Optical film

Abstract

To provide an optical film that constitutes a film element or a sheet element with which it can be expected that front luminance at a light emission face of a direct-type point light source backlight unit and unevenness (homogeneity) of front luminance are made to meet the market needs.SOLUTION: There is provided an optical film mounted between a light source of a direct-type point light source backlight unit and a color conversion sheet. An irregular face is constructed on a side where light from the point light source is emitted from the optical film, and an optical waveguide layer (not including a porous layer) includes particulates for light diffusion and constitutes a layer between a light extraction layer and an optical waveguide introduction layer. The optical waveguide layer is a single triangle prism layer, and an apex angle side of the triangle prism of the triangle prism layer faces the light source, with a face on the apex angle side of the triangle prism constituting a second exposed face. A refractive index of the optical waveguide layer (not including the porous layer) is not smaller than either of the refractive index of the light extraction layer and the refractive index of the optical waveguide introduction layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a direct type point light source backlight unit and a liquid crystal device equipped with the direct type point light source backlight unit. [Background technology]

[0002] Liquid crystal devices are widely used in various information equipment, and based on their basic structure, they can be broadly classified into direct-light types, in which the light source is placed on the rear side of the liquid crystal panel mounted on the liquid crystal device, and edge-light types, in which the light source is placed near the side of the liquid crystal panel.

[0003] In recent years, there has been an increasing demand for thinner and lower-cost liquid crystal devices such as notebook PCs, tablets, car navigation systems, and smartphones. In addition, there is a demand for improved image quality and HDR (High Dynamic Range: expanding the range of brightness) compatibility. As a method for HDR compatibility, a method is being considered in which the light intensity of the backlight is adjusted in addition to the shutter function using liquid crystal by turning on and off the LEDs and adjusting the light intensity for each LED (local dimming) in a direct-type backlight. In the case of a direct-type device using a point light source such as an LED (Light Emitting Diode), there is a demand for increasing the light intensity on the light-emitting surface while at the same time increasing the uniformity of the luminance within the light-emitting surface, and there is also a demand for reducing costs by avoiding an increase in the number of parts.

[0004] To summarise, in order to respond to the multifaceted social needs of recent years, such as lower costs, lighter weight, thinner dimensions, higher brightness and better appearance (reduced unevenness in the brightness of the display screen), for notebook PCs, tablets, car navigation systems, smartphones and the like, the functions of direct-type backlight units using LEDs must be improved even more than before. 1) Reduction in manufacturing costs through the adoption of simple manufacturing methods 2) Reducing manufacturing costs by reducing the number of parts and types of materials and by utilizing common parts and materials. 3) In addition to making the parts themselves thinner, making the whole device thinner by adding multiple functions to each part 4) Uniformity and optimization of brightness on the light exit surface (reduction of brightness unevenness) 5) Higher front luminance at the light exit surface Efforts to improve and develop products from many different perspectives are required. Some of the above factors affect each other in complex ways, and in particular, the demand for uniform luminance (elimination of unevenness in the front luminance on the light exit surface) and the demand for high front luminance (increase in the amount of light exiting from the light exit surface) tend to be contradictory, so it is important to strike an excellent balance between them rather than attempting to improve only one side.

[0005] The basic configuration of a direct type point light source backlight unit in the prior art is generally as disclosed in Patent Document 1. The configuration is shown in Figure 1 of the same document. In terms of its functionality, in short, 1) the light emitted from the LED is once diffused in all directions by a light diffusion plate or light diffusion sheet that exhibits a light diffusion function (also called light guide), and then the light that has been diffused there and exits from the emission surface is collimated by a laminate of prism sheets that are separately arranged.

[0006] When searching the Japan Patent Office's online database with the keyword "direct-type point light source backlight unit," it is found that various proposals have been made to date to meet the above-mentioned social and technical demands for direct-type point light source backlight units among backlight units with such a basic configuration. Among such proposals, improvements in recent years have mainly focused on reducing unevenness in brightness while maintaining or improving the brightness at the light exit surface. These proposals can be broadly divided into those that focus on improving the LED light source itself (e.g., Patent Document 2) and those that focus on controlling the propagation direction of light emitted from the LED (e.g., Patent Document 3). In the latter case, development efforts are focused on reducing the amount of light incident on the light diffusion sheet (light diffusion film) and on increasing the diffusion function to diffuse the light incident on the light diffusion sheet (light diffusion film) as much as possible.

[0007] In recent years, the market has been demanding LCD screens that display colors more vividly than ever before, and in order to meet this demand, some direct-type point light source backlight units use color conversion films (color conversion sheets) such as QD films (quantum dot films) as their color generation source, which has become more common in recent years as the color display on LCD screens becomes more vivid than ever before. In such direct-type point light source backlight units, the blue light emitted from an LED point light source excites particles contained in a color conversion film such as a QD film, which generates red and green (RG) colors out of the three primary colors of RGB, and blue (B) color is generated by using the light of a blue LED itself. The tiny LED package used as a point light source in such a direct-type point light source backlight unit is formed by sealing a blue-emitting LED element with a sealing material, and further covering it with a microlens, but it is necessary to apply the blue light itself to a color conversion film such as a QD film, and therefore this sealing material does not contain fluorescent fine particles that are contained in the LED sealing material of an LED package that becomes a general white point light source. Therefore, the emitted light has a relatively high directivity and a narrow luminous flux width. In addition, the general configuration of such a direct-type point light source backlight unit equipped with a color conversion film such as a QD film is not a white LED point light source as a point light source, in which a fluorescent material is mixed into the sealing material of the LED package and a light diffusion functional member (which may be a single film or may be composed of multiple films) is placed on the upper side of the package, but a light diffusion functional member to be improved by the present invention is placed on the light emission side of a point light source composed of an LED package that does not have a fluorescent material in the sealing material, and a color conversion film such as a QD film is placed on the light emission surface side. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2013-073875 A [Patent Document 2] JP 2013-004408 A [Patent Document 3] International Publication No. 11 / 030594 Brochure DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0009] As mentioned above, the invention disclosed in Patent Document 2 focuses on improvements to LED light sources, and is an invention relating to a direct-type point light source backlight that uses a point light source with a light peak on the high-angle side. The basic premise is that a special LED with a light peak angle of ±50 to 80° is used as the point light source, and the negative factor of increased manufacturing costs is inevitably a problem.

