Optical film and manufacturing method therefor, display device, and method for evaluating extent of particle aggregation

Abstract

This optical film (1) is provided with: a first layer (11) containing inorganic particles and a base resin for incorporating and retaining the inorganic particles; and a second layer (12) overlaid on the first layer (11). With this optical film (1), given that a STEM image by an acceleration voltage of 30 kV in a cross-section along the thickness of the first layer (11) is converted into a binarized image in which 1 μm is equivalent to 1010 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binarized image, an average value A of the proportion of the area that the inorganic particles occupy in each of 80 partial regions into which the rectangular region has been equally divided is computed, and the standard deviation σ of the proportion of the area that the inorganic particles occupy in each of the partial regions is computed, then σ / A is between 19% and 34% inclusive.

Description

Optical film and manufacturing method thereof, display device, and method for evaluating particle aggregation degree

[0001] The present disclosure relates to an optical film, a manufacturing method thereof, a display device, and a method for evaluating the degree of particle aggregation.

[0002] As disclosed in KR101871552B1, an optical film is conventionally known which includes two layers having different refractive indices and has an uneven interface between the two layers.

[0003] The optical film is incorporated into a display device including a display panel such as a liquid crystal panel, an organic EL panel, etc. In this case, the optical film controls the traveling direction of light from the display panel by, for example, refracting or reflecting the light at the interface having the concave-convex shape, in order to improve the viewing angle characteristics of the display device.

[0004] The optical film may contain fine particles. For example, particles of zirconia, titania, etc. may be contained in the optical film to increase the refractive index. Furthermore, particles of silica, etc. may be contained in the optical film to decrease the refractive index.

[0005] The present inventors have discovered that when fine particles such as those described above are incorporated into an optical film, the optical film may exhibit, for example, a lower total light transmittance or higher haze than expected. Through extensive research, the present inventors have found that the values ​​of total light transmittance and haze vary significantly depending on the particle aggregation (bias). The present inventors have then identified conditions under which the decrease in total light transmittance and increase in haze due to particle inclusion can be suppressed, even when particles are incorporated. As described above, when two layers with different refractive indices are overlapped, light transmits more slowly than when a single layer is used, and the light control performance may be significantly impaired due to increased haze. Therefore, in an optical film having a layer structure of two or more layers, it is desirable to have each layer function as desired as much as possible.

[0006] The present disclosure has been made in light of the above circumstances, and its object is to suppress a decrease in the total light transmittance and an increase in haze of a film even when particles are contained in the film.

[0007] The embodiments of the present disclosure relate to the following [1] to

[19] .

[0008] [1] An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section of the first layer in the thickness direction at an acceleration voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 1010 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is equally divided into 80 partial regions, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, whereby σ / A is 19% or more and 34% or less.

[0009] [2] An optical film comprising: a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section of the first layer in the thickness direction at an acceleration voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 505 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is equally divided into 80 partial regions, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, whereby σ / A is 6% or more and 20% or less.

[0010] [3] An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer that is overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted into 256 gradations, the gradation values ​​of the converted STEM image are averaged for each 50 nm square region to calculate an average gradation value, and the average value B and standard deviation σ of the average gradation value are calculated, so that σ / B is 10.9% or more and 19.3% or less.

[0011] [4] An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer that is overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted into 256 gradations, the gradation values ​​of the converted STEM image are averaged for each 100 nm square region to calculate an average gradation value, and the average value B and standard deviation σ of the average gradation value are calculated, so that σ / B is 5.7% or more and 10.6% or less.

[0012] [5] An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer that is overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted into 256 gradations, the gradation values ​​of the converted STEM image are averaged for each 200 nm square region to calculate an average gradation value, and the average value B and standard deviation σ of the average gradation value are calculated, so that σ / B is 3.8% or more and 7.6% or less.

[0013] [6] The optical film according to any one of [1] to [5], wherein the refractive index of the first layer is greater than the refractive index of the second layer.

[0014] [7] The optical film according to any one of [1] to [6], wherein an interface between the first layer and the second layer is formed into an uneven shape including concave and convex portions, and the bottoms of the concave portions and the tops of the convex portions are flat surfaces along the film surface of the optical film.

[0015] [8] The optical film according to any one of [1] to [7], wherein the inorganic particles are made of zirconia.

[0016] [9] The optical film according to any one of [1] to [8], wherein the inorganic particles are contained in the first layer in an amount of 40% by mass or more and 50% by mass or less, when the entire first layer is taken as 100% by mass.

[0017]

[10] The optical film according to any one of [1] to [9], wherein the particle diameter of the inorganic particles is in the range of 10 nm to 40 nm.

[0018]

[11] The optical film according to any one of [1] to

[10] , wherein the base resin contains a cured ultraviolet curable resin.

[0019]

[12] A method for manufacturing an optical film comprising: a first layer containing inorganic particles and a base resin that contains and supports the inorganic particles; and a second layer overlaid on the first layer, the method comprising: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer; the method comprising: converting an STEM image of a cross section in a thickness direction of the first layer taken at an acceleration voltage of 30 kV into a binary image in which 1010 pixels correspond to 1 μm, extracting a rectangular region of 1280 pixels x 768 pixels from the binary image, dividing the rectangular region into 80 equal parts, calculating an average value A of the proportion of the area occupied by the inorganic particles in each of the 80 partial regions, and calculating a standard deviation σ of the proportion of the area occupied by the inorganic particles in each of the partial regions, and manufacturing the optical film so that σ / A is 19% or more and 34% or less.

[0020]

[13] A method for manufacturing an optical film comprising: a first layer containing inorganic particles and a base resin that contains and supports the inorganic particles; and a second layer overlaid on the first layer, the method comprising: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer; the method comprising: converting an STEM image of a cross section in a thickness direction of the first layer taken at an acceleration voltage of 30 kV into a binary image in which 1 μm corresponds to 505 pixels, extracting a rectangular region of 1280 pixels x 768 pixels from the binary image, dividing the rectangular region into 80 equal parts, calculating an average value A of the proportion of the area occupied by the inorganic particles in each of the partial regions, and calculating a standard deviation σ of the proportion of the area occupied by the inorganic particles in each of the partial regions, and manufacturing the optical film so that σ / A is 6% or more and 20% or less.

[0021]

[14] A method for manufacturing an optical film comprising: a first layer containing inorganic particles and a base resin that contains and supports the inorganic particles; and a second layer that is overlaid on the first layer, the method comprising: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer; the method comprising converting an STEM image of a cross section in a thickness direction of the first layer at an acceleration voltage of 30 kV into 256 gray levels, averaging the gray levels of the converted STEM image for each 50 nm square region to calculate an average gray level, and calculating an average value B and standard deviation σ of the average gray level values, the method for manufacturing an optical film such that σ / B is 10.9% or more and 19.3% or less.

[0022]

[15] A method for manufacturing an optical film comprising: a first layer containing inorganic particles and a base resin that contains and supports the inorganic particles; and a second layer that is overlaid on the first layer, the method comprising: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer; the method comprising converting an STEM image of a cross section in a thickness direction of the first layer taken at an acceleration voltage of 30 kV into 256 gray levels, averaging the gray levels of the converted STEM image for each 100 nm square region to calculate an average gray level, and calculating an average value B and standard deviation σ of the average gray level values, the method for manufacturing an optical film such that σ / B is 5.7% or more and 10.6% or less.

[0023]

[16] A method for manufacturing an optical film comprising: a first layer containing inorganic particles and a base resin that contains and supports the inorganic particles; and a second layer that is overlaid on the first layer, the method comprising: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer; the method comprising converting an STEM image of a cross section in a thickness direction of the first layer taken at an acceleration voltage of 30 kV into 256 gray levels, averaging the gray levels of the converted STEM image for each 200 nm square region to calculate an average gray level, and calculating an average value B and standard deviation σ of the average gray level values, the method for manufacturing an optical film such that σ / B is 3.8% or more and 7.6% or less.

