JP2011145544A - Antistatic optical sheet and display unit using the same - Google Patents

Abstract

An optical sheet having an antistatic effect and a wrinkle and sagging suppression effect is provided.
An optical pattern for condensing and / or diffusing, and a charging / deformation preventing convex portion arranged two-dimensionally independently are provided on an exit surface of an optical sheet. The charging / deformation preventing convex portion 32 is higher than the optical pattern 33 and acts as a contact point with the protective film. In a normal optical sheet, static electricity is generated when the protective film is peeled off, and dust and dust are collected on the optical sheet, which causes the appearance of the display device to be damaged. In the present invention, since the charging / deformation preventing convex portion 32 is present, the air filled in the air gap other than the contact point suppresses the movement of the electrostatic charge, so that the generated static electricity remains in a weak state. Will not occur.
[Selection] Figure 3

Description

  The present invention relates to a backlight unit that illuminates, from the back side, a liquid crystal panel on which a display element whose display pattern is defined according to transmission / non-transmission or transparency / scattering states in pixel units is provided. The present invention relates to a lens sheet and a display optical sheet.

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

  In such a liquid crystal display device, a so-called backlight method in which a light source is arranged on the back side (observer side) of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source is employed.

  The backlight unit employed in this type of backlight system is roughly divided into a light source lamp such as a cold cathode fluorescent lamp (CCFL, LED), and a flat light guide plate made of acrylic resin having excellent light transmittance. There are a “light guide plate light guide method” (so-called edge light method) that makes multiple reflections, and a “direct type” method that does not use a light guide plate.

  As a liquid crystal 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.

  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, 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 on the lower surface of the light guide plate 79 by printing or the like. A reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion (not shown).

  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 a mixture of white titanium dioxide (TiO2) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern, and drying and forming the light guide plate. This is a device for increasing the brightness by giving directivity to the light incident in 79 and guiding it to the light exit surface side.

  Furthermore, recently, in order to increase the light utilization efficiency and increase the brightness, as shown in FIG. 7, 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 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.

However, in the apparatus illustrated in FIG. 6, 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. 7, 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 liquid crystal display device, a device illustrated in FIG. 8 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. 8, the control of the viewing angle is left only to the diffusibility of the diffusion film 82, and it is difficult to control, and the center of 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 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 brightness, and thinness are strongly demanded as market needs, and accordingly, the backlight unit mounted on the liquid crystal display device is also light weight, 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.

  On the other hand, for the purpose of improving the performance of optical sheets, there are proposals for various optical patterns as shown in Patent Documents 1 to 5 in addition to conventionally used prisms, lenticular lenses, microlenses and polygonal pyramids. New shapes are expected to increase.

  The optical sheet used for the backlight of the display has a great influence on the appearance of the display, that is, the commercial value, depending on the optical performance, while the ease of handling during assembly and resistance to changes in temperature and humidity after assembly are also produced. This greatly affects the cost on the customer side. More specifically, the optical sheet is covered with a protective film after manufacturing in order to protect the irregular shape such as prisms on the surface, and is used by peeling the protective film during assembly. The ease of peeling off of the protective film and the entry of foreign matter into the backlight due to static electricity generated when the protective film is peeled off greatly affect the yield of the assembly process. As a countermeasure against static electricity, there is a general method of applying an antistatic agent or kneading into an optical sheet.

  In addition, due to temperature and humidity changes in the backlight after assembly, the optical sheet is wrinkled or bent, which causes a problem in appearance. As a countermeasure against wrinkles and sagging, there is a general method for increasing the thickness of the optical sheet and increasing the rigidity.

JP2008-203776 Special table 2008-515026 JP2007-3571 JP2007-304565A JP2008-102497

However, antistatic agents for countermeasures against static electricity have problems that the cost of the antistatic agent itself is added, the cost and yield of the coating process are added, and the antistatic agent is removed due to changes in temperature and humidity. . Although the method of kneading the antistatic agent into the resin can suppress the deterioration more than the application, the type of the antistatic agent that can be used is limited. Increasing the thickness of the optical sheet as a countermeasure against wrinkles and sagging directly increases the product cost, which is contrary to the demand for thinner displays.
The present invention solves these problems easily and inexpensively without increasing the manufacturing cost. At the same time, the optical performance, which is the basic performance of the optical sheet, is not affected.

