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

Abstract

This optical sheet has 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 hollow silica particles. A recess having a width of 0.1-1.5 μm and a depth of 10 nm or more is included in a 10 μm × 10 μm region of the first surface.

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] The outermost surface of conventional display devices is composed of a cover glass. The cover glass is provided with a reflection suppressing function that suppresses reflection of incident light. In recent years, from the perspective of achieving thinner and lighter devices, the use of resin optical sheets instead of cover glass has been considered. The optical sheet has a low refractive index functional layer as a surface layer. The functional layer can be produced by sputtering an inorganic material. As an alternative method, as disclosed in Patent Document 1, the functional layer can be produced by curing a coating film containing hollow silica particles. A low refractive index layer formed by curing a coating film containing low refractive index particles has the advantages of little hue change in obliquely reflected light, excellent chemical stability, and low manufacturing costs.

[0003] Touch-sensing functions are increasingly being applied to display devices such as laptop computers, in addition to smartphones and tablet devices. Optical sheets used in such display devices require scratch resistance appropriate for their intended use. The scratch resistance of functional layers containing hollow silica particles is somewhat inferior to that of inorganic material layers formed by sputtering.

[0004] Patent Document 1: WO2019 / 208786A

[0005] The present disclosure aims to improve the scratch resistance of an optical sheet containing hollow silica particles.

[0006] An optical sheet according to one embodiment of the present disclosure is an optical sheet including a first surface and a second surface opposite to the first surface, and is provided with 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 hollow silica particles, and the first surface includes depressions having a width of 0.1 μm or more and 1.5 μm or less and a depth of 10 nm or more in a 10 μm x 10 μm area.

[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 includes the optical sheet 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 an optical sheet 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 an optical sheet 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 one embodiment of the present disclosure includes, for an optical sheet including a first surface and a second surface opposite to the first surface, a substrate and a functional layer in that order from the second surface to the first surface, the functional layer including a binder component and hollow silica particles, the method comprising the steps of: acquiring an image of a 10 μm x 10 μm area of ​​the first surface; and selecting, based on the image, an optical sheet in which said area includes depressions having a width of 0.1 μm or more and 0.15 μm or less and a depth of 10 nm or more.

[0012] A method for manufacturing an optical sheet according to one embodiment of the present disclosure includes the steps of: preparing an optical sheet including a first surface and a second surface opposite to the first surface, the optical sheet comprising a substrate and a functional layer in that order from the second surface toward the first surface, the functional layer including a binder component and hollow silica particles; and selecting an optical sheet including a depression having a width of 0.1 μm or more and 0.15 μm or less and a depth of 10 nm or more in a 10 μm x 10 μm area on the first surface.

[0013] According to the present invention, the scratch resistance of an optical sheet containing hollow silica particles 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 showing an example of depressions formed on a first surface of the optical sheet. FIG. 3 is a cross-sectional view showing an example of a cross-sectional profile of depressions formed on the first surface of the optical sheet, showing a cross-section along line III-III in FIG. 2. FIG. 4 is a cross-sectional view corresponding to FIG. 3 and showing another example of the cross-sectional profile of the depressions. FIG. 5 is a plan view showing the first surface of the optical sheet and is a diagram showing an example of the distribution of depressions. FIG. 6 is a plan view showing the first surface of the optical sheet and is a diagram showing an example of the distribution of depressions. FIG. 7 is a cross-sectional view corresponding to FIG. 1 and is a diagram showing another example of the optical sheet. FIG. 8 is a perspective view showing an example of a sheet article including the optical sheet. FIG. 9 is a cross-sectional view showing an example of a polarizing plate including the optical sheet. FIG. 10 is a cross-sectional view showing an example of a display device including the optical sheet. FIG. 11 is a cross-sectional view showing an example of a panel including the optical sheet. FIG. 12 is an image showing the surface of Example 1. FIG. 13 is an image showing the surface of Example 2. FIG. 14 is an image showing the surface of Example 3. FIG. 15 is an image showing the surface of Comparative Example 1.

[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 comprising, in this order from the second surface to the first surface, a substrate and a functional layer, the functional layer including a binder component and hollow silica particles, and the first surface including, in a 10 μm × 10 μm region, depressions having a width of 0.1 μm or more and 1.5 μm or less and a depth of 10 nm or more.

[0017] <2> The optical sheet according to <1>, wherein the depth of the depressions is 70 nm or less.

[0018] <3> The optical sheet according to <1> or <2>, wherein the number of the recesses included in the 10 μm×10 μm area on the first surface is three or more.

[0019] <4> The optical sheet according to any one of <1> to <3>, wherein the number of the recesses included in the 10 μm×10 μm area on the first surface is 11 or more.

[0020] <5> The optical sheet according to any one of <1> to <4>, wherein the number of the recesses included in the 10 μm×10 μm area on the first surface is 50 or less.

[0021] <6> The optical sheet according to any one of <1> to <5>, wherein the depression is included in each of four small regions obtained by dividing the 10 μm×10 μm region into two equal parts along each side.

[0022] <7> The optical sheet according to any one of <1> to <6>, wherein the first surface has an arithmetic mean roughness Sa of 8.0 nm or less.

[0023] <8> The optical sheet according to any one of <1> to <7>, wherein the first surface includes a flat portion around the recess.

[0024] <9> The optical sheet according to any one of <1> to <8>, wherein a proportion of the recesses in a 10 μm×10 μm area of ​​the first surface is 15% or less.

[0025] <10> The optical sheet according to any one of <1> to <9>, wherein the ratio of the depth to the width of the depression is 0.030 or more.

[0026] <11> The optical sheet according to any one of <1> to <10>, 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.

[0027] <12> The optical sheet according to any one of <1> to <11>, which has resistance to a scratch resistance test on the first surface using a felt under the following conditions: Scratch resistance test: Using a Jumbo Wearaser (registered trademark), product number CS-7, manufactured by TABER Corporation as a sliding piece, the optical sheet is reciprocated 10,000 times under a load of 200 g, a moving speed of 200 mm / sec, and a one-way moving distance of 50 mm.

[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> A method for selecting an optical sheet, the 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 to the first surface, the functional layer including a binder component and hollow silica particles, the method comprising: acquiring an image of a 10 μm × 10 μm area of ​​the first surface; and selecting, based on the image, an optical sheet in which said area includes depressions having a width of 0.1 μm or more and 0.15 μm or less and a depth of 10 nm or more.

[0035] <20> A method for manufacturing an optical sheet, the method comprising: producing an optical sheet including a first surface and a second surface opposite to the first surface, the optical sheet comprising, in order from the second surface to the first surface, a substrate and a functional layer, the functional layer including a binder component and hollow silica particles; and selecting an optical sheet including an optical sheet having a depression having a width of 0.1 μm or more and 0.15 μm or less and a depth of 10 nm or more in a 10 μm × 10 μm area on the first surface.

[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] The term "sheet surface (film surface, plate surface)" refers to a surface that coincides with the planar direction of the target sheet-like (film-like, plate-like) member when the target sheet-like (film-like, plate-like) member is viewed overall and in a global perspective. The normal direction to the sheet-like (plate-like, film-like) member refers to the normal direction to the sheet surface (plate surface, film surface) of the sheet-like (plate-like, film-like) member.

[0039] 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.

[0040] In order to clarify the relationship between directions between 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 with an x ​​in a circle, as shown in FIG. 1, for example. An arrow pointing out from the paper in a direction perpendicular to the paper surface of the drawing is indicated by a symbol with a dot in a circle, as shown in FIG. 2, for example.

[0041] <<<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 order from the first surface 11 to the second surface 12, a substrate 20 and a functional layer 40. The functional layer 40 includes a binder component 41 and hollow silica particles 43. The refractive index of the functional layer 40 is lower than the refractive index of the binder component 41 due to the inclusion of the hollow silica particles 43. The low-refractive index functional layer 40 can suppress reflection of light incident on the first surface 11.

[0042] The thickness of the functional layer with anti-reflection function is as thin as about 100 nm. In conventional optical sheets, the first surface could be damaged by rubbing the low-refractive index functional layer with a finger, for example. The functional layer contains hollow silica particles to reduce the refractive index. Because of their hollow structure, the hollow silica particles have a relatively large particle diameter. Therefore, the hollow silica particles are easily broken and easily deformed, causing them to fall off from the binder component. For this reason, the scratch resistance of the functional layer surface of conventional optical sheets was insufficient.

[0043] On the other hand, in this embodiment, measures have been taken to improve scratch resistance. Specifically, one or more depressions having a width of 0.1 μm or more and a depth of 10 nm or more are included in a 10 μm × 10 μm square measurement area on the first surface 11. The presence of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more can improve scratch resistance. The details of why the presence of depressions 45 improves scratch resistance are unclear. It is speculated that bleed-out (precipitation) of the leveling agent affects the improvement in scratch resistance. The leveling agent is added to the coating liquid used to form the functional layer 40. The leveling agent floats near the surface of the functional layer 40 during production of the functional layer 40. The leveling agent reduces the surface tension of the functional layer 40 and smooths the surface of the functional layer 40. The leveling agent improves the slipperiness and antifouling properties of the first surface 11.

[0044] When various leveling agents were tested, depressions 45 occurred when a specific combination of leveling agents was used. Furthermore, for optical sheets 10 having depressions 45, the scratch resistance of the first surface 11 was improved. As an example, the scratch resistance of the first surface 11 could be improved by adding a silicone-based leveling agent to a fluorine-based leveling agent. From this phenomenon, it was inferred that the leveling agent bleeds out onto the first surface 11 when a specific combination of leveling agents was used. In this inference, the depressions 45 are thought to be traces of the leveling agent bleeding out. In optical sheets 10 having depressions 45, the leveling agent bleeds out from the functional layer 40 significantly improved the slipperiness of the first surface 11, resulting in improved scratch resistance.

[0045] The depressions 45 are confirmed using an atomic force microscope (AFM). Three measurement samples are cut out from the target optical sheet 10. The three measurement samples are cut out from regions of the optical sheet that are at least 10 mm apart from each other. Each measurement sample is a 5 mm x 5 mm square. The measurement samples are visually confirmed to be free of foreign matter, scratches, etc. For each measurement sample, images of the first surface are obtained using the atomic force microscope in five measurement regions that are spaced apart from each other. The measurement regions are 10 μm x 10 μm squares. Images are obtained using the atomic force microscope for the five measurement regions of each of the three measurement samples, i.e., a total of 15 measurement locations. If depressions 45 are confirmed in 12 or more of the 15 images obtained, it is determined that depressions 45 are present in the 10 μm x 10 μm square measurement region of the first surface 11. If no depression 45 is found in four or more images, it is determined that no depression 45 exists in the 10 μm×10 μm square measurement area on the first surface 11 .