[0024]

[17] A display device comprising the optical film according to any one of [1] to

[11] provided on a display panel.

[0025]

[18] A method for evaluating a particle agglomeration degree for evaluating a degree of agglomeration of particles in a layer containing the particles, comprising: a step of acquiring an STEM image of a cross section in a thickness direction of the layer containing the particles at an acceleration voltage of 30 kV; a step of converting the STEM image into a binary image in which 1 μm corresponds to 505 to 1010 pixels; a step of extracting a rectangular region of 1280 pixels x 768 pixels from the binary image, dividing the rectangular region into 80 equal partial regions, calculating an average value A of the proportion of the area occupied by the particles in each partial region, and calculating a standard deviation σ of the proportion of the area occupied by the particles in each partial region; and a step of evaluating the degree of agglomeration of the particles using σ / A.

[0026]

[19] A method for evaluating a degree of particle agglomeration for evaluating a degree of agglomeration of particles in a layer containing the particles, the method comprising the steps of: acquiring an STEM image of a cross section in a thickness direction of the layer containing the particles at an acceleration voltage of 30 kV; acquiring a converted STEM image by converting the STEM image to 256 gradations; calculating an average gradation value by averaging gradation values ​​of the converted STEM image for each square region of 50 nm or more; calculating an average value B of the average gradation values ​​in the converted STEM image and calculating a standard deviation σ of the average gradation values ​​in the converted STEM image; and evaluating the degree of agglomeration of the particles using σ / B.

[0027] According to the present disclosure, even when particles are contained in a film, a decrease in the total light transmittance of the film and an increase in haze can be suppressed.

[0028] 6A is a schematic cross-sectional view of a display device including an optical film according to an embodiment; FIG. 6B is a perspective view of a first layer constituting the optical film shown in FIG. 1; FIG. 6C is a view showing an STEM image of a cross section of the first layer constituting the optical film shown in FIG. 1; FIG. 6D is a view showing a binarized image converted from the STEM image shown in FIG. 3; FIG. 6E is a view showing a state in which a rectangular region is extracted from the binarized image shown in FIG. 4 and the rectangular region is divided into partial regions; FIG. 6F is a view showing a STEM image according to an example; FIG. 6G is a view showing a STEM image according to an example; FIG. 6H is a view showing a STEM image according to a comparative example; FIG. 6H is a view showing a binarized image converted from each STEM image shown in FIG. 6A; FIG. 6H is a view showing a binarized image converted from each STEM image shown in FIG. 6B; FIG. 6C is a view showing a binarized image converted from each STEM image shown in FIG. 6D.

[0029] An embodiment will be described below with reference to the drawings.

[0030] <Display Device> Fig. 1 is a cross-sectional view of a display device 100 including an optical film 1 according to an embodiment. In the display device 100, the optical film 1 is overlaid on a display panel 101. Specifically, Fig. 1 is a schematic cross-sectional view of the optical film 1 cut in the direction in which the optical film 1 and the display panel 101 overlap.

[0031] The display panel 101 is a liquid crystal panel, but may also be an organic EL panel. The display panel 101 has a light-emitting surface 102 that emits light for image formation. In this embodiment, the optical film 1 overlaps the light-emitting surface 102 and is in direct contact with the light-emitting surface 102. However, the display device 100 may also employ a configuration in which the optical film 1 overlaps the light-emitting surface 102 via another optical member or an air layer.

[0032] <Optical Film> As shown in FIG. 1, the optical film 1 includes a substrate 10 , a first layer 11 , a second layer 12 , and a surface layer 13 .

[0033] The substrate 10 has a front surface 10A and a back surface 10B. A surface layer 13 is bonded to the front surface 10A of the substrate 10. A first layer 11 is bonded to the back surface 10B of the substrate 10. In addition, a second layer 12 is bonded to the surface of the first layer 11 opposite to the substrate 10 side.

[0034] The substrate 10, the first layer 11, the second layer 12, and the surface layer 13 are each in the form of a film. The substrate 10, the first layer 11, the second layer 12, and the surface layer 13 are stacked so that their respective thickness directions coincide. Needless to say, the normal direction to the film surface of the optical film 1, in other words, the thickness direction, coincides with the respective thickness directions of the substrate 10, the first layer 11, the second layer 12, and the surface layer 13. Hereinafter, the direction along the film surface perpendicular to the thickness direction of the optical film 1 may be referred to as the plane direction.

[0035] The substrate 10 is a transparent substrate having optical transparency and made of resin, glass, etc. The material of the substrate 10 may be, for example, polyethylene terephthalate, polyolefin, polycarbonate, polyacrylate, polyamide, glass, triacetyl cellulose, polyimide, polyethylene naphthalate, etc.

[0036] The total light transmittance of the substrate 10 is preferably 87% or more, and more preferably 90% or more. The material of the substrate 10 is preferably a material with low haze. Furthermore, the substrate 10 is preferably colorless and transparent. From this perspective, the material of the substrate 10 is preferably polyethylene terephthalate, triacetyl cellulose, or polyacrylate.

[0037] The refractive index of the substrate 10 is preferably in the range of 1.38 to 1.70, may be 1.57 or less, and more preferably 1.47 to 1.54. The thickness of the substrate 10 is preferably 5 μm to 120 μm, and the lower limit of the thickness of the substrate 10 is preferably 15 μm or more, more preferably 25 μm or more, from the viewpoint of handleability, etc. The upper limit of the thickness of the substrate 10 is preferably 150 μm or less, from the viewpoint of thinning.

[0038] The first layer 11 has a plurality of optical elements 11A that are convex on the side of the second layer 12. More specifically, the first layer 11 in this embodiment has the optical elements 11A and film-like land portions 11B. The land portions 11B are bonded to the rear surface 10B of the substrate 10. The optical elements 11A are integrated with the land portions 11B so as to be convex from the surface of the land portions 11B opposite the substrate 10 side.

[0039] A primer layer for improving adhesion may be provided between the land portion 11B of the first layer 11 and the substrate 10. Such a primer layer may be formed by coating on the substrate 10. The material for forming the primer layer may be, for example, a polyester resin, a polyether resin, a polyurethane resin, or a polyester-polyurethane resin containing a crosslinking agent or the like. The material for forming the primer layer may be thermosetting or photocurable.

[0040] 2 is a perspective view of the first layer 11. As shown in FIG. 2, in this embodiment, the optical elements 11A of the first layer 11 have a longitudinal direction parallel to the surface direction of the optical film 1. The optical elements 11A extend parallel to one another and are arranged at intervals in a direction intersecting the longitudinal directions. More specifically, the optical elements 11A are arranged at a constant pitch in a direction perpendicular to the longitudinal directions. The optical elements 11A extend between opposing sides of the optical film 1.

[0041] The optical element 11A has a top 11T formed by a flat surface along the surface direction of the film surface of the optical film 1, and a pair of side surfaces 11S connecting the top 11T and the land 11B. A gap is provided between adjacent optical elements 11A, and the flat surface of the land 11B is exposed from the gap between adjacent optical elements 11A.

[0042] The first layer 11 and the second layer 12 are bonded to each other with the optical element 11A embedded in the second layer 12. As a result, the interface between the first layer 11 and the second layer 12 has an uneven shape including both concave and convex portions. In this specification, the concave portion of the uneven shape refers to the portion consisting of the portion from the midpoint of the thickness direction of the pair of side surfaces 11S to the land portion 11B and the flat surface of the land portion 11B exposed from the gap between adjacent optical elements 11A. The bottom of this concave portion forms a flat surface parallel to the in-plane direction of the film surface. Furthermore, the convex portion of the uneven shape refers to the portion consisting of the portion from the midpoint of the thickness direction of the pair of side surfaces 11S to the apex 11T of the optical element 11A and the apex 11T. The apex of this convex portion is the apex 11T of the optical element 11A, and therefore forms a flat surface parallel to the in-plane direction of the film surface.

