Optical sheet, sheet article, polarizing plate, touch panel member, display device, lens member, and sensor device

Abstract

This optical sheet includes a first surface and a second surface that face each other in a first direction. The optical sheet includes a functional layer and a substrate in the order from the first surface toward the second surface. The functional layer contains a binder component and hollow silica particles. A second ratio is smaller than a first ratio. The first ratio is the ratio of the fluorescent X-ray intensity of the Si element to the fluorescent X-ray intensity of the C element at a first position in the functional layer. The second ratio is the ratio of the fluorescent X-ray intensity of the Si element to the fluorescent X-ray intensity of the C element at a second position in the functional layer. The first position is a position closer to the second surface by 50 nm from the first surface along the first direction. The second position is a position closer to the second surface by 140 nm from the first surface along the first direction.

Description

Optical sheets, sheet articles, polarizing plates, touch panel components, display devices, lens components, and sensor devices

[0001] This disclosure relates to optical sheets, sheet articles, polarizing plates, touch panel components, display devices, lens components, and sensor devices.

[0002] Optical sheets containing a low refractive index layer are known. The low refractive index layer suppresses the reflection of light of a specific wavelength corresponding to the thickness of the low refractive index layer. The low refractive index layer cannot sufficiently suppress the reflection of light of wavelengths that are significantly different from the specific wavelength. The spectral reflectance of the low refractive index layer changes depending on the wavelength. When the observation angle of an optical sheet containing a low refractive index layer increases, a color may be observed in the optical sheet.

[0003] The invention described in Patent Document 1 aims to provide a broadband reflection suppression function. The optical sheet described in Patent Document 1 includes a low refractive index layer, a high refractive index layer, and a medium refractive index layer in that order. However, these optical sheets cannot exhibit a sufficient reflection suppression function over a broadband.

[0004] Patent Document 1: JP2008-262187A

[0005] This disclosure aims to suppress reflection of light across a wide wavelength range.

[0006] A first optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the second ratio is smaller than the first ratio, the first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0007] A second optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the first ratio being 8.0% or more and 16% or less, the second ratio being 1.5% or more and 4.5% or less, the first ratio being the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio being the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position being a position 50 nm closer to the second surface from the first surface along the first direction, and the second position being a position 140 nm closer to the second surface from the first surface along the first direction.

[0008] A third optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the ratio of the second ratio to the first ratio is 0.094 or more and 0.58 or less, the first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0009] A fourth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0010] A fifth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the second average ratio is smaller than the first average ratio, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the third ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a third position in the functional layer, and the fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a fourth position in the functional layer. The first position is 50 nm closer to the second surface from the first surface along the first direction; the second position is 140 nm closer to the second surface from the first surface along the first direction; the third position is 60 nm closer to the second surface from the first surface along the first direction; and the fourth position is 130 nm closer to the second surface from the first surface along the first direction.

[0011] A sixth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the first average ratio is 8.0% or more and 16% or less, the second average ratio is 1.5% or more and 4.5% or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a second position in the functional layer, and the third ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a third position in the functional layer. The fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction.

[0012] A seventh optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the ratio of the second average ratio to the first average ratio is 0.094 or more and 0.58 or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a second position in the functional layer, and the third ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a third position in the functional layer. The fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction.

[0013] An eighth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the value obtained by subtracting the second average ratio from the first average ratio is 3.5% or more and 14.5% or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a second position in the functional layer, and the third ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a third position in the functional layer. The fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction.

[0014] A ninth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance values ​​at the first surface at wavelengths of 380 nm to 480 nm is 0.60% or less.

[0015] A tenth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance values ​​at the first surface at wavelengths of 680 nm to 780 nm is 0.30% or less.

[0016] An eleventh optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance values ​​at the first surface at wavelengths of 380 nm to 780 nm is 1.0% or less.

[0017] A twelfth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, and the maximum spectral reflectance at the first surface at wavelengths of 380 nm to 780 nm is 1.5% or less.

[0018] A thirteenth optical sheet in one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a first functional layer, a second functional layer, and a substrate in the order from the first surface to the second surface, wherein the first functional layer comprises a binder component and hollow silica particles, the second functional layer comprises a binder component and hollow silica particles, and the refractive index of the first functional layer is smaller than the refractive index of the second functional layer.

[0019] According to this disclosure, reflection of light across a wide wavelength range can be suppressed.

[0020] Figure 1 is a diagram illustrating one embodiment, and is a cross-sectional view showing an example of an optical sheet. Figure 2 is a cross-sectional view corresponding to Figure 1, and shows a modified example of the layer configuration. Figure 3 is a cross-sectional view showing the optical sheet shown in Figure 1. Figure 4 is a diagram illustrating a method for preparing a sample. Figure 5A is a cross-sectional view showing the optical sheet shown in Figure 1, and illustrates a method for obtaining a sample. Figure 5B is a plan view showing a sample obtained from the optical sheet shown in Figure 1. Figure 5C shows an example of an observation image of a sample obtained from an optical sheet. Figure 5D shows another example of an observation image of a sample obtained from an optical sheet. Figure 5E shows yet another example of an observation image of a sample obtained from an optical sheet. Figure 6 is a cross-sectional view showing a specific example of an optical sheet, and is a diagram illustrating the reflection suppression function exhibited by the optical sheet. Figure 7 is a graph showing the amplitude reflectance of the optical sheet shown in Figure 6. Figure 8 is a graph showing the reflection characteristics of several examples of optical sheets. Figure 9 is a graph showing the reflection characteristics of one example of an optical sheet. Figure 10 is a graph showing the reflection characteristics of other examples of optical sheets. Figure 11 is a graph showing the reflective properties of yet another example of an optical sheet. Figure 12 is a perspective view showing an example of a sheet article containing an optical sheet. Figure 13 is a cross-sectional view showing an example of a polarizing plate containing an optical sheet. Figure 14 is a cross-sectional view showing an example of a display device containing an optical sheet. Figure 15 is a cross-sectional view showing an example of a panel containing an optical sheet. Figure 16 is a cross-sectional view showing an example of a lens member containing an optical sheet. Figure 17 is a perspective view showing an example of a wearable display device containing an optical sheet. Figure 18 is a cross-sectional view showing an example of a sensor device containing an optical sheet. Figure 19A is an example of an observation image of a cross section including a first position of the optical sheet. Figure 19B is an example of an observation image of a cross section including a second position of the optical sheet. Figure 20A is another example of an observation image of a cross section including a first position of the optical sheet. Figure 20B is another example of an observation image of a cross section including a second position of the optical sheet. Figure 21A is yet another example of an observation image of a cross section including a first position of the optical sheet. Figure 21B is yet another example of an observation image of a cross section including a second position of the optical sheet. Figure 22 is a cross-sectional view showing an example of a conventional optical sheet. Figure 23 is a graph showing the amplitude reflectance of the optical sheet shown in Figure 22.Figure 24 is a cross-sectional view showing another example of a conventional optical sheet. Figure 25 is a graph showing the amplitude reflectance of the optical sheet shown in Figure 24.

[0021] One embodiment of the present disclosure relates to the following <1> to <50>.

[0022] <1> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein the optical sheet comprises a functional layer and a substrate in the order from the first surface to the second surface, the functional layer comprising a binder component and hollow silica particles, the second ratio being smaller than the first ratio, the first ratio being the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio being the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position being a position 50 nm closer to the second surface from the first surface along the first direction, and the second position being a position 140 nm closer to the second surface from the first surface along the first direction.

[0023] <2> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the first ratio is 8.0% or more and 16% or less, the second ratio is 1.5% or more and 4.5% or less, the first ratio is the ratio of the X-ray fluorescence intensity of Si element to the X-ray fluorescence intensity of C element at a first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of Si element to the X-ray fluorescence intensity of C element at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0024] <3> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the ratio of the second ratio to the first ratio is 0.094 or more and 0.58 or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0025] <4> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less, the first ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of element Si to the fluorescent X-ray intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0026] <5> An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the second average ratio is smaller than the first average ratio, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a second position in the functional layer, the third ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a third position in the functional layer, and the fourth ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a fourth position in the functional layer. An optical sheet wherein the first position is 50 nm closer to the second surface from the first surface along the first direction, the second position is 140 nm closer to the second surface from the first surface along the first direction, the third position is 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is 130 nm closer to the second surface from the first surface along the first direction.

[0027] <6> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the first average ratio is 8.0% or more and 16% or less, the second average ratio is 1.5% or more and 4.5% or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a second position in the functional layer, the third ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a third position in the functional layer, The fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction, in this optical sheet.

[0028] <7> An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a functional layer and a substrate in the order from the first surface to the second surface, wherein the functional layer comprises a binder component and hollow silica particles, the ratio of the second average ratio to the first average ratio is 0.094 or more and 0.58 or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a second position in the functional layer, and the third ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a third position in the functional layer. The fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction, in this optical sheet.

[0029] <8> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the value obtained by subtracting the second average ratio from the first average ratio is 3.5% or more and 14.5% or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a first position in the functional layer, the second ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a second position in the functional layer, the third ratio is the ratio of the fluorescent X-ray intensity of Si element to the fluorescent X-ray intensity of C element at a third position in the functional layer, The fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction, in this optical sheet.

[0030] <9> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance values ​​at the first surface at wavelengths of 380 nm to 480 nm is 0.60% or less.

[0031] <10> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance at the first surface at a wavelength of 680 nm to 780 nm is 0.30% or less.

[0032] <11> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance at the first surface at wavelengths of 380 nm to 780 nm is 1.0% or less.

[0033] <12> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, and the maximum spectral reflectance of the first surface at a wavelength of 380 nm to 780 nm is 1.5% or less.

[0034] <13> An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein the first functional layer, the second functional layer and the substrate are arranged in the order from the first surface to the second surface, the first functional layer comprises a binder component and hollow silica particles, the second functional layer comprises a binder component and hollow silica particles, and the refractive index of the first functional layer is smaller than the refractive index of the second functional layer.

[0035] <14> The optical sheet according to any one of <1> and <3> to <13>, wherein the first ratio is 8.0% or more and 16% or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, and the first position is a position 50 nm closer to the second surface from the first surface along the first direction.

[0036] <15> The optical sheet according to any one of <1> and <3> to <14>, wherein the second ratio is 1.5% or more and 4.5% or less, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0037] <16> The optical sheet according to any one of <1>, <2>, and <4> to <15>, wherein the ratio of the second ratio to the first ratio is 0.094 or more and 0.58 or less, the first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0038] <17> The optical sheet according to any one of <1> to <3> and <5> to <16>, wherein the value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less, the first ratio is the ratio of the fluorescence X-ray intensity of the Si element to the fluorescence X-ray intensity of the C element at a first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of the Si element to the fluorescence X-ray intensity of the C element at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

[0039] <18> The optical sheet according to any one of <1> to <5> and <7> to <17>, wherein the first average ratio is 8.0% or more and 16% or less, the first average ratio is the average value of the first ratio and the third ratio, the first ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at a first position in the functional layer, the third ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at a third position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the third position is a position 60 nm closer to the second surface from the first surface along the first direction.

[0040] <19> The optical sheet according to any one of <1> to <5> and <7> to <18>, wherein the second average ratio is 1.5% or more and 4.5% or less, the second average ratio is the average value of the second ratio and the fourth ratio, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, the fourth ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a fourth position in the functional layer, the second position is a position 140 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction.

[0041] <20> The ratio of the second average ratio to the first average ratio is 0.094 or more and 0.58 or less, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at the first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at the second position in the functional layer, the third ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at the third position in the functional layer, the fourth ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at the fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, The optical sheet according to any one of <1> to <6> and <8> to <19>, wherein the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction.

[0042] <21> The value obtained by subtracting the second average ratio from the first average ratio is between 3.5% and 14.5%, the first average ratio is the average value of the first ratio and the third ratio, the second average ratio is the average value of the second ratio and the fourth ratio, the first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the second position in the functional layer, the third ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the third position in the functional layer, the fourth ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the fourth position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction. The optical sheet according to any one of the claims <1> to <7> and <9> to <20>, wherein the second position is a position 140 nm closer to the second surface from the first surface along the first direction, the third position is a position 60 nm closer to the second surface from the first surface along the first direction, and the fourth position is a position 130 nm closer to the second surface from the first surface along the first direction.

[0043] <22> The optical sheet according to any one of the items <1> to <8> and <10> to <21>, wherein the difference between the maximum and minimum values ​​of the spectral reflectance on the first surface at wavelengths of 380 nm to 480 nm is 0.60% or less.

[0044] <23> The optical sheet according to any one of the items <1> to <9> and <11> to <22>, wherein the difference between the maximum and minimum values ​​of the spectral reflectance on the first surface at wavelengths of 680 nm to 780 nm is 0.30% or less.

[0045] <24> The optical sheet according to any one of <1> to <10> and <12> to <22>, wherein the difference between the maximum and minimum values ​​of the spectral reflectance on the first surface at wavelengths of 380 nm to 780 nm is 1.0% or less.

[0046] <25> The maximum value of the spectral reflectance on the first surface at wavelengths of 380 nm or more and 780 nm or less is 1.5% or less. The optical sheet according to any one of <1> to <11> and <13> to <22>.

[0047] <26> The reflected Y value on the first surface is 2.5% or less. The optical sheet according to any one of <1> to <25>.

[0048] <27> The difference between the maximum value and the minimum value of the spectral reflectance on the first surface at wavelengths of 300 nm or more and 380 nm or less is 1.3% or less. The optical sheet according to any one of <1> to <26>.

[0049] <28> The difference between the maximum value and the minimum value of the spectral reflectance on the first surface at wavelengths of 780 nm or more and 900 nm or less is 0.60% or less. The optical sheet according to any one of <1> to <27>.

[0050] <29> The difference between the maximum value and the minimum value of the spectral reflectance on the first surface at wavelengths of 300 nm or more and 380 nm or less is 1.3% or less, and the difference between the maximum value and the minimum value of the spectral reflectance on the first surface at wavelengths of 780 nm or more and 900 nm or less is 0.60% or less. The optical sheet according to any one of <1> to <28>.

[0051] <30> First a ＊ The absolute value of the difference between the value and the second a ＊ value is 2.0 or less, and the absolute value of the difference between the first b ＊ value and the second b ＊ value is 4.0 or less. The first a ＊ value is the a of the L ＊ a ＊ b ＊ value of the a-b color system measured by the reflected light on the first surface with an incident angle of 5°, and the second a ＊ value is the a of the L ＊ value of the a-b color system measured by the reflected light on the first surface with an incident angle of 60°. The first b ＊ value is the a of the L ＊ value of the a-b color system measured by the reflected light on the first surface with an incident angle of 5°, and the second b ＊ value is the a of the L ＊ value of the a-b color system measured by the reflected light on the first surface with an incident angle of 60°. The first b ＊ value is the a of the L ＊a ＊ b ＊ color system b ＊ The value is, as stated in the second b above. ＊ The value is L, which is measured by the reflected light from the first surface with an incident angle of 60°. ＊ a ＊ b ＊ color system b ＊ An optical sheet, which is one of the values ​​from <1> to <29>.

[0052] <31> The optical sheet according to any one of <1> to <30>, wherein the thickness of the functional layer is 140 nm or more and 280 nm or less.

[0053] <32> The functional layer is an optical sheet according to any one of <1> to <31> that constitutes the first surface.

[0054] <33> The optical sheet according to any one of <1> to <12> or <14> to <32>, wherein the functional layer includes a first functional layer and a second functional layer in order from the first surface to the second surface, and the refractive index of the first functional layer is smaller than the refractive index of the second functional layer.

[0055] <34> An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a first functional layer, a second functional layer, and a substrate in the order from the first surface to the second surface, wherein the first functional layer comprises a binder component and hollow silica particles, the second functional layer comprises a binder component and hollow silica particles, and the refractive index of the first functional layer is smaller than the refractive index of the second functional layer, as described in any one of <1> to <12>, <14> to <32>.

[0056] <35> The optical sheet according to <13>, <33>, or <34>, wherein the refractive index of the first functional layer is 1.15 or more and 1.45 or less, and the refractive index of the second functional layer is 1.25 or more and 1.55 or less.

[0057] <36> The optical sheet according to any one of <13> and <33> to <35>, wherein the thickness of the first functional layer is 60 nm or more and 135 nm or less, and the thickness of the second functional layer is 50 nm or more and 125 nm or less.

[0058] <37> The optical sheet according to any one of <13> and <33> to <36>, wherein the refractive index of the region of the optical sheet adjacent to the two functional layers is greater than the refractive index of the two functional layers.

[0059] <38> The optical sheet according to any one of <13> and <33> to <37>, wherein the refractive index of the region of the optical sheet adjacent to the second functional layer is 1.40 or more and 1.65 or less.

[0060] <39> The optical sheet according to any one of <13> and <33> to <38>, wherein the thickness T31 of the first functional layer, the thickness T36 of the second functional layer, the refractive index n31 of the first functional layer, and the refractive index n36 of the second functional layer satisfy the following formula (1).

[0061]

[0062] <40> An optical sheet according to any one of <13> and <33> to <39>, wherein the thickness T31 of the first functional layer, the thickness T36 of the second functional layer, the refractive index n31 of the first functional layer, the refractive index n36 of the second functional layer, and k, which is an integer of 0 or more, satisfy the following equations (2) and (3).

[0063]

[0064] <41> The optical sheet according to any one of <13> and <33> to <40>, wherein the thickness T31 of the first functional layer, the thickness T36 of the second functional layer, the refractive index n31 of the first functional layer, and the refractive index n36 of the second functional layer satisfy the following formulas (4) and (5).

[0065]

[0066] <42> The optical sheet according to any one of <1> to <41>, further comprising a resin layer located between the functional layer and the substrate in the first direction, wherein the resin layer is adjacent to the functional layer and the resin layer includes a cured resin product.

[0067] <43> The substrate is an optical sheet according to any one of <1> to <42>, adjacent to the functional layer.

[0068] <44> A sheet article comprising multiple optical sheets as described in any one of the items <1> to <43>.

[0069] <45> The sheet article described in <44>, which is wound around a winding axis.

[0070] <46> A polarizing plate comprising an optical sheet described in any one of <1> to <45>, and a polarizer superimposed on the optical sheet.

[0071] <47> A touch panel member comprising an optical sheet described in any one of <1> to <45>, and an electrode layer superimposed on the optical sheet.

[0072] <48> A display device comprising an optical sheet described in any one of <1> to <45>, and a display element superimposed on the optical sheet.

[0073] <49> A lens member comprising an optical sheet described in any one of <1> to <45> and a lens superimposed on the optical sheet.

[0074] <50> A sensor device comprising an optical sheet described in any one of <1> to <45>, and a sensor superimposed on the optical sheet.

[0075] 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.

[0076] 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 called optical films or optical plates solely on the basis of differences in name.

[0077] 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 the sheet-like (film-like, plate-like) member is observed as a whole.

[0078] 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.

[0079] 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.

[0080] <<<Optical Sheet>>> As shown in Figures 1 and 2, the optical sheet 10 according to this embodiment includes a first surface 11 and a second surface 12. The first surface 11 and the second surface 12 face each other in a first direction D1. The optical sheet 10 includes a functional layer 20 and a base material 50 in the order from the first surface 11 to the second surface 12. The functional layer 20 and the base material 50 are laminated in the first direction D1. The first direction D1 is the lamination direction of the optical sheet 10. The first direction D1 is the thickness direction of the optical sheet 10. In the illustrated example, the first surface 11 and the second surface 12 constitute the main surfaces of the optical sheet 10.

[0081] As shown in Figures 1 and 2, the functional layer 20 contains binder components 32 and 37 and hollow silica particles 33 and 38. The hollow silica particles 33 and 38 are silica particles with voids. The hollow silica particles 33 and 38 have a hollow structure. Due to their structure, the hollow silica particles 33 and 38 have a low refractive index. The functional layer 20 containing the hollow silica particles 33 and 38 has a refractive index lower than that of the binder components 32 and 37. The low refractive index functional layer 20 can suppress reflection at the first surface 11. The functional layer 20 containing the hollow silica particles 33 and 38 functions as a low-reflection layer or a reflection-suppressing layer.

[0082] As shown in Figures 1 and 2, the functional layer 20 may include a first surface 21 and a second surface 22. The first surface 21 and the second surface 22 face a first direction D1. The first surface 21 faces the first side in the first direction D1. The first surface 21 faces away from the second surface 12 in the first direction D1. The second surface 22 faces the second side in the second direction. The second surface 22 faces away from the first surface 11 in the first direction D1. The second surface 22 is close to the second surface 12 in the first direction D1 and away from the first surface 11. In the illustrated example, the first surface 21 of the functional layer 20 constitutes the first surface 11 of the optical sheet 10.

[0083] As shown in Figures 1 and 2, the base material 50 may constitute the second surface 12.

[0084] As shown in Figure 1, the optical sheet 10 may further include a resin layer 40. The resin layer 40 is located between the functional layer 20 and the substrate 50. The resin layer 40 may be in contact with the functional layer 20 from the second side in the first direction D1. In the example shown in Figure 1, the resin layer 40 is bonded to the functional layer 20.

[0085] The resin layer 40 may be a layer that is expected to have some function. The resin layer 40 may also contain a cured resin product.

[0086] The resin layer 40 may provide mechanical strength to the optical sheet 10. The resin layer 40 may provide scratch resistance to the optical sheet 10. The resin layer 40 may also be a hard coat layer.

[0087] The resin layer 40 may provide anti-glare properties to the optical sheet 10. The resin layer 40 may have an anti-glare function. The resin layer 40 may have a function to suppress reflections of external images. The optical sheet 10 may also be an anti-glare layer. The resin layer 40 may contain a binder component and particles held by the binder component.

[0088] As shown in Figure 2, the base material 50 may contact the functional layer 20 from the second side in the first direction D1. In the example shown in Figure 2, the base material 50 is bonded to the functional layer 20.

[0089] The layer structure of the optical sheet 10 is not limited to the examples shown in Figures 1 and 2. For example, the optical sheet may include further layers. For example, the optical sheet 10 may include a second resin layer between the resin layer 40 and the substrate 50. The optical sheet 10 may include a surface layer that constitutes the first surface 11. The surface layer may be bonded to the first surface 21 of the functional layer 20. The second resin layer and the surface layer may be layers expected to have some function. The surface layer may be an antistatic layer.

[0090] As shown in Figures 1 and 2, the functional layer 20 may include a first functional layer 31 and a second functional layer 36. The first functional layer 31 and the second functional layer 36 are arranged in this order from the first surface 11 to the second surface 12 along the first direction D1. The first functional layer 31 includes a binder component 32 and hollow silica particles 33. The second functional layer 36 includes a binder component 37 and hollow silica particles 38.