[0046] The atomic force microscope can be an "SPM-9700" manufactured by Shimadzu Corporation. The cantilever can be an NCHR manufactured by Nanoworld (resonance frequency: 320 kHz, spring constant: 42 N / m). The surface shape of the sample can be measured in On-Line (measurement) mode using the "SPM Manager" software that comes with the atomic force microscope. The measurement conditions can be set as follows: - Measurement mode: Phase - Scanning range: 10 μm x 10 μm - Scanning speed: 2.0 to 2.5 Hz (using a 10 μm scanner) - Number of pixels: 512 x 512

[0047] The width W and depth D of the depressions 45 in each measurement area are specified as follows: First, a square measurement area of ​​10 μm×10 μm is observed from the normal direction of the optical sheet 10, and a planar image of the measurement area is obtained. The planar image is an image obtained by observing the first surface 11 from the normal direction of the optical sheet 10 using an atomic force microscope. Based on the planar image of the measurement area, the maximum length L of the depressions 45 present in the measurement area is determined. ＭＡＸ The maximum length LＭＡＸ means the maximum length of a straight line segment connecting two points on the periphery of the recess 45 when observing the measurement area along the normal direction of the optical sheet 10. In other words, the maximum length L ＭＡＸ corresponds to the maximum value of the distance between two parallel lines sandwiching the depression 45. FIG. 2 is a plan view showing an example of the depression 45 from the normal direction of the optical sheet 10. As an example, the depression 45 shown in FIG. 2 has the longest maximum length L ＭＡＸ The recess 45 has the following structure.

[0048] The shape of the recesses 45 when observed from the normal direction of the optical sheet 10, i.e., the planar shape of the recesses 45, is not particularly limited. The planar shape of the recesses 45 may have a curved outline, a linear outline, or an outline consisting of a combination of curves and straight lines. The planar shape of the recesses 45 may be circular, elliptical, or oval. The planar shape of the recesses 45 may also be polygonal, such as triangular, rectangular, or pentagonal.

[0049] Next, a measurement cross-sectional image is acquired by an atomic force microscope. The measurement cross-sectional image is an observation image of a plane parallel to the normal direction of the optical sheet 10. The measurement cross-sectional image is an observation image of a plane that crosses the depression 45 within the measurement region ... ＭＡＸ is an observed image of a plane including two points on the periphery of the depression 45 from which the measured cross-sectional image is obtained. That is, the measured cross-sectional image is a cross-section taken along line III-III in Fig. 2. Fig. 3 shows an example of the measured cross-sectional image.

[0050] The deepest portion 45c of the depression 45 is identified from the cross-sectional profile 45x of the measured cross-sectional image of the depression 45 shown in FIG. 3 . The deepest portion 45c is the lowest position within the depression. Next, a high end portion 45a and a low end portion 45b, which are both ends of the depression 45, are identified in the cross-sectional profile 45x of the depression 45. The high end portion 45a is the higher of the two ends of the depression 45. The low end portion 45b is the lower of the two ends of the depression 45. The high end portion 45a and the low end portion 45b are identified as the first inflection points (local maximum values) in the normal direction of the optical sheet 10, which are located on both sides of the deepest portion 45c in the cross-sectional profile 45x of the depression 45.

[0051] The width W of the recess 45 in each measurement region means the distance between the high end 45 a and the low end 45 b along the sheet surface of the optical sheet 10. In the example shown in FIG. 3 , the width W of the recess 45 means the distance between the high end 45 a and the low end 45 b along the first direction D1. The depth D of the recess 45 in each measurement region means the distance between the low end 45 b and the deepest part 45 c along the normal direction of the optical sheet 10. In the example shown in FIG. 3 , the depth D of the recess 45 means the distance between the low end 45 b and the deepest part 45 c along the third direction D3.

[0052] However, as shown in Figure 4, a small protrusion 45e may exist within the recess 45. When both ends of the recess 45 are identified using the method described above, the large recess located in the center of Figure 4 is divided into two recesses 45 by the protrusion 45e. However, assuming that the improvement in slipperiness of the first surface 11 is due to bleeding out of the leveling agent, the recess located in the center of Figure 4 should be interpreted as one recess 45. Even from the perspective of whether the recess structure physically reduces slipperiness, the recess located in the center of Figure 4 should be interpreted as one recess 45.

[0053] Therefore, when the first distance LX1 between the provisional low end (protrusion 45e) along the normal direction of the optical sheet 10 and the deepest portion 45c described above is 30% or less of the second distance LX2 between the high end 45a and the deepest portion 45c along the normal direction of the optical sheet 10, the provisional low end is treated as the protrusion 45e, not the low end 45b, of the depression 45. In the example shown in Figure 4, the distance LX1 between the deepest portion 45c and the protrusion 45e along the third direction D3 is 30% or less of the distance LX2 between the high end 45a and the deepest portion 45c along the third direction D3. Therefore, the protrusion 45e does not constitute the low end 45b.

[0054] In this manner, the width W of the depression 45 in each measurement region and the depth D of the depression 45 in each measurement region are identified. From the width W and depth D of the depression 45 thus identified, it is determined whether or not the depression in question is a depression having a width of 0.1 μm or more and a depth of 10 nm or more.

[0055] In addition, the maximum length L ＭＡＸ If the width W of the longest recess 45 is 0.1 μm or more but the depth D of the recess is less than 10 nm, the recess does not fall under the category of "a recess having a width of 0.1 μm or more and a depth of 10 nm or more." ＭＡＸ If the depth D of the longest depression 45 is 10 nm or more but the width W of the depression is less than 0.1 μm, the depression does not fall under the category of "a depression having a width of 0.1 μm or more and a depth D of 10 nm or more." In these cases, the investigation continues to determine whether the 10 μm × 10 μm square measurement area includes "a depression having a width of 0.1 μm or more and a depth D of 10 nm or more." Within the 10 μm × 10 μm square measurement area, the maximum length L ＭＡＸ The next longest depression 45 is identified, and the width W and depth D of the identified depression are measured. From the measured values ​​of width W and depth D, it is determined whether the depression being measured corresponds to "a depression having a width W of 0.1 μm or more and a depth D of 10 nm or more." This determination is repeated until a "depression having a width W of 0.1 μm or more and a depth D of 10 nm or more" is found, or until there are no more depressions 45 to be measured.

[0056] In the optical sheet 10 of the present embodiment, from the viewpoint of improving scratch resistance, the width W of the recess 45 is 0.1 μm or more, as described above. From the viewpoint of further improving scratch resistance, the width W of the recess 45 may be 0.2 μm or more, 0.3 μm or more, or 0.4 μm or more. From the viewpoint of improving scratch resistance, the depth D of the recess 45 is 10 nm or more. From the viewpoint of further improving scratch resistance, the depth D of the recess 45 may be 15 nm or more, 18 nm or more, 20 nm or more, or 23 nm or more.

[0057] In the optical sheet 10 of the present embodiment, an upper limit may be set for the width W of the recess 45 formed on the first surface 11. An upper limit may be set for the depth D of the recess 45 formed on the first surface 11. Setting an upper limit also ensures the slipperiness of the first surface 11. This can prevent a decrease in slipperiness caused by the formation of large recesses on the first surface 11, i.e., a decrease in slipperiness caused by physical snagging, etc. From this perspective, the width W of the recess 45 may be 2.0 μm or less, 1.5 μm or less, 1.4 μm or less, 1.1 μm or less, 1.0 μm or less, 0.8 μm or less, 0.6 μm or less, or less than 0.5 μm. The depth D of the recess 45 may be 70 nm or less, 61 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 40 nm or less, 38 nm or less, 30 nm or less, or 24 nm or less.

[0058] The width W of the recess 45 may be 0.1 μm or more and 2.0 μm or less, 0.2 μm or more and 2.0 μm or less, 0.3 μm or more and 2.0 μm or less, or 0.4 μm or more and 2.0 μm or less. The width W of the recess 45 may be 0.1 μm or more and 1.5 μm or less, 0.2 μm or more and 1.5 μm or less, 0.3 μm or more and 1.5 μm or less, or 0.4 μm or more and 1.5 μm or less. The width W of the recess 45 may be 0.1 μm or more and 1.4 μm or less, 0.2 μm or more and 1.4 μm or less, 0.3 μm or more and 1.4 μm or less, or 0.4 μm or more and 1.4 μm or less. The width W of the recess 45 may be 0.1 μm or more and 1.1 μm or less, 0.2 μm or more and 1.1 μm or less, 0.3 μm or more and 1.1 μm or less, or 0.4 μm or more and 1.1 μm or less. The width W of the recess 45 may be 0.1 μm or more and 1.0 μm or less, 0.2 μm or more and 1.0 μm or less, 0.3 μm or more and 1.0 μm or less, or 0.4 μm or more and 1.0 μm or less. The width W of the recess 45 may be 0.1 μm or more and 0.8 μm or less, 0.2 μm or more and 0.8 μm or less, 0.3 μm or more and 0.8 μm or less, or 0.4 μm or more and 0.8 μm or less. The width W of the recess 45 may be 0.1 μm or more and 0.6 μm or less, 0.2 μm or more and 0.6 μm or less, 0.3 μm or more and 0.6 μm or less, or 0.4 μm or more and 0.6 μm or less. The width W of the recess 45 may be 0.1 μm or more and less than 0.5 μm, 0.2 μm or more and less than 0.5 μm, 0.3 μm or more and less than 0.5 μm, or 0.4 μm or more and less than 0.5 μm.

[0059] The depth D of the recess 45 may be 10 nm to 70 nm, 15 nm to 70 nm, 18 nm to 70 nm, 20 nm to 70 nm, or 23 nm to 70 nm. The depth D of the recess 45 may be 10 nm to 61 nm, 15 nm to 61 nm, 18 nm to 61 nm, 20 nm to 61 nm, or 23 nm to 61 nm. The depth D of the recess 45 may be 10 nm to 60 nm, 15 nm to 60 nm, 18 nm to 60 nm, 20 nm to 60 nm, or 23 nm to 60 nm. The depth D of the recess 45 may be 10 nm to 55 nm, 15 nm to 55 nm, 18 nm to 55 nm, 20 nm to 55 nm, or 23 nm to 55 nm. The depth D of the recess 45 may be 10 nm to 50 nm, 15 nm to 50 nm, 18 nm to 50 nm, 20 nm to 50 nm, or 23 nm to 50 nm. The depth D of the recess 45 may be 10 nm to 40 nm, 15 nm to 40 nm, 18 nm to 40 nm, 20 nm to 40 nm, or 23 nm to 40 nm. The depth D of the recess 45 may be 10 nm to 38 nm, 15 nm to 38 nm, 18 nm to 38 nm, 20 nm to 38 nm, or 23 nm to 38 nm. The depth D of the recess 45 may be 10 nm to 30 nm, 15 nm to 30 nm, 18 nm to 30 nm, 20 nm to 30 nm, or 23 nm to 30 nm. The depth D of the recess 45 may be 10 nm to 24 nm, 15 nm to 24 nm, 18 nm to 24 nm, 20 nm to 24 nm, or 23 nm to 24 nm.

[0060] As described above, for one measurement area, the maximum length L ＭＡＸThe width W and depth D of the depressions 45 are measured in the order of their lengths. The width W and depth D of the depressions 45 that are determined to be "depressions having a width W of 0.1 μm or more and a depth D of 10 nm or more" are defined as the width W and depth D of the depressions 45 in the measurement region.