[0043] As shown in FIG. 1 , the side surface 11S is a curved surface that is convex toward the second layer 12. However, the side surface 11S may also be a folded surface (polygonal shape) that is convex toward the second layer 12. The side surface 11S formed as a curved surface may be a curved surface whose curvature gradually changes, may be formed along the arc of a perfect circle, or may be formed along the arc of an ellipse. The side surface 11S may also be a curved or folded surface that is concave toward the second layer 12, or may be a flat surface.

[0044] The first layer 11 having the above-described shape contains inorganic particles and a base resin that contains and holds the inorganic particles. In the present embodiment, the inorganic particles have a refractive index higher than that of the base resin, and are contained in the first layer 11 to increase the refractive index of the entire first layer 11.

[0045] The inorganic particles may be one or a combination of two or more of zirconia (zirconium oxide) particles, alumina (aluminum oxide) particles, and titania (titanium oxide) particles. In this embodiment, the first layer 11 contains inorganic particles made of zirconia. The particle diameter of the inorganic particles is, for example, in the range of 10 nm to 40 nm. In this embodiment, the first layer 11 contains inorganic particles having a particle diameter in the range of 10 nm to 30 nm, and more specifically, the inorganic particles are contained so that the particle diameter distribution of the inorganic particles has a peak between 17.5 nm and 22.5 nm.

[0046] On the other hand, the base resin constituting the first layer 11 can be formed by curing a resin such as an ultraviolet-curable resin, an electron beam-curable resin, or a thermosetting resin. When the first layer 11 is formed by curing an ultraviolet-curable resin, the ultraviolet-curable resin may contain an acrylic resin or an epoxy resin. The first layer 11 may also be formed by pressing a mold having a concave-convex pattern against an uncured forming material to cure the forming material. In this case, the forming material preferably contains an ultraviolet-curable resin. Among them, a radical polymerization type ultraviolet-curable resin is particularly preferred. Radical polymerization type ultraviolet-curable resins cure in a relatively short time when irradiated with ultraviolet light and tend to be easily peeled from the mold.

[0047] In this embodiment, the material for forming the first layer 11 is a dilution mixture of inorganic particles, a first resin composition containing a UV-curable resin, and a solvent. The inventors discovered that diluting the mixture of inorganic particles and the first resin composition with a solvent facilitates uniform dispersion of the inorganic particles during application of the dilution and subsequent curing, in other words, with reduced agglomeration. In particular, when the interface between the first layer 11 and the second layer 12 has an uneven shape, a large amount of pressure is required to distribute the resin composition throughout the entire surface, which tends to increase the agglomeration of the inorganic particles. In contrast, using a solvent in the manufacturing process tends to facilitate suppression of the agglomeration of the inorganic particles. However, the material for forming the first layer is not particularly limited, and a solvent need not be used.

[0048] Furthermore, the molecular weight of the curable resin, such as the ultraviolet curable resin, contained in the first resin composition may affect the degree of aggregation of the inorganic particles during curing. From this perspective, for example, when the particle diameter of the inorganic particles is in the range of 10 nm to 40 nm, the molecular weight of the curable resin may be 300 to 30,000. The molecular weight of the curable resin is preferably 1,000 to 20,000, particularly preferably 2,000 to 10,000. If it is less than 300, there is a problem with the stability of the coating film during coating, and if it exceeds 30,000, there is a risk of problems with filling the liquid into a mold.

[0049] Furthermore, when the solvent used in the dilution liquid has, for example, a high affinity for inorganic particles and a low affinity for resin, or a low affinity for inorganic particles and a high affinity for resin, the degree of aggregation of inorganic particles tends to be easily suppressed during application of the dilution liquid and in the cured state thereafter. From this perspective, the dilution liquid may be methyl ethyl ketone (MEK), propylene glycol monomethyl ether acetate (PGMEA), methanol, or toluene.

[0050] In the present embodiment, the inorganic particles are contained in the first layer 11 in a proportion of 40% by mass or more and 50% by mass or less, when the entire first layer 11 is taken as 100% by mass. However, the content of the inorganic particles is not particularly limited.

[0051] The height of the optical elements 11A in the first layer 11 is, for example, 5 μm or more and 30 μm or less. The thickness of the land portion 11B is, for example, 0.5 μm or more and 30 μm or less. The spacing between adjacent optical elements 11A is, for example, 10 μm or more and 30 μm or less. The width of the optical elements 11A is, for example, 10 μm or more and 30 μm or less. The width of the top portion 11T is, for example, 5 μm or more and 20 μm or less. These dimensions are also not particularly limited.

[0052] In this embodiment, the refractive index of the first layer 11 is greater than the refractive index of the second layer 12. That is, the first layer 11 functions as a high-refractive-index layer, and the second layer 12 functions as a low-refractive-index layer. The refractive index of the first layer 11 is, for example, 1.60 or more and 1.70 or less. Here, the difference in refractive index between the first layer 11 and the second layer 12 (refractive index difference) is, for example, 0.05 or more and 0.60 or less. Such a refractive index difference is basically determined based on the desired optical performance and the shape of the optical element 11A. Then, depending on the determined refractive index difference, the materials for forming the first layer 11 and the second layer 12 are appropriately selected.

[0053] As described above, the second layer 12 is bonded to the first layer 11 with the optical elements 11A embedded therein, thereby forming a plurality of grooves or recesses at a constant pitch in the second layer 12 to accommodate the optical elements 11A.

[0054] In this embodiment, the second layer 12 has adhesive properties and is directly bonded to the light-emitting surface 102 of the display panel 101. More specifically, in this embodiment, the display panel 101 is a liquid crystal panel, the light-emitting surface 102 is formed by the surface of a polarizing plate (not shown), and the second layer 12 is bonded to the polarizing plate. However, the second layer 12 may not have adhesive properties and may be bonded to the light-emitting surface 102 of the display panel 101 with or via an adhesive.

[0055] When the optical film 1 is provided on an organic EL panel, the second layer 12 may be directly bonded to a cover glass that forms the outermost surface of the organic EL panel, or may be indirectly bonded to the cover glass via an adhesive or pressure-sensitive adhesive.

[0056] The second layer 12 may also be formed by curing a resin such as an ultraviolet-curable resin, an electron beam-curable resin, or a thermosetting resin. When the second layer 12 is formed by curing an ultraviolet-curable resin, the ultraviolet-curable resin may contain an acrylic resin or an epoxy resin. The second layer 12 may be formed by applying the material for forming the second layer 12 before curing to the cured first layer 11 from the optical element 11A side, and then curing the material.

[0057] From the viewpoint of curing time, it is particularly preferable that the material for forming the second layer 12 also contains a radical polymerization type ultraviolet curing resin. As described above, the refractive index of the first layer 11 is higher than that of the second layer 12. In order to lower the refractive index of the second layer 12, the second layer 12 may contain inorganic particles such as silica (silicon oxide) particles or hollow silica particles. In this case, the second layer 12 contains inorganic particles and a base resin that contains and supports the inorganic particles.

[0058] The thickness of the second layer 12 is, for example, 10 μm to 100 μm, which is greater than the height of the optical element 11A. The refractive index of the second layer 12 is, for example, 1.55 or less. By including silica particles or the like, the refractive index of the second layer 12 can be reduced to, for example, 1.40 or less, 1.36 or less, or 1.30 or less.