The invention of claim 1
In an optical sheet that collects and / or diffuses incident light,
On one surface of the translucent substrate on the side from which incident light is emitted, a charging / deformation preventing convex portion and an optical pattern for condensing and / or diffusing the light are provided.
The charging / deformation preventing convex portion is an optical sheet characterized in that it is higher in height than the optical pattern and has a convex shape arranged two-dimensionally independently.
The charging / deformation preventing convex part adjusts the adhesion strength with the protective film, suppresses the generation of static electricity, and suppresses wrinkling and sagging of the optical sheet.

The invention of claim 2
2. The optical sheet according to claim 1, wherein when the height of the charging / deformation preventing convex portion is TM <b> 1 and the width is PM <b> 1, the following Expression 1 is satisfied.
Appropriate shape and arrangement of the charging / deformation preventing convex portions are advantageous in assuring the optical performance of the optical sheet.

  Here, R is the average value of the distances between the charging / deformation preventing convex portions which are independently arranged two-dimensionally and another charging / deforming preventing convex portion which is closest.

The invention of claim 3
The following formula 2 is satisfied, where f is the peel strength between the optical sheet and the surface protective film of the optical sheet, and F is the peel strength between the protective film and the acrylic. Optical sheet.
When the shape and arrangement of the charging / deformation preventing convex portions and the peel strength (that is, the adhesion force) of the protective film of the optical sheet are appropriate, it is advantageous to exhibit the effects of the present invention.

The invention of claim 4
The optical sheet according to any one of claims 1 to 3, wherein the convex optical pattern has a shape in which prisms and / or lenses extending in one axial direction are arranged in parallel at a predetermined pitch. The present invention is applicable to a cylindrical prism sheet and a lens sheet that are generally used in the industry.

The invention of claim 5
The optical sheet according to any one of claims 1 to 4, wherein the charging / deformation preventing convex portion has a substantially hemispherical convex shape.
The charging / deformation preventing convex portion of the present invention can be exhibited even in a substantially hemispherical convex shape that is relatively easy to manufacture and shape-controllable.

The invention of claim 6
The width PM1 of the charging / deformation preventing convex portion is set in a range of 1.1 times to 10 times the pitch of the optical pattern,
6. The height TM1 of the charging / deformation preventing convex portion is set in a range of 1.1 to 10 times the height of the optical pattern. It is an optical sheet described in the item.
When the optical pattern of the present invention is a cylindrical prism sheet or lens sheet, the optimal charging / deformation preventing convex portion is shown.

The invention of claim 7
In an optical sheet that collects and / or diffuses incident light,
The one surface of the translucent substrate on which incident light is incident is a substantially flat surface provided with a charging / deformation preventing convex portion or a roughened rough surface. It is an optical sheet described in any one item.
Among the functions of the charging / deformation preventing convex portion, the adhesion strength with the protective film is adjusted to suppress the generation of static electricity even when the charging / deforming preventing convex portion is applied to the opposite surface of the optical pattern.

The invention of claim 8
In an optical sheet that collects and / or diffuses incident light,
The charging / deformation preventing convex portion and the optical pattern for condensing and / or diffusing light are provided on one surface of the translucent substrate on the side on which incident light is incident. The optical sheet described in any one of the above.
Among the functions of the charging / deformation preventing convex portion, the adhesion strength with the protective film is adjusted and the generation of static electricity is suppressed even in an optical sheet having an optical pattern on both sides.

The invention of claim 9
On the light incident side of the image display element that defines the display image,
The light source, a diffusion plate that emits and diffuses light emitted from the light source, and emits the diffused light, and the optical sheet according to any one of claims 1 to 8, It is the backlight unit characterized by having.
The optical sheet of the present invention can be used for a direct type backlight unit.

The invention of claim 10
On the light incident side of the image display element that defines the display image,
A light source, a light guide plate that guides and emits light emitted from the light source, and the optical sheet according to claim 1 that makes the diffused light incident. It is a backlight unit characterized by having.
The optical sheet of the present invention can be used for an edge light type backlight unit.

