JP2008185930A - Optical sheet, and backlight unit and display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which has an integrated constitution and can control warp behavior not causing trouble on display even under the influence of high heat. <P>SOLUTION: In the optical sheet 1, a plurality of optical element layers 4-6 for controlling at least any of the direction, the range, the color, and the luminance distribution of light H made incident are laminated between a nearly flat incident face 2 on which the light H is made incident from a light source 23 and an exit face 3 being a face on the opposite side of the incident face 2. In the optical element layers 4-6, a second layer having a coefficient of thermal expansion lower than that of a thickest first layer is arranged on the exit face 3 side of the first layer 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical sheet, a backlight unit, and a display, and in particular, an optical sheet used for controlling an illumination optical path in a backlight unit for a display mainly using a liquid crystal display element, and the optical sheet is applied. The present invention relates to a backlight unit and a display.

  A display typified by a liquid crystal display device (LCD) is remarkably widespread in a type including a light source necessary for recognizing provided information. In a battery-powered device such as a laptop computer, the power consumed by the light source accounts for a substantial portion of the power consumed by the entire device.

  Thus, reducing the total power required to provide a given brightness increases battery life, which is particularly desirable for battery powered devices.

  A brightness enhancement film (BEF) which is a registered trademark of 3M Corporation of the United States is widely used as an optical sheet for solving this problem.

  As shown in FIG. 5, BEF is a film in which unit prisms 72 having a triangular cross section are periodically arranged in one direction on a member 70. The prism 72 has a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” or “recycle” towards the viewer. To do.

  When using the display (when observing), the BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally the normal direction to the display screen (direction F shown in FIG. 5).

  When the repetitive array structure of the prisms 72 is arranged in only one direction, only the direction change or recycling in the parallel direction is possible, and in order to control the luminance of the display light in the horizontal and vertical directions, the prism groups are arranged in parallel. Two sheets are stacked and combined so that the directions are substantially orthogonal to each other.

  The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption. As patent documents disclosing that a brightness control member having a repetitive array structure of prisms 72 typified by BEF is adopted for a display, many are known as exemplified in Patent Documents 1 to 3. ing.

  In the optical sheet using BEF as a brightness control member as described above, the light H from the light source 20 is finally emitted at a controlled angle φ by the refraction action X as shown in FIG. Thus, it is possible to control to increase the intensity of light in the visual direction F of the viewer. However, at the same time, the light component due to the reflection / refraction action Y is unnecessarily emitted in the lateral direction without proceeding in the visual direction F of the viewer.

  Accordingly, the light intensity distribution emitted from the optical sheet using BEF as shown in FIGS. 5 and 6 has a viewer's visual direction F, that is, an angle with respect to the visual direction F of 0, as shown by the curve in FIG. Although the light intensity at ° (corresponding to the axial direction) is the highest, as shown as a small light intensity peak around ± 90 ° shown on the horizontal axis in the figure, the amount of light emitted from the horizontal direction is increased. There is a problem.

  The characteristic shown in FIG. 7 is the light intensity distribution when only one prism sheet is used, and the curve indicated by “vertical distribution” in FIG. 7 corresponds to the direction in which the prisms 72 are arranged in parallel, and is “horizontal distribution”. The curve shown corresponds to the longitudinal direction of the prism 72.

  In general, a usage form in which two prism sheets are used in combination so that the directions in which the prisms 72 are arranged in parallel is substantially orthogonal. A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution having no light intensity peak around ± 90 ° is more desirable.

  Further, when only the on-axis luminance is excessively improved, the curve shown in FIG. 7 is particularly limited in the characteristics shown in FIG. 7 because the peak width in the vertical distribution curve becomes extremely narrow and the viewing area is extremely limited. In order to widen the width of the mountain appropriately, it is necessary to newly use a light diffusing film which is a separate member from the prism sheet, which is accompanied by an increase in the number of members.

  In order to overcome such a drawback, as shown in FIG. 8, there is also a backlight unit 40 using an optical film 38 having a repetitive array structure of unit lenses 44 instead of a prism (Patent Document 4).