[0059] The surface layer 13 forms the outermost surface of the optical film 1. The surface layer 13 is a low reflective layer (LR (Low Reflective) layer). However, the function of the surface layer 13 is not particularly limited. The surface layer 13 may include a hard coat layer. The surface layer 13 may also include an anti-glare layer (AG layer) that prevents glare on the surface. The surface layer 13 may also have a multilayer structure, and may include, for example, a low reflective layer and a hard coat layer.

[0060] The optical film 1 described above is disposed, as shown in FIG. 1 , with the second layer 12 facing the display panel 101 and the surface layer 13 facing the viewer. In this state, the optical film 1 exerts optical effects such as total reflection, refraction, and transmission on light emitted by the display panel 101, thereby improving the display quality of images displayed on the display panel 101. Specifically, the side surface 11S of the optical element 11A refracts light that would otherwise travel straight from the display panel 101 toward the viewer in an oblique direction, thereby improving the viewing angle. The top surface 11T of the optical element 11A can transmit light that would otherwise travel straight from the display panel 101 toward the viewer without refracting it. This maintains good front brightness.

[0061] In this embodiment, the color change within the viewing angle can be particularly effectively suppressed by having the side surface 11S be a curved surface that is convex toward the second layer 12. However, as described above, the shape of the side surface 11S is not limited to a curved surface that is convex toward the second layer 12.

[0062] In this embodiment, the optical elements 11A have a longitudinal direction parallel to the plane of the film surface and extend between opposing sides of the optical film 1. Instead of such a shape, the optical elements 11A may be arranged two-dimensionally. In this case, the optical elements 11A may be, for example, in the shape of a quadrangular pyramid or a cone. In this embodiment, the second layer 12 faces the display panel 101, but the positions of the first layer 11 and the second layer 12 may be reversed.

[0063] <<State of Inorganic Particles>> Next, the state of the inorganic particles contained in the first layer 11 will be described. In the optical film 1, as described above, the inorganic particles contained in the first layer 11 are uniformly dispersed throughout the first layer 11. In other words, the degree of aggregation of the inorganic particles is kept low throughout the first layer 11. This prevents a decrease in the total light transmittance of the optical film 1 and an increase in haze.

[0064] Specifically, the inorganic particles in the first layer 11 are dispersed so as to satisfy one or more of the following conditions (1) to (5).

[0065] Condition (1): An STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 1010 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is divided into 80 equal parts, and the average value A of the proportion of the area occupied by inorganic particles in each of the partial regions is calculated. In addition, the standard deviation σ of the proportion of the area occupied by the inorganic particles in each of the partial regions is calculated, and σ / A is 19% or more and 34% or less.

[0066] Condition (2): An STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 505 pixels, a rectangular region of 1,280 pixels x 768 pixels is extracted from the binary image, the rectangular region is divided into 80 equal parts, and the average value A of the proportion of the area occupied by the inorganic particles in each of the partial regions is calculated. In addition, the standard deviation σ of the proportion of the area occupied by the inorganic particles in each of the partial regions is calculated, and σ / A is 6% or more and 20% or less.

[0067] Condition (3): When an STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted to 256 gray levels, and the gray levels of the converted STEM image are averaged for each 50 nm square region to calculate an average gray level, and the average value B and standard deviation σ of the average gray levels are calculated, σ / B is 10.9% or more and 19.3% or less.

[0068] Condition (4): When an STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted to 256 gradations, and the gradation values ​​of the converted STEM image are averaged for each 100 nm square region to calculate an average gradation value, and the average value B and standard deviation σ of the average gradation values ​​are calculated, σ / B is 5.7% or more and 10.6% or less.

[0069] Condition (5): An STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted to 256 gray levels, and the gray levels of the converted STEM image are averaged for each 200 nm square region to calculate an average gray level. When the average value B and standard deviation σ of the average gray levels are calculated, σ / B is 3.8% or more and 7.6% or less.

[0070] When one or more of the above conditions (1) to (5) are satisfied, high total light transmittance and low haze can be ensured in the optical film 1. As a result, for example, the front brightness of the display device 100 can be improved and undesired diffusion can be suppressed, thereby improving the image display quality. In the above conditions (1) and (2), the average value A is, for example, in the range of 0.02 to 0.20.

[0071] Even if the average value A is within the above range, if σ / A in condition (1) is less than 19%, there is a risk of interference fringes causing defects in appearance. The reason for this is speculated as follows: If even a few inorganic particles aggregate, their size will be about 0.1 μm (e.g., 20 nm × 5 particles), and if the agglomerates have an excessively low dispersion (e.g., evenly arranged) within one partial region (1.27 μm × 0.76 μm), the average value A will be about 0.06, the spacing between the agglomerates will be about the wavelength of visible light, and interference fringes may occur. In condition (2), if σ / A is less than 6%, based on the same speculation as in condition (1), the average value A will be about 0.03, the spacing between the agglomerates will be about the wavelength of visible light, and interference fringes may occur. Furthermore, if the dispersion is excessively low (for example, a state in which the particles are uniformly arranged), there is a risk of moire occurring due to interference with optical components other than the optical film of the present invention (for example, pixels of a display panel or periodic arrangement patterns of various films).

[0072] Similarly, when σ / B is less than 10.9% under condition (3), when σ / B is less than 5.7% under condition (4), and when σ / B is less than 3.8% under condition (5), the dispersion becomes excessively low, and there is a risk of moire occurring due to interference with optical components other than the optical film of the present invention (for example, pixels of a display panel or periodic arrangement patterns of various films).

[0073] Specifically, as described below, in the evaluations conducted by the present inventors, in Examples that satisfied one or more of the above conditions (1) to (5), the optical film 1 was able to ensure a total light transmittance of 90% or more and suppress haze to 30% or less. The total light transmittance and haze referred to herein are values ​​measured using a haze meter HR-100 manufactured by Murakami Color Research Institute. Furthermore, when the front luminance of the display device 100 without the optical film 1 was taken as 100%, the front luminance of the display device 100 with the optical film 1 was 90% or more. In other words, the display device 100 incorporating the optical film 1 was able to ensure good front luminance while improving the viewing angle characteristics of the optical film 1. The display panel 101 used to evaluate the front luminance was a VA liquid crystal display panel manufactured by Sony Corporation. However, the effect of the optical film 1 in suppressing luminance reduction can be confirmed even when other display panels are used.

[0074] <<Method for Measuring and Evaluating Dispersion State>> A first method for measuring or evaluating the dispersion state of the inorganic particles in the first layer 11 involves acquiring an STEM (Scanning Transmission Electron Microscope) image, binarizing the STEM image, extracting rectangular regions from the binarized image, and calculating the average value and standard deviation. A second method for measuring or evaluating the dispersion state of the inorganic particles in the first layer 11 involves acquiring an STEM image, acquiring a distribution map of the concentration for each pixel in the STEM image, extracting square regions from the distribution map, and calculating the average value and standard deviation for each region. Each of these processes will be described in detail below.

[0075] <First Method> [1] Acquisition of STEM Image When acquiring an STEM image, first, the optical film 1 is cut in the thickness direction. More specifically, the optical film 1 is cut in the thickness direction along cutting lines parallel to each other, and a sample of a portion of the optical film 1 is extracted. The dimension (thickness) between two opposing cut surfaces of the extracted sample is set in the range of 50 nm to 100 nm.

[0076] The sample extracted as described above is placed so that the electron beam from the STEM passes from one cut surface to the other cut surface of the portion of the sample corresponding to the first layer 11, and then a STEM image is acquired. At this time, the acceleration voltage of the STEM is set to 30 kV, and the magnification of the acquired STEM image is set to 50,000 times. Note that the magnification of the STEM image needs only to be 50,000 times or greater. Furthermore, the portion of the sample corresponding to the first layer 11, through which the electron beam from the STEM passes, is the portion corresponding to the optical element 11A.

