Optical sheet, sheet article, polarizing plate, touch panel member, display device, and base material equipped with easy adhesion layer

Abstract

This optical sheet includes a base material and a first functional layer that are laminated in a first direction. The thickness of the first functional layer is 20-250 nm. The change rate of the surface of the first functional layer on the side opposite to the base material in a cross section along the first direction is 1.02-1.19. The change rate is the ratio of the length of the surface positioned within a reference range of the cross section with respect to the length between both ends of the surface positioned within the reference range. The length between both ends of the surface positioned within the reference range is 1.3 μm.

Description

Optical sheet, sheet article, polarizing plate, touch panel member, display device, and substrate with an easy-adhesion layer

[0001] The present disclosure relates to an optical sheet, a sheet article, a polarizing plate, a touch panel member, a display device, and a substrate with an easy-adhesion layer.

[0002] Patent Document 1 discloses an optical sheet including a substrate and a hard coat layer. An optical sheet including a plurality of layers may include a plurality of reflection interfaces. Due to the interference of light reflected at different reflection interfaces, interference fringes may be observed in the optical sheet. The interference fringes are patterns having an iridescent color and, as an example, are streak-shaped.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-12675

[0004] The present disclosure aims to make the interference fringes less conspicuous.

[0005] The optical sheet according to an embodiment of the present disclosure includes a substrate and a first functional layer stacked in a first direction, the thickness of the first functional layer is 20 nm or more and 250 nm or less, the length change rate in a cross-section along the first direction of the surface of the first functional layer opposite to the substrate is 1.02 or more and 1.19 or less, the change rate is a ratio of the length of the surface located within a reference range of the cross-section to the length between both ends of the surface located within the reference range, and the length between both ends of the surface located within the reference range is 1.3 μm.

[0006] The sheet article according to an embodiment of the present disclosure includes a plurality of optical sheets according to an embodiment of the present disclosure.

[0007] The polarizing plate according to an embodiment of the present disclosure includes an optical sheet according to an embodiment of the present disclosure and a polarizer stacked on the optical sheet.

[0008] The touch panel member according to an embodiment of the present disclosure includes an optical sheet according to an embodiment of the present disclosure and an electrode layer stacked on the optical sheet.

[0009] A display device according to one embodiment of the present disclosure comprises an optical sheet according to one embodiment of the present disclosure and a display element superimposed on the optical sheet.

[0010] A substrate with an easy-adhesion layer according to one embodiment of the present disclosure comprises a substrate and a first functional layer stacked in a first direction, wherein the first functional layer is an easy-adhesion layer, the thickness of the first functional layer is 20 nm or more and 250 nm or less, the rate of change in length of the surface of the first functional layer opposite to the substrate in a cross-section along the first direction is 1.02 or more and 1.19 or less, the rate of change is the ratio of the length of the surface located within a reference range of the cross-section to the length between both ends of the surface located within the reference range, and the length between both ends of the surface located within the reference range is 1.3 μm.

[0011] According to this disclosure, interference fringes can be made less noticeable.

[0012] Figure 1 is a diagram illustrating one embodiment, and is a cross-sectional view showing an example of an optical sheet. Figure 2A is a cross-sectional view corresponding to Figure 1, showing one modified layer configuration. Figure 2B is a cross-sectional view corresponding to Figure 1, showing another modified layer configuration. Figure 3 is an observation image of the cross-section of the optical sheet according to Example 2. Figure 4A is a screenshot illustrating a method for measuring the rate of change using image analysis software. Figure 4B is a screenshot illustrating a method for measuring the rate of change using image analysis software. Figure 4C is another example of an observation image of the cross-section of the optical sheet, and is an observation image after trimming. Figure 4D is a screenshot illustrating a method for measuring the rate of change using image analysis software. Figure 4E is a binarized image obtained by binarizing the observation image shown in Figure 4C, and is a diagram illustrating a method for tracing the first interface (first surface) of the optical sheet. Figure 4F is a screenshot illustrating a method for measuring the rate of change using image analysis software. Figure 4G is a screenshot illustrating a method for measuring the rate of change using image analysis software. Figure 4H is a screenshot illustrating a method for measuring the rate of change using image analysis software. Figure 4I is a diagram illustrating a method for measuring the length of a reference range from the binarized image shown in Figure 4E. Figure 5 is a diagram illustrating the average tilt angle for an optical sheet. Figure 6 is a diagram illustrating an optical sheet as a substrate with an easy-adhesion layer. Figure 7 is a perspective view showing an example of a sheet article containing an optical sheet. Figure 8 is a cross-sectional view showing an example of a polarizing plate containing an optical sheet. Figure 9 is a cross-sectional view showing an example of a display device containing an optical sheet. Figure 10 is a cross-sectional view showing an example of a panel containing an optical sheet. Figure 11 is an observation image of a cross-section of an optical sheet according to Comparative Example 1.

[0013] One embodiment of the present disclosure relates to the following <1> to <19>.

[0014] <1> An optical sheet comprising a substrate and a first functional layer stacked in a first direction, wherein the thickness of the first functional layer is 20 nm or more and 250 nm or less, the rate of change in length of the surface of the first functional layer opposite to the substrate in a cross-section along the first direction is 1.02 or more and 1.19 or less, the rate of change is the ratio of the length of the surface located within a reference range of the cross-section to the length between both ends of the surface located within the reference range, and the length between both ends of the surface located within the reference range is 1.3 μm.

[0015] <2> The optical sheet according to <1>, wherein the average inclination angle of the surface in the cross-section is 5.0° or more and 30° or less.

[0016] <3> The optical sheet according to <1> or <2>, wherein the surface in the cross-section includes a plurality of protrusions and / or a plurality of recesses within the reference range.

[0017] <4> The optical sheet according to any one of <1> to <3>, wherein the maximum height difference in the first direction within the reference range of the surface in the cross-section is 25 nm or more and 100 nm or less.

[0018] <5> An optical sheet as described in any one of items <1> to <4>, wherein the transmitted haze is 1.5% or less.

[0019] <6> The first functional layer is an optical sheet according to any one of <1> to <5>, comprising a binder component and particles.

[0020] <7> The substrate is an optical sheet according to any one of <1> to <6>, comprising polyester.

[0021] <8> The optical sheet according to any one of <1> to <7>, wherein the substrate contains a resin derived from biomass material.

[0022] <9> The first functional layer is an optical sheet according to any one of <1> to <8>, comprising a resin derived from biomass material.

[0023] <10> The optical sheet according to any one of <1> to <9>, further comprising a second functional layer superimposed on the first functional layer in the first direction, wherein the first functional layer is located between the substrate and the second functional layer in the first direction.

[0024] <11> The optical sheet according to <10>, wherein the first functional layer comprises a binder component and particles, and the particles are located only within the first functional layer among the first and second functional layers.

[0025] <12> The optical sheet according to any one of <1> to <11>, wherein the surface in the cross-section includes 3 to 12 protrusions within the reference range.

[0026] <13> The optical sheet according to any one of <1> to <12>, wherein the surface in the cross-section includes 3 to 12 recesses within the reference range.

[0027] <14> A sheet article comprising multiple optical sheets as described in any one of items <1> to <13>.

[0028] <15> The sheet article described in <14>, which is wound around a winding axis.

[0029] <16> A polarizing plate comprising an optical sheet described in any one of <1> to <13>, and a polarizer superimposed on the optical sheet.

[0030] <17> A touch panel member comprising an optical sheet described in any one of <1> to <13>, and an electrode layer superimposed on the optical sheet.

[0031] <18> A display device comprising an optical sheet described in any one of <1> to <13>, and a display element superimposed on the optical sheet.

[0032] <19> A substrate with an easy-adhesion layer comprising a substrate and a first functional layer stacked in a first direction, wherein the first functional layer is an easy-adhesion layer, the thickness of the first functional layer is 20 nm or more and 250 nm or less, the rate of change in length of the surface of the first functional layer opposite to the substrate in a cross-section along the first direction is 1.02 or more and 1.19 or less, the rate of change is the ratio of the length of the surface located within a reference range of the cross-section to the length between both ends of the surface located within the reference range, and the length between both ends of the surface located within the reference range is 1.3 μm.

[0033] The following describes in detail one embodiment of the present disclosure. In the drawings attached to this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of illustration and ease of understanding. Components shown in some drawings may be omitted in other drawings. The scale and aspect ratios may differ between drawings.

[0034] In this specification, terms such as "sheet," "film," and "plate" are not distinguished from each other solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished from components such as optical films or optical plates solely on the basis of differences in name.

[0035] In this specification, the normal direction of a sheet-like (film-like, plate-like) member refers to the direction parallel to the normal or perpendicular to the sheet surface (film surface, plate surface) of the sheet-like (film-like, plate-like) member in question. The "sheet surface (film surface, plate surface)" refers to the surface that coincides with the sheet-like (film-like, plate-like) member in question when viewed as a whole and in a broad sense.

[0036] In this specification, multiple candidate upper limits and multiple candidate lower limits for a numerical range may be described in separate sentences. In such descriptions, the numerical range may be constructed by combining any one candidate upper limit and any one candidate lower limit. As an example, consider the description, "Parameter B may be A1 or greater, A2 or greater, A3 or greater. 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 greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, or A3 or greater and A6 or less.

[0037] To clarify the directional relationships between drawings, some drawings show a common first direction D1, second direction D2, and third direction D3 using arrows with a common reference numeral. The tip of the arrow represents the first side in each direction. The opposite side of the arrow represents the second side in each direction. Arrows pointing towards the back of the drawing along a direction perpendicular to the plane of the drawing are indicated by a symbol of an "x" inside a circle, as shown in Figure 1, for example.

[0038] <<<Optical Sheet>>> As shown in Figures 1 to 2B, the optical sheet 10 according to this embodiment includes a base material 20 and a first functional layer 30. The base material 20 and the first functional layer 30 are laminated in a first direction D1. The first direction D1 is the lamination direction of the optical sheet 10. The first direction D1 is also the thickness direction of the optical sheet 10.

[0039] As shown in Figures 1 to 2B, the optical sheet 10 may include a first surface 11 and a second surface 12. In the illustrated example, the first surface 11 and the second surface 12 constitute the main surfaces of the optical sheet 10. The first surface 11 and the second surface 12 face each other in a first direction D1. In the example shown in Figures 1 to 2B, the first surface 11 is made up of one of the main surfaces of the substrate 20. The optical sheet 10 includes the substrate 20 and the first functional layer 30 in the order from the second surface 12 toward the first surface 11.

[0040] As shown in FIGS. 1 to 2B, the first functional layer 30 may include a first surface 31 and a second surface 32. In the illustrated example, the first surface 31 and the second surface 32 constitute the main surfaces of the sheet-like first functional layer 30. The first surface 31 and the second surface 32 face each other in the first direction D1. In the example shown in FIGS. 1 to 2B, the first surface 31 of the first functional layer 30 is close to the first surface 11 of the optical sheet 10 and away from the second surface 12 of the optical sheet 10 in the first direction D1. The first surface 31 of the first functional layer 30 faces the first surface 11 side of the optical sheet 10 and faces the side opposite to the second surface 12 of the optical sheet 10. The second surface 32 of the first functional layer 30 is away from the first surface 11 of the optical sheet 10 and close to the second surface 12 of the optical sheet 10 in the first direction D1. The second surface 32 of the first functional layer 30 faces the side opposite to the first surface 11 of the optical sheet 10 and faces the second surface 12 side of the optical sheet 10.

[0041] As shown in FIGS. 1 to 2B, the first functional layer 30 contacts the base material 20 from the first side in the first direction D1. The first functional layer 30 contacts the base material 20 at the second surface 32. The first functional layer 30 forms a first interface BS1 with the base material 20 at the second surface 32.

[0042] As shown in FIGS. 1 to 2B, the optical sheet 10 may include a second functional layer 40. In the illustrated example, the first functional layer 30 is located between the base material 20 and the second functional layer 40 in the first direction D1. The second functional layer 40 is a layer expected to have some functions.

[0043] The second functional layer 40 may impart mechanical strength to the optical sheet 10. The second functional layer 40 may impart scratch resistance to the optical sheet 10. The second functional layer 40 may be a hard coat layer. The second functional layer 40 may include a cured resin product.

[0044] The second functional layer 40 may impart antiglare properties to the optical sheet 10. The second functional layer 40 may have an antiglare function. The second functional layer 40 may have a function of suppressing the reflection of external images. The optical sheet 10 may be an antiglare layer. The second functional layer 40 may include a binder component and particles held by the binder component.

[0045] The first functional layer 30 is a layer expected to have some function. The first functional layer 30 may be an easy adhesion layer. The first functional layer 30 may be a primer. The first functional layer 30 may have a function of improving the adhesion strength of the second functional layer 40 in the optical sheet 10. The second functional layer 40 may have its adhesion strength to the base material 20 improved by the first functional layer 30.

[0046] As shown in FIGS. 1 to 2B, the second functional layer 40 may include a first surface 41 and a second surface 42. In the illustrated example, the first surface 41 and the second surface 42 constitute the main surfaces of the sheet-like second functional layer 40. The first surface 41 and the second surface 42 face each other in the first direction D1. In the example shown in FIG. 1, the second surface 42 of the second functional layer 40 is away from the first surface 11 of the optical sheet 10 and close to the second surface 12 of the optical sheet 10 in the first direction D1. The second surface 42 of the second functional layer 40 faces the side opposite to the first surface 11 of the optical sheet 10 and faces the second surface 12 side of the optical sheet 10.

[0047] As shown in FIGS. 1 to 2B, the first functional layer 30 contacts the second functional layer 40 from the second side in the first direction D1. The first functional layer 30 contacts the second functional layer 40 on the first surface 31. The first functional layer 30 forms a second interface BS2 with the second functional layer 40 on the first surface 31. The second functional layer 40 contacts the first functional layer 30 from the first side in the first direction D1. The second functional layer 40 contacts the first functional layer 30 on the second surface 42. The second functional layer 40 forms a second interface BS2 with the first functional layer 30 on the second surface 42.

[0048] In the example shown in FIG. 1, the first surface 41 of the second functional layer 40 constitutes the first surface 11 of the optical sheet 10 and is away from the second surface 12 of the optical sheet 10 in the first direction D1. The first surface 41 of the second functional layer 40 faces the side opposite to the second surface 12 of the optical sheet 10.

[0049] As shown in Figure 2A, the optical sheet 10 may further include a third functional layer 51. The optical sheet 10 shown in Figure 2A includes a substrate 20, a first functional layer 30, a second functional layer 40, and a third functional layer 51, in the order from the second surface 12 to the first surface 11. The third functional layer 51 may be in contact with the second functional layer 40 from the first side in the first direction D1. In the example shown in Figure 2A, a third interface BS3 is formed between the second functional layer 40 and the third functional layer 51.

[0050] The third functional layer 51 is a layer expected to perform some function. In the example shown in Figure 2A, the second functional layer 40 is located between the first functional layer 30 and the third functional layer 51 in the first direction D1. The third functional layer 51 constitutes the first surface 11 of the optical sheet 10.

[0051] As shown in Figure 2B, the optical sheet 10 may further include a third functional layer 51 and a fourth functional layer 52. The optical sheet 10 shown in Figure 2B includes, in order from the second surface 12 toward the first surface 11, a substrate 20, a first functional layer 30, a second functional layer 40, a fourth functional layer 52, and a third functional layer 51. The third functional layer 51 may contact the fourth functional layer 52 from the first side in the first direction D1. The fourth functional layer 52 may contact the second functional layer 40 from the first side in the first direction D1. In the example shown in Figure 2B, a third interface BS3 is formed between the second functional layer 40 and the fourth functional layer 52. In the example shown in Figure 2B, a fourth interface BS4 is formed between the fourth functional layer 52 and the third functional layer 51.

[0052] The third functional layer 51 and the fourth functional layer 52 are layers expected to perform some function. In the example shown in Figure 2B, the fourth functional layer 52 is located between the second functional layer 40 and the third functional layer 51 in the first direction D1. The third functional layer 51 constitutes the first surface 11 of the optical sheet 10. In the example shown in Figure 2B, the second functional layer 40 is located between the first functional layer 30 and the fourth functional layer 52 in the first direction D1. The third functional layer 51 constitutes the first surface 11 of the optical sheet 10.

[0053] In the examples shown in Figures 2A and 2B, the first surface 41 of the second functional layer 40 is close to the first surface 11 of the optical sheet 10 and away from the second surface 12 of the optical sheet 10 in the first direction D1. The first surface 41 of the second functional layer 40 faces the first surface 11 of the optical sheet 10 and faces away from the second surface 12 of the optical sheet 10.