  A lens 44 for guiding the light traveling in the optical film 38 to the liquid crystal panel 42 is provided on the surface of the transparent base 39 of the optical film 38 on the liquid crystal panel 42 side. As shown in the perspective view of FIG. 9, the lens 44 has a plurality of unit lenses 44 that repeatedly form an array structure. Further, on the other surface, a reflector 48 having a stripe pattern having an opening 46 in the vicinity of the focal plane of the lens 44 is provided.

The reflector 48 is obtained by mixing a mixture of white titanium dioxide (TiO ₂ ) powder with a transparent adhesive solution or the like in a predetermined pattern (when the unit lens 44 is a semi-cylindrical convex cylindrical lens group, a unit lens). 44 is formed in a stripe shape having an opening 46 corresponding to 1: 1, and is formed (or transferred).

  FIG. 10 is an explanatory diagram showing optical path control characteristics of a backlight unit to which the optical sheets of FIGS. 8 and 9 are applied. As shown in FIG. 8, the light H emitted from the light source 23 housed in the lamp house 21 is diffused by the diffusion plate 26 and then enters the diffusion film 32. Furthermore, as shown in FIG. 10, only the light α that has passed through the opening 46 out of the light H incident on the diffusion film 32 is incident on the lens 44 and emitted after being condensed in a certain direction by the lens 44. Is done. The emitted light then enters the polarizing plate 49 as shown in FIG. 8, and only the light having a predetermined polarization component is guided to the liquid crystal panel 42.

  On the other hand, the light β that could not pass through the opening 46 is reflected by the reflecting material 48, returned to the diffusion plate 26 side, and guided to the reflecting plate 27 provided at the bottom of the lamp house 21. Then, the light is incident on the diffuser plate 26 again by being reflected by the reflecting plate 27 and is diffused again on the diffuser plate 26. As shown in FIG. 10, the light is incident on the lens 44 and is emitted within a predetermined angle φ.

  In the backlight unit 40 using such an optical film 38, the size and the position of the opening 46 of the optical film 38 are adjusted to increase the light utilization efficiency, and the light is emitted from the lens 44 in the front direction F. It can be controlled to increase the proportion of light.

  By the way, in a display having a large screen such as a liquid crystal TV or a monitor for a personal computer instead of a display having a relatively small screen such as a mobile phone or a mobile terminal, the luminance distribution in the screen is made uniform. Above, it is preferable to adopt a direct backlight unit in which the light source 23 is housed in the lamp house 21 behind the screen, rather than a backlight unit including an edge light and a light guide plate.

As shown in FIG. 11, the backlight unit in the liquid crystal display device is a lamp house in which each element such as a diffusion film or DBEF 80, a prism sheet or optical film 81, a diffusion film 82, or a diffusion plate 83 is housed in a light source 23. 21 is stacked on top of each other. Hereinafter, the light control functions of the diffusion film or DBEF 80, the prism sheet or optical film 81, the diffusion film 82, the diffusion plate 83, etc. are collectively referred to as an optical element.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A JP 2006-106197 A

  However, such a conventional backlight unit has the following problems.

  That is, in such a conventional backlight unit, as the price of the display is reduced and the size is increased, the diffusion plate 83 and other optical elements are integrated from the viewpoint of reducing the number of members and improving the rigidity of the optical sheet. Is desired.

  In this case, the laminated structure form of the backlight unit is as shown in FIG. That is, an integrated optical element 86 in which optical elements such as a prism sheet or optical film 81, a diffusion film 82, and a diffusion plate 83 are integrated is formed, and the integrated optical element 86 and the diffusion film or DBEF 80 serve as a light source. 23 are arranged in order on the lamp house 21 in which 23 are housed.

  Alternatively, if the required optical characteristics are satisfied, a simple configuration in which the diffusion film 80 is omitted and only the integrated optical element 86 is disposed on the lamp house 21 is most desirable as shown in FIG.

  Although the configuration as shown in FIG. 13 is ideal, various drawbacks due to the simplification of the configuration remain unsolved and have not yet reached the commercialization level. In particular, since the integrated optical element 86 itself is rigid, the integrated optical element 86 is warped due to the influence of high heat generated when the light source 23 is turned on, the liquid crystal panel 42 is pressed, and the display becomes abnormal. There is a problem that the panel 42 may be damaged.