[0077] Fig. 3 shows an actual STEM image of the first layer 11. In the STEM image shown in Fig. 3, the whitish areas correspond to inorganic particles. The fact that the inorganic particles are not clearly displayed as white means that the inorganic particles are uniformly dispersed.

[0078] [2] Binarization Processing In the binarization processing, the STEM image acquired as described above is first imported into ImageJ (manufactured by the National Institutes of Health, USA), an image processing software. Then, using the "Find Maxima" function of ImageJ, the STEM image is converted into a binarized image in which 1 μm corresponds to 1010 pixels or a binarized image in which 1 μm corresponds to 505 pixels. In the binarized image in which 1 μm corresponds to 1010 pixels, white or black is expressed for each pixel with a pixel size of 0.00099 μm. In the binarized image in which 1 μm corresponds to 505 pixels, white or black is expressed for each pixel with a pixel size of 0.00198 μm. That is, the former is a binarized image with an image resolution of 0.00099 μm, and the latter is a binarized image with an image resolution of 0.00198 μm.

[0079] Figure 4 is a diagram showing a binarized image converted from the STEM image shown in Figure 3. In the binarized image shown in Figure 4, the white marks correspond to inorganic particles. The white marks are displayed very small and are uniformly dispersed throughout the binarized image, making them almost undetectable. This means that the inorganic particles are uniformly dispersed.

[0080] [3] Extraction of Rectangular Regions Rectangular regions are extracted from the binarized image generated as described above. The extraction of rectangular regions is performed by extracting a rectangular region of 1280 pixels x 768 pixels from the binarized image as described above. In this case, a rectangular region of approximately 1.27 μm x 0.76 μm is extracted from a binarized image in which 1 μm corresponds to 1010 pixels. Furthermore, a rectangular region of approximately 2.53 μm x 1.52 μm is extracted from a binarized image in which 1 μm corresponds to 505 pixels. The 1280 pixel x 768 pixel rectangular region is then divided into 80 equal parts to identify partial regions. Each partial region has a size of 128 pixels x 96 pixels.

[0081] FIG. 5 shows a rectangular region X extracted from a binarized image, and also shows 80 equal-sized partial regions Y obtained by dividing the rectangular region X, which are delimited by auxiliary lines SL for the sake of convenience.

[0082] [4] Calculation of Average Value and Standard Deviation After each partial region is identified as described above, the average value A and standard deviation σ are calculated. When calculating the average value A, first, the proportion of the area occupied by inorganic particles in each partial region is calculated by counting the number of white pixels among the pixels in each partial region. Specifically, each partial region contains 12,288 pixels, and the proportion of the area occupied by inorganic particles in the partial region is calculated by counting the number of white pixels among these. The calculated proportions for each partial region are then added together and divided by 80 to form the average value A.

[0083] On the other hand, the standard deviation σ is calculated by the following formula (1).

[0084] In formula (1), n ​​takes a value of 1 to 80. An is the proportion of inorganic particles in the nth partial region, and A is the average value calculated as described above.

[0085] The degree of aggregation of the inorganic particles is evaluated by calculating the standard deviation σ / average value A and evaluating this value. The lower the value of the standard deviation σ / average value A, the lower the degree of aggregation of the inorganic particles.

[0086] In the process described above, the image to be binarized is resolved at a resolution of 0.00099 μm or 0.00198 μm. A portion of the binarized image with such resolution is then divided into multiple partial regions, and the average value A of the proportion of the area occupied by inorganic particles in each partial region and the standard deviation σ of the proportion of the area occupied by inorganic particles in each partial region are calculated. The standard deviation σ / average value A is then used as an evaluation index for the dispersion state of the inorganic particles.

[0087] Through extensive research, the present inventors have found that by using the standard deviation σ / average value A based on a binarized image of the above-described resolution as an evaluation index for the dispersion state of inorganic particles, the dispersion state of nano-order inorganic particles can be evaluated with an appropriate correlation. Therefore, the dispersion state of inorganic particles can be appropriately evaluated by using this index. In other words, the present inventors have found that the dispersion state of inorganic particles can be appropriately evaluated from the standard deviation σ / average value A calculated by the first method. Furthermore, by using this index, it is possible to provide products whose dispersion state has been appropriately evaluated, and to appropriately supply the optical film 1 intended by the present disclosure.

[0088] Although the above describes examples in which the binary image is resolved at a resolution of 0.00099 μm or 0.00198 μm, the resolution of the binary image may be 0.00099 μm or more and 0.00198 μm or less. That is, a binary image in which 1 μm corresponds to 505 pixels or more and 1010 pixels or less may be generated from the STEM image, and the dispersion state of the inorganic particles can be appropriately evaluated by using the standard deviation σ / average value A derived from a binary image in which 1 μm corresponds to 505 pixels or more and 1010 pixels or less.

[0089] <Second Method> [1] Acquisition of STEM Image In the second method, a STEM image is acquired in the same manner as described above. When acquiring a STEM image in the second method, the acceleration voltage of the STEM is also set to 30 kV. The image acquired for measurement or evaluation by the first method may be used for measurement or evaluation by the second method.

[0090] [2] Obtaining a concentration distribution map The STEM image is imported into ImageJ (manufactured by the National Institutes of Health), an image processing software. The STEM image is converted into an image with 256 gradations in ImageJ. Hereinafter, the STEM image converted into 256 gradations will also be referred to as a STEM-converted image. The lower the density of a pixel constituting the STEM image, the higher the gradation value of that pixel in the STEM-converted image. A distribution map of the concentration of each pixel is obtained from the STEM-converted image. The distribution map includes the gradation value of each pixel constituting the STEM-converted image.

[0091] [3] Extraction of Square Regions A square region is extracted from the STEM converted image obtained as described above. The square region may be a 50 nm x 50 nm region, a 100 nm x 100 nm region, or a 200 nm x 200 nm region in the STEM converted image. A 50 nm x 50 nm region may be referred to as a 50 nm square region. A 100 nm x 100 nm region may be referred to as a 100 nm square region. A 200 nm x 200 nm region may be referred to as a 200 nm square region.

[0092] [4] Calculation of the average gradation value From the distribution map obtained as described above, the average gradation value is calculated by averaging the gradation values ​​for each square region. Specifically, the average value of the gradation values ​​located in the part of the distribution map that corresponds to the square region is calculated.

[0093] [5] Calculation of the average value B and standard deviation σ The average value B and standard deviation σ are calculated from the average gradation value calculated as above. The average value B is the average value of the average gradation values ​​of the square regions included in the 2.5 μm × 1.5 μm region of the STEM converted image. The standard deviation σ is the standard deviation of the average gradation values ​​of all the square regions included in the STEM converted image.

[0094] On the other hand, the standard deviation σ is calculated by the following equation (2).

[0095] In equation (2), m is the number of square regions included in the STEM-converted image. j takes a value within a range of values ​​from 1 as the minimum value to m as the maximum value. Bj is the average gradation value of the j-th square region, and B is the average value of the above-mentioned average gradation values ​​in the STEM-converted image.

[0096] The standard deviation σ / average value B is then calculated and evaluated to evaluate the degree of condensation of the inorganic particles. The standard deviation σ / average value B is based on the gradation value of the STEM converted image. The lower the value of the standard deviation σ / average value B, the lower the degree of condensation of the inorganic particles.

[0097] Through extensive research, the present inventors have found that the dispersion state of nano-order inorganic particles can be evaluated with an appropriate correlation by using the standard deviation σ / average value B based on the average gradation value of the above-mentioned square region as an evaluation index for the dispersion state of the inorganic particles. Therefore, the dispersion state of the inorganic particles can be appropriately evaluated by using this index. In other words, the present inventors have found that the dispersion state of the inorganic particles can also be appropriately evaluated from the standard deviation σ / average value B calculated by the second method. Furthermore, the use of this index also makes it possible to provide products with an appropriately evaluated dispersion state, thereby enabling the appropriate supply of the optical film 1 intended by the present disclosure.