[0091] As shown in Figures 1 and 2, the first functional layer 31 may include a first surface 31a and a second surface 31b. The first surface 31a and the second surface 31b face the first direction D1. The first surface 31a faces the first side in the first direction D1. The first surface 31a faces away from the second surface 12 in the first direction D1. The second surface 31b faces the second side in the first direction D1. The second surface 31b faces away from the first surface 11 in the first direction D1. The second surface 31b is close to the second surface 12 in the first direction D1 and away from the first surface 11. In the illustrated example, the first surface 31a constitutes the first surface 11 of the optical sheet 10 and the first surface 21 of the functional layer 20.

[0092] As shown in Figures 1 and 2, the second functional layer 36 may include a first surface 36a and a second surface 36b. The first surface 36a and the second surface 36b face the first direction D1. The first surface 36a faces the first side in the first direction D1. The first surface 36a faces away from the second surface 12 in the first direction D1. The first surface 36a is close to the first surface 11 in the first direction D1 and away from the second surface 12. The second surface 36b faces the second side in the first direction D1. The second surface 36b faces away from the first surface 11 in the first direction D1. The second surface 36b is close to the second surface 12 in the first direction D1 and away from the first surface 11. In the illustrated example, the second surface 36b constitutes the second surface 22 of the functional layer 20.

[0093] In the examples shown in Figures 1 and 2, the first surface 11 of the optical sheet 10 is the outermost surface of the optical sheet 10. The first surface 11 of the optical sheet 10 (first surface 21 and first surface 31a) forms a first interface BS1 between itself and the air layer. In the examples shown in Figures 1 and 2, a second interface BS2 is formed between the first functional layer 31 and the second functional layer 36.

[0094] In the examples shown in Figures 1 and 2, the second surface 22 of the functional layer 20 (the second surface 36b of the second functional layer 36) forms a third interface BS3 between the functional layer 20 and an adjacent region 15 adjacent to the first direction D1. In the example shown in Figure 1, the adjacent region 15 is composed of a resin layer 40. The third interface BS3 is formed between the functional layer 20 and the resin layer 40. In the example shown in Figure 2, the adjacent region 15 is composed of a substrate 50. The third interface BS3 is formed between the functional layer 20 and the substrate 50.

[0095] In conventional optical sheets, the reflection suppression function of the low refractive index layer is particularly effective for light of specific wavelengths. However, this function deteriorates for light of wavelengths significantly deviating from the specific wavelength. The spectral reflectance at the first surface of the optical sheet changes in the visible light wavelength range. As the angle of incidence increases, the optical path length within the low refractive index layer increases. As a result, the spectral reflectance at the first surface of the optical sheet changes more significantly in the visible light wavelength range. Therefore, at large observation angles, the optical sheet may appear colored. This coloration constitutes a defect in the appearance of the optical sheet.

[0096] In this specification, the wavelength of visible light is defined as 380 nm to 780 nm.

[0097] The angle of incidence (°) is the angle between the direction of propagation of light incident on the object and the normal direction of the object. The angle of incidence (°) on the optical sheet is the angle between the direction of propagation of light incident on the optical sheet and the first direction D1. The angle of incidence is between 0° and 90°.

[0098] The observation angle (°) is the angle between the observation direction and the normal direction of the object being observed. The observation angle (°) of an optical sheet is the angle between the direction in which the optical sheet is observed and the first direction D1. The observation angle is between 0° and 90°.

[0099] The optical sheet according to this embodiment incorporates features to address these problems. The optical sheet according to this embodiment can suppress reflection of light across a wide wavelength range due to the features described below. Furthermore, the optical sheet according to this embodiment can suppress the coloration of the optical sheet even at large observation angles.

[0100] <<First and Second Ratios>> The optical sheet according to this embodiment may have one or more of the following features (A) to (D): (A): The second ratio is smaller than the first ratio. (B): The first ratio is 8.0% or more and 16% or less, and the second ratio is 1.5% or more and 4.5% or less. (C): The ratio of the second ratio to the first ratio is 0.094 or more and 0.58 or less. (D): The value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less.

[0101] The first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at the first position P1 within the functional layer 20. As shown in Figure 3, the first position P1 is located 50 nm closer to the second surface 12 from the first surface 11 along the first direction D1. In other words, the first position P1 is located 50 nm away from the first surface 11 toward the second surface 12 along the first direction D1. The distance along the first direction D1 from the first position P1 to the first surface 11 is 50 nm. The first ratio is expressed as a percentage. The unit of the first ratio is "%".

[0102] The second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at the second position P2 within the functional layer 20. The second position P2 is located 140 nm closer to the second surface 12 from the first surface 11 along the first direction D1. In other words, the second position P2 is located 140 nm away from the first surface 11 toward the second surface 12 along the first direction D1. The distance along the first direction D1 from the second position P2 to the first surface 11 is 140 nm. The second ratio is expressed as a percentage. The unit of the second ratio is "%".

[0103] ((Fluorescent X-ray Intensity of C and Si Elements)) Features (A) to (D) relate to the first ratio of fluorescent X-ray intensities of Si and C elements measured at the first position P1, and the second ratio of fluorescent X-ray intensities of Si and C elements measured at the second position P2. The fluorescent X-ray intensities of the elements used to calculate the first and second ratios are the detected amounts of fluorescent X-rays measured by fluorescent X-ray analysis. The unit of fluorescent X-ray intensity is cps (count per second). Energy-dispersive fluorescent X-ray analysis is used as the fluorescent X-ray analysis method. The "fluorescent X-ray intensity" defined in Features (A) to (D) is measured as follows.

[0104] (Sample) The section to be measured for fluorescence X-ray intensity is obtained by the following method. First, a sample is cut from the optical sheet to be measured. The size of the sample is approximately 1 mm × 10 mm when observed from the direction normal to the optical sheet. As shown in Figure 4, the sample S10 is attached to the resin plate 17 using adhesive 16. Next, the resin plate 17 holding the sample S10 is fixed to the carrier 18 using adhesive 19. The carrier 18 includes a sample support surface 18a. A groove 18b is formed in the sample support surface 18a. Adhesive 19 is filled into the groove 18b. The sample S10 is fixed to the support surface 18a such that a part of the sample S10 is positioned on the groove 18b.

[0105] Next, a section is cut from sample S10 using an ultramicrotome. The carrier 18 is an accessory for the ultramicrotome. The carrier 18 supporting sample S10 is attached to the sample holder of the ultramicrotome. The carrier 18 is fixed to the sample holder of the ultramicrotome so that the cut surface of the sample is horizontal.

[0106] As shown in Figure 5A, the sample is cut along a plane inclined at an angle of 2° to 3° with respect to the plane perpendicular to the first direction D1 of the optical sheet, and sections are obtained from the sample. Therefore, the carrier 18 is fixed to the ultramicrotome such that the surface of the sample S10 corresponding to the first surface of the optical sheet is inclined at an angle of 2° to 3° with respect to the horizontal direction. In Figure 5A, the cutting direction is indicated by the dotted line CD. The thickness of the section is about 80 nm, which is an appropriate thickness for measuring the fluorescence X-ray intensity.

[0107] As an example of an ultramicrotome, the Leica UC7 is given. As an example of a blade used in an ultramicrotome, the Dia Ultra35 is given.

[0108] Figure 5B shows an example of a section 10X of an optical sheet obtained using an ultramicrotome. Figure 5B shows the section 10X from the normal direction of the unfolded section. The section 10X of the optical sheet 10 includes a position corresponding to the first surface 11 (first interface BS1) of the optical sheet 10 and a position corresponding to the second surface 22 (third interface BS3) of the functional layer 20. The section 10X of the optical sheet 10 includes the interface between the first functional layer 31 and the second functional layer 36 (second interface BS2, second surface 31b, first surface 36a). The distance L20X between the first surface 11 and the second surface 22 of the functional layer 20 in the unfolded section 10X is about 20 to 30 times the distance T20 (see Figure 3) from the first surface 11 to the second surface 22 in the cross-section of the optical sheet 10 along the first direction D1, and is a size appropriate for measuring the fluorescence X-ray intensity.

[0109] A section 10X of the optical sheet 10 includes a first position P1 and a second position P2. As shown in Figure 5A, the first position P1 is defined as a position at a distance LP1 from the first surface 11 in the unfolded section 10X. The second position P2 is defined as a position at a distance LP2 from the first surface 11 in the unfolded section 10X. Distances LP1 and LP2 are lengths on the section 10X unfolded on a plane, along the direction in which the first surface 21 and the second surface 22 of the functional layer 20 in the section 10X face each other.

[0110] Distances LP1 and LP2 are determined as follows using the thickness T20 of the functional layer 20 and distance L20X. The method for measuring the thickness of each layer contained in the optical sheet will be described later. Distance LP1 (μm) = 50 × L20X (μm) / T20 (nm) Distance LP2 (μm) = 140 × L20X (μm) / T20 (nm)

[0111] (Measurement of X-ray fluorescence intensity) When a substance is irradiated with X-rays, fluorescent X-rays are generated. The fluorescent X-rays generated from a substance include characteristic X-rays. Characteristic X-rays have element-specific energies (keV). In other words, characteristic X-rays are emitted from specific elements. Based on the energy of the characteristic X-rays, the element that emits those characteristic X-rays can be identified. By measuring the detection intensity of the characteristic X-rays, the content of the specific element corresponding to the characteristic X-rays in the substance can be evaluated.

[0112] An energy-dispersive X-ray spectrometer (EDX) is used to measure the intensity of X-ray fluorescence. The following instrument may be used as the energy-dispersive X-ray spectrometer: • Manufacturer: Oxford Instruments • Model: X-MaxN 100TLE • Detector element area: 100 mm² ２ , windowless type

[0113] The X-ray fluorescence intensity at the first position P1 is measured by setting the measurement area AP1 of the section 10X to include the first position P1, as shown in Figure 5B. The X-ray fluorescence intensity at the second position P2 is measured by setting the measurement area AP2 of the section 10X to include the second position P2, as shown in Figure 5B. The measurement areas AP1 and AP2 of the X-ray fluorescence analyzer are set while observing the section 10X using a scanning transmission electron microscope (STEM) linked to the X-ray fluorescence analyzer. Measurement areas AP1 and AP2 are rectangular in shape. The size of measurement areas AP1 and AP2 is approximately 1.3 μm on the long side and approximately 0.90 μm on the short side. The long side of measurement area AP1 and AP2 are aligned in a direction perpendicular to the first direction D1. No conductive treatment or staining is performed on the section 10X.

[0114] Figures 5C to 5E are examples of images obtained by observing section 10X obtained by the method described above using a scanning transmission electron microscope. Figures 5C to 5E are observation images for Example 2, which will be described later. Measurement areas AP1 and AP2 are selected from areas where no significant particle loss has occurred. Measurement areas AP1 and AP2 are selected from areas in section 10X where no significant particle overlap in the thickness direction has occurred.

[0115] As an example of a scanning transmission electron microscope, the SU-9000 scanning transmission electron microscope manufactured by Hitachi High-Tech Corporation is used. When using this microscope, the mode may be set to "TE", the acceleration voltage to "30.0 kV", the emission current to "20 μA", and the W.D. to "8.0 mm". The magnification can be set to a magnification that allows each layer to be distinguished, for example, around 100,000x, while adjusting the focus, contrast, and brightness. The SU-9000 scanning transmission electron microscope manufactured by Hitachi High-Tech Corporation is equipped with the "X-MaxN 100TLE" manufactured by Oxford Instruments, as mentioned above.

[0116] Note that features (Ax) to (Dx) may be satisfied instead of features (A) to (D), or features (Ax) to (Dx) may be satisfied along with features (A) to (D). (Ax): The second mean ratio is smaller than the first mean ratio. (Bx): The first mean ratio is between 8.0% and 16%, and the second mean ratio is between 1.5% and 4.5%. (Cx): The ratio of the second mean ratio to the first mean ratio is between 0.094 and 0.58. (Dx): The value obtained by subtracting the second mean ratio from the first mean ratio is between 3.5% and 14.5%.

[0117] The first average ratio is the average of the first ratio and the third ratio described above. The third ratio is the ratio of the fluorescence X-ray intensity of Si element to the fluorescence X-ray intensity of C element at the third position P3 in the functional layer 20. As shown in Figure 3, the third position P3 is located 60 nm closer to the second surface 12 from the first surface 11 along the first direction D1. In other words, the third position P3 is located 60 nm away from the first surface 11 toward the second surface 12 along the first direction D1. The distance along the first direction D1 from the third position P3 to the first surface 11 is 60 nm. The first average ratio and the third ratio are expressed as percentages, similar to the first ratio. The unit of the first average ratio and the third ratio is "%", similar to the first ratio.

[0118] The second average ratio is the average of the second ratio and the fourth ratio described above. The fourth ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at the fourth position P4 in the functional layer 20. As shown in Figure 3, the fourth position P4 is located 130 nm closer to the second surface 12 from the first surface 11 along the first direction D1. In other words, the fourth position P4 is located 130 nm away from the first surface 11 toward the second surface 12 along the first direction D1. The distance along the first direction D1 from the fourth position P4 to the first surface 11 is 130 nm. The second average ratio and the fourth ratio are expressed as percentages, similar to the second ratio. The unit of the second average ratio and the fourth ratio is "%", similar to the second ratio.

[0119] The "fluorescent X-ray intensity" used to calculate the first and second ratios defined in features (A) to (D) is measured from a 10X intercept under the following conditions. Other conditions conform to the "energy dispersion method" in JIS K0119:2008.

[0120] (Measurement conditions) Measurement channel: C-Sc Voltage: 15kV Current: 100μA Filter: None Smoothing: None Integration time: Live Time 100sec Atmosphere: Vacuum

[0121] Before measuring the sections of the optical sheets to be evaluated, a standard sample will be pre-measured. The standard sample will be an aluminum plate, which is a standard accessory sample for the analytical instrument used in X-ray fluorescence analysis. In the pre-measurement results, it will be confirmed that the detection rate of aluminum is 80% or higher, and that Sn and Cu are detected.

[0122] From the measurement results obtained above, the background is manually subtracted. By subtracting the background from the measured values, the fluorescent X-ray intensity at the first position P1 and the fluorescent X-ray intensity at the second position P2 are obtained. From the obtained fluorescent X-ray intensities, the intensity corresponding to element C (cps) and the intensity corresponding to element Si (cps) are measured. By dividing the fluorescent X-ray intensity of element Si by the fluorescent X-ray intensity of element C and multiplying by 100, the first ratio (%) and the second ratio (%) are obtained.

[0123] The first ratio is the arithmetic mean of the five first ratio values. The five first ratio values ​​are calculated from the fluorescent X-ray intensity at the first position P1 measured at five measurement positions on the optical sheet being evaluated. The five measurement positions are located at least 10 mm apart from each other.

[0124] The second ratio is the arithmetic mean of the five second ratio values. The five second ratio values ​​are calculated from the fluorescent X-ray intensity at the second position P2 measured at five measurement locations on the optical sheet being evaluated. The five measurement locations are located at least 10 mm apart from each other.

[0125] The third ratio is the arithmetic mean of the five third ratio values. The five third ratio values ​​are calculated from the fluorescent X-ray intensity at the third position P3 measured at five measurement positions on the optical sheet being evaluated. The five measurement positions are located at least 10 mm apart from each other.

[0126] The fourth ratio is the arithmetic mean of the five fourth ratio values. The five fourth ratio values ​​are calculated from the fluorescent X-ray intensity at the fourth position P4 measured at five measurement positions on the optical sheet being evaluated. The five measurement positions are located at least 10 mm apart from each other.

[0127] <Feature (A)> The optical sheet may have feature (A). (A): The second ratio is smaller than the first ratio.

[0128] The first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the first position P1 within the functional layer 20. The second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at the second position P2 within the functional layer 20. The first ratio serves as an indicator of the element Si content at the first position P1. The second ratio serves as an indicator of the element Si content at the second position P2. When the first and second ratios are large, the element Si content is large. When the first and second ratios are small, the element Si content is small.

[0129] As shown in Figure 5A, the first position P1 and the second position P2 are located within the functional layer 20. The functional layer 20 contains hollow silica particles 33 and 38. In the functional layer 20, the hollow silica particles 33 and 38 are held in place by binder components 32 and 37. The hollow silica particles 33 and 38 typically have a refractive index significantly smaller than that of the binder components 32 and 37. The functional layer 20 has a low refractive index due to the inclusion of the hollow silica particles 33 and 38. The functional layer 20 containing the hollow silica particles 33 and 38 functions as a low refractive index layer. The refractive index of the functional layer 20 containing the hollow silica particles 33 and 38 is smaller than the refractive index of the adjacent region 15 adjacent to the functional layer 20 in the first direction D1.

[0130] According to feature (A), the functional layer 20 can be divided into a first functional layer 31 containing a large amount of Si elements and a second functional layer 36 containing a small amount of Si elements. According to feature (A), the functional layer 20 can be divided into a second functional layer 36 having a low refractive index and a first functional layer 31 having an even lower refractive index than the second functional layer 36.

[0131] As shown in Figure 3, the first position P1 is located 50 μm away from the first surface 11, which is the surface layer of the optical sheet 10, along the first direction D1, which is the thickness direction. The second position P2 is located 140 μm away from the first surface 11, which is the surface layer of the optical sheet 10, along the first direction D1, which is the thickness direction.

[0132] Therefore, according to feature (A), the optical sheet 10 includes a low refractive index layer (first functional layer 31), a medium refractive index layer (second functional layer 36), and a high refractive index layer (adjacent region 15 (resin layer 40 or substrate 50)) in order along the first direction D1 from the first surface 11. In other words, according to feature (A), the optical sheet 10 includes three adjacent layers in order along the first direction D1 from the first surface 11, with the refractive index gradually increasing.

[0133] In the examples shown in Figures 1 to 5, the low refractive index layer is composed of the first functional layer 31. In the examples shown in Figures 1 to 5, the medium refractive index layer is composed of the second functional layer 36. In the examples shown in Figures 1 to 5, the high refractive index layer is composed of the adjacent region 15 (resin layer 40 or substrate 50).

[0134] The inventors confirmed that an optical sheet containing a low refractive index layer, a medium refractive index layer, and a high refractive index layer in that order from the incident side could suppress the reflection of light across a wide wavelength range. The inventors also confirmed that when the optical sheet containing a low refractive index layer, a medium refractive index layer, and a high refractive index layer in that order from the incident side was observed from an oblique angle, the coloration of the optical sheet could be effectively suppressed. The reasons why this embodiment provides excellent reflection suppression are explained below.

[0135] In conventional optical sheets, a low refractive index layer may be placed on the surface. As shown in Figure 22, a conventional optical sheet 110 includes a low refractive index layer 111 and a high refractive index layer 112. The surface of the low refractive index layer 111 forms a first interface BS1 with the air layer. The back surface of the low refractive index layer 111 forms a second interface BS2 with the high refractive index layer 112.

[0136] The low refractive index layer 111 can exhibit a reflection suppression function by adjusting its thickness. This reflection suppression function utilizes the interference between reflected light LBS1 reflected from the surface (first interface BS1) of the low refractive index layer 111 and reflected light LBS2 reflected from the back surface (second interface BS2) of the low refractive index layer 111. The thickness T111 of the low refractive index layer 111 is set to approximately 1 / 4 of the wavelength of the light whose reflection should be suppressed. The phase of the reflected light LBS2 on the back surface of the low refractive index layer 111 shifts by π (rad), which corresponds to half a wavelength, from the phase of the reflected light on the surface of the low refractive index layer 111, as it travels back and forth across the low refractive index layer 111. Therefore, the reflected light LBS1 on the surface of the low refractive index layer 111 and the reflected light LBS2 on the back surface of the low refractive index layer 111 cancel each other out.

[0137] This reflection suppression function is effective for light of wavelengths corresponding to the thickness of the low refractive index layer 111. In conventional optical sheets 110, the reflection suppression function of the low refractive index layer 111 is particularly effective for light of specific wavelengths. The reflection suppression function of the low refractive index layer 111 decreases for light of wavelengths that deviate significantly from the specific wavelength.

[0138] To facilitate understanding, we will consider a simplified system. First, we assume that ambient light is incident on the optical sheet 110 at an incident angle of 0°. The overall amplitude reflectance r, considering the interference of reflected light LBS1 and reflected light LBS2, is expressed by the amplitude reflectance given by equation (a): r = r1 + r2 × cosθ2 ... equation (a)

[0139] In equation (a), "r1" is the reflectance at the first interface BS1. In equation (a), "r2" is the reflectance at the second interface BS2. "r1" and "r2" are reflectances that do not take phase into consideration and are determined by the refractive indices of the two regions that form the interface. "r1" and "r2" are obtained by taking the sum of the refractive indices of the two regions that form the interface as the denominator and the absolute value of the difference between the refractive indices of the two regions that form the interface as the numerator. If the refractive indices of the two regions that form the interface are "nx" and "ny", respectively, then "r1" and "r2" become "(|nx - ny|) / (nx + ny)". The reflectances "r1" and "r2" obtained from this equation have no units, and the maximum value of "r1" and "r2" is 1.

[0140] In equation (a), "θ²" represents the phase difference (rad) of the reflected light LBS2 at the second interface BS2 with respect to the reflected light LBS1 at the first interface BS1. Specifically, it is expressed by the following equation (b). In equation (b), "λ" is the wavelength (nm) of the reflected light LBS2. In equation (b), "T111" is the thickness (nm) of the low refractive index layer 111. In equation (b), "n111" is the refractive index of the low refractive index layer 111.

[0141]

[0142] Figure 23 shows the amplitude reflectance expressed by equation (a). In the graph shown in Figure 23, the vertical axis represents the amplitude reflectance (unit: none), and the horizontal axis represents the wavelength (nm). The solid line in Figure 23 represents the overall amplitude reflectance "r" in equation (a). The dotted line in Figure 23 represents the reflectance "r1" in equation (a). That is, the dotted line in Figure 23 represents the reflectance of reflected light LBS1 at the first interface BS1. The dashed line in Figure 23 represents the reflectance "r2 × cosθ2" in equation (a). That is, the dashed line in Figure 23 represents the amplitude reflectance of reflected light LBS2 at the second interface BS2.

[0143] In the examples shown in Figures 22 and 23, the thickness T111 of the low refractive index layer 111 is 100 nm, and the refractive index n111 of the low refractive index layer 111 is 1.30. In the examples shown in Figures 22 and 23, the refractive index n112 of the high refractive index layer 112 is 1.50. In the examples shown in Figures 22 and 23, for light with a wavelength of 520 nm, the reflected light LBS2 at the second interface BS2 cancels out the reflected light LBS1 at the first interface BS1. The overall amplitude reflectance r is smallest for light at the canceling wavelength (520 nm). As the wavelength moves away from the canceling wavelength (520 nm), the overall amplitude reflectance r increases.