  The present invention has been made in view of such circumstances, and even under the influence of high heat, it is possible to control the warping behavior of the optical sheet so as not to affect the deterioration of the image quality of the displayed image. An object of the present invention is to provide an optical sheet having an integrated structure.

  In addition, by using such an optical sheet, a backlight unit and a display that do not cause abnormal display due to deformation of the optical sheet or damage to the liquid crystal panel even under the influence of high temperature generated when the light source is turned on are provided. The purpose is to do.

  That is, according to the first aspect of the present invention, the direction, range, color, and luminance of incident light between a substantially planar incident surface on which light from a light source is incident and an exit surface that is a surface opposite to the incident surface. An optical sheet formed by laminating a plurality of optical element layers for controlling at least one of the distributions, the second layer having a lower linear expansion coefficient than the thickest first layer among the optical element layers Is disposed closer to the emission surface than the first layer.

The invention according to claim 2 is the optical sheet according to claim 1, wherein the total thickness of the laminated optical element layers is 1.5 × 10 ⁻³ m or more.

Furthermore, the invention of claim 3 is the optical sheet of the invention of claim 1, wherein the thickness of the second layer is 20 × 10 ⁻⁶ m or more.

  The invention according to claim 4 is the optical sheet according to any one of claims 1 to 3, wherein the second layer has a thermal contraction rate larger than that of the first layer.

  The invention according to claim 5 is the optical sheet according to any one of claims 1 to 4, wherein the first layer and the second layer are joined.

  The invention according to claim 6 is the optical sheet according to claim 5 in which the first layer and the second layer are joined together by at least one of an adhesive, an adhesive, and excimer adhesion.

  According to a seventh aspect of the present invention, at least one of a surface treatment of antistatic treatment, scratch prevention treatment, antireflection treatment, and mat treatment is performed on the incident surface side of the first layer. An optical sheet according to any one of the inventions.

  The invention according to claim 8 is provided with a treatment layer of at least one of an antistatic layer, a scratch prevention layer, an antireflection layer, and a mat treatment layer on the incident surface side of the first layer. 6 is an optical sheet according to any one of the inventions.

The invention according to claim 9 is the optical sheet according to claim 8, wherein the thickness of the treatment layer is 10 × 10 ⁻⁶ m or less.

  The invention of claim 10 includes the optical sheet of any one of claims 1 to 9 and a light source that is disposed on the incident surface side of the optical sheet and supplies light incident from the incident surface. Backlight unit.

  Further, the invention of claim 11 comprises the backlight unit of the invention of claim 10 and an image display element comprising a liquid crystal display element that defines a display image in accordance with transmission / shading in pixel units, A display that is a cold cathode ray tube or LED.

  According to the present invention, from the viewpoint of reducing the number of members and improving the rigidity, a plurality of optical elements are integrated, and the thickest first layer is used as a support, on the emission surface side with respect to the first layer, By providing the second layer that shrinks more than the first layer at a high temperature, an optical sheet in which the light source side is naturally convex at a high temperature when using the backlight can be realized.

  In the present invention, the shrinkage difference between the first layer and the second layer is given by two kinds of properties. One is a difference in expansion coefficient at a high temperature expressed by a linear expansion coefficient, which is a reversible phenomenon, and thus a convex shape appears only at a high temperature, that is, when a backlight is used. Another is the difference in heat shrinkage rate, which is irreversible, and once it develops, the convex shape is maintained not only when used at high temperature but also after returning to normal temperature when not in use. Both phenomena can be used together.

  Furthermore, by using such an optical sheet, a backlight unit and a display that do not cause abnormal display due to deformation of the optical sheet or damage to the liquid crystal panel even under the influence of high temperatures generated when the light source is turned on are realized. can do.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  Fig.1 (a) and FIG.1 (b) are side views which show the structural example of the optical sheet which concerns on embodiment of this invention.