[0098] <<Method for Manufacturing Optical Film>> The following describes an example of a method for manufacturing the optical film 1. In the method for manufacturing the optical film 1 described here, a dilution solution preparation step, a first layer formation step, and a second layer formation step are performed in this order.

[0099] [Diluted Liquid Preparation Process] In the diluted liquid preparation process, a diluted liquid is prepared by mixing inorganic particles, a first resin cured product containing an ultraviolet curable resin, and a solvent. First, a mixed liquid is prepared by mixing the inorganic particles and the solvent. Next, a first resin composition is mixed into the mixed liquid. The diluted liquid is prepared by mixing the first resin composition and the mixed liquid.

[0100] The solvent may be a polar solvent such as an alcohol, ketone, ether, ester, or chlorine-based solvent, or a non-polar solvent such as a hydrocarbon. As described above, a solvent that has a high affinity for inorganic particles and a low affinity for resin, or a solvent that has a low affinity for inorganic particles and a high affinity for resin, tends to more easily suppress the degree of aggregation of inorganic particles during application of the diluted solution and in the subsequent cured state. From this perspective, the diluted solution may be methyl ethyl ketone (MEK), propylene glycol monomethyl ether acetate (PGMEA), methanol, or toluene. A solvent that has a high affinity for resin may be, for example, a ketone-based solvent consisting of one or more of acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), or a mixed solvent of MEK and MIBK. In this example, a ketone-based solvent is used.

[0101] [First Layer Formation Process] Next, the diluted solution is dried and the UV-cured resin is cured to form a first layer. The first layer formation process includes a drying process, an application process, and a mold-curing process. In the first layer formation process, first, the diluted solution is dried in the drying process. In the drying process, some or all of the solvent in the diluted solution is evaporated. The drying process may be performed by heating the diluted solution using a heater, or by allowing the diluted solution to dry naturally. A second resin composition is obtained by the drying process. The second resin composition contains a UV-curable resin and inorganic particles dispersed in the UV-curable resin. In the first layer formation process, the second resin composition is applied onto the substrate 10 in the application process. In the mold-curing process, the second resin composition is cured while pressed against a mold. In the mold-curing process, the second resin composition is placed between the substrate 10 and the mold. In this example, since the second resin composition contains an ultraviolet-curable resin, the second resin composition is cured by irradiation with ultraviolet light from the substrate 10 side, thereby forming the first layer 11. In the above-described mold-curing step, the second resin composition pressed against the mold is cured, so that the first layer 11 has the above-described optical elements 11A and land portions 11B.

[0102] [Second Layer Formation Step] In the second layer formation step, a material for forming the second layer 12 is applied to the first layer 11 formed on the substrate 10. In this example, the resin composition contained in the material for forming the second layer 12 includes an ultraviolet curable resin, and the resin composition is cured by ultraviolet irradiation to form the second layer 12.

[0103] The optical film 1 according to the present embodiment described above includes a first layer 11 containing inorganic particles and a base resin that contains and supports the inorganic particles, and a second layer 12 that is overlaid on the first layer 11. The optical film 1 satisfies one or more of the following conditions (1) to (5): Condition (1): When an STEM image of a cross section of the first layer 11 in the thickness direction, taken at an acceleration voltage of 30 kV, is converted into a binary image in which 1 μm corresponds to 1010 pixels, a rectangular region of 1280 pixels by 768 pixels is extracted from the binary image, the rectangular region is equally divided into 80 partial regions, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, σ / A is 19% or more and 34% or less. Condition (2): When an STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 505 pixels, a rectangular region of 1,280 pixels by 768 pixels is extracted from the binary image, the rectangular region is equally divided into 80 partial regions, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, σ / A is 6% or more and 20% or less. Condition (3): When an STEM image of a cross section of the first layer 11 in the thickness direction taken at an acceleration voltage of 30 kV is converted into 256 grayscale levels, an average grayscale value is calculated by averaging the grayscale values ​​of the converted STEM image for each 50 nm square region, and an average value B and standard deviation σ of the average grayscale values ​​are calculated, σ / B is 10.9% or more and 19.3% or less. Condition (4): When an STEM image of a cross section in the thickness direction of the first layer 11 taken at an acceleration voltage of 30 kV is converted to 256 gray levels, the gray levels of the converted STEM image are averaged for each 100 nm square region to calculate an average gray level, and the average value B and standard deviation σ of the average gray levels are calculated, σ / B is 5.7% or more and 10.6% or less. Condition (5): When an STEM image of a cross section in the thickness direction of the first layer 11 taken at an acceleration voltage of 30 kV is converted to 256 gray levels, the gray levels of the converted STEM image are averaged for each 200 nm square region to calculate an average gray level, and the average value B and standard deviation σ of the average gray levels are calculated, σ / B is 3.8% or more and 7.6% or less.

[0104] The optical film 1 as described above can ensure high total light transmittance and low haze in the optical film 1. As a result, for example, the front luminance of the display device 100 can be improved and undesired diffusion can be suppressed, thereby improving the image display quality.

[0105] Examples of the optical film 1 according to the above-described embodiment and comparative examples thereof will be described below.

[0106] In this example, the above-described optical film 1 was actually produced as Examples 1 and 2, and Comparative Examples 1 to 3. The dispersion state of the inorganic particles in each of the produced Examples 1 and 2 and Comparative Examples 1 to 3 was evaluated using the evaluation method described in the above embodiment. Furthermore, the total light transmittance and haze were evaluated as the optical performance of Examples 1 and 2 and Comparative Examples 1 to 3. Furthermore, Examples 1 and 2 and Comparative Examples 1 to 3 were incorporated into a display device, and the front brightness was evaluated.

[0107] Examples 1 and 2 and Comparative Examples 1, 2, and 3 have the same basic shape and material, and have a shape conforming to the optical film 1 described in the above embodiment. On the other hand, Examples 1 and 2 and Comparative Examples 1, 2, and 3 differ from each other in the dispersion state of the inorganic particles.

[0108] The basic shape and material conditions common to Examples 1 and 2 and Comparative Examples 1, 2, and 3 are as follows: The substrate 10 is made of polyethylene terephthalate (PET) and has a thickness of 80 μm. The first layer 11 contains inorganic particles (average particle size 10 nm) made of zirconia and a base resin made of a cured product of ultraviolet-curable resin. The refractive index of the first layer 11 is 1.65. The height of the optical elements 11A in the first layer 11 is 25 μm. The thickness of the land portion 11B is 16 μm. The width of the optical elements 11A is 16.5 μm, and the pitch of the optical elements 11A is 32 μm. The angle formed by a line passing between the endpoints of the side surface of the optical element 11A and the thickness direction is 12 degrees. The difference between the maximum and minimum angles formed by the side surface of the optical element 11A and the thickness direction is 15 degrees. The second layer 12 includes a base resin made of a cured product of an ultraviolet curable resin. The refractive index of the second layer 12 is 1.48. The thickness of the second layer 12 is 50 μm. The surface layer 13 includes a low-reflection layer (LR layer) and a hard coat layer. The thickness of the hard coat is 8 μm. The thickness of the low-reflection layer (LR layer) is 0.1 μm.

[0109] In Examples 1 and 2, a diluted solution is prepared by mixing zirconia, a first resin composition containing an ultraviolet curable resin, and a solvent, and the diluted solution is cured to form the first layer 11. Example 2 differs from Example 1 in that, while in Example 1, zirconia is dispersed in MEK, in Example 2, zirconia is dispersed in toluene.

[0110] Comparative Example 1 differs from Example 1 in that no solvent was used when forming the portion corresponding to the first layer 11, but dispersion was performed using benzyl acrylate.