[0061] As described above, for one optical sheet 10 to be evaluated, the presence or absence of "indentations having a width W of 0.1 μm or more and a depth D of 10 nm or more" is determined in a total of 15 measurement regions. The arithmetic mean value of the widths W of the indentations 45 measured in 12 or more measurement regions determined to have "indentations having a width W of 0.1 μm or more and a depth D of 10 nm or more" is defined as the width W of the indentations 45 for the optical sheet to be evaluated. The arithmetic mean value of the depths D of the indentations 45 measured in 11 or more measurement regions determined to have "indentations having a width W of 0.1 μm or more and a depth D of 10 nm or more" is defined as the depth D of the indentations 45 for the optical sheet to be evaluated. For example, if the 15 measurement regions for a certain optical sheet include two measurement regions where no indentations 45 exist, the arithmetic mean value of the measurements in 13 measurement regions is used as the width W and depth D of the indentations 45 for that optical sheet.

[0062] A lower limit may be set for the ratio (D / W) of the depth D to the width W of the recess 45. By setting a lower limit for the ratio (D / W), it is possible to stably improve the scratch resistance of the first surface 11 of the optical sheet 10. The ratio (D / W) may be 0.030 or more, 0.035 or more, 0.040 or more, 0.044 or more, or 0.048 or more.

[0063] There is no particular upper limit set for the ratio (D / W) of the depth D to the width W of the recess 45. The ratio (D / W) may be 0.15 or less, 0.10 or less, or 0.075 or less.

[0064] The ratio (D / W) may be 0.030 or more and 0.15 or less, 0.035 or more and 0.15 or less, 0.040 or more and 0.15 or less, 0.044 or more and 0.15 or less, or 0.048 or more and 0.15 or less. The ratio of D (D / W) may be 0.030 or more and 0.10 or less, 0.035 or more and 0.10 or less, 0.040 or more and 0.10 or less, 0.044 or more and 0.10 or less, or 0.048 or more and 0.10 or less. The ratio of D (D / W) may be 0.030 or more and 0.075 or less, 0.035 or more and 0.075 or less, 0.040 or more and 0.075 or less, 0.044 or more and 0.075 or less, or 0.048 or more and 0.075 or less.

[0065] The ratio (D / W) of the depth D of the recess 45 to the width W is obtained by dividing the depth D of the recess 45 of the optical sheet 10 to be evaluated, which is identified by the method described above, by the width W of the recess 45 of the optical sheet 10 to be evaluated, which is identified by the method described above. When calculating the ratio, the units of the width W of the recess 45 and the depth D of the recess 45 are the same. The ratio (D / W) has no unit.

[0066] As shown in FIGS. 5, 6, and 12 to 14, in an example in which the first surface includes a plurality of depressions 45, the plurality of depressions 45 may be discretely located. In other words, the plurality of depressions 45 may be located apart from one another. As shown in FIGS. 5, 6, and 12 to 14, the first surface 11 may have a flat portion 47 around the depression 45. The first surface 11 may include a flat portion 47 between the depressions 45. The first surface 11 may be configured with the flat portion 47 in the region between the depressions 45. The flat portion 47 is a surface in which the difference in height along the normal direction of the optical sheet 10 is less than the depth D of the depressions 45 in the optical sheet.

[0067] The presence or absence of the flat portion 47 is determined based on observation images acquired by an atomic force microscope. FIGS. 12 to 14 show examples of planar images of the measurement area acquired by an atomic force microscope. The images shown in FIGS. 12 to 14 are images observed with an atomic force microscope. Darker colored positions in the images represent lower height positions within the measurement area. Lighter colored positions in the images represent higher height positions within the measurement area. In the images shown in FIGS. 12 to 14, the color is represented by brown. The scale bar in the lower right of the images shown in FIGS. 12 to 14 indicates the relationship between color density and height. A histogram corresponding to the scale bar is shown in the lower right of the image. The histogram represents the frequency distribution of the areas represented by each color on the scale bar.

[0068] The inventors of the present invention have confirmed that the flat portions 47 located around the depressions 45 can improve the slipperiness on the first surface 11 of the optical sheet 10. Meanwhile, the functional layer 40 exerts some expected function in areas other than the depressions 45. The flat portions 47 exert some expected function. As an example, the functional layer 40 may exert a low-reflection function or a reflection-suppressing function in the flat portions 47 other than the depressions 45.

[0069] The flat portions 47 around the recesses 45 can prevent physical snagging at the flat portions 47. An external object rubbing against the optical sheet 10 can come into contact with the first surface 11 at the periphery of the recesses 45, i.e., at the boundary between the recesses 45 and the flat portions 47. It is presumed that this can promote the contacting object rubbing against the first surface 11 at the periphery of the recesses 45. Therefore, the improved slipperiness at the periphery of the recesses 45 can effectively improve the scratch resistance of the optical sheet 10.

[0070] An upper limit may be set for the proportion of depressions 45 in a 10 μm × 10 μm measurement area on first surface 11. By setting an upper limit, the functional layer 40 can fully perform the expected function in optical sheet 10 with improved scratch resistance. The proportion of depressions 45 in a 10 μm × 10 μm measurement area on first surface 11 may be 15% or less, 12% or less, 10% or less, or 5.0% or less.

[0071] A lower limit may be set for the proportion of depressions 45 in a 10 μm × 10 μm measurement area on first surface 11. Setting a lower limit makes it possible to stably improve the scratch resistance of first surface 11 of optical sheet 10. The proportion of depressions 45 in a 10 μm × 10 μm measurement area on first surface 11 may be 0.50% or more, 0.75% or more, 1.0% or more, 1.5% or more, or 2.0% or more.

[0072] The proportion of depressions 45 in the measurement region may be 0.50% to 15% or less, 0.75% to 15% or less, 1.0% to 15% or less, 1.5% to 15% or less, or 2.0% to 15% or less. The proportion of depressions 45 in the measurement region may be 0.50% to 12% or less, 0.75% to 12% or less, 1.0% to 12% or less, 1.5% to 12% or less, or 2.0% to 12% or less. The proportion of depressions 45 in the measurement region may be 0.50% to 10% or less, 0.75% to 10% or less, 1.0% to 10% or less, 1.5% to 10% or less, or 2.0% to 10% or less. The proportion of depressions 45 in the measurement area may be 0.50% or more and 5.0% or less, 0.75% or more and 5.0% or less, 1.0% or more and 5.0% or less, 1.5% or more and 5.0% or less, or 2.0% or more and 5.0% or less.

[0073] The ratio of the depressions 45 in the 10 μm×10 μm measurement area of ​​the first surface 11 is the ratio of the area occupied by the depressions 45 when observed from the normal direction of the optical sheet 10. This ratio is expressed as a percentage, and the unit of ratio is "%". The ratio is calculated by multiplying the maximum length L ＭＡＸThe ratio is calculated based on a planar image of the measurement area used to identify the depressions 45 having the above-mentioned features. That is, the ratio is calculated based on an image acquired by an atomic force microscope, which shows the first surface 11 from the normal direction of the optical sheet 10. Image processing software such as ImageJ and Fiji can be used for image processing. 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.

[0074] In the optical sheet 10 of the present embodiment, a lower limit may be set for the number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more that can be included in a 10 μm × 10 μm square measurement region on the first surface 11. By setting this lower limit, a certain number or more depressions 45 of a predetermined size are included in one measurement region. According to this example, slipperiness can be stably imparted to the first surface 11, thereby stably imparting excellent scratch resistance to the first surface 11. From this perspective, the number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more that can be included in one measurement region may be 3 or more, 4 or more, 9 or more, 11 or more, 12 or more, 17 or more, or 20 or more.

[0075] An upper limit may be set for the number of recesses 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in a 10 μm × 10 μm square measurement area on the first surface 11. By setting this lower limit, only a certain number of recesses 45 of a predetermined size are contained in one measurement area. This example also ensures the slipperiness of the first surface 11. If too many recesses are formed on the first surface 11, the slipperiness of the first surface 11 may be reduced due to physical snags or the like. From this perspective, the number of recesses 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in one measurement area may be 50 or less, 40 or less, 35 or less, or 32 or less.

[0076] The number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in one measurement region may be 3 to 50, 4 to 50, 9 to 50, 11 to 50, 12 to 50, 17 to 50, or 20 to 50. The number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in one measurement region may be 3 to 40, 4 to 40, 9 to 40, 11 to 40, 12 to 40, 17 to 40, or 20 to 40. The number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in one measurement region may be 3 to 35, 4 to 35, 9 to 35, 11 to 35, 12 to 35, 17 to 35, or 20 to 35. The number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in one measurement region may be 3 to 32, 4 to 32, 9 to 32, 11 to 32, 12 to 32, 17 to 32, or 20 to 32.

[0077] The number of depressions 45 having a predetermined size included in each measurement area is determined based on the maximum length L ＭＡＸThe measurement is based on an image of the measurement area used to identify the depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more. That is, based on an image of the first surface 11 acquired by an atomic force microscope, the number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in each measurement area is counted. Whether the number of depressions 45 having a width of 0.1 μm or more and a depth of 10 nm or more contained in a 10 μm × 10 μm square measurement area on the first surface 11 satisfies the condition is determined based on the average of the measured values ​​in five measurement areas for each of three measurement samples, i.e., the average of a total of 15 measured values. However, as with the width W of the depressions 45 and the depth D of the depressions 45, measurement areas determined to not contain depressions 45 having the above-mentioned predetermined size are not taken into consideration. For example, if two measurement areas containing no depressions 45 are included in the 15 measurement areas of a certain optical sheet, the arithmetic average of the measured values ​​in the 13 measurement areas is used as the number of depressions 45 on that optical sheet.

[0078] The inventors of the present invention have confirmed that the abrasion resistance of the first surface 11 can be stably improved by dispersing a relatively large number of relatively small depressions 45 .

[0079] Specifically, by including 11 or more depressions 45 having a width of 0.1 μm or more and 0.8 μm or less in a 10 μm × 10 μm square measurement area, scratch resistance can be stably improved. In this example, the width of the depressions 45 included in the measurement area may be 0.1 μm or more and 0.6 μm or less, or may be 0.1 μm or more and less than 0.5 μm. The number of depressions 45 having a width of 0.1 μm or more and 0.8 μm or less included in the measurement area may be 12 or more, 17 or more, or 20 or more. The number of depressions 45 having a width of 0.1 μm or more and 0.8 μm or less included in the measurement area may be 50 or less, 40 or less, 35 or less, or 32 or less.

[0080] In the optical sheet 10 of this embodiment, as shown in FIG. 5 , a 10 μm × 10 μm square measurement area DR is divided into two equal parts along each side to form four first small areas SS1, each of which may include a depression. In this example, the depressions 45 are dispersed within the measurement area DR. This improves the slipperiness at each position within the measurement area DR. This allows for consistent and consistent improvement in scratch resistance within the optical sheet 10.

[0081] As shown in Fig. 6, a 10 μm × 10 μm square measurement area is divided into three equal parts along each side to form nine second small areas SS2, each of which may include a depression 45. According to the example shown in Fig. 6, scratch resistance can be improved more uniformly and stably within the optical sheet 10.

