is less than 35%, the emitted light distribution of the microlens 32 is mixed with the emitted light distribution of the ridge shape 33, and the effect on appearance is lost. If it exceeds 60%, the luminance decreases.

The ridge shape 33 is preferably a shape in which the ridge shapes extending in one direction are parallel to each other and the interval between adjacent ridge shapes is 10 μm to 200 μm. If the thickness is smaller than 10 μm, the diffraction of incident light increases, resulting in a decrease in luminance. If the thickness is larger than 200 μm, the ridge shape 33 interferes with the liquid crystal panel, and moire occurs.
The height of the ridge shape 33 is not constant, and fluctuates in the range of 8% to 108% with respect to the height of the microlens 32. That is, the ridge line of the ridge shape is not curved in the arrangement direction (AA ′ direction in FIG. 4) orthogonal to the extending direction of the ridge, but is a curve that sways only in the height direction. .
4 shows an AA ′ section (a) and a BB ′ section (b) in FIG. The figure shows how the height of the prism changes. When the height of the microlens 32 is h, the fluctuation range Δh of the prism height is 0.8 h or less.
In the case of a prism having a triangular cross section, the apex angle θ is preferably 70 ° to 110 °. If it is less than 70 °, the production is difficult, and if it is more than 110 °, luminance cannot be obtained.

  FIG. 6 is a top view showing a location where a mura defect occurs. When the height of the ridge shape 33 is constant, a portion 36 where the top of the ridge shape 33 shown in FIG. This is because the emission light comes out as stray light by connecting the top of the ridge shape and the slope of the microlens. Since the distribution of bright spots is recognized as a nonuniformity defect on the screen, it cannot be used as an optical sheet having high performance simply by combining the ridge shape 33 and the microlens 32. Although it may be possible to precisely adjust the positions of the ridge shape 33 and the microlens 32 in order not to generate a bright spot, it is very difficult and impractical. On the other hand, when the height of the ridge shape is not constant as in the present invention, no bright spot is generated at the boundary with the microlens 32. However, when the height of the microlens 32 exceeds the range of 8% to 108%, the diffused light component increases and the luminance decreases.

FIG. 5 is a sectional view showing the shape of the back surface of the optical sheet 1. The surface is omitted in the figure. Fig.5 (a) shows the case where a back surface is a substantially plane. (C) shows the case where the back surface has a protrusion. The protrusions are provided for the purpose of preventing scratches, and the shapes thereof include a substantially hemispherical shape and a trapezoidal shape. The height is desirably 10 μm or more and 100 μm or less. If it is smaller than 10 μm, the effect of preventing scratches is hardly obtained, and if it is larger than 100 μm, the optical sheet bends.
The maximum shape diameter is desirably 10 μm or more and 300 μm or less. If it is smaller than 10 μm, the production is difficult, and if it is larger than 300 μm, it appears as a point defect. However, since the back surface is less visible than the front surface, a larger shape than the front surface can be selected.

  FIGS. 5B and 5D show the case where the back surface is roughened. Since the back surface is basically composed of a flat part, if this part is measured, it can be expressed by normal roughness. The roughness is preferably Rz 0.1 μm to 1.5 μm. If it is smaller than 0.1 μm, the point defect concealment performance is not exhibited, and if it is larger than 1.5 μm, the luminance is remarkably lowered. When a roughness larger than 1.5 μm is required, it is preferable that the entire roughening is limited to Rz 1.5 μm and a projection is partially provided.

  As the main material of the optical sheet 1, for example, polycarbonate, acrylic-styrene copolymer, polystyrene, styrene-butadiene-acrylonitrile copolymer, or cycloolefin polymer may be used. Further, transparent particles dispersed in the main material may be provided, and the refractive index of these main materials and the refractive index of the transparent particles are different. The difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, the refractive index difference is 0.5 or less. The transparent particles preferably have an average particle size of 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 crosslinked 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 particular, the substrate 31 of the optical sheet 1 may have a single layer structure or a multilayer structure, and may include a transparent layer.

  The optical sheet is manufactured by an extrusion method, a casting method, or an injection method, and those having a thickness of 12 μm or more and 1 mm or less can be used. If the thickness is less than 12 μm, there is no rigidity that can withstand the processing, and if it exceeds 1 mm, there is no flexibility that can withstand the processing.

Alternatively, the optical sheet may be manufactured by a UV curing method.
When prepared by the UV curing method, a UV curable resin is applied on a substrate, a mold having a desired shape is pressed, and UV irradiation is performed to obtain an optical layer. As the substrate, PET (polyethylene terephthalate), polycarbonate, acrylic, polypropylene films, etc. well known in the art can be used.

  The diffusion plate and the light guide plate can be made of the same main material as that of the optical sheet, and may be configured to include the transparent particles described above. The refractive index of these main materials and the refractive index of transparent particles need to be different. The difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. The difference in refractive index is preferably 0.5 or less. This is because if it is higher than 0.5, the light collecting function of the optical sheet may be reduced by unexpected stray light. In addition, since the light incident on the optical layer needs to be transmitted while being scattered, the average particle size of the transparent particles is preferably 0.5 to 30.0 μm. Alternatively, the main material may have a structure having fine cavities containing air, and the diffusion performance may be obtained by the difference in refractive index between the main material and air. Further, a reflection pattern or a geometric structure may be provided on the surface.

FIG. 7 is a diagram illustrating another embodiment of the optical sheet according to the present invention.
Unlike the optical sheets shown in FIGS. 3 and 4, the effect of the present invention is exhibited even when the height of the microlens 32 is around the height of the ridge shape 33 as shown in FIG. 7.
In addition, if there exists a part with the height of the microlens 32 more than the height of the protruding item | line shape 33, the adhesion prevention and the moire prevention effect can be anticipated.