[0054] In the examples shown in Figures 1 to 2B, the first direction D1 is perpendicular to the first surface 11 and the second surface 12. In the examples shown in Figures 1 to 2B, the first direction D1 is perpendicular to the main surfaces 31, 32, 41, and 42 of each layer. The multiple layers 20, 30, 40, 51, and 52 contained in the optical sheet 10 are superimposed in the first direction D1. Each layer 20, 30, 40, 51, and 52 has a perpendicular or normal line parallel to the first direction D1. Each layer 20, 30, 40, 51, and 52 extends in the second direction D2 and the third direction D3, which are perpendicular to the first direction D1. In the illustrated examples, the second direction D2 and the third direction D3 are perpendicular to each other.

[0055] The optical sheet may be used together with a display element, as will be described later. The optical sheet may be applied to a display device. In this example, the first surfaces 11, 31, and 41 may be the observer's side. The first surfaces 11, 31, and 41 may also be the incident surfaces of ambient light in the environment in which the optical sheet is installed. The image light from the display element may travel from the second surfaces 12, 32, and 42 to the first surfaces 11, 31, and 41.

[0056] Incidentally, interference fringes can be observed in optical sheets containing multiple layers. Interference fringes are patterns with iridescent colors. Interference fringes may include streaky regions that appear as different colors from each other. Interference fringes result in an appearance defect of the optical sheet. Interference fringes that occur in optical sheets applied to display devices degrade the displayed image. Interference fringes are more likely to occur in optical sheets containing layers with a thickness of 1 μm or more. Interference fringes are also more likely to occur in optical sheets having a reflection suppression function or a layer having a reflection suppression function.

[0057] The optical sheet according to this embodiment incorporates features to reduce the visibility of interference fringes, as will be explained below.

[0058] <<Thickness of the First Functional Layer>> The optical sheet according to this embodiment has the following feature (A): (A): The thickness of the first functional layer is 20 nm or more and 250 nm or less.

[0059] In optical sheets containing multiple layers, it is preferable to suppress the reflection of ambient light from the optical sheet. From this viewpoint, the refractive indices of the layers included in the optical sheet usually increase gradually from the first surface to the second surface. For example, the refractive index of the first functional layer 30 is greater than that of the second functional layer 40. The refractive index of the substrate 20 is greater than that of the first functional layer 30. The reflection of light incident on the optical sheet from the first surface at the second interface BS2 between the second functional layer and the first functional layer is a fixed-end reflection. The reflection of light incident on the optical sheet from the first surface at the first interface BS1 between the first functional layer and the substrate is a fixed-end reflection.

[0060] According to feature (A), an upper limit is set on the thickness of the first functional layer. According to feature (A), the thickness of the first functional layer is 250 nm or less. According to feature (A), the optical path length of light traveling back and forth through the first functional layer is likely to be less than the wavelength of visible light. Therefore, constructive interference between light incident on the optical sheet 10 from the first surface 11 and reflected at the second interface BS2 (first surface 31) and light incident on the optical sheet 10 from the first surface 11 and reflected at the first interface BS1 (second surface 32) can be suppressed.

[0061] Furthermore, by setting an upper limit on the thickness of the first functional layer, the optical path length of light traveling back and forth through the first functional layer can be set to approximately half the wavelength of visible light. By setting the optical path length of light traveling back and forth through the first functional layer to half the wavelength of visible light, the light incident on the optical sheet 10 from the first surface 11 and reflected at the second interface BS2 (second surface 32) and the light incident on the optical sheet 10 from the first surface 11 and reflected at the first interface BS1 (first surface 31) can interfere with each other in a destructive manner.

[0062] Based on the above, as feature (A), by setting an upper limit on the thickness of the first functional layer, interference fringes caused by the interference of reflected light on both main surfaces 31 and 32 of the first functional layer can be made less noticeable. The thickness of the first functional layer may be 250 nm or less, 220 nm or less, 200 nm or less, 180 nm or less, 165 nm or less, or 150 nm or less.

[0063] The thickness of each layer in an optical sheet refers to the length of the layer in question along the first direction D1.

[0064] According to feature (A), a lower limit is set for the thickness of the first functional layer. By setting a lower limit for the thickness of the first functional layer, the first functional layer can perform the expected function. For example, the first functional layer, as an easy-adhesion layer or primer, can adhere stably to the substrate by having a thickness of 20 nm or more. The first functional layer, as an easy-adhesion layer or primer, can adhere stably to the second functional layer by having a thickness of 20 nm or more.

[0065] Furthermore, by setting a lower limit on the thickness of the first functional layer, the optical path length of light traveling back and forth through the first functional layer can be set to approximately half the wavelength of visible light. By setting the optical path length of light traveling back and forth through the first functional layer to half the wavelength of visible light, the light incident on the optical sheet 10 from the first surface 11 and reflected at the second interface BS2 (second surface 32) and the light incident on the optical sheet 10 from the first surface 11 and reflected at the first interface BS1 (first surface 31) can interfere with each other in a destructive manner.

[0066] From the above perspective, the thickness of the first functional layer may be 20 nm or more, 50 nm or more, 80 nm or more, 100 nm or more, 110 nm or more, or 120 nm or more.

[0067] The thickness of the first functional layer may be 20 nm to 250 nm, 50 nm to 250 nm, 80 nm to 250 nm, 100 nm to 250 nm, 110 nm to 250 nm, or 120 nm to 250 nm. The thickness of the first functional layer may be 20 nm to 220 nm, 50 nm to 220 nm, 80 nm to 220 nm, 100 nm to 220 nm, 110 nm to 220 nm, or 120 nm to 220 nm. The thickness of the first functional layer may be 20 nm to 200 nm, 50 nm to 200 nm, 80 nm to 200 nm, 100 nm to 200 nm, 110 nm to 200 nm, or 120 nm to 200 nm. The thickness of the first functional layer may be 20 nm to 180 nm, 50 nm to 180 nm, 80 nm to 180 nm, 100 nm to 180 nm, 110 nm to 180 nm, or 120 nm to 180 nm. The thickness of the first functional layer may be 20 nm to 165 nm, 50 nm to 165 nm, 80 nm to 165 nm, 100 nm to 165 nm, 110 nm to 165 nm, or 120 nm to 165 nm. The thickness of the first functional layer may be 20 nm to 150 nm, 50 nm to 150 nm, 80 nm to 150 nm, 100 nm to 150 nm, 110 nm to 150 nm, or 120 nm to 150 nm.

[0068] (Method for measuring thickness) The "thickness" used for each layer 20, 30, 40, 51, and 52 contained in the optical sheet shall be the value specified by (A1) to (A3) below.

[0069] (A1) Observe an image of the cross-section of the optical sheet using a scanning transmission electron microscope (STEM). Determine the imaging area so that the first direction, which is the thickness direction of the layer to be measured, is aligned with the short side of the rectangular imaging area. Set the magnification during imaging to an appropriate magnification such that the thickness of the layer to be measured is between 1 / 15 and 1 / 3 of the length of the short side of the imaging area.

[0070] (A2) The thickness of the target layer at the central position in the captured image, along a direction perpendicular to the first direction, and the thickness of the target layer at a pair of lateral positions located on either side of the central position are measured. The lateral positions are defined as positions shifted to either side of the central position in a direction perpendicular to the first direction by a length five times the thickness measurement value at the central position. The lateral positions may be positions not included in the same observation image as the central position.

[0071] (A3) Perform the above steps (A1) and (A2) 10 times on the layer to be measured, and measure the thickness of the layer at a total of 30 measurement positions. The average of the 30 thickness measurements shall be taken as the thickness of the layer to be measured.

[0072] (Observation images of the optical sheet) The observation images of the cross-section of the optical sheet are images obtained as follows.

[0073] First, cut a sample from the optical sheet to be measured. The cut sample should be in the shape of a strip. The size of the cut sample should be 3 mm wide x 10 mm long when observed from the direction normal to the optical sheet.

[0074] Next, the cut sample is embedded in the embedding resin. First, the cut sample is placed in the embedding plate. The embedding resin is poured into the embedding plate on which the cut sample is placed. The embedding resin is allowed to harden by leaving it at room temperature for 12 hours. In this way, an embedded sample containing the cut sample and the hardened embedding resin is prepared. By removing the embedded sample from the embedding plate, an embedded sample in which the cut sample is embedded in the embedding resin is obtained. The embedding resin is a cold-curing type epoxy two-component curable resin.

[0075] Section samples are cut from the embedded sample using a microtome. First, the block-shaped embedded sample is roughly cut with a glass knife to create a surface of approximately 100 μm x 20 μm, including the cross-section of the optical sheet (rough trimming). Sections are then cut from this surface using a diamond knife to raise them to the water. Section samples are obtained by collecting the floating sections using a mesh.

[0076] As described above, by vertically cutting the block-shaped embedded sample with a microtome, a section sample with the cross-section of the optical sheet exposed is obtained. The cross-section of the optical sheet observed in the section sample is the cross-section along the first direction D1 of the optical sheet. The thickness of the section sample should be between 50 nm and 300 nm, which is an appropriate thickness for observation with a scanning transmission electron microscope.

[0077] Sectional samples obtained using a scanning transmission electron microscope are observed to acquire cross-sectional images of the optical sheet. The magnification is adjusted so that each layer can be distinguished, while controlling the focus, contrast, and brightness. The magnification during observation using the scanning transmission electron microscope can be set to, for example, 10,000x to 100,000x.

[0078] <<Rate of Change>> In addition to the above-described feature (A), the optical sheet according to this embodiment has the following feature (B): (B): The rate of change in length in the cross-section along the first direction on the side of the first functional layer opposite to the substrate is 1.02 or more and 1.19 or less.

[0079] In feature (B), the "cross-section along the first direction" refers to the cross-section along the lamination direction shown in Figures 1 to 2B. As shown in Figures 1 to 2B, the "surface of the first functional layer opposite to the substrate" in feature (B) is the first surface 31. The rate of change in feature (B) is the ratio (LX / LY) of the length LX of the first surface 31 of the first functional layer 30 located within the reference range SR10 in the cross-section along the first direction D1 to the length LY between both ends of the first surface 31 of the first functional layer 30 located within the reference range SR10. The rate of change is a unitless ratio. The length LY between both ends of the first surface 31 of the first functional layer 30 located within the reference range SR10 is 1.3 μm.

[0080] "The length LY between the two ends of the first surface 31 of the first functional layer 30 located within the reference range SR10" is the distance between the two ends of the first surface 31 of the first functional layer 30 located within the reference range SR10. To put it another way, "the length LY between the two ends of the first surface 31 of the first functional layer 30 located within the reference range SR10" is the length of the straight line connecting the two ends of the first surface 31 of the first functional layer 30 located within the reference range SR10.

[0081] The rate of change is an indicator of the percentage change in position relative to the first direction D1 for the first surface of the first functional layer.

[0082] The length LY between the two ends of the first surface 31 of the first functional layer 30 located within the reference range SR10 is determined based on a binarized image obtained from an observation image of the optical sheet. The observation image of the optical sheet is a STEM observation image obtained by observing a section sample with a scanning transmission electron microscope, as described above. First, an observation image of the optical sheet is obtained using the method described above. Figure 3 is an example of an observation image showing a cross-section of the optical sheet 10 along the first direction D1 according to this embodiment.

[0083] Next, the reference range SR10 is determined in the acquired observation image. The reference range SR10 is determined such that the length between the two ends of the first surface 31 located within the reference range is 1.3 μm, with two significant figures.

[0084] Length LX is defined as the length of the first surface 31 located within the set reference range SR10. When calculating the rate of change, length LX is defined as a number with three significant figures. Length LY is defined as the length between the two ends of the first surface 31 located within the set reference range SR10. When calculating the rate of change, length LY is defined as a number with three significant figures.

[0085] Lengths LX and LY are values ​​measured using image analysis software. The image analysis software used is ImageJ (Version 1.54g) and Fiji. 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 plugin package for ImageJ.

[0086] First, length calibration is performed using the scale bar of the STEM observation image. As shown in Figure 3, in the image analysis software ImageJ, a straight line SL is drawn between the ends of the scale bar where the length of the STEM observation image has been determined. As shown in Figure 4A, by executing "Measure" from the "Analyze" tab of ImageJ, the length of the straight line SL on the STEM observation image is displayed in pixels in "Length". In the STEM observation image shown in Figure 3, this number of pixels corresponds to 500 nm.

[0087] Next, as shown in Figure 4B, select "Set scale" from the "Analyze" tab in ImageJ. For the STEM observation image shown in Figure 3, enter "500.00" in "Known distance" and "nm" in "Unit of length". Check "Global". Then click "OK" to complete the length calibration for the STEM observation image.

[0088] Next, as shown in Figure 4C, the STEM observation image is cropped. Cropping removes scale bars and other elements from the cross-sectional image. The cropped STEM observation image shown in Figure 4C is an image centered on the first surface (second interface) of the first functional layer that is the target of length measurement.

[0089] Next, the cropped STEM observation image is binarized. ImageJ is used for the binarization process. First, select "Subtract Background" from the "Process" tab in ImageJ and the Background subtraction process is executed. Select and enter an appropriate value for "Rolling ball radius" so that the first surface of the first functional layer can be clearly observed. Check "Preview". Then click "OK" to finish the Background subtraction process.

[0090] Next, by selecting "Adjust" and then "Threshold" in order from the "Image" tab in ImageJ, a binarized image is output. By comparing the STEM observation image before binarization with the binarized image, the threshold value of "Threshold" is appropriately selected and set so that the first surface of the first functional layer can be clearly observed. Figure 4E is a binarized image obtained by binarizing the STEM observation image shown in Figure 4C.

[0091] Subsequently, the length LX of the first surface 31 of the first functional layer 30 located within the reference range SR10 and the length LY between the ends of the first surface 31 of the first functional layer 30 located within the reference range SR10 are measured on the binarized image. The reference range is set so that the length between the ends of the first surface 31 located within the reference range is 1.3 μm.

[0092] To measure the length LX, the "Segmented Line" is used, as shown in Figure 4F. The position of the first surface 31 of the first functional layer 30 is traced on the binarized image. Tracing is performed by clicking the mouse while the mouse pointer is positioned over the first surface 31. As shown in Figure 4E, a rectangular marker is displayed at the position identified as the location on the first surface 31.

[0093] As described above, the "Threshold" threshold during the binarization process is adjusted so that the position of the first plane does not become unclear in the binarized image. If the position of the first plane still becomes unclear in the binarized image, the position of the first plane is determined by comparing the STEM observation image before binarization (as shown in Figure 4C) with the binarized image.

[0094] When tracing the first surface within a single reference range SR10, more than 30 locations on the first surface are identified. That is, the number of markers on the binarized image is also 30 or more. On the binarized image, the profile of the first surface of the first functional layer is traced by a set of linear segments, i.e., polylines, formed by sequentially connecting two adjacent markers in the first direction D1. The number of markers is set to a number that can sufficiently represent the profile of the first surface by a set of linear segments, i.e., polylines, formed by sequentially connecting two adjacent markers in the first direction D1.

[0095] As shown in Figure 4E, the markers on the binarized image for tracing the profile of the first surface include markers located at both ends in the first direction D1 within the reference range SR10.

[0096] The profile of the first surface 31 of the first functional layer 30 may include extreme points. The extreme points include maximal points that form convex portions (local maximums) in the profile and minimum points that form concave portions (local minimums) in the profile. Markers on the binarized image for tracing the profile of the first surface include each of the maximal points of the first surface or their vicinity located within the reference range SR 10. Markers on the binarized image for tracing the profile of the first surface include each of the local minimum points of the first surface or their vicinity located within the reference range SR 10.

[0097] Next, as shown in Figure 4G, selecting "Measure" from the "Analyze" tab outputs the total length of multiple straight lines formed by sequentially connecting two adjacent points in the first direction D1, i.e., the length of the polyline. This output value becomes the length LX of the first surface 31 of the first functional layer 30 located within the reference range SR10.

[0098] To measure the length LY, "Straight Line" is used, as shown in Figure 4H. As shown in Figure 4I, the mouse pointer is positioned on the first surface at the ends of the first direction D1 within the reference range SR10 on the binarized image, and the mouse is clicked. As shown in Figure 4I, a rectangular marker is displayed at the position identified as the position on the first surface 31.

[0099] Next, selecting "Measure" from the "Analyze" tab outputs the distance between two points located at both ends in the first direction D1 within the reference range SR10. This output value becomes the length LY between the two ends of the first surface 31 located within the reference range SR10.

[0100] In Figure 4I, a marker indicating the midpoint between the two markers indicating the ends of the first surface in the first direction D1 within the reference range SR10 is also displayed. The marker indicating the midpoint is automatically displayed by image processing software. The distance between the two markers indicating the ends is measured as length LY.

[0101] The rate of change (LX / LY) is calculated from the lengths LX and LY measured by image analysis software. The rate of change is specified as a numerical value with three significant figures. When calculating the rate of change (LX / LY), the units of length LX and length LY are the same. The units of length LX and length LY may be either "μm" or "nm".