The invention of claim 11
An image display element that defines a display image according to transmission / shading in pixel units;
A display device comprising the backlight unit according to claim 9 on a back surface of the image display element.
If the backlight unit of the present invention is used, an inexpensive and high-performance display device can be realized.

The invention of claim 12
It is a molding plate in which the shape of the optical sheet according to any one of claims 1 to 8 or a shape opposite to the concave and convex portions is formed.
The optical sheet of the present invention is easily produced at low cost by the original molding plate. Before forming the optical sheet, the molding plate may be subjected to a plurality of transfer processes using a plurality of molding plates from the mother die, and there may be one having the same shape as the optical sheet and one having an inverted concave and convex shape. As an advantage of increasing the transfer process, the deterioration of the master mold can be delayed when the production quantity is large.

  The present invention provides the optical sheet with a charging / deformation preventing convex portion that controls the adhesion of the protective film, suppresses generation of static electricity, and resists deformation of the sheet. This charging / deformation preventing convex portion is imparted to the mold that is the base of the optical sheet, and exhibits performance over a long period of time without increasing the material cost, and without performance degradation or peeling due to deterioration during use. Furthermore, an excellent point of the present invention is that the good optical performance inherent in the optical sheet is not lowered by the provision of the charging / deformation preventing convex portion.

Explanatory drawing which shows the cross section of the backlight structural example using the optical sheet of this invention. Explanatory drawing which shows the cross section of the backlight structural example using the optical sheet of this invention. The figure which shows partial expansion of the optical sheet of this invention, and an optical sheet. The figure which shows the B-B 'cross section of FIG. Explanatory drawing which shows the back surface of the optical sheet of this invention in a B-B 'cross section. Explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. Explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. Explanatory drawing which shows the structural example of the liquid crystal display device by a prior art.

Embodiments of the present invention will be described below.
1 and 2 show a cross section of a backlight configuration example using the optical sheet of the present invention. Hereinafter, the upper side of FIGS. 1 and 2 is expressed as the upper side, the lower side is expressed as the lower side, the surface facing the upper side is expressed as the front surface, and the surface facing the lower side is expressed as the back surface. FIG. 1 shows an example of the configuration of an edge light type backlight. 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 layer 19 sandwiched between the polarizing plates 21. 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 a direct type backlight. 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 layer 19 sandwiched between the polarizing plates 21. 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.

  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 size and shape of the optical sheet 1 are adjusted so that it can be incorporated into a predetermined backlight. When a part of one side of the optical sheet 1 is enlarged, as shown in FIG. 3A, the charging / deformation preventing convex portion 32 (shown in a substantially hemispherical convex shape in the drawing) and the optical pattern 33 (shown in the drawing). (Indicated by a prism). The optical sheet 1 has a thickness, and the thickness portion is shown as a base material 31 in the drawing. Reference numeral 31 a denotes an incident surface side of the optical sheet 1. The base material 31, the charging / deformation preventing convex portion 32, and the optical pattern 33 constituting the optical sheet 1 may be made of different materials or the same material.

  The charging / deformation preventing convex portion 32 is higher than the optical pattern 33 and acts as a contact point with the protective film. In a normal optical sheet, static electricity is generated when the protective film is peeled off, and dust and dirt are collected on the optical sheet, causing the appearance of the display device to be damaged (peeling charging). In general, in order to suppress static electricity, there is a method of suppressing the generation of electric charge by quickly releasing the generated charge by improving the conductivity of the material in which static electricity occurs or by reducing the electric conductivity. However, there is a limit to the materials that can be used for the optical sheet, both of which are resin materials and the conductivity is about 105Ω / □, which is halfway. The optical sheet 1 of the present invention also basically generates static electricity at the contact point. If there is no charging / deformation preventing convex portion 32, the generated electric charge moves, is distributed in a lump and becomes strong static electricity. However, since the charging / deformation preventing convex portion 32 suppresses the movement of static electricity due to the air filled in the gap other than the contact point, the generated static electricity remains weak and apparently generates static electricity. Will not be. The inventors discovered this fact while repeating the verification of the charging / deformation preventing convex portion 32. Furthermore, the combination of the charging / deformation preventing convex portion 32 and the protective film, which is advantageous in exerting the effects of the present invention, was created.

