Optical sheet, sheet article, polarizing plate, display device, panel, optical sheet selection method, and optical sheet manufacturing method

Abstract

This optical sheet includes a first surface and a second surface facing the first surface. The optical sheet includes a base material and a functional layer in the stated order from the second surface to the first surface. The functional layer includes a binder component and metal oxide particles. The average area of Voronoi regions having metal oxide particles observed on the first surface as generation points is 2500 nm2 or more.

Description

Optical sheet, sheet article, polarizing plate, display device, panel, method for selecting optical sheet, and method for manufacturing optical sheet

[0001] The present disclosure relates to an optical sheet, a sheet article, a polarizing plate, a display device, a panel, a method for selecting an optical sheet, and a method for manufacturing an optical sheet.

[0002] As disclosed in Patent Document 1, an optical sheet including a functional layer is known. The functional layer includes metal oxide particles. The functional layer is expected to provide optical functions due to the metal oxide particles. In Patent Document 1, the functional layer functions as a low-reflection layer containing hollow silica.

[0003] During use of the optical sheet, the metal oxide particles may fall off from the functional layer. During use of the optical sheet, the metal oxide particles may become deformed. Due to the falling off and deformation of the metal oxide particles, the scratch resistance of the optical sheet including the functional layer is low.

[0004] Patent Document 1: WO2021 / 020504

[0005] The present disclosure aims to improve the scratch resistance of an optical sheet including a functional layer.

[0006] An optical sheet according to an embodiment of the present disclosure includes a first surface and a second surface opposite to the first surface, the optical sheet including a substrate and a functional layer in this order from the second surface to the first surface, the functional layer including a binder component and metal oxide particles, and an average area of ​​Voronoi regions observed on the first surface and having the metal oxide particles as generating points is 2500 nm ２ That's all.

[0007] A sheet article according to an embodiment of the present disclosure includes a plurality of optical sheets according to an embodiment of the present disclosure.

[0008] A polarizing plate according to an embodiment of the present disclosure includes a first protective sheet, a polarizer, and a second protective sheet, wherein at least one of the first protective sheet and the second protective sheet is any one of the optical sheets according to an embodiment of the present disclosure.

[0009] A display device according to an embodiment of the present disclosure includes: an image forming device; and any one of the optical sheets according to an embodiment of the present disclosure superimposed on the image forming device.

[0010] A panel according to an embodiment of the present disclosure includes: an article to be joined; and any one of the optical sheets according to an embodiment of the present disclosure joined to the article to be joined.

[0011] A method for selecting an optical sheet according to an embodiment of the present disclosure includes, for an optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet including a substrate and a functional layer in this order from the second surface to the first surface, the functional layer including a binder component and metal oxide particles, the method comprising the steps of: measuring an average area of ​​Voronoi regions having the metal oxide particles observed on the first surface as generating points; and determining the average area (nm ２ and selecting an optical sheet for which the difference (i.e., the difference between the optical properties of the optical sheet and the optical characteristics of the optical sheet) is equal to or greater than a predetermined value.

[0012] A method for manufacturing an optical sheet according to an embodiment of the present disclosure includes the steps of: preparing an optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet including a substrate and a functional layer in this order from the second surface to the first surface, the functional layer including a binder component and metal oxide particles; and measuring an average area (nm ) of Voronoi regions having the metal oxide particles observed on the first surface as generating points. ２ and selecting an optical sheet for which the difference (i.e., the difference between the optical properties of the optical sheet and the optical characteristics of the optical sheet) is equal to or greater than a predetermined value.

[0013] According to the present disclosure, the scratch resistance of an optical sheet including a functional layer can be improved.

[0014] FIG. 1 is a diagram for explaining one embodiment and is a cross-sectional view showing an example of an optical sheet. FIG. 2 is a plan view for explaining Voronoi regions and generating points. FIG. 3 is a diagram corresponding to FIG. 1 and is a cross-sectional view showing another example of an optical sheet. FIG. 4 is a perspective view showing an example of a sheet article including an optical sheet. FIG. 5 is a cross-sectional view showing an example of a polarizing plate including an optical sheet. FIG. 6 is a cross-sectional view showing an example of a display device including an optical sheet. FIG. 7 is a cross-sectional view showing an example of a panel including an optical sheet. FIG. 8A is an observation image showing the first surface of the optical sheet according to Example 1. FIG. 8B is an image obtained by binarizing the image showing the first surface of the optical sheet according to Example 1. FIG. 8C is an image showing the distribution of center positions of metal oxide particles observed on the first surface of the optical sheet according to Example 1. FIG. 9A is an image showing a Voronoi diagram obtained from the observation image of the first surface of the optical sheet according to Example 1. FIG. 9B is an image showing a Voronoi diagram obtained from the observation image of the first surface of the optical sheet according to Example 2. FIG. 9C is an image showing a Voronoi diagram obtained from the observation image of the first surface of the optical sheet according to Example 3. Fig. 9D is an image showing a Voronoi diagram obtained from an observation image of the first surface of the optical sheet according to Example 4. Fig. 9E is an image showing a Voronoi diagram obtained from an observation image of the first surface of the optical sheet according to Example 5. Fig. 9F is an image showing a Voronoi diagram obtained from an observation image of the first surface of the optical sheet according to Comparative Example 1. Fig. 9G is an image showing a Voronoi diagram obtained from an observation image of the first surface of the optical sheet according to Comparative Example 2.

[0015] One embodiment of the present disclosure relates to the following <1> to <20>.

[0016] <1> An optical sheet including a first surface and a second surface opposite to the first surface, the optical sheet including a substrate and a functional layer in this order from the second surface toward the first surface, the functional layer including a binder component and metal oxide particles, and an average area of ​​Voronoi regions having the metal oxide particles as generating points observed on the first surface is 2500 nm ２ That's it for the optical sheet.

[0017] <2> The average area of ​​the Voronoi region is 3200 nm ２The optical sheet according to <1>, wherein

[0018] <3> The standard deviation of the area of ​​the Voronoi region is 950 nm ２ The optical sheet according to <1> or <2>,

[0019] <4> The optical sheet according to any one of <1> to <3>, wherein a ratio of a standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions is 0.30 or more.

[0020] <5> The optical sheet according to any one of <1> to <4>, wherein a sliding piece is a "Jumbo Wearaser (registered trademark) CS-6" manufactured by TABER Corporation, and the dynamic friction coefficient of the first surface between the sliding piece and the first surface when a load of 200 g is applied is 0.95 or less.

[0021] <6> The optical sheet according to any one of <1> to <5>, which has resistance to a steel wool scratch resistance test on the first surface under the following conditions: Scratch resistance test: Using steel wool #0000 as a sliding piece, the sheet is moved back and forth 1000 times under a load of 1000 g, a moving speed of 80 mm / sec, and a one-way moving distance of 40 mm.

[0022] <7> The optical sheet according to any one of <1> to <6>, which has resistance to a rubber scratch resistance test on the first surface under the following conditions: Scratch resistance test: Using a Jumbo Wearaser (registered trademark), product number: CS-6, manufactured by TABER Corporation as a sliding piece, the optical sheet is moved back and forth 150 times under a load of 200 g, a moving speed of 200 mm / sec, and a one-way moving distance of 50 mm.

[0023] <8> The optical sheet according to any one of <1> to <7>, wherein the functional layer contains hollow silica particles.

[0024] <9> The optical sheet according to any one of <1> to <8>, wherein the functional layer contains alumina particles.

[0025] <10> The optical sheet according to any one of <1> to <9>, wherein the functional layer contains a siloxane-based compound.

[0026] <11> The optical sheet according to any one of <1> to <10>, wherein the functional layer includes a cured product of an ultraviolet-curable siloxane-based compound-containing composition.

[0027] <12> The optical sheet according to any one of <1> to <11>, wherein the functional layer has a thickness of 60 nm or more and 120 nm or less.

[0028] <13> The optical sheet according to any one of <1> to <12>, further comprising a resin layer located between the substrate and the functional layer, wherein the resin layer contains a cured product of a curable resin composition.

[0029] <14> A sheet article comprising a plurality of the optical sheets according to any one of <1> to <13>.

[0030] <15> The sheet article according to <14>, which is wound around a winding axis.

[0031] <16> A polarizing plate comprising a first protective sheet, a polarizer, and a second protective sheet, wherein at least one of the first protective sheet and the second protective sheet includes the optical sheet according to any one of <1> to <13>.

[0032] <17> A display device comprising: an image forming device; and the optical sheet according to any one of <1> to <13> superimposed on the image forming device.

[0033] <18> A panel comprising: an article to be joined; and the optical sheet according to any one of <1> to <13> joined to the article to be joined.

[0034] <19> An optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet including a substrate and a functional layer in this order from the second surface toward the first surface, the functional layer including a binder component and metal oxide particles, the optical sheet comprising: a step of measuring an average area of ​​Voronoi regions having the metal oxide particles observed on the first surface as generating points; and a step of measuring the average area (nm ２ and selecting an optical sheet for which the difference (i.e., the difference between the optical sheet thickness and the optical sheet thickness) is equal to or greater than a predetermined value.

[0035] <20> An optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet including a substrate and a functional layer in this order from the second surface to the first surface, the functional layer including a binder component and metal oxide particles, and a method for producing the optical sheet, the method comprising: ２ and selecting an optical sheet in which the difference between the optical properties of the optical sheet and the optical fiber is equal to or greater than a predetermined value.

[0036] In the drawings accompanying this specification, the scale and aspect ratios of the actual objects have been appropriately changed and exaggerated for the sake of clarity and ease of understanding.

[0037] In this specification, terms such as "sheet," "film," and "plate" are not distinguished from one another solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished from a member called an optical film or an optical plate solely on the basis of differences in name.

[0038] In this specification, multiple upper limit candidate values ​​and multiple lower limit candidate values ​​for a numerical range may be described in separate sentences. In this description, the numerical range may be constructed by combining any one upper limit candidate value and any one lower limit candidate value. As an example, consider the description, "Parameter B may be A1 or more, A2 or more, or A3 or more. Parameter B may be A4 or less, A5 or less, or A6 or less." In this example, the numerical range of parameter B may be A1 or more and A4 or less, A1 or more and A5 or less, A1 or more and A6 or less, A2 or more and A4 or less, A2 or more and A5 or less, A2 or more and A6 or less, A3 or more and A4 or less, A3 or more and A5 or less, or A3 or more and A6 or less.

[0039] In order to clarify the relationship between directions between the drawings, common directions are indicated in several drawings by arrows with common symbols. The tip of the arrow is the first side of each direction. The side opposite the tip of the arrow is the second side of each direction. An arrow pointing into the paper in a direction perpendicular to the paper surface of the drawing is indicated by a symbol of an x ​​in a circle, as shown in Figure 1, for example.

[0040] <<<Optical Sheet 10>>> As shown in Fig. 1 , the optical sheet 10 according to the present embodiment includes a first surface 11 and a second surface 12. The optical sheet 10 includes, in this order from the second surface 12 to the first surface 11, a substrate 20 and a functional layer 40. The functional layer 40 includes a binder component 41 and metal oxide particles 42. The functional layer 40 can exhibit a function according to the metal oxide particles 42. The functional layer 40 may be one or more of a low-reflection layer or anti-reflection layer, an antifouling layer, a hard coat layer, and an antistatic layer.

[0041] As an example, the functional layer 40 may include hollow silica particles 43 as the metal oxide particles 42. The hollow silica particles 43 are silica particles having holes. The hollow silica particles 43 have a hollow structure. The hollow silica particles 43 have a low refractive index due to their structure. The functional layer 40 including the hollow silica particles 43 as the metal oxide particles 42 has a refractive index lower than the refractive index of the binder component 41. The low-refractive-index functional layer 40 can suppress reflection on the first surface 11. The low-refractive-index functional layer 40 functions as a low-reflection layer or anti-reflection layer.

[0042] During use, an optical sheet may be subjected to external forces. For example, the optical sheet may be rubbed. When an external force is applied to the optical sheet, metal oxide particles may fall off from the functional layer. When an external force is applied to the optical sheet, the metal oxide particles may deform. As the metal oxide particles fall off or deform, defects such as scratches are likely to occur on the surface of the optical sheet. The thickness of the functional layer is usually thinner than the thickness of the substrate. When an external force is applied to the optical sheet, the functional layer may peel off from the optical sheet. Optical sheets having a functional layer tend to have poor scratch resistance.

[0043] In a functional layer containing hollow silica particles as metal oxide particles, the hollow silica particles may fall off from the functional layer during use of the optical sheet. During use of the optical sheet, the hollow silica particles are easily crushed due to their voids. Falling off or deformation of the hollow silica particles easily causes defects such as scratches on the surface of the optical sheet. The thickness of the functional layer serving as a low refractive index layer or antireflection layer is approximately 100 nm. The functional layer serving as a low refractive index layer or antireflection layer is easily peeled off and scratched. Optical sheets containing hollow silica particles have poor scratch resistance.

[0044] <<Average Area of ​​Voronoi Regions>> In the optical sheet 10 of the present embodiment, the average area of ​​the Voronoi regions having the metal oxide particles 42 as generating points observed on the first surface 11 is 2500 nm ２ The average area of ​​the Voronoi regions having the metal oxide particles 42 as the generating points observed on the first surface 11 is 2500 nm ２ According to the optical sheet 10 of the present embodiment configured as described above, the first surface 11 has excellent scratch resistance. The average area of ​​the Voronoi regions observed on the first surface 11, each having a hollow silica particle 42 as a generating point, is 2500 nm ２ According to the optical sheet 10 configured as described above, the first surface 11 has stable and very excellent scratch resistance. Although the details of the reason for the improved scratch resistance are not clear, it is presumed that the following factors contribute to the improved scratch resistance. However, the present disclosure is not bound by the following presumptions.

[0045] As shown in FIG. 2, a Voronoi region 80 is a region defined by a Voronoi boundary 80L. One Voronoi region 80 is defined for each generating point 80C. As shown in FIG. 2, the Voronoi boundary 80L is the bisector of two generating points 80C. The Voronoi boundary 80L, which is the bisector of the two generating points 80C, is perpendicular to the line 80CL connecting the two generating points 80C. The two generating points 80C that define one Voronoi boundary 80L are the generating points 80C that correspond to the two Voronoi regions 80 defined by the Voronoi boundary 80L. The intersection of the Voronoi boundaries 80L is a Voronoi point 80P. One Voronoi point 80P is the boundary point of three or more Voronoi regions 80. The distances from the three or more generating points 80C corresponding to the three or more Voronoi regions 80 to the Voronoi point 80P are the same.

[0046] 9A to 9G show Voronoi diagrams. A Voronoi diagram is a diagram in which a plane area is divided into Voronoi regions 80 corresponding to each of the generating points 80C. A Voronoi diagram can be said to be a diagram in which a plane in which many generating points 80C are dispersed is divided into parts for each of the nearest generating points 80C.

[0047] The average area of ​​the Voronoi regions is an index indicating the density of the metal oxide particles 42 located on the first surface 11. Setting a lower limit for the average area of ​​the Voronoi regions indicates that the metal oxide particles 42 serving as base points are sparsely located on the first surface 11. To impart a certain function to the functional layer 40, it is necessary to contain a predetermined amount or ratio of metal oxide particles 42 in the functional layer 40. By limiting the amount of metal oxide particles 42 appearing on the first surface 11 under this constraint, the adhesion between the binder component 41 and the metal oxide particles 42 near the first surface 11 and the surface condition of the first surface 11 can be improved. As a result, it is presumed that the scratch resistance of the first surface 11 formed by the functional layer 40 is enhanced.