[0102] The above rate of change calculation is performed based on nine binarized images related to nine measurement positions on the optical sheet to be evaluated. The arithmetic mean of the nine calculated rates of change is taken as the rate of change of the optical sheet to be evaluated. The nine measurement positions are the approximate center positions of the nine regions of the optical sheet to be evaluated. The nine regions are obtained by dividing the optical sheet to be evaluated into three equal parts in each of two orthogonal directions. For rectangular optical sheets, the nine regions are determined by dividing them into three equal parts along the short side and three equal parts along the long side.

[0103] Feature (B) sets upper and lower limits on the rate of change. The rate of change defined in Feature (B) is an indicator of the amount of positional change in the first direction D1 for the first surface 31 of the first functional layer 30. In other words, the rate of change is an indicator of the ratio of positional change in the first direction D1 for the second interface BS2 between the first functional layer 30 and the second functional layer 40.

[0104] Interference fringes that can be observed on an optical sheet are caused by the reinforcement of reflected light at each interface within the optical sheet. The reflected light is, for example, reflected ambient light incident on the optical sheet from the first surface. If the reflection at each interface is a fixed-end reflection, the reflected light at two different interfaces reinforces when the difference in optical path length between the two interfaces is a natural number multiple of the wavelength. A color corresponding to the wavelength can be observed at the location of the reinforcement on the optical sheet.

[0105] In feature (B), a lower limit is set for the rate of change. Therefore, within the reference range, the optical path length of the light reflected at the first surface 31 (second interface BS2) of the first functional layer 30 changes. By increasing the rate of change, the amount of change in optical path length within the reference range SR10 increases.

[0106] By varying the position of the first surface 31 in the first direction D1 within a minute reference range SR10, the brightness contrast of interference fringes associated with reflected light of a specific wavelength on the first surface 31 can be reduced. In other words, the brightness contrast can be reduced for light of each wavelength in the visible light range. In this case, the color corresponding to each wavelength is suppressed from being observed intensely only in specific minute regions. The color corresponding to each wavelength becomes easier to observe faintly over a wide range. Furthermore, by the overlapping, or color mixing, of interference fringes of various wavelengths with reduced brightness contrast, the interference fringes observed on the optical sheet can be made less conspicuous.

[0107] In this specification, the wavelength of visible light is defined as 380 nm or more and 780 nm or less.

[0108] The above-described feature (A) makes interference fringes caused by the interference of reflected light on both main surfaces 31 and 32 of the first functional layer 30 less noticeable. The combination of feature (A) and feature (B) makes interference fringes caused by the interference of reflected light on both main surfaces 31 and 32 of the first functional layer less noticeable more effectively. In other words, the generation of interference fringes by the installation of the first functional layer 30 can be effectively suppressed.

[0109] In addition, the first surface 31 of the first functional layer 30 is in contact with the second surface 42 of the second functional layer 40, forming a second interface BS2. The rate of change of the first surface 31 directly affects not only the optical path length of light traveling back and forth through the first functional layer 30, but also the optical path length of light traveling back and forth through the second functional layer 40. Therefore, by setting a lower limit on the rate of change in feature (B), interference fringes caused by the interference of reflected light on both main surfaces 41 and 42 of the second functional layer 40 can be effectively made less noticeable.

[0110] When the thickness of the second functional layer 40 is greater than half a wavelength of visible light, the reflected light from both main surfaces 41 and 42 of the second functional layer 40 may interfere constructively. When the thickness of the second functional layer 40 is greater than 1.0 μm, interference fringes due to the interference of reflected light from both main surfaces 41 and 42 of the second functional layer 40 are easily observed. When the thickness of the second functional layer 40 is greater than 2.0 μm, the thickness variation of the second functional layer 40 tends to be large, and interference fringes due to the interference of reflected light from both main surfaces 41 and 42 of the second functional layer 40 become more noticeable. In an optical sheet including such a second functional layer 40, feature (B) can effectively make the interference fringes less noticeable.

[0111] From the above viewpoint, a lower limit may be set for the rate of change of the surface of the first functional layer opposite to the substrate in the cross-section along the first direction. The lower limit of the rate of change may be 1.02 or higher, 1.03 or higher, 1.05 or higher, 1.06 or higher, 1.08 or higher, or 1.10 or higher.

[0112] In feature (B), an upper limit is set on the rate of change. The rate of change is an indicator of the amount of positional change in the first direction D1 for the first surface 31 of the first functional layer 30. When the rate of change is large, the light transmitted through the optical sheet may be diffused on the first surface 31 of the first functional layer 30. By setting an upper limit on the rate of change in feature (B), light diffusion on the first surface 31 (second interface BS2) can be suppressed. The rate of change may be 1.19 or less, 1.17 or less, 1.15 or less, or 1.12 or less.

[0113] The lower limit of the rate of change may be 1.02 or more and 1.19 or less, 1.03 or more and 1.19 or less, 1.05 or more and 1.19 or less, 1.06 or more and 1.19 or less, 1.08 or more and 1.19 or less, or 1.10 or more and 1.19 or less. The lower limit of the rate of change may be 1.02 or more and 1.17 or less, 1.03 or more and 1.17 or less, 1.05 or more and 1.17 or less, 1.06 or more and 1.17 or less, 1.08 or more and 1.17 or less, or 1.10 or more and 1.17 or less. The lower limit of the rate of change may be 1.02 or more and 1.15 or less, 1.03 or more and 1.15 or less, 1.05 or more and 1.15 or less, 1.06 or more and 1.15 or less, 1.08 or more and 1.15 or less, or 1.10 or more and 1.15 or less. The lower limit of the rate of change may be 1.02 or more and 1.12 or less, 1.03 or more and 1.12 or less, 1.05 or more and 1.12 or less, 1.06 or more and 1.12 or less, 1.08 or more and 1.12 or less, or 1.10 or more and 1.12 or less.

[0114] <<Average tilt angle>> In addition to features (A) and (B), the optical sheet may also include the following feature (C): (C): The average tilt angle of the surface of the first functional layer opposite to the substrate in a cross-section along the first direction is 5.0° or more and 30° or less.

[0115] In feature (C), the "cross-section along the first direction" refers to the cross-section along the lamination direction shown in Figures 1 to 2B. As shown in Figures 1 to 2B, the "surface opposite the substrate of the first functional layer" in feature (C) is the first surface 31.

[0116] The average inclination angle is calculated using the sum of the height differences H31 between the extreme points included in the reference range SR10, ΣH31, and the length LZ along the direction perpendicular to the first direction D1 of the reference range SR10. As described in feature (B), the reference range SR10 is determined such that the length between the two ends of the first surface 31 located within the reference range is 1.3 μm, with two significant figures.

[0117] Figure 5 is a cross-sectional view of an optical sheet showing an example of the profile of the first surface 31 of the first functional layer 30. The profile of the first surface 31 of the first functional layer 30 may include extreme points within the reference range SR10 in the STEM observation image. The extreme points include a maximum point 31X that forms a convex portion (maximum value) 33X in the profile, and a minimum point 31Y that forms a concave portion (minimum value) 33Y in the profile. The height difference between the extreme points is the distance along the first direction D1 between two adjacent extreme points (adjacent maximum point 31X and minimum point 31Y) in a direction perpendicular to the first direction D1. The height difference between the extreme points is measured from the STEM observation image of the cross section of the optical sheet along the first direction, similar to the thickness of feature (A).

[0118] In the example shown in Figure 5, the first surface 31 within the reference range SR10 includes four local maximum points 31X and three local minimum points 31Y. The height difference H31a to H31f between two adjacent local maximum points is measured at six locations. In the example shown in Figure 5, the sum of the height differences H31a to H31f is the sum of the height differences between local maximum points included in the reference range SR10, ΣH31.

[0119] The length LZ of the reference range SR10 is the distance along the direction perpendicular to the first direction D1 between the two ends of the first surface 31 contained within the reference range SR10. The length LZ of the reference range SR10 is measured from STEM observation images of the cross section of the optical sheet along the first direction, similar to the height difference between extreme points.

[0120] The average incline angle θ31 is calculated using the sum of the measured height differences ΣH31 and the length LZ, using the following formula: Average incline angle θ31 (°) = tan －１ (Total ΣH31 / Length LZ)

[0121] The average tilt angle described above is calculated from nine STEM observation images acquired at nine measurement positions on the optical sheet being evaluated. The arithmetic mean of the nine calculated average tilt angles is taken as the average tilt angle of the optical sheet being evaluated. The nine measurement positions are the same as the nine measurement positions used to measure the rate of change.

[0122] The average tilt angle is an indicator of the average change in position relative to the first direction D1 for the first surface 31 of the first functional layer 30 within a predetermined length range along a direction perpendicular to the first direction D1. In feature (C), a lower limit is set for the average tilt angle. Therefore, within the reference range, the optical path length of the light reflected by the first surface 31 (second interface BS2) of the first functional layer 30 changes. Increasing the average tilt angle increases the amount of change in optical path length within the reference range SR10. The reference range SR10 is a minute range where the length between both ends of the first surface 31 located within the reference range is 1.3 μm.

[0123] By varying the position of the first surface 31 in the first direction D1 within a minute reference range SR10, the brightness contrast of interference fringes associated with reflected light of a specific wavelength on the first surface 31 can be reduced. In other words, the brightness contrast can be reduced for light of each wavelength in the visible light range. As interference fringes of various wavelengths with reduced brightness contrast overlap, the interference fringes observed on the optical sheet can be made less conspicuous.

[0124] From the above viewpoint, a lower limit may be set for the average inclination angle of the surface of the first functional layer opposite to the substrate in the cross-section along the first direction. The average inclination angle may be 5.0° or more, 8.0° or more, 10° or more, 12° or more, 14° or more, or 18° or more.

[0125] Feature (C) sets an upper limit on the average tilt angle. The average tilt angle is an indicator of the average change in position relative to the first direction D1 over a predetermined length range along a direction perpendicular to the first direction D1 for the first surface 31 of the first functional layer 30. When the average tilt angle is large, the light transmitted through the optical sheet may be diffused on the first surface 31 of the first functional layer 30. By setting an upper limit on the average tilt angle in feature (C), light diffusion on the first surface 31 (second interface BS2) can be suppressed. The average tilt angle may be 30° or less, 27° or less, 23° or less, or 21° or less.

[0126] The average slope angle may be 5.0° or more and 30° or less, 8.0° or more and 30° or less, 10° or more and 30° or less, 12° or more and 30° or less, 14° or more and 30° or less, or 18° or more and 30° or less. The average slope angle may be 5.0° or more and 27° or less, 8.0° or more and 27° or less, 10° or more and 27° or less, 12° or more and 27° or less, 14° or more and 27° or less, or 18° or more and 27° or less. The average slope angle may be 5.0° or more and 23° or less, 8.0° or more and 23° or less, 10° or more and 23° or less, 12° or more and 23° or less, 14° or more and 23° or less, or 18° or more and 23° or less. The average slope angle may be 5.0° or more and 21° or less, 8.0° or more and 21° or less, 10° or more and 21° or less, 12° or more and 21° or less, 14° or more and 21° or less, or 18° or more and 21° or less.

[0127] <<Extreme points, protrusions, recesses>> In addition to features (A) and (B), the optical sheet may also include the following feature (D): (D): The surface of the first functional layer opposite to the substrate in a cross-section along the first direction includes a plurality of protrusions and / or a plurality of recesses within the reference range SR10.

[0128] In feature (D), the "cross-section along the first direction" refers to the cross-section along the lamination direction shown in Figures 1 to 2B. As shown in Figures 1 to 2B, the "surface opposite to the substrate of the first functional layer" in feature (D) is the first surface 31. The reference range SR10 is determined, as explained in feature (B), such that the length between the two ends of the first surface 31 located within the reference range is 1.3 μm, with two significant figures. The convex portion 33X defined in feature (D) is formed by the maximum value point 31X on the first surface 31. The concave portion 33Y defined in feature (D) is formed by the minimum value point 31Y on the first surface 31.

[0129] In feature (D), the reference range SR10 includes a plurality of protrusions 33X and / or a plurality of recesses 33Y. In the reference range SR10 which includes the plurality of protrusions 33X and / or a plurality of recesses 33Y, the first surface 31 includes a portion inclined to one side with respect to the first direction D1 and a portion inclined to the other side. Therefore, according to feature (D), the brightness contrast of interference fringes related to reflected light of a specific wavelength on the first surface 31 can be effectively reduced. In other words, according to feature (D), the brightness contrast can be effectively reduced for light of each wavelength in the visible light range. According to feature (D), the interference fringes observed on the optical sheet can be effectively made less conspicuous by the overlapping of interference fringes of various wavelengths with reduced brightness contrast.

[0130] The presence or absence of the convex portion 33X and the concave portion 33Y is determined based on a STEM observation image of the cross-section of the optical sheet along the first direction, similar to the thickness measurement of feature (A). If multiple convex portions and / or multiple concave portions are included in the reference range SR10 in all nine STEM observation images acquired at the nine measurement positions of the optical sheet to be evaluated, the optical sheet is determined to have feature (D). The nine measurement positions are the same as the nine measurement positions for measuring the rate of change.

[0131] From the viewpoint of making interference fringes less noticeable, the surface of the first functional layer opposite to the substrate in a cross-section along the first direction may contain two or more protrusions, three or more protrusions, four or more protrusions, or five or more protrusions within the reference range SR10. Furthermore, by setting a lower limit on the number of protrusions located within the reference range SR10, the adhesion between the first functional layer and the second functional layer under high temperature and high humidity conditions can be improved.

[0132] If there are too many protrusions within the reference range SR10, the height of each protrusion may decrease. From the viewpoint of making interference fringes less noticeable, the surface of the first functional layer opposite the substrate in the cross-section along the first direction may contain 12 or fewer protrusions, 10 or fewer protrusions, 8 or fewer protrusions, 7 or fewer protrusions, or 6 or fewer protrusions within the reference range SR10. Furthermore, by setting an upper limit on the number of protrusions located within the reference range SR10 in combination with feature (B), the adhesion between the first functional layer and the second functional layer under high temperature and high humidity conditions can be improved.

[0133] The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 12 protrusions, 3 to 12 protrusions, 4 to 12 protrusions, or 5 to 12 protrusions within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 10 protrusions, 3 to 10 protrusions, 4 to 10 protrusions, or 5 to 10 protrusions within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 8 protrusions, 3 to 8 protrusions, 4 to 8 protrusions, or 5 to 8 protrusions within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 7 protrusions, 3 to 7 protrusions, 4 to 7 protrusions, or 5 to 7 protrusions within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 6 protrusions, 3 to 6 protrusions, 4 to 6 protrusions, or 5 to 6 protrusions within the reference range SR10.

[0134] The number of protrusions 33X within the reference range SR10 is determined based on a STEM observation image of the cross-section of the optical sheet along the first direction, similar to the thickness measurement in feature (A). The number of protrusions is measured from STEM observation images acquired at nine measurement positions of the optical sheet to be evaluated. The arithmetic mean of the number of protrusions of the nine positions is taken as the number of protrusions of the optical sheet to be evaluated. The nine measurement positions are the same as the nine measurement positions used to measure the rate of change.

[0135] From the viewpoint of making interference fringes less noticeable, the surface of the first functional layer opposite the substrate in the cross-section along the first direction may contain two or more recesses, three or more recesses, four or more recesses, or five or more recesses within the reference range SR10. Furthermore, by setting a lower limit on the number of recesses located within the reference range SR10, the adhesion between the first functional layer and the second functional layer under high temperature and high humidity conditions can be improved.

[0136] If there are too many recesses within the reference range SR10, the depth of each recess will decrease. From the viewpoint of making interference fringes less noticeable, the surface of the first functional layer opposite the substrate in the cross-section along the first direction may contain 12 or fewer recesses, 10 or fewer recesses, 8 or fewer recesses, 7 or fewer recesses, or 6 or fewer recesses within the reference range SR10. Furthermore, by setting an upper limit on the number of recesses located within the reference range SR10 in combination with feature (B), the adhesion between the first functional layer and the second functional layer under high temperature and high humidity conditions can be improved.

[0137] The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 12 recesses, 3 to 12 recesses, 4 to 12 recesses, or 5 to 12 recesses within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 10 recesses, 3 to 10 recesses, 4 to 10 recesses, or 5 to 10 recesses within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 8 recesses, 3 to 8 recesses, 4 to 8 recesses, or 5 to 8 recesses within the reference range SR10. The surface of the first functional layer opposite the substrate in a cross-section along the first direction may contain 2 to 7 recesses, 3 to 7 recesses, 4 to 7 recesses, or 5 to 7 recesses within the reference range SR10. The surface of the cross-section of the first functional layer opposite to the substrate in the first direction may contain two to six recesses, three to six recesses, four to six recesses, or five to six recesses within the reference range SR10.