[0010] Furthermore, the invention disclosed in Patent Document 3 cited in the same document focuses on improving the light diffusion performance of the light diffusion film by making the upper surface (light exit surface) of the light diffusion film into a waffle shape with an inverted pyramid-shaped recess. However, Patent Document 2 points out that this alone is insufficient, and it is necessary to use an LED with controlled light directivity of the light source itself (a special LED with a light peak angle of ±50 to 80°).

[0011] Among the various proposals made so far, some have involved inserting a separate light-diffusing functional component between the LED point light source and the light-diffusing film (or sheet) to change the directionality of the directional light from the LED. However, from the perspective of reducing the number of parts and the types of parts, reducing manufacturing costs by utilizing common parts and parts, or making the parts themselves thinner, as well as making the whole product thinner by giving one part multiple functions, it is difficult to say that these fully meet the social and technological needs mentioned above.

[0012] In addition, direct type point light source backlight units equipped with color conversion films such as QD film are quite recent, and therefore, while fully recognizing the above-mentioned issues specific to such direct type point light source backlight units, it appears that there is still no product that can meet the practical industrial issues of reducing manufacturing costs by adopting simple manufacturing methods, reducing the number of parts and types of materials, and reducing manufacturing costs by utilizing common parts and materials, and further reducing the thickness of the parts themselves as well as making the entire product thinner by making one part multifunctional, and that can also achieve an excellent balance between the demand for uniform luminance (elimination of uneven front luminance on the light exit surface) and the demand for high front luminance (increasing the amount of light exiting from the light exit surface).

[0013] Now, in a direct-type point light source backlight unit, when attempting to uniformize the brightness at the light exit surface while at the same time maintaining the amount of light from the light exit surface (preventing a decrease in light transmittance) or increasing the amount of exiting light (increasing the front brightness at the light exit surface), a commonly conceived approach would be to increase the content of light-diffusing microparticles contained within the light diffusion film in order to improve its light diffusion ability in order to uniformize the brightness at the light exit surface; however, doing so would result in a decrease in the amount of light exiting from the light exit surface of the direct-type point light source backlight unit.

[0014] Conversely, if you try to increase the amount of light emitted from the light exit surface of a direct-type point light source backlight unit, you will naturally need to reduce the amount of light-diffusing fine particles contained in the light diffusion film, but this will cause a strong eyeball-shaped lamp image (hot spot) to appear directly above the point light source, resulting in significant non-uniformity in the front brightness. As is clear from this simple simulation, uniforming the brightness at the light exit surface and maintaining the amount of light from the light exit surface (preventing a decrease in light transmittance) are mutually contradictory characteristics.

[0015] As a solution to this problem, it is possible to increase the number of point light sources used to increase the light source density, or to use a special point light source with a large peak angle of light from the point light source, but this would result in the inconvenience of a dramatic increase in manufacturing costs. Another option is to increase the distance between the light source and the light incident surface of the direct-type point light source backlight unit facing it, but this clearly creates a problem that contradicts the demand for a slimmer display. [Means for solving the problem]

[0016] In order to solve the above problems, the present inventors have made extensive research and efforts, and as a result, the above problems, particularly, 1) Reduction of manufacturing costs through manufacturing methods suitable for mass production 2) Reducing manufacturing costs by reducing the number of parts and types of materials and by utilizing common parts and materials. 3) In addition to making the parts themselves thinner, making the whole device thinner by adding multiple functions to each part 4) We discovered that it was possible to achieve an excellent balance between the need for uniformity and optimization of the brightness at the light exit surface (reduction of brightness unevenness) and the need to maintain the amount of light from the light exit surface (preventing a decrease in light transmittance) or increase the amount of light (increasing the front brightness at the light exit surface), and thus completed the present invention.

[0017] That is, the first invention is a direct-type point light source backlight unit in which an optical film is mounted between a light source and a color conversion sheet, the light source being composed of a blue LED package that does not have a fluorescent material in the sealing material of the LED package and arranged in a lattice shape at a predetermined pitch, and The optical film has an integral structure including an optical waveguide introduction layer on a light incident side, a light extraction layer on a light exit side, and an optical waveguide layer between the optical waveguide introduction layer and the light extraction layer, the light extraction layer has a first exposed surface on a surface side where light from the point light source is emitted from the optical film, the first exposed surface configuring an uneven surface with a random pattern, the optical waveguide layer includes light diffusing particles and constitutes a layer between the light extraction layer and the optical waveguide introduction layer; The optical waveguide introduction layer constitutes a single triangular prism layer and has a second exposed surface made of triangular prism surfaces in a regular pattern, the second exposed surface being disposed on the side where light from the point light source enters the optical film. It is characterized by: The optical waveguide introduction layer has a feature of changing one beam of light into two beams of light. The direct-type point light source backlight unit is characterized by the above.

[0018] The second invention is characterized in that, in the first invention, the cross-sectional shape of the prisms contained in the triangular prism layer is a triangular shape in a cross section perpendicular to the longitudinal direction, the triangular shape being an isosceles triangle, and the apex angle is 65 to 100 degrees.

[0019] A third invention according to the first or second invention is characterized in that the prisms having an isosceles triangular cross section are arranged at an array pitch of 20 to 100 μm.

[0020] The fourth invention is characterized in that, in any one of the first to third inventions, the mounting manner of the optical film is such that at least two of the optical films are stacked, each with the triangular prism layer facing the light source side, and the longitudinal directions of the prisms of the isosceles triangular cross section of the triangular prism layer are arranged so as not to coincide with each other.

[0021] The fifth invention is characterized in that, in the fourth invention, the arrangement is such that at least two of the optical films are stacked together and arranged so that the longitudinal directions of the prisms of the isosceles triangular cross section of the triangular prism layer are perpendicular to each other.

[0022] A sixth aspect of the present invention is a liquid crystal display device equipped with a direct type point light source backlight unit according to one of the first to fifth aspects of the present invention.

[0023] The seventh invention is characterized in that, in the sixth invention, the optical film is mounted in such a manner that at least two of the optical films are stacked on top of each other, with the triangular prism layer facing the light source side and the longitudinal directions of the prisms of the isosceles triangular cross section of the triangular prism layer not coinciding with each other.