[0048] In the above-mentioned Patent Document 1 (WO2021 / 020504), inorganic oxide particles are used to form convex portions on the surface. The metal oxide particles in Patent Document 1 are expected to protect the hollow silica particles by forming convex portions on the surface. In the present embodiment, metal oxide particles 42 are used in the expectation of achieving a significantly different effect from Patent Document 1. The optical sheet 10 according to the present embodiment has a configuration that is significantly different from Patent Document 1 in terms of surface shape, yet can achieve significantly better scratch resistance than Patent Document 1. In this respect, the effects of the present embodiment are remarkable and far exceed the range predicted from the state of the art at the time of filing.

[0049] The average area of ​​the Voronoi region is 2500 nm as mentioned above. ２ or more, and further, 2900 nm ２ or more, 3000 nm ２ or more, 3200 nm ２ or more, 3500 nm ２ Even 3600 nm or more is fine ２ More than that is fine.

[0050] The upper limit of the average area of ​​the Voronoi regions does not need to be set in particular. From the viewpoint of enhancing the function of the functional layer 40 due to the metal oxide particles 42, the upper limit of the average area of ​​the Voronoi regions may be set. The average area of ​​the Voronoi regions is 7000 nm ２ It may be less than 6000 nm ２ It may be less than 5000 nm ２ or less, 4900 nm ２ The following is also acceptable.

[0051] The average area of ​​the Voronoi region is 2500 nm ２ 7000nm or more ２ or less, 2900 nm ２ 7000nm or more ２ It may be less than 3000 nm ２ 7000nm or more ２ or less, 3200 nm ２ 7000nm or more ２ or less, 3500 nm ２ 7000nm or more ２Even below 3600 nm ２ 7000nm or more ２ The average area of ​​the Voronoi region may be 2500 nm or less. ２ 6000nm or more ２ or less, 2900 nm ２ 6000nm or more ２ It may be less than 3000 nm ２ 6000nm or more ２ or less, 3200 nm ２ 6000nm or more ２ or less, 3500 nm ２ 6000nm or more ２ Even below 3600 nm ２ 6000nm or more ２ The average area of ​​the Voronoi region may be 2500 nm or less. ２ 5000nm or more ２ or less, 2900 nm ２ 5000nm or more ２ It may be less than 3000 nm ２ 5000nm or more ２ or less, 3200 nm ２ 5000nm or more ２ or less, 3500 nm ２ 5000nm or more ２ Less than 3600 nm is also acceptable ２ 5000nm or more ２ The average area of ​​the Voronoi region may be 2500 nm or less. ２ More than 4900 nm ２ or less, 2900 nm ２ More than 4900 nm ２ It may be less than 3000 nm ２ More than 4900 nm ２ or less, 3200 nm ２ More than 4900 nm ２ or less, 3500 nm ２ More than 4900 nm ２ Less than 3600 nm is also acceptable ２ More than 4900 nm ２ The following is also acceptable.

[0052] <Method for calculating the average area of ​​a Voronoi region> The average area of ​​a Voronoi region is a value determined by the following procedure. The following procedure for obtaining the average area of ​​a Voronoi region includes the steps of obtaining an observation image of the first surface 11, determining generating points from the observation image, and determining the area of ​​the Voronoi region by determining the Voronoi region from the generating points.

[0053] (Step of Obtaining Observation Image of First Surface) The step of obtaining an observation image of the first surface is performed as follows: A sample measuring 5 mm x 5 mm is cut out from the optical sheet 10 to be evaluated. Conductive double-sided tape is attached to the entire surface of the sample, which corresponds to the second surface 12 of the optical sheet 10. Furthermore, the conductive double-sided tape attached to the sample is attached to a planar sample stage. In this way, the sample is fixed to the planar sample stage using the conductive double-sided tape. The planar sample stage is an accessory of a scanning electron microscope (SEM) used to observe the sample. The conductive double-sided tape is not particularly limited. The conductive double-sided tape may be SEM carbon tape with an aluminum substrate manufactured by Nissin EM Co., Ltd.

[0054] Carbon paste is applied to the four corners of a sample fixed to a flat sample stage. The carbon paste is not particularly limited. Colloidal graphite No. 7141 (solvent: isopropanol) manufactured by Nissin EM Co., Ltd. may be used as the carbon paste.

[0055] Next, a PtPd vapor deposition film is formed on the sample using an ion sputtering device. The ion sputtering conditions are as follows: Ar gas is introduced into the chamber containing the sample; Target: PtPd; Vacuum level: 8 Pa; Discharge current value: 15 mA; Vapor deposition time: 15 seconds.

[0056] After forming the vapor-deposited film, the standard sample stage on which the sample is fixed is attached to the standard sample holder of the scanning electron microscope. The scanning electron microscope observation conditions are as follows, and an observation image of the surface of the sample corresponding to the first surface 11 of the optical sheet 10 to be evaluated is obtained. The scanning electron microscope used is an ultra-high resolution field emission scanning electron microscope SU-9000 from Hitachi High-Technologies Corporation. FIG. 8A shows an example of the observed image. Measurement mode: SE Acceleration voltage: 1.0 kV Emission current: 10 μA WD (working distance): 3 mm or more and 3.5 mm or less Lens mode: High Observation magnification: 25,000x Data size: 1,280 pixels x 960 pixels Pixel size: 3.96875 nm

[0057] (Step of identifying kernel points from observed image) The step of identifying kernel points from the observed image acquired above is performed as follows. From the observed image, only unnecessary parts such as the scale bar, which are not the image of the sample, are removed. By removing the unnecessary parts, image data for image processing is obtained.

[0058] Next, the image data is subjected to a binarization process. Through the binarization process, light areas of the image data become white areas, and dark areas of the image data become black areas. An image is obtained in which circular white areas are dispersed within a background of black areas. The white areas generally appear at positions where metal oxide particles 42 are present.

[0059] ImageJ and Fiji are used as image processing software for the binarization process. ImageJ is open-source, public domain image processing software whose development began at the National Institutes of Health in the United States. Fiji is a plug-in package for ImageJ. The following Fiji commands are used for the binarization process. By performing binarization under the following conditions, a white area is generated independently for each metal oxide particle observed independently in the microscope image. Figure 8B shows an image obtained by binarizing the image in Figure 8A. - Noise removal: Despeckle - Binarization process: AutoLocal Threshold (Method=Midgray, Radius=50) - Noise removal: Open - Filling holes in black areas: FillHoles - Separating white areas: Watershed

[0060] (Step of Determining the Area of ​​Voronoi Regions) The step of determining the area of ​​Voronoi regions is performed as follows: The binarized image data is processed to determine the coordinates of the center of gravity of each white portion, which represents a metal oxide particle. A binary image is generated in which one pixel located at the coordinates of the center of gravity of each white portion is white and the rest is a black background. The Analyze Particles function of Fiji is used to generate the binary image. Figure 8C is a binary image generated based on the image of Figure 8B.

[0061] The generated binary image is further processed to create a Voronoi diagram. The Voronoi diagram is generated using the center of gravity of the metal oxide particles as the generating points. The average area of ​​the Voronoi regions is calculated from the generated Voronoi diagram. The Voronoi command in Fiji is used to generate the Voronoi diagram and calculate the average area of ​​the Voronoi regions. The average area of ​​the Voronoi regions is calculated as the average value of the areas of the Voronoi regions contained in the image.

[0062] The value calculated as described above is set as the average area of ​​the Voronoi region having the metal oxide particles 42 observed on the first surface 11 as the generating points. The calculated average area of ​​the Voronoi region is compared with a predetermined value, and the optical sheet 10 is evaluated based on the average area of ​​the Voronoi region.

[0063] <<Standard Deviation of the Area of ​​Voronoi Regions>> By adjusting the area of ​​the Voronoi regions, it is possible to impart excellent scratch resistance to the first surface 11 of the optical sheet 10. A lower limit and an upper limit may be set for the standard deviation of the area of ​​these Voronoi regions. By setting a lower limit and an upper limit for the standard deviation of the area of ​​the Voronoi regions in combination with the numerical range of the average area of ​​the Voronoi regions described above, it is possible to stably impart excellent scratch resistance to the entire first surface 11. Similarly, a lower limit and an upper limit may be set for the ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions, i.e., the coefficient of variation. By setting a lower limit and an upper limit for this coefficient of variation in combination with the numerical range of the average area of ​​the Voronoi regions, it is possible to stably impart excellent scratch resistance to the entire first surface 11.

[0064] The standard deviation of the area of ​​the Voronoi region is 950 nm ２ or more, 1000 nm ２ or more, 1041 nm ２ or more, 1056 nm ２ or more, 1114 nm ２ or more, 1191 nm ２ The ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions, i.e., the coefficient of variation, may be 0.30 or more, 0.34 or more, or 0.35 or more.

[0065] The standard deviation of the area of ​​the Voronoi region is 2200 nm ２ or less, 2110 nm ２ or less, 1890 nm ２ or less, 1775 nm ２ or less, 1754 nm ２ The ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions may be 0.50 or less, 0.47 or less, 0.45 or less, or 0.42 or less.

[0066] The standard deviation of the area of ​​the Voronoi region is 950 nm ２ 2200nm or more ２ It may be less than 1000 nm ２ 2200nm or more ２ or less, 1041 nm ２2200nm or more ２ or less, 1056 nm ２ 2200nm or more ２ or less, 1114 nm ２ 2200nm or more ２ or less, 1191 nm ２ 2200nm or more ２ The standard deviation of the area of ​​the Voronoi region is 950 nm ２ 2110nm or more ２ It may be less than 1000 nm ２ 2110nm or more ２ or less, 1041 nm ２ 2110nm or more ２ or less, 1056 nm ２ 2110nm or more ２ or less, 1114 nm ２ 2110nm or more ２ or less, 1191 nm ２ 2110nm or more ２ The standard deviation of the area of ​​the Voronoi region is 950 nm ２ 1890nm or more ２ It may be less than 1000 nm ２ 1890nm or more ２ or less, 1041 nm ２ 1890nm or more ２ or less, 1056 nm ２ 1890nm or more ２ or less, 1114 nm ２ 1890nm or more ２ or less, 1191 nm ２ 1890nm or more ２ The standard deviation of the area of ​​the Voronoi region is 950 nm ２ 1775nm or more ２ It may be less than 1000 nm ２ 1775nm or more ２ or less, 1041 nm ２ 1775nm or more ２ or less, 1056 nm ２ 1775nm or more ２ or less, 1114 nm ２ 1775nm or more２ or less, 1191 nm ２ 1775nm or more ２ The standard deviation of the area of ​​the Voronoi region is 950 nm ２ or more, 1000 nm ２ 1754nm or more ２ or less, 1041 nm ２ 1754nm or more ２ or less, 1056 nm ２ 1754nm or more ２ or less, 1114 nm ２ 1754nm or more ２ or less, 1191 nm ２ 1754nm or more ２ The following is also acceptable.

[0067] The coefficient of variation, which is the ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions, may be 0.30 to 0.50, 0.34 to 0.50, or 0.35 to 0.50. The coefficient of variation may be 0.30 to 0.47, 0.34 to 0.47, or 0.35 to 0.47. The coefficient of variation may be 0.30 to 0.45, 0.34 to 0.45, or 0.35 to 0.45. The coefficient of variation may be 0.30 to 0.42, 0.34 to 0.42, or 0.35 to 0.42.

[0068] As will be demonstrated in the examples below, the standard deviation of the area of ​​the Voronoi region is set to 1450 nm ２ 2150nm or more ２ Further, 1458 nm ２ 2110nm or more ２ The scratch resistance against steel wool could be improved by setting the standard deviation of the area of ​​the Voronoi region to 1450 nm or less. ２ 1800nm ​​or more ２ Further, 1458 nm ２ 1775nm or more ２ By setting the following, the scratch resistance of rubber could be improved.

[0069] As demonstrated in the examples described later, a coefficient of variation of the area of ​​the Voronoi region of 0.38 or more improved the scratch resistance against steel wool, and a coefficient of variation of the area of ​​the Voronoi region of 0.40 or more improved the scratch resistance against rubber.

[0070] <<Abrasion Resistance Test>> The optical sheet 10 with the adjusted average area of ​​the Voronoi regions has excellent abrasion resistance. In an abrasion resistance test using steel wool on the first surface 11, the optical sheet 10 may have high resistance. In an abrasion resistance test using rubber on the first surface 11, the optical sheet 10 may have high resistance.

[0071] <Steel Wool Scratch Resistance> The steel wool scratch resistance test is an index showing resistance to defects such as scratches that occur when steel wool is pressed against a test sample to be evaluated and the test sample is moved relative to the test sample. The optical sheet 10 may be resistant to the steel wool scratch resistance test performed under the conditions described below.

[0072] The test sample of the optical sheet to be evaluated is rectangular. The short side of the rectangle is 50 mm and the long side is 100 mm. The test sample is visually checked to ensure that there are no abnormalities such as dust or scratches. The rectangular sample is spread out on the testing machine along a horizontal plane so as not to cause wrinkles or warping. The four corners of the spread sample are fixed to the testing machine using mending tape. The mending tape may be "810-3-18" manufactured by 3M.

[0073] The steel wool used as a slider is brought into contact with the surface of the sample formed by the first side of the optical sheet. The steel wool used is "Bonstar B-204" with a count of #0000 manufactured by Japan Steel Wool Co., Ltd. The Bonstar B-204 is a commercial size with a width of approximately 390 mm, a length of approximately 75 mm, and a thickness of approximately 110 mm. The contact area between the test sample and the slider is 20 mm x 20 mm. A load of 1000 g is applied to the slider from above in the vertical direction, and the test sample, which has been spread out along a horizontal surface, is pressed against the slider.

[0074] With the slider pressed against the test sample from above in the vertical direction, the slider and the sample are moved relative to each other in the horizontal direction. The slider and the test sample are moved relative to each other in a direction parallel to the direction in which the steel wool fibers mainly extend. The relative movement is a reciprocating movement along a linear path. The reciprocating movement cycle is 1000 times. The reciprocating movement speed is 80 mm / sec. The stroke of the reciprocating movement is 40 mm for both the outward and return paths. The reciprocating movement is in a direction parallel to the long side of the sample.

[0075] The test environment is set at a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The test samples are placed in the test environment for 16 hours before the start of the test.

[0076] An unused sliding piece is used. Before conducting a test on the evaluation target, the steel wool is rubbed against the preparation sample to pretreat the steel wool. The testing machine used to test the sample to be evaluated is also used for the steel wool pretreatment. The preparation sample is a polyethylene terephthalate film. The preparation sample is rectangular with short sides of 50 mm and long sides of 100 mm. Steel wool is rubbed against the untreated surface of the polyethylene terephthalate film. The preparation sample is spread along a horizontal plane, and the four corners of the preparation sample are fixed to the testing machine with mending tape. Steel wool is pressed against the preparation sample from above in the vertical direction. The contact area between the preparation sample and the steel wool is 20 mm x 20 mm. The load pressing the steel wool against the preparation sample is 300 g. The steel wool pressed against the preparation sample is moved horizontally relative to the preparation sample. The steel wool and the preparation sample are moved relative to each other in a direction parallel to the main extension direction of the steel wool fibers. The relative movement is a reciprocating movement. The reciprocating movement cycle is 300 times. The reciprocating movement speed is 80 mm / sec. The reciprocating stroke is 40 mm for both the forward and backward movements. The steel wool pressed against the preparation sample in this manner is used for the test to be evaluated.