  That is, the optical sheet 1 according to the embodiment of the present invention has a substantially flat incident surface 2 on which light H from the light source 23 housed in the lamp house 21 is incident and an exit surface that is the surface opposite to the incident surface 2. The optical sheet 1 is formed by laminating a plurality of optical element layers 4 to 6 that control at least one of the direction, range, color, and luminance distribution of incident light H between the surface 3 and the surface 3. The optical sheet 1 includes a simple diffusion plate and an optical element, a fine diffusion plate in which some or all of the functions of the diffusion plate are integrated into the optical element, and a simple transparent plate. Examples of the material of the diffusion plate, the fine diffusion plate, and the transparent plate include polycarbonate, acrylic, polystyrene, or a mixture of these materials in an arbitrary ratio, which are well known in the field. From the function of a general optical sheet, these plate materials correspond to the first layer. The light source 23 is, for example, a cold cathode ray tube or an LED.

  Although not necessarily limited, for example, the optical element layer 4 is a diffusion plate. The optical element layer 5 is a base material. The optical element layer 6 is a prism sheet or an optical film having a repetitive array structure of unit lenses 44 as shown in FIG. And among the optical element layers 4-6, the 2nd layer which has a lower linear expansion coefficient than the thickest 1st layer is arrange | positioned at the output surface 3 side rather than the 1st layer.

  For example, as shown in FIG. 1A, when the thickest first layer is the optical element layer 4, the second layer is either the optical element layer 5 or the optical element layer 6. Further, as shown in FIG. 1B, when the thickest first layer is the optical element layer 5, the second layer is the optical element layer 6.

Further, the first layer may be subjected to surface treatment of at least one of antistatic treatment, scratch prevention treatment, antireflection treatment, and mat treatment on the incident surface 2 side. Alternatively, a treatment layer of at least one of an antistatic layer, a scratch prevention layer, an antireflection layer, and a mat treatment layer may be further provided on the incident surface 2 side of the first layer. In this case, the thickness of the treatment layer is 10 × 10 ⁻⁶ m or less.

The total thickness of the laminated optical element layers 4 to 6 is 1.5 × 10 ⁻³ m or more, and the thickness of the second layer is 20 × 10 ⁻⁶ m or more. Further, the second layer has a thermal contraction rate larger than that of the first layer.

  1A and 1B show an example in which three optical element layers are laminated, the optical sheet 1 according to the embodiment of the present invention is limited to three layers. Instead, it may be four or more layers. Although not shown, a bonding layer (adhesive layer) for bonding the layers may be provided as appropriate.

  Due to the function of a general optical sheet, the second layer is an optical element itself such as a prism or lens having a condensing function, a bead dispersion type diffusion layer having a relatively large particle diameter having both a condensing function and a diffusing function, or It corresponds to the base material which supports these. The optical element and plate material listed here can be joined directly to the optical element with a thermoplastic or UV curable material, and beads, a diffusing agent, and a reflective agent are dissolved in a solvent together with a resin as a binder. The method of apply | coating directly on a board is mentioned. As thermoplastic materials, UV curable materials, binder resins, polycarbonate, acrylic, polypropylene, cycloolefin polymers well known in the field, as beads and diffusing agents, inorganic fillers such as glass and silica, organic fillers Examples of the diffusing agent include titanium dioxide and barium sulfate.

  As another bonding method, a method in which an optical element is applied to a base material of PET, PC (polycarbonate) or acrylic with a thermoplastic or UV curable material as described above, a bead or a diffusing agent is used as a binder. There is also a method of joining the substrate and the plate through a method of dissolving in a solvent together with the resin to be applied and applying the solution onto the substrate. Examples of the method for bonding the substrate and the plate include a method using a pressure-sensitive adhesive or adhesive well known in the art, and a method for directly bonding the substrate and the plate with heat or pressure after surface treatment with an excimer laser. It is done.

  Any combination of the materials and methods described above may be used as long as the second layer is disposed closer to the emission surface 3 than the first layer.

  The optical sheet 1 having such a configuration forms a backlight unit together with the light source 23. Further, this backlight unit is disposed on the emission surface 3 side and forms a display by combining with a liquid crystal panel 7 composed of a liquid crystal display element that defines a display image according to transmission / light shielding in pixel units.