  The charging / deformation preventing convex part 32 is a convex shape arranged two-dimensionally independently (separated from each other). More specifically, the height of the arbitrary charging / deformation preventing convex part 32 is TM1, When PM is PM1, the following formula 1 is satisfied.

Here, R is the average value of the distances between the charging / deformation preventing convex portions which are independently arranged two-dimensionally and another charging / deforming preventing convex portion which is closest.
At this time, if TM1 / PM1 is less than 0.3, the adhesion point is too wide and the static electricity suppressing effect is small. There is no upper limit to TM1 / PM1, and the closer to infinity, the higher the static electricity suppressing effect, but the protective film is less likely to adhere as will be described later. Similarly, when R is less than twice PM1, the contact point is too close and the static electricity suppressing effect is small. Similarly, there is no upper limit of R, and the closer to infinity, the higher the static electricity suppressing effect, but the protective film is less likely to adhere as will be described later.

Since the optical sheet 1 and the protective film are required to have a certain degree of adhesion, the charging / deformation preventing convex portion 32 is more suitably a gentle spherical shape such as a substantially hemisphere than a sharp shape such as a polygonal pyramid. . That is, when TM1 / PM1 exceeds 1.0, the protective film becomes difficult to adhere. Similarly, when R exceeds 7 times PM1, the number of contact points is too small and the protective film is difficult to adhere. There is no problem with the close contact between TM1 / PM1 and R because there is no problem even in the absence of the charging / deformation preventing convex portion 32.
The optical sheet 1 is generally cut according to the size to be used. At this time, since the protective film strongly pressed into the optical sheet 1 by the cutting blade is firmly attached to the cut end surface, a phenomenon that it is difficult to peel off in the manual process of peeling the protective film occurs. In the present invention, since the charging / deformation preventing convex portion 32 acts as a cushion including a gap at the time of cutting, the protective film does not adhere tightly to the cut end face, and the protective film is easily peeled off even in a state of wearing protective gloves. be able to. Regarding ease of peeling, the effect is small when TM1 / PM1 is less than 0.3, and the effect is small when R exceeds 7 times PM1. There is no upper limit of TM1 / PM1 in the ease of peeling, and the effect is reduced when R is less than 0.5 times PM1.

  The protective film that can be used in the present invention has a peel angle of 180 ° with the optical sheet 1, a peel strength of 5000 mm / min, f (g / 20 mm), a peel angle of 90 ° with acrylic, and a peel rate of 200 mm / min. When the strength is F (cN / 25 mm), the following formula 2 is satisfied.

  That is, as a result of trial and error, the present inventors obtained 30 times the product of the reciprocal of the PM1 coefficient of the average value of the closest distance of the charging / deformation preventing convex portion 32 and the peel strength between the protective film and the optical sheet 1, It has been discovered that TM1 / PM1 is effective unless it exceeds the product of the peel strength of the protective film and acrylic. This indicates that there is a strong relationship between the movement of electrostatic charges, the adhesion of the protective film, and the arrangement of the charging / deformation preventing convex portions 32.

The width of the charging / deformation preventing convex portion 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 charging / deformation preventing convex portion 32 itself may appear as a point defect. The arrangement of the charging / deformation preventing convex portions 32 may be regular or irregular.
The optical sheet 1 of the present invention has a significant static electricity suppressing effect even when an antistatic agent is not used when combined with an appropriate protective film, and the optical sheet 1 of the present invention can be positioned as an antistatic optical sheet. it can.

  The optical pattern 33 is a general cylindrical prism, lens, microlens, polygonal pyramid, or a shape that does not belong to any of those listed in Patent Documents 1 to 5, or a combination shape. If it does not exceed the height, it is applicable. These shapes determine the optical performance of the optical sheet 1 and are appropriately selected depending on the desired performance of the display. For display applications, these shapes preferably have a pitch of 10 μm to 200 μm. If it is smaller than 10 μm, the diffraction of incident light increases and the luminance is lowered. If it is larger than 200 μm, the optical pattern 33 interferes with the liquid crystal panel, and moire occurs.