[0144] On the other hand, the optical sheet 10 having feature (A) may include a low refractive index layer (first functional layer 31), a medium refractive index layer (second functional layer 36), and a high refractive index layer (adjacent region 15), as shown in Figure 6. As shown in Figure 6, light incident on the optical sheet 10 from the first surface 11 is mainly reflected at the first interface BS1, the second interface BS2, and the third interface BS3. The reflected light from the optical sheet 10 is the sum of the reflected light LBS1 at the first interface BS1, the reflected light LBS2 at the second interface BS2, and the reflected light LBS3 at the third interface BS3.

[0145] The total reflectance r, considering the interference of reflected light LBS1, reflected light LBS2, and reflected light LBS3, is expressed as the amplitude reflectance given by equation (c): r = r1 + r2 × cosθ2 + r3 × cosθ3 ... equation (c)

[0146] In equation (c), "r1" is the reflectance at the first interface BS1. In equation (c), "r2" is the reflectance at the second interface BS2. In equation (c), "r3" is the reflectance at the third interface BS1. "r1", "r2", and "r3" are reflectances that do not take phase into consideration and are determined by the refractive indices of the two regions that form the interface. "r1", "r2", and "r3" are obtained by taking the sum of the refractive indices of the two regions that form the interface as the denominator and the absolute value of the difference between the refractive indices of the two regions that form the interface as the numerator. If the refractive indices of the two regions that form the interface are "nx" and "ny", respectively, then "r1", "r2", and "r3" are "(|nx - ny|) / (nx + ny)". The reflectances "r1", "r2", and "r3" obtained from this equation are "unitless".

[0147] In equation (c), "θ²" represents the phase difference (rad) of the reflected light LBS2 at the second interface BS2 with respect to the reflected light LBS1 at the first interface BS1. Specifically, it is expressed by the following equation (d). In equation (c), "θ³" represents the phase difference (rad) of the reflected light LBS3 at the third interface BS3 with respect to the reflected light LBS1 at the first interface BS1. Specifically, it is expressed by the following equation (e).

[0148] In equations (d) and (e), "λ" is the wavelength (nm) of the reflected light. In equations (d) and (e), "T31" is the thickness of the first functional layer 31 as a low refractive index layer. In equations (d) and (e), "n31" is the refractive index of the first functional layer 31 as a low refractive index layer. In equation (e), "T36" is the thickness of the second functional layer 36 as a medium refractive index layer. In equation (e), "n36" is the refractive index of the second functional layer 36 as a medium refractive index layer.

[0149]

[0150]

[0151] Figure 7 shows the amplitude reflectance r expressed by equation (c). In the graph shown in Figure 7, the vertical axis represents amplitude reflectance (unit: none), and the horizontal axis represents wavelength (nm). The solid line in Figure 7 represents the total amplitude reflectance "r" in equation (c). The dotted line in Figure 7 represents the reflectance "r1" in equation (c). That is, the dotted line in Figure 7 represents the reflectance of reflected light LBS1 at the first interface BS1. The dashed line in Figure 7 represents the reflectance "r2 × cosθ2" in equation (c). That is, the dashed line in Figure 7 represents the amplitude reflectance of reflected light LBS2 at the second interface BS2. The double dashed line in Figure 7 represents the reflectance "r3 × cosθ3" in equation (c). That is, the double dashed line in Figure 7 represents the amplitude reflectance of reflected light LBS3 at the third interface BS3.

[0152] In the examples shown in Figures 6 and 7, the thickness T31 of the first functional layer 31 as a low refractive index layer was set to 102 nm. The refractive index n31 of the first functional layer 31 as a low refractive index layer was set to 1.300. In the examples shown in Figures 6 and 7, the thickness T36 of the second functional layer 36 as a medium refractive index layer was set to 92 nm. The refractive index n36 of the second functional layer 36 as a medium refractive index layer was set to 1.445. In the examples shown in Figures 6 and 7, the refractive index n40 of the adjacent region 15 as a high refractive index layer was set to 1.500.

[0153] In the examples shown in Figures 6 and 7, for light with a wavelength of 530 nm, the phase of the reflected light LBS2 at the second interface BS2 is shifted by π (rad), which corresponds to half a wavelength, from the phase of the reflected light LBS1 at the first interface BS1. That is, in the examples shown in Figures 6 and 7, for light with a wavelength of 530 nm, the reflected light LBS2 at the second interface BS2 cancels out the reflected light LBS1 at the first interface BS1 the most. Furthermore, in the examples shown in Figures 6 and 7, across the entire visible light wavelength range, the reflected light LBS2 at the second interface BS2 cancels out the reflected light LBS1 at the first interface BS1.

[0154] In the examples shown in Figures 6 and 7, for light with a wavelength of 530 nm, the shortest optical path length when light travels back and forth through the second functional layer 36, which acts as a medium refractive index layer, in the first direction D1 is half the wavelength. Therefore, in the examples shown in Figures 6 and 7, for light with a wavelength of 530 nm, the phase of the reflected light LBS3 at the third interface BS3 is shifted by π (rad), which corresponds to half a wavelength, from the phase of the reflected light LBS2 at the second interface BS2.

[0155] In the examples shown in Figures 6 and 7, for light with a wavelength of 530 nm, the reflected light LBS3 at the third interface BS3 destructively interferes with the reflected light LBS2 at the second interface BS2, and reinforces the reflected light LBS1 at the first interface BS1. Therefore, with the installation of the second functional layer 36, which functions as a medium refractive index layer, the minimum reflectivity of the optical sheet 10 increases.

[0156] However, the minimum reflectivity of the optical sheet 10 can be reduced by adjusting the refractive index difference at the first interface BS1, the refractive index difference at the second interface BS2, and the refractive index difference at the third interface BS3.

[0157] As shown in Figure 7, the amplitude reflectance of reflected light LBS3 at the third interface BS3 (r3 × cosθ3) is symmetric to the amplitude reflectance of reflected light LBS2 at the second interface BS2 (r2 × cosθ2). That is, the amplitude reflectance of reflected light LBS3 at the third interface BS3 increases in the wavelength range where the amplitude reflectance of reflected light LBS3 at the second interface BS2 decreases. The amplitude reflectance of reflected light LBS3 at the third interface BS3 decreases in the wavelength range where the amplitude reflectance of reflected light LBS2 at the second interface BS2 increases. In particular, the reflected light LBS3 at the third interface BS3 cancels out the reflected light LBS1 at the first interface BS1 in the wavelength range where the amplitude reflectance of reflected light LBS2 at the second interface BS2 increases. More specifically, in the low wavelength range (380 nm to 415 nm) and the high wavelength range (700 nm to 780 nm) of the visible light wavelength range, the reflected light LBS3 at the third interface BS3 cancels out the reflected light LBS1 at the first interface BS1.

[0158] As a result, an optical sheet including a low refractive index layer, a medium refractive index layer, and a high refractive index layer, which can be realized by feature (A), can reduce reflectivity over a wide wavelength band. Conventional optical sheets showed increased reflectivity for both low-wavelength and high-wavelength visible light. An optical sheet including a low refractive index layer, a medium refractive index layer, and a high refractive index layer, which can be realized by feature (A), can effectively reduce reflectivity for both low-wavelength and high-wavelength visible light. In other words, an optical sheet including a low refractive index layer, a medium refractive index layer, and a high refractive index layer, which can be realized by feature (A), can suppress changes in reflectivity depending on wavelength over a wide wavelength band.

[0159] Therefore, the observation of color in the optical sheet can be suppressed. In particular, in the example shown in Figure 7, the reflectance can be reduced across the entire visible light wavelength range. Changes in reflectance depending on the wavelength in the visible light wavelength range can be suppressed. Therefore, the coloration of the optical sheet can be effectively suppressed. Even when observed at a large observation angle, the coloration of the optical sheet can be suppressed.

[0160] Furthermore, as shown in Figure 24, Patent Document 1 (JP2008-262187A), which describes prior art, proposes an optical sheet 120 containing a low refractive index layer 121, a high refractive index layer 122, and a medium refractive index layer 123 in that order. Compared with this optical sheet 120, the reflective properties of the optical sheet containing the low refractive index layer, medium refractive index layer, and high refractive index layer that can be realized by feature (A) are superior.

[0161] In the optical sheet 120, the refractive index of the high refractive index layer 122 is greater than that of the medium refractive index layer 123, and the refractive index of the medium refractive index layer 123 is greater than that of the low refractive index layer 121. As shown in Figure 24, light incident on the optical sheet 120 from the first surface 11 is mainly reflected at the first interface BS1, the second interface BS2, and the third interface BS3. The reflected light from the optical sheet 10 is the sum of the reflected light LBS1 at the first interface BS1, the reflected light LBS2 at the second interface BS2, and the reflected light LBS3 at the third interface BS3.

[0162] The total reflectance r, considering the interference of reflected light LBS1, reflected light LBS2, and reflected light LBS3, is expressed as the amplitude reflectance given by equation (f): r = r1 + r2 × cosθ2 + r3 × cosθ3 ... equation (f)

[0163] In equation (f), "r1", "r2", and "r3" are the same as "r1", "r2", and "r3" in equation (c), respectively. In equation (f), "r1", "r2", and "r3" are reflectances (%) that do not take phase into consideration and are determined by the refractive indices of the two regions that form the interface.

[0164] In equation (f), "θ²" represents the phase difference (rad) of the reflected light LBS2 at the second interface BS2 with respect to the reflected light LBS1 at the first interface BS1. Specifically, it is expressed by the following equation (g). Equation (g) is determined in the same way as equations (b) and (d) above.

[0165]

[0166] In equation (f), "θ3" represents the phase difference (rad) between the reflected light LBS1 at the first interface BS1 and the reflected light LBS3 at the third interface BS3. Specifically, it is expressed by the following equation (h). Reflections at the first interface BS1 and the second interface BS2 are fixed-end reflections. Reflections at the third interface BS3 are free-end reflections. Therefore, the phase expressed by equation (h) is shifted by a further π than the phase expressed by equation (e).

[0167]

[0168] In equations (g) and (h), "λ" is the wavelength (nm) of the reflected light. In equations (g) and (h), "T121" is the thickness of the low refractive index layer 121. In equations (g) and (h), "n121" is the refractive index of the low refractive index layer 121. In equation (h), "T122" is the thickness of the high refractive index layer 122. In equation (h), "n122" is the refractive index of the high refractive index layer 122.

[0169] Figure 25 shows the amplitude reflectance expressed by equation (f). In the graph shown in Figure 25, the vertical axis represents amplitude reflectance (unit: none), and the horizontal axis represents wavelength (nm). The solid line in Figure 25 represents the overall amplitude reflectance "r" in equation (f). The dotted line in Figure 25 represents the reflectance "r1" in equation (f). That is, the dotted line in Figure 25 represents the reflectance of reflected light LBS1 at the first interface BS1. The dashed line in Figure 25 represents the reflectance "r2 × cosθ2" in equation (f). That is, the dashed line in Figure 25 represents the amplitude reflectance of reflected light LBS2 at the second interface BS2. The double dashed line in Figure 25 represents the reflectance "r3 × cosθ3" in equation (f). That is, the double dashed line in Figure 25 represents the amplitude reflectance of reflected light LBS3 at the third interface BS3.

[0170] In the examples shown in Figures 24 and 25, the thickness T121 of the low refractive index layer 121 was set to 100 nm. The refractive index n121 of the low refractive index layer 121 was set to 1.30. In the examples shown in Figures 24 and 25, the thickness T122 of the high refractive index layer 122 was set to 155 nm. The refractive index n122 of the high refractive index layer 122 was set to 1.67. In the examples shown in Figures 24 and 25, the refractive index n123 of the medium refractive index layer 123 was set to 1.58.

[0171] In the examples shown in Figures 24 and 25, for light with a wavelength of 520 nm, the phase of the reflected light LBS2 at the second interface BS2 is shifted by π (rad), which corresponds to half a wavelength, from the phase of the reflected light LBS1 at the first interface BS1. That is, in the examples shown in Figures 24 and 25, for light with a wavelength of 520 nm, the reflected light LBS2 at the second interface BS2 cancels out the reflected light LBS1 at the first interface BS1 the most. Furthermore, in the examples shown in Figures 24 and 25, across the entire visible light wavelength range, the reflected light LBS2 at the second interface BS2 cancels out the reflected light LBS1 at the first interface BS1.

[0172] In the examples shown in Figures 24 and 25, for light with a wavelength of 520 nm, the shortest optical path length when traveling back and forth through the high refractive index layer 122 in the first direction D1 is one wavelength. Furthermore, the reflection at the third interface BS3 is a free-end reflection, and the phase increases by π (rad), which corresponds to half a wavelength. Therefore, in the examples shown in Figures 6 and 7, for light with a wavelength of 520 nm, the phase of the reflected light LBS3 at the third interface BS3 is shifted by π (rad), which corresponds to half a wavelength, from the phase of the reflected light LBS2 at the second interface BS2.

[0173] In the examples shown in Figures 24 and 25, for light with a wavelength of 520 nm, the reflected light LBS3 at the third interface BS3 destructively interferes with the reflected light LBS2 at the second interface BS2. For light with a wavelength of 520 nm, the reflected light LBS3 at the third interface BS3 reinforces the reflected light LBS1 at the first interface BS1.

[0174] On the other hand, the amplitude reflectance (r3 × cosθ3) of the reflected light LBS3 at the third interface BS3 decreases in the visible light wavelength range shifted from 520 nm to both higher and lower wavelengths. The reflected light LBS3 at the third interface BS3 destructively interferes with the reflected light LBS1 at the first interface BS1 in the visible light wavelength range shifted from 520 nm to both higher and lower wavelengths.

[0175] As a result, the optical sheet 120, which includes a low refractive index layer 121, a high refractive index layer 122, and a medium refractive index layer 123 in this order, can be expected to suppress changes in spectral reflectance to some extent over a wide wavelength band.

[0176] However, as clearly shown in the graph in Figure 25, the amplitude reflectance of the reflected light LBS3 at the third interface BS3 (r3 × cosθ3) is not sufficiently symmetrical with the amplitude reflectance of the reflected light LBS2 at the second interface BS2 (r2 × cosθ2).

[0177] The amplitude reflectance (r² × cosθ²) of the reflected light LBS2, shown by the dashed line in Figure 25, has a minimum value around a wavelength of 520 nm. As the wavelength decreases from 520 nm within the visible light wavelength range, the amplitude reflectance of the reflected light LBS2 increases monotonically.

[0178] The amplitude reflectance (r3 × cosθ3) of the reflected light LBS3, shown by the dashed line in Figure 25, has a maximum value around a wavelength of 520 nm. Furthermore, the amplitude reflectance of the reflected light LBS3 has a minimum value around a wavelength of 400 nm. The amplitude reflectance of the reflected light LBS3 has a minimum value around a wavelength of 780 nm.

[0179] Therefore, as the wavelength decreases within the visible light wavelength range from 520 nm to 400 nm, the amplitude reflectance of reflected light LBS3 decreases monotonically. As the wavelength decreases further from 400 nm, the amplitude reflectance of reflected light LBS3 increases, similar to the amplitude reflectance of reflected light LBS2. As a result, the total reflectance, shown by the solid line in Figure 25, increases sharply as the wavelength decreases from around 420 nm.

[0180] Similarly, as the wavelength increases within the visible light wavelength range from 520 nm to 780 nm, the amplitude reflectance of reflected light LBS3 decreases monotonically. As the wavelength increases further beyond 780 nm, the amplitude reflectance of reflected light LBS3 increases, similar to the amplitude reflectance of reflected light LBS2. As a result, the total reflectance, shown by the solid line in Figure 25, increases sharply as the wavelength decreases from around 700 nm.

[0181] In the optical sheet 120 shown in Figure 24, the refractive index of the high refractive index layer 122 is greater than that of the medium refractive index layer 123. The high refractive index layer 122, together with the medium refractive index layer 123, forms a third interface BS3. Light LBS3 traveling through the high refractive index layer 122 and incident on the third interface BS3 undergoes free-end reflection at the third interface BS3. For the reflected light LBS2 at the second interface BS2 and the reflected light LBS3 at the third interface BS3 to cancel each other out, the thickness T122 of the high refractive index layer 122 must be about half the wavelength, not about 1 / 4 the wavelength. Therefore, the phase difference of light traveling back and forth through the high refractive index layer 122 changes significantly as it moves away from the wavelength intended for reflection suppression (520 nm in the example in Figure 25). As a result, the amplitude reflectance of the reflected light LBS3, shown by the dashed line in Figure 25, includes multiple extreme values.

[0182] In contrast, in the optical sheet 10 shown in Figure 6, which includes a low refractive index layer 31, a medium refractive index layer 36, and a high refractive index layer 15 in that order, all reflections at the first to third interfaces BS1 to BS3 are free-point reflections. Therefore, the thickness T31 of the first functional layer 31 and the thickness T36 of the second functional layer 36 can both be about 1 / 4 of the wavelength for which reflection suppression is intended.

[0183] Therefore, as shown by the dashed line in Figure 7, the amplitude reflectance of the reflected light LBS3 at the third interface BS3 may have a single extreme value in the visible light wavelength range. Consequently, the amplitude reflectance of the reflected light LBS3 decreases monotonically as the wavelength decreases within the visible light wavelength range from the wavelength at which it takes its maximum value within the visible light wavelength range. The amplitude reflectance of the reflected light LBS3 also decreases monotonically as the wavelength increases within the visible light wavelength range from the wavelength at which it takes its maximum value within the visible light wavelength range. As a result, compared to the overall amplitude reflectance shown by the solid line in Figure 25, the overall amplitude reflectance shown by the solid line in Figure 7 shows a significantly reduced change depending on the wavelength.

[0184] As explained above, the functional layer 20 containing hollow silica particles 33 and 38 functions as a low refractive index layer. The refractive index of the functional layer 20 containing hollow silica particles 33 and 38 is smaller than the refractive index of the adjacent region 15 adjacent to the functional layer 20 in the first direction D1 (the resin layer 40 in Figure 1 and the substrate 50 in Figure 2). Furthermore, according to feature (A), the functional layer 20 can be divided into a first functional layer 31 containing a large amount of Si elements and a first functional layer 31 containing a small amount of Si elements. According to feature (A), the functional layer 20 can be divided into a second functional layer 36 having a low refractive index and a first functional layer 31 having an even lower refractive index than the second functional layer 36.

[0185] According to feature (A), the optical sheet 10 includes a low refractive index layer (first functional layer 31), a medium refractive index layer (second functional layer 36), and a high refractive index layer (adjacent region 15 (resin layer 40 or substrate 50)) in order along the first direction D1 from the first surface 11. In other words, according to feature (A), the optical sheet 10 includes three adjacent layers in order along the first direction D1 from the first surface 11, with the refractive index gradually increasing.

[0186] An optical sheet including a low refractive index layer, a medium refractive index layer, and a high refractive index layer, which can be realized by feature (A), can reduce reflectivity over a wide wavelength range. Furthermore, it can suppress changes in reflectivity depending on the wavelength over a wide wavelength range. Therefore, it can suppress the observation of color in the optical sheet. In particular, it can reduce reflectivity over the entire visible light wavelength range. It can suppress changes in reflectivity depending on the wavelength in the visible light wavelength range. Therefore, it can effectively suppress the observation of color in the optical sheet. Even when observed at a large observation angle, it can effectively suppress the optical sheet from taking on color.

[0187] When light of the same wavelength is incident on an optical sheet at different angles of incidence, the reflectance changes depending on the angle of incidence. The reflectance when light of the same wavelength is incident on an object at different angles of incidence can be substantially the same as the reflectance when light of different wavelengths is incident on the object at the same angle of incidence. Therefore, when the range of incident angles of light incident on an optical sheet is wide, the reflectance on the optical sheet differs depending on the angle of incidence. An optical sheet having feature (A) can reduce reflectance in a wide wavelength band, thus reducing the reflectance of light incident from a wide range of incident angles. An optical sheet having feature (A) can suppress changes in reflectance depending on wavelength in a wide wavelength band, thus suppressing changes in reflectance depending on the angle of incidence of light incident from a wide range of incident angles.

[0188] As described above, the optical sheet may satisfy feature (Ax) instead of feature (A). Feature (Ax) provides the same effect as feature (A). (Ax): The second mean ratio is smaller than the first mean ratio.

[0189] <Feature B> The optical sheet may have feature (B). (B): The first ratio is 8.0% or more and 16% or less, and the second ratio is 1.5% or more and 4.5% or less.

[0190] In feature (B), upper and lower limits are set for the first ratio. In feature (B), upper and lower limits are set for the second ratio. In feature (B), the lower limit of the first ratio is greater than the upper limit of the second ratio. An optical sheet having feature (B) also has feature (A). In this respect, feature (B) makes it possible to reduce reflectivity over a wide wavelength band. Furthermore, feature (B) makes it possible to suppress changes in reflectivity depending on the wavelength over a wide wavelength band.

[0191] By setting upper and lower limits for the first ratio, the refractive index of the functional layer around the first position P1 can be adjusted. By setting upper and lower limits for the first ratio, the refractive index of the first functional layer among the functional layers can be adjusted.

[0192] By setting upper and lower limits for the second ratio, the refractive index of the functional layer around the second position P2 can be adjusted. By setting upper and lower limits for the second ratio, the refractive index of the second functional layer among the functional layers can be adjusted.

[0193] Feature (B) allows for the appropriate provision of reflected light LBS1 at the first interface BS1, reflected light LBS2 at the second interface BS2, and reflected light LBS3 at the third interface BS3. Therefore, with feature (B), the superposition of reflected light LBS1 at the first interface BS1, reflected light LBS2 at the second interface BS2, and reflected light LBS3 at the third interface BS3 allows for a more effective reduction of reflectivity over a wide wavelength range. Furthermore, with feature (B), changes in reflectivity depending on wavelength over a wide wavelength range can be more effectively suppressed. Therefore, the coloration of the optical sheet can be more effectively suppressed. In addition, since the optical sheet having feature (B) can reduce reflectivity over a wide wavelength range, the reflectivity of incident light from a wide range of incident angles can be reduced. Since the optical sheet having feature (B) can suppress changes in reflectivity depending on wavelength over a wide wavelength range, changes in reflectivity depending on the incident angle of incident light from a wide range of incident angles can be suppressed.

[0194] By setting a lower limit on the first ratio, the refractive index of the functional layer around the first position P1 can be reduced. By setting a lower limit on the first ratio, the refractive index of the first functional layer can be reduced. Therefore, by reducing the refractive index difference at the first interface BS1, the reflectance at the first interface BS1 can be reduced. As a result, by setting a lower limit on the first ratio, the reflection Y value can be reduced. By setting a lower limit on the first ratio, the reflection Y value can be stably kept below 1.0%. The first ratio may be 8.0% or higher, 8.5% or higher, 8.8% or higher, 9.0% or higher, 9.5% or higher, or 10% or higher.