[0024] According to an eighth aspect of the present invention, in the seventh aspect of the present invention, the arrangement is such that at least two of the optical films are stacked and arranged so that the longitudinal directions of the prisms of the isosceles triangular cross section of the triangular prism layer are mutually perpendicular. The liquid crystal display device is characterized in that Effect of the Invention

[0025] 1) The optical film according to the present invention can be obtained by a simple method suitable for mass production, in which a large-area continuous film is first integrally molded by a roll-to-roll production method, and then the continuous film is cut into pieces of required dimensions. From this perspective, the manufacturing cost can be reduced. 2) Furthermore, in a direct-type point light source backlight unit equipped with the optical film of the present invention, it is possible to achieve an excellent balance between the brightness and appearance (uniform brightness or elimination of brightness unevenness) at the light exit surface simply by stacking optical films of the same material and configuration so that the extension direction of the triangular prisms in the triangular prism layer is at a specified angle, which leads to a reduction in the number of parts and types of materials and a reduction in manufacturing costs by utilizing common parts and materials. 3) The optical film of the present invention has an integrated structure that includes an optical waveguide introduction layer that deflects the light incident from an LED light source to convert a single beam of light into two beams of light, an optical waveguide layer that diffuses the light from this optical waveguide introduction layer, and a layer that extracts the diffused light from this optical waveguide layer. This integrated structure is expected to enable the optical film to have multiple functions in one component, thereby making it thinner overall. 4) The direct-type point light source backlight unit of the present invention can be obtained simply by replacing the light diffusion sheet or film installed in a conventional direct-type point light source backlight unit (e.g., see FIG. 1), in which light from a point light source is directly incident on a light diffusion sheet or film, with the laminated optical sheet of the present invention (two-sheet laminated type or multi-layer type), making it easy to design and simple in structure. 5) According to the direct type point light source backlight unit of the present invention, it is important to achieve an optimal balance between the two opposing characteristics of the variation in brightness at the light exit surface and the front brightness, but this optimal balance can be achieved. 6) The above-mentioned effects 1) to 5) can be obtained either alone or in combination, and these effects can also be said to be true for a liquid crystal display device equipped with a direct-type point light source backlight unit according to the present invention.

[0026] Furthermore, when evaluating the properties of the optical film of the present invention, as described below, when a blue LED that does not use a fluorescent material as an LED encapsulant is used as a point light source in a direct-type point light source backlight unit equipped with a color conversion sheet, the optical film has the unique property that, when the haze increases on the light exit surface from the backlight unit, the front brightness increases, i.e., the front brightness and haze value on the light exit surface show a positive correlation. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a conceptual diagram showing a cross section of a direct-type point light source backlight unit according to the prior art, which is equipped with a color conversion film such as a QD film. [Diagram 2] FIG. 2 is a conceptual diagram showing a schematic enlarged cross section (particularly enlarged in the thickness direction) of an optical film (one sheet) constituting the laminated optical sheet according to the present invention. [Diagram 3] FIG. 3 is a photograph taken from directly above an example of a random pattern uneven surface on the surface (exposed surface) of the light extraction layer of the optical film according to the present invention (magnification is as shown in the figure). [Figure 4]FIG. 4 is a conceptual diagram showing a cross-sectional configuration of a direct type point light source backlight unit equipped with a laminated optical sheet according to the present invention. [Diagram 5] FIG. 5 diagrammatically shows the size and positional relationship between one cell and an LED point light source when the measurement range is divided during luminance measurement in the examples and comparative examples. [Figure 6] FIG. 6 shows a schematic diagram of the number of LED point light sources covered by one cell during measurement. [Figure 7] FIG. 7 is a graph showing the measurement data in Table 2, with the standard deviation of luminance on the vertical axis and the average luminance normalized with the average luminance of Comparative Example 1 set to 100 on the horizontal axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The optical film according to the present invention has a three-layer structure including a light extraction layer (top layer, light exit layer) as a first optical property layer, an optical waveguide layer (middle layer) as a second optical property layer, and an optical waveguide introduction layer (bottom layer, light entrance layer) as a third optical property layer, and these layers have the following characteristics and properties.

[0029] 1. Light extraction layer (top layer) (Manufacturing method / materials used) The method for producing the light extraction layer according to the present invention can be suitably adopted according to the method disclosed in Japanese Patent Application Laid-Open No. 6-59108 or Japanese Patent Application Laid-Open No. 2003-032074 filed by the same applicant. The outline of the method is to fix the first light diffusing fine particles to one side of the optical waveguide layer described in detail below with a light-transmitting organic adhesive, and more specifically, the kneaded product (mixture) of the first light diffusing fine particles and the light-transmitting organic adhesive is applied almost uniformly to one side of a resin film containing the second light diffusing fine particles described in detail below, and the kneaded product (mixture) is cured to fix the first light diffusing fine particles to the surface, and the first light diffusing fine particles (however, each fine particle is covered with a cured coating of the light-transmitting organic adhesive) fixed to the surface form a random pattern uneven surface. As the light-transmitting organic adhesive used here, at least one resin selected from polyester resin, acrylic resin, silicone acrylic resin, fluororesin, fluorine-acrylic resin, or a resin obtained by adding a crosslinkable resin having a curing function to these resins, or a curable resin such as a polyurethane resin or an epoxy resin, etc. It goes without saying that a curing method most suitable for the light-transmitting organic adhesive used can be appropriately adopted as a curing method for this kneaded product.

[0030] In this case, the mixing ratio (weight ratio or volume ratio) of the first light diffusing fine particles to the light-transmitting organic adhesive can be suitably used such that after the light-transmitting organic adhesive is cured, at least a part of the light diffusing fine particles form unevenness on the surface together with the cured body (cured film) of the light-transmitting organic adhesive. Specifically, the mixing ratio is such that Ssk (skewness: degree of bias), which is an index of the profile shape characteristics of the unevenness on the surface, is preferably 3.0 or less, more preferably 1.40 to 2.30, and the Haze value of only the light extraction layer is preferably within the range of 20% to 70%, more preferably 40% to 60%. However, such a numerical range may be influenced by other variable factors such as the arrangement pitch of the LED light source mounted in the direct-type point light source backlight unit and the characteristics of the Lambertian distribution of the light emitted from the light source, so such numerical values ​​are merely a reference level, and it goes without saying that any numerical range can be used as long as the effects of the present invention can be obtained as a whole.