[0111] Comparative Example 2 differs from Example 1 in that no solvent was used when forming the portion corresponding to the first layer 11, but dispersion was performed using a bifunctional acrylate.

[0112] Comparative Example 3 differs from Example 1 in that no solvent was used when forming the portion corresponding to the first layer 11, but dispersion was performed using a bifunctional epoxy acrylate.

[0113] FIG. 6A shows a STEM image of the first layer in Example 1. FIG. 6B shows a STEM image of the first layer in Example 2. FIG. 6C shows a STEM image of the first layer in Comparative Example 1. FIG. 6D shows a STEM image of the first layer in Comparative Example 2. FIG. 7A shows a binarized image corresponding to the STEM image of the first layer in Example 1. FIG. 7B shows a binarized image corresponding to the STEM image of the first layer in Example 2. FIG. 7C shows a binarized image corresponding to the STEM image of the first layer in Comparative Example 1. FIG. 7D shows a binarized image corresponding to the STEM image of the first layer in Comparative Example 2. Each STEM image and binarized image was acquired according to the technique described in the evaluation method described in the above embodiment.

[0114] Table 1 below shows the results of calculating "standard deviation σ / average value A" from binarized images in which 1 μm corresponds to 1010 pixels (px) and the results of calculating "standard deviation σ / average value A" from binarized images in which 1 μm corresponds to 505 pixels (px) for Example 1, Example 2, Comparative Example 1, and Comparative Example 2, using the first method described above.

[0115] Table 1 also shows the measurement results of total light transmittance, haze measurement results, and evaluation results of front luminance when incorporated into a display device for Example 1, Example 2, Comparative Example 1, and Comparative Example 2. Total light transmittance and haze are values ​​measured using a haze meter HR-100 manufactured by Murakami Color Research Institute. Front luminance was evaluated as the ratio of the value of front luminance measured with a luminance meter when an optical film was provided on a VA liquid crystal display panel manufactured by Sony Corporation, to the value of front luminance measured with a luminance meter when no optical film was provided on the VA liquid crystal display panel.

[0116]

[0117] As is clear from the value of standard deviation σ / average value A shown in Table 1, the degree of aggregation of inorganic particles in Examples 1 and 2 is significantly smaller than that in Comparative Examples 1 and 2 even when evaluated quantitatively.

[0118] The total light transmittance of Examples 1 and 2 is higher than that of Comparative Examples 1 and 2. The haze of Examples 1 and 2 is lower than that of Comparative Examples 1 and 2. The front brightness of the display device incorporating Examples 1 and 2 is higher than that of the display device incorporating Comparative Examples 1 and 2. These evaluation results support the effectiveness of the optical film 1 according to the present disclosure.

[0119] Table 2 below shows the results of calculating "standard deviation σ / average value B" from 256-level STEM-converted images using the second method described above for Example 1, Example 2, and Comparative Examples 1 to 3. The values ​​in the "50 nm" and "standard deviation σ / average value B" columns in Table 2 indicate the average and standard deviation of the average grayscale values ​​obtained by averaging the grayscale values ​​of the STEM-converted images for each 50 nm square region. The values ​​in the "100 nm" and "standard deviation σ / average value B" columns in Table 2 indicate the average and standard deviation of the average grayscale values ​​obtained by averaging the grayscale values ​​of the STEM-converted images for each 100 nm square region. The values ​​in the "200 nm" and "standard deviation σ / average value B" columns in Table 2 indicate the average and standard deviation of the average grayscale values ​​obtained by averaging the grayscale values ​​of the STEM-converted images for each 200 nm square region.

[0120] Table 2 also shows the measurement results of total light transmittance, haze measurement results, and evaluation results of front luminance when incorporated into display devices for Example 1, Example 2, and Comparative Examples 1 to 3. Table 2 also shows the results of visual observation of moire for the optical films incorporated into display devices. The total light transmittance and haze are values ​​measured using a haze meter HR-100 manufactured by Murakami Color Research Institute. The front luminance was evaluated as the ratio of the value of the front luminance measured with a luminance meter when the optical film was provided on a VA liquid crystal display panel manufactured by Sony Corporation to the value of the front luminance measured with a luminance meter when the optical film was not provided on the VA liquid crystal display panel.

[0121]

[0122] As is clear from the values ​​of standard deviation σ / average value B shown in Table 2, the degree of aggregation of the inorganic particles in Examples 1 and 2 is significantly smaller than that in Comparative Examples 1 to 3.

[0123] The total light transmittance of Examples 1 and 2 is higher than that of Comparative Examples 1 to 3. The haze of Examples 1 and 2 is lower than that of Comparative Examples 1 to 3. The front brightness of the display devices incorporating Examples 1 and 2 is higher than that of the display devices incorporating Comparative Examples 1 to 3. These evaluation results support the effectiveness of the optical film 1 according to the present disclosure.

[0124] In addition, the entry "A" in the "Moire" column of Table 2 means that no noticeable moire was observed.

[0125] Furthermore, in this example, the above-described optical film 1 was actually produced as Examples 3 to 6 and Comparative Example 4. The dispersion state of the inorganic particles in each of the produced Examples 3 to 6 and Comparative Example 4 was evaluated using the evaluation method described in the above embodiment. Furthermore, the total light transmittance and haze were evaluated as the optical performance of Examples 3 to 6 and Comparative Example 4. Furthermore, Examples 3 to 6 and Comparative Example 4 were incorporated into display devices, and the front brightness was evaluated.

[0126] Examples 3, 4, 5, 6 and Comparative Example 4 have the same basic shape and material, and have a shape conforming to the optical film 1 described in the above embodiment. On the other hand, Examples 3, 4, 5, 6 and Comparative Example 4 differ from each other in the dispersion state of the inorganic particles.

[0127] The basic shape and material conditions common to Examples 3, 4, 5, and 6 and Comparative Example 4 are as follows: The substrate 10 is made of polyethylene terephthalate (PET) and has a thickness of 80 μm. The first layer 11 contains inorganic particles made of hollow silica and a base resin made of a cured product of an ultraviolet-curable resin. The refractive index of the first layer 11 is 1.40. The height of the optical elements 11A in the first layer 11 is 25 μm. The thickness of the land portion 11B is 16 μm. The width of the optical elements 11A is 16.5 μm, and the pitch of the optical elements 11A is 32 μm. The angle formed by a line passing between the endpoints of the side surface of the optical element 11A and the thickness direction is 12 degrees. The difference between the maximum angle and the minimum angle formed by the side surface of the optical element 11A and the thickness direction is 15 degrees. The second layer 12 includes a base resin made of a cured product of an ultraviolet curable resin. The refractive index of the second layer 12 is 1.57. The thickness of the second layer 12 is 50 μm. The surface layer 13 includes a low-reflection layer (LR layer) and a hard coat layer. The thickness of the hard coat is 8 μm. The thickness of the low-reflection layer (LR layer) is 0.1 μm.

[0128] In Examples 3, 4, 5, and 6, hollow silica, a first resin composition containing an ultraviolet curable resin, and a solvent are mixed to prepare a diluted solution, which is then cured to form the first layer 11. Examples 3, 4, 5, and 6 differ in that Example 3 contains 31%, Example 4 35%, Example 5 32%, and Example 6 34% hollow silica by weight percent.

[0129] Comparative Example 4 differs from Example 3 in that the average particle size of the hollow silica is 20 nm, which is 50 nm.

[0130] Table 3 below shows the results of calculating "standard deviation σ / average value B" from 256-level STEM-converted images using the second method described above for Examples 3 to 6 and Comparative Example 4. The values ​​in the "50 nm" and "standard deviation σ / average value B" columns in Table 3 indicate the average and standard deviation of the average gradation values ​​obtained by averaging the gradation values ​​of the STEM-converted images for each 50 nm square region. The values ​​in the "100 nm" and "standard deviation σ / average value B" columns in Table 3 indicate the average and standard deviation of the average gradation values ​​obtained by averaging the gradation values ​​of the STEM-converted images for each 100 nm square region. The values ​​in the "200 nm" and "standard deviation σ / average value B" columns in Table 3 indicate the average and standard deviation of the average gradation values ​​obtained by averaging the gradation values ​​of the STEM-converted images for each 200 nm square region.