(Example)
Next, specific examples of the optical sheet according to the embodiment of the present invention configured as described above will be described with reference to FIG.

Case 1 shown in FIG. 2 is a 2 × 10 ⁻³ m thick polycarbonate as a first layer, a 75 × 10 ⁻⁶ m thick PET substrate as a second layer, and UV as an optical element on the PET substrate. A cylindrical lens was formed with a curable acrylic resin, and then a white reflective layer was formed as described in Patent Document 4. Alternatively, the prism may be formed of UV curable acrylic resin instead of the cylindrical lens. Nothing is performed as the light source side surface treatment of the first layer. And the 1st layer and the 2nd layer were joined with the board | plate material previously cut into 415 mm x 730 mm, and the acrylic adhesive of thickness 20x10 < ^-6 > m, and the optical sheet 1 was created. The linear expansion coefficient of the first layer is 6.7 × 10 ⁻⁵ cm / cm / ° C., and the linear expansion coefficient of the second layer arranged closer to the emission surface than the first layer is 2.7. × 10 ⁻⁵ cm / cm / ° C.

  An optical sheet 10 in which a cylindrical lens is formed of a UV curable acrylic resin as an optical element on a PET substrate will be described with reference to FIGS. 3 and 4.

  The optical sheet 10 includes a plurality of light reflecting portions 14 that are provided with one surface on the emission surface 12 side and reflect light scattered by the light scattering layer 13 that is the first layer to the light scattering layer 13 side. ing. Furthermore, a plurality of light transmitting portions 15 each including an air layer provided between two adjacent light reflecting portions 14 and transmitting light scattered by the light scattering layer 13 to the lenticular sheet 17 on the non-light scattering layer side are provided. I have. By such a light transmitting portion 15, it is possible to collect only the light transmitted through the light transmitting portion 15 out of the light H from the light source 23 scattered by the light scattering layer 13 and guide it to the unit convex cylindrical lens 16. It becomes.

  Furthermore, the optical sheet 10 includes a lens unit in which a plurality of unit convex cylindrical lenses 16 are arranged in parallel on the liquid crystal panel 30 side, and a surface 19 opposite to the lens unit, and is transmitted by the light transmitting unit 15. A lenticular sheet 17 having a non-lens surface 19 on which the incident light enters. The lenticular sheet excluding the lens portion corresponds to the second layer.

  The plurality of unit convex cylindrical lenses 16 are, for example, lenticular lenses, and the lenticular sheet 17 is made of PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP (cycloolefin polymer), etc. It is formed by an extrusion molding method, an injection molding method, or a hot press molding method well known in the art. Alternatively, by an ultraviolet curing molding method in which PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), PE (polyethylene), etc. are used as a base material, and an ultraviolet curing resin is disposed thereon. Form.

  Each of the plurality of light transmitting portions 15 corresponds to each of the plurality of unit convex cylindrical lenses 16 in a 1: 1 manner, and includes a perpendicular V from the vertex T of the corresponding unit convex cylindrical lens 16 to the non-lens surface 19. In addition, the light scattered by the light scattering layer 13 is provided at a position where the corresponding unit convex cylindrical lens 16 exits from the front surface on the liquid crystal panel 30 side, and each of the plurality of light reflecting portions 14 is well known in the art. 3 is formed using a printing method, a transfer method, or a photolithography method, and is formed so as to form a convex portion with respect to the non-lens surface 19, and the longitudinal direction X (in FIG. 3) of each unit convex cylindrical lens 16 It is arranged along the front-rear direction and the X direction in FIG. The adhesive layer 18 adheres the light reflecting portions 14 and the light scattering layer 13.

Case 2 is a case where the first layer in Case 1 is changed from polycarbonate to polystyrene having the same thickness. The linear expansion coefficient of polystyrene is 7.0 × 10 ⁻⁵ cm / cm / ° C.

Case 3 is a case where the first layer in Case 1 is changed from polycarbonate to MS resin. MS resin is a copolymer of acrylic and polystyrene, and has a linear expansion coefficient of 7.0 × 10 ⁻⁵ cm / cm / ° C. Three types of thicknesses of MS resin were prepared: 1.5 × 10 ⁻³ m, 2 × 10 ⁻³ m, and 3 × 10 ⁻³ m.