[0138] The number of recesses 33Y within the reference range SR10 is determined based on the STEM observation image of the cross-section of the optical sheet along the first direction, as described in feature (A). The number of recesses is measured from nine binarized images at nine measurement positions of the optical sheet to be evaluated. The arithmetic mean of the number of recesses for the nine positions is taken as the number of protrusions on the optical sheet to be evaluated. The nine measurement positions are the same as the nine measurement positions used to measure the rate of change.

[0139] <<Maximum Height Difference>> In addition to features (A) and (B), the optical sheet may also include the following feature (E): (E): The maximum height difference in the first direction, within a reference range, on the side of the first functional layer opposite to the substrate in a cross-section along the first direction, is 25 nm or more and 100 nm or less.

[0140] In feature (E), the "cross-section along the first direction" refers to the cross-section along the lamination direction shown in Figures 1 to 2B. As shown in Figures 1 to 2B, the "surface opposite the substrate of the first functional layer" in feature (E) is the first surface 31. The reference range SR10 is determined, as explained in feature (B), such that the length between the two ends of the first surface 31 located within the reference range is 1.3 μm, with two significant figures.

[0141] The maximum height difference in the first direction, as defined by feature (E), is measured from a STEM observation image of the cross-section of the optical sheet along the first direction, similar to the thickness in feature (A). The maximum height difference is the distance along the first direction D1 between the highest and lowest points within the reference range SR10.

[0142] The highest point is located on the first surface within the reference range SR10, furthest to the first side in the first direction D1. The highest point is also furthest from the substrate in the first direction D1 on the first surface within the reference range SR10. The lowest point is located on the first surface within the reference range SR10, furthest to the second side in the first direction D1. The lowest point is also closest to the substrate in the first direction D1 on the first surface within the reference range SR10.

[0143] The above calculation of the maximum height difference is performed based on nine STEM observation images acquired at nine measurement positions on the optical sheet to be evaluated. The arithmetic mean of the nine calculated maximum height differences is taken as the maximum height difference of the optical sheet to be evaluated. The nine measurement positions are the same as the nine measurement positions used to measure the rate of change.

[0144] The maximum height difference serves as an indicator of the height difference in the first direction D1 for the first surface 31 of the first functional layer 30. Feature (E) sets a lower limit on the maximum height difference. Therefore, within the reference range, the optical path length of light reflected from the first surface 31 (second interface BS2) of the first functional layer 30 changes. Increasing the maximum height difference increases the amount of change in optical path length within the reference range SR10. The reference range SR10 is a minute range where the distance between the two ends of the first surface 31 located within the reference range is 1.3 μm.

[0145] By varying the position of the first surface 31 in the first direction D1 within a minute reference range SR10, the brightness contrast of interference fringes associated with reflected light of a specific wavelength on the first surface 31 can be reduced. In other words, the brightness contrast can be reduced for light of each wavelength in the visible light range. As interference fringes of various wavelengths with reduced brightness contrast overlap, the interference fringes observed on the optical sheet can be made less conspicuous.

[0146] Feature (E) is that by setting a lower limit on the maximum height difference, the adhesion between the first and second functional layers under high temperature and high humidity conditions can be improved.

[0147] From the above viewpoint, a lower limit may be set for the maximum height difference in the first direction within the reference range on the surface of the first functional layer opposite to the substrate in a cross-section along the first direction. The maximum height difference may be 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, or 45 nm or more.

[0148] Feature (E) sets an upper limit on the maximum height difference. The maximum height difference is an indicator of the height difference with respect to the first direction D1 within a predetermined length range along a direction perpendicular to the first direction D1 for the first surface 31 of the first functional layer 30. When the maximum height difference is large, the light transmitted through the optical sheet may be diffused on the first surface 31 of the first functional layer 30. By setting an upper limit on the maximum height difference in feature (E), light diffusion on the first surface 31 (second interface BS2) can be suppressed.

[0149] Feature (E) is that by setting an upper limit on the maximum height difference, the adhesion between the first and second functional layers under high temperature and high humidity conditions can be appropriately improved.

[0150] From the above perspective, the maximum height difference may be 100 nm or less, 90 nm or less, 80 nm or less, 75 nm or less, or 69 nm or less.

[0151] The maximum height difference may be 25 nm to 100 nm, 30 nm to 100 nm, 35 nm to 100 nm, 40 nm to 100 nm, or 45 nm to 100 nm. The maximum height difference may be 25 nm to 90 nm, 30 nm to 90 nm, 35 nm to 90 nm, 40 nm to 90 nm, or 45 nm to 90 nm. The maximum height difference may be 25 nm to 80 nm, 30 nm to 80 nm, 35 nm to 80 nm, 40 nm to 80 nm, or 45 nm to 80 nm. The maximum height difference may be 25 nm to 75 nm, 30 nm to 75 nm, 35 nm to 75 nm, 40 nm to 75 nm, or 45 nm to 75 nm. The maximum height difference may be 25 nm to 69 nm, 30 nm to 69 nm, 35 nm to 69 nm, 40 nm to 69 nm, or 45 nm to 69 nm.

[0152] <<Refractive Index>> The refractive index of the first functional layer may be a refractive index between the refractive index of the substrate and the refractive index of the second functional layer. For example, the refractive index of the first functional layer may be smaller than the refractive index of the substrate and larger than the refractive index of the second functional layer. The refractive index of the first functional layer may be larger than the refractive index of the substrate and smaller than the refractive index of the second functional layer.

[0153] By adjusting the refractive index of the first functional layer 30 in this way, interference fringes caused by the interference of reflected light on both main surfaces 31 and 32 of the first functional layer 30 having the thickness defined in feature (A) above can be effectively made less noticeable.

[0154] The refractive index of the first functional layer can be adjusted by selecting the refractive index of the material used in the first functional layer. As shown in Figure 3, the first functional layer 30 may contain a binder component 36 and particles 37. The refractive index of the particles may differ from that of the binder component. According to the example shown in Figure 3, the refractive index of the first functional layer 30 can be adjusted by selecting the material for the binder component 36, the material for the particles 37, and the amount of particles 37 included.

[0155] The particles 37 may contain one or more organic and inorganic particles. Examples of particles 37 include antimony pentoxide, zinc oxide, titanium oxide, cerium oxide, tin-doped indium oxide, antimony-doped tin oxide, yttrium oxide, zirconium oxide, and aluminum oxide. These particles tend to increase the refractive index of the first functional layer. Examples of particles 37 include hollow silica, solid silica, and magnesium fluoride particles. These particles tend to decrease the refractive index of the first functional layer.

[0156] The refractive index of the material constituting the resin layer is measured in accordance with Method A of JIS K7142:2014. The light ray used for measurement is the D line (wavelength 589 nm). An Abbe refractometer is used for the measurement. The "Abbe Refractometer D-M2" manufactured by Atago Co., Ltd. can be used as the Abbe refractometer.

[0157] If the first functional layer 30 contains particles 37, the particles 37 may be located only within the first functional layer 30 of the two functional layers 30. The second functional layer 40 does not have to contain particles 37. The particles 37 do not have to migrate from the first functional layer 30 to the second functional layer 40. The particles 37 do not have to penetrate from the first functional layer 30 to the second functional layer 40.

[0158] In this example, the refractive index of the first functional layer 30 and the refractive index of the second functional layer 40 can be precisely adjusted. The refractive index difference at the interface BS2 between the first functional layer 30 and the second functional layer 40 can be precisely adjusted. As a result, the combined effect of features (A) and (B) is effectively achieved, and the interference fringes observed on the optical sheet can be made even less noticeable.

[0159] Furthermore, whether or not the particles 37 contained in the first functional layer 30 are present in the second functional layer 40 is determined by energy-dispersive X-ray spectroscopy, also known as EDX. According to EDX, the elements and their quantities can be identified for the particles observed in the first and second functional layers in the cross-sectional observation image of the optical sheet acquired by a scanning transmission electron microscope. Based on the detected elements and their quantities, it can be determined whether or not the particles 37 contained in the first functional layer 30 are present in the second functional layer 40.

[0160] <<Total Light Transmittance>> The total light transmittance of an optical sheet may be 50% or more, 70% or more, 80% or more, 90% or more, or 95% or more. There is no particular upper limit to the total light transmittance of an optical sheet. The total light transmittance of an optical sheet may be 100% or less, or less than 100%. The total light transmittance of an optical sheet may be 50% or more and 100% or less, 70% or more and 100% or less, 80% or more and 100% or less, 90% or more and 100% or less, or 95% or more and 100% or less. The total light transmittance of an optical sheet may be 50% or more and less than 100%, 70% or more and less than 100%, 80% or more and less than 100%, 90% or more and less than 100%, or 95% or more and less than 100%.

[0161] Before measuring the total light transmittance of the sample, the light source lamp is lit for 15 minutes to stabilize its output. The angle of incidence on the sample when measuring the total light transmittance is 0°. The incident surface when measuring the total light transmittance of the optical sheet is the second surface of the optical sheet. The overall spectral characteristics are a combination of the photopic standard luminous efficiency V(λ) (IEC 60050-845) and the CIE standard optics D65. The test environment when measuring the total light transmittance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before the start of the test. Other measurement conditions when measuring the total light transmittance follow JIS K7361-1:1997.

[0162] The total light transmittance shall be the arithmetic mean of the five measured values. The five measured values ​​shall be taken at five different measurement locations on the optical sheet being evaluated. The five measurement locations shall be at least 10 mm apart from each other.

[0163] <<Transmission Haze>> The transmission haze of the optical sheet may be 1.5% or less, 1.2% or less, 1.0% or less, 0.8% or less, or 0.5% or less. The transmission haze of the optical sheet may be 0% or more, or greater than 0. The transmission haze of the optical sheet may be 0% or more, or greater than 0. The transmission haze of the optical sheet may be 0% or more and 1.5% or less, 0% or more and 1.2% or less, 0% or more and 1.0% or less, 0% or more and 0.8% or less, or 0% or more and 0.5% or less. The transmission haze of the optical sheet may be greater than 0 and 1.5% or less, greater than 0 and 1.2% or less, greater than 0 and 1.0% or less, greater than 0 and 0.8% or less, or greater than 0 and 0.5% or less.

[0164] Before measuring the transmitted haze of the sample, the light source lamp is lit for 15 minutes to stabilize its output. The angle of incidence to the sample when measuring the total light transmittance is 0°. The incident surface when measuring the transmitted haze of the optical sheet is the second surface of the optical sheet. The overall spectral characteristics are a combination of the photopic standard luminous efficiency V(λ) (IEC 60050-845) and the CIE standard optics D65. The test environment when measuring the transmitted 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 the start of the test. Other measurement conditions when measuring the transmitted haze follow JIS K7136:2000.

[0165] The transmitted haze is the arithmetic mean of five measurements. The five measurements are taken at five different measurement locations on the optical sheet being evaluated. The five measurement locations are located at least 10 mm apart from each other.

[0166] <<Layers included in the optical sheet>> The layers that may be included in the optical sheet will be described in more detail below. The optical sheet 10 shown in Figure 1 includes a base material 20, a first functional layer 30, and a second functional layer 40, extending from the second surface 12 to the first surface 11. The optical sheet 10 shown in Figure 2A includes a base material 20, a first functional layer 30, a second functional layer 40, and a third functional layer 51, extending from the second surface 12 to the first surface 11. The optical sheet 10 shown in Figure 2B includes a base material 20, a first functional layer 30, a second functional layer 40, a fourth functional layer 52, and a third functional layer 51, extending from the second surface 12 to the first surface 11.

[0167] In the example shown in Figure 2A, the third functional layer 51 is exemplified as a low refractive index layer having a refractive index lower than that of the adjacent layer. The third functional layer 51 as a low refractive index layer can exhibit a low reflection function or reflection suppression function that suppresses reflection on the first surface 11.

[0168] In the example shown in Figure 2B, the third functional layer 51 is an example of a low refractive index layer having a refractive index lower than that of the adjacent layer. In the example shown in Figure 2B, the fourth functional layer 52 is an example of a high refractive index layer having a refractive index higher than that of the two adjacent layers. The third functional layer 51 and the fourth functional layer 52 can exhibit a low reflection function or reflection suppression function that suppresses reflection on the first surface 11.

[0169] The optical sheet 10 may have a different layer configuration than those shown in Figures 1 to 2B. The optical sheet 10 may include one or more antistatic layers and antifouling layers.

[0170] <Substrate> The substrate supports the first functional layer and the second functional layer. The substrate also supports other layers included in the optical sheet. As shown in Figures 1 to 2B, the substrate 20 may constitute the second surface 12 of the optical sheet 10. The second surface 12 may be a flat surface. The second surface 12 may be a surface perpendicular to the lamination direction of the layers included in the optical sheet 10.

[0171] The substrate may be transparent. Transparency means that the total light transmittance is 50% or more. The total light transmittance of the substrate may be 70% or more, 80% or more, or 90% or more. The total light transmittance of the substrate may be 100% or less, or less than 100%.

[0172] The base material is not particularly limited; it may be a resin or glass. Resin is preferred because it is lightweight and easy to manufacture.

[0173] The resin used for the base material may be an olefin resin such as polyethylene or polypropylene. The resin used for the base material may be a vinyl resin such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, or ethylene-vinyl alcohol copolymer. The resin used for the base material may be an acrylic resin such as poly(meth)acrylate or poly(meth)acrylate ethyl. The resin used for the base material may be a styrene resin such as polystyrene, a polyamide resin such as nylon 6 or nylon 66, or a cellulose resin such as triacetylcellulose. Further examples of resins used for the base material include resins such as polycarbonate, polyimide resins, and cycloolefin resins obtained from cycloolefins such as norbornene and dicyclopentadiene.

[0174] The resin used as the base material may be polyester such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate. The base material may also contain polyester. Polyester means a copolymer of at least a diol component and a dicarboxylic acid component.

[0175] (Biomass-derived resin) The base material may contain a resin derived from biomass materials. The base material may contain a polyester derived from biomass materials. A polyester derived from biomass materials is also called biomass polyester. The base material may contain polyethylene terephthalate derived from biomass materials. The base material may contain a polyester derived from fossil fuels. The base material may contain both a polyester derived from biomass materials and a polyester derived from fossil fuels.

[0176] Biomass polyester refers to polyester in which at least a portion of the raw material monomers are derived from biomass materials such as plants. Examples of such plants include sugarcane and corn. Fossil fuel-derived polyester refers to polyester in which all of the raw material monomers are derived from fossil fuels such as petroleum.

[0177] Biomass polyesters with a higher biomass content contribute more to reducing environmental impact. However, the biomass content does not need to be 100%.

[0178] Polyester may have diol units derived from a diol component and dicarboxylic acid units derived from a dicarboxylic acid component. In biomass polyester, at least a portion of the diol component may be derived from biomass material. In biomass polyester, at least a portion of the dicarboxylic acid component may be derived from biomass material. In biomass polyester, at least a portion of the diol component and at least a portion of the dicarboxylic acid component may both be derived from biomass material.

[0179] Biomass polyester may contain diol units derived from ethylene glycol derived from biomass materials and dicarboxylic acid units derived from dicarboxylic acid components derived from fossil fuels. Biomass polyester may contain diol units derived from ethylene glycol derived from fossil fuels and dicarboxylic acid units derived from dicarboxylic acid components derived from biomass materials. Biomass polyester may contain diol units derived from ethylene glycol derived from biomass materials and dicarboxylic acid units derived from dicarboxylic acid components derived from biomass materials.

[0180] Biomass-derived ethylene glycol can be obtained from ethanol produced using biomass materials as a raw material (hereinafter also referred to as "biomass ethanol"). For example, biomass-derived ethylene glycol can be obtained by methods such as producing ethylene glycol from biomass ethanol via ethylene oxide. Commercially available biomass-derived ethylene glycol may also be used as a base material.

[0181] The diol component is not limited to ethylene glycol. The diol component is not particularly limited. The diol component may be diethylene glycol, triethylene glycol, propanediol, butanediol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, and styrene glycol, etc. The diol component may consist of only one of the above-mentioned types, or it may consist of two or more of the above-mentioned types.

[0182] Examples of dicarboxylic acid components include dicarboxylic acids and derivatives of dicarboxylic acids. Examples of dicarboxylic acids include aromatic dicarboxylic acids and aliphatic dicarboxylic acids. Examples of dicarboxylic acid derivatives include alkyl esters (monoalkyl esters or dialkyl esters) and acid anhydrides of dicarboxylic acids.

[0183] Examples of biomass-derived dicarboxylic acids include aliphatic dicarboxylic acids obtained from plant raw materials such as recycled oil. Examples of biomass-derived aliphatic dicarboxylic acids include succinic acid, glutaric acid, adipic acid, sebacic acid, and dimer acid. The dicarboxylic acid component may consist of only one of the above-mentioned types, or it may consist of two or more of the above-mentioned types.