[0195] By setting an upper limit on the first ratio, the refractive index difference at the first interface BS1 can be appropriately secured, thereby ensuring the reflected light LBS1 at the first interface BS1. As a result, reflection suppression utilizing the interference of reflected light at each interface can be expected over a wide wavelength band. In addition, by setting an upper limit on the first ratio, it is possible to suppress the amount of added particles from becoming excessive. Therefore, by setting an upper limit on the first ratio, the thickness of the functional layer and the first functional layer can be stabilized within the desired range. The first ratio may be 16% or less, 14% or less, 13% or less, 12% or less, or 11% or less.

[0196] The first ratio may be 8.0% or more and 16% or less, 8.5% or more and 16% or less, 8.8% or more and 16% or less, 9.0% or more and 16% or less, 9.5% or more and 16% or less, and 10% or more and 16% or less. The first ratio may be 8.0% or more and 14% or less, 8.5% or more and 14% or less, 8.8% or more and 14% or less, 9.0% or more and 14% or less, 9.5% or more and 14% or less, and 10% or more and 14% or less. The first ratio may be 8.0% or more and 13% or less, 8.5% or more and 13% or less, 8.8% or more and 13% or less, 9.0% or more and 13% or less, 9.5% or more and 13% or less, and 10% or more and 13% or less. The first ratio may be 8.0% or more and 12% or less, 8.5% or more and 12% or less, 8.8% or more and 12% or less, 9.0% or more and 12% or less, 9.5% or more and 12% or less, or 10% or more and 12% or less. The first ratio may be 8.0% or more and 11% or less, 8.5% or more and 11% or less, 8.8% or more and 11% or less, 9.0% or more and 11% or less, 9.5% or more and 11% or less, or 10% or more and 11% or less.

[0197] By setting a lower limit on the second ratio, the refractive index of the functional layer around the second position P2 can be reduced. Therefore, by increasing the refractive index difference at the third interface BS3, the reflected light LBS3 at the third interface BS3 can be appropriately secured. As a result, reflection suppression using the interference of reflected light at each interface can be expected over a wide wavelength band. In particular, by setting a lower limit on the second ratio in combination with the first ratio within the appropriate range described above, the reflected Y value can be reduced. For example, the reflected Y value can be stably reduced to 1.0% or less. The second ratio may be 1.5% or more, 2.0% or more, 2.1% or more, or 2.2% or more.

[0198] By setting an upper limit on the second ratio, the refractive index difference at the second interface BS2 can be appropriately secured, thereby ensuring adequate reflected light LBS2 at the second interface BS2. As a result, reflection suppression utilizing the interference of reflected light at each interface can be expected over a wide wavelength band. The second ratio may be 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, or 2.7% or less.

[0199] The second ratio may be between 1.5% and 4.5%, between 2.0% and 4.5%, between 2.1% and 4.5%, or between 2.2% and 4.5%. The second ratio may be between 1.5% and 4.0%, between 2.0% and 4.0%, between 2.1% and 4.0%, or between 2.2% and 4.0%. The second ratio may be between 1.5% and 3.5%, between 2.0% and 3.5%, between 2.1% and 3.5%, or between 2.2% and 3.5%. The second ratio may be between 1.5% and 3.0%, between 2.0% and 3.0%, between 2.1% and 3.0%, or between 2.2% and 3.0%. The second ratio may be between 1.5% and 2.7%, between 2.0% and 2.7%, between 2.1% and 2.7%, or between 2.2% and 2.7%.

[0200] As described above, the optical sheet may satisfy feature (Bx) instead of feature (B). Feature (Bx) provides the same effects as feature (B). The "first average ratio" in feature (Bx) may be set within the same numerical range as the "first ratio" in feature (B). The "second average ratio" in feature (Bx) may be set within the same numerical range as the "second ratio" in feature (B). (Bx): The first average ratio is 8.0% or more and 16% or less, and the second average ratio is 1.5% or more and 4.5% or less.

[0201] The first average ratio may be 8.0% or more and 16% or less, 8.5% or more and 16% or less, 8.8% or more and 16% or less, 9.0% or more and 16% or less, 9.5% or more and 16% or less, and 10% or more and 16% or less. The first average ratio may be 8.0% or more and 14% or less, 8.5% or more and 14% or less, 8.8% or more and 14% or less, 9.0% or more and 14% or less, 9.5% or more and 14% or less, and 10% or more and 14% or less. The first average ratio may be 8.0% or more and 13% or less, 8.5% or more and 13% or less, 8.8% or more and 13% or less, 9.0% or more and 13% or less, 9.5% or more and 13% or less, and 10% or more and 13% or less. The first average ratio may be 8.0% or more and 12% or less, 8.5% or more and 12% or less, 8.8% or more and 12% or less, 9.0% or more and 12% or less, 9.5% or more and 12% or less, or 10% or more and 12% or less. The first average ratio may be 8.0% or more and 11% or less, 8.5% or more and 11% or less, 8.8% or more and 11% or less, 9.0% or more and 11% or less, 9.5% or more and 11% or less, or 10% or more and 11% or less.

[0202] The second average ratio may be between 1.5% and 4.5%, between 2.0% and 4.5%, between 2.1% and 4.5%, or between 2.2% and 4.5%. The second average ratio may be between 1.5% and 4.0%, between 2.0% and 4.0%, between 2.1% and 4.0%, or between 2.2% and 4.0%. The second average ratio may be between 1.5% and 3.5%, between 2.0% and 3.5%, between 2.1% and 3.5%, or between 2.2% and 3.5%. The second average ratio may be between 1.5% and 3.0%, between 2.0% and 3.0%, between 2.1% and 3.0%, or between 2.2% and 3.0%. The second average ratio may be between 1.5% and 2.7%, between 2.0% and 2.7%, between 2.1% and 2.7%, or between 2.2% and 2.7%.

[0203] <Feature C> The optical sheet may have feature (C). (C): The ratio of the second ratio to the first ratio is 0.094 or more and 0.58 or less.

[0204] In feature (C), upper and lower limits are set for the ratio of the second ratio to the first ratio. The ratio of the second ratio to the first ratio is calculated by dividing the second ratio by the first ratio and has no units. In feature (C), the ratio of the second ratio to the first ratio is less than 1. An optical sheet having feature (C) also has feature (A). In this respect, feature (C) allows for a reduction in reflectivity over a wide wavelength band. Furthermore, feature (C) allows for the suppression of changes in reflectivity depending on the wavelength over a wide wavelength band.

[0205] By setting upper and lower limits on the ratio of the second ratio to the first ratio, the refractive index difference at the second interface BS2 can be appropriately adjusted. Therefore, the amount of reflected light LBS2 at the second interface BS2 can be appropriately adjusted in relation to the reflected light LBS1 at the first interface BS1 and the reflected light LBS3 at the third interface BS3.

[0206] According to feature (C), the superposition of reflected light LBS1 at the first interface BS1, reflected light LBS2 at the second interface BS2, and reflected light LBS3 at the third interface BS3 allows for a more effective reduction of reflectivity over a wide wavelength range. Furthermore, according to feature (C), changes in reflectivity depending on the wavelength over a wide wavelength range can be more effectively suppressed. Therefore, the observation of color on the optical sheet can be more effectively suppressed. In addition, since the optical sheet having feature (C) can reduce reflectivity over a wide wavelength range, the reflectivity of incident light from a wide range of incident angles can be reduced. Since the optical sheet having feature (C) can suppress changes in reflectivity depending on the wavelength over a wide wavelength range, changes in reflectivity depending on the incident angle of incident light from a wide range of incident angles can be suppressed.

[0207] By setting an upper limit on the ratio of the second ratio to the first ratio, a sufficient refractive index difference at the second interface BS2 can be ensured. Therefore, a sufficient amount of reflected light LBS2 at the second interface BS2 can be ensured. The ratio of the second ratio to the first ratio may be 0.58 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.25 or less, or 0.23 or less.

[0208] By setting a lower limit on the ratio of the second ratio to the first ratio, the refractive index difference at the second interface BS2 can be reduced. Therefore, reflection at the second interface BS2 can be appropriately suppressed. The ratio of the second ratio to the first ratio may be 0.094 or higher, 0.10 or higher, 0.15 or higher, 0.17 or higher, 0.20 or higher, or 0.21 or higher.

[0209] The ratio of the second ratio to the first ratio may be 0.094 or more and 0.58 or less, 0.094 or more and 0.50 or less, 0.094 or more and 0.40 or less, 0.094 or more and 0.30 or less, 0.094 or more and 0.25 or less, or 0.094 or more and 0.23 or less. The ratio of the second ratio to the first ratio may be 0.10 or more and 0.58 or less, 0.10 or more and 0.50 or less, 0.10 or more and 0.40 or less, 0.10 or more and 0.30 or less, 0.10 or more and 0.25 or less, or 0.10 or more and 0.23 or less. The ratio of the second ratio to the first ratio may be 0.15 or more and 0.58 or less, 0.15 or more and 0.50 or less, 0.15 or more and 0.40 or less, 0.15 or more and 0.30 or less, 0.15 or more and 0.25 or less, or 0.15 or more and 0.23 or less. The ratio of the second ratio to the first ratio may be 0.17 or more and 0.58 or less, 0.17 or more and 0.50 or less, 0.17 or more and 0.40 or less, 0.17 or more and 0.30 or less, 0.17 or more and 0.25 or less, or 0.17 or more and 0.23 or less. The ratio of the second ratio to the first ratio may be 0.20 or more and 0.58 or less, 0.20 or more and 0.50 or less, 0.20 or more and 0.40 or less, 0.20 or more and 0.30 or less, 0.20 or more and 0.25 or less, or 0.20 or more and 0.23 or less. The ratio of the second ratio to the first ratio may be 0.21 or more and 0.58 or less, 0.21 or more and 0.50 or less, 0.21 or more and 0.40 or less, 0.21 or more and 0.30 or less, 0.21 or more and 0.25 or less, or 0.21 or more and 0.23 or less.

[0210] As described above, the optical sheet may satisfy feature (Cx) instead of feature (C). Feature (Cx) provides the same effects as feature (C). The "ratio of the second average ratio to the first average ratio" in feature (Cx) may be set to the same numerical range as the "ratio of the second ratio to the first ratio" in feature (C). (Cx): The ratio of the second average ratio to the first average ratio is between 0.094 and 0.58.

[0211] The ratio of the second mean ratio to the first mean ratio may be 0.094 or more and 0.58 or less, 0.094 or more and 0.50 or less, 0.094 or more and 0.40 or less, 0.094 or more and 0.30 or less, 0.094 or more and 0.25 or less, or 0.094 or more and 0.23 or less. The ratio of the second mean ratio to the first mean ratio may be 0.10 or more and 0.58 or less, 0.10 or more and 0.50 or less, 0.10 or more and 0.40 or less, 0.10 or more and 0.30 or less, 0.10 or more and 0.25 or less, or 0.10 or more and 0.23 or less. The ratio of the second mean ratio to the first mean ratio may be 0.15 or more and 0.58 or less, 0.15 or more and 0.50 or less, 0.15 or more and 0.40 or less, 0.15 or more and 0.30 or less, 0.15 or more and 0.25 or less, or 0.15 or more and 0.23 or less. The ratio of the second mean ratio to the first mean ratio may be 0.17 or more and 0.58 or less, 0.17 or more and 0.50 or less, 0.17 or more and 0.40 or less, 0.17 or more and 0.30 or less, 0.17 or more and 0.25 or less, or 0.17 or more and 0.23 or less. The ratio of the second mean ratio to the first mean ratio may be 0.20 or more and 0.58 or less, 0.20 or more and 0.50 or less, 0.20 or more and 0.40 or less, 0.20 or more and 0.30 or less, 0.20 or more and 0.25 or less, or 0.20 or more and 0.23 or less. The ratio of the second mean ratio to the first mean ratio may be 0.21 or more and 0.58 or less, 0.21 or more and 0.50 or less, 0.21 or more and 0.40 or less, 0.21 or more and 0.30 or less, 0.21 or more and 0.25 or less, or 0.21 or more and 0.23 or less.

[0212] <Feature D> The optical sheet may have feature (D). (D): The value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less.

[0213] In feature (D), upper and lower limits are set for the value obtained by subtracting the second ratio from the first ratio. The value obtained by subtracting the second ratio from the first ratio is expressed using the unit "%", similar to the first and second ratios. In feature (D), the value obtained by subtracting the second ratio from the first ratio is greater than 0. An optical sheet having feature (D) also has feature (A). In this respect, feature (D) allows for a reduction in reflectivity over a wide wavelength band. Furthermore, feature (D) allows for the suppression of changes in reflectivity depending on the wavelength over a wide wavelength band.

[0214] By setting upper and lower limits on the value obtained by subtracting the second ratio from the first ratio, the refractive index difference at the second interface BS2 can be appropriately adjusted. Therefore, the amount of reflected light LBS2 at the second interface BS2 can be appropriately adjusted in relation to the reflected light LBS1 at the first interface BS1 and the reflected light LBS3 at the third interface BS3.

[0215] According to feature (D), the superposition of reflected light LBS1 at the first interface BS1, reflected light LBS2 at the second interface BS2, and reflected light LBS3 at the third interface BS3 allows for a more effective reduction of reflectivity over a wide wavelength range. Furthermore, according to feature (D), the change in reflectivity depending on the wavelength over a wide wavelength range can be more effectively suppressed. Therefore, the observation of color on the optical sheet can be more effectively suppressed. In addition, since the optical sheet having feature (D) can reduce reflectivity over a wide wavelength range, the reflectivity of incident light from a wide range of incident angles can be reduced. Since the optical sheet having feature (D) can suppress the change in reflectivity depending on the wavelength over a wide wavelength range, the change in reflectivity depending on the incident angle of incident light from a wide range of incident angles can be suppressed.

[0216] By setting a lower limit on the value obtained by subtracting the second ratio from the first ratio, a sufficient refractive index difference at the second interface BS2 can be ensured. Therefore, a sufficient amount of reflected light LBS2 at the second interface BS2 can be ensured. The value obtained by subtracting the second ratio from the first ratio may be 3.5% or more, 5.0% or more, 6.0% or more, 7.0% or more, 7.3% or more, or 8.4% or more.

[0217] By setting an upper limit on the value obtained by subtracting the second ratio from the first ratio, the refractive index difference at the second interface BS2 can be reduced. Therefore, reflection at the second interface BS2 can be appropriately suppressed. The value obtained by subtracting the second ratio from the first ratio may be 14.5% or less, 12.5% ​​or less, 11% or less, 10% or less, or 9.2% or less.

[0218] The value obtained by subtracting the second ratio from the first ratio may be 3.5% or more and 14.5% or less, 5.0% or more and 14.5% or less, 6.0% or more and 14.5% or less, 7.0% or more and 14.5% or less, 7.3% or more and 14.5% or less, or 8.4% or more and 14.5% or less. The value obtained by subtracting the second ratio from the first ratio may be 3.5% or more and 12.5% ​​or less, 5.0% or more and 12.5% ​​or less, 6.0% or more and 12.5% ​​or less, 7.0% or more and 12.5% ​​or less, 7.3% or more and 12.5% ​​or less, or 8.4% or more and 12.5% ​​or less. The value obtained by subtracting the second ratio from the first ratio may be 3.5% or more and 11% or less, 5.0% or more and 11% or less, 6.0% or more and 11% or less, 7.0% or more and 11% or less, 7.3% or more and 11% or less, or 8.4% or more and 11% or less. The value obtained by subtracting the second ratio from the first ratio may be 3.5% or more and 10% or less, 5.0% or more and 10% or less, 6.0% or more and 10% or less, 7.0% or more and 10% or less, 7.3% or more and 10% or less, or 8.4% or more and 10% or less. The value obtained by subtracting the second ratio from the first ratio may be 3.5% or more and 9.2% or less, 5.0% or more and 9.2% or less, 6.0% or more and 9.2% or less, 7.0% or more and 9.2% or less, 7.3% or more and 9.2% or less, or 8.4% or more and 9.2% or less.

[0219] As described above, the optical sheet may satisfy feature (Dx) instead of feature (D). Feature (Dx) provides the same effects as feature (D). The value obtained by subtracting the second average ratio from the first average ratio in feature (Dx) may be set to the same numerical range as the value obtained by subtracting the second ratio from the first ratio in feature (D). (Dx): The value obtained by subtracting the second average ratio from the first average ratio is between 3.5% and 14.5%.

[0220] The value obtained by subtracting the second average ratio from the first average ratio may be 3.5% or more and 14.5%, 5.0% or more and 14.5%, 6.0% or more and 14.5%, 7.0% or more and 14.5%, 7.3% or more and 14.5%, or 8.4% or more and 14.5%. The value obtained by subtracting the second average ratio from the first average ratio may be 3.5% or more and 12.5%, 5.0% or more and 12.5%, 6.0% or more and 12.5%, 7.0% or more and 12.5%, 7.3% or more and 12.5%, or 8.4% or more and 12.5%. The value obtained by subtracting the second average ratio from the first average ratio may be 3.5% or more and 11% or less, 5.0% or more and 11% or less, 6.0% or more and 11% or less, 7.0% or more and 11% or less, 7.3% or more and 11% or less, or 8.4% or more and 11% or less. The value obtained by subtracting the second average ratio from the first average ratio may be 3.5% or more and 10% or less, 5.0% or more and 10% or less, 6.0% or more and 10% or less, 7.0% or more and 10% or less, 7.3% or more and 10% or less, or 8.4% or more and 10% or less. The value obtained by subtracting the second average ratio from the first average ratio may be 3.5% or more and 9.2% or less, 5.0% or more and 9.2% or less, 6.0% or more and 9.2% or less, 7.0% or more and 9.2% or less, 7.3% or more and 9.2% or less, or 8.4% or more and 9.2% or less.

[0221] In the examples shown in Figures 1 to 3, the low refractive index layer is composed of a first functional layer 31 containing hollow silica particles 33, and the medium refractive index layer is composed of a second functional layer 36 containing hollow silica particles 38. The refractive index of the first functional layer 31 can be adjusted with a high degree of freedom by changing the amount of hollow silica particles 33 added. The refractive index of the second functional layer 36 can be adjusted with a high degree of freedom by changing the amount of hollow silica particles 38 added. In other words, by including a first functional layer 31 containing hollow silica particles 33 and a second functional layer 36 containing hollow silica particles 38 in the optical sheet 10, one or more of the above-mentioned features (A) to (D) and features (Ax) to (Dx) can be easily and stably realized. Therefore, by using a first functional layer 31 containing hollow silica particles 33 and a second functional layer 36 containing hollow silica particles 38, an optical sheet with excellent reflective properties can be manufactured with high productivity.

[0222] <<Reflection Characteristics>> According to the above-described features (A) to (D) and features (Ax) to (Dx), excellent reflection characteristics can be obtained. Figure 8 shows the spectral reflectance on the first surface of the optical sheet according to Examples 2 to 4 described later. Figures 9 to 11 show the spectral reflectance on the first surface of the optical sheet according to Examples 2 to 4 described later for various incident angles. The optical sheet according to this embodiment may have the following characteristics regarding reflection characteristics.

[0223] The method for measuring spectral reflectance, that is, the method for measuring reflectance for each wavelength, is as follows. First, cut out a sample from the optical sheet to be evaluated. Visually check the sample for any abnormalities such as dust or scratches. A black plate is attached to the surface of the sample, which is formed by the second surface of the optical sheet, via an optical transparent adhesive sheet. The optical transparent adhesive sheet is "Panaclean PD-S1" manufactured by Panac Co., Ltd. The black plate is "Comoglass DFA2CG 502K (black) series" manufactured by Kuraray Co., Ltd. The thickness of the black plate is 2 mm. The total light transmittance of the black plate is 0% or more and 1% or less. Based on the above, evaluation sample A including the optical sheet, optical transparent adhesive sheet, and black plate is prepared.

[0224] The test environment for measuring spectral reflectance shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Evaluation sample A shall be placed in the test environment for 16 hours before the start of the test. Before measuring spectral reflectance, the light source of the measuring device (auxiliary illuminant C, described later) shall be turned on for 15 minutes to stabilize the output of the light source.

[0225] The reflectance for each wavelength as spectral reflectance is the reflectance Y value. The reflectance Y value is also called luminous reflectance. The reflectance Y value is the Y value of the tristimulus values ​​XYZ in the CIE 1931 standard color system. The reflectance Y value is the reflectance of specularly reflected light. The reflectance Y value is measured using a spectrophotometer. When measuring the reflectance Y value, light is shone at an incident angle of 5° onto the surface of evaluation sample A, which is composed of the first surface of an optical sheet. The reflectance (reflection Y value) of the evaluation sample is measured based on the specularly reflected light from evaluation sample A. The reflectance Y value is measured using an auxiliary illuminant C and a 2-degree field of view. Other measurement conditions when measuring the reflectance Y value follow JIS Z 8722:2009.

[0226] The wavelengths used for measuring spectral reflectance are those at 0.5 nm intervals, including integer wavelengths within the wavelength range to be evaluated. For example, "maximum spectral reflectance at the first surface in the range of 380 nm to 480 nm" means the maximum luminous reflectance Y value measured for light at wavelengths (nm) in 0.5 nm intervals from 380 nm to 480 nm. "Minimum spectral reflectance at the first surface in the range of 380 nm to 480 nm" means the minimum luminous reflectance Y value measured for light at wavelengths (nm) in 0.5 nm intervals from 380 nm to 480 nm.

[0227] The spectral reflectance is the arithmetic mean of five measurements. The five measurements are taken at five different locations on the sample. The five measurement locations are located at least 10 mm apart from each other.

[0228] <Feature (E)> The optical sheet may have feature (E). (E): The difference between the maximum and minimum spectral reflectance of the first surface at wavelengths of 380 nm to 480 nm is 0.60% or less.

[0229] In feature (E) and features (F), (G), (I), and (J) described later, an upper limit is set on the value obtained by subtracting the minimum value of spectral reflectance (%) from the maximum value of spectral reflectance (%). The value obtained by subtracting the minimum value of spectral reflectance from the maximum value of spectral reflectance is expressed using the unit "%", just like the maximum value and the minimum value of spectral reflectance.

[0230] As shown in Figures 23 and 25, in conventional optical sheets, the reflectance increases in the low wavelength range of the visible light wavelength range. Also, in conventional optical sheets, the reflectance changes significantly in the low wavelength range of the visible light wavelength range. On the other hand, as shown in Figures 8 to 11, the optical sheet according to this embodiment can reduce the reflectance in the low wavelength range of the visible light wavelength range, as defined in feature (E). The optical sheet according to this embodiment can suppress changes in reflectance in the low wavelength range of the visible light wavelength range, as defined in feature (E).

[0231] In feature (E), an upper limit is set on the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 480 nm. By setting an upper limit on the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 480 nm, it is possible to suppress the deposition of color on the optical sheet, for example, the optical sheet appearing blue. The difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 480 nm may be 0.60% or less, 0.50% or less, 0.40% or less, 0.30% or less, 0.25% or less, 0.23% or less, or 0.21% or less.

[0232] There is no lower limit set for the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 480 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 480 nm may be 0% or greater, or it may be greater than 0%.