[0082] An optical sheet 10 including depressions having a width of 0.1 μm or more and a depth of 10 nm or more in a 10 μm × 10 μm area on its first surface has excellent scratch resistance. Optical sheets with excellent scratch resistance have excellent steel wool resistance and felt resistance. Pencil hardness is known as an index of scratch resistance on the surface of an optical sheet. Pencil hardness is an index indicating resistance when a hard substance comes into contact with the optical sheet at a stress close to a point load. However, repeated friction or long-term use can cause minor scratches due to gentle surface loads. It is appropriate to evaluate this scratch resistance as steel wool resistance and felt resistance. The optical sheet 10 may have high resistance in a scratch resistance test using steel wool on the first surface 11. The optical sheet 10 may have high resistance in a scratch resistance test using felt on the first surface 11.

[0083] The present inventors have confirmed that by including depressions of a predetermined size in a 10 μm × 10 μm region on the first surface, the optical sheet 10 can be reliably provided with excellent scratch resistance against felt. Conventionally, pencil hardness and scratch resistance against steel wool could be improved by adjusting the mechanical properties, such as the surface hardness, of the optical sheet 10. Recently, scratch resistance against fingers or input pens in combination with touch panel functions, as well as scratch resistance against wiping with a cloth, have also been required for optical sheets. However, while pencil hardness and steel wool scratch resistance could be improved by simply improving mechanical properties, it has been difficult to reliably ensure excellent scratch resistance against felt. The effect of providing depressions having a width of 0.1 μm or more and a depth of 10 nm or more in a 10 μm × 10 μm region on the first surface, which reliably ensures excellent scratch resistance against felt, is remarkable and exceeds the range predicted by the state of the art.

[0084] <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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] If scratches that would be a problem when applied to a display device are observed on the test sample, the optical sheet 10 to be evaluated is determined to not have resistance to the 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 scratches that would be a problem when applied to a display device occur in any of the five tests, the optical sheet 10 to be evaluated is determined to have resistance to the steel wool scratch resistance test on the first surface 11. The steel wool is replaced after each of the five tests. The above-mentioned steel wool pretreatment is performed before the start of each of the five tests.

[0092] <Felt Resistance> The felt scratch resistance test is an index showing resistance to defects such as scratches that occur when a felt is pressed against a test sample to be evaluated and moved relative to the sample. The optical sheet 10 may be resistant to a scratch resistance test under the following conditions using a TABER Jumbo Wearaser (registered trademark) CS-7 as a sliding piece.

[0093] 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.

[0094] A felt piece serving as a slider is brought into contact with the surface of the sample, which is formed by the first side of the optical sheet. The felt is a "Jumbo Wearaser (registered trademark) CS-7" manufactured by TABER. The contact area between the test sample and the slider is 20 mm x 20 mm. A load of 200 g is applied to the slider from above in the vertical direction, and the test sample, which is spread out along a horizontal plane, is pressed against the slider.

[0095] 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 along a linear path. The reciprocating movement cycle is 10,000 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.

[0096] 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.

[0097] An unused sliding piece is used. Before conducting the test on the evaluation target, the felt is rubbed against the preparation sample to pretreat the felt. The testing machine used to test the sample to be evaluated is also used for pretreating the felt. The preparation sample is a "single-sided easy-adhesion type: A4160" manufactured by Toyobo Co., Ltd. The preparation sample is rectangular with a short side of 50 mm and a long side of 100 mm. The preparation sample is spread along a horizontal plane, and the four corners of the side of the preparation sample that has not been easily treated for adhesion (the side where the PET is exposed) are fixed to the testing machine with mending tape. The felt is rubbed against the untreated surface of the preparation sample. The felt is pressed against the preparation sample from above in the vertical direction. The contact area between the preparation sample and the felt is a circle with a diameter of 12 mm. The load pressing the felt against the preparation sample is 600 g. The felt pressed against the preparation sample is moved horizontally relative to the preparation sample. The relative movement is a reciprocating motion. The reciprocating motion cycle is 150 times. The reciprocating motion speed is 220 mm / sec. The reciprocating stroke is 50 mm for both the forward and backward motions. The felt pressed against the preparation sample in this way is used for the test of the evaluation object. The test is carried out after confirming that the smoothed surface of the pressed felt is free of fuzz and flat.

[0098] 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.

[0099] If scratches that would be a problem in application to a display device are observed on the test sample, the optical sheet 10 to be evaluated is determined to not have resistance to the scratch resistance test on the first surface 11 using CS-7 as a sliding piece. The scratch resistance test is performed five times on one optical sheet 10 to be evaluated. If no scratches that would be a problem in application to a display device occur in the five tests, the optical sheet 10 to be evaluated is determined to have resistance to the scratch resistance test on the first surface 11 using CS-7 as a sliding piece. The same CS-7 is used in all five tests. The above-mentioned CS-7 pretreatment is performed before the start of each of the five tests.

[0100] <Arithmetic mean roughness Sa> In the optical sheet 10 of the present embodiment, the arithmetic mean roughness Sa on the first surface 11 may be 8.0 nm or less, 7.5 nm or less, 5.0 nm or less, 4.5 nm or less, or 4.1 nm or less. By reducing the arithmetic mean roughness Sa to 8.0 nm or less, excellent slipperiness is imparted to the first surface 11. By providing physical unevenness on the first surface 11 by the depressions 45 while maintaining a low arithmetic mean roughness Sa, the slipperiness of the first surface 11 can be improved, thereby improving the scratch resistance of the first surface 11. There is no particularly preferred lower limit for the arithmetic mean roughness Sa on the first surface 11. The arithmetic mean roughness Sa on the first surface 11 may be 0 nm or more, 0.1 nm or more, or 3.0 nm or more.

[0101] The arithmetic mean roughness Sa is the three-dimensional arithmetic mean roughness defined in ISO 25178. The three-dimensional arithmetic mean roughness is a three-dimensional extension of the arithmetic mean roughness Ra relating to two-dimensional roughness. The arithmetic mean roughness Sa is calculated by the following formula (i) where the orthogonal coordinate axes X and Y are placed on a reference plane, the roughness curve is Z(x, y), and the size of the reference plane is Lx and Ly. In formula (i), A = Lx × Ly.

[0102]

[0103] The arithmetic mean roughness Sa is a value obtained using an atomic force microscope (AFM). Three measurement samples are cut out from the target optical sheet 10 at positions at least 10 mm apart from each other. Each measurement sample is a 5 mm x 5 mm square. The measurement samples are visually confirmed to be free of foreign matter or scratches. For each measurement sample, images of five measurement areas spaced apart from each other are obtained using the atomic force microscope. The measurement areas are 10 μm x 10 μm squares. The arithmetic mean height Sa is calculated from the images obtained for the five measurement areas of each of the three measurement samples, i.e., for a total of 15 measurement locations, using surface analysis software provided with the atomic force microscope. The average of the 15 measurement values ​​is defined as the arithmetic mean roughness Sa (nm) of the optical sheet.

[0104] <Luminous Reflectance> Optical sheet 10 according to the present embodiment has a reflection suppressing function that suppresses reflection of light incident on first surface 11. The luminous reflectance Y value on first surface 11 measured at an incident angle of 5° may be 1.5% 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 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.

[0107] 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.

[0108] 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.

[0109] Other measurement conditions for measuring the luminous reflectance are in accordance with JIS Z 8722:2009.

[0110] 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.

[0111] <Total Light Transmittance> The total light transmittance of the optical sheet 10 may be 50% or more, 70% or more, 80% or more, 90% or more, or 95% 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%.

[0112] A D65 light source is used to measure the total luminous transmittance (%). Before measuring the total luminous 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 luminous transmittance is 0°. The incident surface when measuring the total luminous transmittance is the second surface 12 of the optical sheet 10. The test environment when measuring the total luminous 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 luminous transmittance are in accordance with JIS K7361-1:1997.

[0113] 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.

[0114] <Transmission Haze> The transmission haze of the optical sheet 10 may be 1.0% or less, 0.5% or less, 0.3% or less, or 0.2% or less. The transmission haze of the optical sheet 10 does not have a particular lower limit. The transmission haze of the optical sheet 10 may be 0% or greater than 0%.

[0115] 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.

[0116] 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.

[0117] As shown in FIG. 1 , the optical sheet 10 may include a resin layer 30 located between the substrate 20 and the functional layer 40. The resin layer 30 may include a cured product of a curable resin composition. The resin layer 30 including the cured product of the curable resin composition has high strength and high hardness. By stacking and supporting the functional layer 40 on the resin layer 30, the scratch resistance of the first surface 11 can be further improved.

[0118] Each layer of the optical sheet 10 shown in FIG. 1 will be described in more detail below. 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, i.e., 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. The third direction D3 is the normal direction of the optical sheet 10. The third direction D3 is also the normal direction of each layer included in the optical sheet 10. 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.

[0119] 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 may 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.

[0120] <<Substrate 20>> 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.

[0121] 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.

[0122] 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 substrate 20 may contain only one of the above-mentioned resins, or two or more of the above-mentioned resins.

[0123] The thickness of the resin substrate 20 is not particularly limited. From the viewpoint of ease of handling, 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 500 μm or more.

[0124] 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.

[0125] 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.

[0126] <<Functional Layer 40>> The functional layer 40 includes a binder component 41 and 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.

[0127] The functional layer 40 can suppress the reflection of incident light due to its refractive index and thickness. The reflection suppression 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 reflection suppression 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. Furthermore, 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.

[0128] From the viewpoint of the anti-reflection function, the refractive index and 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. The refractive index used for the components constituting the optical sheet is the refractive index at a wavelength of 589.3 nm. 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.

[0129] <Binder component 41> 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.

[0130] 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.

[0131] 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.

[0132] 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 (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups. 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 compound having a (meth)acryloyl group. The ionizing radiation curable compound may be a siloxane compound containing a siloxane bond.

[0133] Hereinafter, a (meth)acrylate compound containing four or more ethylenically unsaturated bond groups will be referred to as a "polyfunctional (meth)acrylate compound," and a (meth)acrylate compound containing two to three ethylenically unsaturated bond groups will be referred to as a "low-functional (meth)acrylate compound."

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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. To increase affinity with silica particles, suppress particle aggregation, and adjust the C / Si ratio within the above range, 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] <Particles (hollow silica particles 43, solid silica particles 44)> The functional layer 40 includes hollow silica particles 43 in addition to the binder component 41. The functional layer 40 may include other particles. Other examples include inorganic particles such as magnesium fluoride particles and organic particles.

[0144] The functional layer 40 includes hollow silica particles 43 as silica particles. 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.

[0145] The hollow silica particles 43 may be uniformly dispersed in the functional layer 40. Uniform dispersion of the hollow silica particles 43 in the functional layer 40 smoothes the first surface 11, reducing the arithmetic mean roughness Sa of the first surface 11. This improves the slipperiness of the first surface 11 and enhances the scratch resistance of the first surface 11. The hollow silica particles 43 can be uniformly dispersed in the functional layer 40 by reducing the particle size variation of the hollow silica particles 43, adjusting the average particle size of the hollow silica particles 43 relative to the average film thickness of the binder component 41, adjusting the affinity between the hollow silica particles 43 and the binder component 41, adjusting the content ratio or average particle size ratio between the hollow silica particles 43 and other particles, adjusting the affinity between the hollow silica particles 43 and other particles, etc.