[0184] (Biomass content) The biomass content of the base material is 10% or more, may be 12% or more, may be 15% or more, or may be 18% or more. Such base materials can reduce the environmental burden. The biomass content of the base material may be 100%, may be greater than 0% and 98% or less, may be greater than 0% and 90% or less, may be greater than 0% and 80% or less, may be greater than 0% and 70% or less, may be greater than 0% and 60% or less, may be greater than 0% and 50% or less, may be greater than 0% and 40% or less, or greater than 0% and 30% or less.

[0185] "Biomass content" is also called biobased carbon content. "Biomass content" is a value obtained by correcting pMC (percent Modern Carbon), measured according to ASTM D6866-22 Method B, with δ¹³C. Specifically, first, the sample is burned to produce carbon dioxide (CO₂).２ ) is generated and purified in a vacuum line. Next, the purified carbon dioxide is reduced with hydrogen using iron as a catalyst to produce graphite. Subsequently, the 14C count and carbon isotope ratio (14C / 12C, 13C / 12C) of the obtained graphite are measured by accelerator mass spectrometry (AMS). A dedicated 14C-AMS instrument (manufactured by NEC Corporation) can be used as the measuring instrument. Oxalic acid (HO₂O₃) provided by the National Institute of Standards (NIST) is used as a standard sample. ｘ II) is used. Measurements of this standard sample and background sample are also performed simultaneously. From the obtained carbon isotope ratio, the relative ratio (pMC) of the sample's 14C / 12C to the standard sample is calculated. δ¹³C is the value obtained by measuring the 13C / 12C of the sample carbon and expressing the deviation from the reference sample as a percent deviation.

[0186] The bio-based carbon content is obtained by multiplying pMC by a correction factor, given the excess of 14C in the atmosphere due to nuclear testing. Since the excess 14C in the atmosphere is continuously decreasing, the correction factor shall conform to ASTM D6866-22.

[0187] Materials derived from fossil fuels do not contain radioactive carbon (¹⁴C) with a mass number of 14, whereas materials derived from plants do. Therefore, the two can be distinguished by their biomass content, which is based on the amount of ¹⁴C they contain. Thus, materials derived from fossil fuels are known to have a biomass content of approximately 0%. Biomass content is an index that represents the mixing ratio of materials derived from fossil fuels and materials derived from plants.

[0188] To measure the biomass content of an entire optical sheet, a sample should be prepared from the optical sheet. To measure the biomass content of individual layers within an optical sheet, the target layer should be separated from the optical sheet and a sample prepared from that layer.

[0189] The polyester content in the base material may be more than 50% by mass, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, or 95% or more by mass. The polyester content in the base material may be 100% or less, or less than 100%.

[0190] The substrate may contain only one type of resin as described above, or it may contain two or more types of resin as described above. The substrate may contain only a single layer, or it may contain multiple layers. The substrate may be stretched. The stretching may be uniaxial stretching or biaxial stretching.

[0191] The thickness of the resin substrate is not particularly limited. From the viewpoint of handling, the thickness of the resin substrate may be 10 μm or more, 20 μm or more, or 50 μm or more. The thickness of the resin substrate may be 500 μm or less, 400 μm or less, or 300 μm or less. The thickness of the glass substrate may be 500 μm or more. The thickness of the glass substrate may be 5 mm or less.

[0192] In the application of optical sheets to foldable applications, the substrate 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 is used laminated with glass, the thickness of the resin substrate may be 40 μm or more and 100 μm or less from the viewpoint of preventing glass from shattering.

[0193] The base material may contain additives. Examples of additives include ultraviolet absorbers, light stabilizers, antioxidants, heat stabilizers, antistatic agents, slippery particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, flame retardants, gelling inhibitors, and surfactants. The base material may contain only one of the above-mentioned additives, or it may contain two or more of the above-mentioned additives.

[0194] <First Functional Layer> The first functional layer has a thickness of 20 nm to 250 nm along the first direction D1. The first functional layer includes a first surface and a second surface. The first surface of the first functional layer may be an uneven surface in order to realize the above-described features (B) to (D). The thickness of the first functional layer is set as described above.

[0195] The first functional layer may also be an easy-adhesion layer to improve the adhesion of the second functional layer to the substrate. The first functional layer as an easy-adhesion layer can improve the adhesion of the second functional layer to the substrate. The first functional layer as an easy-adhesion layer is located between the second functional layer and the substrate and is in contact with both the second functional layer and the substrate. The first functional layer as an easy-adhesion layer is bonded to both the second functional layer and the substrate. The first functional layer as an easy-adhesion layer can improve the adhesion of each layer contained in the optical sheet, especially the adhesion of the second functional layer.

[0196] As described above, the first functional layer 30 may contain a binder component 36 and particles 37 (see Figure 3). The first functional layer may further contain additives.

[0197] The binder component may function as a binder for film formation. The binder component may also be an element that holds particles. The second layer may maintain its film shape by holding particles contained in the second layer with the binder component. The binder component may also be the base material of the first functional layer. The first functional layer may not contain particles and be composed mainly of the binder component. The first functional layer may not contain particles and be composed of the binder component and additives. The first functional layer may not contain particles and be composed only of the binder component. The binder component may contain a resin. The resin contained in the binder component may be a natural resin or a synthetic resin.

[0198] Examples of resins included in the first functional layer as an easy-adhesion layer include thermoplastic resins such as polyester, polyurethane, and (meth)acrylic resin, as well as thermosetting resins.

[0199] The polyurethane component may contribute to improved adhesion. The polyester component may contribute to both improved adhesion and improved strength of the first functional layer. The resin contained in the first functional layer may contain both the polyester component and the polyurethane component. The amount of polyester component may be greater than the amount of polyurethane component. By increasing the amount of polyester component compared to the polyurethane component, phase separation can be suppressed. From the viewpoint of suppressing phase separation, the mass ratio of the polyester component and the polyurethane component (polyester component: polyurethane component) may be 95:5 to 60:40, or 90:10 to 60:40.

[0200] The resin included in the first functional layer may be a resin derived from biomass materials, a resin derived from fossil fuels, or a mixed resin of a resin derived from biomass materials and a resin derived from fossil fuels. For example, the thermoplastic resins such as polyester, polyurethane, and (meth)acrylic resins mentioned above, and thermosetting resins, may each be a resin derived from biomass materials, a resin derived from fossil fuels, or a mixed resin of a resin derived from biomass materials and a resin derived from fossil fuels.

[0201] The first functional layer containing a resin derived from biomass material has a high environmental impact. The first functional layer containing a resin derived from biomass material has high affinity with a substrate (polyester film) containing biomass polyester. The first functional layer containing a resin derived from biomass material can change shape in accordance with the shape changes of the substrate containing biomass polyester. An optical sheet containing a substrate containing a resin derived from biomass material and a first functional layer containing a resin derived from biomass material has excellent processability. The first functional layer may contain biomass polyester or biomass polyethylene terephthalate.

[0202] The biomass content of the first functional layer may be 10% or more, 12% or more, 15% or more, or 18% or more. The biomass content of the first functional layer may be 98% or less, 90% or less, 80% or less, 70% or less, 60% or less, or 50% or less.

[0203] The biomass content of the first functional layer may be 10% to 98%, 12% to 98%, 15% to 98%, or 18% to 98%. The biomass content of the first functional layer may be 10% to 90%, 12% to 90%, 15% to 90%, or 18% to 90%. The biomass content of the first functional layer may be 10% to 80%, 12% to 80%, 15% to 80%, or 18% to 80%. The biomass content of the first functional layer may be 10% to 70%, 12% to 70%, 15% to 70%, or 18% to 70%. The biomass content of the first functional layer may be 10% to 60%, 12% to 60%, 15% to 60%, or 18% to 60%. The biomass content of the first functional layer may be 10% to 50%, 12% to 50%, 15% to 50%, or 18% to 50%.

[0204] The first functional layer may contain only one type of resin as described above, or it may contain two or more types of resins as described above.

[0205] The content ratio of the above resin in the first functional layer may be more than 50% by mass and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, or 95% by mass or more and 100% by mass or less.

[0206] The number-average molecular weight of the resin contained in the first functional layer may be 10,000 or more, or 15,000 or more. The number-average molecular weight of the resin contained in the first functional layer may be 100,000 or less, or 60,000 or less. The number-average molecular weight of the resin contained in the first functional layer may be 10,000 or more and 100,000 or less, or 15,000 or more and 100,000 or less. The number-average molecular weight of the resin contained in the first functional layer may be 10,000 or more and 60,000 or less, or 15,000 or more and 60,000 or less. Such resins can suppress cohesive breakdown of the first functional layer. The number-average molecular weight refers to the polystyrene equivalent value measured by gel permeation chromatography in accordance with JIS K7252-1:2016.

[0207] The glass transition temperature of the resin contained in the first functional layer may be 30°C or higher, 50°C or higher, or 70°C or higher. The glass transition temperature of the resin contained in the first functional layer may be 120°C or lower, 110°C or lower, or 90°C or lower. The glass transition temperature of the resin contained in the first functional layer may be 30°C or higher and 120°C or lower, 50°C or higher and 120°C or lower, or 70°C or higher and 120°C or lower. The glass transition temperature of the resin contained in the first functional layer may be 30°C or higher and 110°C or lower, 50°C or higher and 110°C or lower, or 70°C or higher and 110°C or lower. The glass transition temperature of the resin contained in the first functional layer may be 30°C or higher and 90°C or lower, 50°C or higher and 90°C or lower, or 70°C or higher and 90°C or lower. The glass transition temperature is the intermediate glass transition temperature obtained by differential scanning calorimetry (DSC) in accordance with JIS K7121:2012.

[0208] If the glass transition temperature of the resin constituting the first functional layer is 30°C or higher, it is possible to suppress the flow of the first functional layer and the generation of internal stress due to heat during the manufacturing process. Examples of heat during the manufacturing process include the heat generated during the drying process of the coating liquid for the functional layer and the heat generated when bonding the optical sheet to a polarizer or the like. If the glass transition temperature of the resin contained in the first functional layer is 120°C or lower, it is possible to reduce thermal stress caused by the difference in thermal behavior between the first functional layer and the substrate due to heat during the manufacturing process. By reducing thermal stress, it is possible to suppress the occurrence of cracks and other damage in the first functional layer due to thermal stress.

[0209] The first functional layer may contain additives. Examples of additives include refractive index modifiers, dyes, pigments, leveling agents, ultraviolet absorbers, antioxidants, and light stabilizers. The first functional layer may contain crosslinking agents to adjust hardness or viscosity. The first functional layer may contain one or more of these components. Examples of crosslinking agents include xylylene diisocyanate crosslinking agents, isophorone diisocyanate crosslinking agents, hexamethylene diisocyanate crosslinking agents, and ionizing radiation-curable polyfunctional monomers.

[0210] The first functional layer may be manufactured by a wet process. The first functional layer may also be manufactured using a coating solution for the first functional layer. The first functional layer may also be manufactured by drying or curing the coating film of the coating solution for the first functional layer. The coating solution for the first functional layer may contain a resin composition, particles, additives, crosslinking agents, etc.

[0211] The coating liquid for the first functional layer may be applied to the substrate by an in-line coating method during the formation of the resin film as the substrate. The coating liquid for the first functional layer may also be applied to the substrate by an off-line coating method after the formation of the resin film as the substrate. The coating liquid for the first functional layer may also be applied to the substrate by a general-purpose coating method. The first functional layer can be formed by drying the coating film of the coating liquid for the first functional layer applied to the substrate.

[0212] The coating solution for the first functional layer may contain a solvent. The solvent can dissolve the components constituting the first functional layer. The solvent can disperse the components constituting the first functional layer. The solvent can adjust the viscosity of the coating solution for the first functional layer. Examples of solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ethers such as dioxane and tetrahydrofuran; aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated carbons such as dichloromethane and dichloroethane; esters such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; alcohols such as isopropyl alcohol, butanol, and cyclohexanol; cellosolves such as methyl cellosolve and ethyl cellosolve; glycol ethers such as propylene glycol monomethyl ether acetate; cellosolve acetates; sulfoxides such as dimethyl sulfoxide; and amides such as dimethylformamide and methylacetamide.

[0213] <Second Functional Layer> The second functional layer is a layer expected to perform some function. The thickness of the second functional layer is set appropriately according to the effects and benefits expected from the second functional layer. The thickness of the second functional layer may be 1 μm or more, 2 μm or more, 3 μm or more, or 5 μm or more. The thickness of the second functional layer may be 20 μm or less, or 10 μm or less. The thickness of the second functional layer may be 1 μm or more and 20 μm or less, 2 μm or more and 20 μm or less, 3 μm or more and 20 μm or less, or 5 μm or more and 20 μm or less. The thickness of the second functional layer may be 1 μm or more and 10 μm or less, 2 μm or more and 10 μm or less, 3 μm or more and 10 μm or less, or 5 μm or more and 10 μm or less. The second functional layer may also be a hard coat layer. An example where the second functional layer is a hard coat layer will be described below.

[0214] The second functional layer, which serves as a hard coat layer, may contain a cured resin product. The cured resin product is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may also be an ionizing radiation-curable resin composition. The second functional layer may contain a cured product of a thermosetting resin composition and a cured product of an ionizing radiation-curable resin composition. The cured product of the curable resin composition imparts high strength and hardness to the light diffusion layer, improving the scratch resistance of the optical sheet. Ionizing radiation-curable resin compositions are particularly useful from the viewpoint of improving scratch resistance.

[0215] A thermosetting resin composition contains a thermosetting compound. The thermosetting compound is a resin that hardens upon heating. The thermosetting compound is not particularly limited. Examples of thermosetting compounds include phenolic resins, urea resins, diallyl phthalate resins, melamine resins, guanamine resins, unsaturated polyester resins, polyurethane resins, epoxy resins, amino alkyd resins, melamine-urea cocondensation resins, silicon resins, and the like. The thermosetting resin composition may contain one or more of these thermosetting compounds.

[0216] Ionizing radiation-curable resin compositions contain compounds having ionizing radiation-curable functional groups. Hereinafter, compounds having ionizing radiation-curable functional groups will also be referred to as "ionizing radiation-curable compounds." Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups.

[0217] Ionizing radiation-curable compounds may contain two or more ionizing radiation-curable functional groups. Ionizing radiation-curable compounds may also be compounds having ethylenically unsaturated bonding groups. Ionizing radiation-curable compounds may also be (meth)acrylate compounds having (meth)acryloyl groups. Ionizing radiation-curable compounds may also be siloxane compounds containing siloxane bonds.

[0218] (Meth)acrylate compounds containing four or more ethylenically unsaturated bonding groups are called "polyfunctional (meth)acrylate compounds." (Meth)acrylate compounds containing two to three ethylenically unsaturated bonding groups are called "low-functional (meth)acrylate compounds."

[0219] The (meth)acrylate compound may be a monomer or an oligomer. An ionizing radiation-curable compound containing a low-functionality (meth)acrylate compound can suppress uneven shrinkage during curing and smooth the surface of the second functional layer.

[0220] The proportion of low-functional (meth)acrylate compounds 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 100% by mass. From the viewpoint of suppressing uneven shrinkage during curing and smoothing the uneven surface shape of the second functional layer, the low-functional (meth)acrylate compound may be a (meth)acrylate compound containing two ethylenically unsaturated bonding groups. When the ionizing radiation-curable compound contains a large amount of polyfunctional (meth)acrylate compounds, the surface of the second functional layer can be smoothed by appropriately adjusting the type of solvent and drying conditions, as described later.

[0221] Examples of (meth)acrylate compounds include difunctional (meth)acrylate compounds such as isocyanuric acid di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, polyalkylene glycol di(meth)acrylate such as 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 with four or more functions include pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol tetra(meth)acrylate. The (meth)acrylate compound may be modified as described later.

[0222] 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 the reaction of a polyhydric alcohol and an organic diisocyanate with hydroxy (meth)acrylate. Epoxy (meth)acrylate may also be a (meth)acrylate obtained by reacting a trifunctional or higher aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc. with (meth)acrylic acid. Epoxy (meth)acrylate may also be a (meth)acrylate obtained by reacting a bifunctional or higher aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc. with a polybasic acid and (meth)acrylic acid. Epoxy (meth)acrylate may also be a (meth)acrylate obtained by reacting a bifunctional or higher aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc. with phenols and (meth)acrylic acid.

[0223] The second functional layer may contain additives. Examples of additives include refractive index modifiers, dyes, pigments, leveling agents, UV absorbers, antioxidants, and light stabilizers. When the second functional layer contains additives, the resin of the second functional layer functions as a binder component. The binder component holds the additives. The binder component may also function as a binder for film formation.