[0233] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 480 nm may be 0% to 0.60%, 0% to 0.50%, 0% to 0.40%, 0% to 0.30%, 0% to 0.25%, 0% to 0.23%, or 0% to 0.21%. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 480 nm may be greater than 0% and 0.60% or less, greater than 0% and 0.50% or less, greater than 0% and 0.40% or less, greater than 0% and 0.30% or less, greater than 0% and 0.25% or less, greater than 0% and 0.23%, or greater than 0% and 0.21% or less.

[0234] <Feature (F)> The optical sheet may have feature (F). (F): The difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 680 nm to 780 nm is 0.30% or less.

[0235] As shown in Figures 23 and 25, in conventional optical sheets, the reflectance increases in the high wavelength range of the visible light wavelength range. Also, in conventional optical sheets, the reflectance changes significantly in the high wavelength range of the visible light wavelength range. On the other hand, as shown in Figures 8 to 11, the optical sheet according to this embodiment can reduce the reflectance in the high wavelength range of the visible light wavelength range, as defined by feature (F). The optical sheet according to this embodiment can suppress changes in reflectance in the high wavelength range of the visible light wavelength range, as defined by feature (F).

[0236] In feature (F), an upper limit is set on the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 680 nm to 780 nm. By setting an upper limit on the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 680 nm to 780 nm, it is possible to suppress the deposition of color on the optical sheet, for example, the optical sheet appearing red. The difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 680 nm to 780 nm may be 0.30% or less, 0.28% or less, 0.26% or less, 0.25% or less, or 0.21% or less.

[0237] There is no lower limit set for the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 680 nm to 780 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 680 nm to 780 nm may be 0% or greater, or it may be greater than 0%.

[0238] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 680 nm to 780 nm may be 0% to 0.30%, 0% to 0.28%, 0% to 0.26%, 0% to 0.25%, or 0% to 0.21%. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 680 nm to 780 nm may be greater than 0% and 0.30%, greater than 0% and 0.28%, greater than 0% and 0.26%, greater than 0% and 0.25%, or greater than 0% and 0.21%.

[0239] <Feature (G)> The optical sheet may have feature (G). (G): The difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 380 nm to 780 nm is 1.0% or less.

[0240] As shown in Figures 23 and 25, in conventional optical sheets, the reflectance increases in both the low-wavelength and high-wavelength regions of the visible light spectrum. Furthermore, in conventional optical sheets, the reflectance changes significantly in both the low-wavelength and high-wavelength regions of the visible light spectrum. On the other hand, as shown in Figures 8 to 11, the optical sheet according to this embodiment can reduce the reflectance in both the low-wavelength and high-wavelength regions of the visible light spectrum, as defined in feature (G). The optical sheet according to this embodiment can suppress changes in reflectance in both the low-wavelength and high-wavelength regions of the visible light spectrum, as defined in feature (G).

[0241] In feature (G), an upper limit is set on the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 780 nm. By setting an upper limit on the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 780 nm, it is possible to suppress the optical sheet from taking on a color tint. The difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 780 nm may be 1.0% or less, 0.80% or less, 0.59% or less, 0.50% or less, 0.40% or less, or 0.29% or less.

[0242] There is no lower limit set for the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 780 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 780 nm may be 0% or greater, or it may be greater than 0%.

[0243] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 780 nm may be 0% to 1.0%, 0% to 0.80%, 0% to 0.59%, 0% to 0.50%, 0% to 0.40%, or 0% to 0.29%. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 780 nm may be greater than 0% and 1.0%, greater than 0% and 0.80%, greater than 0% and 0.59%, greater than 0% and 0.50%, greater than 0% and 0.40%, or greater than 0% and 0.29%.

[0244] <Feature (H)> The optical sheet may have feature (H). (H): The maximum spectral reflectance of the first surface at wavelengths of 380 nm to 780 nm is 1.5% or less.

[0245] As shown in Figures 23 and 25, in conventional optical sheets, reflectance increases in both the low-wavelength and high-wavelength regions of the visible light spectrum. On the other hand, as shown in Figures 8 to 11, the optical sheet according to this embodiment can reduce reflectance in both the low-wavelength and high-wavelength regions of the visible light spectrum, as defined in feature (H).

[0246] In feature (H), an upper limit is set on the maximum spectral reflectance of the first surface in the wavelength range of 380 nm to 780 nm. By setting an upper limit on the maximum spectral reflectance of the first surface in the wavelength range of 380 nm to 780 nm, it is possible to suppress the optical sheet from taking on a color tint. The maximum spectral reflectance of the first surface in the wavelength range of 380 nm to 780 nm may be 1.5% or less, 1.2% or less, 1.0% or less, 0.91% or less, 0.71% or less, or 0.53% or less.

[0247] There is no lower limit set for the maximum spectral reflectance of the first surface in the wavelength range of 380 nm to 780 nm. The maximum spectral reflectance of the first surface in the wavelength range of 380 nm to 780 nm may be 0% or greater, or it may be greater than 0%.

[0248] The maximum spectral reflectance of the first surface at wavelengths of 380 nm to 780 nm may be 0% to 1.5%, 0% to 1.2%, 0% to 1.0%, 0% to 0.91%, 0% to 0.71%, or 0% to 0.53%. The maximum spectral reflectance of the first surface at wavelengths of 380 nm to 780 nm may be greater than 0% and 1.5%, greater than 0% and 1.2%, greater than 0% and 1.0%, greater than 0% and 0.91%, greater than 0% and 0.71%, or greater than 0% and 0.53%.

[0249] <Feature (I)> The optical sheet may have feature (I). (I): The difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 300 nm to 380 nm is 1.3% or less.

[0250] As shown in Figures 23 and 25, in conventional optical sheets, the reflectance increases in the low wavelength range. Also, in conventional optical sheets, the reflectance changes significantly in the low wavelength range. On the other hand, as shown in Figure 8, the optical sheet according to this embodiment can reduce the reflectance in the ultraviolet wavelength range, as defined in feature (I). The optical sheet according to this embodiment can suppress changes in reflectance in the ultraviolet wavelength range, as defined in feature (I).

[0251] In feature (I), an upper limit is set on the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 300 nm to 380 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 300 nm to 380 nm may be 1.3% or less, 1.2% or less, 1.1% or less, 1.0% or less, 0.9% or less, or 0.80% or less.

[0252] There is no lower limit set for the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 300 nm to 380 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 300 nm to 380 nm may be 0% or greater, or it may be greater than 0%.

[0253] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 300 nm to 380 nm may be 0% to 1.3%, 0% to 1.2%, 0% to 1.1%, 0% to 1.0%, 0% to 0.9%, or 0% to 0.80%. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 300 nm to 380 nm may be greater than 0% and 1.3% or less, greater than 0% and 1.2% or less, greater than 0% and 1.1% or less, greater than 0% and 1.0% or less, greater than 0% and 0.9%, or greater than 0% and 0.80% or less.

[0254] <Feature (J)> The optical sheet may have feature (J). (J): The difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 780 nm to 900 nm is 0.60% or less.

[0255] As shown in Figures 23 and 25, in conventional optical sheets, the reflectivity increases in the high wavelength range. Also, in conventional optical sheets, the reflectivity changes significantly in the high wavelength range. On the other hand, as shown in Figure 8, with the optical sheet according to this embodiment, as defined in feature (J), the reflectivity can be reduced in the near-infrared wavelength range. With the optical sheet according to this embodiment, as defined in feature (J), the change in reflectivity in the near-infrared wavelength range can be suppressed.

[0256] In feature (J), an upper limit is set on the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm may be 0.60% or less, 0.50% or less, 0.40% or less, 0.35% or less, 0.34% or less, or 0.33% or less.

[0257] There is no lower limit set for the difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm may be 0% or greater, or it may be greater than 0%.

[0258] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm may be 0% to 0.60%, 0% to 0.50%, 0% to 0.40%, 0% to 0.35%, 0% to 0.34%, or 0% to 0.33%. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm may be greater than 0% and 0.60%, greater than 0% and 0.50%, greater than 0% and 0.40%, greater than 0% and 0.35%, greater than 0% and 0.34%, or greater than 0% and 0.33%.

[0259] <Feature (K)> The optical sheet may have feature (K). (K): The reflection Y value on the first surface is 2.5% or less.

[0260] The first reflection Y value of the optical sheet may be 2.5% or less, 2.0% or less, 1.5% or less, 1.1% or less, 0.81% or less, or 0.79% or less. There is no particular lower limit to the reflection Y value on the first surface of the optical sheet. The reflection Y value on the first surface of the optical sheet may be 0% or more, or greater than 0%.

[0261] The first reflection Y value of the optical sheet may be 0% or more and 2.5% or less, 0% or more and 2.0% or less, 0% or more and 1.5% or less, 0% or more and 1.1% or less, 0% or more and 0.81% or less, or 0% or more and 0.79% or less. The first reflection Y value of the optical sheet may be greater than 0% and 2.5% or less, greater than 0% and 2.0% or less, greater than 0% and 1.5% or less, greater than 0% and 1.1% or less, greater than 0% and 0.81% or less, or greater than 0% and 0.79% or less.

[0262] The reflected Y value is also called the luminous reflectance. The reflected Y value is the Y value of the tristimulus values ​​XYZ in the CIE 1931 standard color system. The reflected Y value is the reflectance of specularly reflected light. The reflected Y value is measured using a spectrophotometer as follows:

[0263] Using the optical sheet to be evaluated, an evaluation sample A is prepared in the same manner as when measuring spectral reflectance.

[0264] The test environment for measuring the reflectance Y value shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Evaluation sample A shall be placed in the test environment for 16 hours before the start of the test. Before measuring the reflectance Y value, the light source of the measuring device (auxiliary illuminant C, described later) shall be turned on for 15 minutes to stabilize the output of the light source.

[0265] When measuring the reflected Y value, light is shone at an incident angle of 5° onto the surface of evaluation sample A, which is composed of the first surface of the optical sheet. Based on the specular reflected light from evaluation sample A, the reflected Y value of the evaluation sample is measured. Using an auxiliary illuminant C and a 2-degree field of view, the luminous reflectance Y (%) is determined from the specular reflectance measured at 0.5 nm intervals in the range from 300 nm to 900 nm. Other measurement conditions when measuring the reflected Y value follow JIS Z 8722:2009.

[0266] The reflection Y value is the arithmetic mean of the five measured values. The five measured values ​​are taken at five different measurement locations on the sample. The five measurement locations are located at least 10 mm apart from each other.

[0267] <Features (L) and (M)> The optical sheet may have at least one of features (L) and (M). (L): 1a ＊ Value and 2a ＊ The absolute value of the difference from the value is 2.0 or less. (M): 1st b ＊ Value and 2b ＊ The absolute value of the difference from the given value is 4.0 or less.

[0268] As shown in Figures 23 and 25, conventional optical sheets exhibit a significant change in reflectivity in the visible light wavelength range. This change in reflectivity with respect to wavelength becomes more pronounced as the angle of incidence increases. Therefore, when conventional optical sheets are observed at a large observation angle, the sheets may appear colored. On the other hand, as shown in Figures 8 to 11, the optical sheet according to this embodiment can suppress the change in reflectivity in the visible light wavelength range.

[0269] Feature (L) "1a ＊ The value is L, measured by specular reflection from the first surface at an incident angle of 5°. ＊ a ＊ b ＊ a color system ＊ This is a value. Feature (L) "2a ＊ The value is L, measured by specular reflection from the first surface at an incident angle of 60°. ＊ a ＊ b ＊ a color system ＊It is a value. Feature (M) "1st b ＊ The value is L, measured by specular reflection from the first surface at an incident angle of 5°. ＊ a ＊ b ＊ color system b ＊ This is a value. The "2nd b" in Feature (M) ＊ The value is L, measured by specular reflection from the first surface at an incident angle of 60°. ＊ a ＊ b ＊ color system b ＊ It is a value.

[0270] L ＊ a ＊ b ＊ The color system is defined in CIE 1976. ＊ a ＊ b ＊ a color system ＊ Value and b ＊ The values ​​are measured using a spectrophotometer as follows:

[0271] Using the optical sheet to be evaluated, an evaluation sample A is prepared in the same manner as when measuring spectral reflectance.

[0272] a ＊ Value and b ＊ The test environment for measuring the values ​​shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Evaluation sample A shall be placed in the test environment for 16 hours before the start of the test. Before measuring the reflectance Y value, the light source of the measuring device (auxiliary illuminant C, described later) shall be turned on for 15 minutes to stabilize the output of the light source.

[0273] Light is shone onto the surface of evaluation sample A, which is composed of the first surface of the optical sheet. Based on the specular reflected light from evaluation sample A, the a of the evaluation sample is determined. ＊ Value and b ＊ The value is measured. Using an auxiliary illuminant C and a 2-degree field of view, the specular reflectance is measured at 0.5 nm intervals in the range from 300 nm to 900 nm, and L is measured based on this value. ＊ a ＊ b ＊ a in the color system ＊ Value and b ＊ Find the value. 1a ＊ Value and 1b ＊The value is measured with an incident angle of 5°. Second a ＊ value and second b ＊ value are measured with an incident angle of 60°. a ＊ value and b ＊ Other measurement conditions when measuring the values shall comply with JIS Z 8722:2009.

[0274] First a ＊ value, second a ＊ value, first b ＊ value, and second b ＊ values shall each be the arithmetic mean value of five measured values. The five measured values shall be the measured values at five measurement positions of the measurement sample. At each measurement position, first a ＊ value, second a ＊ value, first b ＊ value, and second b ＊ values are each measured.

[0275] In feature (L), an upper limit is set for the absolute value of the difference between first a ＊ value and second a ＊ value. By setting an upper limit for the absolute value of the difference between first a ＊ value and second a ＊ value, it is possible to suppress the change in the color tone of the optical sheet when the observation angle is changed. First a ＊ value and second a ＊ The absolute value of the difference between value may be 2.0 or less, 1.8 or less, 1.6 or less, 1.4 or less, 1.2 or less, 1.0 or less.

[0276] First a ＊ value and second a ＊ value. No lower limit is particularly set for the absolute value of the difference between first a ＊ value and second a ＊ value. The absolute value of the difference between first a

[0277] value and second a ＊ value may be 0 or more, greater than 0. ＊ The absolute value of the difference between value may be 0 or more and 2.0 or less, 0 or more and 1.8 or less, 0 or more and 1.6 or less, 0 or more and 1.4 or less, 0 or more and 1.2 or less, 0 or more and 1.0 or less. First a ＊ value and second a＊ The absolute value of the difference from the value may be greater than 0 and not more than 2.0, may be greater than 0 and not more than 1.8, may be greater than 0 and not more than 1.6, may be greater than 0 and not more than 1.4, may be greater than 0 and not more than 1.2, or may be greater than 0 and not more than 1.0.

[0278] In feature (L), the first b ＊ value and the second b ＊ An upper limit is set for the absolute value of the difference from the value. For the first b ＊ value and the second b ＊ By setting an upper limit for the absolute value of the difference from the value, it is possible to suppress the change in the color tone of the optical sheet when the observation angle is changed. For the first b ＊ value and the second b ＊ The absolute value of the difference from the value may be not more than 4.0, may be not more than 3.7, may be not more than 3.1, may be not more than 2.7, may be not more than 2.4, or may be not more than 1.8.

[0279] The first b ＊ value and the second b ＊ No particular lower limit is set for the absolute value of the difference from the value. For the first b ＊ value and the second b ＊ The absolute value of the difference from the value may be 0 or more, or may be greater than 0.

[0280] The first b ＊ value and the second b ＊ The absolute value of the difference from the value may be from 0 to 4.0, may be from 0 to 3.7, may be from 0 to 3.1, may be from 0 to 2.7, may be from 0 to 2.4, or may be from 0 to 1.8. For the first b ＊ value and the second b ＊ The absolute value of the difference from the value may be greater than 0 and not more than 4.0, may be greater than 0 and not more than 3.7, may be greater than 0 and not more than 3.1, may be greater than 0 and not more than 2.7, may be greater than 0 and not more than 2.4, or may be greater than 0 and not more than 1.8.

[0281] <<Refractive Index and Thickness>> As shown in Figures 1 to 3, the functional layer 20 may include a first functional layer 31 and a second functional layer 36. As shown in Figures 1 and 2, the first functional layer 31 includes a binder component 32 and hollow silica particles 33. The inclusion of hollow silica particles 33 reduces the refractive index of the first functional layer 31. The second functional layer 36 includes a binder component 37 and hollow silica particles 38. The inclusion of hollow silica particles 38 reduces the refractive index of the second functional layer 36.

[0282] The functional layer 20 may include a first functional layer 31 and a second functional layer 36 in order from the first surface 11 to the second surface 12 of the optical sheet 10. The second functional layer 36 may be located between the first functional layer 31 and the substrate 50 in the first direction D1. The second functional layer 36 may be located between the first functional layer 31 and the resin layer 40 in the first direction D1.

[0283] The refractive index n31 of the first functional layer 31 may be smaller than the refractive index n36 of the second functional layer 36. The refractive index n36 of the second functional layer 36 may be smaller than the refractive index of the adjacent region 15 adjacent to the second functional layer 36 from the second side in the first direction D1. In the example shown in Figure 1, the refractive index n36 of the second functional layer 36 may be smaller than the refractive index of the resin layer 40. In the example shown in Figure 2, the refractive index n36 of the second functional layer 36 may be smaller than the refractive index of the substrate 50.

[0284] With reference to the above-mentioned effects and benefits explained with reference to Figures 6 and 7, etc., namely, the reduction of reflectance over a wide wavelength band and the suppression of changes in reflectance over a wide wavelength band, the thickness and refractive index of each layer included in the optical sheet may be set as follows.

[0285] The functional layer 20 may be located at least between the first surface 11 along the first direction D1 and a position 150 nm closer to the second surface from the first surface 11 along the first direction D1. The functional layer 20 may be located at least between the first surface 11 along the first direction D1 and a position 160 nm closer to the second surface from the first surface 11 along the first direction D1. The functional layer 20 may be located at least between the first surface 11 along the first direction D1 and a position 170 nm closer to the second surface from the first surface 11 along the first direction D1. The functional layer 20 may be located at least between the first surface 11 along the first direction D1 and a position 190 nm closer to the second surface from the first surface 11 along the first direction D1. The functional layer 20 may be located at least between the first surface 11 along the first direction D1 and a position 200 nm closer to the second surface from the first surface 11 along the first direction D1. The functional layer 20 may constitute the first surface 11 of the optical sheet 10.

[0286] The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm or more, 150 nm or more, 160 nm or more, 170 nm or more, 180 nm or more, 190 nm or more, or 200 nm or more. The thickness T20 of the functional layer 20 (see Figure 3) may be 280 nm or less, 270 nm or less, 260 nm or less, 250 nm or less, 240 nm or less, 230 nm or less, or 220 nm or less.

[0287] The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm to 280 nm, 150 nm to 280 nm, 160 nm to 280 nm, 170 nm to 280 nm, 180 nm to 280 nm, 190 nm to 280 nm, or 200 nm to 280 nm. The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm to 270 nm, 150 nm to 270 nm, 160 nm to 270 nm, 170 nm to 270 nm, 180 nm to 270 nm, 190 nm to 270 nm, or 200 nm to 270 nm. The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm to 260 nm, 150 nm to 260 nm, 160 nm to 260 nm, 170 nm to 260 nm, 180 nm to 260 nm, 190 nm to 260 nm, or 200 nm to 260 nm. The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm to 250 nm, 150 nm to 250 nm, 160 nm to 250 nm, 170 nm to 250 nm, 180 nm to 250 nm, 190 nm to 250 nm, or 200 nm to 250 nm. The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm to 240 nm, 150 nm to 240 nm, 160 nm to 240 nm, 170 nm to 240 nm, 180 nm to 240 nm, 190 nm to 240 nm, or 200 nm to 240 nm. The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm to 230 nm, 150 nm to 230 nm, 160 nm to 230 nm, 170 nm to 230 nm, 180 nm to 230 nm, 190 nm to 230 nm, or 200 nm to 230 nm.The thickness T20 of the functional layer 20 (see Figure 3) may be 140 nm or more and 220 nm or less, 150 nm or more and 220 nm or less, 160 nm or more and 220 nm or less, 170 nm or more and 220 nm or less, 180 nm or more and 220 nm or less, 190 nm or more and 220 nm or less, or 200 nm or more and 220 nm or less.

[0288] The thickness T31 of the first functional layer 31 (see Figure 3) may be 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, or 105 nm or more. The thickness T31 of the first functional layer 31 (see Figure 3) may be 135 nm or less, 130 nm or less, 120 nm or less, or 110 nm or less.

[0289] The thickness T31 of the first functional layer 31 (see Figure 3) may be 60 nm to 135 nm, 70 nm to 135 nm, 80 nm to 135 nm, 90 nm to 135 nm, 100 nm to 135 nm, or 105 nm to 135 nm. The thickness T31 of the first functional layer 31 (see Figure 3) may be 60 nm to 130 nm, 70 nm to 130 nm, 80 nm to 130 nm, 90 nm to 130 nm, 100 nm to 130 nm, or 105 nm to 130 nm. The thickness T31 of the first functional layer 31 (see Figure 3) may be 60 nm to 120 nm, 70 nm to 120 nm, 80 nm to 120 nm, 90 nm to 120 nm, 100 nm to 120 nm, or 105 nm to 120 nm. The thickness T31 of the first functional layer 31 (see Figure 3) may be 60 nm to 110 nm, 70 nm to 110 nm, 80 nm to 110 nm, 90 nm to 110 nm, 100 nm to 110 nm, or 105 nm to 110 nm.

[0290] The thickness T36 of the second functional layer 36 (see Figure 3) may be 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 95 nm or more. The thickness T31 of the first functional layer 31 (see Figure 3) may be 125 nm or less, 120 nm or less, 110 nm or less, or 100 nm or less.

[0291] The thickness T36 of the second functional layer 36 (see Figure 3) may be 50 nm to 125 nm, 60 nm to 125 nm, 70 nm to 125 nm, 80 nm to 125 nm, 90 nm to 125 nm, or 95 nm to 125 nm. The thickness T36 of the second functional layer 36 (see Figure 3) may be 50 nm to 120 nm, 60 nm to 120 nm, 70 nm to 120 nm, 80 nm to 120 nm, 90 nm to 120 nm, or 95 nm to 120 nm. The thickness T36 of the second functional layer 36 (see Figure 3) may be 50 nm to 110 nm, 60 nm to 110 nm, 70 nm to 110 nm, 80 nm to 110 nm, 90 nm to 110 nm, or 95 nm to 110 nm. The thickness T36 of the second functional layer 36 (see Figure 3) may be 50 nm to 100 nm, 60 nm to 100 nm, 70 nm to 100 nm, 80 nm to 100 nm, 90 nm to 100 nm, or 95 nm to 100 nm.