[0146] As shown in FIG. 1 , the functional layer 40 may include solid silica particles 44 in addition to hollow silica particles 43. The solid silica particles 44 are non-hollow silica particles. The solid silica particles 44 are particles that do not have internal cavities. The solid silica particles 44 may be solid silica particles. The solid silica particles improve the scratch resistance of the functional layer 40 by being dispersed in the binder component 41.

[0147] 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 smoothes the first surface 11, reducing the arithmetic mean roughness Sa of the first surface 11. This improves the slipperiness of the first surface 11 and enhances the scratch resistance of the first surface 11. By adjusting the content ratio or average particle size ratio of the solid silica particles 44 to other particles such as the hollow silica particles 43, the affinity between the solid silica particles 44 and other particles such as the hollow silica particles 43 can be adjusted, thereby enabling the solid silica particles 44 to be uniformly dispersed in the functional layer 40 together with the hollow silica particles 43. In the example shown in FIG. 1 , the hollow silica particles 43 and the solid silica particles 44 are uniformly dispersed in the functional layer 40.

[0148] The functional layer 40 may contain metal oxide particles other than silica particles. The metal oxide particles other than silica particles increase the strength and hardness of the functional layer 40 and improve the scratch resistance of the first surface 11. Examples of metal oxide particles include a single oxide or a mixture of oxides of titanium, tantalum, zirconium, chromium, niobium, cerium, hafnium, and yttrium.

[0149] The metal oxide particles may include alumina particles. Alumina particles have a relatively low refractive index among metal oxides. Alumina is Al ２ O ３ The aluminum oxide is represented by the formula (1), 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. The metal oxide particles may be hollow particles having an internal space, or may be solid particles having no internal space.

[0150] The shape of the particles dispersed in the functional layer 40, such as the hollow silica particles 43 and the solid silica particles 44, is not particularly limited. The shape of the particles dispersed in the functional layer 40, such as the hollow silica particles 43 and the solid silica particles 44, 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 dispersed in the functional layer 40, such as the hollow silica particles 43 and the solid silica particles 44, 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.

[0151] The surfaces of the particles dispersed in the functional layer 40, such as the hollow silica particles 43 and the solid silica particles 44, may be coated with a silane coupling agent. The silane coupling agent may contain a (meth)acryloyl group or an epoxy group. By treating the particles 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 in the binder component.

[0152] 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 derivative include 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. The silane coupling agent may be one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane.

[0153] As shown in FIG. 1 , particles contained in the functional layer 40, such as hollow silica particles 43 and solid silica particles 44, may be present in the functional layer 40 at a high concentration and may be uniformly dispersed within the functional layer 40. With this configuration, as described above, the first surface 11 is smoothed and the dynamic friction coefficient of the first surface 11 is reduced, thereby improving the scratch resistance of the first surface 11. As shown in FIG. 1 , hollow silica particles 43 with a large average particle size are uniformly dispersed within the functional layer 40. The solid silica particles 44 are dispersed within the functional layer 40 so as to fill the spaces between the hollow silica particles 43. The solid silica particles 44 are arranged in close proximity to the hollow silica particles 43 within the functional layer 40.

[0154] 1 , hollow silica particles 43 with a large average particle size are uniformly dispersed within the functional layer 40, and solid silica particles 44 with a small average particle size are filled within the functional layer 40 so as to fill the spaces between the hollow silica particles 43. According to this example, the functional layer 40 has high hardness and a smooth surface. This reduces the arithmetic mean roughness Sa of the first surface 11 and the dynamic friction coefficient of the first surface 11, and can improve the scratch resistance of the first surface 11.

[0155] The average particle diameter of the hollow silica particles 43 may be 50 nm or more, or 65 nm or more, and may be 100 nm or less, or 80 nm or less.

[0156] The average particle diameter of the solid silica particles 44 may be 5 nm or more, or 10 nm or more. The average particle diameter of the solid silica particles 44 may be 20 nm or less, or 15 nm or less. The average particle diameter of the solid silica particles 44 may be smaller than the average particle diameter of the hollow silica particles 43.

[0157] By setting a lower limit for the average particle size of the solid silica particles 44, the solid silica particles 44 can contribute to reinforcing the strength and hardness of the functional layer 40. By setting an upper limit for the average particle size of the hollow silica particles 43, the binder component 41 can stably hold the hollow silica particles 43. This means that the hollow silica particles 43 are prevented from falling off the functional layer 40, improving scratch resistance. By setting an upper limit for the average particle size of the solid silica particles 44 and a lower limit for the hollow silica particles 43, the solid silica particles 44 can be arranged in close proximity to hollow silica particles 43 with a larger average particle size. This means that the hollow silica particles 43 and solid silica particles 44 can be uniformly dispersed at a high concentration within the functional layer 40. This provides the functional layer 40 and the optical sheet 10 with stable and excellent scratch resistance.

[0158] The "average particle diameter" used for particles such as hollow silica particles 43 and solid silica particles 44 is a value specified by the following (1) to (3). (1) A 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 diameters of each particle are measured. The particle diameter (nm) is defined as the distance between two parallel lines that maximize the distance between the particles observed in the image. In other words, the particle diameter is the maximum length of the particle in the observation image. (3) The above steps (1) and (2) are performed five times for the same optical sheet to be measured, and the particle diameters of a total of 50 particles are measured. The average of the 50 particle diameter measurements is defined as the average particle diameter (nm) of the particles.

[0159] 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 sheet surface of the optical sheet and at positions shifted 100 nm on both sides from the center position along the sheet 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 sheet surface of the optical sheet. (6) For the same optical sheet to be measured, steps (4) and (5) above are performed five times to measure the thickness of the functional layer at a total of 15 positions. The average of the 15 thickness measurements is defined as the average thickness (nm) of the functional layer.

[0160] The average particle size of the particles and the thickness of the porous layer can be measured using a scanning transmission electron microscope (STEM), a type of transmission electron microscope, such as an electron microscope H-7650 manufactured by Hitachi High-Technologies Corporation.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] The content of the solid silica particles may be 30 parts by mass or more, 35 parts by mass or more, or 40 parts by mass or more relative to 100 parts by mass of the hollow silica particles, and 80 parts by mass or less, 75 parts by mass or less, or 70 parts by mass or less relative to 100 parts by mass of the binder component.

[0165] <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. 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.

[0166] The functional layer coating liquid contains a leveling agent. The leveling agent is an additive that smoothes the surface of the functional layer 40. The leveling agent suppresses defects such as repelling, dents, pinholes, and orange peel caused by uneven surface tension in the functional layer 40. By including a leveling agent in the functional layer coating liquid, the formation of a Benard cell structure on the surface of the functional layer can be suppressed. When a coating film made from the applied functional layer coating liquid is dried, a difference in surface tension occurs between the surface and inner surfaces of the coating film, causing numerous convection currents within the coating film. The structure created by this convection is called a Benard cell structure, and can cause orange peel-like defects on the surface of the functional layer. The use of a leveling agent suppresses uneven surface tension and suppresses the formation of a Benard cell structure.

[0167] The leveling agent contained in the functional layer coating liquid is not particularly limited. Examples of leveling agents include compounds having a polyether group, a polyurethane group, an epoxy group, a carboxyl group, an acrylate group, a methacrylate group, a carbinol group, or a hydroxyl group. These leveling agents may have a polyether group, a polyurethane group, an epoxy group, a carboxyl group, an acrylate group, a methacrylate group, a carbinol group, or a hydroxyl group at the end (one end or both ends) of the main chain, on a side chain, or both at the end of the main chain and the side chain. The leveling agent is not particularly limited as long as it is a compound having a polyether group, a polyurethane group, an epoxy group, a carboxyl group, an acrylate group, a methacrylate group, a carbinol group, or a hydroxyl group. Examples of leveling agents include silicone-based, fluorine-based, silicone-fluorine-based, acrylic, methacrylic, vinyl, and aromatic leveling agents. The coating liquid for the functional layer may contain a fluorine-based leveling agent or a silicone-based leveling agent from the viewpoint of suppressing coating defects such as repelling, or an acrylic-based leveling agent or a vinyl-based leveling agent from the viewpoint of improving recoatability.

[0168] As described above, the formation of depressions 45 on the first surface 11 improves the scratch resistance of the first surface 11. It is presumed that depressions 45 on the first surface 11 may be caused by bleeding out of a leveling agent. Experimental results show that the formation of depressions 45 on the first surface 11 can be promoted by including two or more types of leveling agents in the functional layer coating liquid. In particular, the formation of depressions 45 on the first surface 11 can be promoted by including two or more types of leveling agents in the functional layer coating liquid: a fluorine-based leveling agent, a silicone-based leveling agent, and a silicone / fluorine-based leveling agent. Although the details are unclear, depressions 45 were more likely to be formed on the first surface 11 when two or more types of leveling agents were used. In particular, depressions 45 were more likely to be formed on the first surface 11 when both a fluorine-based leveling agent and a silicone / fluorine-based leveling agent were used.

[0169] The content of the leveling agent can also promote the formation of depressions 45 on the first surface 11. Increasing the content of the leveling agent relative to the binder component 41 can promote the formation of depressions 45 on the first surface 11. If the content of the leveling agent relative to the binder component 41 is too high, the width and depth of the depressions 45 will become too large, and the number of depressions 45 will be too large. In view of these points, the content of the leveling agent may be 1 part by mass or more, 2 parts by mass or more, 5 parts by mass or more, or 8 parts by mass or more relative to 100 parts by mass of the binder component. The content of the leveling agent may be 45 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 20 parts by mass or less relative to 100 parts by mass of the binder component. Furthermore, reducing the content of particles relative to the binder component 41 also makes depressions 45 more easily formed on the first surface 11. Specifically, as described above, by determining the content of particles relative to the binder component 41 , the depressions 45 are more easily formed on the first surface 11 .

[0170] When the leveling agent includes both a fluorine-based leveling agent and a silicone / fluorine-based leveling agent, the content of each leveling agent may be set as follows, from the viewpoint of promoting the formation of depressions on first surface 11. The fluorine-based leveling agent may be 5 parts by mass or more, 8 parts by mass or more, or 10 parts by mass or more, relative to 100 parts by mass of the binder component. The fluorine-based leveling agent may be 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less, relative to 100 parts by mass of the binder component. The silicone / fluorine-based leveling agent may be 5 parts by mass or more, 8 parts by mass or more, or 10 parts by mass or more, relative to 100 parts by mass of the fluorine-based leveling agent. The silicone / fluorine-based leveling agent may be less than 100 parts by mass, 35 parts by mass or less, 30 parts by mass or less, or 25 parts by mass or less, relative to 100 parts by mass of the fluorine-based leveling agent.