[0224] The second functional layer may be manufactured by a wet process. The second functional layer may also be manufactured using a coating solution for the second functional layer. The second functional layer may also be manufactured by drying and curing the coating film of the coating solution for the second functional layer. The coating solution for the second functional layer contains a curable resin composition. The coating solution for the second functional layer may also contain additives such as antistatic agents, antioxidants, surfactants, dispersants, and crosslinking agents.

[0225] When using UV-curable compounds, the coating solution for the second functional layer may contain additives such as photopolymerization initiators and photopolymerization accelerators. Examples of photopolymerization initiators include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler ketone, benzoin, benzyldimethylketal, benzoylbenzoate, α-acyloxime ester, α-aminoalkylphenone, thioxanthones, etc. Photopolymerization accelerators reduce polymerization inhibition by air during curing and accelerate the curing speed. Examples of photopolymerization accelerators include one or more selected from p-dimethylaminobenzoate isoamyl ester, p-dimethylaminobenzoate ethyl ester, etc.

[0226] The coating solution for the second functional layer may contain a silicone-based leveling agent (silicone compound) as an additive. By including a silicone-based leveling agent in the coating solution for the second functional layer, the protrusion of particles from the surface of the light-diffusing layer can be suppressed, and the first surface can be smoothed. This improves the slipperiness of the first surface and enhances its scratch resistance. The silicone-based leveling agent can impart excellent slipperiness and excellent antifouling properties (fingerprint wiping ability, large contact angle with pure water and hexadecane) to the first surface formed by the light-diffusing layer.

[0227] By using a silicone-based leveling agent instead of a fluorine-based leveling agent, the formation of PFAS as an impurity can be suppressed. PFAS, as an artificial organofluorine compound, is a cause for concern due to its bioaccumulation potential. Suppressing the formation of PFAS can contribute to reducing environmental impact.

[0228] The coating solution for the second functional layer may contain a solvent. The solvent can dissolve the components constituting the second functional layer. The solvent can disperse the components constituting the second functional layer. The solvent can adjust the viscosity of the coating solution for the second functional layer.

[0229] Examples of solvents include ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, heptane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), halogenated carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, propyl acetate, butyl acetate, etc.), alcohols (isopropyl alcohol, isopropanol, butanol, cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), glycol ethers (propylene glycol monomethyl ether acetate, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), amides (dimethylformamide, dimethylacetamide, etc.), etc. The coating solution for the second functional layer may contain one or more solvents.

[0230] The inventors of this case have confirmed that when the second functional layer is fabricated on the first functional layer by a wet method, features (B) to (D) can be imparted to the first functional layer. Specifically, features (B) to (D) can be imparted to the first functional layer by dissolving the first surface 31 of the first functional layer with the solvent contained in the coating solution for the second functional layer. Features (B) to (D) can be imparted to the first functional layer by the type and amount of solvent contained in the coating solution for the second functional layer, the composition of the coating solution for the second functional layer, and the drying conditions of the coating solution for the second functional layer, in combination with the first functional layer.

[0231] After careful consideration, the following conclusion was reached. However, this embodiment is not bound by this conclusion.

[0232] The solvent contained in the coating solution for the second functional layer can penetrate the amorphous region of the resin material of the first functional layer, such as polyethylene terephthalate. The solvent that penetrates the resin material of the first functional layer widens the distance between polymer chains, causing the first functional layer to swell. The swollen surface of the first functional layer becomes softer, and irregularities may occur on the first surface of the first functional layer. Therefore, by appropriately combining the resin of the first functional layer with the solvent of the coating solution for the second functional layer, and by appropriately setting the drying conditions of the coating film of the second functional layer according to the combination of the resin of the first functional layer and the solvent of the coating solution for the second functional layer, the rate of change, the average inclination angle, the number of protrusions, the number of recesses, and the maximum height difference can be adjusted to the range described above.

[0233] As an example, by using a glycol ether-based solvent in the coating solution for the second functional layer, the rate of change, average inclination angle, number of protrusions, number of recesses, and maximum height difference can be increased. An alcohol-based solvent may also be used. By increasing the amount of solvent blended, the rate of change, average inclination angle, number of protrusions, number of recesses, and maximum height difference can be increased. By using a combination of resin for the first functional layer and solvent for the coating solution for the second functional layer that has high compatibility, it is easier to increase the rate of change, average inclination angle, number of protrusions, number of recesses, and maximum height difference.

[0234] The coating film formed by applying the coating solution for the second functional layer onto the first functional layer may be dried in two stages. The drying conditions for the two-stage drying may include one or more of the following conditions: (Condition 1) The wind speed in the first stage is slower than the wind speed in the second stage. (Condition 2) The drying temperature in the first stage is lower than the drying temperature in the second stage.

[0235] By drying in two stages, the initial drying of the coating film for the second functional layer can be slowed, promoting the penetration of the solvent into the first functional layer. By appropriately combining the resin of the first functional layer and the solvent of the coating film for the second functional layer, and by drying the coating film of the second functional layer on the first functional layer in two stages under the drying conditions of (Condition 1) and / or (Condition 2) described above, it is easier to increase the rate of change, average inclination angle, number of protrusions, number of recesses, and maximum height difference.

[0236] However, the method for producing the first functional layer having the above features (B) to (D) is not particularly limited. The first functional layer having features (B) to (D) may be produced by roughening the surface of the first functional layer before producing the second functional layer. Roughening may be done by mechanical processing such as polishing, or by chemical processing such as etching. In these examples, if the first functional layer is an easy-adhesion layer, the optical sheet 10 including the substrate and the first functional layer can be used as a substrate 15 with an easy-adhesion layer.

[0237] As shown in Figure 6, the substrate 15 with the easy-adhesion layer includes a first surface 16 and a second surface 17 facing the first direction D1. The first surface 16 of the substrate with the easy-adhesion layer constitutes the first surface 11 of the optical sheet 10, which includes only the substrate 20 and the first functional layer 30. The second surface 17 of the substrate 15 with the easy-adhesion layer constitutes the second surface 12 of the optical sheet 10, which includes only the substrate 20 and the first functional layer 30. The optical sheet 10 may also be manufactured by creating a second functional layer 40 on the substrate 15 with the easy-adhesion layer.

[0238] Furthermore, the second functional layer is not limited to the hard coat layer described above. The second functional layer may be an anti-glare layer. The second functional layer may include a first surface as an uneven surface. The second functional layer as an anti-glare layer may include binder components and particles. The second functional layer may include protrusions on the first surface caused by particles.

[0239] The binder component is an element that holds particles. The binder component may also function as a binder for coating film formation. The second functional layer may maintain its film shape by holding the particles contained in the second functional layer with the binder component. The binder component may also contain a resin. The resin contained in the binder component may be the same as the resin contained in the second functional layer as a hard coat layer.

[0240] The particles may be organic particles. The particles may also be inorganic particles. The second functional layer, which acts as an anti-glare layer, may contain both organic and inorganic particles. Examples of materials for organic particles include polymethyl methacrylate, polyacrylic-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone, fluororesin, and polyester resin. Examples of materials for inorganic particles include silica, alumina, zirconia, and titania.

[0241] <Third Functional Layer> The optical sheet 10 shown in Figure 2A further includes a third functional layer 51. The third functional layer 51 constitutes the first surface 11. The illustrated third functional layer 51 is a low refractive index layer. The low refractive index layer has a refractive index lower than that of the adjacent layer. As a low refractive index layer, the third functional layer 51 is a low reflection layer or reflection suppression layer that has the function of suppressing reflection.

[0242] In terms of specific configuration, the third functional layer may include a binder resin and particles. The particles may be low refractive index particles. The refractive index of the particles may be lower than that of the binder resin. The refractive index of the third functional layer is reduced by including low refractive index particles. In the example shown in Figure 2A, the refractive index of the third functional layer is lower than that of the second functional layer.

[0243] The third functional layer can exert a function of suppressing the reflection of incident light due to its refractive index and thickness. The anti-reflection function of the third functional layer is based on the interference of light reflected from both sides of the third functional layer. From the viewpoint of making this reflection suppression function effective, the refractive index of the third functional layer may be between the refractive indices of two regions adjacent to the third functional layer from both sides. The thickness (nm) of the third functional layer may be about 1 / 4 of the wavelength λ (nm) of the light whose reflection is to be suppressed.

[0244] From the viewpoint of reflection suppression function, the refractive index and average thickness of the third functional layer can be set as follows: The refractive index of the functional layer may be 1.10 or higher, 1.20 or higher, 1.26 or higher, 1.28 or higher, or 1.30 or higher. The refractive index of the functional layer may be 1.48 or lower, 1.45 or lower, 1.40 or lower, 1.38 or lower, or 1.35 or lower. The refractive index of the functional layer may be 1.10 or higher and 1.48 or lower, 1.20 or higher and 1.48 or lower, 1.26 or higher and 1.48 or lower, 1.28 or higher and 1.48 or lower, or 1.30 or higher and 1.48 or lower. The refractive index of the functional layer may be 1.10 or more and 1.45 or less, 1.20 or more and 1.45 or less, 1.26 or more and 1.45 or less, 1.28 or more and 1.45 or less, or 1.30 or more and 1.45 or less. The refractive index of the functional layer may be 1.10 or more and 1.40 or less, 1.20 or more and 1.40 or less, 1.26 or more and 1.40 or less, 1.28 or more and 1.40 or less, or 1.30 or more and 1.40 or less. The refractive index of the functional layer may be 1.10 or more and 1.38 or less, 1.20 or more and 1.38 or less, 1.26 or more and 1.38 or less, 1.28 or more and 1.38 or less, or 1.30 or more and 1.38 or less. The refractive index of the functional layer may be 1.10 to 1.35, 1.20 to 1.35, 1.26 to 1.35, 1.28 to 1.35, or 1.30 to 1.35. The refractive index used for the components constituting the optical sheet is the refractive index for a wavelength of 589.3 nm.

[0245] The thickness of the third functional layer may be 80 nm or more, 85 nm or more, or 90 nm or more. The thickness of the functional layer may be 150 nm or less, 110 nm or less, or 105 nm or less. The thickness of the third functional layer may be 80 nm or more and 150 nm or less, 85 nm or more and 150 nm or less, or 90 nm or more and 150 nm or less. The thickness of the third functional layer may be 80 nm or more and 110 nm or less, 85 nm or more and 110 nm or less, or 90 nm or more and 110 nm or less. The thickness of the third functional layer may be 80 nm or more and 105 nm or less, 85 nm or more and 105 nm or less, or 90 nm or more and 105 nm or less.

[0246] The binder resin included in the third functional layer may be the same as the resin included in the second functional layer. The binder resin included in the third functional layer may also include a cured product of a curable resin composition. The curable resin composition may include one or more thermosetting resin compositions and ionizing radiation curable resin compositions.

[0247] The particles contained in the third functional layer may be the same as those contained in the first functional layer described above. The third functional layer may contain one or more organic particles and inorganic particles. The third functional layer may contain one or more hollow silica, solid silica, and magnesium fluoride particles as inorganic particles.

[0248] Hollow silica particles have an outer shell layer made of silica. In hollow silica particles, the inside of the particle surrounded by the outer shell layer is hollow. Air may be contained within the hollow space. Due to the presence of the internal hollow space, hollow silica particles have a refractive index lower than that of silica. The refractive index of hollow silica particles decreases as the volume of the internal hollow space increases. Hollow silica particles reduce the refractive index of the entire third functional layer.

[0249] The third functional layer may be manufactured by a wet process, similar to the first and second functional layers. The third functional layer may also be manufactured using a coating solution for the third functional layer. The third functional layer may also be manufactured by drying and curing the coating film of the coating solution for the third functional layer. The coating solution for the third functional layer may contain additives that can be applied to the coating solution for the first functional layer or the coating solution for the second functional layer.

[0250] <Fourth Functional Layer> The optical sheet 10 shown in Figure 2B includes a third functional layer 51 and a fourth functional layer 52. In the example shown in Figure 2B, the third functional layer 51 can be configured in the same way as the third functional layer 51 described above included in the optical sheet 10 shown in Figure 2A. That is, the third functional layer 51 constitutes the first surface 11. The third functional layer 51 is a low refractive index layer. The low refractive index layer has a refractive index lower than that of the adjacent fourth functional layer 52.

[0251] The fourth functional layer is located between the third and second functional layers in the first direction D1, which is the stacking direction. The fourth functional layer has a refractive index that is between the refractive index of the second functional layer and the refractive index of the third functional layer. The third functional layer, as a low refractive index layer, and the fourth functional layer, as a high refractive index layer, function as a low-reflection layer or reflection-suppressing layer, suppressing reflection on the first surface.

[0252] Specifically, the fourth functional layer may contain a binder resin and particles. The particles may be high refractive index particles. The refractive index of the particles may be higher than that of the binder resin. The refractive index of the fourth functional layer is increased by containing high refractive index particles. The refractive index of the fourth functional layer is higher than that of the second functional layer.

[0253] From the viewpoint of reflection suppression function, the refractive index of the fourth functional layer and the average thickness of the functional layer may be set as follows: The refractive index of the fourth functional layer may be 1.55 or more and 1.85 or less, 1.56 or more and 1.85 or less, 1.55 or more and 1.75 or less, or 1.56 or more and 1.75 or less. The thickness of the fourth functional layer may be 50 nm or more and 200 nm or less, or 50 nm or more and 180 nm or less.

[0254] The binder resin included in the fourth functional layer may be the same as the resin included in the second functional layer. The binder resin included in the fourth functional layer may also include a cured product of a curable resin composition. The curable resin composition may include one or more thermosetting resin compositions and ionizing radiation curable resin compositions.

[0255] The particles included in the fourth functional layer may be the same as those included in the first functional layer. The fourth functional layer may contain one or more organic and inorganic particles. Examples of particles included in the fourth functional layer include antimony pentoxide, zinc oxide, titanium oxide, cerium oxide, tin-doped indium oxide, antimony-doped tin oxide, yttrium oxide, and zirconium oxide.

[0256] The fourth functional layer may be manufactured by a wet process, similar to the first and second functional layers. The fourth functional layer may also be manufactured using a coating solution for the fourth functional layer. The fourth functional layer may also be manufactured by drying and curing the coating film of the coating solution for the fourth functional layer. The coating solution for the fourth functional layer may contain additives that can be applied to the coating solution for the first functional layer or the coating solution for the second functional layer.

[0257] <<<Sheet Articles>>> According to the manufacturing method of optical sheets 10 by the wet method, as shown in Figure 7, a long sheet article 5 containing a large number of optical sheets 10 can be manufactured. Optical sheets 10 can be obtained by cutting the long sheet article 5 to a predetermined size. In this example, optical sheets 10 having various dimensions can be obtained from the long sheet article 5 according to the needs. Therefore, optical sheets 10 having various dimensions can be provided in a timely manner. As shown in Figure 7, the handling of the sheet article 5 can be improved by handling the sheet article 5 as a roll 7 wound on a winding core with the winding axis RA as the center.

[0258] <<<Polarizing Plate>>> The optical sheet 10 according to this embodiment may be applied to a polarizing plate 60. In the example shown in Figure 8, 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 cover the polarizer 62 from both sides, with the polarizer 62 sandwiched in between. At least one of the first protective sheet 61 and the second protective sheet 63 may include the optical sheet 10. The first protective sheet 61 located on the first side (observer side) in the first direction D1 may include the optical sheet 10. If only one of the first protective sheet 61 and the second protective sheet 63 includes the optical sheet 10, the other protective sheet may be a resin film.

[0259] As described above, the optical sheet 10 makes interference fringes caused by the reflection of ambient light less noticeable. Therefore, the area behind the polarizing plate 60, including the optical sheet 10, can be clearly observed.

[0260] The polarizer 62 transmits one linearly polarized component and blocks the other linearly polarized component. The polarizer 62 may also be an absorbing polarizer that absorbs the other linearly polarized component. The polarizer 62 may also be a reflective polarizer that reflects the other linearly polarized component. The polarizer 62 may also be a sheet-type polarizer made of a polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, or ethylene-vinyl acetate copolymer saponified film dyed with iodine or the like and stretched. The polarizer 62 may also be a wire grid type polarizer consisting of many metal wires arranged in parallel. The polarizer 62 may also be a coated polarizer coated with lyotropic liquid crystal or a dichroic guest-host material, or a multilayer thin-film type polarizer.

[0261] <<<Image Display Device>>> The optical sheet 10 according to this embodiment may be applied to a display device 65. In the example shown in Figure 9, the display device 65 includes a display element 66 and an optical sheet 10. The display element 66 has an image forming surface 66a for displaying an image. The optical sheet 10 is superimposed on the display element 66 such that its second surface 12 faces the image forming surface 66a. The optical sheet 10 may be bonded to the display element 66 via a bonding layer containing an adhesive or tack. The display element 66 is not particularly limited. Examples of the display element 66 include liquid crystal display elements, EL display elements, plasma display elements, electronic paper elements, and the like.