[0031] By employing the above-described simple method as the method for forming the light extraction layer according to the present invention, the process can be simplified, and the manufacturing cost can be reduced.

[0032] In addition to the above-mentioned coating method, other possible methods for forming the random pattern uneven surface on this surface include a method in which a mold (master) with an inverted uneven shape having the desired specified Ssk value is prepared, and a thermosetting resin or ultraviolet-curing resin is poured between this mold and one side of the light diffusion film that constitutes the light guide layer described below, and then the resin is cured to transfer the shape of the master to one surface of the light diffusion film that constitutes the light guide layer, a method in which the shape of the master is transferred to one surface of the light diffusion film by heat pressing, or a method in which the surface of the light diffusion film is directly roughened by a method such as sandblasting.

[0033] Although the technical scope of the present invention is not limited in any way, the presence of the first fine particles for light diffusion is not essential, and as long as the purpose and function of the light extraction layer constituting a part of the present invention can be obtained by providing a randomly uneven surface, a configuration without the first fine particles for light scattering can be suitably used. From a general optical viewpoint, when two substances with different refractive indices are in contact with each other at an interface, when light traveling from one substance A to the other substance B hits the interface, a phenomenon occurs in which part of the light is refracted at the interface and propagates into substance B, and part of the remaining light is reflected at the interface and returns to the direction of substance A. Therefore, if the light extraction layer does not exist and the light exit surface of the optical waveguide layer is exposed (in contact with the atmosphere), it can be said that the reflection phenomenon (reflection into the optical waveguide layer) occurs on the back side of the light exit surface (the inner surface of the optical waveguide layer) due to the difference between the refractive index of the atmosphere (1.0) and the refractive index of the resin used in the optical waveguide layer (1.58 when polycarbonate is used) (the greater this difference, the greater the loss of the amount of emitted light due to reflection into the optical waveguide layer). However, the fine structure of this light extraction layer is complex, and some of the first fine particles for light diffusion protrude beyond the thickness of the resin binder that fixes them, and the protruding parts are covered with an extremely thin film of the fixing resin binder, so the propagation behavior of the light passing through them is extremely complex. Furthermore, coupled with the fact that there may be parts only of the fixing resin binder, a phenomenon that cannot be predicted by the general light refraction and reflection phenomenon at the boundary surface has appeared. As a result, as will be described in detail below, when the haze value of the light extraction layer is increased, and an optical film of the present invention having such a light extraction layer is placed directly above the light source of a direct-type point light source backlight unit equipped with a color conversion film, the front luminance at the light exit surface of the backlight unit increases, resulting in a poor appearance (the standard deviation from the average front luminance becomes large), so in some cases, making the refractive index of the light extraction layer higher than the refractive index of the optical waveguide layer (increasing the amount of reflected light at the boundary surface) may provide the preferable effect sought by the present invention.

[0034] As the first fine particles for light diffusion, fine particles made of at least one material selected from inorganic materials such as glass and silica, and organic materials such as urethane, polyamide, polycarbonate, polymethyl methacrylate, polyacrylonitrile, polyester, silicone, polyethylene, epoxy, melamine-formaldehyde condensate, benzoguanamine-formaldehyde condensate, or benzoguanamine-melamine-formaldehyde condensate can be preferably used, but fine particles such as urethane, polyamide, polycarbonate, and more preferably polymethyl methacrylate can be preferably used. However, in selecting the material, it goes without saying that any material can be used as long as the refractive index of the material is close to the refractive index of the resin so that the diffuse reflection due to the difference between the refractive index of the material and the refractive index of the resin constituting the light extraction layer does not increase in the environment in which the optical film according to the present invention is used.

[0035] Furthermore, the particle size is preferably about 1 to 20 μm, and more preferably about 5 to 15 μm. If the particle size is less than 1 μm, the light extraction function of the light extraction layer in the present invention (the extraction function meaning the function of extracting light diffused in the optical waveguide layer described in detail below from the light exit surface) is insufficient. Also, although it depends on the viscosity of the light-transmitting organic adhesive used and the mixing ratio of the first light-diffusing fine particles, if the particle size is large, it becomes difficult to control the Ssk of the surface (exposed surface, light exit surface) after the light-transmitting adhesive described below hardens and the first light-diffusing fine particles are fixed, making coating more difficult. Furthermore, the layer thickness of the entire optical film becomes too thick. Therefore, the upper limit of the particle size range that can express the characteristics of the present invention is considered to be about 20 μm. However, it is considered that any particle size can be suitably adopted as long as the same effect as the optical film of the present invention can be obtained.

[0036] Generally, when light enters from one optical material to another at the boundary between two optical materials with different refractive indices, due to the difference in the refractive indices of the two materials, not all of the light is refracted at the interface as it propagates into the other optical material. If the angle of incidence becomes large, a phenomenon occurs in which part of the light is reflected at the interface and returned to one of the optical materials.

[0037] In short, the function of the light extraction layer is to refract light at the interface between the light extraction layer and the optical waveguide layer, thereby allowing light that has propagated from one material toward the interface to propagate into the other material. However, the light extraction layer contains light-diffusing microparticles, and the presence of these microparticles causes light to propagate in a much more complex manner than if this layer were made of a single resin. Therefore, in order to optimize the amount of light that reflects from the optical waveguide layer at the interface and returns to the optical waveguide layer as required by the present invention, it may be necessary to find the right combination of material configurations and refractive indices to be used by trial and error.

[0038] As the light-transmitting organic adhesive, at least one resin selected from urethane resin, polyether resin, polyester resin, acrylic resin, silicone acrylic resin, fluorine resin or fluorine-acrylic resin, urethane-acrylic resin, etc., or a crosslinkable resin based on these resins, such as ultraviolet curing, electron beam curing, heat curing, isocyanate curing, and amine epoxy curing, or a mixture thereof, can be suitably used. In some cases, it is also considered that a thermoplastic resin can be used. As described above, in view of the fact that the propagation of light at the interface between the light extraction layer and the optical waveguide layer shows a complex behavior, the refractive index should be appropriately selected in relation to the refractive index of the resin used in the optical waveguide layer, and any value can be suitably used as long as the propagation behavior does not deviate from the purpose and intent of the present invention.