[0171] <<Resin Layer 30 (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 may be adjacent to the functional layer 40 in the third direction D3. 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 curable resin composition used to form the resin layer 30 may include a cured product of a thermosetting resin or an ionizing radiation curable compound included in the curable resin composition used to form the functional layer 40.

[0172] 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.

[0173] The refractive index of the resin layer 30 may be lower 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.

[0174] 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, and the functional layer 40 as a high-refractive index layer and a low-refractive index layer, thereby further reducing reflectance. The refractive index of the resin layer 30 can be adjusted by the resin and particles contained in the curable resin composition.

[0175] 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.

[0176] 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.

[0177] 7 , 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 may be adjacent to the functional layer 40 in the third direction D3. As described immediately above, 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.

[0178] 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.

[0179] As shown in FIG. 7 , the second functional layer 50 may include a binder resin 51 and particles 52. The particles 52 are particles for adjusting the refractive index and may have an average particle diameter on the nanometer order. The binder resin 51 may be prepared using a curable resin composition, similar to the binder component 41 serving as the resin of 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.

[0180] The particles 52 may be particles having a refractive index higher than that of the binder resin 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.

[0181] 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 increasing 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 resin 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 resin 51.

[0182] 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.

[0183] <<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 which a coating liquid containing the components constituting each layer 30, 40, and 50 is applied to the substrate 20, dried, and cured. 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.

[0184] The optical sheet 10 including the substrate 20 and the functional layer 40 can 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.

[0185] 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 film 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.

[0186] 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. A second functional layer coating liquid for forming the second functional layer 50 is applied to the resin layer 30, and the coating film is dried and cured to obtain the second functional layer 50. Next, the functional layer 40 is formed on the second functional layer 50 to obtain 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.

[0187] 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.

[0188] If the solvent evaporates too quickly, the unevenness of the functional layer 40 becomes large, and it becomes difficult to form the depressions 45. One reason for this is thought to be that the solvent evaporates too quickly, preventing the leveling agent from sufficiently rising to the surface within the coating film of the coating liquid. On the other hand, by reducing the evaporation rate of the solvent, the unevenness of the functional layer 40 becomes smaller, and it becomes easier to form the depressions 45. From this perspective, the coating liquid may contain a solvent with a slow evaporation rate.

[0189] If the solvent evaporates too quickly, the solvent will convect vigorously when the coating solution dries. Particles contained in the coating solution, such as hollow silica particles 43, solid silica particles 44, metal oxide particles, and particles 52, may be unevenly distributed due to convection caused by solvent evaporation when the coating solution dries. In other words, the particles in the coating film will no longer be uniformly dispersed. From this perspective, the coating solution may also contain a solvent with a slow evaporation rate.

[0190] The relative evaporation rate of the solvent contained in the coating liquid may be 70 or less, or may be 30 or more and 60 or less. The relative evaporation rate is expressed by comparing the evaporation rate of the target solvent with the evaporation rate of n-butyl acetate, which 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.

[0191] 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.

[0192] In order to suppress convection of the solvent during drying of the coating liquid, the drying temperature during drying of the coating liquid may be lowered to slow down the drying speed. In particular, the drying temperature during drying of the functional layer coating liquid may be lowered. The drying temperature of the coating film made of the applied coating liquid may be appropriately set in consideration of the formation of the depressions 45, the type of solvent, the dispersibility of the particles, the production speed, etc.

[0193] As described above, by adjusting the type and blend of the solvent and the drying conditions of the coating film, it is possible to control the presence or absence of depressions 45 on the first surface 11, the size of the depressions 45, and the number of depressions 45. By adjusting the type and blend of the solvent and the drying conditions of the coating film, it is possible to control the dispersion of particles such as hollow silica particles 43 and solid silica particles 44 in the functional layer 40.

[0194] 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.

[0195] According to the above-described wet method for manufacturing an optical sheet 10, a long sheet product 5 including a large number of optical sheets 10 can be manufactured, as shown in FIG. 8 . 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. 8 , 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.

[0196] In addition to the above-described step of manufacturing an optical sheet, the method for manufacturing an optical sheet may further include a step of selecting the manufactured optical sheet 10. The step of selecting the optical sheet 10 may include a step of acquiring an image of a 10 μm × 10 μm measurement area on the first surface, and a step of selecting an optical sheet having one or more depressions of a predetermined size in the measurement area based on the image of the measurement area. Here, the predetermined size is a size having a width of 0.1 μm or more and a depth of 10 nm or more. An optical sheet 10 having depressions 45 of a predetermined size in the measurement area has excellent scratch resistance. This selection step allows for highly accurate selection of an optical sheet with excellent scratch resistance without performing a scratch test using felt or steel wool.

[0197] The selection step may further include a step of determining whether or not any one or more of the following conditions A to K are satisfied, and selecting an optical sheet 10 that satisfies the conditions. [A] The width of the depression is 1.5 μm or less. [B] The depth of the depression is 70 nm or less. [C] There are three or more depressions in a 10 μm × 10 μm measurement area of ​​the first surface. [D] There are 11 or more depressions in a 10 μm × 10 μm measurement area of ​​the first surface. [E] There are 50 or fewer depressions in a 10 μm × 10 μm measurement area of ​​the first surface. [F] The 10 μm × 10 μm measurement area is divided into two equal parts along each side, and each of the four small areas contains one or more depressions. [G] The 10 μm × 10 μm measurement area is divided into three equal parts along each side, and each of the nine small areas contains one or more depressions. [H] The arithmetic mean roughness Sa of the first surface is 8.0 nm or less. [I] The first surface includes flat areas around the depressions. [J] The ratio of depressions in a 10 μm×10 μm area on the first surface is 15% or less. [K] The ratio of the depth to the width of the depressions is 0.030 or more.

[0198] <<<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. 9 , 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.

[0199] 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.

[0200] <<<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. 10 , 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.

[0201] <<<Panel 70>>> The optical sheet 10 according to this embodiment can be applied to a variety of applications. FIG. 11 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.

[0202] The present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

[0203] 1. Measurement and Evaluation Measurement and evaluation were performed on the optical sheets of 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.

[0204] 1-1. Luminous reflectance Y value Samples measuring 5 cm x 5 cm were cut out from the optical sheets according to Examples 1 to 3 and Comparative Example 1. The samples were visually inspected to ensure 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.

[0205] 1-2. Total Light Transmittance and Transmission Haze Samples measuring 5 cm x 10 cm were cut out from the optical sheets according to Examples 1 to 3 and Comparative Example 1. The samples were visually inspected to ensure 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 (Tt) are shown in the "Tt" column of Table 1.

[0206] Samples measuring 5 cm x 10 cm were cut out from the optical sheets according to Examples 1 to 3 and Comparative Example 1. The samples were visually inspected to ensure there were no abnormalities 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 (Hz) are shown in the "Hz" column of Table 1.

[0207] 1-3. Evaluation of recesses Three measurement samples were cut from each of the optical sheets of the example and comparative example. The measurement samples were 5 mm x 5 mm squares. Each sample was visually inspected to ensure there were no abnormalities such as dust or scratches. An atomic force microscope was used to observe the surface of each measurement sample, which was formed by the first surface of the optical sheet. An atomic force microscope (AFM) "SPM-9700" manufactured by Shimadzu Corporation was used to observe the surface of the measurement samples.

[0208] First, multiple flat, circular metal plates with a diameter of 15 mm and a thickness of 1 mm were prepared. Double-sided carbon tape manufactured by Nissin EM Co., Ltd. was attached to each metal plate. One measurement sample was placed on the double-sided tape to secure the measurement sample to the metal plate. The surface of each measurement sample, which was formed by the first surface of the optical sheet, was facing upward. To ensure proper adhesion between the tape and the measurement sample, the metal plates with the samples attached were left overnight in a desiccator. After leaving overnight, the metal plates with the samples attached were fixed with magnets onto the measurement stage of an atomic force microscope (product name "SPM-9700" manufactured by Shimadzu Corporation). Images of the surface of a 10 μm square measurement area for each measurement sample were acquired using the tapping mode of the atomic force microscope. Five 10 μm square measurement areas were selected for each measurement sample, and images of the five measurement areas were acquired.

[0209] The surface shape of the sample was measured in On-Line (measurement) mode using the software "SPM Manager" that comes with the atomic force microscope. The measurement conditions were as follows: (AFM measurement conditions) - Measurement mode: Phase - Scanning range: 10 μm x 10 μm - Scanning speed: 2.0 to 2.5 Hz (using a 10 μm scanner) - Number of pixels: 512 x 512 - Cantilever used: NCHR manufactured by Nanoworld (resonance frequency: 320 kHz, spring constant 42 N / m)

[0210] Fig. 12 is an image showing one measurement area in Example 1. Fig. 13 is an image showing one measurement area in Example 2. Fig. 14 is an image showing one measurement area in Example 3. Fig. 15 is an image showing one measurement area in Comparative Example 1.

[0211] As shown in Figures 12 to 15, images observed with an atomic force microscope express height using shades of color. Darker colored positions in the images represent positions with lower height within the measurement area. Lighter colored positions in the images represent positions with higher height within the measurement area. In the images shown in Figures 12 to 15, the color is expressed as brown. The scale bar in the lower right of the images shown in Figures 12 to 15 indicates the relationship between shades of color and height. A histogram is shown in the lower right of the image corresponding to the scale bar. The histogram represents the frequency distribution of the areas indicated by each color on the scale bar. The histogram was automatically acquired in conjunction with the acquisition of images with the atomic force microscope.

[0212] In the images shown in Figures 12 to 14, depressions are identified as dark areas. That is, the presence or absence of recesses that may correspond to depressions having a predetermined size can be identified from the images acquired by the atomic force microscope shown in Figures 12 to 15.

[0213] The atomic force microscope obtains three-dimensional data of the surface of the measurement area corresponding to the first surface of the optical sheet and forms an image. The atomic force microscope can generate cross-sectional data across the depression in any direction. That is, the cross-sectional profile 45x shown in Figures 3 and 4 can be obtained. As described above, the width and depth of the depression can be measured based on the planar image and the cross-sectional profile.

[0214] Using an atomic force microscope, images were taken of five measurement regions for each of the three measurement samples for each of the Examples and Comparative Examples. That is, 15 images were taken for each of the Examples and Comparative Examples. Based on these images, the following measurements and evaluations were performed for each of the Examples and Comparative Examples. The results are shown in Table 1.

[0215] (Evaluation 1) Presence or Absence of Depressions As an example, in the planar images shown in FIGS. 12 to 15, depressions with long maximum lengths were identified, and the cross-sectional profiles of the depressions were used to confirm whether the width of the depressions was 0.1 μm or more and the depth of the depressions was 10 nm or more. Depressions with a width of 0.1 μm or more and a depth of 10 nm or more are also simply referred to as "depressions having a predetermined size." If depressions having a predetermined size were present in 12 or more of the 15 measurement regions for each example, it was determined that the depressions having the predetermined size were included in the measurement region, and an "A" was entered in the "Evaluation 1: Presence or Absence of Depressions" column in Table 1. If depressions having a predetermined size were not present in 4 or more of the 15 measurement regions for each example, it was determined that the depressions having the predetermined size were not included in the measurement region, and a "B" was entered in the "Evaluation 1: Presence or Absence of Depressions" column in Table 1. Of the 15 measurement regions for each of Examples 1 to 6, 15 measurement regions had depressions having the predetermined size.