[0292] The refractive index of the first functional layer 31 may be 1.15 or higher, 1.18 or higher, 1.20 or higher, 1.21 or higher, or 1.25 or higher. The refractive index of the first functional layer 31 may be 1.45 or lower, 1.40 or lower, 1.35 or lower, 1.33 or lower, or 1.29 or lower.

[0293] The refractive index of the first functional layer 31 may be 1.15 or more and 1.45 or less, 1.18 or more and 1.45 or less, 1.20 or more and 1.45 or less, 1.21 or more and 1.45 or less, or 1.25 or more and 1.45 or less. The refractive index of the first functional layer 31 may be 1.15 or more and 1.40 or less, 1.18 or more and 1.40 or less, 1.20 or more and 1.40 or less, 1.21 or more and 1.40 or less, or 1.25 or more and 1.40 or less. The refractive index of the first functional layer 31 may be 1.15 or more and 1.35 or less, 1.18 or more and 1.35 or less, 1.20 or more and 1.35 or less, 1.21 or more and 1.35 or less, or 1.25 or more and 1.35 or less. The refractive index of the first functional layer 31 may be 1.15 or more and 1.33 or less, 1.18 or more and 1.33 or less, 1.20 or more and 1.33 or less, 1.21 or more and 1.33 or less, or 1.25 or more and 1.33 or less. The refractive index of the first functional layer 31 may be 1.15 or more and 1.29 or less, 1.18 or more and 1.29 or less, 1.20 or more and 1.29 or less, 1.21 or more and 1.29 or less, or 1.25 or more and 1.29 or less.

[0294] The refractive index of the second functional layer 36 may be 1.25 or higher, 1.30 or higher, 1.35 or higher, 1.40 or higher, or 1.44 or higher. The refractive index of the second functional layer 36 may be 1.55 or lower, 1.50 or lower, 1.48 or lower, or 1.45 or lower.

[0295] The refractive index of the second functional layer 36 may be 1.25 or more and 1.55 or less, 1.30 or more and 1.55 or less, 1.35 or more and 1.55 or less, 1.40 or more and 1.55 or less, or 1.44 or more and 1.55 or less. The refractive index of the second functional layer 36 may be 1.25 or more and 1.50 or less, 1.30 or more and 1.50 or less, 1.35 or more and 1.50 or less, 1.40 or more and 1.50 or less, or 1.44 or more and 1.50 or less. The refractive index of the second functional layer 36 may be 1.25 or more and 1.48 or less, 1.30 or more and 1.48 or less, 1.35 or more and 1.48 or less, 1.40 or more and 1.48 or less, or 1.44 or more and 1.48 or less. The refractive index of the second functional layer 36 may be 1.25 or more and 1.45 or less, 1.30 or more and 1.45 or less, 1.35 or more and 1.45 or less, 1.40 or more and 1.45 or less, or 1.44 or more and 1.45 or less.

[0296] The refractive index of the adjacent region 15 of the optical sheet 10 adjacent to the second functional layer 36 from the second side in the first direction D1 may be 1.40 or higher, 1.45 or higher, 1.50 or higher, or 1.53 or higher. The refractive index of the adjacent region 15 may be 1.65 or lower, 1.60 or lower, 1.57 or lower, or 1.55 or lower.

[0297] The refractive index of the adjacent region 15 of the optical sheet 10 adjacent to the second functional layer 36 from the second side in the first direction D1 may be 1.40 or more and 1.65 or less, 1.45 or more and 1.65 or less, 1.50 or more and 1.65 or less, or 1.53 or more and 1.65 or less. The refractive index of the adjacent region 15 of the optical sheet 10 adjacent to the second functional layer 36 from the second side in the first direction D1 may be 1.40 or more and 1.60 or less, 1.45 or more and 1.60 or less, 1.50 or more and 1.60 or less, or 1.53 or more and 1.60 or less. The refractive index of the adjacent region 15 of the optical sheet 10 adjacent to the second functional layer 36 from the second side in the first direction D1 may be 1.40 or more and 1.57 or less, 1.45 or more and 1.57 or less, 1.50 or more and 1.57 or less, or 1.53 or more and 1.57 or less. The refractive index of the adjacent region 15 of the optical sheet 10 adjacent to the second functional layer 36 from the second side in the first direction D1 may be 1.40 or more and 1.55 or less, 1.45 or more and 1.55 or less, 1.50 or more and 1.55 or less, or 1.53 or more and 1.55 or less.

[0298] <Feature N> The optical sheet may have features (N) relating to thickness and refractive index. (N): The thickness T31 of the first functional layer 31, the thickness T36 of the second functional layer 36, the refractive index n31 of the first functional layer 31, and the refractive index n36 of the second functional layer 36 satisfy the following formula (i).

[0299]

[0300] For the optical sheet 10 shown in Figure 6, the amplitude reflectance when the first surface 11 is the incident surface is expressed by the above-mentioned equation (c). An example of the amplitude reflectance expressed by equation (c) is shown by a solid line in Figure 7. The dashed line in Figure 7 shows the amplitude reflectance of the reflected light LBS2 at the second interface BS2, with reference to the phase of the reflected light LBS1 at the first interface BS1. The double dashed line in Figure 7 shows the amplitude reflectance of the reflected light LBS3 at the third interface BS3, with reference to the phase of the reflected light LBS1 at the first interface BS1.

[0301] As described above, when the amplitude reflectance of reflected light LBS3 does not contain a minimum value in the visible light wavelength range, the reflectance can be reduced across the entire visible light wavelength range, and changes in reflectance in the visible light wavelength range can be suppressed. The phase of reflected light LBS3 at the third interface BS3, with respect to the phase of amplitude reflected light LBS1 at the first interface BS1, is expressed by equation (e) above. By making the difference between the phase of reflected light LBS3 at a wavelength of 380 nm and the phase of reflected light LBS3 at a wavelength of 780 nm less than 2π (rad), it is possible to suppress the amplitude reflectance of reflected light LBS3 from containing a minimum value in the visible light wavelength range. And, when equation (i) is satisfied, the difference between the phase of reflected light LBS3 for light at a wavelength of 380 nm and the phase of reflected light LBS3 for light at a wavelength of 780 nm becomes less than 2π (rad).

[0302] In other words, according to feature (N), the reflectance can be reduced across the entire visible light wavelength range, and changes in reflectance in the visible light wavelength range can be suppressed.

[0303] <Feature O> The optical sheet may have the following feature (O) relating to thickness and refractive index: (O): The thickness T31 of the first functional layer, the thickness T36 of the second functional layer, the refractive index n31 of the first functional layer, the refractive index n36 of the second functional layer, and k, which is an integer of 0 or more, satisfy the following equations (j) and (k).

[0304]

[0305] When equation (j) is satisfied, the difference between the phase of the reflected light LBS3 at wavelength 780 nm and the phase of the reflected light LBS3 at the visible light wavelength where the amplitude reflectance is maximum is less than π (rad). In other words, when equation (j) is satisfied, the amplitude reflectance will not be minimum at wavelengths between the visible light wavelength where the amplitude reflectance is maximum and 780 nm.

[0306] When equation (k) is satisfied, the difference between the phase of the reflected light LBS3 at wavelength 380 nm and the phase of the reflected light LBS3 at the visible light wavelength where the amplitude reflectance is maximum is less than π (rad). In other words, when equation (k) is satisfied, the amplitude reflectance will not be minimum at wavelengths between the visible light wavelength where the amplitude reflectance is maximum and 380 nm.

[0307] In other words, when equations (j) and (k) are satisfied, the amplitude reflectance of the reflected light LBS3 does not contain a minimum value in the visible light wavelength range. Therefore, according to feature (O), the reflectance can be reduced over the entire visible light wavelength range, and changes in reflectance in the visible light wavelength range can be suppressed.

[0308] <Feature P> The optical sheet may have features (P) relating to its thickness and refractive index. (P): The thickness T31 of the first functional layer 31, the thickness T36 of the second functional layer 36, the refractive index n31 of the first functional layer 31, and the refractive index n36 of the second functional layer 36 satisfy the following equations (l) and (m).

[0309]

[0310] Equation (l) is the same as equation (j) defined in feature (O), but with "k" set to 0. Equation (m) is the same as equation (k) defined in feature (O), but with "k" set to 0. When equations (l) and (m) are satisfied, the thickness T31 of the first functional layer 31 and the thickness T36 of the second functional layer 36 can be made sufficiently small. Therefore, even if the observation angle is large, the optical path length of the reflected light LBS3 is short, which makes it possible to more effectively suppress the coloration of the optical sheet.

[0311] From the above, when equations (l) and (m) are satisfied, the amplitude reflectance of the reflected light LBS3 does not contain a minimum value in the visible light wavelength range. Furthermore, the thickness T31 of the first functional layer 31 and the thickness T36 of the second functional layer 36 can be made sufficiently small. As a result, according to feature (P), the reflectance can be reduced over the entire visible light wavelength range, and changes in reflectance in the visible light wavelength range can be suppressed. Moreover, according to feature (P), the coloration of the optical sheet can be suppressed more effectively.

[0312] (Method for measuring thickness) The "thickness" used for each layer 20, 31, 36, 40, and 50 contained in the optical sheet is the dimension along the first direction D1. The "thickness" shall be the value specified by (A1) to (A3) below.

[0313] (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.

[0314] (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 that are not included in the same observation image as the central position.

[0315] (A3) Perform the above steps (A1) and (A2) three times on the layer to be measured, and measure the thickness of the layer to be measured at a total of nine measurement positions. The average of the total nine thickness measurements shall be taken as the thickness of the layer to be measured.

[0316] (Observation image of optical sheet) The observation image of the cross-section of the optical sheet used for thickness measurement shall be the image obtained as follows.

[0317] First, a sample is cut from the optical sheet to be measured. The sample size should be 1 mm x 10 mm when observed from the direction normal to the optical sheet. This sample is embedded in embedding resin. The embedding resin is a cold-curing type two-part epoxy resin. The embedding resin is cured by leaving it at room temperature for 24 hours or more to prepare the embedded sample. Sections are cut from the embedded sample using an ultramicrotome. The thickness of the sections should be between 70 nm and 300 nm, which is appropriate for observation with a scanning transmission electron microscope. The sections obtained using a scanning transmission electron microscope are observed to acquire an observation image of the cross-section of the optical sheet.

[0318] As an example of a scanning transmission electron microscope that can be used to acquire observation images, the Hitachi High-Technologies Corporation's S4800 scanning transmission electron microscope is provided. When using this microscope, the detector may be set to "TE", the acceleration voltage to "30 kV", and the emission current to "10 μA". The magnification can be set to a magnification that allows each layer to be distinguished, for example, 10,000x to 100,000x, while adjusting the focus, contrast, and brightness. Furthermore, the condenser lens may be set to "5.0" and the W.D. to "8.8 mm".

[0319] (Method for measuring refractive index) The refractive index used for the constituent elements of the optical sheet shall be the refractive index at a wavelength of 589.3 nm.

[0320] The refractive index of the materials constituting each 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 measurement. The "Abbe Refractometer D-M2" manufactured by Atago Co., Ltd. can be used as the Abbe refractometer.

[0321] <<Total Light Transmittance>> The total light transmittance of the 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 the optical sheet. The total light transmittance of the optical sheet may be 100% or less, or less than 100%.

[0322] The total light transmittance of the optical sheet may be 50% or more and 100%, 70% or more and 100%, 80% or more and 100%, 90% or more and 100%, or 95% or more and 100%. The total light transmittance of the 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%.

[0323] For measuring total light transmittance, a light source that mimics the spectrum of the D65 standard light (also simply called the "D65 light source") is used. Before measuring total light transmittance, the D65 light source is lit for 15 minutes to stabilize its output. The angle of incidence to the sample when measuring 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 test environment when measuring total light transmittance is 23°C ± 2°C and 50% ± 5% relative humidity. The sample is placed in the test environment for 16 hours before the start of the test. Other measurement conditions when measuring total light transmittance follow JIS K7361-1:1997.

[0324] 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.

[0325] <<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%.

[0326] The transmitted 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 transmitted 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.

[0327] For measuring transmitted haze, a light source that mimics the spectrum of the D65 standard light (also simply called the "D65 light source") is used. Before measuring transmitted haze, the D65 light source is lit for 15 minutes to stabilize its output. The angle of incidence to the sample when measuring transmitted haze is 0°. The incident surface when measuring transmitted haze on an optical sheet is the second surface of the optical sheet. The test environment when measuring transmitted haze is 23°C ± 2°C and 50% ± 5% relative humidity. The sample is placed in the test environment for 16 hours before the start of the test. Other measurement conditions when measuring transmitted haze follow JIS K7136:2000.

[0328] The transmitted haze is defined as the arithmetic mean of five measurements. The five measurements are taken at five different locations on the optical sheet being evaluated. The five measurement locations are spaced at least 10 mm apart from each other.

[0329] <<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 functional layer 20, a resin layer 40, and a base material 50, extending from the first surface 11 to the second surface 12. The optical sheet 10 shown in Figure 2 includes a functional layer 20 and a base material 50, extending from the first surface 11 to the second surface 12. In the optical sheet 10 shown in Figures 1 and 2, the functional layer 20 includes a first functional layer 31 and a second functional layer 36, extending from the first surface 11 to the second surface 12.

[0330] The first direction D1 is the lamination direction. The functional layer 20, the first functional layer 31, the second functional layer 36, the resin layer 40, and the substrate 50 extend in the second direction D2 and the third direction D3, which are perpendicular to the first direction D1. In the illustrated example, the second direction D1 and the third direction D3 are perpendicular to each other. In the optical sheet 10 shown in Figure 1, the first surface 11 is composed of the functional layer 20.

[0331] The optical sheet 10 may have a different layer configuration than that shown in Figures 1 and 2. The optical sheet 10 may include one or more antistatic layers and antifouling layers. The antistatic layer and antifouling layer may be supported by the functional layer 20 to constitute the first surface 11.

[0332] <Substrate> The substrate supports the functional layer and the resin layer. The substrate may be transparent. Transparency means that the total light transmittance is 50% or more, and the total light transmittance may be 70% or more, 80% or more, or 90% or more.

[0333] 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.

[0334] The resin used for the base material may be a polyolefin 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 a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate. 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, norbornene, and cycloolefin resins obtained from cycloolefins such as dicyclopentadiene. The base material may contain only one of the above-mentioned resins, or it may contain two or more of the above-mentioned resins.

[0335] The base material may contain raw materials derived from biomass. The base material may contain resins derived from biomass and resins derived from fossil fuels. By using raw materials derived from biomass, the environmental impact can be reduced.

[0336] The base material may contain polyester derived from biomass materials. The base material may contain polyethylene terephthalate derived from biomass materials. The base material may contain both polyester derived from biomass materials and polyester derived from fossil fuels. Examples of polyester derived from biomass materials include polyester in which at least a portion of the raw material monomers are monomers derived from biomass materials such as plants. Examples of the above-mentioned plants include sugarcane and corn.

[0337] 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.

[0338] The thickness of the resin substrate may be 10 μm or more and 500 μm or less, 20 μm or more and 500 μm or less, or 50 μm or more and 500 μm or less. The thickness of the resin substrate may be 10 μm or more and 400 μm or less, 20 μm or more and 400 μm or less, or 50 μm or more and 400 μm or less. The thickness of the resin substrate may be 10 μm or more and 300 μm or less, 20 μm or more and 300 μm or less, or 50 μm or more and 300 μm or less.

[0339] In the application of optical sheets to foldable applications, the substrate may be flexible. In this example, the thickness of the resin substrate may be between 10 μm and 40 μm. When the optical sheet is used laminated with glass, the thickness of the resin substrate may be between 40 μm and 100 μm from the viewpoint of preventing glass from shattering.

[0340] The substrate may consist of only a single layer or multiple layers. The substrate may also consist of a primer layer such as an easy-adhesion layer.

[0341] 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.

[0342] <Functional Layer> The functional layer contains a binder component and hollow silica particles. As described above, the functional layer may include a first functional layer and a second functional layer. The first functional layer may contain a binder component and hollow silica particles. The second functional layer may contain a binder component and hollow silica particles.

[0343] The binder component used in the first functional layer may be the same as the binder component used in the second functional layer. The binder component used in the first functional layer may be different from the binder component used in the second functional layer.

[0344] The particle size and particle size distribution of the hollow silica particles used in the first functional layer may be the same as those of the hollow silica particles used in the second functional layer. Alternatively, the particle size and particle size distribution of the hollow silica particles used in the first functional layer may differ from those of the hollow silica particles used in the second functional layer.

[0345] The proportion of hollow silica particles contained in the first functional layer (e.g., by mass%) may be greater than the proportion of hollow silica particles contained in the first functional layer. By increasing the proportion of hollow silica particles, the refractive index can be reduced.

[0346] The functional layer, the first functional layer, and the second functional layer may contain additives. Examples of additives include refractive index modifiers, dyes, pigments, leveling agents, UV absorbers, antioxidants, and light stabilizers. The binder component holds the additives.

[0347] (Binder component) The binder component is an element that holds hollow silica particles. The binder component may also function as a binder for coating film formation. The functional layer, the first functional layer, and the second functional layer may maintain their film shape by holding the particles contained in the functional layer, the first functional layer, and the second functional layer. The binder component may contain a resin. The resin contained in the binder component may be a natural resin or a synthetic resin. The binder component may encase the particles contained in the functional layer, the first functional layer, and the second functional layer. The binder component may completely enclose each particle contained in the functional layer, the first functional layer, and the second functional layer, or it may partially expose at least some of the particles contained in the functional layer, the first functional layer, and the second functional layer.

[0348] The binder component may include 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 be an ionizing radiation curable resin composition. The binder component may include at least one of a cured product of a thermosetting resin composition and a cured product of an ionizing radiation curable resin composition. The cured resin product imparts high strength and high hardness to the functional layer, the first functional layer, and the second functional layer, and can improve the scratch resistance of the first surface. Ionizing radiation curable resin compositions are particularly useful from the viewpoint of improving scratch resistance.

[0349] A thermosetting resin composition contains a thermosetting resin. The thermosetting resin composition hardens upon heating. Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, unsaturated polyester resins, and silicone resins. The thermosetting resin composition may also contain a curing agent.

[0350] The ionizing radiation-curable resin composition contains an ionizing radiation-curable compound. The ionizing radiation-curable compound contains an ionizing radiation-curable functional group. Examples of 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. The ionizing radiation-curable compound may contain two or more ionizing radiation-curable functional groups. The ionizing radiation-curable compound may also be a compound having an ethylenically unsaturated bonding group. The ionizing radiation-curable compound may also be a (meth)acrylate compound having a (meth)acryloyl group. The ionizing radiation-curable compound may also be a siloxane compound containing a siloxane bond.

[0351] (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."

[0352] 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 surfaces of the functional layer, the first functional layer, and the second functional layer.

[0353] The weight-average molecular weight of the monomer may be greater than 0 and less than 1000, greater than 0 and 800 or less, or greater than 0 and 600 or less. The weight-average molecular weight of the oligomer may be between 1500 and 20000, between 2000 and 15000, or between 3000 and 12000. The weight-average molecular weight is the average molecular weight measured by GPC analysis and converted to standard polystyrene.

[0354] Ionizing radiation can be electromagnetic waves or charged particle beams. Ionizing radiation has energy quanta that can polymerize or bridge molecules. Examples of ionizing radiation include ultraviolet (UV) rays, electron beams (EB), X-rays, gamma rays, alpha rays, and ion beams.

[0355] 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 surface irregularities of the functional layer, the first functional layer, and 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 surfaces of the functional layer, the first functional layer, and the second functional layer can be smoothed by appropriately adjusting the type of solvent and drying conditions, as described later.

[0356] 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.

[0357] 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.

[0358] (Meth)acrylate compounds may have a part of their molecular skeleton modified to suppress uneven shrinkage due to crosslinking. (Meth)acrylate compounds may be modified with, for example, ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc. The above (meth)acrylate compounds may be modified with alkylene oxides such as ethylene oxide and propylene oxide. The proportion of alkylene oxide-modified (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. The alkylene oxide-modified (meth)acrylate compounds may be low-functional (meth)acrylate compounds or (meth)acrylate compounds having two ethylenically unsaturated bonding groups.

[0359] Examples of (meth)acrylate compounds having two ethylenically unsaturated bonding groups modified with alkylene oxide include bisphenol F alkylene oxide-modified di(meth)acrylate, bisphenol A alkylene oxide-modified di(meth)acrylate, isocyanuric acid alkylene oxide-modified di(meth)acrylate, and polyalkylene glycol di(meth)acrylate. The average repeating units of the alkylene glycol contained in polyalkylene glycol di(meth)acrylate may be 3 to 5. The alkylene glycol contained in polyalkylene glycol di(meth)acrylate may be ethylene glycol and / or polyethylene glycol. Examples of (meth)acrylate compounds having three ethylenically unsaturated bonding groups modified with alkylene oxide include trimethylolpropane alkylene oxide-modified tri(meth)acrylate and isocyanuric acid alkylene oxide-modified tri(meth)acrylate.

[0360] Examples of siloxane compounds include (poly)dimethylsiloxane, (poly)diethylsiloxane, (poly)diphenylsiloxane, (poly)methylphenylsiloxane, alkyl-modified (poly)dimethylsiloxane, azo group-containing (poly)dimethylsiloxane, dimethyl silicone, phenylmethyl silicone, alkyl / aralkyl-modified silicone, fluorosilicone, polyether-modified silicone, fatty acid ester-modified silicone, methyl hydrogen silicone, silanol-containing silicone, alkoxy-containing silicone, phenol-containing silicone, methacrylic-modified silicone, acrylic-modified silicone, amino-modified silicone, carboxylic acid-modified silicone, carbinol-modified silicone, epoxy-modified silicone, mercapto-modified silicone, fluorine-modified silicone, and polyether-modified silicone.

[0361] The binder component may contain one ionizing radiation-curable compound alone, or it may contain two or more ionizing radiation-curable compounds.

[0362] When the ionizing radiation-curable compound is an ultraviolet-curable compound, the curable resin composition that forms the binder component 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, benzyldimethyl ketal, benzoyl benzoate, 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.

[0363] (Hollow Silica Particles and Other Particles) 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 inside the hollow space. Hollow silica particles have a refractive index lower than that of silica due to the presence of an internal cavity. The refractive index of hollow silica particles decreases as the volume of the internal cavity increases. Hollow silica particles reduce the refractive index of the functional layer, the first functional layer, and the second functional layer. By using hollow silica particles with a larger particle size that have a higher proportion of internal space, the refractive index of the functional layer, the first functional layer, and the second functional layer can be further reduced.

[0364] The average particle diameter of hollow silica particles may be 50 nm to 100 nm, 50 nm to 90 nm, or 50 nm to 80 nm. The average particle diameter of hollow silica particles may be 55 nm to 100 nm, 55 nm to 90 nm, or 55 nm to 80 nm. The average particle diameter of hollow silica particles may be 60 nm to 100 nm, 60 nm to 90 nm, or 60 nm to 80 nm. The average particle diameter of hollow silica particles may be 65 nm to 100 nm, 65 nm to 90 nm, or 65 nm to 80 nm.