[0077] After the scratch resistance test, the surface of the test sample formed by the first surface of the optical sheet is observed with the naked eye. The observation distance is 30 cm. The illuminance on the surface of the sample to be observed is 800 Lx or more and 1200 Lx or less.

[0078] If defects such as scratches that would be problematic in application to a display device are observed on the test sample, the test sample of the optical sheet 10 to be evaluated is determined to not have resistance to a steel wool scratch resistance test on the first surface 11. The scratch resistance test is performed five times on one optical sheet 10 to be evaluated. If no defects that would be problematic in application to a display device occur in any of the five tests, the optical sheet 10 to be evaluated is determined to have resistance to a steel wool scratch resistance test on the first surface 11. Defects that would be problematic in application to a display device are defects that fall under a rating of "4" or "5" on a six-point scale from "0" to "5" as described in the Examples below. The steel wool is replaced after each of the five tests. The above-described steel wool pretreatment is performed before the start of each of the five tests.

[0079] <CS6 Resistance> The rubber abrasion resistance test is an index showing resistance to defects such as scratches that occur when rubber is pressed against a test sample to be evaluated and moved relative to the sample. The optical sheet 10 may be resistant to an abrasion resistance test under the following conditions using a CS-6 Jumbo Wearer (registered trademark) manufactured by TABER Corporation as a sliding piece.

[0080] The test sample of the optical sheet to be evaluated is rectangular. The short side of the rectangle is 50 mm and the long side is 100 mm. The test sample is visually checked to ensure that there are no abnormalities such as dust or scratches. The rectangular sample is spread out on the testing machine along a horizontal plane so as not to cause wrinkles or warping. The four corners of the spread sample are fixed to the testing machine using mending tape. The mending tape may be "810-3-18" manufactured by 3M.

[0081] The sliding piece "Jumbo Wearaser (registered trademark) CS-6" is primarily composed of rubber. The sliding piece CS-6 has a roughly cylindrical shape. The tip surface of the cylindrical shape of this sliding piece is brought into contact with the surface of the sample formed by the first surface of the optical sheet. The contact area between the test sample and the sliding piece is a circle with a diameter of 12 mm.

[0082] The sliding piece CS-6 is held by a holder. The holder is fixed to the cylindrical side of the sliding piece. When CS-6 is held by the holder, the tip surface of the cylindrical shape protrudes from the holder by 2 mm. By limiting the length of protrusion of CS-6 from the holder, deformation of CS-6 during testing is limited. The sliding piece held by the holder is pressed from above in the vertical direction against a test sample spread out along a horizontal plane. The load pressing the sliding piece against the test sample is 200 g.

[0083] With the slider pressed against the test sample from above in the vertical direction, the slider and the sample are moved relative to each other in the horizontal direction. The relative movement is a reciprocating movement. The reciprocating movement cycle is 150 times. The reciprocating movement speed is 200 mm / sec. The stroke of the reciprocating movement is 50 mm for both the forward and backward movements. The reciprocating movement is in a direction parallel to the long side of the sample.

[0084] The test environment is set at a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The test samples are placed in the test environment for 16 hours before the start of the test.

[0085] Before conducting the test on the evaluation target, the preparatory sample is rubbed with CS-6 to perform pretreatment with CS-6. The testing machine used to test the sample to be evaluated is also used for pretreatment with CS-6. The preparatory sample is a "single-sided easy-adhesion type: A4160" manufactured by Toyobo Co., Ltd. The preparatory sample is spread along a horizontal plane, and the four corners of the side of the preparatory sample that has not been treated for easy adhesion (the side where the PET is exposed) are fixed to the testing machine with mending tape. CS-6 is pressed against the preparatory sample from above in the vertical direction. The contact area between the preparatory sample and CS-6 is a circle with a diameter of 12 mm. The load pressing CS-6 against the preparatory sample is 600 g. The CS-6 pressed against the preparatory sample is moved relative to the preparatory sample in the horizontal direction. The relative movement is a reciprocating motion. The reciprocating motion cycle is 150 times. The reciprocating motion speed is 220 mm / sec. The stroke of the reciprocating motion is 50 mm for both the forward and backward movements. The CS-6 pressed against the preparation sample in this way is used for the test to be evaluated. The test is conducted after confirming that the surface of the pressed CS-6 is flat and free of rubber shavings.

[0086] After the scratch resistance test, the surface of the test sample formed by the first surface of the optical sheet is observed with the naked eye. The observation distance is 30 cm. The illuminance on the surface of the sample to be observed is 800 Lx or more and 1200 Lx or less.

[0087] If defects such as scratches that would be problematic in application to a display device are observed on the test sample, the test sample of the optical sheet 10 to be evaluated is determined to be insufficient to withstand the scratch resistance test on the first surface 11 using CS-6 as a sliding piece. The scratch resistance test is performed five times on each optical sheet 10 to be evaluated. If no defects that would be problematic in application to a display device occur in the five tests, the optical sheet 10 to be evaluated is determined to be resistant to the scratch resistance test on the first surface 11 using CS-6 as a sliding piece. Defects that would be problematic in application to a display device are defects that fall under a rating of "4" or "5" on a six-point scale from "0" to "5" as described in the Examples below. The same CS-6 is used in all five tests. The above-described pretreatment of the CS-6 is performed before the start of each of the five tests.

[0088] <<Dynamic Friction Coefficient>> An upper limit may be set for the dynamic friction coefficient of the first surface 11. By setting an upper limit for the dynamic friction coefficient of the first surface 11, the slipperiness of the first surface 11 can be improved, and the abrasion resistance can be improved. The dynamic friction coefficient of the first surface 11 may be 0.95 or less, 0.93 or less, 0.91 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.78 or less, 0.75 or less, or 0.70 or less.

[0089] There is no particular lower limit set for the dynamic friction coefficient on the first surface 11. The dynamic friction coefficient on the first surface 11 may be 0 or greater, may be greater than 0, may be 0.50 or greater, or may be 0.60 or greater.

[0090] The dynamic friction coefficient of the first surface 11 may be 0 to 0.95, 0 to 0.93, 0 to 0.91, 0 to 0.90, 0 to 0.85, 0 to 0.80, 0 to 0.78, 0 to 0.75, or 0 to 0.70. The dynamic friction coefficient of the first surface 11 may be 0 to 0.95, 0 to 0.93, 0 to 0.91, 0 to 0.90, 0 to 0.85, 0 to 0.80, 0 to 0.78, 0 to 0.75, or 0 to 0.70. The dynamic friction coefficient on the first surface 11 may be 0.50 or more and 0.95 or less, 0.50 or more and 0.93 or less, 0.50 or more and 0.91 or less, 0.50 or more and 0.90 or less, 0.50 or more and 0.85 or less, 0.50 or more and 0.80 or less, 0.50 or more and 0.78 or less, 0.50 or more and 0.75 or less, or 0.50 or more and 0.70 or less. The dynamic friction coefficient on the first surface 11 may be 0.60 or more and 0.95 or less, 0.60 or more and 0.93 or less, 0.60 or more and 0.91 or less, 0.60 or more and 0.90 or less, 0.60 or more and 0.85 or less, 0.60 or more and 0.80 or less, 0.60 or more and 0.78 or less, 0.60 or more and 0.75 or less, or 0.60 or more and 0.70 or less.

[0091] The dynamic friction coefficient is determined by cutting a test sample from the optical sheet to be measured and averaging 20 measurements of the dynamic friction coefficient obtained for the test sample. The test sample is visually inspected to ensure that there are no abnormalities such as dust or scratches. The dynamic friction coefficient of the test sample is measured as follows.

[0092] A test sample of an optical sheet is fixed to a dynamic friction coefficient measuring device as follows. First, the test sample is spread out on a table serving as a sample fixing stand, taking care not to cause wrinkles or warping. The table is spread out along a horizontal plane. The test sample is spread out along a horizontal plane. The size of the test sample is 15 cm x 25 cm. The four corners of the spread test sample are fixed to the table with mending tape. The mending tape may be "810-3-18" manufactured by 3M. With the test sample of an optical sheet fixed to the table, the second surface is in contact with the table, and the first surface faces away from the table.

[0093] Next, a sliding piece is prepared, which will be used to measure the coefficient of friction between itself and the first surface 11. The sliding piece is CS-6 from the Jumbo Wearaser (registered trademark) manufactured by TABER. The main component of CS-6 is rubber. The CS-6 sliding piece is held by a holder, similar to the above-mentioned scratch resistance test using CS-6 as the sliding piece. The sliding piece held by the holder is pressed vertically from above against a test sample spread out along a horizontal surface. The sliding piece is brought into contact with the first surface of the test sample. The contact surface between the sliding piece and the test sample is circular and has a diameter of 12 mm. The contact surface is spread out on a horizontal surface. A weight is attached to the holder with double-sided tape. The load pressing the sliding piece against the sample is 200 g. A nylon thread can be attached to the holder.

[0094] The slider is pressed vertically from above against the first surface of the test sample with a load of 200 g, and the slider is moved horizontally. The nylon thread connected to the holder with a hook is pulled horizontally to move the slider together with the holder and weight. The slider moves in the direction along the long side of the sample. The slider movement speed is 15 mm / sec. The slider stroke is 5 cm. While the slider moves one stroke, the horizontal kinetic friction force acting on the slider is measured every 0.01 seconds. The coefficient of kinetic friction is calculated by dividing the average measured value of kinetic friction force by the pressing load (200 g) pressing the slider against the sample.

[0095] The test environment is set at a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The test samples are placed in the test environment for 16 hours before the start of the test.

[0096] Before conducting the test on the evaluation object, CS-6 is rubbed onto the preparation sample to perform pretreatment with CS-6. The pretreatment of CS-6 in the evaluation test of the dynamic friction coefficient is performed in the same manner as the pretreatment in the above-mentioned abrasion resistance test using CS-6 as the sliding piece. Twenty measurements are performed on one test sample. The average value of the dynamic friction coefficient measurements calculated in the 20 tests is taken as the value of the dynamic friction coefficient of the evaluation object. The same CS-6 is used in the 20 tests on the evaluation object. The pretreatment of CS-6 is performed in each of the 20 tests.

[0097] The dynamic friction coefficient is measured under conditions other than those mentioned above in accordance with JIS K7125:1999.

[0098] <<Average Particle Diameter of Metal Oxide Particles>> An upper limit may be set for the average particle diameter of the metal oxide particles 42 contained in the functional layer 40. By setting the lower limit of the average area of ​​the Voronoi regions in combination with the upper limit of the average particle diameter, it is possible to more effectively control the dispersion state of the metal oxide particles 42 on the first surface 11. The adhesion between the binder component 41 and the metal oxide particles 42 in the vicinity of the first surface 11 and the surface state of the first surface 11 are improved, and the scratch resistance of the first surface 11 can be effectively improved.

[0099] The average particle diameter of the metal oxide particles 42 may be smaller than the average thickness of the functional layer 40. The average particle diameter of the metal oxide particles 42 may be 80% or less of the average thickness of the functional layer 40, 75% of the average thickness of the functional layer 40, 70% of the average thickness of the functional layer 40, 60% of the average thickness of the functional layer 40, or 50% of the average thickness of the functional layer 40.

[0100] When the functional layer 40 functions as a low-reflection layer or an anti-reflection layer, the functional layer 40 may be thin and may contain hollow silica particles 43 as metal oxide particles. The hollow silica particles 43 typically have a larger average particle diameter than the other particles contained in the functional layer 40. In this example, the surface condition of the first surface 11 is largely dependent on the relationship between the average thickness of the functional layer 40 and the average particle diameter of the hollow silica particles 43. In this example, an upper limit may be set for the average particle diameter of the hollow silica particles 43. By setting the lower limit of the average area of ​​the Voronoi region in combination with the upper limit of the average particle diameter of the hollow silica particles 43, the scratch resistance of the first surface 11 can be more effectively improved.

[0101] The average particle diameter of the hollow silica particles 43 may be smaller than the average thickness of the functional layer 40. The average particle diameter of the hollow silica particles 43 may be 80% or less of the average thickness of the functional layer 40, 75% or less of the average thickness of the functional layer 40, 70% or less of the average thickness of the functional layer 40, 60% or less of the average thickness of the functional layer 40, or 50% or less of the average thickness of the functional layer 40.

[0102] The "average particle diameter" used for particles such as metal oxide particles 42 and hollow silica particles 43 is a value specified by the following (1) to (3). Although particles may aggregate, the average particle diameter is the average primary particle diameter. (1) The cross section of an optical sheet containing particles is observed with a transmission electron microscope (TEM), and an observation image is obtained by imaging. (2) Ten particles are randomly selected from the observation image, and the particle diameter of each particle is measured. The particle diameter (nm) is defined as the distance between two parallel lines that maximize the distance between the cross section of the particle. In other words, the particle diameter is the maximum length of the particle in the observation image. The particle diameter is specified as the particle diameter (maximum length) of each particle. In other words, the particle diameter is the primary particle diameter. (3) For the same optical sheet to be measured, steps (1) and (2) above are performed five times to measure the particle diameters of a total of 50 particles. The average value of a total of 50 particle diameter measurements is taken as the average particle diameter (nm) of the particles.

[0103] The "average thickness" of the functional layer 40 is a value determined by the following steps (4) to (6): (4) A cross section of the optical sheet including the functional layer is imaged using a transmission electron microscope (TEM). (5) In the image, the thickness of the functional layer at the center position along the surface of the optical sheet and at positions 100 nm shifted from the center position on both sides along the surface of the optical sheet are measured. The thickness is defined as the length (nm) of the functional layer along the direction perpendicular to the surface of the optical sheet. (6) Steps (4) and (5) above are performed five times for the same optical sheet to be measured, and the thickness of the functional layer is measured at a total of 15 positions. The average of the 15 thickness measurements is defined as the average thickness (nm) of the functional layer.

[0104] <<Luminous Reflectance>> The optical sheet 10 may have a reflection suppressing function that suppresses reflection of light incident on the first surface 11. The luminous reflectance Y value on the first surface 11 measured at an incident angle of 5° may be 1.7% or less, 1.5% or less, 1.4% or less, 1.0% or less, 0.8% or less, 0.7% or less, 0.6% or less, or 0.5% or less.

[0105] There is no particular lower limit for the luminous reflectance. The luminous reflectance Y value on the first surface 11 measured at an incident angle of 5° may be 0% or greater, or may be greater than 0%.

[0106] The luminous reflectance Y value of the first surface 11 measured at an incident angle of 5° may be greater than or equal to 0% and less than or equal to 1.7%, greater than or equal to 1.5%, greater than or equal to 1.4%, greater than or equal to 1.0%, greater than or equal to 0.8%, greater than or equal to 0.7%, greater than or equal to 0.6%, or greater than or equal to 0.5%. The luminous reflectance Y value of the first surface 11 measured at an incident angle of 5° may be greater than or equal to 0% and less than or equal to 1.7%, greater than or equal to 1.5%, greater than or equal to 1.4%, greater than or equal to 1.0%, greater than or equal to 0.8%, greater than or equal to 0.7%, greater than or equal to 0.6%, or greater than or equal to 0.5%.

[0107] The luminous reflectance Y value is the luminous reflectance Y value of the CIE 1931 standard color system. The luminous reflectance Y value (%) is measured using a spectrophotometer as follows.