[0216] (Evaluation 2) Indentation Width For measurement regions where indentations of a predetermined size were determined to exist, the width of the indentations of the predetermined size confirmed to exist in the measurement region was measured from a cross-sectional profile across the indentations. The arithmetic mean value of the measured indentation widths for each example was calculated, and the average of the calculated measurements was used as the indentation width for that example. The indentation width for each example was entered in the "Evaluation 2: Indentation Width" column in Table 1. The modulus used to calculate the arithmetic mean value was the number of measurement regions in each example where the indentations having the maximum length were determined to have a width of 0.1 μm or more and a depth of 10 nm or more (i.e., 15). The same applies to the following (Evaluation 3) Indentation Depth and (Evaluation 4) Indentation Number.

[0217] For Comparative Examples 2 and 3, it was determined in (Evaluation 1) that no depressions of the predetermined size were formed. In the column "Evaluation 2: Depression Width" in Table 1, the width of the depression that was determined to have the longest maximum length was entered. Depressions were confirmed on the first surface of the optical sheets of Comparative Examples 2 and 3. The depressions formed in Comparative Example 2 had larger shapes in plan view compared to the depressions formed in Examples 1 to 6. The depressions formed in Comparative Example 3 had smaller shapes in plan view compared to the depressions formed in Examples 1 to 6.

[0218] (Evaluation 3) Depth of Indentations For measurement areas where it was determined that indentations of a predetermined size were present, the depth of the indentations of a predetermined size confirmed to be present in the measurement area was measured from a cross-sectional profile intersecting the indentations. The arithmetic mean value of the measured indentation depths for each example was calculated, and the mean value of the calculated measurements was used as the indentation depth for that example. The depth of the indentations for each example was entered in the "Evaluation 3: Depth of Indentations" column in Table 1.

[0219] For Comparative Examples 2 and 3, it was determined in (Evaluation 1) that no depressions of the predetermined size were present. The depth of the depression that was determined to have the longest maximum length was entered in the column "Evaluation 3: Depth of depression" in Table 1. The depressions formed in Comparative Example 2 had a greater depth than the depressions formed in Examples 1 to 6. The depressions formed in Comparative Example 3 had a shallower depth than the depressions formed in Examples 1 to 6.

[0220] (Evaluation 4) Number of dents For measurement areas where dents having a predetermined size were determined to be present, the number of dents confirmed to be present in the measurement area was measured from the planar image and cross-sectional profile. The arithmetic mean value of the measured values ​​of the number of dents having a predetermined size for each example was calculated, and the average of the calculated measurements was used as the number of dents for that example. The number of dents having a predetermined size for each example was entered in the column "Evaluation 4: Number of dents" in Table 1.

[0221] For Comparative Examples 2 and 3, it was determined in (Evaluation 1) that no depressions of the specified size were present. However, it was confirmed that depressions not of the specified size were formed in Comparative Examples 2 and 3. In Comparative Example 2, an average of 12 depressions not of the specified size were confirmed in each measurement area. In Comparative Example 3, an average of 15 depressions not of the specified size were confirmed in each measurement area.

[0222] (Evaluation 5) Aspect Ratio The aspect ratio (D / W) was calculated by dividing the depth D of the depression calculated in (Evaluation 3) by the width W of the depression calculated in (Evaluation 2). The aspect ratio for each example was entered in the column "Evaluation 5: Aspect Ratio" in Table 1. When calculating the aspect ratio, the units for the depth D and the width W were the same.

[0223] (Evaluation 6) Area Ratio For Examples 1 to 3, the area ratio of depressions in a 10 μm × 10 μm region on the first surface was measured. The area ratio of depressions in each measurement area where it was determined that depressions having a predetermined size were present was measured. The area ratio (%) was measured by image analysis of the planar image. For each of Examples 1 to 3, the arithmetic mean value of the area ratios measured for each measurement area where it was determined that depressions having a predetermined size were present was taken as the area ratio (%) of depressions in the measurement area. The area ratio for Example 1 was 2.9%. The area ratio for Example 2 was 1.5%. The area ratio for Example 3 was 4.2%.

[0224] 1-4. Evaluation of arithmetic mean roughness Sa Three measurement samples were cut from each of the optical sheets of the example and comparative example. The measurement samples were 5 mm x 5 mm squares. Each sample was visually inspected for the absence of any abnormalities such as dust or scratches. For each measurement sample, images of five measurement areas spaced apart from each other were obtained using an atomic force microscope. The measurement areas were the surface of each sample that was formed by the first surface of the optical sheet.

[0225] The atomic force microscope used was an "SPM-9700" manufactured by Shimadzu Corporation. The surface shape of the sample was measured in On-Line (measurement) mode using the "SPM Manager" software that came with the atomic force microscope. The measurement conditions were as follows: (AFM measurement conditions) - Measurement mode: Phase - Scanning range: 10 μm x 10 μm - Scanning speed: 2.0 to 2.5 Hz (using a 10 μm scanner) - Number of pixels: 512 x 512 - Cantilever used: NCHR manufactured by Nanoworld (resonance frequency: 320 kHz, spring constant 42 N / m)

[0226] When acquiring data, five measurement areas spaced apart from each other were selected for each measurement sample, and data on the surface shape was acquired for each of three measurement samples x five measurement areas (a total of 15 measurement areas). For each example of the examples and comparative examples, the arithmetic mean roughness Sa was measured for the 15 measurement areas, and the arithmetic mean value of the 15 measurements was taken as the arithmetic mean roughness Sa for each example. The measurement results of the arithmetic mean roughness Sa were entered in the "Arithmetic mean roughness Sa (nm)" column in Table 1.

[0227] 1-5. Steel Wool Resistance Samples of 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. The evaluators were 20 healthy individuals in their 30s with eyesight of 0.7 or higher. Using the method described above, a steel wool scratch resistance test was conducted on the optical sheets according to each Example. For the steel wool scratch resistance test, a Gakushin-type rub fastness tester "AB-301-S" manufactured by Tester Sangyo Co., Ltd. was used.

[0228] After the steel wool scratch resistance test was completed at a load of 1000 g and 1000 cycles, the sample was removed from the tester, and the surface of the sample, which was formed by the first side of the optical sheet, was observed under the observation conditions described above. Each sample was evaluated according to the following criteria. The evaluators were 20 healthy individuals in their 30s with visual acuity of 0.7 or higher. In the following criteria, "AA" indicates the highest scratch resistance, and "AA" and "A" indicate optical sheets that were evaluated as having resistance to the steel wool scratch resistance test. "B" indicates optical sheets that were evaluated as not having resistance to the steel wool scratch resistance test. The test conditions of "1000 g load, 1000 cycles" in the steel wool scratch resistance test are more severe than the conditions typically required for anti-reflection sheets (AR sheets, LR sheets) that are bonded to the display surface of a display device.

[0229] The evaluation results for each example of the Examples and Comparative Examples are shown in the "SW Resistance" column of "Evaluation Results" in Table 1. AA: 18 or more evaluators were unable to observe any scratches on the surface. Even when scratches were observed, the scratches were thin and did not pose a problem as a product. A: 12 or more evaluators were unable to observe any scratches on the surface. Even when scratches were observed, the scratches were thin and did not pose a problem as a product. B: 11 or fewer evaluators were unable to observe any scratches on the surface. Alternatively, any of the evaluators found scratches on the surface that were problematic as a product.

[0230] 1-6. Felt Resistance Samples of 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 defects such as dust or scratches. A felt scratch resistance test was carried out on the optical sheets according to the above-mentioned method. For the felt scratch resistance test, a Gakushin-type rub fastness tester "AB-301-S" manufactured by Tester Sangyo Co., Ltd. was used.

[0231] After completing the felt scratch resistance test of 10,000 cycles at a load of 200 g, the sample was removed from the tester, and the surface of the sample formed by the first side of the optical sheet was observed under the observation conditions described above. Each sample was evaluated according to the following criteria. The evaluators were 20 healthy individuals in their 30s with a visual acuity of 0.7 or higher. In the following criteria, "AA" indicates the highest scratch resistance, and "AA" and "A" are optical sheets evaluated as having resistance in the felt scratch resistance test. "B" is an optical sheet evaluated as not having resistance in the felt scratch resistance test.

[0232] The evaluation results for each example of the Examples and Comparative Examples are shown in the "Felt Resistance" column of "Evaluation Results" in Table 1. AA: 18 or more evaluators were unable to observe any scratches on the surface. Even when scratches were observed, the scratches were thin and did not pose a problem as a product. A: 12 or more evaluators were unable to observe any scratches on the surface. Even when scratches were observed, the scratches were thin and did not pose a problem as a product. B: 11 or fewer evaluators were unable to observe any scratches on the surface. Alternatively, any of the evaluators found scratches on the surface that were problematic as a product.

[0233] 2. Preparation of Optical Sheet [Comparative Example 1] A resin layer coating solution 1 (HC layer coating solution 1) having the following formulation was applied to a triacetyl cellulose substrate having a thickness of 80 μm, and then dried at 70° C. for 1 minute to volatilize the solvent. ２ A resin layer (hard coat layer) having a dry thickness of 10 μm was prepared by irradiating the coated film with ultraviolet light at 1000 kJ / cm.

[0234] Next, a coating solution 1 for a second functional layer (coating solution 1 for a high refractive index layer) having the following formulation was applied onto the resin layer, and then dried at 70°C for 1 minute to volatilize the solvent. ２ A second functional layer (high refractive index layer) having a dry thickness of 150 nm was formed by irradiating the coated layer with ultraviolet light at 1000 kJ / cm.

[0235] Next, functional layer coating liquid 1 (low refractive index layer coating liquid 1) having the following formulation was applied onto the second functional layer, and the coating film was dried under the conditions of 50°C x 30 seconds (drying air speed 0.5 m / s), and further dried under the conditions of 50°C x 30 seconds (drying air speed 5 m / s) to volatilize the solvent. ２ By irradiating the film with ultraviolet light at 100 .mu.m, a functional layer (low refractive index layer) having a dry thickness of 100 nm was formed, and an optical sheet of Comparative Example 1 was obtained.