[0039] (Features / Characteristics) The mixing ratio of the light-diffusing fine particles to the light-transmitting organic adhesive is such that after the light-transmitting organic adhesive is cured, at least a part of the light-diffusing fine particles combine with the cured body (cured film) of the light-transmitting organic adhesive to form unevenness on the surface. The mixing ratio is such that Ssk (skewness: degree of deviation), which is an index of the profile shape characteristics of the unevenness on the surface, is preferably 3.0 or less, more preferably 1.40 to 2.30. However, such a numerical range may be influenced by other variable factors such as the arrangement pitch of the LED light sources mounted in the direct-type point light source backlight unit and the characteristics of the Lambertian distribution of the light emitted from the light source, so such numerical values ​​are merely for reference, and it goes without saying that any numerical range can be used as long as the effects of the present invention can be obtained as a whole.

[0040] The light extraction layer is characterized not only by the above-mentioned surface irregularity characteristics, but also by the composite refractive index of the light extraction layer finally obtained by curing the adhesive being within the range of 1.30 to 1.70, preferably within the range of 1.45 to 1.55, and the haze value of the entire light extraction layer (composite of resin and light diffusing fine particles) being within the range of 20% to 70%, preferably within the range of 40% to 60%. In view of the fact that the main function of the first light diffusing fine particles in the light extraction layer is light diffusion and light scattering as described above, the mixing amount (see FIG. 3) of the first light diffusing fine particles contained in the light extraction layer is preferably selected so that the first light diffusing fine particles form a single layer (a state in which the fine particles do not overlap each other) on the light exit surface of the optical waveguide layer, without any limitation to the scope of the invention.

[0041] The main function of the light extraction layer included in the present invention is to improve the front luminance at the light exit surface (increase in luminance), and has the following three functions. (1) Light is extracted from the optical waveguide layer, which will be described in detail below; that is, the light diffused in all directions by the optical waveguide layer is returned to the front, thereby improving the front brightness. (2) Promoting the guiding of light (diffusion of light) by the optical waveguide layer described in detail below, thereby increasing the amount of light emitted from a point other than the point directly above the point light source. (3) It has the effect of preventing a significant decrease in front luminance by suppressing light absorption and loss.

[0042] 2. Optical waveguide layer (intermediate layer) (Manufacturing method / materials used) The optical waveguide layer is preferably made of a milky white translucent plastic film, and can be manufactured by the same manufacturing method as that of a general light diffusing film, specifically, before forming a transparent resin into a film or sheet, inorganic fine particles such as titanium oxide, barium sulfate, calcium carbonate, aluminum hydroxide, magnesium carbonate, or aluminum oxide, or organic fine particles such as urethane, polyamide, polycarbonate, or silicone (second fine particles for light diffusion) are added to the transparent resin to obtain a pellet so as to be milky translucent, and the pellet is formed into a film by a film extrusion molding method (T-die method). As the second fine particles for light diffusion, those having the same chemical composition (type) as the above-mentioned first fine particles for light diffusion (however, powder properties such as particle size and particle size distribution may differ) can be used, but silicone fine particles are preferably used.

[0043] From the viewpoint of the light guiding ability of the optical waveguide layer, the resin of the above-mentioned plastic film constituting the optical waveguide layer is preferably a transparent resin such as polycarbonate, polymethyl methacrylate, or a styrene-methyl methacrylate copolymer, the refractive index of which is suitable for the present invention. From the viewpoints of reliability and availability, however, polycarbonate is more preferably used.

[0044] When selecting a resin for the above plastic film, it is necessary to consider the components of the backlight unit. When using white LEDs as point light sources, it is sufficient to select taking into consideration the light transmittance of only visible light. However, when using a configuration that uses a QD film or a color conversion film that uses phosphors, light with wavelengths shorter than that of visible light is also converted into visible light, so it is necessary to select a resin that absorbs less short-wavelength light.

[0045] With regard to the thickness of the plastic film constituting the optical waveguide layer, from the viewpoint of improving the optical waveguide effect, it can be said that the thicker the film, the better. However, there are also constraints from the viewpoint of making the entire backlight unit thinner. Also, from the viewpoint of the roll-to-roll production method that is preferably adopted as the manufacturing method for the optical film of the present invention, a thickness of approximately 400 μm is considered to be the maximum.

[0046] The content of the fine particles contained in the optical waveguide layer is not particularly limited as long as it is within the range in which the effects of the present invention can be obtained, but a content that makes the haze value of the optical waveguide layer alone preferably fall within the range of 25% to 85%, more preferably within the range of 50% to 70% is preferably adopted. Also, although there is no direct one-to-one correspondence with these numerical ranges, from the viewpoint of weight percent, it is empirically preferable that the content be 5 weight percent or less, more preferably 1 weight percent or less, relative to the weight of the plastic constituting the optical waveguide layer.

[0047] As for the type of such fine particles, basically any fine particles can be used as long as they have a light diffusing function and can obtain the effects of the present invention. However, when a color conversion film using a QD film or a phosphor is used in the backlight unit, light with a shorter wavelength than the wavelength of visible light is also converted into visible light, so it is necessary to use fine particles that absorb little short-wavelength light. From this point of view, it is preferable not to select TiO2 particles because they have absorption on the short-wavelength side.

[0048] (Features / Characteristics) The refractive index of the plastic constituting the optical waveguide layer is automatically determined when the type of plastic to be used is determined, but in the present invention, as described above, polycarbonate can be preferably used, and in this case, the nominal refractive index is 1.58. Note that in the optical waveguide layer according to the present invention, the above-mentioned second fine particles for light diffusion are dispersed in this polycarbonate.

[0049] The optical film according to the present invention has a feature that the refractive index of the plastic constituting the optical waveguide layer and the refractive index of the plastic constituting the optical waveguide introduction layer, which will be described in detail below, can be controlled independently of each other.