[0108] A sample is cut out from the optical sheet 10 to be evaluated. The sample is visually inspected for any abnormalities such as dust or scratches. A black plate is attached to the surface of the sample, which is made up of the second surface of the optical sheet, via an optically transparent adhesive sheet. The optically transparent adhesive sheet is "Panaclean PD-S1" manufactured by Panac Corporation. The black plate is "Comoglass DFA2CG 502K (black) series" manufactured by Kuraray Co., Ltd. The thickness of the black plate is 2 mm. The total light transmittance of the black plate is 1% or less. In this way, evaluation sample A is prepared, which includes the optical sheet, optically transparent adhesive sheet, and black plate.

[0109] Light is irradiated onto the surface of evaluation sample A, which is formed by the first surface of the optical sheet, at an incident angle of 5°. The reflectance (luminous reflectance Y value) of the evaluation sample is measured based on the specularly reflected light from evaluation sample A. Using auxiliary illuminant C and a 2-degree visual field, the luminous reflectance Y (%) is calculated based on the specular reflectance measured at 0.5 nm intervals in the range of 300 nm to 780 nm. Before measuring the luminous reflectance Y value of the optical sheet 10, auxiliary illuminant C is turned on for 15 minutes to stabilize the output of auxiliary illuminant C. The test environment for measuring the luminous reflectance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before starting the test.

[0110] Other measurement conditions for measuring the luminous reflectance are in accordance with JIS Z 8722:2009.

[0111] The luminous reflectance is the arithmetic mean value of five measurements taken at five measurement positions on the optical sheet to be evaluated, the five measurement positions being spaced at least 10 mm apart from each other.

[0112] <<Total Light Transmittance>> The total light transmittance of the optical sheet 10 may be 50% or more, 70% or more, 80% or more, or 90% or more. The total light transmittance of the optical sheet 10 does not have a particular upper limit. The total light transmittance of the optical sheet 10 may be 100% or less, or may be less than 100%.

[0113] The total light transmittance of the optical sheet 10 may be 50% or more and 100% or less, 70% or more and 100% or less, 80% or more and 100% or less, or 90% or more and 100% or less. The total light transmittance of the optical sheet 10 may be 50% or more and less than 100%, 70% or more and less than 100%, 80% or more and less than 100%, or 90% or more and less than 100%.

[0114] A light source simulating the spectrum of D65 standard light (also referred to as a "D65 light source") is used to measure the total light transmittance (%). Before measuring the total light transmittance of the optical sheet 10, the D65 light source is turned on for 15 minutes to stabilize the output of the D65 light source. The angle of incidence on the sample when measuring the total light transmittance is 0°. The incident surface when measuring the total light transmittance is the second surface 12 of the optical sheet 10. The test environment when measuring the total light transmittance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before starting the test. Other measurement conditions when measuring the total light transmittance are in accordance with JIS K7361-1:1997.

[0115] The total light transmittance is the arithmetic mean value of five measured values, which are measured at five measurement positions on the optical sheet to be evaluated, and which are located at least 10 mm apart from each other.

[0116] <<Transmission Haze>> The transmission haze of the optical sheet 10 may be 1.0% or less, 0.5% or less, or 0.2% or less. The transmission haze of the optical sheet 10 has no particular lower limit. The transmission haze of the optical sheet 10 may be 0% or more, or may be greater than 0%.

[0117] The transmission haze of the optical sheet 10 may be 0% or more and 1.0% or less, 0% or more and 0.5% or less, or 0% or more and 0.2% or less. The transmission haze of the optical sheet 10 may be greater than 0% and 1.0% or less, greater than 0% and 0.5% or less, or greater than 0% and 0.2% or less.

[0118] A D65 light source is used to measure the transmission haze (%). Before measuring the transmission haze of the optical sheet 10, the D65 light source is turned on for 15 minutes to stabilize the output of the D65 light source. The angle of incidence on the sample when measuring the transmission haze is 0°. The incident surface when measuring the transmission haze is the second surface 12 of the optical sheet 10. The test environment when measuring the transmission haze is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before starting the test. Other measurement conditions when measuring the transmission haze are in accordance with JIS K7136:2000.

[0119] The transmission haze is the arithmetic mean value of five measurements taken at five measurement positions on the optical sheet to be evaluated, the five measurement positions being spaced 10 mm or more apart from each other.

[0120] Each layer included in the optical sheet 10 will be described in further detail with reference to the optical sheet 10 shown in FIG. 1 . As shown in FIG. 1 , the optical sheet 10 may further include a resin layer 30. In the example shown in FIG. 1 , the substrate 20, the resin layer 30, and the functional layer 40 are stacked in the third direction D3. The illustrated functional layer 40 contains hollow silica particles 43 as metal oxide particles 42. In the following description, the functional layer 40 will be described as a low-reflection layer or anti-reflection layer having the function of suppressing reflection. This functional layer 40 has a refractive index lower than that of the adjacent layer (the resin layer 30 in the illustrated example).

[0121] The third direction D3 is the stacking direction. The substrate 20, the resin layer 30, and the functional layer 40 extend in a first direction D1 and a second direction D2 that are perpendicular to the third direction D3. In the illustrated example, the first direction D1 and the second direction D2 are perpendicular to each other. In the optical sheet 10 shown in FIG. 1 , the first surface 11 is formed by the functional layer 40. The second surface 12 is formed by the substrate 20.

[0122] The optical sheet 10 may further include an antistatic layer or an antifouling layer, and these layers may be supported by the functional layer 40 to form the first surface 11. These antistatic layers, antifouling layers, etc. are very thin layers. Otherwise, the functional layer 40 would not be able to effectively exhibit its anti-reflection function. Therefore, even in cases where the first surface 11 is formed by an antistatic layer, antifouling layer, etc., the scratch resistance of the first surface 11 is affected by the functional layer 40. In other words, the above-described functional layer 40 can significantly improve the scratch resistance of the first surface 11.

[0123] <<Substrate>> The substrate 20 supports the resin layer 30 and the functional layer 40. The substrate 20 may be transparent. Transparent means that the total light transmittance in accordance with JIS K7361-1:1997 is 50% or more, and may be 70% or more, 80% or more, or 90% or more.

[0124] The material of the substrate 20 is not particularly limited, and may be resin or glass. Resin is preferable because it is lightweight and easy to manufacture.

[0125] The resin used for the substrate 20 may be a polyolefin-based resin such as polyethylene or polypropylene. The resin used for the substrate 20 may be a vinyl-based resin such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, or ethylene-vinyl alcohol copolymer. The resin used for the substrate 20 may be a polyester-based resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate. The resin used for the substrate 20 may be an acrylic-based resin such as polymethyl(meth)acrylate or polyethyl(meth)acrylate. The resin used for the substrate 20 may be a styrene-based resin such as polystyrene, a polyamide-based resin such as nylon 6 or nylon 66, or a cellulose-based resin such as triacetyl cellulose. Further examples of resins used for the substrate 20 include resins such as polycarbonate, polyimide-based resins, and cycloolefin resins derived from cycloolefins such as norbornene and dicyclopentadiene. The resin layer 30 may contain only one of the above-mentioned resins, or two or more of the above-mentioned resins.

[0126] The thickness of the resin substrate 20 is not particularly limited. From the viewpoint of handleability, the thickness of the resin substrate 20 may be 10 μm or more, 20 μm or more, or 50 μm or more. The thickness of the resin substrate 20 may be 500 μm or less, 400 μm or less, or 300 μm or less. The thickness of the resin substrate 20 may be 10 μm or more and 500 μm or less, 20 μm or more and 500 μm or less, or 50 μm or more and 500 μm or less. The thickness of the resin substrate 20 may be 10 μm or more and 400 μm or less, 20 μm or more and 400 μm or less, or 50 μm or more and 400 μm or less. The thickness of the resin substrate 20 may be 10 μm or more and 300 μm or less, 20 μm or more and 300 μm or less, or 50 μm or more and 300 μm or less. The thickness of the resin substrate 20 may be 500 μm or more.

[0127] When the optical sheet 10 is used for foldable applications, the substrate 20 may be flexible. In this example, the thickness of the resin substrate 20 may be 10 μm or more and 40 μm or less. When the optical sheet 10 is used laminated with glass, the thickness of the resin substrate 20 may be 40 μm or more and 100 μm or less from the viewpoint of preventing the glass from shattering.

[0128] The substrate 20 may include only a single layer or multiple layers. The substrate 20 may include a primer layer such as an easy-adhesion layer.

[0129] <<Functional Layer>> The functional layer 40 includes a binder component 41 and metal oxide particles 42. The metal oxide particles 42 may include hollow silica particles 43. The metal oxide particles 42 may further include particles other than the hollow silica particles 43. The functional layer 40 has a reduced refractive index due to the inclusion of the hollow silica particles 43. The functional layer 40 may have a refractive index lower than that of the binder component 41. The refractive index of the functional layer 40 may be lower than that of the substrate 20. The refractive index of the functional layer 40 may be lower than that of a layer adjacent to the functional layer 40.

[0130] The functional layer 40 can suppress reflection of incident light due to its refractive index and thickness. The anti-reflection function of the functional layer 40 is based on the interference of light reflected on both surfaces of the functional layer 40. From the viewpoint of making this anti-reflection function effective, the refractive index of the functional layer 40 may be between the refractive indices of the two regions adjacent to the functional layer 40 on both sides. The thickness (nm) of the functional layer 40 may be approximately 1 / 4 of the wavelength λ (nm) of the light whose reflection is to be suppressed.

[0131] The thickness of the functional layer may be 60 nm to 120 nm, 70 nm to 120 nm, or 80 nm to 120 nm. The thickness of the functional layer may be 60 nm to 110 nm, 70 nm to 110 nm, or 80 nm to 110 nm. The thickness of the functional layer may be 60 nm to 100 nm, 70 nm to 100 nm, or 80 nm to 100 nm.

[0132] From the viewpoint of the anti-reflection function, the refractive index of the functional layer and the average thickness of the functional layer can be set as follows: The refractive index of the functional layer may be 1.10 or more, 1.20 or more, 1.26 or more, 1.28 or more, or 1.30 or more. The refractive index of the functional layer may be 1.48 or less, 1.45 or less, 1.40 or less, 1.38 or less, or 1.35 or less.

[0133] The refractive index of the functional layer may be 1.10 or more and 1.48 or less, 1.20 or more and 1.48 or less, 1.26 or more and 1.48 or less, 1.28 or more and 1.48 or less, or 1.30 or more and 1.48 or less. The refractive index of the functional layer may be 1.10 or more and 1.45 or less, 1.20 or more and 1.45 or less, 1.26 or more and 1.45 or less, 1.28 or more and 1.45 or less, or 1.30 or more and 1.45 or less. The refractive index of the functional layer may be 1.10 or more and 1.40 or less, 1.20 or more and 1.40 or less, 1.26 or more and 1.40 or less, 1.28 or more and 1.40 or less, or 1.30 or more and 1.40 or less. The refractive index of the functional layer may be 1.10 to 1.38, 1.20 to 1.38, 1.26 to 1.38, 1.28 to 1.38, or 1.30 to 1.38. The refractive index of the functional layer may be 1.10 to 1.35, 1.20 to 1.35, 1.26 to 1.35, 1.28 to 1.35, or 1.30 to 1.35.

[0134] The refractive index used for the components that make up the optical sheet is the refractive index for a wavelength of 589.3 nm.

[0135] The thickness of the functional layer may be 80 nm or more, 85 nm or more, or 90 nm or more. The thickness of the functional layer may be 150 nm or less, 110 nm or less, or 105 nm or less. The thickness of the functional layer may be 80 nm or more to 150 nm or less, 85 nm or more to 150 nm or less, or 90 nm or more to 150 nm or less. The thickness of the functional layer may be 80 nm or more to 110 nm or less, 85 nm or more to 110 nm or less, or 90 nm or more to 110 nm or less. The thickness of the functional layer may be 80 nm or more to 105 nm or less, 85 nm or more to 105 nm or less, or 90 nm or more to 105 nm or less.

[0136] <Binder Component> The binder component 42 is an element that holds the metal oxide particles 42. The binder component 42 may function as a binding agent for forming a coating film. The binder component 42 may hold the particles contained in the functional layer 40, thereby allowing the functional layer 40 to maintain a film form. The binder component 42 may contain a resin. The resin contained in the binder component 42 may be a natural resin or a synthetic resin. The binder component 42 may encapsulate the particles contained in the functional layer 40. The binder component 42 may encapsulate the particles contained in the functional layer 40. The binder component 42 may completely surround each particle contained in the functional layer 40, or may partially expose at least some of the particles contained in the functional layer 40.

[0137] The binder component 41 may include a cured product of a curable resin composition. The curable resin composition may include one or more of a thermosetting resin composition and an ionizing radiation curable resin composition. The cured product of the curable resin composition can impart high strength and high hardness to the functional layer 40 and improve the scratch resistance of the first surface 11. The ionizing radiation curable resin composition is particularly useful from the viewpoint of improving scratch resistance.

[0138] The thermosetting resin composition contains a thermosetting resin. The thermosetting resin composition is cured by heating. Examples of the thermosetting resin include acrylic resin, urethane resin, phenolic resin, urea melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. The thermosetting resin composition may contain a curing agent.

[0139] The ionizing radiation-curable resin composition contains an ionizing radiation-curable compound. The ionizing radiation-curable compound contains an ionizing radiation-curable functional group. Examples of the ionizing radiation-curable functional group include ethylenically unsaturated bond groups such as a (meth)acryloyl group, a vinyl group, and an allyl group, as well as an epoxy group and an oxetanyl group. The ionizing radiation-curable compound may contain two or more ionizing radiation-curable functional groups. The ionizing radiation-curable compound may be a compound having an ethylenically unsaturated bond group. The ionizing radiation-curable compound may be a (meth)acrylate-based compound having a (meth)acryloyl group.

[0140] The ionizing radiation-curable compound may be a siloxane-based compound containing a siloxane bond. That is, an ultraviolet-curable siloxane-based compound-containing composition may be used. By forming a functional layer using an ultraviolet-curable siloxane-based compound-containing composition, the average area of ​​the Voronoi regions can be increased.

[0141] Compared with pentaerythritol triacrylate, which is often used in functional layers, ultraviolet-curable siloxane-based compound-containing compositions are less likely to penetrate into underlying layers. Therefore, ultraviolet-curable siloxane-based compound-containing compositions are more likely to coat metal oxide particles contained in functional layer coating solutions. In other words, metal oxide particles are more likely to be enveloped in resin in the functional layer. As a result, functional layers fabricated using ultraviolet-curable siloxane-based compound-containing compositions tend to have larger average areas of Voronoi regions, with the average area of ​​the Voronoi regions increasing to 2500 nm or less. ２ It can do more than that.

[0142] The functional layer produced using the ultraviolet-curable siloxane-based compound-containing composition contains a cured product of the ultraviolet-curable siloxane-based compound-containing composition. The binder component of the functional layer produced using the ultraviolet-curable siloxane-based compound-containing composition contains a cured product of the ultraviolet-curable siloxane-based compound-containing composition. The functional layer produced using the ultraviolet-curable siloxane-based compound-containing composition contains a siloxane-based compound. The binder component of the functional layer produced using the ultraviolet-curable siloxane-based compound-containing composition contains a siloxane-based compound. Therefore, in a functional layer containing a siloxane-based compound, the average area of ​​the Voronoi regions tends to be large, and the average area of ​​the Voronoi regions is reduced to 2500 nm ２ It can do more than that.

[0143] The presence or absence of siloxane-based compounds is confirmed by detecting organic Si components by X-ray photoelectron spectroscopy. If organic Si components are detected by X-ray photoelectron spectroscopy, it is determined that siloxane-based compounds are present. If organic Si components are not detected by X-ray photoelectron spectroscopy, it is determined that siloxane-based compounds are not present.