[0262] The observer observes the image displayed by the display element 66 through the optical sheet 10. As described above, the optical sheet 10 can make interference fringes caused by the reflection of ambient light less noticeable. Therefore, it can effectively suppress the degradation of the image displayed by the display device 65. The observer can observe a high-quality image.

[0263] <<<Panel>>> The optical sheet 10 according to this embodiment is applicable to various uses. Figure 10 shows a panel 70 to which the optical sheet 10 is applied. The panel 70 includes the optical sheet 10 and the article to be bonded 71 to which the optical sheet 10 is bonded. The panel 70 can obtain effects corresponding to the second functional layer 40 of the optical sheet 10, such as improved mechanical properties. The optical sheet 10 is placed on top of the article to be bonded 71 with its second surface 12 facing the article to be bonded 71. The optical sheet 10 may be bonded to the article to be bonded 71 via a bonding layer containing an adhesive or tack. Examples of the article to be bonded 71 include instrument panels, clocks, showcases, display windows, and windows.

[0264] This disclosure will be further described in detail by examples. This disclosure is not limited to the following examples.

[0265] <<<1. Preparation of Optical Sheets>>> Optical sheets according to Examples 1 to 10 and Comparative Examples 1 to 2 were prepared. As shown in Figure 1, the optical sheets according to Examples 1 to 6 and Comparative Examples 1 and 2 contained a substrate, a first functional layer as an easy-adhesion layer, and a second functional layer as a hard coat layer, in this order from the second surface to the first surface. As shown in Figure 2A, the optical sheets according to Examples 7 and 8 contained a substrate, a first functional layer, a second functional layer, and a third functional layer as a low refractive index layer, in this order from the second surface to the first surface. As shown in Figure 2B, the optical sheets according to Examples 9 and 10 contained a substrate, a first functional layer, a second functional layer, a fourth functional layer as a high refractive index layer, and a third functional layer, in this order from the second surface to the first surface.

[0266] <<Example 1>> A polyethylene terephthalate film with a thickness of 80 μm was prepared as a base material. Terephthalic acid and ethylene glycol were reacted in a reaction vessel at 210°C to obtain polyethylene terephthalate (PET). The obtained PET was fed into a uniaxially stretched extruder. In the extruder, the PET was melted at 300°C and extruded from the T-die, and cast onto a casting drum with a controlled surface temperature. A casting film was obtained. The obtained film was heated at 120°C. Furthermore, the film was stretched in the flow direction (MD) while heating the film from both sides with a radiation heater. The stretching ratio was 1.5 times. After stretching, the film was cooled. A uniaxially stretched polyethylene terephthalate film with a thickness of 80 μm was obtained.

[0267] The coating liquid 1 for the first functional layer (coating liquid 1 for the easy-adhesion layer) according to the following formulation was applied to the substrate to form a coating film of the coating liquid 1 for the first functional layer. The coating film of the coating liquid 1 for the first functional layer was dried at 80°C for 30 seconds (drying air velocity of 5 m / s) to evaporate the solvent. By drying the coating film, the first functional layer was formed on the substrate. As a result, a substrate with an easy-adhesion layer according to Example 1, including the substrate and the first functional layer, was obtained.

[0268] <Coating solution 1 for the first functional layer (coating solution 1 for the easily adhering layer)> ・Water 36.71 parts by mass ・Isopropyl alcohol 37.42 parts by mass ・Zirconia sol 1.22 parts by mass ・Polyester aqueous dispersion Aw 20.06 parts by mass (solid content concentration 25% by mass) ・Crosslinking agent P solution 3.14 parts by mass (solid content concentration 40% by mass) ・Surfactant 0.25 parts by mass (fluorine-based, solid content concentration 10% by mass)

[0269] The polyester aqueous dispersion Aw contained in the coating solution 1 for the first functional layer was prepared using a copolymerized polyester resin (A) as follows.

[0270] <Polymerization of Copolymer Polyester Resin (A) for Coating Layers> Composition (A), having the following composition, was polymerized using an autoclave. The autoclave was equipped with a stirrer, a thermometer, and a partial reflux condenser. Composition A was transesterified at a temperature of 160°C to 220°C for 4 hours, and then 60.7 parts by mass of sebaciate were added and the transesterification reaction was continued. Next, the temperature of the reaction system was raised to 270°C, the reaction system was gradually depressurized, and the reaction was continued under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain copolymer polyester resin (A). The obtained copolymer polyester resin (A) was pale yellow and transparent.

[0271] (Composition A) 350.0 parts by mass of 2,6-Naphthalenedicarboxylate, 30 parts by mass of dimethyl terephthalate, 30 parts by mass of dimethyl-5-sodium sulfoisophthalate, 200.0 parts by mass of ethylene glycol, 120 parts by mass of hexanediol, and 1 part by mass of tetra-n-butyl titanate.

[0272] <Preparation of Polyester Resin Aqueous Dispersion (Aw)> A reactor equipped with a stirrer, thermometer, and reflux device was prepared. 25 parts by mass of copolymerized polyester resin (A) and 20 parts by mass of ethylene glycol-n-butyl ether were placed in the reactor and heated and stirred at 110°C to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water were added to the polyester solution while stirring. After the addition, the polyester solution was cooled to room temperature while stirring to obtain a milky white polyester resin aqueous dispersion Aw with a solid content of 25.0% by mass.

[0273] The crosslinking agent P solution contained in the coating solution 1 for the first functional layer was synthesized as follows.

[0274] In a flask, 100 parts by mass of a polyisocyanate compound (NCO concentration 23.1%) and 20 parts by mass of N-methylpyrrolidone were mixed with 40.00 parts by mass of 3,5-dimethylpyrazole, and the mixture was maintained at 70°C for 1 hour under a nitrogen atmosphere. The flask was equipped with a stirrer, thermometer, and reflux condenser. The polyisocyanate compound was obtained from 1,6-hexamethylene diisocyanate by an existing method. The polyisocyanate compound had an isocyanurate structure.

[0275] Subsequently, 12.50 parts by mass of dimethylolpropionic acid was added dropwise to the flask. Next, the infrared spectrum of the reaction solution was measured, and it was confirmed that the absorption of the isocyanate group had disappeared. After confirmation, 10 parts by mass of N,N-dimethylethanolamine was added to the flask. The contents of the flask were stirred for 1 hour, and then an appropriate amount of water was added to obtain a block isocyanote aqueous dispersion with a solid content of 40% by mass. The obtained block isocyanote aqueous dispersion was used as the crosslinking agent P solution.

[0276] Next, the second functional layer coating solution 1 (hard coat layer coating solution 1) according to the following formulation was applied to the first functional layer to form a coating film of the second functional layer coating solution 1. The coating film of the second functional layer coating solution 1 was dried at 50°C for 30 seconds (drying air velocity 5 m / s), and then dried at 70°C for 1 minute (drying air velocity 5 m / s) to evaporate the solvent. In other words, in Example 1, the drying of the coating film of the second functional layer coating solution 1 was performed in two stages.

[0277] Subsequently, the coating film of the second functional layer coating liquid 1 is subjected to an integrated light intensity of 100 mJ / cm². ２ The material was irradiated with ultraviolet light. By curing the coating film, a resin layer (hard coat layer) with a dry thickness of 10 μm was created on the first functional layer. As a result, an optical sheet according to Example 1, including the substrate, the first functional layer, and the second functional layer, was obtained.

[0278] <Coating Solution 1 for the Second Functional Layer (Coating Solution 1 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 113 parts by mass・n-butanol 127 parts by mass

[0279] <<Example 2>> Example 2 differs from Example 1 in that the coating liquid 1 for the second functional layer is changed to the coating liquid 2 for the second functional layer described below. Otherwise, the optical sheet of Example 2 was obtained using the same materials and methods as in Example 1.

[0280] <Coating Solution 2 for the Second Functional Layer (Coating Solution 2 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 113 parts by mass ・Propylene glycol monomethyl ether (PGME) 127 parts by mass

[0281] <<Example 3>> Example 3 differs from Example 1 in that the coating liquid 1 for the second functional layer is changed to the coating liquid 3 for the second functional layer described below. Otherwise, the optical sheet of Example 3 was obtained using the same materials and methods as in Example 1.

[0282] <Coating Solution 3 for the Second Functional Layer (Coating Solution 3 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 240 parts by mass

[0283] <<Example 4>> Example 4 differs from Example 1 in that the coating liquid 1 for the second functional layer was changed to the coating liquid 4 for the second functional layer described below, and the drying conditions were changed. Otherwise, the optical sheet of Example 4 was obtained using the same materials and methods as in Example 1. In Example 4, the coating film of the coating liquid 4 for the second functional layer was dried at 55°C for 30 seconds (drying air velocity 5 m / s), and then the solvent was evaporated by drying at 70°C for 1 minute (drying air velocity 5 m / s).

[0284] <Coating Solution 4 for the Second Functional Layer (Coating Solution 4 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 113 parts by mass ・Butyl acetate 127 parts by mass

[0285] <<Example 5>> Example 5 differs from Example 1 in that the coating liquid 1 for the second functional layer is changed to the coating liquid 5 for the second functional layer described below. Otherwise, the optical sheet of Example 5 was obtained using the same materials and methods as in Example 1.

[0286] <Coating Solution 5 for the Second Functional Layer (Coating Solution 5 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 113 parts by mass・Methyl ethyl ketone (MEK) 127 parts by mass

[0287] <<Example 6>> Example 6 differs from Example 2 in that the substrate is changed to a cycloolefin polymer substrate with a thickness of 25 μm, the coating solution 1 for the first functional layer is changed to the coating solution 2 for the first functional layer (coating solution 2 for the easily adhering layer) prepared as described below, and the conditions for preparing the first functional layer are changed. Otherwise, the optical sheet of Example 6 was obtained using the same materials and methods as in Example 2.

[0288] <Preparation of Cycloolefin Polymer Substrate> Pellets of cycloolefin polymer (product name ZEONOR®, manufactured by Nippon Zeon Co., Ltd.) were dried at 100°C for 5 hours. The pellets were fed into an extruder. The pellets were melted in the extruder and extruded in a sheet form from a T-die onto a casting drum through a polymer pipe and polymer filter, and then cooled. A cycloolefin polymer film with a thickness of 25 μm was obtained.

[0289] <Method for preparing the coating solution 2 for the first functional layer (coating solution 2 for the easy-adhesion layer)> The coating solution 2 for the first functional layer (coating solution 2 for the easy-adhesion layer) was prepared by diluting the polyolefin resin (modified polyolefin) "Unistol P-802 (trade name)" (solid content 22%, manufactured by Mitsui Chemicals, Inc.) with a solvent until the solid content concentration (paint concentration) was 2.1%. The solvent was a mixture of butyl acetate and toluene in a mass ratio of 90:10.

[0290] The above-mentioned coating liquid 2 for the first functional layer was applied to one side of the 25 μm thick cycloolefin polymer film obtained above using a bar coater (#4). The coating film of the coating liquid 2 for the first functional layer was dried at 100°C for 60 seconds (drying air velocity of 5 m / sec) to evaporate the solvent. By drying the coating film, the first functional layer was formed on the substrate. Thus, a substrate with an easy-adhesion layer according to Example 6, including the substrate and the first functional layer, was obtained.

[0291] Subsequently, a second functional layer was fabricated on the first functional layer in the same manner as in Example 1. Thus, an optical sheet according to Example 6, comprising the substrate, the first functional layer, and the second functional layer, was obtained.

[0292] <<Example 7>> Example 7 differs from Example 2 in that a third functional layer (low refractive index layer) is formed on the second functional layer of Example 2, and otherwise the optical sheet of Example 7 is obtained using the same materials and methods as in Example 2. That is, a laminate including a substrate, a first functional layer, and a second functional layer is formed in the same manner as the optical sheet of Example 2, and further, a third functional layer as a low refractive index layer is formed on the second functional layer.

[0293] Specifically, the optical sheet of Example 7 was prepared as follows. The coating solution 1 for the third functional layer (coating solution 1 for the low refractive index layer) with the following formulation was applied to the second functional layer. Then, the coating film of the coating solution 1 for the third functional layer was dried at 70°C for 1 minute to evaporate the solvent. Next, the coating film of the coating solution 1 for the third functional layer was exposed to an integrated light intensity of 100 mJ / cm². ２ Ultraviolet light was irradiated onto the material. As a result, a third functional layer (low refractive index layer) with a dry thickness of 95 nm was formed. Thus, an optical sheet of Example 7 was obtained, comprising the substrate, the first functional layer, the second functional layer, and the third functional layer in that order.

[0294] <Coating solution 1 for the third functional layer (coating solution 1 for the low refractive index layer)> ・Hollow silica particles 1000 parts by mass (Particles with an average primary particle diameter of 65 nm, surface-treated with a silane coupling agent having methacryloyl groups, solid content concentration 20% by mass) ・Solid silica particles 72 parts by mass (Particles with an average primary particle diameter of 80 nm, surface-treated with a silane coupling agent having methacryloyl groups, solid content concentration 42% by mass) ・Alumina particles 100 parts by mass (Particles with an average primary particle diameter of 15.0 nm, surface-treated with a silane coupling agent having methacryloyl groups, solid content concentration 30% by mass) ・UV-curable acrylate-containing composition 100 parts by mass (Manufactured by Toagosei Co., Ltd., product name "Aronics M-305", solid content concentration 100% by mass) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content concentration 100% by mass - Leveling agent 36 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) - Methyl isobutyl ketone (MIBK) 13,728 parts by mass - Propylene glycol monomethyl ether acetate (PGMEA) 1,627 parts by mass

[0295] <<Example 8>> Example 8 differs from Example 7 in that the substrate is changed to a cycloolefin polymer substrate with a thickness of 25 μm, the coating liquid 1 for the first functional layer is changed to the coating liquid 2 for the first functional layer (coating liquid 2 for the easily adhering layer) prepared as described above, and the conditions for manufacturing the first functional layer are changed. Otherwise, the optical sheet of Example 8 was obtained using the same materials and methods as in Example 7.

[0296] In Example 8, the same cycloolefin polymer substrate as in Example 6 was used. In Example 8, the first functional layer was prepared on the substrate under the same conditions as in Example 6, using the coating solution 2 for the first functional layer used in Example 6.

[0297] <<Example 9>> Example 9 differs from Example 7 in that a fourth functional layer (high refractive index layer) is formed between the second and third functional layers of Example 7, and otherwise the optical sheet of Example 9 is obtained using the same materials and methods as in Example 7. That is, a laminate including a substrate, a first functional layer, and a second functional layer is formed in the same manner as the optical sheet of Example 7, then a fourth functional layer as a high refractive index layer is formed on the second functional layer, and then a third functional layer is formed using the same materials and methods as in Example 7.

[0298] The fourth functional layer (high refractive index layer) is formed using the coating solution for the fourth functional layer as follows. Specifically, the coating solution 1 for the fourth functional layer (coating solution 1 for the high refractive index layer) with the following formulation was applied onto the second functional layer. Then, the coating film of the coating solution 1 for the fourth functional layer was dried at 70°C for 1 minute to evaporate the solvent. Next, the coating film of the coating solution 1 for the fourth functional layer was exposed to an integrated light intensity of 100 mJ / cm². ２ Ultraviolet light was irradiated onto the material. As a result, a fourth functional layer (high refractive index layer) with a dry thickness of 150 nm was formed. Subsequently, a third functional layer (low refractive index layer) was formed on the fourth functional layer using the same material and method as in Example 7 to obtain the optical sheet of Example 9.

[0299] <Coating Solution 1 for the 4th Functional Layer (Coating Solution 1 for the High Refractive Index Layer)> ・High refractive index particles 429 parts by mass (manufactured by Nippon Shokubai Co., Ltd., trade name "Zircostar", solid content 70%) ・UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., trade name "MAC-SQ SI20", solid content concentration 100% by mass) ・Photopolymerization initiator 16 parts by mass (manufactured by IGM Resins, trade name "Omnirad 127", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., trade name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 5779 parts by mass ・Propylene glycol monomethyl ether (PGME) 5914 parts by mass

[0300] <<Example 10>> Example 10 differs from Example 9 in that the substrate is changed to a cycloolefin polymer substrate with a thickness of 25 μm, the coating liquid 1 for the first functional layer is changed to the coating liquid 2 for the first functional layer (coating liquid 2 for the easily adhering layer) prepared as described above, and the conditions for manufacturing the first functional layer are changed. Otherwise, the optical sheet of Example 10 is obtained using the same materials and methods as in Example 9.

[0301] In Example 10, the same cycloolefin polymer substrate as in Example 6 was used. In Example 10, the first functional layer was fabricated on the substrate under the same conditions as in Example 6, using the coating solution 2 for the first functional layer used in Example 6.