[0050] The function of the optical waveguide layer included in the present invention is to provide light diffusion, and has the following three functions. 1) By guiding light in all horizontal directions along the optical waveguide layer, the amount of light in places other than directly above the LED point light source is increased. 2) By scattering the guided light, the amount of light emitted from the front is increased in places other than directly above the LED point light source. 3) By suppressing light absorption and loss, a significant decrease in front brightness is prevented.

[0051] 3. Optical waveguide introduction layer (bottom layer) (Manufacturing method / materials used) The optical waveguide introduction layer included in the present invention can be formed from any resin as long as it is transparent, and is suitably formed by applying such a resin in an uncured state onto one side of the plastic film constituting the optical waveguide layer, and pressing it against a forming roller on the surface of which a pattern of fine prisms (prisms with a cross section of an approximately isosceles triangle) arranged in parallel in one direction is formed, thereby transferring the uneven shape of the roller surface. The resin to be used is preferably polycarbonate resin, urethane resin, polyether resin, polyester resin, acrylic resin, silicone acrylic resin, fluorine resin or fluorine-acrylic resin, urethane-acrylic resin, etc., or at least one resin selected from ultraviolet-curable, electron-beam-curable, heat-curable, isocyanate-curable, and amine-epoxy-curable crosslinkable resins based on these resins, or a mixture thereof. In some cases, it is considered that a simple thermoplastic resin can also be used. As a variation of the manufacturing method, a suitably selected resin is molded into a film and surface-bonded to one side of the plastic film that constitutes the optical waveguide layer described above, and a molding roll having a pattern of fine prisms (prisms with a cross section of approximately isosceles triangles) arranged in one direction on the surface is used to transfer the prism pattern with a cross section of approximately isosceles triangles to the surface of the molded film that has been surface-bonded.

[0052] The optical film according to the present invention has a feature that the refractive index of this optical waveguide introduction layer (the refractive index of the resin constituting the optical waveguide introduction layer) and the refractive index of the optical waveguide layer adjacent thereto in a planar manner (the refractive index of the resin used in the optical waveguide layer) can be controlled independently of each other.

[0053] In this case, the apex angle of the triangle in the prism having an approximately isosceles triangular cross section is preferably 60° to 100°, more preferably 70° to 90°, and most preferably 75° to 85°, but the apex does not necessarily have to be the intersection of two straight lines, and may be somewhat rounded or have a slightly flat surface as long as the effects of the present invention are obtained. Also, the apex may have a small recess (recess) and a small protrusion (protrusion) of approximately isosceles triangular cross section formed therein.

[0054] The arrangement pitch of the prisms having an approximately isosceles triangular cross section cannot be uniformly determined in relation to the arrangement pitch of the LED point light sources mounted in a direct-type point light source backlight unit; however, in the case of a typical arrangement pitch of LED point light sources, it is preferably 20 to 100 μm; however, if a single ray of light entering the triangular prism layer (light guide introduction layer) from the LED point light source is branched or deflected by the triangular prism layer, and the effect of light appearing to be emitted from two or more light sources is obtained at the light emission surface from the triangular prism layer, a pitch exceeding this range may be used; further, in consideration of the principles of light refraction, even if a random mixture of triangular prisms having similar cross-sectional shapes but different cross-sectional sizes is formed, the same effect of light appearing to be emitted from two or more light sources can be obtained, and therefore such an embodiment can also be suitably applied.

[0055] (characteristic) The optical film according to the present invention has the characteristic that the refractive index of the optical waveguide introduction layer (the refractive index of the resin constituting the optical waveguide introduction layer) and the refractive index of the optical waveguide layer in planar contact therewith (the refractive index of the resin used in the optical waveguide layer) can be controlled independently of each other, but there may be a difference in the refractive index between these layers, or they may be the same.

[0056] On the premise that the present invention does not restrict its technical scope in any way, it is considered that the remarkable effect is exhibited when combined with a special point light source in which the width of the light flux from the blue LED point light source used in a direct-type point light source backlight unit equipped with a color conversion film such as a QD film is narrow and the directivity of the light is extremely high, and the mechanism is assumed to be that the propagation direction of the light is divided and branched (deflected) into multiple parts by a geometric shape such as the triangular prism layer used in the light guide introduction layer, and the branched light is propagated through functional layers each having a different diffusion function to eliminate the unevenness of the final front brightness. Therefore, the branching (deflection) phenomenon of the optical axis due to the shape of the surface unevenness on the light incident surface side of the light guide introduction layer is a very important factor. Even with a similar shape, it is also possible to change the deflection angle by increasing the refractive index and further promote the guide of light. From this perspective, it can be said that the optical waveguide introduction layer can be suitably used regardless of the shape of its exposed surface or the material thereof, as long as it can split and branch (deflect) the propagation direction of light into multiple parts and the branched light can propagate through a functional layer having a diffusion function.

[0057] The optical waveguide introduction layer included in the present invention is intentionally interposed between the LED point light source and the above-mentioned optical waveguide layer, and has the following three functions in a direct-type point light source backlight unit equipped with a color conversion film such as a QD film: (1) Reduce the amount of light (frontal light) in the vicinity of 0° directly above the LED point light source. (2) By deflecting the highly directional light from an LED point light source to any angle, it is possible to promote the guidance of light emitted from the optical waveguide introduction layer to the optical waveguide layer. (3) By suppressing the absorption and loss of light from the LED point light source, it has the effect of preventing a significant decrease in front brightness.

[0058] Incidentally, the interface between each layer prepared by the above-mentioned manufacturing method and having the above-mentioned characteristics is not necessarily required to be flat, and it goes without saying that even if it has fine waves, it can be suitably adopted as long as it does not go beyond the scope of the object and purpose of the present invention.

[0059] 4.Laminated optical sheet (two-layer type) (Production method) A laminated optical sheet is obtained by stacking two (or more) of the optical films described above in detail (optical films consisting of three layers, a light extraction layer, an optical waveguide layer, and an optical waveguide introduction layer, and having the same configuration) in such a manner that the prism layer with a cross section of approximately isosceles triangle that constitutes the optical waveguide introduction layer faces the light source side. In this case, the method of stacking can be preferably adopted such that the longitudinal directions of the prisms with a cross section of approximately isosceles triangle of the triangular prism layer are mutually orthogonal. Note that it is also preferably adopted to fix the stacked optical films in some way so that the relative positions do not change.