[0144] X-ray photoelectron spectroscopy (XPS) is used to determine whether the functional layer contains an organic Si component. An example of an X-ray photoelectron spectroscopy is the AXIS-Nova X-ray photoelectron spectroscopy analyzer manufactured by KRATOS ANALYCAL.

[0145] In the quantitative analysis of elements present in the functional layer by X-ray photoelectron spectroscopy, the X-ray photoelectron spectra of the C1s orbital, O1s orbital, Si2p orbital, and F1s orbital on the functional layer surface of a measurement sample are measured under the conditions described below.

[0146] (Measurement conditions) Measurement method: Wide / Narrow X-ray source: Monochrome A1Kα X-ray output: 150 W Emission current: 10 mA Acceleration voltage: 15 kV Charge neutralization mechanism: ON Measurement area: 300 μm x 700 μm Pass Energy: Survey: 160 eV, Narrow: 40 eV Photoelectron acceptance angle: 90° Auto Z: ON Peak shift correction: Corrected so that the C-C peak is 285.0 eV in the C1s peak Waveform separation of narrow peak: Performed using the GL function in the analysis software attached to the device Etching ions: Ar monatomic ions

[0147] Examples of siloxane compounds include (poly)dimethylsiloxane, (poly)diethylsiloxane, (poly)diphenylsiloxane, (poly)methylphenylsiloxane, alkyl-modified (poly)dimethylsiloxane, azo group-containing (poly)dimethylsiloxane, dimethylsilicone, phenylmethylsilicone, alkyl-aralkyl-modified silicone, fluorosilicone, polyether-modified silicone, fatty acid ester-modified silicone, methylhydrogen silicone, silanol group-containing silicone, alkoxy group-containing silicone, phenol group-containing silicone, methacrylic-modified silicone, acrylic-modified silicone, amino-modified silicone, carboxylic acid-modified silicone, carbinol-modified silicone, epoxy-modified silicone, mercapto-modified silicone, fluorine-modified silicone, polyether-modified silicone, and the like.

[0148] The thickness of the functional layer containing a siloxane compound may be 60 nm or more, 70 nm or more, or 80 nm or more, and may be 120 nm or less, 110 nm or less, or 100 nm or less.

[0149] The thickness of the functional layer containing a siloxane compound may be 60 nm to 120 nm, 70 nm to 120 nm, or 80 nm to 120 nm. The thickness of the functional layer containing a siloxane compound may be 60 nm to 110 nm, 70 nm to 110 nm, or 80 nm to 110 nm. The thickness of the functional layer containing a siloxane compound may be 60 nm to 100 nm, 70 nm to 100 nm, or 80 nm to 100 nm.

[0150] When a functional layer having a thickness in this range contains a siloxane-based compound, the average area of ​​the Voronoi region tends to become large. ２ It can do more than that.

[0151] The functional layer containing a siloxane compound can achieve a predetermined thickness with high precision because the formation of a permeation layer is suppressed. Furthermore, the dispersibility of hollow silica particles is improved in the functional layer containing a siloxane compound. Therefore, by setting the thickness of the functional layer containing a siloxane compound within the above-mentioned numerical range, for example, 60 nm or more and 120 nm or less, the resulting functional layer has a desired thickness and is homogeneous. In other words, a highly accurate anti-reflection function or low-reflection function can be imparted to the functional layer. Furthermore, the average area of ​​the Voronoi region described above tends to increase, and the average area of ​​the Voronoi region can be increased to 2500 nm or less. ２ As a result, the scratch resistance of the first surface can be improved.

[0152] A (meth)acrylate compound having four or more ethylenically unsaturated bond groups is referred to as a "polyfunctional (meth)acrylate compound." A (meth)acrylate compound having two to three ethylenically unsaturated bond groups is referred to as a "low-functional (meth)acrylate compound."

[0153] The (meth)acrylate compound may be a monomer or an oligomer. An ionizing radiation curable compound containing a low-functional (meth)acrylate compound can suppress uneven shrinkage during curing and smooth the surface of the functional layer 40.

[0154] The proportion of the low-functional (meth)acrylate compound in the ionizing radiation-curable compound may be 60% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or even 100% by mass. From the viewpoint of suppressing uneven shrinkage during curing and smoothing the irregularities on the surface of the functional layer 40, the low-functional (meth)acrylate compound may be a (meth)acrylate compound containing two ethylenically unsaturated bond groups. When the ionizing radiation-curable compound contains a large amount of a polyfunctional (meth)acrylate compound, the surface of the functional layer can be smoothed by appropriately adjusting the type of solvent and drying conditions, as described below.

[0155] Among the (meth)acrylate compounds, examples of bifunctional (meth)acrylate compounds include polyalkylene glycol di(meth)acrylates such as isocyanuric acid di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and polybutylene glycol di(meth)acrylate, bisphenol A tetraethoxydiacrylate, bisphenol A tetrapropoxydiacrylate, and 1,6-hexanediol diacrylate. Examples of trifunctional (meth)acrylate compounds include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and isocyanuric acid-modified tri(meth)acrylate. Examples of polyfunctional (meth)acrylate compounds having tetrafunctional or higher functionality include pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol tetra(meth)acrylate. The (meth)acrylate compound may be modified as described below.

[0156] Examples of (meth)acrylate oligomers include acrylate polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and polyether (meth)acrylate. Urethane (meth)acrylate can be obtained, for example, by reacting a polyhydric alcohol and an organic diisocyanate with a hydroxy (meth)acrylate. The epoxy (meth)acrylate may be a (meth)acrylate obtained by reacting a trifunctional or higher aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, or the like with (meth)acrylic acid. The epoxy (meth)acrylate may be a (meth)acrylate obtained by reacting a difunctional or higher aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, or the like with a polybasic acid and (meth)acrylic acid. The epoxy (meth)acrylate may be a (meth)acrylate obtained by reacting a difunctional or higher aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, or the like with a phenol and (meth)acrylic acid.

[0157] The (meth)acrylate compound may have a portion of its molecular skeleton modified to suppress uneven shrinkage due to crosslinking. The (meth)acrylate compound may be modified with, for example, ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, an alkyl, a cyclic alkyl, an aromatic, a bisphenol, or the like. The (meth)acrylate compound may be modified with an alkylene oxide such as ethylene oxide or propylene oxide. The proportion of the alkylene oxide-modified (meth)acrylate compound in the ionizing radiation-curable compound may be 60% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or even 100% by mass. The alkylene oxide-modified (meth)acrylate compound may be a low-functional (meth)acrylate compound or a (meth)acrylate compound having two ethylenically unsaturated bond groups.

[0158] Examples of alkylene oxide-modified (meth)acrylate compounds having two ethylenically unsaturated bond groups include bisphenol F alkylene oxide-modified di(meth)acrylate, bisphenol A alkylene oxide-modified di(meth)acrylate, isocyanuric acid alkylene oxide-modified di(meth)acrylate, and polyalkylene glycol di(meth)acrylate. The average number of repeating units of the alkylene glycol contained in the polyalkylene glycol di(meth)acrylate may be 3 to 5. The alkylene glycol contained in the polyalkylene glycol di(meth)acrylate may be ethylene glycol and / or polyethylene glycol. Examples of alkylene oxide-modified (meth)acrylate compounds having three ethylenically unsaturated bond groups include trimethylolpropane alkylene oxide-modified tri(meth)acrylate and isocyanuric acid alkylene oxide-modified tri(meth)acrylate.

[0159] One type of ionizing radiation curable compound may be used alone, or two or more types of ionizing radiation curable compounds may be used in combination.

[0160] When the ionizing radiation-curable compound is an ultraviolet-curable compound, the curable resin composition forming the binder component 41 may contain additives such as a photopolymerization initiator or a photopolymerization accelerator. Examples of the photopolymerization initiator include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzyl dimethyl ketal, benzoyl benzoate, α-acyloxime ester, α-aminoalkylphenone, thioxanthones, and the like. The photopolymerization accelerator reduces polymerization inhibition by air during curing and increases the curing rate. Examples of the photopolymerization accelerator include one or more selected from p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, and the like.

[0161] <Metal Oxide Particles and Other Particles> The metal oxide particles 42 contained in the functional layer 40 may include hollow silica particles 43. The metal oxide particles 42 may include particles other than the hollow silica particles 43. As shown in Fig. 1 , the functional layer 40 may include solid silica particles 44 as the metal oxide particles 42. The functional layer 40 may include inorganic particles or organic particles other than the metal oxide particles 42. The inorganic particles may be magnesium fluoride particles.

[0162] The hollow silica particles 43 have an outer shell layer made of silica. The hollow silica particles 43 have a hollow interior surrounded by the outer shell layer. Air may be contained within the hollow interior. Due to the inclusion of an internal cavity, the hollow silica particles 43 have a refractive index lower than that of silica. The refractive index of the hollow silica particles 43 decreases as the volume of the internal cavity increases. The hollow silica particles 43 reduce the refractive index of the entire functional layer 40. By using hollow silica particles 43 with a large particle diameter and a high ratio of internal space, the refractive index of the functional layer 40 can be further reduced.

[0163] The hollow silica particles 43 may be uniformly dispersed in the functional layer 40. By uniformly dispersing the hollow silica particles 43 in the functional layer 40, the hollow silica particles 43 are prevented from protruding from the first surface 11, and the first surface 11 is smoothed. This improves the slipperiness of the first surface 11 and enhances the scratch resistance of the first surface 11. By uniformly dispersing the hollow silica particles 43 in the functional layer 40, the standard deviation of the area of ​​the Voronoi region can be reduced.

[0164] From the viewpoint of uniformly dispersing the hollow silica particles 43 in the functional layer 40, the following adjustments are effective: The particle size variation of the hollow silica particles 43 may be reduced. The average particle size of the hollow silica particles 43 relative to the average film thickness of the binder component 41 may be adjusted as described above. The affinity between the hollow silica particles 43 and the binder component 41 may be adjusted. The ratio of the content or the average particle size of the hollow silica particles 43 to the other particles contained in the functional layer 40 may be adjusted. The affinity between the hollow silica particles 43 and the other particles contained in the functional layer 40 may be adjusted.

[0165] In order to uniformly disperse the hollow silica particles in the functional layer, the binder component of the functional layer may contain a siloxane-based compound. A functional layer containing hollow silica particles and a siloxane-based compound allows the hollow silica particles to be uniformly dispersed in the functional layer. Furthermore, the functional layer can be given a desired thickness. Therefore, the functional layer can be given a highly accurate anti-reflection function or low-reflection function.

[0166] The solid silica particles 44 are non-hollow silica particles. The solid silica particles 44 are particles that do not have an internal cavity. The solid silica particles 44 may be solid silica particles.

[0167] The average particle size of the solid silica particles 44 is generally smaller than the average particle size of the hollow silica particles 43. Therefore, the solid silica particles 44 can be embedded between adjacent hollow silica particles 43 in the functional layer 40. By including the solid silica particles 44 in the functional layer 40, the strength and hardness of the functional layer 40 are enhanced, further improving the scratch resistance of the first surface 11. The refractive index of the solid silica particles 44 is lower than the refractive index of many metal oxide particles 42. Therefore, by including the solid silica particles 44 in the functional layer 40, the refractive index of the functional layer 40 can be reduced. By including the solid silica particles 44 in the functional layer 40, the reflection suppression function of the functional layer 40 can be reinforced.

[0168] The solid silica particles 44 may be uniformly dispersed in the functional layer 40 together with the hollow silica particles 43. Uniform dispersion of the solid silica particles 44 together with the hollow silica particles 43 in the functional layer 40 suppresses protrusion of the metal oxide particles 42 from the first surface 11, smoothing the first surface 11. This improves the slipperiness of the first surface 11 and enhances the scratch resistance of the first surface 11. Uniform dispersion of the metal oxide particles 42 in the functional layer 40 reduces the standard deviation of the area of ​​the Voronoi region. By adjusting the content ratio or average particle size ratio of the solid silica particles 44 to other particles, the solid silica particles 44 can be uniformly dispersed in the functional layer 40 together with the hollow silica particles 43. By adjusting the affinity between the solid silica particles 44 and other particles, the solid silica particles 44 can be uniformly dispersed in the functional layer 40 together with the hollow silica particles 43.

[0169] The functional layer 40 may contain metal oxide particles 42 other than silica particles. The metal oxide particles 42 other than silica particles may increase the strength and hardness of the functional layer 40 and improve the scratch resistance of the first surface 11. Examples of the metal oxide particles 42 include a single oxide or a mixture of oxides of any of alumina, titanium, tantalum, zirconium, chromium, niobium, cerium, hafnium, and yttrium. The metal oxide particles 42 other than silica may be hollow particles having an internal space, or may be solid particles having no internal space.

[0170] By including metal oxide particles 42 other than silica particles in addition to hollow silica particles 43 in the functional layer 40, the scratch resistance of the first surface 11 can be further improved. Although the details of the reason for the improved scratch resistance are not clear, it is presumed that the following factors contribute to the improved scratch resistance. However, the present disclosure is not bound by the following presumption.

[0171] In addition to hollow silica particles 43, metal oxide particles 42 other than silica particles are dispersed within the binder component 41. The average particle diameter of the hollow silica particles 43 is typically larger than the average particle diameter of the metal oxide particles 42 other than silica particles. Therefore, the metal oxide particles 42 other than silica particles can be interposed between the hollow silica particles 43 within the binder component 41. This allows the hydroxyl groups of the metal oxide particles 42 other than silica particles to form hydrogen bonds with the hydroxyl groups of the hollow silica particles 43. The hydroxyl groups of the metal oxide particles 42 other than silica particles can also form hydrogen bonds with the hydroxyl groups of the binder component. In other words, it is presumed that crosslinking in the functional layer 40 is promoted by the dispersion of the metal oxide particles 42 other than silica particles in addition to the hollow silica particles 43 within the binder component 41. The metal oxide particles 42 other than silica particles can connect the hollow silica particles 43 to each other. The metal oxide particles 42 other than silica particles can connect the hollow silica particles 43 to the binder component 41. From the above, it is presumed that the strength and hardness of the functional layer 40 are enhanced by the functional layer 40 containing metal oxide particles 42 other than silica particles together with hollow silica particles 43, and the scratch resistance of the first surface 11 formed by the functional layer 40 is enhanced.

[0172] The functional layer 40 may contain alumina particles as the metal oxide particles 42 other than silica particles. Alumina particles have a relatively low refractive index among metal oxides. Alumina is a metal oxide having a refractive index of Al ２ O ３ The aluminum oxide is represented by the formula: and α-type, γ-type, σ-type, and mixtures thereof are known. The alumina particles may be surface-modified alumina particles. Examples of modified alumina particles include (meth)acrylic-modified alumina particles and silicone-modified alumina particles.

[0173] Alumina, an oxide of aluminum, can bond with the hollow silica particles 43 and the binder component 41 within the functional layer 40. This promotes cross-linking within the functional layer 40, further reinforcing the functional layer 40. This increases the strength and hardness of the functional layer 40, further improving the scratch resistance of the first surface 11. The average particle diameter of the alumina particles is usually smaller than the average particle diameter of the hollow silica particles 43. Therefore, the alumina particles can penetrate between the hollow silica particles 43 within the functional layer 40. This effectively improves the scratch resistance of the first surface 11.

[0174] Furthermore, the alumina particles can be distributed in the surface direction near the surface of the functional layer 40. This effectively strengthens the strength and hardness near the surface of the functional layer 40. This effectively improves the abrasion resistance against rubber, which is considered to be more severe.