[0365] The "average particle diameter" used for particles such as hollow silica particles shall be the value specified by (B1) to (B3) below. Although particles may aggregate, the average particle diameter is the average primary particle diameter. (B1) Observe the cross-section of the optical sheet containing the particles with a scanning transmission electron microscope (STEM) and acquire an observation image by imaging. The observation image of the cross-section of the optical sheet shall be the image acquired in the same manner as when measuring the thickness. (B2) Extract any 10 particles from the observation image and measure the particle diameter of each individual particle. The particle diameter (nm) is the maximum distance between two parallel lines when the particle is sandwiched between them. In other words, the particle diameter is the maximum length of the particle in the observation image. The particle diameter is specified as the particle diameter (maximum length) of each individual particle. That is, the particle diameter is the primary particle diameter. (B3) Perform the above steps (1) and (2) five times on the same optical sheet to be measured and measure the particle diameter of a total of 50 particles. The average of 50 particle size measurements is taken as the average particle size (nm) of the particle in question.

[0366] As the proportion of hollow silica particles increases, the refractive index of the functional layer, the first functional layer, and the second functional layer decreases. The proportion of hollow silica particles may be adjusted so that the above-mentioned refractive index is achieved.

[0367] The content of hollow silica particles may be 100 parts by mass or more and 400 parts by mass or 150 parts by mass or 400 parts by mass or 175 parts by mass or more and 400 parts by mass relative to the binder component by mass. The content of hollow silica particles may be 100 parts by mass or more and 300 parts by mass or 150 parts by mass or 300 parts by mass or 175 parts by mass or more and 300 parts by mass relative to 100 parts by mass of the binder component. The content of hollow silica particles may be 100 parts by mass or more and 250 parts by mass or 150 parts by mass or 250 parts by mass or 175 parts by mass or more relative to 100 parts by mass of the binder component.

[0368] The content of hollow silica particles may be 5 to 200 parts by mass, 5 to 150 parts by mass, or 5 to 100 parts by mass per 100 parts by mass of binder component. The content of hollow silica particles may be 10 to 200 parts by mass, 10 to 150 parts by mass, or 10 to 100 parts by mass per 100 parts by mass of binder component. The content of hollow silica particles may be 20 to 200 parts by mass, 20 to 150 parts by mass, or 20 to 100 parts by mass per 100 parts by mass of binder component.

[0369] The functional layer, the first functional layer, and the second functional layer may contain particles other than hollow silica particles. The functional layer, the first functional layer, and the second functional layer may contain inorganic particles other than hollow silica particles. The functional layer, the first functional layer, and the second functional layer may contain magnesium fluoride particles in addition to hollow silica particles. The functional layer, the first functional layer, and the second functional layer may contain metal oxide particles other than hollow silica particles. The functional layer, the first functional layer, and the second functional layer may contain solid silica particles in addition to hollow silica particles. The functional layer, the first functional layer, and the second functional layer may contain organic particles in addition to hollow silica particles.

[0370] Solid silica particles are non-hollow silica particles. Solid silica particles are particles that do not have internal cavities. Solid silica particles may also be solid silica particles.

[0371] The average particle size of solid silica particles is generally smaller than that of hollow silica particles. Therefore, solid silica particles can fit between adjacent hollow silica particles within the functional layer, the first functional layer, and the second functional layer. By containing solid silica particles in appropriate proportions within the functional layer, the first functional layer, and the second functional layer, hollow silica particles can be uniformly dispersed within the functional layer, the first functional layer, and the second functional layer.

[0372] The average particle size of solid silica particles is not particularly limited. The average particle size of solid silica particles may be between 5 nm and 20 nm, or between 5 nm and 15 nm.

[0373] The content of the solid silica particles may be 10 parts by mass or more, 50 parts by mass or more, 70 parts by mass or more, or 100 parts by mass or more with respect to 100 parts by mass of the binder component. The content of the solid silica particles may be 200 parts by mass or less, 150 parts by mass or less, or 100 parts by mass or less with respect to 100 parts by mass of the binder component.

[0374] The content of the solid silica particles may be 10 parts by mass or more and 200 parts by mass or less, 50 parts by mass or more and 200 parts by mass or less, 70 parts by mass or more and 200 parts by mass or less, or 100 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the binder component. The content of the solid silica particles may be 10 parts by mass or more and 150 parts by mass or less, 50 parts by mass or more and 150 parts by mass or less, 70 parts by mass or more and 150 parts by mass or less, or 100 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the binder component. The content of the solid silica particles may be 10 parts by mass or more and 100 parts by mass or less, 50 parts by mass or more and 100 parts by mass or less, 70 parts by mass or more and 100 parts by mass or less, or 100 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the binder component.

[0375] The functional layer, the first functional layer, and the second functional layer may contain particles other than silica particles. Examples of the particles other than silica particles contained in the functional layer, the first functional layer, and the second functional layer include simple substances of oxides of any one of alumina, titanium, tantalum, zirconium, chromium, niobium, cerium, hafnium, and yttrium or mixtures of oxides. The particles other than silica particles contained in the functional layer, the first functional layer, and the second functional layer may be hollow particles having an internal space. The particles other than silica particles contained in the functional layer, the first functional layer, and the second functional layer may be solid particles having no internal space.

[0376] The functional layer, the first functional layer, and the second functional layer may contain alumina particles as particles other than silica particles. Alumina particles have a relatively low refractive index among metal oxides. Alumina is Al ２ O ３It is aluminum oxide represented by . As alumina, α-type, γ-type, σ-type, and mixtures thereof are known. The alumina particles may be modified alumina particles with a modified surface. Examples of the modified alumina particles include (meth)acrylic modified alumina particles and silicone modified alumina particles.

[0377] The average particle diameter of the particles other than the silica particles and the average particle diameter of the alumina particles may be 5 nm or more and 20 nm or less, may be 5 nm or more and 15 nm or less, may be 10 nm to 20 nm or less, or may be 10 nm to 15 nm or less.

[0378] The shapes of the particles such as hollow silica particles, solid silica particles, and alumina dispersed in the functional layer, the first functional layer, and the second functional layer are not particularly limited. The shapes of the particles contained in the functional layer, the first functional layer, and the second functional layer may be substantially spherical shapes such as true spherical, ellipsoidal of revolution, polyhedral shapes approximating a sphere, rod-shaped, plate-shaped, fibrous, irregular shapes, etc.

[0379] The particles contained in the functional layer, the first functional layer, and the second functional layer may be coated with a silane coupling agent. The silane coupling agent may contain a (meth)acryloyl group or an epoxy group. By subjecting the particles to surface treatment with the silane coupling agent, the affinity between the particles and the binder component is improved, and the particles are less likely to aggregate. By coating the hollow silica particles with the silane coupling agent, the hollow silica particles can be uniformly dispersed in the functional layer, the first functional layer, and the second functional layer.

[0380] Silane coupling agents include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl Examples include rubylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, 1,6-bis(trimethoxysilyl)hexane, trifluoropropyltrimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane. In particular, one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane may be used.

[0381] (Method for producing the functional layer, the first functional layer, and the second functional layer) The functional layer, the first functional layer, and the second functional layer may be produced by a wet method. The functional layer, the first functional layer, and the second functional layer may also be produced using a coating liquid for the functional layer. The functional layer, the first functional layer, and the second functional layer may also be produced by drying and curing a coating film of the coating liquid for the functional layer. The coating liquid for the functional layer contains a curable resin composition. The coating liquid for the functional layer may also contain additives such as antistatic agents, antioxidants, surfactants, dispersants, and crosslinking agents.

[0382] The coating solution for the functional layer may contain a silicone-based leveling agent (silicone compound) as an additive. The inclusion of a silicone-based leveling agent in the functional layer coating solution suppresses the protrusion of hollow silica particles from the first surface, resulting in a smoother first surface. The inclusion of a silicone-based leveling agent in the functional layer coating solution allows for uniform dispersion of hollow silica particles within the functional layer. Therefore, variations in the thickness of the functional layer are suppressed, and the observation of coloration on the optical sheet is prevented. The silicone-based leveling agent provides the surface of the functional layer with excellent slipperiness and excellent antifouling properties (fingerprint wiping ability, large contact angle with pure water and hexadecane).

[0383] 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.

[0384] The coating solution for the functional layer may contain a solvent. The viscosity of the coating solution for the functional layer may be adjusted by the solvent. By adjusting the viscosity of the coating solution for the functional layer, each component can be dissolved or dispersed within the coating solution for the functional layer. The solvent may be one or more of the following: ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), halogenated carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, butyl acetate, etc.), alcohols (butanol, cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), glycol ethers (1-methoxy-2-propyl acetate, etc.), amides (dimethylformamide, dimethylacetamide, etc.).

[0385] <Resin Layer> The resin layer is a layer that is expected to perform some function. The thickness of the resin layer is set appropriately according to the effect that is expected of the resin layer. The thickness of the resin 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 resin 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.

[0386] The resin layer may also be a hard coat layer. The following describes an example where the resin layer is a hard coat layer.

[0387] The resin layer 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 be an ionizing radiation curable resin composition. The resin 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 high hardness to the resin layer and can improve the scratch resistance of the optical sheet. Ionizing radiation curable resin compositions are particularly useful from the viewpoint of improving scratch resistance.

[0388] The curable resin composition used to form the resin layer may be the same as the curable resin composition used to form the functional layer. The thermosetting resin and ionizing radiation-curable compound used to form the resin layer may be the same as the thermosetting resin and ionizing radiation-curable compound used to form the functional layer.

[0389] The resin layer may contain additives. Examples of additives include refractive index modifiers, dyes, pigments, leveling agents, UV absorbers, antioxidants, and light stabilizers. When the resin layer contains additives, the resin in the resin layer functions as a binder component. The binder component holds the additives. The binder component may also function as a binder for film formation.

[0390] The resin layer may be produced by a wet process. The resin layer may also be produced using a resin layer coating solution for forming the resin layer. The resin layer may also be produced by drying and curing the coating film of the resin layer coating solution. The resin layer coating solution for producing the resin layer contains a curable resin composition. The resin layer coating solution may contain additives such as antistatic agents, antioxidants, surfactants, dispersants, and crosslinking agents. The resin layer coating solution may contain the same solvent as the functional layer coating solution.

[0391] Furthermore, the resin layer is not limited to the hard coat layer described above. The resin layer may also be an anti-glare layer. The resin layer may include an uneven surface. The resin layer as an anti-glare layer may include a binder resin and particles. The resin layer may include protrusions on its surface caused by the particles.

[0392] The binder resin is an element that holds particles. The binder resin may also function as a binder for coating film formation. The resin layer may maintain its film shape by holding the particles contained in the resin layer with the binder resin. The resin contained in the binder resin may be the same as the resin contained in the resin layer as the hard coat layer.

[0393] The particles may be organic particles. The particles may also be inorganic particles. The resin layer 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.

[0394] <<Manufacturing Method for Optical Sheets>> The first functional layer, second functional layer, and resin layer contained in the optical sheet can be manufactured by a wet process. In the wet process, a coating solution containing the components that make up each layer is prepared. First, the coating solution is applied to the surface on which each layer is to be manufactured. Next, each layer is obtained by drying and curing the coating film of the coating solution. The coating solution may contain a solvent in addition to the resin composition and particles used to form each layer. The resin composition may contain solid components that make up each layer and additives such as polymerization initiators.

[0395] An optical sheet including a substrate and a functional layer may be manufactured as follows: First, a coating solution for the second functional layer is prepared to form the second functional layer. Next, the coating solution for the second functional layer is applied to the substrate to form a coating film. After that, the coating film is dried, and then the coating film is cured. In this way, the second functional layer is manufactured on the substrate.

[0396] Next, a coating solution for the first functional layer is prepared to form the first functional layer. Then, the coating solution for the first functional layer is applied onto the second functional layer to form a coating film. After that, the coating film is dried, and then cured. Through the above steps, the first functional layer is created on the second functional layer. Alternatively, the second functional layer may be created in an uncured or semi-cured state, and the second functional layer may be completely cured together with the first functional layer when the first functional layer is cured.

[0397] As a result, an optical sheet shown in Figure 2 is obtained, comprising the substrate, the second functional layer, and the first functional layer in this order. By adjusting the hollow silica content ratio of the coating solution for the first functional layer and the coating solution for the second functional layer, an optical sheet having one or more of the above-described features (A)-(P) can be produced.

[0398] If the optical sheet includes a resin layer in addition to the functional layer, the resin layer is prepared on the substrate before the second functional layer is prepared. The resin layer is obtained by applying a resin layer coating solution to the substrate and drying and curing the coating film. Next, the optical sheet shown in Figure 1 is obtained by sequentially preparing the second functional layer and the first functional layer on the resin layer.

[0399] Alternatively, the resin layer may be manufactured in an uncured or semi-cured state, and when the second functional layer is cured, the resin layer may be completely cured together with the second functional layer.

[0400] <<<Sheet Articles>>> According to the manufacturing method of optical sheets 10 by the wet method, as shown in Figure 12, 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 12, 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.

[0401] <<<Polarizing Plate>>> The optical sheet 10 according to this embodiment may be applied to a polarizing plate 60. In the example shown in Figure 13, 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. The optical sheet 10 is laminated on the polarizer 62 such that the second surface 12 faces the polarizer 62 and the first surface 11 is away from the polarizer 62.

[0402] As described above, the optical sheet 10 can reduce reflectivity over a wide wavelength range. Furthermore, it can suppress changes in reflectivity depending on the wavelength over a wide wavelength range. Therefore, the area behind the polarizing plate 60, including the optical sheet 10, can be observed clearly without causing any change in color.

[0403] 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.

[0404] <<<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 14, 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 display elements 66 include liquid crystal display elements, EL display elements, plasma display elements, electronic paper elements, etc. The optical sheet 10 is laminated on the display element 66 such that its second surface 12 faces the display element 66 and its first surface 11 is separated from the display element 66.

[0405] The observer observes the image displayed by the display element 66 through the optical sheet 10. As described above, the optical sheet 10 suppresses the observation of color on the optical sheet. Therefore, it effectively suppresses the degradation of the image displayed by the display device 65. The observer can observe a high-quality image.

[0406] <<<Panel>>> The optical sheet 10 according to this embodiment is applicable to various uses. Figure 15 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 optical sheet 10 is superimposed on 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. The optical sheet 10 is laminated on the display element 66 with its second surface 12 facing the article to be bonded 71 and its first surface 11 away from the article to be bonded 71.

[0407] As described above, according to the optical sheet 10, the reflectance can be reduced in a wide wavelength band. Also, the change in reflectance according to the wavelength in the wide wavelength band can be suppressed. Therefore, the back of the panel 70 including the optical sheet 10 can be clearly observed without causing a change in color tone.

[0408] <<<Lens member>>> The optical sheet 10 according to the present embodiment may be applied to the lens member 72. In the example shown in FIG. 16, the lens member 72 includes a lens 73 and the optical sheet 10. The lens 73 may be a spherical lens or an aspherical lens. The lens 73 may be a convex lens or a concave lens. The lens 73 may be a double-sided lens or a single-sided lens.

[0409] The optical sheet 10 may be laminated on one side of the lens 73. The optical sheet 10 may be laminated on the lens surface of the lens 73. The optical sheet 10 may be laminated on the non-lens surface of the lens 73. The optical sheet 10 may be laminated on both sides of the lens 73. The optical sheet 10 is laminated on the lens 73 such that the second surface 12 faces the lens 73 and the first surface 11 is away from the lens 73.

[0410] As described above, according to the optical sheet 10, the reflectance can be reduced in a wide wavelength band. Also, the change in reflectance according to the wavelength in the wide wavelength band can be suppressed. Therefore, the back of the lens member 72 including the optical sheet 10 can be clearly observed without causing a change in color tone. According to the optical sheet 10, the surface hardness of the lens member 72 can be improved. According to the optical sheet 10, the scratch resistance of the lens member 72 can be improved.

[0411] According to the optical sheet 10, since the reflectance can be reduced in a wide wavelength band, the reflectance of incident light from a wide incident angle range can be reduced. According to the optical sheet 10, since the change in reflectance according to the wavelength in the wide wavelength band can be suppressed, the change in reflectance according to the incident angle of incident light from a wide incident angle range can be suppressed.

[0412] Depending on the application of the lens member 72, the range of incident angles of light on the lens member 72 can be wide. For example, the lens member 72 applied to a wearable display device 74 (Figure 17) can receive light from a wide range of incident angles. The lens member 72 can reduce the reflectance of incident light from a wide range of incident angles. The lens member 72 can suppress changes in reflectance depending on the incident angle of incident light from a wide range of incident angles.

[0413] Since the lens member 72 applied to the wearable display device 74 is positioned close to the wearer's eyeball, the incident angle range of the light incident on the lens member 72 is wide. Therefore, the lens member 72 including the optical sheet 10 is suitable for the wearable display device 74. Examples of wearable display devices 74 include those that display virtual reality (VR) images or augmented reality (AR) images.

[0414] As shown in Figure 17, the wearable display device 74 may include a mounting device 75 and lens members 72. The mounting device 75 is worn by the user. The mounting device 75 is held on the user's head. The mounting device 75 is not particularly limited. The mounting device 75 may be goggles or a helmet. The wearable display device 74 may include a plurality of lens members 72. The lens members 72 may be held by the mounting device 75 in a position facing the wearer's eyeballs.

[0415] <<<Sensor device 76>>> The optical sheet 10 according to this embodiment may be applied to the sensor device 76. In the example shown in Figure 18, the sensor device 76 includes a sensor 77 and a sensor cover 78. The sensor 77 is not particularly limited. The sensor 77 may include a light receiving unit. The sensor 77 may be a LiDAR. The sensor 77 may be sensitive to light in various wavelength ranges. The sensor cover 78 includes a cover body 79 and the optical sheet 10. The cover body 79 may be a transparent resin film.

[0416] In the example shown in Figure 18, the optical sheet 10 is laminated on the cover body 79. The cover body 79 includes a first surface 79a facing the sensor 77 and a second surface 79b opposite to the first surface 79a. The optical sheet 10 may be placed only on the first surface 79a of the cover body 79. The optical sheet 10 may be placed only on the second surface 79b of the cover body 79. The optical sheet 10 may be placed on both the first surface 79a and the second surface 79b of the cover body 79. The optical sheet 10 may be laminated on the sensor 77 (or cover body 79) such that the second surface 12 faces the sensor 77 (or cover body 79) and the first surface 11 is away from the sensor 77 (or cover body 79).

[0417] As described above, the optical sheet 10 can reduce reflectivity over a wide wavelength range. It can also suppress changes in reflectivity depending on the wavelength over a wide wavelength range. The optical sheet 10 and the sensor cover 78 can reduce the reflectivity of incident light from a wide range of incident angles. The optical sheet 10 and the sensor cover 78 can suppress changes in reflectivity depending on the incident angle of incident light from a wide range of incident angles. As a result, the optical sheet 10 can improve the sensitivity of the sensor device 76 without depending on the wavelength and incident angle of the incident angle. The optical sheet 10 can improve the surface hardness of the sensor 77 and the sensor cover 78. The optical sheet 10 can improve the scratch resistance of the sensor 77 and the sensor cover 78.

[0418] This disclosure will be further described in detail by examples. This disclosure is not limited to the following examples.

[0419] <<<1. Preparation of Optical Sheets>>> Optical sheets according to Examples 1 to 5 and Comparative Examples 1 to 5 were prepared. As shown in Figure 1, the optical sheets according to each example contained a base material, a resin layer, and a functional layer in this order from the second surface to the first surface. The functional layer contained a second functional layer and a first functional layer in this order from the second surface to the first surface.

[0420] <<Example 1>> A polymethyl methacrylate film with a thickness of 40 μm was prepared as the substrate. The glass transition temperature of the polymethyl methacrylate film was 125°C.

[0421] The resin layer coating solution 1 (hard coat layer coating solution 1) according to the following formulation was applied to the substrate to form a coating film of resin layer coating solution 1. The coating film of resin layer coating solution 1 was dried at 70°C for 1 minute (drying air velocity 0.2 m / s) to evaporate the solvent. After that, an integrated light intensity of 50 mJ / cm² was applied to the coating film of resin layer coating solution 1. ２ The substrate was irradiated with ultraviolet light. By curing the coating film, a resin layer (hard coat layer) was created on the substrate.

[0422] Next, the coating solution 1 for the second functional layer, according to the following formulation, was applied to the resin layer. Then, the coating film of the coating solution 1 for the second functional layer was dried at 50°C for 1 minute (drying air velocity 0.2 m / s) to evaporate the solvent. Afterward, the coating film of the coating solution 1 for the second functional layer was exposed to an integrated light intensity of 100 mJ / cm². ２ The material was then irradiated with ultraviolet light. By curing the coating film, a second functional layer was created on the resin layer.

[0423] Furthermore, the coating solution 1 for the first functional layer, according to the following formulation, was applied to the second functional layer. The coating film of the first functional layer 1 was then dried at 50°C for 1 minute (drying air velocity 0.2 m / s) to evaporate the solvent. Afterward, the coating film of the first functional layer 1 was exposed to an integrated light intensity of 200 mJ / cm². ２ The material was irradiated with ultraviolet light. By curing the coating film, the first functional layer was created on the second functional layer.

[0424] Based on the above, an optical sheet was obtained having a first functional layer (low refractive index layer), a second functional layer (medium refractive index layer), and a resin layer (high refractive index layer) in the order from the first surface to the second surface.

[0425] <Coating Liquid for Resin Layer 1> ・Urethane acrylate oligomer 71 parts by mass (average number of functional groups 3, weight-average molecular weight 700-1200, solids content 70%) ・UV-curable acrylate-containing composition 30 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solids content 100%) ・Monofunctional acrylic monomer 20 parts by mass (Kyoeisha Chemical Co., Ltd., product name "Light Acrylate PO-A", solids content 100%) ・Leveling agent 0.6 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solids content 50%) ・Photopolymerization initiator 6 parts by mass (IGM Resins, product name "Omnirad 184", solids content 100%) ・Methyl ethyl ketone (MEK) 28 parts by mass・Methyl isobutyl ketone (MIBK) 198 parts by mass

[0426] <Coating Solution 1 for the Second Functional Layer> ・Hollow silica particles 100 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 100 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 0.72 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solid content 50%) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl isobutyl ketone (MIBK) 3505 parts by mass ・Propylene glycol monomethyl ether acetate (PMA) 896 parts by mass

[0427] <Coating Solution 1 for the First Functional Layer> ・Hollow silica particles 600 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 10 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 450 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) ・Leveling agent 11 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "KP-420", solid content 100%) ・Photopolymerization initiator 5 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl ethyl ketone (MEK) 2008 parts by mass・Methyl isobutyl ketone (MIBK) 4496 parts by mass of propylene glycol monomethyl ether acetate (PMA) and 3147 parts by mass of propylene glycol monomethyl ether acetate (PMA).