[0302] <<Comparative Example 1>> Comparative Example 1 differs from Example 1 in that the coating liquid 1 for the second functional layer was changed to the coating liquid 7 for the second functional layer described below, and the drying conditions were changed. Otherwise, the optical sheet of Comparative Example 1 was obtained using the same materials and methods as in Example 1. In Comparative Example 1, the solvent was evaporated by drying the coating film of the coating liquid 7 for the second functional layer at 70°C for 1 minute (drying air velocity of 5 m / s). In Comparative Example 1, the drying of the coating film of the coating liquid 7 for the second functional layer was performed in one stage, not two stage drying.

[0303] <Coating Solution 7 for the Second Functional Layer (Coating Solution 7 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 113 parts by mass・Methyl acetate 127 parts by mass

[0304] <<Comparative Example 2>> Comparative Example 2 differs from Example 1 in that the coating liquid 1 for the second functional layer was changed to the coating liquid 8 for the second functional layer described below. Otherwise, the optical sheet of Comparative Example 2 was obtained using the same materials and methods as in Example 1. In Comparative Example 2, the drying of the coating film of the coating liquid 8 for the second functional layer was performed in two stages, as in Example 1. That is, in Comparative Example 2, the coating film of the coating liquid 8 for the second functional layer was dried at 50°C for 30 seconds (drying air velocity 5 m / s), and then dried at 70°C for 1 minute (drying air velocity 5 m / s) to evaporate the solvent.

[0305] <Coating Solution 8 for the Second Functional Layer (Coating Solution 8 for the Hard Coat Layer)> ・UV-curable acrylate-containing composition 100 parts by mass (manufactured by Nikka Fine Techno Co., Ltd., product name "DPHA", solid content concentration 100% by mass) ・UV-curable acrylate-containing composition 31 parts by mass (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "New Frontier R-1403MB", solid content concentration 80% by mass) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 184", solid content concentration 100% by mass) ・Silicone-based leveling agent 8 parts by mass (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "10-301", solid content concentration 5% by mass) ・Methyl isobutyl ketone (MIBK) 113 parts by mass ・Cyclohexanone 127 parts by mass

[0306] <<<2. Measurement and Evaluation>>> As described below, the optical sheets of the examples and comparative examples were measured and evaluated. The measurement environment for each measurement and evaluation was set to 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 measurement environment for 16 hours.

[0307] <<2-1. Thickness of the First Functional Layer>> Cut samples measuring 3 mm wide x 10 mm long were cut from the optical sheets of the Examples and Comparative Examples. Embedding samples were prepared from the cut samples of each example using the method described above. Section samples were cut from the embedding samples using a microtome. The thickness of the section samples was approximately 70 nm.

[0308] For embedding, a mixture of "Epofix" (product name from Storuas) and "Epofix Hardener" (product name from Storuas) in a ratio of 10:1.2 was used as the epoxy resin. For the embedding plate, a silicone embedding material from Dosaka EM Co., Ltd. was used.

[0309] A Leica Macro Systems EM UC7 ultramicrotome was used as the microtome. The cutting conditions using the diamond knife were set to SPEED: 1.40 mm / s and FEED: 70 nm.

[0310] Observation images of sectioned samples obtained using a scanning transmission electron microscope (STEM) were acquired. A Hitachi High-Technologies Corporation S4800 scanning transmission electron microscope was used. The observation conditions for the scanning transmission electron microscope were as follows: Detector: TE; Acceleration voltage: 30 kV; Emission current: 10 μA; Magnification: 100,000x; Condenser lens: 5.0; W.D.: 8.8 mm

[0311] The thickness (nm) of the first functional layer was measured using the observation image as described above. The measurement results are shown in the "Thickness" column of Table 1.

[0312] <<2-2. Rate of Change>> Nine cut samples were cut from the optical sheets relating to the examples and comparative examples using the method described above, and nine section samples were obtained from each cut sample. Observation images of the section samples obtained were acquired using a scanning transmission electron microscope (STEM). The conditions and equipment for acquiring the observation images were the same as those used for acquiring the observation images for measuring the thickness of the first functional layer.

[0313] As an example, Figure 3 is a cross-sectional view of the optical sheet according to Example 2. Figure 11 is a cross-sectional view of the optical sheet according to Comparative Example 1.

[0314] Binarized images were obtained from each of the nine STEM observation images using image analysis software, following the methods and conditions described above. Lengths LX and LY were measured from the binarized images using image analysis software, following the methods and conditions described above, and the rate of change was calculated from the measured values ​​of length LX and length LY. ImageJ (Version 1.54g) and Fiji were used as image analysis software. The rate of change for each case was obtained by calculating the arithmetic mean of the rates of change identified from each of the nine binarized images. The rate of change for each case is shown in the "Rate of Change" column of Table 1.

[0315] <<2-3. Average Inclination Angle>> The average inclination angle was measured from STEM observation images acquired to measure thickness, according to the method and conditions described above. The average inclination angle for each case was obtained by calculating the arithmetic mean of the average inclination angles identified from each of the nine STEM observation images. The average inclination angle (°) for each case is shown in the "Average Inclination Angle" column of Table 1.

[0316] <<2-4. Number of protrusions and recesses>> The number of protrusions and recesses located within the reference range SR10 was measured from STEM observation images acquired to measure thickness. The number of protrusions for each example was obtained by calculating the arithmetic mean of the number of protrusions identified from each of the nine observation images. The number of recesses for each example was obtained by calculating the arithmetic mean of the number of recesses identified from each of the nine observation images. The number of protrusions for each example is shown in the "Protrusions" column of Table 1. The number of recesses for each example is shown in the "Recesses" column of Table 1.

[0317] <<2-5. Maximum Height Difference>> The maximum height difference was measured from STEM observation images acquired to measure thickness, according to the methods and conditions described above. The maximum height difference for each example was obtained by calculating the arithmetic mean of the maximum height differences identified from each of the nine binarized images. The maximum height difference (nm) for each example is shown in the "Maximum Height Difference" column of Table 1.

[0318] <<2-6. Component Analysis>> For the optical sheets according to Examples 1 to 6, energy-dispersive X-ray spectroscopy (EDX) was used to confirm whether particles contained in the first functional layer were present in the second functional layer. For the component analysis using energy-dispersive X-ray spectroscopy, the energy-dispersive X-ray spectrometer attached to the scanning transmission electron microscope used for measuring the thickness of the first functional layer (see "2-1. Thickness of the First Functional Layer") was used. For all of the optical sheets according to Examples 1 to 6, it was confirmed that the zirconia particles in the first functional layer had not migrated to or penetrated into the second layer.

[0319] <<2-7. Total Light Transmittance>> A 5 ​​cm x 10 cm sample was cut from the optical sheet relating to the examples and comparative examples. The sample was visually inspected to ensure there were no abnormalities such as dust or scratches. The total light transmittance (%) of the optical sheet relating to each example was measured using the method described above. A haze meter "HM-150" manufactured by Murakami Color Technology Laboratory was used to measure the total light transmittance. The measurement results of the total light transmittance are shown in the "Tt" column of Table 1.

[0320] <<2-8. Transmitted Haze>> A 5 ​​cm x 10 cm sample was cut from the optical sheets of the examples and comparative examples. The samples were visually inspected to ensure there were no abnormalities such as dust or scratches. The transmitted haze (%) of the optical sheets of each example was measured using the method described above. A haze meter "HM-150" manufactured by Murakami Color Technology Laboratory was used to measure the transmitted haze. The measurement results of the transmitted haze are shown in the "Hz" column of Table 1.

[0321] <<2-9. Sensory Evaluation of Interference Fringes>> 10 cm x 10 cm samples were cut from the anti-glare sheets of the examples and comparative examples. A black board (10 cm x 10 cm) was attached to the second surface of the sample to be evaluated in each example via an optically transparent adhesive sheet. The optically transparent adhesive sheet was "Panaclean PD-S1" manufactured by Panac Co., Ltd. The black board was "Comoglass 502K (black)" manufactured by Kuraray Co., Ltd. Visual inspection was performed to confirm that there were no abnormalities such as dust or scratches on the first surface of the evaluation sample prepared by attaching the black board.

[0322] The evaluation sample was placed on a horizontal platform 70 cm high with its first surface facing upwards. In a brightly lit room, the evaluators observed the evaluation sample from various directions. The lighting device was positioned 2 m vertically above the horizontal platform. The light-emitting part of the lighting device was an Hf32 type straight tube tri-wavelength daylight white fluorescent lamp. The illuminance on the first surface of the evaluation sample was set to between 500 lux and 1000 lux. The evaluators' eye level was approximately 160 cm from the floor. The evaluators were 20 healthy individuals in their 30s with visual acuity of 0.7 or better. The observation results of the first surface of the evaluation sample in an area covered with black boards were evaluated according to the following evaluation criteria. The evaluation results are shown in the "Interference Fringe" column of Table 1. Evaluations "AA" and "A" indicate that the product was of a quality that would be considered good in normal product inspection. Evaluations "B" and "C" indicate that the product was of a quality that would be considered poor in normal product inspection.

[0323] <Evaluation Criteria> AA: Three or fewer evaluators confirmed the presence of interference fringes. A: Four to six evaluators confirmed the presence of interference fringes. B: Seven to ten evaluators confirmed the presence of interference fringes. C: Eleven or more evaluators confirmed the presence of interference fringes.

[0324] Comparative Example 2 exhibited high haze compared to the other examples, which limited its use as an optical sheet. However, because the interference fringes were less visible due to the high haze, Comparative Example 2 received a better evaluation of the interference fringes than Comparative Example 1. Examples 1 to 10 were able to suppress haze while making the interference fringes less noticeable.

[0325] <<2-10. Adhesion Evaluation>> Samples were cut from the optical sheets according to Examples 1-6 and Comparative Examples 1 and 2. For each sample, the adhesion between the first functional layer and the second functional layer after the moist heat test was evaluated.

[0326] For the moist heat test, each sample was left in an environment with a temperature of 80°C and a humidity of 90% RH for 100 hours.

[0327] After the moist heat test, eleven straight vertical cuts and eleven straight horizontal cuts were made on the surface of each sample composed of the second functional layer (first surface 11 in Figure 1) using a cutter blade. The eleven vertical cuts and eleven horizontal cuts divided the second functional layer of the optical sheet into a grid-like area of ​​100 squares. The vertical spacing of the eleven vertical cuts was 1 mm. The vertical spacing of the eleven horizontal cuts was also 1 mm. The cutter blade used was NT Corporation product number "BA-52P".

[0328] Next, as a cellophane adhesive tape conforming to JIS Z1522:2009, Cellotape (registered trademark) (manufactured by Nichiban, model number No. 405-1P, 24 mm width, adhesive strength: 3.93 N / 10 mm, tensile strength: 41.6 N / 10 mm, elongation: 23%, all physical properties are catalog values) was prepared. Under test conditions of a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%, 25 cm of cellophane adhesive tape was unwound from the roll. To create a handle on the unwound cellophane adhesive tape, 5 cm from both ends was folded back and attached to the next 5 cm. As a result, the cellophane adhesive tape included a handle consisting of a 5 cm folded portion, a 5 cm portion with the adhesive surface exposed on one side, and a handle consisting of a 5 cm folded portion.

[0329] Next, the 5 cm adhesive portion of the cellophane tape was attached to the surface of each sample, which was composed of a grid-like second functional layer. Then, a 2 kg pressure roller was passed back and forth twice to press the 5 cm adhesive portion of the cellophane tape onto the first surface of each sample. After that, the cellophane tape was pressed again onto the first surface of the sample with a finger to ensure that no air was trapped between the adhesive tape and the first surface of the sample.

[0330] A peel test was conducted by peeling cellophane adhesive tape from the first surface of the sample. In the peel test, the cellophane adhesive tape was peeled from the first surface of the sample at a speed of 5 cm / s. The peel test was performed only once for each sample. During peeling, the handle portion on one side of the cellophane adhesive tape was pulled in a direction as perpendicular as possible to the first surface. In other words, the peel test was conducted as a 90° peel test. The peeling direction on the first surface of the cellophane adhesive tape was either the longitudinal or transverse direction in which the cuts extended.

[0331] The peel test was conducted in accordance with the cross-cut method specified in JIS K5600-5-6:1999, under conditions other than those mentioned above.

[0332] After the peel test, the surface of the cellophane adhesive tape and the sample was observed to confirm whether the second functional layer had peeled off from the first functional layer. Each sample was evaluated according to the following evaluation criteria. The evaluation results are shown in the "Adhesion" column of Table 1. "A" indicates a level of quality that would be considered good in normal product inspection. Evaluations "B" and "C" indicate a level of quality that would be considered poor in normal product inspection.

[0333] <Evaluation Criteria> A: The second functional layer is not peeling. The second functional layer is peeling along the edges of the cuts and / or at intersections. The affected area in the cross-cut portion is clearly no more than 15%. B: The second functional layer is partially or completely peeling along the edges of the cuts and / or partially or completely peeling in various parts of the eye. The affected area in the cross-cut portion is clearly more than 15% but no more than 35%. C: The second functional layer is partially or completely peeling along the edges of the cuts and / or partially or completely peeling in several places in the eye.

[0334]

[0335] 5: Sheet article, 6: Winding core, 7: Winding, 10: Optical sheet, 11: First surface, 12: Second surface, 15: Substrate with easy-adhesion layer, 16: First surface, 17: Second surface, 20: Substrate, 30: First functional layer, 31: First surface, 31X: Maximum value point, 31Y: Minimum value point, 32: Second surface, 33X: Convex part, 33Y: Concave part, 36: Binder component, 37: Particles, 40: Second functional layer, 41: First surface, 42: Second surface, 51: Third functional layer 52: Fourth functional layer, 60: Polarizing plate 60, 61: First protective sheet, 62: Polarizer, 63: Second protective sheet, 65: Display device, 66: Display element, 66a: Image forming surface, 70: Panel, 71: Joined article, SR10: Reference range, D1: First direction, D2: Second direction, D3: Third direction, RA8: Winding axis, BS1: First interface BS1, BS2: Second interface BS2, BS3: Third interface BS3, BS4: Fourth interface BS4

Claims

1. An optical sheet comprising a substrate and a first functional layer stacked in a first direction, wherein the thickness of the first functional layer is 20 nm or more and 250 nm or less, the rate of change in length of the surface of the first functional layer opposite to the substrate in a cross-section along the first direction is 1.02 or more and 1.19 or less, the rate of change is the ratio of the length of the surface located within a reference range of the cross-section to the length between both ends of the surface located within the reference range, and the length between both ends of the surface located within the reference range is 1.3 μm.

2. The optical sheet according to claim 1, wherein the average inclination angle of the surface in the cross-section is 5.0° or more and 30° or less.

3. The optical sheet according to claim 1, wherein the surface in the cross-section includes a plurality of protrusions and / or a plurality of recesses within the reference range.

4. The optical sheet according to claim 1, wherein the maximum height difference in the first direction within the reference range of the surface in the cross-section is 25 nm or more and 100 nm or less.

5. The optical sheet according to claim 1, wherein the transmitted haze is 1.5% or less.

6. The optical sheet according to claim 1, wherein the first functional layer comprises a binder component and particles.

7. The optical sheet according to claim 1, wherein the substrate comprises polyester.

8. The optical sheet according to claim 1, wherein the substrate comprises a resin derived from biomass material.

9. The optical sheet according to claim 1, wherein the first functional layer comprises a resin derived from biomass material.

10. The optical sheet according to claim 1, further comprising a second functional layer superimposed on the first functional layer in the first direction, wherein the first functional layer is located between the substrate and the second functional layer in the first direction.

11. The optical sheet according to claim 10, wherein the first functional layer comprises a binder component and particles, and the particles are located only within the first functional layer among the first and second functional layers.

12. A sheet article comprising a plurality of optical sheets as described in any one of claims 1 to 11.

13. The sheet article according to claim 12, which is wound around a winding axis.

14. A polarizing plate comprising an optical sheet as described in any one of claims 1 to 11, and a polarizer superimposed on the optical sheet.

15. A touch panel member comprising an optical sheet as described in any one of claims 1 to 11, and an electrode layer superimposed on the optical sheet.

16. A display device comprising an optical sheet as described in any one of claims 1 to 11, and a display element superimposed on the optical sheet.

17. A substrate with an easy-adhesion layer comprising a substrate and a first functional layer stacked in a first direction, wherein the first functional layer is an easy-adhesion layer, the thickness of the first functional layer is 20 nm or more and 250 nm or less, the rate of change in length of the surface of the first functional layer opposite to the substrate in a cross-section along the first direction is 1.02 or more and 1.19 or less, the rate of change is the ratio of the length of the surface located within a reference range of the cross-section to the length between both ends of the surface located within the reference range, and the length between both ends of the surface located within the reference range is 1.3 μm.

Images