[0175] By using metal oxide particles 42 other than silica particles, it is possible to increase the total amount of metal oxide particles 42 in the functional layer 40 while suppressing the protrusion of the metal oxide particles 42 from the first surface 11. This improves the slipperiness of the first surface 11 and enhances the scratch resistance of the first surface 11. By uniformly dispersing the metal oxide particles 42 in the functional layer 40, it is possible to reduce the standard deviation of the area of ​​the Voronoi region.

[0176] When there is a large difference between the average particle size of the hollow silica particles 43 and the average particle size of the metal oxide particles 42 other than silica particles, aggregation of the metal oxide particles 42 other than silica particles progresses. Two adjacent hollow silica particles 43 are more firmly connected via the aggregated metal oxide particles 42 other than silica particles. The hollow silica particles 43 and the binder component 41 are more firmly connected via the aggregated metal oxide particles 42 other than silica particles. This increases the strength and hardness of the functional layer 40, further improving the scratch resistance of the first surface 11.

[0177] The metal oxide particles 42 other than silica particles can also bond with the solid silica particles 44. The metal oxide particles 42 other than silica particles can also form hydrogen bonds with the solid silica particles 44, thereby promoting cross-linking within the functional layer 40. From this point of view, the functional layer 40 may contain, as the metal oxide particles 42, solid silica particles 44 and metal oxide particles other than silica particles.

[0178] The shape of the hollow silica particles 43, solid silica particles 44, alumina, and other particles dispersed in the functional layer 40 is not particularly limited. The shape of the particles contained in the functional layer 40 may be spherical, spheroidal, substantially spherical such as a polyhedral shape that can approximate a sphere, rod-shaped, plate-shaped, fibrous, irregular, or the like. By making the shape of the particles contained in the functional layer 40 spherical, spheroidal, or substantially spherical, the slipperiness of the first surface 11 is improved, and the scratch resistance of the first surface 11 is enhanced.

[0179] The surfaces of the particles contained in the functional layer 40 may be coated with a silane coupling agent. The silane coupling agent may contain a (meth)acryloyl group or an epoxy group. By subjecting the particles to surface treatment with a silane coupling agent, the affinity between the particles and the binder component is improved, making the particles less likely to aggregate. This allows the particles to be more uniformly dispersed within the binder component.

[0180] Silane coupling agents include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylethyl)

[0033] Examples of the silane derivatives include trimethylsilane, trimethylsilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, 1,6-bis(trimethoxysilyl)hexane, trifluoropropyltrimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane. In particular, it may be one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane.

[0181] The average particle diameter of the hollow silica particles 43 may be larger than the average particle diameter of the solid silica particles 44 and the metal oxide particles other than silica particles 42. The average particle diameter of the hollow silica particles 43 may be 50 nm or more, or 65 nm or more. The average particle diameter of the hollow silica particles 43 may be 100 nm or less, or 80 nm or less.

[0182] The average particle size of the solid silica particles 44 is not particularly limited. The average particle size of the solid silica particles 44 may be 5 nm or more, or 10 nm or more. The average particle size of the solid silica particles 44 may be 20 nm or less, or 15 nm or less. In addition to or instead of the solid silica particles 44 with such an average particle size, the functional layer 40 may contain solid silica particles 44 with an average particle size of 60 μm or more and 100 μm or less.

[0183] The average particle size of the metal oxide particles 42 other than silica and the average particle size of the alumina particles may be 5 nm or more, or 10 nm or more, and the average particle size of the metal oxide particles 42 other than silica and the average particle size of the alumina particles may be 20 nm or less, or 15 nm or less.

[0184] Increasing the content of the hollow silica particles 43 reduces the refractive index of the functional layer 40, allowing the functional layer 40 to exhibit excellent anti-reflection properties. That is, from the viewpoint of the anti-reflection properties of the functional layer 40, a lower limit may be set for the content of the hollow silica particles 43. Setting a lower limit for the content of particles other than the hollow silica particles 43 can ensure the smoothness, strength, and hardness of the functional layer 40. Setting a lower limit for the content of the binder component 41 allows the binder component 41 to stably hold the particles. This prevents the particles from falling off, ensuring excellent scratch resistance. Setting an upper limit for the content of the binder component 41 reduces the refractive index of the functional layer 40, allowing the functional layer 40 to exhibit excellent anti-reflection properties. Setting an upper limit for the content of each particle can prevent significant aggregation of the particles.

[0185] The content of the hollow silica particles may be 100 parts by mass or more, 150 parts by mass or more, or 175 parts by mass or more per 100 parts by mass of the binder component, and 400 parts by mass or less, 300 parts by mass or less, or 250 parts by mass or less per 100 parts by mass of the binder component.

[0186] The content of the solid silica particles may be 10 parts by mass or more, 50 parts by mass or more, 70 parts by mass or more, or 100 parts by mass or more, relative to 100 parts by mass of the binder component, and 200 parts by mass or less, 150 parts by mass or less, or 100 parts by mass or less, relative to 100 parts by mass of the binder component.

[0187] <Method of Producing Functional Layer 40> The functional layer 40 may be produced using a coating liquid containing a curable resin composition and particles. The functional layer 40 may be obtained by curing a coating film of the coating liquid. In this example, the functional layer coating liquid used to produce the functional layer 40 may contain additives such as an antistatic agent, an antioxidant, a surfactant, a dispersant, and an ultraviolet absorber.

[0188] The functional layer coating liquid may contain a silicone-based leveling agent (a silicone-based compound) as an additive. When the functional layer coating liquid contains a silicone-based leveling agent, protrusion of the hollow silica particles 43 from the first surface 11 is suppressed, and the first surface 11 is smoothed. This improves the slipperiness of the first surface 11 and enhances the scratch resistance of the first surface 11. The silicone-based leveling agent can impart excellent slipperiness and excellent antifouling properties (fingerprint wipeability, large contact angle with pure water and hexadecane) to the surface of the functional layer 40.

[0189] By using a silicone-based leveling agent instead of a fluorine-based leveling agent, it is possible to suppress the generation of PFAS as an impurity. PFAS is an artificial organic fluorine compound, and there are concerns about its bioaccumulation. Suppressing the generation of PFAS can contribute to reducing the environmental impact.

[0190] <<Resin Layer (Hard Coat Layer)>> The optical sheet 10 may include a resin layer 30 between the substrate 20 and the functional layer 40. The resin layer 30 includes a cured product of a curable resin composition. The curable resin composition may include one or more of a thermosetting resin composition and an ionizing radiation curable resin composition. The curable resin composition may include one or more of a thermosetting resin and an ionizing radiation curable compound. The resin layer 30 may be a hard coat layer. The resin layer 30 imparts high strength and high hardness to the optical sheet 10 and the first surface 11, and can improve the scratch resistance of the first surface 11. The curable resin composition used to form the resin layer 30 may be the same as the curable resin composition used to form the functional layer 40. The thermosetting resin and ionizing radiation curable compound used to form the resin layer 30 may be the same as the thermosetting resin and ionizing radiation curable compound used to form the functional layer 40.

[0191] The thickness of the resin layer 30 may be 0.1 μm or more, 0.5 μm or more, or 1 μm or more. The thickness of the resin layer 30 may be 100 μm or less, 20 μm or less, or 10 μm or less. By setting the thickness of the resin layer 30 in this manner, it is possible to ensure excellent scratch resistance while suppressing the occurrence of cracks during processing such as cutting of the optical sheet 10.

[0192] The refractive index of the resin layer 30 may be higher than the refractive index of the functional layer 40, from the viewpoint of the anti-reflection function of the functional layer 40. The refractive index of the resin layer 30 may be 1.45 or more and 1.70 or less.

[0193] When the optical sheet 10 includes a high-refractive index layer (described later), the refractive index of the resin layer 30 may be lower than that of the high-refractive index layer. In this example, the refractive index of the resin layer 30 may be 1.50 or higher, or 1.55 or higher. In this example, the refractive index of the resin layer 30 may be 1.65 or lower, or 1.60 or lower. By setting the refractive index of the resin layer 30 in this manner, the resin layer 30 functions as a medium-refractive index layer. This enables interference between the three layers of the resin layer 30 as a medium-refractive index layer, the second functional layer as a high-refractive index layer, and the functional layer as a low-refractive index layer, thereby further reducing reflectance. The refractive index of the resin layer 30 can be adjusted by the resin or particles contained in the curable resin composition.

[0194] The refractive index is a value determined by fitting a reflection spectrum measured by a reflectance photometer to a reflection spectrum calculated from an optical model of a multilayer thin film using Fresnel coefficients.

[0195] The resin layer 30 may be produced using a coating liquid containing a curable resin composition. The resin layer 30 may be obtained by curing a coating film of the coating liquid. In this example, the resin layer coating liquid for producing the resin layer 30 may contain an additive that can be applied to the functional layer coating liquid. That is, the resin layer coating liquid may contain a photopolymerization initiator or a photopolymerization accelerator. The resin layer coating liquid may also contain a leveling agent.

[0196] 3 , the optical sheet 10 may further include a second functional layer 50. The second functional layer 50 is located between the functional layer 40 and the resin layer 30 in the third direction D3, which is the stacking direction. The second functional layer 50 is configured as a layer with a higher refractive index than the resin layer 30 and the functional layer 40, and enhances the reflection suppression function of the optical sheet 10.

[0197] From the viewpoint of the anti-reflection function, the refractive index of the second functional layer and the average thickness of the functional layer can be set as follows: The refractive index of the second functional layer may be 1.55 or more, or 1.56 or more. The refractive index of the second functional layer may be 1.85 or less, or 1.75 or less. The thickness of the second functional layer may be 50 nm or more. The thickness of the second functional layer may be 200 nm or less, or 180 nm or less.

[0198] As shown in FIG. 3 , the second functional layer 50 may include a binder component 51 and particles 52. The binder component 51 is an element that holds the particles 52. The binder component 51 may function as a binding agent for forming a coating film. The binder component 51 may hold the particles contained in the second functional layer 50, thereby allowing the second functional layer 50 to maintain a film form. The binder component 51 may include a resin. The binder component 51 may be configured in the same manner as the binder component 41 of the functional layer 40.

[0199] The particles 52 are particles for adjusting the refractive index and may have an average particle diameter on the nano-order. The second functional layer 50 may be made using a curable resin composition, similar to the functional layer 40. The curable resin composition may include one or more of a thermosetting resin composition and an ionizing radiation curable resin composition. The curable resin composition may include one or more of a thermosetting resin and an ionizing radiation curable compound. The thermosetting resin and ionizing radiation curable compound used to form the second functional layer 50 may be the same as the thermosetting resin and ionizing radiation curable compound used to form the functional layer 40.

[0200] The particles 52 may be particles having a refractive index higher than that of the binder component 51. Examples of the particles 52 include antimony pentoxide, zinc oxide, titanium oxide, cerium oxide, tin-doped indium oxide, antimony-doped tin oxide, yttrium oxide, and zirconium oxide. Zirconium oxide, antimony pentoxide, and titanium oxide impart high strength and high hardness to the second functional layer 50, and can contribute to improving the scratch resistance of the first surface 11.

[0201] The average particle diameter of the particles 52 may be 5 nm or more, or 10 nm or more. The average particle diameter of the particles 52 may be 200 nm or less, 100 nm or less, or 80 nm or less. The content of the particles 52 can be set from the viewpoint of increasing the refractive index of the second functional layer 50 and the strength of the second functional layer 50. The content of the particles 52 may be 100 parts by mass or more, 300 parts by mass or more, or 500 parts by mass or more, per 100 parts by mass of the binder component 51. The content of the particles 52 may be 2500 parts by mass or less, 2200 parts by mass or less, or 2000 parts by mass or less, per 100 parts by mass of the binder component 51.

[0202] The second functional layer 50 may be produced using a coating liquid containing a curable resin composition and particles 52. The second functional layer 50 may be obtained by curing a coating film of the coating liquid. In this example, the second functional layer coating liquid used to produce the second functional layer 50 may contain additives that can be applied to the functional layer coating liquid. That is, the second functional layer coating liquid may contain a photopolymerization initiator or a photopolymerization accelerator. The second functional layer coating liquid may contain an antistatic agent, an antioxidant, a surfactant, a dispersant, an ultraviolet absorber, a leveling agent, etc.

[0203] <<Method for Manufacturing Optical Sheet>> The resin layer 30, functional layer 40, and second functional layer 50 included in the optical sheet 10 can be produced by a wet method. In the wet method, a coating liquid containing components constituting each layer 30, 40, and 50 is prepared. First, the coating liquid is applied to the surface on which each layer 30, 40, and 50 is to be produced. Next, the coating film of the coating liquid is dried and cured to obtain each layer 30, 40, and 50. The coating liquid may contain a solvent in addition to the resin composition and particles used to form each layer. The resin composition may contain solid components constituting each layer and additives such as a polymerization initiator.

[0204] The optical sheet 10 including the substrate 20 and the functional layer 40 may be produced as follows. First, a functional layer coating liquid for forming the functional layer 40 is prepared. Next, the functional layer coating liquid is applied to the substrate 20 to form a coating film. Thereafter, the coating film is dried, and then the coating film is cured. In this manner, the functional layer 40 is produced on the substrate 20, and the optical sheet 10 is obtained.

[0205] When the optical sheet 10 includes a resin layer 30 in addition to the functional layer 40, the resin layer 30 is formed on the substrate 20 before the functional layer 40 is formed. A resin layer coating liquid for forming the resin layer 30 is applied to the substrate 20, and the coating is dried and cured to obtain the resin layer 30. Next, the functional layer 40 is formed on the resin layer 30 to obtain the optical sheet 10. Note that the resin layer 30 may be formed on the substrate 20 in an uncured or semi-cured state, and the resin layer 30 may be completely cured together with the functional layer 40 when the functional layer 40 is cured.

[0206] When the optical sheet 10 includes a second functional layer 50 in addition to the resin layer 30 and the functional layer 40, the second functional layer 50 is formed on the resin layer 30 after the resin layer 30 is formed and before the functional layer 40 is formed. The second functional layer 50 is obtained by applying a second functional layer coating liquid for forming the second functional layer 50 onto the resin layer 30 and drying and curing the coating. Next, the functional layer 40 is formed on the second functional layer 50, thereby obtaining the optical sheet 10. Note that one or more of the resin layer 30 and the second functional layer 50 may be formed in an uncured or semi-cured state, and one or more of the resin layer 30 and the second functional layer 50 may be completely cured together with the functional layer 40 when the functional layer 40 is cured.

[0207] By adding a solvent to the coating liquid, the viscosity of the coating liquid can be adjusted and each component can be dissolved or dispersed in the coating liquid. The solvent may be, for example, one or more of ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), halogenated carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, butyl acetate, etc.), alcohols (butanol, cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), glycol ethers (1-methoxy-2-propyl acetate, etc.), amides (dimethylformamide, dimethylacetamide, etc.), etc.

[0208] If the solvent evaporates too quickly, the solvent will convect vigorously as the coating solution dries. Metal oxide particles 42 contained in the coating solution, such as hollow silica particles 43, may migrate toward the surface of the coating film due to convection caused by solvent evaporation as the coating solution dries. Particles that migrate toward the surface of the coating film may protrude from the first surface or form convex portions on the first surface 11 in the produced optical sheet. In this optical sheet, a large number of metal oxide particles are observed on the first surface 11, and the average area of ​​the Voronoi regions is small.