  The height TM1 of the charging / deformation preventing convex portion 32 is more preferably in the range of 1.1 to 10 times the height of the optical pattern 33. The height of the charging / deformation preventing convex portion 32 is 3 μm to 200 μm from Equation 1 according to Equation 1. Accordingly, the height of the optical pattern 33 is preferably 0.3 μm to 181.8 μm. Although the height of the optical pattern 33 used on the front surface is generally 10 μm or more even if it is low, the optical pattern on the back surface described later may be less than 0.3 μm. Therefore, in the present invention, the lower limit of the optical pattern 33 is 0. 3 μm. When the optical pattern 33 is a prism, the apex angle θ shown in FIG. 3 is preferably 70 ° to 110 °. If it is less than 70 °, it is difficult to manufacture, and if it is more than 110 °, the brightness required for the display device cannot be obtained.

FIG. 4 shows a BB ′ cross section of FIG. A protective film 10 is bonded to one side of the optical sheet 1. As shown in FIG. 4, the charging / deformation preventing convex portion 32 is higher than the optical pattern 33, and exists across the plurality of optical patterns 33.
By the way, when the optical pattern 33 has a cylindrical shape and does not have the charging / deformation preventing convex portion 32, there is a phenomenon that the optical sheet curls with the surface of the optical pattern 33 facing outward due to an increase in temperature or humidity. At this time, curl is generated in the BB ′ cross section perpendicular to the direction in which the optical pattern 33 extends, and almost no curl is generated in the AA ′ cross section parallel to the cylindrical shape. The reason why the curl is generated in the BB ′ cross section is considered to be because it is easy to bend because there is a valley of the optical pattern 33 compared to the AA ′ cross section.
When there is an optical sheet in the display, the curl is restrained from moving and appears in the appearance as wrinkles and sagging.
On the other hand, the optical sheet 1 of the present invention shows no curling due to temperature rise or humidity rise. This is presumably because the ease of bending in the BB ′ cross section is suppressed by the presence of the charging / deformation preventing convex portion 32. Further, when there is another optical sheet on the optical sheet 1 in the display, the gap with the upper optical sheet formed by the charging / deformation preventing convex portion 32 becomes an escape route for air containing heat and water. There is also an effect. In order to obtain this effect, TM1 / PM1 is 0.2 or more, R is 8 times or less of PM1, and the width PM1 of the charging / deformation preventing convex portion 32 is 1 with respect to the pitch of the optical pattern 33. The height TM1 of the charging / deformation preventing convex portion 32 is preferably 1.1 times or more with respect to the height of the optical pattern 33. Since the effect increases as the charging / deformation preventing convex portions 32 increase, there is no upper limit for curling. As described above, the width (pitch) of the charging / deformation preventing convex portion 32 and the optical pattern 33 is preferably 10 μm to 200 μm, but considering the suppression of curling, the lower limit of PM1 of the charging / deformation preventing convex portion 32 is 11 μm. The upper limit of the pitch of the optical pattern 33 is more preferably 181.8 μm.

From the above, it is preferable that Formula 1 and Formula 2 are satisfied in order for the optical sheet 1 to sufficiently adhere to the antistatic optical sheet and the protective film. Further, if it is desired to suppress wrinkles and sagging caused by curling, the width PM1 of the charging / deformation preventing convex portion 32 is 1.1 times or more the pitch of the optical pattern 33, and the height TM1 is the height of the optical pattern 33. It is preferable that it is 1.1 times or more.
The charging / deformation preventing convex portions 32 having various effects are preferably arranged at a minimum so as not to affect the luminance and the like as long as they can be selected within the scope of the present invention.