[0236] <Coating liquid 1 for resin layer (coating liquid 1 for hard coat layer)> 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 77 parts by mass (Dai-ichi Kogyo Co., Ltd., trade name "New Frontier R-1403MB", solid content 80%) Fluorine-based leveling agent 5 parts by mass (DIC Corporation, trade name "Megafac F-568") Photopolymerization initiator 5 parts by mass (IGM Resins, trade name "Omnirad 184", solid content 100%) Methyl isobutyl ketone 68 parts by mass Methyl ethyl ketone 200 parts by mass

[0237] <Coating Liquid 1 for Second Functional Layer (Coating Liquid 1 for High Refractive Index Layer)> PETA 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) High refractive index particles 300 parts by mass (Nippon Shokubai Co., Ltd., trade name "Zircostar", solid content 70%) Fluorine-based leveling agent 0.7 parts by mass (DIC Corporation, trade name "Megafac F251", solid content 100%) Photopolymerization initiator 9 parts by mass (manufactured by IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 3173 parts by mass Propylene glycol monomethyl ether 3173 parts by mass

[0238] <Coating Liquid 1 for Functional Layer (Coating Liquid 1 for Low Refractive Index Layer)> Polyfunctional acrylic ester composition 100 parts by mass (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name "New Frontier MF-001") Hollow silica particles 200 parts by mass (particles having an average primary particle diameter of 75 nm and having a surface treated with a silane coupling agent having a methacryloyl group) Solid silica particles 110 parts by mass (particles having an average primary particle diameter of 12.5 nm and having a surface treated with a silane coupling agent having a methacryloyl group) Silicone leveling agent 13 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-22-164E", solid content 100%) Photopolymerization initiator 4.3 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Solvent 14,867 parts by mass (Mixed solvent of methyl isobutyl ketone and 1-methoxy-2-propyl acetate. Mass ratio = 68 / 32)

[0239] [Example 1] A resin layer (hard coat layer) having a dry thickness of 10 μm was prepared by applying a resin layer coating solution 2 (HC layer coating solution 2) having the following formulation onto a substrate and drying and curing the coating film. The substrate used in Example 1 was the same as the substrate used in the above-mentioned Comparative Example 1. The resin layer in Example 1 differed from the above-mentioned Comparative Example 1 in that the resin layer coating solution was changed, but was otherwise produced by the same method and under the same conditions as Comparative Example 1.

[0240] Next, functional layer coating liquid 2 (low refractive index layer coating liquid 2) having the following formulation was applied onto the resin layer, and the coating film was dried and cured to form a functional layer (low refractive index layer) with a dry thickness of 100 nm, thereby obtaining the optical sheet of Example 1. That is, the optical sheet of Example 1 did not include a second functional layer, unlike the optical sheet of Comparative Example 1. The functional layer in Example 1 differed from the above-mentioned Comparative Example 1 in that the functional layer coating liquid was changed, but was otherwise manufactured by the same method and under the same conditions as Comparative Example 1.

[0241] <Coating liquid 2 for resin layer (coating liquid 2 for hard coat layer)> UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-450", solid content 100%) Solid silica particles 109 parts by mass (average primary particle diameter 12.5 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 46%) Silicone-based leveling agent 2 parts by mass (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., trade name "10-301", solid content 5%) Photopolymerization initiator 4 parts by mass (IGM Resins, trade name "Omnirad 184", solid content 100%) Methyl isobutyl ketone 69 parts by mass Methyl ethyl ketone 297 parts by mass Propylene glycol monomethyl ether 33 parts by mass

[0242] <Coating liquid 2 for functional layer (coating liquid 2 for low refractive index layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 43 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 1,143 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 50 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 83 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 633 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 113 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 6 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 19354 parts by mass Propylene glycol monomethyl ether acetate 2320 parts by mass

[0243] [Example 2] Example 2 differs from the above-mentioned Example 1 in that functional layer coating liquid 2 was changed to the following functional layer coating liquid 3, and otherwise the optical sheet of Example 2 was obtained using the same materials and the same method as Example 1.

[0244] <Coating Liquid 3 for Functional Layer (Coating Liquid 3 for Low Refractive Index Layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 43 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 1,111 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 36 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 60 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 201 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 54 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 6 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 15511 parts by mass Propylene glycol monomethyl ether acetate 1851 parts by mass

[0245] [Example 3] Example 3 differs from the above-mentioned Example 1 in that the functional layer coating liquid 2 was changed to the following functional layer coating liquid 4, and otherwise the optical sheet of Example 3 was obtained using the same materials and the same method as Example 1.

[0246] <Coating Liquid 4 for Functional Layer (Coating Liquid 4 for Low Refractive Index Layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 11 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 777 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 39 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 65 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 457 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 82 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 5 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 14,107 parts by mass Propylene glycol monomethyl ether acetate 1,580 parts by mass

[0247] [Example 4] Example 4 differs from the above-mentioned Example 1 in that functional layer coating liquid 2 was changed to the following functional layer coating liquid 5, and otherwise the optical sheet of Example 4 was obtained using the same materials and method as Example 1.

[0248] <Coating Liquid 5 for Functional Layer (Coating Liquid 5 for Low Refractive Index Layer)> UV-curable acrylate-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "Aronix M-305", solid content 100%) Hollow silica particles 650 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 67 parts by mass (average primary particle diameter 12.5 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 37%) Leveling agent 128 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 34 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 7 parts by mass (IGM Resins Co., Ltd., trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 8828 parts by mass Propylene glycol monomethyl ether acetate 1034 parts by mass

[0249] [Example 5] Example 5 differs from the above-mentioned Example 1 in that functional layer coating liquid 2 was changed to the following functional layer coating liquid 6, and otherwise the optical sheet of Example 5 was obtained using the same materials and the same method as Example 1.

[0250] <Coating Liquid 6 for Functional Layer (Coating Liquid 6 for Low Refractive Index Layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 43 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 1,194 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 57 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 96 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 660 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 125 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 6 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 20207 parts by mass Propylene glycol monomethyl ether acetate 2424 parts by mass

[0251] [Example 6] Example 6 differs from the above-mentioned Example 1 in that functional layer coating liquid 2 was changed to the following functional layer coating liquid 7, and otherwise the optical sheet of Example 6 was obtained using the same materials and the same method as Example 1.

[0252] <Coating Liquid 7 for Functional Layer (Coating Liquid 7 for Low Refractive Index Layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 44 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 1,148 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 50 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 84 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 847 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 169 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 6 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 21,125 parts by mass Propylene glycol monomethyl ether acetate 2,538 parts by mass

[0253] [Comparative Example 2] Comparative Example 2 differs from the above-mentioned Example 1 in that functional layer coating liquid 2 was changed to the following functional layer coating liquid 8; otherwise, the optical sheet of Comparative Example 2 was obtained using the same materials and the same method as in Example 1.

[0254] <Coating Liquid 8 for Functional Layer (Coating Liquid 8 for Low Refractive Index Layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 42 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 1,137 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 49 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 83 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 1049 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 280 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 5 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 22851 parts by mass Propylene glycol monomethyl ether acetate 2753 parts by mass

[0255] [Comparative Example 3] Comparative Example 3 differs from the above-mentioned Example 1 in that functional layer coating liquid 2 was changed to the following functional layer coating liquid 9; otherwise, the optical sheet of Comparative Example 3 was obtained using the same materials and the same method as in Example 1.

[0256] <Coating Liquid 9 for Functional Layer (Coating Liquid 9 for Low Refractive Index Layer)> UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "AS-SQ TA-100", solid content 100%) UV-curable acrylate-containing composition 43 parts by mass (manufactured by Toagosei Co., Ltd., product name "Aronix M-305", solid content 100%) Hollow silica particles 1,138 parts by mass (average primary particle diameter 65 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) Solid silica particles 49 parts by mass (average primary particle diameter 9.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 50%) Alumina particles 83 parts by mass (average primary particle diameter 15.0 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 30%) Leveling agent 104 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "X-71-1203M", solid content 20%) Leveling agent 13 parts by mass (Shin-Etsu Chemical Co., Ltd., trade name "KP-422", solid content 15%) Photopolymerization initiator 6 parts by mass (IGM Resins, trade name "Omnirad 127", solid content 100%) Methyl isobutyl ketone 15,312 parts by mass Propylene glycol monomethyl ether acetate 1,825 parts by mass

[0257]

[0258] 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, 43: Hollow silica particles, 44: Solid silica particles, 45: Depression, 45a: High end, 45b: Low end, 45c: Deepest part, 45e: Convex part, 45x: Cross-sectional profile, 50: Second functional layer, 51: Binder resin, 52: Particle, 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: Bonded article

Claims

1. An optical sheet comprising a first surface and a second surface opposite to the first surface, comprising, in the order from the second surface to the first surface, a substrate and a functional layer, the functional layer comprising a binder component and hollow silica particles, and comprising a depression having a width of 0.1 μm or more and 1.5 μm or less and a depth of 10 nm or more in a 10 μm x 10 μm area of ​​the first surface.

2. The optical sheet according to claim 1, wherein the depth of the recesses is 70 nm or less.

3. The optical sheet according to claim 1, wherein the number of depressions included in the 10 μm×10 μm area of ​​the first surface is three or more.

4. The optical sheet according to claim 1, wherein the number of depressions included in the 10 μm×10 μm area of ​​the first surface is 11 or more.

5. The optical sheet according to claim 1, wherein the number of depressions included in the 10 μm×10 μm area of ​​the first surface is 50 or less.

6. The optical sheet according to claim 1, wherein the depression is included in each of four small areas obtained by dividing the 10 μm×10 μm area into two equal parts along each side.

7. The optical sheet according to claim 1, wherein the arithmetic mean roughness Sa of the first surface is 8.0 nm or less.

8. The optical sheet according to claim 1, wherein the first surface includes a flat portion around the recess.

9. The optical sheet according to claim 1, wherein the proportion of the recesses in a 10 μm×10 μm area of ​​the first surface is 15% or less.

10. The optical sheet according to claim 1, wherein the ratio of the depth to the width of the recess is greater than or equal to 0.

030.

11. 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.

12. The optical sheet according to claim 1, which is resistant to a scratch resistance test using a felt on the first surface under the following conditions: Scratch resistance test: Using a Jumbo Wearaser (registered trademark, product number: CS-7) manufactured by TABER Corporation as a sliding piece, the sheet is moved back and forth 10,000 times with a load of 200 g, a moving speed of 200 mm / sec, and a one-way moving distance of 50 mm.

13. 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.

14. A sheet article comprising a plurality of the optical sheets according to any one of claims 1 to 13.

15. The sheet article of claim 14, wound about a winding axis.

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 comprises the optical sheet according to any one of claims 1 to 13.

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

18. A panel comprising: a bonded article; and an optical sheet according to any one of claims 1 to 13 bonded to the bonded article.

19. A method for selecting an optical sheet comprising an optical sheet having a first surface and a second surface opposite to the first surface, the optical sheet comprising, in the order from the second surface to the first surface, a substrate and a functional layer, the functional layer including a binder component and hollow silica particles, the method comprising the steps of: acquiring an image of a 10 μm x 10 μm area of ​​the first surface; and selecting, based on the image, an optical sheet in which the area includes a depression having a width of 0.1 μm or more and 1.5 μm or less and a depth of 10 nm or more.

20. A method for manufacturing an optical sheet, comprising: a step of producing an optical sheet including a first surface and a second surface opposite to the first surface, the optical sheet comprising, in the order from the second surface to the first surface, a substrate and a functional layer, the functional layer including a binder component and hollow silica particles; and a step of selecting an optical sheet including, in a 10 μm x 10 μm area on the first surface, a depression having a width of 0.1 μm or more and 1.5 μm or less and a depth of 10 nm or more.

Images