[0209] From the viewpoint of increasing the average area of ​​the Voronoi region, the coating liquid may contain a solvent with a slow evaporation rate. The relative evaporation rate of the solvent contained in the coating liquid may be 70 or less, or may be 30 to 60. The relative evaporation rate is expressed by comparing the evaporation rate of the target solvent with the evaporation rate of n-butyl acetate, where the evaporation rate of n-butyl acetate is set to 100. As an example, the relative evaporation rate of isobutyl alcohol is 64. The relative evaporation rate of 1-butanol is 47. The relative evaporation rate of 1-methoxy-2-propyl acetate is 44. The relative evaporation rate of ethyl cellosolve is 38. The relative evaporation rate of cyclohexanone is 32.

[0210] The solvent having a relative evaporation rate of 70 or less may account for 10% by mass to 50% by mass, or 20% by mass to 40% by mass, of the total solvent. In this example, the coating liquid may contain a solvent having excellent resin solubility as a solvent other than the solvent having a relative evaporation rate of 70 or less. The relative evaporation rate of the solvent having excellent resin solubility may be 100 or more.

[0211] A high-boiling point solvent may be used as a solvent with a slow relative evaporation rate. An example of a high-boiling point solvent is PMA: propylene glycol monomethyl ether acetate. An example of a solvent with a higher boiling point than PMA is diacetone alcohol. An example of a solvent with a higher boiling point than diacetone alcohol is benzyl acetate. By using a coating liquid for forming a functional layer that contains a larger amount of a high-boiling point solvent, the average area of ​​the Voronoi region can be increased.

[0212] The drying temperature during drying of the coating liquid may be adjusted. The air volume and air speed of the drying air during drying of the coating liquid may be adjusted. Adjusting the drying conditions can also prevent the metal oxide particles 42 from moving toward the surface of the coating film during drying of the coating liquid. Therefore, in the produced optical sheet, the metal oxide particles 42 can be prevented from protruding from the first surface or from forming convex portions on the first surface 11. As a result, the average area of ​​the Voronoi regions can be increased.

[0213] By weakening the drying conditions, it is possible to suppress the rapid evaporation of the solvent, and to suppress the generation of a strong upward flow within the coating film. Therefore, it is possible to suppress the metal oxide particles 42 from gathering on the surface of the coating film. This makes it possible to increase the average area of ​​the Voronoi region.

[0214] Drying conditions can be appropriately selected depending on the characteristics of the material used. When using a coating liquid that easily penetrates into the base layer, the drying time can be shortened. By reducing the amount of penetration into the base layer, it is possible to prevent the metal oxide particles 42 from gathering on the surface of the coating film. When using metal oxide particles 42 that easily aggregate, it is possible to prevent the metal oxide particles 42 from gathering on the surface of the coating film by shortening the drying time. As a result, it is possible to increase the average area of ​​the Voronoi region.

[0215] Furthermore, if the substrate 20 is heated during drying of the coating liquid, the penetration of the coating liquid into the substrate 20 is promoted. Therefore, the drying temperature may be gradually increased to dry the coating liquid while suppressing the penetration of the coating liquid into the substrate 20. Furthermore, during drying of the coating liquid, the drying conditions may be changed between the first half and the second half.

[0216] Furthermore, the proportion of solids in the coating liquid for forming the functional layer may be adjusted. Increasing the proportion of solids increases the viscosity of the coating liquid for forming the functional layer. In this example, the resin is more likely to remain attached to the metal oxide particles 42. Therefore, in the produced optical sheet, it is possible to prevent the metal oxide particles 42 from protruding from the first surface or forming convex portions on the first surface 11. As a result, the average area of ​​the Voronoi region can be increased.

[0217] Decreasing the percentage of solids increases the drying time. Decreasing the percentage of solids can also increase the average area of ​​the Voronoi region in combination with other conditions.

[0218] Examples of means for curing the coating film for forming each layer include irradiation with ionizing radiation such as ultraviolet rays or electron beams, and heating. Curing treatment by irradiation with ionizing radiation is excellent in productivity because it allows curing in a short time.

[0219] In this manner, the optical sheet 10 can be manufactured.

[0220] As described above, the average area of ​​the Voronoi regions having the metal oxide particles 42 observed on the first surface 11 as the generating points can be increased by adjusting the type and composition of the solvent and the drying conditions of the coating film. However, instead of or in addition to these methods, other methods may be used to increase the average area of ​​the Voronoi regions. For example, the optical sheet 10 may include an overcoat layer. The overcoat layer may be provided on the functional layer 40. The overcoat layer may cover the metal oxide particles located on the surface of the functional layer 40. The overcoat layer may constitute the first surface 11 of the optical sheet 10. In other words, the functional layer 40 may be located between the overcoat layer and the substrate 20 in the first direction D1. The thickness of the overcoat layer may be thinner than the thickness of the functional layer 40.

[0221] The average area of ​​the Voronoi regions can also be adjusted by the affinity between the metal oxide particles 42 and the binder component 41. By using a binder component 41 that has a high affinity with the metal oxide particles 42, the binder component 41 can easily surround the metal oxide particles 42. This can prevent the metal oxide particles 42 from protruding from the binder component 41 or from forming convex portions on the first surface 11. The average area of ​​the Voronoi regions may be increased by the combination of the metal oxide particles 42 and the binder component 41.

[0222] The average area of ​​the Voronoi regions can also be adjusted by the affinity between the metal oxide particles 42 contained in the functional layer 40. By using multiple types of metal oxide particles 42 with appropriate affinity, the metal oxide particles 42 can be uniformly dispersed within the binder component 41. This makes it possible to prevent the metal oxide particles 42 from protruding from the binder component 41 or from forming convex portions on the first surface 11. The average area of ​​the Voronoi regions may be increased by combining the metal oxide particles 42 contained in the functional layer 40.

[0223] According to the above-described wet method for manufacturing the optical sheet 10, a long sheet product 5 including a large number of optical sheets 10 can be manufactured, as shown in FIG. 4 . The long sheet product 5 is cut to a predetermined size to obtain the optical sheets 10. According to this example, optical sheets 10 having various dimensions can be obtained from the long sheet product 5 according to needs. Therefore, optical sheets 10 having various dimensions can be provided in a timely manner. As shown in FIG. 4 , by handling the sheet product 5 as a roll 7 wound around a winding core about a winding axis RA, the handling of the sheet product 5 can be improved.

[0224] In addition to the step of manufacturing the optical sheet described above, the method for manufacturing the optical sheet may further include a step of selecting the manufactured optical sheet 10. The step of selecting the optical sheet 10 includes a step of measuring the average area of ​​the Voronoi regions having the metal oxide particles observed on the first surface 11 as generating points, and a step of determining the average area (nm ２ The method may further include a step of selecting an optical sheet in which the value of the reflection coefficient (μm) is equal to or greater than a predetermined value. ２ The average area of ​​the Voronoi regions having metal oxide particles observed on the first surface as generating points is 2500 nm ２ The optical sheet having the above properties has excellent scratch resistance. According to this selection step, an optical sheet having excellent scratch resistance can be selected with high accuracy without performing a scratch test using steel wool or the like.

[0225] <<<Polarizing Plate 60>>> The optical sheet 10 according to the present embodiment may be applied to a polarizing plate 60. In the example shown in Fig. 5 , the polarizing plate 60 includes a first protective sheet 61, a polarizer 62, and a second protective sheet 63. The first protective sheet 61 and the second protective sheet 63 sandwich the polarizer 62 therebetween and cover it from both sides. At least one of the first protective sheet 61 and the second protective sheet 63 may include the optical sheet 10. When only one of the first protective sheet 61 and the second protective sheet 63 includes the optical sheet 10, the other protective sheet may include a substrate 20.

[0226] The polarizer 62 transmits one linearly polarized component and blocks the other linearly polarized component. The polarizer 62 may be an absorptive polarizer that absorbs the other linearly polarized component. The polarizer 62 may be a reflective polarizer that reflects the other linearly polarized component. The polarizer 62 may be a sheet-type polarizer such as a stretched polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, or saponified ethylene-vinyl acetate copolymer film dyed with iodine or the like. The polarizer 62 may be a wire-grid polarizer made of a large number of metal wires arranged in parallel. The polarizer 62 may be a coated polarizer coated with a lyotropic liquid crystal or a dichroic guest-host material, or a multilayer thin-film polarizer.

[0227] <<<Image Display Device 65>>> The optical sheet 10 according to the present embodiment may be applied to a display device 65. In the example shown in FIG. 6 , the display device 65 includes an image forming device 66 and the optical sheet 10. The image forming device 66 has a display surface 66a that displays an image. The optical sheet 10 is overlaid on the image forming device 66 with its second surface 12 facing the display surface 66a. The optical sheet 10 may be bonded to the image forming device 66 via a bonding layer including an adhesive, a sticky material, or the like. A viewer can clearly observe an image displayed by the image forming device 66 through the optical sheet 10 while suppressing reflection on the first surface 11 of the optical sheet 10. The image forming device 66 is not particularly limited. Examples of the image forming device 66 include a liquid crystal display element, an EL display element, a plasma display element, and an electronic paper element.

[0228] <<<Panel 70>>> The optical sheet 10 according to this embodiment can be applied to a variety of applications. FIG. 7 shows a panel 70 to which the optical sheet 10 is applied. The panel 70 includes the optical sheet 10 and a bonded article 71 to which the optical sheet 10 is bonded. The panel 70 constitutes a reflection-suppressing article that has the function of suppressing reflection by the optical sheet 10. The optical sheet 10 is overlaid on the bonded article 71 with its second surface 12 facing the bonded article 71. The optical sheet 10 may be bonded to the bonded article 71 via a bonding layer containing an adhesive, a pressure-sensitive adhesive, or the like. Examples of the bonded article 71 include an instrument panel, a clock, a showcase, a show window, and a window.

[0229] The present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

[0230] <<<<1. Preparation of Optical Sheets>>> Optical sheets according to Examples 1 to 8 and Comparative Examples 1 to 3 were prepared.

[0231] Example 1 Coating liquid 1 for resin layer (coating liquid 1 for HC layer) having the following formulation was applied to a substrate made of triacetyl cellulose with a thickness of 80 μm. Next, the coating film of Coating liquid 1 for resin layer was dried at 70° C. for 1 minute to volatilize the solvent. Thereafter, the coating film of Coating liquid 1 for resin layer was irradiated with an integrated light intensity of 100 mJ / cm. ２ In this way, a resin layer (hard coat layer) having a dry thickness of 10 μm was formed on the substrate.

[0232] Next, functional layer coating liquid 1 (low refractive index layer coating liquid 1) having the following formulation was applied onto the resin layer. The coating film of functional layer coating liquid 1 was then dried at 50°C for 30 seconds (drying air speed: 0.5 m / s), and further dried at 50°C for 30 seconds (drying air speed: 5 m / s) to volatilize the solvent. Next, the coating film of functional layer coating liquid 1 was irradiated with an integrated light intensity of 200 mJ / cm. ２ As a result, a functional layer (low refractive index layer) having a dry thickness of 100 nm was formed, and the optical sheet of Example 1 was obtained.

[0233] <Coating Solution 1 for Resin Layer (Coating Solution 1 for Hard Coat Layer)> Solid silica particles 145 parts by mass (average particle size 12.5 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 46%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-450", solid content 100%) UV-curable acrylate-containing composition 42 parts by mass (manufactured by Daiichi Kogyo Co., Ltd., trade name "New Frontier R-1403MB", solid content 80%) Photopolymerization initiator 11 parts by mass (manufactured by IGM Resins, trade name "Omnirad 184", solid content 100%) Silicone-based leveling agent 6 parts by mass (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., trade name "10-301", solid content 5%) Methyl isobutyl ketone (MIBK) 238 parts by mass Methyl ethyl ketone (MEK) 200 parts by mass Propylene glycol monomethyl ether (PGME) 40 parts by mass

[0234] <Coating Liquid 1 for Functional Layer (Coating Liquid 1 for Low Refractive Index Layer)> Hollow silica particles 2,633 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 229 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI-20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (manufactured by IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,371 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 40,663 parts by mass Propylene glycol monomethyl ether acetate (PMA) 4,879 parts by mass

[0235] <<Example 2>> Example 2 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 2, and otherwise the optical sheet of Example 2 was obtained using the same materials and method as in Example 1.

[0236] <Coating liquid 2 for functional layer (coating liquid 2 for low refractive index layer)> Hollow silica particles 2,633 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 229 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,371 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 35,873 parts by mass Propylene glycol monomethyl ether acetate (PMA) 9,758 parts by mass

[0237] <<Example 3>> Example 3 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 3, and otherwise the optical sheet of Example 3 was obtained using the same materials and method as in Example 1.

[0238] <Coating Liquid 3 for Functional Layer (Coating Liquid 3 for Low Refractive Index Layer)> Hollow silica particles 2,633 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 229 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,371 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 30,904 parts by mass Propylene glycol monomethyl ether acetate (PMA) 14,642 parts by mass

[0239] <<Example 4>> Example 4 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 4, and otherwise the optical sheet of Example 4 was obtained using the same materials and method as in Example 1.

[0240] <Coating Solution 4 for Functional Layer (Coating Solution 4 for Low Refractive Index Layer)> Hollow silica particles 2,633 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 229 parts by mass (manufactured by Toagosei Co., Ltd., trade name "AAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,371 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 30,904 parts by mass Diacetone alcohol 14,642 parts by mass

[0241] <<Example 5>> Example 5 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 5, and otherwise the optical sheet of Example 5 was obtained using the same materials and method as in Example 1.

[0242] <Coating Solution 5 for Functional Layer (Coating Solution 5 for Low Refractive Index Layer)> Hollow silica particles 2,687 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 236 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,398 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 13,687 parts by mass Diacetone alcohol 7,291 parts by mass

[0243] <<Example 6>> Example 6 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 6. Otherwise, the optical sheet of Example 6 was obtained using the same materials and the same method as in Example 1.

[0244] <Coating Solution 6 for Functional Layer (Coating Solution 6 for Low Refractive Index Layer)> Hollow silica particles 2,687 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 236 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,398 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 13,687 parts by mass Benzyl acetate 7,291 parts by mass

[0245] <<Example 6A>> ​​Example 6A differs from the above-described Example 6 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 6A. Otherwise, the optical sheet of Example 6A was obtained using the same materials and the same method as in Example 6.

[0246] <Coating Solution 6A for Functional Layer (Coating Solution 6A for Low Refractive Index Layer)> Hollow silica particles 2,642 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 116 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 193 parts by mass (average particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) UV-curable siloxane compound-containing composition 231 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,462 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 14,296 parts by mass Benzyl acetate 7,616 parts by mass

[0247] <<Example 6B>> Example 6B differs from the above-described Example 6 in that a second functional layer (high refractive index layer) was formed between the functional layer and the resin layer. Otherwise, the optical sheet of Example 6B was obtained using the same materials and the same method as in Example 6.

[0248] Specifically, an optical sheet of Example 6B was produced as follows. A resin layer was formed on a substrate using the same materials and method as in Example 1. Next, coating liquid 1 for second functional layer (coating liquid 1 for high refractive index layer) having the following formulation was applied onto the resin layer. Thereafter, the coating film of coating liquid 1 for second functional layer was dried at 70°C for 1 minute to volatilize the solvent. Next, the coating film of coating liquid 1 for second functional layer was irradiated with an integrated light intensity of 100 mJ / cm. ２ The laminate was irradiated with ultraviolet light at 1000 kJ / cm². This resulted in a second functional layer (high refractive index layer) with a dry thickness of 150 nm. A functional layer (low refractive index layer) was then formed on the second functional layer using the same materials and method as in Example 1, thereby obtaining the optical sheet of Example 6B.