Case 4 is a case where the second layer in Case 3 is changed from PET to an acrylic film having a thickness of 100 × 10 ⁻⁶ m. The linear expansion coefficient of the acrylic film is 7.0 × 10 ⁻⁵ cm / cm / ° C. The thickness of the MS resin as the first layer was 2 × 10 ⁻³ m.

In case 4.5, the first layer is MS resin having a linear expansion coefficient of 7.0 × 10 ⁻⁵ cm / cm / ° C. and a thickness of 1.5 × 10 ⁻³ m, and the second layer is the first layer. An acrylic layer having a linear expansion coefficient of 6.0 × 10 ⁻⁵ cm / cm / ° C. and a thickness of 20 × 10 ⁻⁶ m containing styrene beads having an average particle diameter of 15 × 10 ⁻⁶ m directly coated on the case, and a case 5 shows a case in which a scratch preventing layer made of acrylic having a thickness of 20 × 10 ⁻⁶ m is further provided on the light source side of the first layer in the case 4.5. (Because I wrote it in case 4.5)
Case 6 is a case where the thickness of the scratch-preventing layer made of acrylic in case 5 is 10 × 10 ⁻⁶ m.

Case 7 is a case where an antireflection layer made of a PET layer having a thickness of 50 × 10 ⁻⁶ m is provided on the light source side of the first layer, instead of the scratch-proof layer made of acrylic in case 5. The linear expansion coefficient of the PET layer is 1.5 × 10 ⁻⁵ cm / cm / ° C.

Case 8 is a case where the thickness of the antireflection layer made of the PET layer in Case 7 is 10 × 10 ⁻⁶ m.

Case 9 is a case where an antistatic layer having a thickness of 1 to 2 × 10 ⁻⁶ m is provided in place of the antireflection layer in case 8.

Case 9.5 is a case where the thickness of the second layer in case 4.5 is changed from 20 × 10 ⁻⁶ m to 18 × 10 ⁻⁶ m.

  Note that the combination of layers as shown in FIG. 2 is an example of the configuration of the optical sheet of the present invention, and the optical sheet of the present invention is not limited to these configurations.

  The optical sheet of each case created as described above was incorporated into a display, the light source 23 was turned on, and the display state of the image was confirmed 24 hours later. When the optical sheet 1 is in a high temperature environment when the light source is turned on, the optical sheet 1 naturally deforms into a convex shape toward the light source 23 due to the influence of temperature. For this reason, even under the influence of high heat, display abnormality due to deformation of the optical sheet and damage to the liquid crystal panel do not occur.

From the result of confirming the display state of the image displayed from the display, the second layer having a lower linear expansion coefficient than the first layer is on the light source side, and the total thickness of the laminated optical elements is 1.5 × 10 ^{− For} cases 1 to 3 and 4.5 that are ³ m or more, the convex shape due to thermal deformation is stably maintained, and the liquid crystal panel 7 is pressed while the light source 23 is turned on, and the display becomes abnormal. There was no breakage and good results were obtained.

  On the other hand, in case 4 where the linear expansion coefficient of the second layer is not lower than the linear expansion coefficient of the first layer, the convex shape due to thermal deformation is not maintained in a stable state, and is not stable during lighting of the light source 23. As a result, regular deflection occurred, and a part of the liquid crystal panel 7 was brought into contact with the liquid crystal panel 7 to cause a defect.

In addition, the second layer having a lower linear expansion coefficient than the first layer is on the light source side, and the total thickness of the laminated optical elements is 1.5 × 10 ⁻³ m or more. As for the surface treatment on the light source side, cases 5 and 7 having a surface treatment with a thickness of 20 × 10 ⁻⁶ m or more are deformed convexly toward the liquid crystal panel 7 while the light source 23 is turned on, and the center of the screen As a result, it was found that there was a problem with the image display in a wide range centering on.