[0060] 5. Direct-type point light source backlight unit and liquid crystal display device of the present invention (Production method) In a conventional direct-type point light source backlight unit equipped with a color conversion film such as a QD film, the light diffusion film or sheet that is mounted so as to directly receive light from the point light source (i.e., so that there is an air layer between it and the point light source) is simply replaced with the laminated optical sheet (at least two sheets laminated) of the present invention, that is, without increasing the number of parts, a direct-type point light source backlight unit and a liquid crystal display device that exhibit the remarkable effects of the present invention can be obtained. EXAMPLES

[0061] An embodiment in which the optical films according to the present invention are stacked to form a laminated optical sheet and mounted in a direct-type point light source backlight unit will be described in detail below.

[0062] 1. Configuration of a direct-type point light source backlight unit according to the present invention (cross-sectional conceptual diagram): The cross-sectional structure of the direct type point light source backlight unit used in the evaluation of the examples is as shown in the conceptual diagram in Fig. 4. In the part corresponding to the bottom layer in the diagram, blue LED point light sources are arranged at a predetermined pitch (generally in a grid pattern), on top of which a laminated optical sheet in an embodiment in which two optical films according to the present invention are stacked is arranged parallel to a plane passing through all of the LED point light sources, on top of which a series of sheet-like bodies including a color conversion sheet are arranged in the same arrangement as in the conventional type, and on the topmost layer a diffuser is arranged to constitute a direct type point light source backlight unit according to the present invention.

[0063] 2.LED point light source (470): The LED used was manufactured by EPISTER (model number: ES-FFBCPE05C), and the driving current during use was 11.4 mA, and the driving voltage was 30 V. As the light source of the direct-type point light source backlight unit according to the present invention, blue LED point light sources (470) using the above-mentioned LED elements were used, arranged in a grid pattern of 20 x 20 with a pitch of 2.5 mm x 2.5 mm. The light quantity characteristics at this time were set as follows when measured from the front. Maximum Brightness: 16494.747 cd / cm2 Minimum Luminance: 204.847 cd / cm2 Min / Max Brightness: 1.24% Average brightness: 821.365 cd / cm2 Standard deviation: 1.7980

[0064] 3. Laminated optical sheet (laminated type of optical film 450 and optical film 450): A laminated optical sheet obtained by stacking two optical films (450, 460) according to the present invention as described above, with the extension directions of the triangular prisms of the triangular prism layer being perpendicular to each other, was placed on the blue LED point light sources arranged as described above. The distance from the upper end of this blue LED point light source to the plane formed by the apexes of the triangular prisms of the lower optical film (in FIG. 4 ) constituting the laminated optical sheet according to the present invention was intentionally set to almost zero so that hot spots on the light emission surface of the direct-type point light source backlight unit equipped with the laminated optical sheet are most likely to appear (i.e., so that comparison and examination can be performed under the worst conditions), but during actual use, it can be appropriately set in consideration of the total thickness required for the direct-type point light source backlight unit.

[0065] The pitch of the triangular prisms in this triangular prism layer (reference number 230 in FIG. 2) is 41 μm. The apex angle of the triangular prisms in the triangular prism layer is 80°. The resin constituting a part of this triangular prism layer (reference number 210 in FIG. 2) is an acrylic resin. Its refractive index after curing is 1.58.

[0066] The resin used for the optical waveguide layer constituting a part of the two optical films according to the present invention constituting the laminated optical sheet is polycarbonate resin. The thickness of this optical waveguide layer is 200 μm.

[0067] The second microparticles for diffusing light dispersed and contained within the optical waveguide layer are silicone microparticles, which are dispersed microparticles with a refractive index of 1.42 and an average particle size of approximately 4 μm, are roughly spherical, and their content is such that the haze value of the optical waveguide layer alone is 58%.

[0068] The resin (reference number 210 in FIG. 2) that fixes the particles in the light extraction layer of the optical film is an acrylic urethane resin, which has a refractive index of 1.52 after curing, into which light diffusing particles (reference number 200 in FIG. 2) with a refractive index of 1.49 are fixed. The haze value of the light extraction layer alone in this case is 45%. Sa and Ssk, which are roughness indexes of the uneven surface of the random pattern of the light extraction layer, are 1.74 and 1.92, respectively.

[0069] 4. Color conversion sheet (reference number 440 in Figure 4): A color conversion film (440) is placed on top of the laminated optical sheet described above, with a specified gap between them, and is laminated with a specified functional film material. The light exit surface of the lower optical film, designated by reference number 480 in FIG. 4, is an uneven surface, and the lower surface of the upper optical film, designated by reference number 470, placed above it, has triangular prisms protruding from it, and is placed so that the protrusions do not bite into the uneven surface of the lower optical film. The configuration and mutual spacing of the 3M BEFs (420, 430) placed above the light exit surface of this color conversion film (440) are the same as those in the conventional direct-type point light source backlight unit. Comparative Example

[0070] Comparative Example 1: A direct-type point light source backlight unit was constructed and evaluated using the same conditions as in the above examples, except that a conventional optical film was used in which only the triangular prism layer was removed from the optical film configuration used in the above examples.

[0071] Comparative Example 2: Instead of the optical film used in the above examples, a direct-type point light source backlight unit was constructed and evaluated using the same conditions as in the above examples, except that the light exit layer and the light input layer were made of a three-layer structure different from the material composition of the light extraction layer of the optical film used in the above examples (see Table 1), and the optical waveguide layer was made of a transparent PET (polyethylene terephthalate) layer (not containing light-diffusing particles) with a thickness of 188 μm, so that the front brightness was as close as possible to the front brightness in the examples. Note that the configuration of Comparative Example 2 is conceptually a configuration that applies the configuration of the invention disclosed in JP-A-6-59108 by the same applicant.

[0072] Comparative Example 3: The optical films used were the same as those used in the examples, but when two of them were stacked and mounted, they were inverted upside down and stacked so that the triangular prism layer of each optical film faced the light exit surface side to form a direct-type point light source backlight unit and evaluate it.