  5A to 5C show B-B ′ cross-sectional views of the types of back surface shapes applicable to the optical sheet 1. The surface is not shown in the figure, and the charging / deformation preventing convex portion 32 is indicated by a substantially hemispherical convex shape, and the optical pattern 33 is indicated by a hairline having a triangular cross section. Fig.5 (a) shows the case where a back surface is a substantially plane. The incident surface 31a may be roughened by blasting, polishing, bead coating, or the like as long as it is substantially flat. (B) shows the case where the back surface has the charging / deformation preventing convex portion 32. The charging / deformation preventing convex portion 32 that exhibits various effects on the front surface can be applied to the back surface. The shape and arrangement are the same as those on the surface. Further, the portion without the charging / deformation preventing convex portion 32 is substantially flat and may be roughened as described above. If it is difficult to roughen only the substantially flat surface while avoiding the charging / deformation preventing convex portion 32, the charging / deformation preventing convex portion 32 may be roughened within the range of Equation 1. . (C) shows the case where the back surface has the charging / deformation preventing convex portion 32 and the optical pattern 33. Although the optical pattern 33 on the back surface is different from that on the front surface, it can be appropriately selected according to the desired performance from the shape raised on the front surface to the shape of a finer, lower hairline or the like. In addition, when the back surface of (c) is selected, the curl behavior of the optical sheet 1 becomes more complicated. Therefore, it is difficult to completely eliminate the curl although there is a suppression effect.

  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. If it is higher than 0.5, the light collecting function of the optical sheet may deteriorate due to unexpected stray light. 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 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 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 the 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 and the like 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. Further, the refractive index difference may be 0.5 or less. 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.

  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, mold rolls engraved with various charging / deformation preventing convex portions 32 (substantially hemispherical convex shapes) and optical patterns 33 (cylindrical prisms) were prepared for the front and back surfaces. Details are given in Table 1.
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 shape on the surface. A protective film (Hitalex L-7330, F = 330) was immediately applied to the extruded sheet. In addition, a protective film having a different F is used, but a small piece is prepared for verification and is not a ready-made product.
M1201 from Teijin Chemicals Ltd. was used as the thermoplastic polycarbonate.
All the extruded sheets had a thickness of 320 μm and were cut into 415 mm × 730 mm squares and used for evaluation.

(Brightness evaluation of optical sheet)
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 is an edge light system, and a light guide plate on which white spots are printed in order from the bottom, a diffusion film of Hz 89, the optical sheet 1, and a polarization separation reflection sheet DBEF. In the case of the direct type, only the diffuser plate and the optical sheet 1 having a total light transmittance of 65% were used. The results are expressed as a reference ratio using a prism sheet without the charging / deformation preventing convex portion 32 as a reference. Table 2 shows the results of the edge light method.

(Evaluation of optical sheet peeling performance)
What was peeled off naturally before evaluation of the bonded protective film was an adhesion failure, and it was set as x in the table. The results are limited to those with sufficient adhesion.
The ease of peeling was evaluated using 10 optical sheets to determine whether a worker wearing rubber gloves peeled off the protective film at one time from the edge of the protective film. The number of peelings at one time is shown in Table 2, and the higher the number, the better the performance. The peel strength of the sample cut to a width of 20 mm was measured with HEIDON-14 manufactured by HEIDON under the conditions of a peel rate of 5000 mm / min and a peel angle of 180 degrees.

(Electrical sheet charging evaluation)
Whether the surface resistance of the optical sheet changes depending on the presence or absence of the charging / deformation preventing convex portion 32 was measured with an MCP-HT450 manufactured by Mitsubishi Chemical Corporation in an environment of 25 ° C. and 60%. The actual charged state was confirmed by quickly sprinkling 3 g of charge distribution determination toner manufactured by Kasuga Denki Co., Ltd. on the optical sheet after the above worker peeled off the protective film at once. Evaluation is made with 10 optical sheets, toner adhesion due to charging is determined by color density, and the number of toner adhesions that are so thin that the image on the back is visible when the optical sheet is watermarked is shown in Table 2. The more the better, the better the performance.

(Curl evaluation of optical sheet)
The protective film of the optical sheet was peeled off and placed on a flat glass plate with the back side up. After confirming that there was no curling, the film was placed in an environment of 60 ° C. and 65%, and the state of curling was observed. Table 2 shows the height of the gap from the glass plate to the optical sheet caused by curling.