On the other hand, the second layer having a lower linear expansion coefficient than the first layer is on the light source side, the total thickness of the laminated optical elements is 1.5 × 10 ⁻³ m or more, and the light source of the first layer For cases 6, 8, and 9 where surface treatment with a thickness of 10 × 10 ⁻⁶ m or less is performed as the surface treatment on the side, the convex shape on the light source side due to thermal deformation is stably maintained, and the light source is turned on The liquid crystal panel 7 was pushed inside, the display did not become abnormal, and the liquid crystal panel 7 was not damaged, and good results were obtained.

Although it can be easily understood physically that the force that pulls the adjacent layer at the time of expansion / contraction is larger, the incident side that does not adversely affect the second layer having a thickness of 20 × 10 ⁻⁶ m or more of the present invention. It was found that the thickness of the surface treatment was at least 10 × 10 ⁻⁶ m or less.

  As described above, when the optical sheet 1 according to the embodiment of the present invention is in a high temperature environment when the light source is turned on, the optical sheet 1 is naturally deformed into a convex shape toward the light source 23 due to the temperature, and presses the liquid crystal panel. Because there is no, there is no problem with the display.

In particular, by making the total thickness of the laminated optical element layers 1.5 × 10 ⁻³ m or more, or in addition to making the thickness of the second layer 20 × 10 ⁻⁶ m or more, Since the rigidity of the optical sheet is increased and the degree of deformation is effectively expressed, this convex shape is stably maintained even in a high temperature environment when the light source 23 is turned on. In addition, when surface treatment is performed on the incident surface side of the first layer, or when a surface treatment layer is provided, there is a possibility that warpage that protrudes toward the light source side may be hindered. Actually, when the thickness is 20 × 10 ⁻⁶ m or more, it may cause a problem when displaying an image, but when it is 10 × 10 ⁻⁶ m or less, there is no problem.

  As a result, the liquid crystal panel 7 is not pushed during use and the display does not become abnormal or the liquid crystal panel 7 is not damaged.

From the result of Case 9.5, since the warp was irregular when the thickness of the second layer was 18 × 10 ⁻⁶ m, it was not possible to stably maintain the convex shape on the light source side with this thickness. It turned out to be sufficient. That is, it has been found that the effect of the present invention cannot be realized unless at least the second layer has a thickness of 20 × 10 ⁻⁶ m or more.

  In addition, it is well known to those skilled in the art that a plate material used for a backlight at a high temperature and a plate-integrated optical functional member that replaces the plate material require a thickness of at least 1.5 mm or more.

  In addition, it is known that a normal material expands by heating, but a material produced through a stretching process represented by PET is thermally contracted by heating. By utilizing this phenomenon, the convex shape on the light source side can be further stabilized. FIG. 2 shows the shape of the optical sheet removed from the display after the test. The optical sheets of cases 1 to 9.5 are all initially flat, but their shapes after removal are different. Of the materials used this time, only PET exhibits thermal shrinkage, but any of the convex shapes after removal had a surface with PET relative to the first layer. From this, it is clear that providing a layer having a higher thermal contraction rate than the first layer in the second layer makes it more likely to protrude toward the light source.

  As described above, according to the present invention, a plurality of optical elements are integrated from the viewpoints of reducing the number of members and improving the rigidity, and warp even under the influence of high heat. It is possible to realize an optical sheet with an integrated structure that can be convex toward the light source.

  Furthermore, by using such an optical sheet, a backlight unit and a display that do not cause abnormal display due to deformation of the optical sheet or damage to the liquid crystal panel even under the influence of high temperatures generated when the light source is turned on are realized. It becomes possible to do.

  The best mode for carrying out the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to such a configuration.

  As shown in the examples, the gist of the present invention is that the thickest first layer is a support, and the second layer shrinks more than the first layer at a high temperature on the exit surface side with respect to the first layer. By providing the optical sheet, it is possible to realize an optical sheet in which the light source side is naturally convex at a high temperature when the backlight is used, and the material and the type and shape of the optical functional member are not limited.

  Within the scope of the invented technical idea of the scope of claims, a person skilled in the art can conceive of various changes and modifications. The technical scope of the present invention is also applicable to these changes and modifications. It is understood that it belongs to.