[0249] <Coating Liquid 1 for Second Functional Layer (Coating Liquid 1 for High Refractive Index Layer)> High refractive index particles: 429 parts by mass (Nippon Shokubai Co., Ltd., trade name "Zircostar", solid content 70%) UV-curable siloxane compound-containing composition: 100 parts by mass (Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) Photopolymerization initiator: 16 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Silicone leveling agent: 8 parts by mass (Dainichiseika Color & Chemicals Mfg. Co., Ltd., trade name "10-301", solid content 5%) Methyl isobutyl ketone: 5779 parts by mass Propylene glycol monomethyl ether (PGME): 5914 parts by mass

[0250] <<Example 7>> Example 7 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 7, and the optical sheet of Example 7 was obtained using the same materials and the same method as in Example 1.

[0251] <Coating Solution 7 for Functional Layer (Coating Solution 7 for Low Refractive Index Layer)> Hollow silica particles 2,687 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 236 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,398 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 11,255 parts by mass Benzyl acetate 9,723 parts by mass

[0252] <<Example 8>> Example 8 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 8, and the optical sheet of Example 8 was obtained using the same materials and the same method as in Example 1.

[0253] <Coating Solution 8 for Functional Layer (Coating Solution 8 for Low Refractive Index Layer)> Hollow silica particles 2,669 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) UV-curable siloxane compound-containing composition 234 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 13 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Leveling agent 1,389 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 6,106 parts by mass Benzyl acetate 6,273 parts by mass

[0254] <<Comparative Example 1>> Comparative Example 1 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 9, and otherwise the optical sheet of Comparative Example 1 was obtained using the same materials and the same method as in Example 1.

[0255] <Coating Solution 9 for Functional Layer (Coating Solution 9 for Low Refractive Index Layer)> Hollow silica particles 2,645 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 117 parts by mass (average particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 193 parts by mass (average particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) UV-curable siloxane compound-containing composition 231 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content 100%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator: 14 parts by mass (IGM Resins, trade name "Esacure 1001M", solid content 100%) Silicone leveling agent: 97 parts by mass (Dainichiseika Color & Chemicals Mfg. Co., Ltd., trade name "10-301", solid content 5%) Methyl isobutyl ketone (MIBK): 37,986 parts by mass

[0256] <<Comparative Example 2>> Comparative Example 2 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 10. Otherwise, the optical sheet of Comparative Example 2 was obtained using the same materials and the same method as in Example 1.

[0257] <Coating Liquid 10 for Functional Layer (Coating Liquid 10 for Low Refractive Index Layer)> Hollow silica particles 374 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 120 parts by mass (average particle diameter 12.5 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 46%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 4 parts by mass (manufactured by IGM Resins, trade name "Omnirad 127", solid content 100%) Leveling agent 115 parts by mass (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 8544 parts by mass Propylene glycol monomethyl ether acetate (PMA) 1000 parts by mass

[0258] <<Comparative Example 3>> Comparative Example 3 differs from the above-described Example 1 in that functional layer coating liquid 1 was changed to the following functional layer coating liquid 11. Otherwise, the optical sheet of Comparative Example 3 was obtained using the same materials and the same method as in Example 1.

[0259] <Coating Liquid 11 for Functional Layer (Coating Liquid 11 for Low Refractive Index Layer)> Hollow silica particles 603 parts by mass (average particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 54 parts by mass (average particle diameter 12.5 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 46%) UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Photopolymerization initiator 4 parts by mass (manufactured by IGM Resins, trade name "Omnirad 127", solid content 100%) Leveling agent 123 parts by mass (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Methyl isobutyl ketone (MIBK) 8,296 parts by mass Propylene glycol monomethyl ether acetate (PMA) 990 parts by mass

[0260] <<<2. Measurement and Evaluation>>> Measurement and evaluation were carried out on the optical sheets according to the examples and comparative examples as described below. The test environment for each measurement and evaluation was a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Before starting each measurement and evaluation, the target sample was placed in the above-mentioned test environment for 16 hours.

[0261] <<2-1. Luminous reflectance Y>> Samples measuring 5 cm x 5 cm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure that there were no abnormalities such as dust or scratches. The luminous reflectance Y (%) of the optical sheet according to each example was measured using the method described above. The luminous reflectance Y was measured using a UV-Visible-Near-Infrared Spectrophotometer "V780" manufactured by JASCO Corporation. The measurement results of the luminous reflectance Y are shown in Table 1.

[0262] <<2-2. Total Light Transmittance>> Samples measuring 10 cm x 5 cm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure that there were no defects such as dust or scratches. The total light transmittance (%) of the optical sheets according to each example was measured using the method described above. The total light transmittance was measured using a haze meter "HM-150" manufactured by Murakami Color Research Laboratory. The measurement results of the total light transmittance are shown in Table 1.

[0263] <<2-3. Transmission Haze Value>> Samples measuring 10 cm x 5 cm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure there were no defects such as dust or scratches. The transmission haze (%) of the optical sheets according to each example was measured using the method described above. The transmission haze was measured using a haze meter "HM-150" manufactured by Murakami Color Research Laboratory. The measurement results of the transmission haze are shown in Table 1.

[0264] <<2-4. Average Area of ​​Voronoi Regions>> Samples measuring 5 mm x 5 mm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure that there were no defects such as dust or scratches. Using the method described above, the average area (nm ) of Voronoi regions with metal oxide particles observed on the first surface as generating points was calculated for the optical sheets according to each example. ２ ) was measured.

[0265] First, an observation image of the first surface was obtained using a scanning electron microscope (SEM). The scanning electron microscope used was an ultra-high resolution field emission scanning electron microscope SU-9000 manufactured by Hitachi High-Technologies Corporation. As an example, an observation image of Example 1 obtained using the scanning electron microscope is shown in FIG. 8A.

[0266] Next, the images acquired by the scanning electron microscope were binarized using the image processing software "ImageJ" and "Fiji." As an example, the binarized image of the first surface for Example 1 is shown in FIG. 8B. The image shown in FIG. 8B was obtained by binarizing the observed image of the first surface shown in FIG. 8A.

[0267] Thereafter, using "ImageJ" and "Fiji," the mother points were identified from the positions of the metal oxide particles observed on the first surface 11 based on the binarized image. As an example, the distribution of the mother points identified for Example 1 is shown in FIG. 8C. The mother point distribution shown in FIG. 8C was generated based on the observed image of the first surface shown in FIG. 8B.

[0268] Next, a Voronoi diagram was created using the image processing software "ImageJ" and "Fiji," and the area of ​​the Voronoi region (nm ２ From the area measurement results, the average area (nm ２ From the area measurement results, the standard deviation (nm ２ The ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions was calculated. The average area of ​​the Voronoi regions (nm ２ ), the standard deviation of the area of ​​the Voronoi region (nm ２ ), and the ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions are shown in the columns "Average Area," "Standard Deviation," and "Standard Deviation / Average Area" in Table 1, respectively.

[0269] 9A to 9E show Voronoi diagrams obtained from observation images of the first surfaces of the optical sheets according to Examples 1 to 5, respectively. Figures 9F and 9G show Voronoi diagrams obtained from observation images of the first surfaces of the optical sheets according to Comparative Examples 1 and 2, respectively. The Voronoi diagram shown in Fig. 9A was generated from the distribution of generating points shown in Fig. 8C.

[0270] <<2-5. Dynamic Friction Coefficient>> Samples measuring 15 cm x 25 cm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure there were no abnormalities such as dust or scratches. The dynamic friction coefficient of the optical sheets according to each example was measured using the method described above. The dynamic friction coefficient was measured using a device that combined a Shimadzu EZ-LX compact desktop testing machine with a friction coefficient measuring device available from Shimadzu as a friction test jig. The measurement results of the dynamic friction coefficient are shown in Table 1.

[0271] <<2-6. Steel Wool Scratch Resistance Test>> Samples measuring 50 mm x 100 mm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure there were no abnormalities such as dust or scratches. A steel wool scratch resistance test was carried out on the optical sheets according to each example using the method described above. For the steel wool scratch resistance test, a Gakushin-type rub fastness tester "AB-301-S" manufactured by Tester Sangyo Co., Ltd. was used.

[0272] After completing the steel wool scratch resistance test at a load of 1000 g for 1000 cycles, the sample was removed from the tester, and the surface of the sample, which was composed of the first side of the optical sheet, was observed under the observation conditions described above. Each sample was evaluated according to the following criteria. In the following criteria, "0" indicates the highest scratch resistance, and scratch resistance decreases from "0" to "5." Five samples were evaluated for each example, and the worst evaluation result for each example is shown in Table 1. For examples shown in Table 1, all five samples were evaluated as "0." A rating of "0," "1," "2," or "3" does not pose a problem in application to display devices. Therefore, optical sheets rated "0," "1," "2," or "3" are evaluated as having resistance to the steel wool scratch resistance test. Optical sheets rated "4" or "5" are evaluated as not having resistance to the steel wool scratch resistance test. The test conditions for the steel wool scratch resistance test, "load 1000 g, 1000 cycles," are more severe than the conditions normally required for anti-reflection sheets (AR sheets, LR sheets) that are attached to the display surface of a display device.

[0273] (Evaluation criteria) 5: Peeling of the functional layer occurred. 4: Scratches that will cause problems when applied to a display device were observed. 3: Discoloration due to deformation of the hollow silica and patterns resembling shallow scratches were observed on the surface. The discoloration and patterns were not serious enough to cause problems when applied to a display device. 2: Discoloration due to deformation of the hollow silica was observed on the surface, but no scratches or patterns were observed. The discoloration was not serious enough to cause problems when applied to a display device. 1: Slight discoloration was observed by careful observation, but was not noticeable under normal observation. 0: No discoloration, patterns, etc. were observed at all.

[0274] <<2-7. Rubber Scratch Resistance Test (CS6 Scratch Resistance Test)>> Samples measuring 50 mm x 100 mm were cut out from the optical sheets according to the examples and comparative examples. The samples were visually inspected to ensure there were no abnormalities such as dust or scratches. Using the method described above, a rubber scratch resistance test was carried out on the optical sheets according to each example. As described above, the sliding piece was a "Jumbo Wearer (registered trademark) CS-6" manufactured by TABER Co., Ltd. For the rubber scratch resistance test, a Gakushin-type abrasion fastness tester "AB-301-S" manufactured by Tester Sangyo Co., Ltd. was used.

[0275] After completing the 1000-cycle rubber abrasion resistance test under a load of 250 g, the sample was removed from the tester, and the surface of the sample, which was composed of the first side of the optical sheet, was observed under the observation conditions described above. Each sample was evaluated according to the following criteria. In the following criteria, "0" indicates the highest abrasion resistance, and abrasion resistance decreases from "0" to "5." Five samples were evaluated for each example, and the worst evaluation result for each example is shown in Table 1. For examples shown in Table 1, all five samples were evaluated as "0." A rating of "0," "1," "2," or "3" does not pose a problem in application to display devices. Therefore, optical sheets rated "0," "1," "2," or "3" are evaluated as having resistance to the rubber abrasion resistance test. Optical sheets rated "4" or "5" are evaluated as not having resistance to the rubber abrasion resistance test.

[0276] (Evaluation criteria) 5: Peeling of the functional layer occurred. 4: Scratches that will cause problems when applied to a display device were observed. 3: Discoloration due to deformation of the hollow silica and patterns resembling shallow scratches were observed on the surface. The discoloration and patterns were not serious enough to cause problems when applied to a display device. 2: Discoloration due to deformation of the hollow silica was observed on the surface, but no scratches or patterns were observed. The discoloration was not serious enough to cause problems when applied to a display device. 1: Slight discoloration was observed by careful observation, but was not noticeable under normal observation. 0: No discoloration, patterns, etc. were observed at all.

[0277]

[0278]

[0033] 5: Sheet article, 6: Winding core, 7: Roll, 10: Optical sheet, 11: First surface, 12: Second surface, 20: Substrate, 30: Resin layer, 40: Functional layer, 41: Binder component, 42: Metal oxide particles, 43: Hollow silica particles, 44: Solid silica particles, 50: Second functional layer, 51: Binder component, 52: Particles, 60: Polarizing plate, 61: First protective sheet, 62: Polarizer, 63: Second protective sheet, 65: Display device, 66: Image forming device, 66a: Display surface, 70: Panel, 71: Article to be bonded

Claims

1. An optical sheet including a first surface and a second surface opposite to the first surface, comprising a substrate and a functional layer in the order from the second surface toward the first surface, the functional layer including a binder component and metal oxide particles, and an average area of ​​a Voronoi region having the metal oxide particles as a base point observed on the first surface is 2500 nm ２ That's it for the optical sheet.

2. The average area of ​​the Voronoi region is 3200 nm ２ The optical sheet according to claim 1 .

3. The standard deviation of the area of ​​the Voronoi region is 950 nm ２ The optical sheet according to claim 1 .

4. The optical sheet according to claim 1, wherein a ratio of the standard deviation of the area of ​​the Voronoi regions to the average area of ​​the Voronoi regions is 0.30 or more.

5. The optical sheet according to claim 1, wherein the sliding piece is a "Jumbo Wearaser (registered trademark), product number: CS-6" manufactured by TABER Corporation, and the dynamic friction coefficient of the first surface between the sliding piece and a load of 200 g is applied is 0.95 or less.

6. The optical sheet according to claim 1, which is resistant to a steel wool scratch resistance test on the first surface under the following conditions: Scratch resistance test: Using steel wool #0000 as a sliding piece, the sheet is moved back and forth 1000 times with a load of 1000 g, a moving speed of 80 mm / sec, and a one-way moving distance of 40 mm.

7. The optical sheet according to claim 1, which is resistant to a rubber scratch resistance test on the first surface under the following conditions: Scratch resistance test: A Jumbo Wearaser (registered trademark, product number: CS-6) manufactured by TABER is used as a sliding piece, and the piece is moved back and forth 150 times with a load of 200 g, a moving speed of 200 mm / sec, and a one-way moving distance of 50 mm.

8. The optical sheet according to claim 1, wherein the functional layer contains hollow silica particles.

9. The optical sheet according to claim 1, wherein the functional layer contains alumina particles.

10. The optical sheet according to claim 1, wherein the functional layer contains a siloxane-based compound.

11. The optical sheet according to claim 1, further comprising a resin layer located between the substrate and the functional layer, the resin layer including a cured product of a curable resin composition.

12. A sheet article comprising a plurality of the optical sheets according to any one of claims 1 to 11.

13. The sheet article of claim 12, wound about a winding axis.

14. A polarizing plate comprising a first protective sheet, a polarizer, and a second protective sheet, wherein at least one of the first protective sheet and the second protective sheet comprises the optical sheet according to any one of claims 1 to 11.

15. A display device comprising: an image forming device; and an optical sheet according to any one of claims 1 to 11 superimposed on the image forming device.

16. A panel comprising: a bonded article; and an optical sheet according to any one of claims 1 to 11 bonded to the bonded article.

17. An optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet comprising a base material and a functional layer in this order from the second surface toward the first surface, the functional layer including a binder component and metal oxide particles, the optical sheet comprising: a step of measuring an average area of ​​Voronoi regions having the metal oxide particles observed on the first surface as mother points; and a step of measuring the average area (nm ２ and selecting an optical sheet for which the difference between the optical characteristics is equal to or greater than a predetermined value.

18. An optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet including a base material and a functional layer in the order from the second surface toward the first surface, the functional layer including a binder component and metal oxide particles, the optical sheet being produced; and ２ and selecting an optical sheet having a predetermined value or more of the characteristic of the optical sheet.

Images