First, the surface resistance value was 106Ω / □ or more in all samples without any difference between the comparative example and the example, and there was no difference depending on the surface shape. Next, the results of the charge distribution determination toner are largely divided between the comparative example and the example. From this, the inventors have understood the antistatic mechanism that the optical sheet of the present invention does not generate static electricity but inhibits the movement of charges.
In the examples, the protective film was easily peeled off and the charge distribution determination toner was light. Samples with a light charge distribution determination toner did not feel the occurrence of static electricity as a feeling of handling. A toner with a light charge distribution determination toner satisfies Formula 2. On the other hand, the ease of peeling off the protective film was not particularly related to Formula 2. Separately, a protective film having an F value of 50 to 500 cN / 25 mm was also tested in the same manner, but all satisfied Formula 2 and the degree of charge distribution determination toner was weak.
In addition, since the example uses a cylindrical prism as an optical pattern, a curl suppressing effect was also observed. However, when the optical pattern is not cylindrical, the curl suppressing effect cannot be expected.
The luminance ratio with respect to the reference was determined to be within a range of 0.2 where the difference cannot be seen by human eyes when two displays are arranged, that is, 0.98 or more. All the optical sheets of the present invention maintain optical performance in which the difference from the reference cannot be recognized. In the table, the edge light method was used for verification, but regarding the luminance ratio, even in the direct type, all the examples passed 0.98 or more and passed. From this result, there is almost no luminance loss of the optical sheet 1 compared to the reference, and therefore, it can be used without any problem even if it is used in other backlight configurations.
As described above, by using the present invention, an optical sheet having an antistatic effect and a wrinkle and sagging suppressing effect can be provided easily and inexpensively without impairing the optical performance of the display device.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Reflection type polarization separation sheet 3 Diffusion sheet 5 Light guide plate 6 Diffusion plate 10 Protective film 15 Light source 17 Reflection plate 19 Liquid crystal layer 21 Polarizing plate 31 Base material 31a Incident surface 32 Charging / deformation preventing convex portion 33 Optical pattern K Light source Light from
L Light emitted from optical member S Display viewing direction

Claims (12)

In an optical sheet that collects and / or diffuses incident light,
On one surface of the translucent substrate on the side from which incident light is emitted, a charging / deformation preventing convex portion and an optical pattern for condensing and / or diffusing the light are provided.
The charging / deformation preventing convex portion is higher in height than the optical pattern and has a convex shape arranged two-dimensionally independently. 2. The optical sheet according to claim 1, wherein when the height of the charging / deformation preventing convex portion is TM1 and the width is PM1, the following expression 1 is satisfied.

Here, R is the average value of the distances between the charging / deformation preventing convex portions which are independently arranged two-dimensionally and another charging / deforming preventing convex portion which is closest. The following formula 2 is satisfied, where f is the peel strength between the optical sheet and the surface protective film of the optical sheet, and F is the peel strength between the protective film and the acrylic. Optical sheet.

  4. The optical sheet according to claim 1, wherein the convex optical pattern has a shape in which prisms and / or lenses extending in one axial direction are arranged in parallel at a predetermined pitch.   The optical sheet according to claim 1, wherein the charging / deformation preventing convex portion has a substantially hemispherical convex shape. The width PM1 of the charging / deformation preventing convex portion is set in a range of 1.1 times to 10 times the pitch of the optical pattern,
6. The height TM1 of the charging / deformation preventing convex portion is set in a range of 1.1 to 10 times the height of the optical pattern. The optical sheet described in the item. In an optical sheet that collects and / or diffuses incident light,
The one surface of the translucent substrate on which incident light is incident is a substantially flat surface provided with a charging / deformation preventing convex portion or a roughened rough surface. The optical sheet described in any one of the items. In an optical sheet that collects and / or diffuses incident light,
The charging / deformation preventing convex portion and the optical pattern for condensing and / or diffusing light are provided on one surface of the translucent substrate on the side on which incident light is incident. The optical sheet described in any one of the above. On the light incident side of the image display element that defines the display image,
The light source, a diffusion plate that emits and diffuses light emitted from the light source, and emits the diffused light, and the optical sheet according to any one of claims 1 to 8, Backlight unit characterized by having. On the light incident side of the image display element that defines the display image,
A light source, a light guide plate that guides and emits light emitted from the light source, and the optical sheet according to claim 1 that makes the diffused light incident. A backlight unit characterized by An image display element that defines a display image according to transmission / shading in pixel units;
A display device comprising the backlight unit according to claim 9 on a back surface of the image display element.   A molding plate in which the shape of the optical sheet according to any one of claims 1 to 8 or a shape opposite to the concaves and convexes is formed.

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