The side view which shows the structural example of the optical sheet which concerns on embodiment of this invention. The figure which summarized the specific structural example and examination result of the examined optical sheet. The conceptual diagram which shows the structural example of the optical sheet formed by forming a cylindrical lens as an optical element. The perspective view which shows the structural example of the optical sheet formed by forming a cylindrical lens as an optical element. The perspective view which shows the structural example of BEF which is an optical sheet of a prior art. The schematic diagram for demonstrating the optical path control characteristic of the backlight unit using BEF. The graph which shows the optical path control characteristic of the backlight unit using BEF. The figure which shows the structural example of the display using the optical sheet of a prior art different type from BEF. The perspective view of the optical sheet of FIG. The schematic diagram for demonstrating the optical path control characteristic of the backlight unit using the optical sheet of FIG. The conceptual diagram which shows the structural example of the backlight unit formed by laminating | stacking several optical elements. The conceptual diagram which shows the structural example of the backlight unit using the integrated optical element which integrated the some optical element (when there exists a diffusion film). The conceptual diagram which shows the structural example of the backlight unit using the integrated optical element which integrated the some optical element (when there is no diffusion film).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical sheet, 2 ... Incident surface, 3 ... Output surface, 4-6 ... Optical element layer, 7 ... Liquid crystal panel, 10 ... Optical sheet, 12 ... Output surface, 13 ... Light-scattering layer, 14 ... Light reflection part, DESCRIPTION OF SYMBOLS 15 ... Light transmission part, 16 ... Unit convex cylindrical lens, 17 ... Lenticular sheet, 18 ... Adhesive layer, 19 ... Non-lens surface, 20 ... Light source, 21 ... Lamp house, 23 ... Light source, 26 ... Diffusing plate, 27 ... Reflection Plate, 30 ... Liquid crystal panel, 32 ... Diffusion film, 38 ... Optical film, 39 ... Transparent substrate, 40 ... Backlight unit, 42 ... Liquid crystal panel, 44 ... Unit lens, 46 ... Opening, 48 ... Reflector, 49 ... Polarizing plate, 70 ... Member, 72 ... Unit prism, 80 ... Diffusion film or DBEF, 81 ... Prism sheet or optical film, 82 ... Diffusion film, 83 ... Diffusion plate, 86 ... Integrated optical element

Claims (11)

At least one of the direction, range, color, and luminance distribution of the incident light between a substantially flat incident surface on which light from the light source is incident and an exit surface that is the surface opposite to the incident surface An optical sheet formed by laminating a plurality of optical element layers for controlling
An optical sheet obtained by disposing a second layer having a linear expansion coefficient lower than that of the thickest first layer among the optical element layers on the emission surface side of the first layer. The optical sheet according to claim 1, wherein a total thickness of the plurality of laminated optical element layers is 1.5 × 10 ⁻³ m or more. The optical sheet according to claim 1, wherein the second layer has a thickness of 20 × 10 ⁻⁶ m or more.   The optical sheet according to any one of claims 1 to 3, wherein the second layer has a thermal contraction rate larger than that of the first layer.   The optical sheet according to claim 1, wherein the first layer and the second layer are bonded.   The optical sheet according to claim 5, wherein the first layer and the second layer are bonded together by at least one of a pressure-sensitive adhesive, an adhesive, and excimer bonding.   The surface treatment of any one of claims 1 to 6, wherein at least one of antistatic treatment, scratch prevention treatment, antireflection treatment, and mat treatment is performed on the incident surface side of the first layer. The optical sheet according to 1.   7. The method according to claim 1, further comprising a treatment layer of at least one of an antistatic layer, a scratch prevention layer, an antireflection layer, and a mat treatment layer on the incident surface side of the first layer. The optical sheet according to item 1. The optical sheet according to claim 8, wherein the treatment layer has a thickness of 10 × 10 ⁻⁶ m or less. The optical sheet according to any one of claims 1 to 9,
A backlight unit including a light source that is disposed on the incident surface side of the optical sheet and supplies light incident from the incident surface. The backlight unit according to claim 10;
An image display element composed of a liquid crystal display element that defines a display image according to transmission / shading in pixel units,
The display is a cold cathode ray tube or LED.

Images