[0073] Detailed data on the configurations of the above-mentioned Examples and Comparative Examples are shown in the table below. TIFF2025013837000002.tif25278

[0074] In the above configurations of the example and comparative example, the luminance at each pixel point on the light exit surface (light exit surface from the diffuser) was measured under the following conditions. The luminance measuring device used was a two-dimensional luminance and chromaticity measuring device, ACE3-2000, manufactured by Hyland. The measurement conditions were as follows: Measurement range: Area equivalent to 8 x 8 LED point light sources placed in the center of the backlight unit (rectangular area with each side measuring approximately 17.5 mm) Number of divisions: 64 x 64 (total 4096 cells) Compression: 0% (no compression) Measurement size: 4 pixels (1 pixel is 1 pixel of the measurement camera) Measurement area (measurement position): Center of 64 x 64 cells Shutter speed: Auto (high dynamic sampling mode) The relative size relationship between the LED point light sources and the divided cells is as shown in FIGS.

[0075] The appearance evaluation (evaluation of the degree of elimination of uneven brightness) was performed by taking the average brightness value of the 4096 cells as the evaluation value of front brightness and its standard deviation as the evaluation value of appearance. The evaluation results are shown in the table below. TIFF2025013837000003.tif25060

[0076] As is clear from the above comparison data, the average luminance of the Example is slightly higher than that of the Comparative Example (0.24% higher than that of the Comparative Example), and at the same time, the standard deviation value of the luminance (i.e., the variation (appearance evaluation factor)) is reduced from 202.318 to 178.901. In other words, the Example has improved appearance while maintaining the luminance compared to the Comparative Example.

[0077] The measurement data in Table 2 above is plotted on a graph in Fig. 7, with the standard deviation of brightness on the vertical axis and the average brightness normalized to the average brightness of Comparative Example 1 set at 100 on the horizontal axis. It is clear from Fig. 7 that the example maintains almost the same average brightness as Comparative Example 2, while improving the appearance indicated by the standard deviation.

[0078] Although the present invention has been described in detail above based on the representative embodiments, it goes without saying that various variations may be adopted without departing from the scope of the object and spirit of the present invention. [Industrial Applicability]

[0079] The laminated optical sheet, the backlight unit, and the liquid crystal display device according to the present invention can be used for digital signage in the display devices of various digital devices. [Explanation of symbols]

[0080] 1: Direct-type point light source backlight unit using conventional technology 100: Diffuser 110: 3M BEF (The triangular prism faces upwards and its extension direction is parallel to the paper surface) 120: 3M BEF (The triangular prism faces upwards and its extension direction is perpendicular to the paper surface) 130: Color conversion film 140: BLT 150: Light diffusion sheet 160:Blue LED light source 2: Optical film of the present invention 200: Microparticles fixed to the light extraction layer 210: Resin for light extraction layer (after hardening) 220: Optical waveguide layer 230: Optical waveguide introduction layer (extension direction of triangular prism is perpendicular to the paper surface) 4: Cross-sectional conceptual diagram of a direct-type point light source backlight unit of the present invention 410: Diffuser 420: 3M BEF (The triangular prism faces upwards and its extension direction is parallel to the paper surface) 430: 3M BEF (The triangular prism faces upwards and its extension direction is perpendicular to the paper surface) 440: Color conversion film 450:BLT 460: The optical film of the present invention arranged on the upper side (see FIG. 2). As described in the specification, it has a three-layer structure, and is composed of a light extraction layer, a light guide layer, and a light guide introduction layer (the extension direction of the triangular prisms in the triangular prism layer is parallel to the paper surface) from top to bottom of the paper, but the three-layer structure is not shown in the drawing. In addition, the internal structures of the light extraction layer and the light guide layer are not shown. 470: The optical film of the present invention arranged on the lower side (see FIG. 2). As described in the specification, it has a three-layer structure, and is composed of a light extraction layer, a light guide layer, and a light guide introduction layer (the extension direction of the triangular prisms in the triangular prism layer is perpendicular to the paper surface) from top to bottom of the paper, but the three-layer structure is not shown in the drawing. In addition, the internal structures of the light extraction layer and the light guide layer are not shown. 480:Blue LED point light source 500: 1 cell range 510:Blue LED point light source 520: 1 measurement size (4 pixels) 600: Full measurement range (64 x 64 cells) 610: Enlarged view of the area covering four LED point sources in the total measurement range 620: One cell (corresponding to reference number 500 in Figure 5) 630: Corresponding to reference number 520 in Figure 5 (one measurement size (4 pixels)) 640: Individual blue LED point light source (corresponding to reference number 510 in FIG. 5)

Claims

1. An optical film to be mounted between a light source of a direct-type point light source backlight unit and a color conversion sheet, The optical film has an integral structure including an optical waveguide introduction layer on a light incident side, a light extraction layer on a light exit side, and an optical waveguide layer between the optical waveguide introduction layer and the light extraction layer, the light extraction layer has a first exposed surface on a surface side where light from the point light source is emitted from the optical film, the first exposed surface configuring an uneven surface with a random pattern, the optical waveguide layer (excluding the porous layer) contains light diffusing particles and constitutes a layer between the light extraction layer and the optical waveguide introduction layer; the optical waveguide introduction layer is a single triangular prism layer, an apex side of a triangular prism of the triangular prism layer faces the light source, and a surface of the triangular prism on the apex side constitutes a second exposed surface; The refractive index of the optical waveguide layer (excluding the porous layer) is not smaller than either the refractive index of the light extraction layer or the refractive index of the optical waveguide introduction layer. An optical film characterized by:

2. The shape of the prisms included in the triangular prism layer in a cross section perpendicular to the longitudinal direction is an isosceles triangle, and the apex angle is 65 to 100 degrees.

2. The optical film according to claim 1 .

3. The arrangement pitch of the prisms is 20 to 100 μm.

3. The optical film according to claim 1 or 2.

4. The optical film is mounted by stacking at least two of the optical films, with the triangular prism layer facing the light source side and the longitudinal directions of the prisms of the triangular prism layer being arranged so as to be perpendicular to each other.

4. The optical film according to claim 1, wherein the optical film is a polyimide film.

5. A direct-type point light source backlight unit comprising the optical film according to any one of claims 1 to 4.

6. A liquid crystal display device equipped with the direct type point light source backlight unit according to claim 5.

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