[0131] Table 3 also shows the measurement results of total light transmittance, haze measurement results, and evaluation results of front luminance when incorporated into display devices for Examples 3 to 6 and Comparative Example 4. Furthermore, Table 3 also shows the results of visual observation of moire for the optical films incorporated into display devices. The total light transmittance and haze are values ​​measured using a haze meter HR-100 manufactured by Murakami Color Research Institute. The front luminance was evaluated as the ratio of the value of the front luminance measured with a luminance meter when the optical film was provided on a VA liquid crystal display panel manufactured by Sony Corporation, to the value of the front luminance measured with a luminance meter when the optical film was not provided on the VA liquid crystal display panel.

[0132]

[0133] As is clear from the value of standard deviation σ / average value B shown in Table 3, the dispersion degree of the inorganic particles in Comparative Example 4 is significantly lower than those in Examples 3 to 6.

[0134] The designation "A" in the "Moiré" column of Table 3 means that no noticeable moiré was observed. The designation "B" in the "Moiré" column of Table 3 means that no noticeable moiré was observed. The results in the "Moiré" column shown in Table 3 mean that no noticeable moiré was observed in any of Examples 3 to 6, whereas noticeable moiré was observed in Comparative Example 4. These evaluation results support the effectiveness of the optical film 1 according to the present disclosure.

[0135] Although multiple embodiments and modifications of the present disclosure have been described above, various modifications may be made to the above-described embodiments, and such other modifications may also fall within the technical scope of the present disclosure.

Claims

1. An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer taken at an accelerating voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 1010 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is divided into 80 equal parts, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, so that σ / A is 19% or more and 34% or less.

2. An optical film comprising: a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer taken at an accelerating voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 505 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is divided into 80 equal parts, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, so that σ / A is 6% or more and 20% or less.

3. An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer at an accelerating voltage of 30 kV is converted to 256 gradations, the gradation values ​​of the converted STEM image are averaged for each 50 nm square region to calculate an average gradation value, and the average value B and standard deviation σ of the average gradation value are calculated, so that σ / B is 10.9% or more and 19.3% or less.

4. An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted to 256 gradations, the gradation values ​​of the converted STEM image are averaged for each 100 nm square region to calculate an average gradation value, and the average value B and standard deviation σ of the average gradation value are calculated, so that σ / B is 5.7% or more and 10.6% or less.

5. An optical film comprising: a first layer including inorganic particles and a base resin that contains and holds the inorganic particles; and a second layer overlaid on the first layer; wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted to 256 gradations, and an average gradation value is calculated by averaging the gradation values ​​of the converted STEM image for each 200 nm square region, and the average value B and standard deviation σ of the average gradation value are calculated, so that σ / B is 3.8% or more and 7.6% or less.

6. An optical film according to any one of claims 1 to 5, wherein the refractive index of the first layer is greater than the refractive index of the second layer.

7. The optical film described in claim 6, wherein the interface between the first layer and the second layer is formed into an uneven shape including concave and convex portions, and the bottoms of the concave portions and the tops of the convex portions are flat surfaces that fit along the film surface of the optical film.

8. The optical film according to any one of claims 1 to 5, wherein the inorganic particles are made of zirconia.

9. The optical film according to claim 8, wherein the inorganic particles are contained in the first layer in a proportion of 40% by mass or more and 50% by mass or less, when the entire first layer is taken as 100% by mass.

10. The optical film according to claim 8, wherein the particle diameter of the inorganic particles is in the range of 10 nm to 40 nm.

11. The optical film according to any one of claims 1 to 5, wherein the base resin comprises a cured ultraviolet curable resin.

12. A method for manufacturing an optical film comprising a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles, and a second layer overlaid on the first layer, the method comprising the steps of: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer, wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted into a binary image in which 1010 pixels correspond to 1 μm, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is divided into 80 equal parts, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and the optical film is manufactured so that σ / A is 19% or more and 34% or less.

13. A method for manufacturing an optical film comprising a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles, and a second layer overlaid on the first layer, the method comprising the steps of: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer, wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted into a binary image in which 1 μm corresponds to 505 pixels, a rectangular region of 1280 pixels x 768 pixels is extracted from the binary image, the rectangular region is equally divided into 80 partial regions, an average value A of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and a standard deviation σ of the proportion of the area occupied by the inorganic particles in each partial region is calculated, and the optical film is manufactured so that σ / A is 6% or more and 20% or less.

14. A method for manufacturing an optical film comprising a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles, and a second layer overlaid on the first layer, the method comprising the steps of: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer, wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted to 256 gradations, an average gradation value is calculated by averaging the gradation values ​​of the converted STEM image for each 50 nm square region, and an average value B and standard deviation σ of the average gradation values ​​are calculated, and the optical film is manufactured so that σ / B is 10.9% or more and 19.3% or less.

15. A method for manufacturing an optical film comprising a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles, and a second layer overlaid on the first layer, the method comprising the steps of: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer, wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted to 256 gradations, an average gradation value is calculated by averaging the gradation values ​​of the converted STEM image for each 100 nm square region, and an average value B and standard deviation σ of the average gradation values ​​are calculated, and the optical film is manufactured so that σ / B is 5.7% or more and 10.6% or less.

16. A method for manufacturing an optical film comprising a first layer containing inorganic particles and a base resin that contains and holds the inorganic particles, and a second layer overlaid on the first layer, the method comprising the steps of: mixing the inorganic particles, a first resin composition containing an ultraviolet curable resin, and a solvent to prepare a diluted solution; drying the diluted solution and curing the ultraviolet curable resin to form the first layer; and forming the second layer on the first layer, wherein an STEM image of a cross section in the thickness direction of the first layer at an acceleration voltage of 30 kV is converted to 256 gradations, an average gradation value is calculated by averaging the gradation values ​​of the converted STEM image for each 200 nm square region, and an average value B and standard deviation σ of the average gradation values ​​are calculated, and the optical film is manufactured so that σ / B is 3.8% or more and 7.6% or less.

17. A display device comprising an optical film according to any one of claims 1 to 5 provided on a display panel.

18. A method for evaluating a particle agglomeration degree for evaluating a degree of agglomeration of particles in a layer containing the particles, comprising the steps of: acquiring an STEM image of a cross section in the thickness direction of a layer containing the particles at an acceleration voltage of 30 kV; converting the STEM image into a binary image in which 1 μm corresponds to 505 pixels or more and 1010 pixels or less; extracting a rectangular region of 1280 pixels x 768 pixels from the binary image, dividing the rectangular region into 80 equal partial regions, calculating an average value A of the proportion of the area occupied by the particles in each of the partial regions, and calculating a standard deviation σ of the proportion of the area occupied by the particles in each of the partial regions; and evaluating the degree of agglomeration of the particles based on σ / A.

19. A method for evaluating a particle agglomeration degree for evaluating a degree of agglomeration of particles in a layer containing the particles, comprising the steps of: acquiring an STEM image of a cross section in the thickness direction of a layer containing the particles at an acceleration voltage of 30 kV; acquiring a STEM converted image by converting the STEM image to 256 gradations; calculating an average gradation value by averaging the gradation values ​​of the STEM converted image for each square region of 50 nm or more; calculating an average value B of the average gradation values ​​in the STEM converted image and calculating a standard deviation σ of the average gradation values ​​in the STEM converted image; and evaluating the degree of agglomeration of the particles using σ / B.

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