  As the optical sheet on the light source side used in combination with the optical sheet of the present invention, a reflection type polarization separation sheet, a diffusion sheet, a prism sheet and the like well known in the art are appropriately used.

(Optical sheet manufacturing method)
First, a mold roll engraved with various hemispherical microlenses and prisms, and a mold roll for the back surface were prepared.
A mold roll was placed close to the extruder. A thermoplastic polycarbonate resin sheet was melted and molded by the extruder, and was molded by the mold roll before the sheet was cooled and cured to obtain an extruded sheet having a surface shape. The thickness was 320 μm.
M1201 from Teijin Chemicals Ltd. was used as the thermoplastic polycarbonate.
All extruded sheets were cut into 10 mm × 10 mm squares and used for evaluation.

(Measurement of brightness of optical sheet and evaluation of concealment)
The obtained optical sheet was incorporated into a simple display, a white screen was displayed, and the brightness of the center was measured from the normal direction of the screen at a distance of 50 cm with SR-3A manufactured by Topcon. The configuration of the backlight was 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. Visual evaluation was performed by three or more subjects because there were individual differences.
The results are shown in Table 1.

In Table 1, the actual height at which the ridge shape fluctuates is called the real height, and the height up to the center of the deflection width of the real height is called the nominal height.
Luminance passed 0.90 or higher.
First, No. 1 in Table 1 was used. 14, when the height of the ridge shape is constant, that is, when the deflection width of the substantial height is 0, a bright spot unevenness defect occurs and becomes NG. On the other hand, no. As shown in FIG. 16, when the swing height of the substantial height is too large, it is difficult to create a shape even for a small sample, and the luminance is lowered. No. 17 and No. No. 22 is not roughened on the back surface, and the concealing property is Δ, but it is considered that there is no problem when a plurality of other optical sheets are used. If the surface is made too rough, the brightness will decrease. Other than that, there is no problem in both the concealing property and the bright spot unevenness defect, but it was judged that the condition where the luminance was less than 0.90 was not practical. Specifically, when the aspect ratio of the microlens is too small (No. 1) or too large (No. 4), when the area ratio is too large (No. 7), the nominal height of the ridge shape / microlens When the height is too low (No. 9), when the height is too high (No. 13). No. Although Table 5 has no problem in the table, it was judged that the side lobe due to the luminance distribution was generated because the number of microlenses was too small, which is not preferable for use. The difference in back surface shape was not particularly affected.
In the examples, for the simplest comparison, the backlight is composed of a Teijin Chemicals diffusion plate 65HLW and an optical sheet. However, the optical sheet of the present invention is impaired in performance even when used in combination with other optical sheets. There is no.

  In the present invention, the optical sheet is provided with a surface shape composed of a combination of a substantially hemispherical microlens and a ridge shape, and the height of the ridge shape is varied with a width, thereby simply combining the microlens and the ridge shape. It is possible to suppress the uneven defect that occurs at the boundary between the two, which occurs occasionally, and to provide an optical sheet that achieves both good luminance performance and diffusion performance.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Reflection type polarization separation sheet 3 Diffusion sheet 5 Light guide plate 6 Diffusion plate 10 Optical member 15 Light source 17 Reflection plate 19 Liquid crystal layer 20 Polarizing plate 21 Edge light type backlight unit 22 Edge light type display device 23 Direct type Backlight unit 24 Direct-type display device 31 Base material 31a Incident surface 32 Micro lens 33 Projection line shape 34 Roughened surface 35 Projection portion 36 Bright spot portion K Light from light source
L Light emitted from optical member S Display viewing direction

Claims (5)

In an optical sheet that collects and / or diffuses incident light,
On the light exit surface of the exit side of and transmits the incident light of the planar plate-like base material having translucency, and a plurality of micro lenses convex hemispherical shape, a plurality of projections extending in one direction while projecting A strip shape is formed,
The aspect ratio of the height to the diameter of the light exit surface of the microlens is 50% ,
The ratio of the surface on which the microlens is formed to the entire surface of the light exit surface is in the range of 40% to 60% in plan view,
The convex shape is a prism shape or a lenticular lens shape,
The heights of the plurality of microlenses are constant,
The height of the plurality of ridge shapes varies with a runout width,
The value obtained by dividing the nominal height, which is the height to the center of the swing width of the plurality of convex-shaped heights, with respect to the light exit surface, is 10% or more and 90%. Within the following range:
Based on the light exit surface, a plurality of ridge-shaped height swing widths are within a range of ± 20% to ± 40% of the nominal height,
The flat portion of the back surface of the light emitting surface is roughened, and the surface roughness is in the range of 0.5 μm to 1.5 μm.
An optical sheet characterized by that.   2. The optical sheet according to claim 1, wherein the ridge shape is the prism shape having a triangular cross section, and an apex angle is set in a range of 70 to 110 degrees. The optical sheet according to claim 1, wherein a plurality of protrusions protrude from a light incident surface on which incident light of the substrate is incident. A light source;
A diffusing plate that enters and diffuses light emitted from a light source and emits it as diffused light; and
The optical sheet according to any one of claims 1 to 3, wherein the diffused light is incident;
A backlight unit comprising at least A liquid crystal panel in which an image display element for displaying an image by controlling transmission / non-transmission of light in pixel units is disposed;
A display device comprising the backlight unit according to claim 4 on a back surface of the liquid crystal panel.

Images