[0428] <<Example 2>> Example 2 differs from Example 1 in the amount of each coating solution applied, the use of coating solution 2 for the second functional layer instead of coating solution 1 for the second functional layer, and the use of coating solution 2 for the first functional layer instead of coating solution 1 for the first functional layer. Otherwise, an optical sheet according to Example 2 was obtained in the same manner as in Example 1.

[0429] <Coating Solution 2 for the Second Functional Layer> ・Hollow silica particles 125 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 100 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 0.75 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solid content 50%) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl isobutyl ketone (MIBK) 3629 parts by mass ・Propylene glycol monomethyl ether acetate (PMA) 932 parts by mass

[0430] <Coating Solution 2 for the First Functional Layer> ・Hollow silica particles 500 parts by mass (Particles with an average particle diameter of 100 nm, surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 10 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 450 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) ・Leveling agent 10 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "KP-420", solid content 100%) ・Photopolymerization initiator 5 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl ethyl ketone (MEK) 1822 parts by mass・Methyl isobutyl ketone (MIBK) 4109 parts by mass of propylene glycol monomethyl ether acetate (PMA) and 2867 parts by mass of propylene glycol monomethyl ether acetate (PMA).

[0431] <<Example 3>> Example 3 differs from Example 1 in the amount of each coating solution applied, in that a second functional layer coating solution 2 similar to that in Example 2 was used instead of the second functional layer coating solution 1, and in that a first functional layer coating solution 3 was used instead of the first functional layer coating solution 1. Otherwise, an optical sheet according to Example 3 was obtained in the same manner as in Example 1.

[0432] <Coating solution 3 for the first functional layer> ・500 parts by mass of hollow silica particles (average particle size 75 nm, particles surface-treated with a silane coupling agent having methacryloyl groups, solid content 20%) ・350 parts by mass of hollow silica particles (average particle size 100 nm, particles surface-treated with a silane coupling agent having methacryloyl groups, solid content 20%) ・100 parts by mass of UV-curable siloxane compound-containing composition (manufactured by Toagosei Co., Ltd., product name "MAC-SQ™-100", solid content 100%) ・13.5 parts by mass of leveling agent (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KP-420", solid content 100%) ・5 parts by mass of photopolymerization initiator (manufactured by IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl ethyl ketone (MEK) 2250 parts by mass of methyl isobutyl ketone (MIBK), 4946 parts by mass of propylene glycol monomethyl ether acetate (PMA), 3375 parts by mass

[0433] <<Example 4>> Example 4 differs from Example 1 in that the amount of each coating solution applied and that the same second functional layer coating solution 2 as in Example 2 was used instead of the second functional layer coating solution 1, and in all other respects the optical sheet according to Example 4 was obtained in the same manner as in Example 1.

[0434] <<Example 5>> Example 5 differs from Example 1 in the amount of each coating solution applied, the use of coating solution 3 for the second functional layer instead of coating solution 1 for the second functional layer, and the use of coating solution 4 for the first functional layer instead of coating solution 1 for the first functional layer. Otherwise, an optical sheet according to Example 5 was obtained in the same manner as in Example 1.

[0435] <Coating Solution 3 for the Second Functional Layer> ・Hollow silica particles 75 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 100 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 0.69 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solid content 50%) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl isobutyl ketone (MIBK) 3380 parts by mass ・Propylene glycol monomethyl ether acetate (PMA) 860 parts by mass

[0436] <Coating Solution 4 for the First Functional Layer> ・Hollow silica particles 700 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable siloxane compound-containing composition 100 parts by mass (manufactured by Toagosei Co., Ltd., product name "MAC-SQ™-100", solid content 100%) ・Leveling agent 12 parts by mass (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KP-420", solid content 100%) ・Photopolymerization initiator 5 parts by mass (manufactured by IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl ethyl ketone (MEK) 2005 parts by mass ・Methyl isobutyl ketone (MIBK) 4452 parts by mass ・Propylene glycol monomethyl ether acetate (PMA) 3007 parts by mass

[0437] <<Comparative Example 1>> Comparative Example 1 differs from Example 1 in the following ways: the amount of each coating solution applied, the substrate was changed, resin layer coating solution 2 was used instead of resin layer coating solution 1, the first functional layer was formed on the substrate without forming a second functional layer, and first functional layer coating solution 5 was used instead of first functional layer coating solution 1. In all other respects, the optical sheet according to Comparative Example 1 was obtained in the same manner as in Example 1. A triacetylcellulose film with a thickness of 80 μm was used as the substrate for Comparative Example 1.

[0438] <Coating Liquid for Resin Layer 2> ・UV-curable acrylate-containing composition 62.5 parts by mass (Daiichi Kogyo Co., Ltd., product name "New Frontier R-1403MB", solids content 80%) ・UV-curable acrylate-containing composition 30 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solids content 100%) ・Monofunctional acrylic monomer 20 parts by mass (Kyoeisha Chemical Co., Ltd., product name "Light Acrylate PO-A", solids content 100%) ・Leveling agent 0.6 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solids content 50%) ・Photopolymerization initiator 6 parts by mass (IGM Resins, product name "Omnirad 184", solids content 100%) ・Methyl ethyl ketone (MEK) 124 parts by mass・Methyl isobutyl ketone (MIBK) 111 parts by mass

[0439] <Coating Solution 5 for the First Functional Layer> ・Hollow silica particles 500 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 10 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 450 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) ・Leveling agent 10 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "KP-420", solid content 100%) ・Photopolymerization initiator 5 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl ethyl ketone (MEK) 1822 parts by mass・Methyl isobutyl ketone (MIBK) 4109 parts by mass of propylene glycol monomethyl ether acetate (PMA) and 2867 parts by mass of propylene glycol monomethyl ether acetate (PMA).

[0440] <<Comparative Example 2>> Comparative Example 2 differs from Example 1 in the following ways: the amount of each coating solution applied, the substrate was changed, the same resin layer coating solution 2 as in Comparative Example 1 was used instead of resin layer coating solution 1, the second functional layer coating solution 5 was used instead of second functional layer coating solution 1, and the first functional layer coating solution 6 was used instead of first functional layer coating solution 1. In all other respects, the optical sheet according to Comparative Example 2 was obtained in the same manner as in Example 1. A triacetylcellulose film with a thickness of 80 μm was used as the substrate for Comparative Example 2.

[0441] <Coating Solution 5 for the Second Functional Layer> ・Zirconium oxide particles 500 parts by mass (average particle size 20 nm, solid content 15%) ・UV-curable acrylate-containing composition 25 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 0.6 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solid content 50%) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl isobutyl ketone (MIBK) 681 parts by mass ・Propylene glycol monomethyl ether (PGME) 1107 parts by mass

[0442] <Coating Solution 6 for the First Functional Layer> ・Hollow silica particles 550 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 10 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 450 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "X-71-1203M", solid content 20%) ・Leveling agent 10.5 parts by mass (Shin-Etsu Chemical Co., Ltd., product name "KP-420", solid content 100%) ・Photopolymerization initiator 5 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl ethyl ketone (MEK) 1915 parts by mass・Methyl isobutyl ketone (MIBK) 4302 parts by mass of propylene glycol monomethyl ether acetate (PMA) and 3007 parts by mass of propylene glycol monomethyl ether acetate (PMA).

[0443] <<Comparative Example 3>> Comparative Example 3 differs from Example 1 in the following ways: the amount of each coating solution applied, the substrate was changed, the same resin layer coating solution 2 as in Comparative Example 1 was used instead of the resin layer coating solution 1, the same second functional layer coating solution 6 was used instead of the second functional layer coating solution 1, and the same first functional layer coating solution 6 as in Comparative Example 2 was used instead of the first functional layer coating solution 1. In all other respects, the optical sheet according to Comparative Example 3 was obtained in the same way as in Example 1. A triacetylcellulose film with a thickness of 80 μm was used as the substrate for Comparative Example 3.

[0444] <Coating Solution 6 for the Second Functional Layer> ・Zirconium oxide particles 567 parts by mass (average particle size 20 nm, solid content 15%) ・UV-curable acrylate-containing composition 15 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 0.6 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solid content 50%) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl isobutyl ketone (MIBK) 625 parts by mass ・Propylene glycol monomethyl ether (PGME) 1107 parts by mass

[0445] <<Comparative Example 4>> Comparative Example 4 differs from Example 1 in the following ways: the amount of each coating solution applied, the substrate was changed, the same resin layer coating solution 2 as in Comparative Example 1 was used instead of the resin layer coating solution 1, the first functional layer was formed on the substrate without forming a second functional layer, and the same first functional layer coating solution 5 as in Comparative Example 1 was used instead of the first functional layer coating solution 1. In all other respects, the optical sheet according to Comparative Example 4 was obtained in the same way as in Example 1. A triacetylcellulose film with a thickness of 80 μm was used as the substrate for Comparative Example 4.

[0446] <<Comparative Example 5>> Comparative Example 5 differs from Example 1 in the amount of each coating solution applied, in that coating solution 7 for the second functional layer was used instead of coating solution 1 for the second functional layer, and in that coating solution 4 for the first functional layer, similar to that in Example 5, was used instead of coating solution 1 for the first functional layer. In all other respects, the optical sheet according to Comparative Example 4 was obtained in the same manner as in Example 1. A triacetylcellulose film with a thickness of 80 μm was used as the substrate for Comparative Example 4.

[0447] <Coating liquid 7 for the second functional layer> ・Hollow silica particles 250 parts by mass (average particle size 75 nm, particles surface-treated with a silane coupling agent having a methacryloyl group, solid content 20%) ・UV-curable acrylate-containing composition 100 parts by mass (Nippon Kayaku Co., Ltd., product name "PET-30", solid content 100%) ・Leveling agent 0.9 parts by mass (Kyoeisha Chemical Co., Ltd., product name "LE-304", solid content 50%) ・Photopolymerization initiator 4 parts by mass (IGM Resins, product name "Omnirad 127", solid content 100%) ・Methyl isobutyl ketone (MIBK) 4252 parts by mass ・Propylene glycol monomethyl ether acetate (PMA) 1113 parts by mass

[0448] <<<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.

[0449] <<2-1. Thickness of the first functional layer, second functional layer, and resin layer>> 1 mm x 10 mm samples were cut from the optical sheets of the examples and comparative examples. Sections were cut from the samples of each example using an ultramicrotome in the manner described above. A Leica UC7 was used as the ultramicrotome. An Ultra35 from Dia was used as the blade for the ultramicrotome.

[0450] Observation images of sections 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: 30.0 kV; Emission current: 10 μA; Magnification: (numerical value)x; Condenser lens: 5.0; W.D.: 8.8 mm

[0451] Using the method described above, the thicknesses (nm) of the first functional layer, the second functional layer, and the resin layer were measured from the observed images. The measurement results are shown in the "Thickness" column of Tables 1 and 2.

[0452] <<2-2. Refractive Index of the First Functional Layer, Second Functional Layer, and Resin Layer>> The refractive indices of the first functional layer, second functional layer, and resin layer were measured using the method described above. An Abbe Refractometer D-M2 manufactured by Atago Co., Ltd. was used to measure the refractive index. The measurement results are shown in the "Refractive Index" column of Tables 1 and 2.

[0453] <<2-3. First and Second Ratios>> 2 mm x 5 mm samples were cut from the optical sheets of the Examples and Comparative Examples. Sections were cut from the samples of each example using an ultramicrotome in the manner described above. A Leica UC7 was used as the ultramicrotome. An Ultra35 manufactured by Dia was used as the blade for the ultramicrotome.

[0454] Sections obtained using a scanning transmission electron microscope (STEM) were observed to determine the measurement region including the first position, the measurement region including the second position, the measurement region including the third position, and the measurement region including the fourth position. A Hitachi High-Technologies Corporation SU-9000 scanning transmission electron microscope was used. The observation conditions for the scanning transmission electron microscope were as follows: Detector: TE; Acceleration voltage: 30.0 kV; Emission current: 20 μA; Magnification: 100,000x; W.D.: 8.0 mm

[0455] Figure 19A is an observation image showing the measurement area including the first position for Example 1. Figure 19B is an observation image showing the measurement area including the second position for Example 1. Figure 20A is an observation image showing the measurement area including the first position for Example 2. Figure 20B is an observation image showing the measurement area including the second position for Example 2. Figure 21A is an observation image showing the measurement area including the first position for Example 3. Figure 21B is an observation image showing the measurement area including the second position for Example 3.

[0456] The fluorescence X-ray intensity of element C and element Si was measured in the measurement region including positions 1 to 4 of the section. For fluorescence X-ray intensity measurement, the following energy-dispersive X-ray analyzer (EDX) mounted on a scanning transmission electron microscope SU-9000 manufactured by Hitachi High-Tech Corporation was used: • Manufacturer: Oxford Instruments • Model: X-MaxN 100TLE • Detector element area: 100 mm² ２ , windowless type

[0457] The fluorescence X-ray intensity of element C and element Si were measured in the measurement region including the first position of the intersection. Using the method described above, the first ratio of the fluorescence X-ray intensity of element Si to that of element C was calculated from the measurement results. The first ratio (%) is shown in the "First Ratio" column of Tables 1 and 2.

[0458] The fluorescence X-ray intensity of element C and element Si was measured in the measurement region including the second position of the intersection. Using the method described above, the second ratio of the fluorescence X-ray intensity of element Si to that of element C was calculated from the measurement results. The second ratio (%) is shown in the "Second Ratio" column of Tables 1 and 2.

[0459] Using the method described above, the ratio of the second ratio to the first ratio was calculated by dividing the second ratio by the first ratio. The ratio of the second ratio to the first ratio is shown in the "Second Ratio / First Ratio" column of Tables 1 and 2.

[0460] Using the method described above, the difference between the first ratio and the second ratio was calculated by subtracting the second ratio from the first ratio. The value (%) obtained by subtracting the second ratio from the first ratio is shown in the "First Ratio - Second Ratio" column of Tables 1 and 2.

[0461] The fluorescence X-ray intensity of element C and element Si was measured in the measurement region including the third position of the intercept. Using the method described above, the third ratio of the fluorescence X-ray intensity of element Si to that of element C was calculated from the measurement results. The third ratio (%) is shown in the "Third Ratio" column of Tables 1 and 2. The first average ratio (%) was calculated as the average of the first and third ratios. The first average ratio (%) is shown in the "First Average Ratio" column of Tables 1 and 2.

[0462] The fluorescence X-ray intensity of element C and element Si was measured in the measurement region including the fourth position of the intercept. Using the method described above, the fourth ratio of the fluorescence X-ray intensity of element Si to that of element C was calculated from the measurement results. The fourth ratio (%) is shown in the "Fourth Ratio" column of Tables 1 and 2. The second average ratio (%) was calculated as the average of the second and fourth ratios. The second average ratio (%) is shown in the "Second Average Ratio" column of Tables 1 and 2.

[0463] Using the method described above, the ratio of the second average ratio to the first average ratio was calculated by dividing the second average ratio by the first average ratio. The ratio of the second average ratio to the first average ratio is shown in the "Second Average Ratio / First Average Ratio" column of Tables 1 and 2.

[0464] Using the method described above, the difference between the first average ratio and the second average ratio was calculated by subtracting the second average ratio from the first average ratio. The value (%) obtained by subtracting the second average ratio from the first average ratio is shown in the "First Average Ratio - Second Average Ratio" column of Tables 1 and 2.

[0465] <<2-4. Spectral Reflectance>> 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. As described above, a black board was attached to the surface of the sample, which is composed of the second surface of the optical sheet, 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 DFA2CG 502K (black)" manufactured by Kuraray Co., Ltd. The spectral reflectance (%) of the optical sheet relating to each example was measured using the method described above. A UV-Vis-Near-Infrared Spectrophotometer "V780" manufactured by JASCO Corporation was used to measure the spectral reflectance (%). The spectral reflectance was measured for each wavelength in 1 nm increments within the range of 300 nm to 900 nm.

[0466] From the spectral reflectance measurement results, the difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 480 nm was calculated. The difference between the maximum and minimum spectral reflectance values ​​on the first surface in the wavelength range of 380 nm to 480 nm is shown in the "Maximum Difference between 380 and 480 nm" column of Tables 1 and 2.

[0467] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 680 nm to 780 nm was calculated. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 680 nm to 780 nm is shown in the "Maximum Difference between 680 and 780 nm" column of Tables 1 and 2.

[0468] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 780 nm was calculated. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 380 nm to 780 nm is shown in the "Maximum Difference between 380 and 780 nm" column of Tables 1 and 2.

[0469] The maximum spectral reflectance of the first surface was measured at wavelengths between 380 nm and 780 nm. The maximum spectral reflectance of the first surface at wavelengths between 380 nm and 780 nm is shown in the "380-780 nm maximum value" column of Tables 1 and 2.

[0470] The difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths between 300 nm and 380 nm was calculated. The difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths between 300 nm and 380 nm is shown in the "Maximum Difference between 300 and 380 nm" column of Tables 1 and 2.

[0471] The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm was calculated. The difference between the maximum and minimum spectral reflectance values ​​at the first surface in the wavelength range of 780 nm to 900 nm is shown in the "780-900 nm Maximum Difference" column of Tables 1 and 2.

[0472] The graph shown in Figure 8 shows the spectral reflectance of Example 2-4 and Comparative Example 2-4. The graph shown in Figure 9 shows the spectral reflectance of Example 2. The graph shown in Figure 10 shows the spectral reflectance of Example 3. The graph shown in Figure 11 shows the spectral reflectance of Example 4.

[0473] <<2-5. Reflection Y Value>> A 5 ​​cm x 5 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. As described above, a black board was attached to the surface of the sample, which is composed of the second surface of the optical sheet, 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 DFA2CG 502K (black)" manufactured by Kuraray Co., Ltd. The reflection Y value (%) of the optical sheet relating to each example was measured using the method described above. A UV-Vis-Near-Infrared Spectrophotometer "V780" manufactured by JASCO Corporation was used to measure the reflection Y value. The measurement results of the reflection Y value are shown in the "Reflection Y Value" column of Tables 1 and 2.

[0474] <<2-6. 1a ＊ Value, 2a ＊ Value, 1st b ＊ Value, 2b ＊ Value >> 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. As described above, a black board was attached to the surface of the sample, which is composed of the second surface of the optical sheet, via an optical transparent adhesive sheet. The optical transparent adhesive sheet was "Panaclean PD-S1" manufactured by Panac Co., Ltd. The black board was "Comoglass DFA2CG 502K (black)" manufactured by Kuraray Co., Ltd. Using the method described above, L was applied to the optical sheet relating to each example. ＊ a ＊ b ＊ 1a in the color system ＊ Value, 2a ＊ Value, 1st b ＊ Value, 2b ＊ The value was measured. a ＊ Value and b ＊ The values ​​were measured using the V780 ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation.

[0475] Using the method described above, from the measurement results, 1a ＊ Value and 2a ＊ The absolute value of the difference from the value, and the first b ＊ Value and 2b ＊The absolute value of the difference from the value was calculated. 1a ＊ Value and 2a ＊ The absolute value of the difference from the value is shown in "Δa" in Tables 1 and 2. ＊ This is shown in the section marked "1b". ＊ Value and 2b ＊ The absolute value of the difference from the value is shown in Tables 1 and 2 as "Δb". ＊ This will be shown in the " " column.

[0476]

[0477]

[0478] D1: First direction, D2: Second direction, D3: Third direction, RA: Winding axis, P1: First position, P2: Second position, BS1: First interface, BS2: Second interface, BS3: Third interface, AP1: Measurement area, AP2: Measurement area, 5: Sheet article, 6: Winding core, 7: Winding, 10: Optical sheet, 10X: Section, 11: First surface, 12: Second surface, 15: Adjacent area, 20: Functional layer, 21: First surface, 22: Second surface, 31: First functional layer, 31a: First surface, 31b: Second surface, 32: Binder component, 33: Hollow Silica particles, 36: Second functional layer, 36a: First surface, 36b: Second surface, 37: Binder component, 38: Hollow silica particles, 40: Resin layer, 50: Substrate, 60: Polarizing plate, 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, 110: Optical sheet, 111: Low refractive index layer, 112: High refractive index layer, 120: Optical sheet, 121: Low refractive index layer, 122: High refractive index layer, 123: Medium refractive index layer

Claims

1. An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the second ratio is smaller than the first ratio, the first ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio is the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

2. An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein the optical sheet comprises a functional layer and a substrate in the order from the first surface to the second surface, the functional layer comprising a binder component and hollow silica particles, the first ratio being 8.0% or more and 16% or less, the second ratio being 1.5% or more and 4.5% or less, the first ratio being the ratio of the X-ray fluorescence intensity of Si element to the X-ray fluorescence intensity of C element at a first position in the functional layer, the second ratio being the ratio of the X-ray fluorescence intensity of Si element to the X-ray fluorescence intensity of C element at a second position in the functional layer, the first position being a position 50 nm closer to the second surface from the first surface along the first direction, and the second position being a position 140 nm closer to the second surface from the first surface along the first direction.

3. An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein the optical sheet comprises a functional layer and a substrate in the order from the first surface to the second surface, the functional layer comprising a binder component and hollow silica particles, the ratio of the second ratio to the first ratio being 0.094 or more and 0.58 or less, the first ratio being the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a first position in the functional layer, the second ratio being the ratio of the X-ray fluorescence intensity of element Si to the X-ray fluorescence intensity of element C at a second position in the functional layer, the first position being a position 50 nm closer to the second surface from the first surface along the first direction, and the second position being a position 140 nm closer to the second surface from the first surface along the first direction.

4. An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein the functional layer and the substrate are arranged in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, the value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

5. An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance values ​​at the first surface at wavelengths of 380 nm to 480 nm is 0.60% or less.

6. An optical sheet comprising a first surface and a second surface facing each other in a first direction, wherein a functional layer and a substrate are provided in the order from the first surface to the second surface, the functional layer comprises a binder component and hollow silica particles, and the difference between the maximum and minimum spectral reflectance values ​​at the first surface at wavelengths of 680 nm to 780 nm is 0.30% or less.

7. The optical sheet according to any one of claims 1 and 3 to 6, wherein the first ratio is 8.0% or more and 16% or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, and the first position is a position 50 nm closer to the second surface from the first surface along the first direction.

8. The optical sheet according to any one of claims 1 and 3 to 6, wherein the second ratio is 1.5% or more and 4.5% or less, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

9. The optical sheet according to any one of claims 1, 2, and 4 to 6, wherein the ratio of the second ratio to the first ratio is 0.094 or more and 0.58 or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

10. The optical sheet according to any one of claims 1 to 3, 5, and 6, wherein the value obtained by subtracting the second ratio from the first ratio is 3.5% or more and 14.5% or less, the first ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a first position in the functional layer, the second ratio is the ratio of the fluorescence X-ray intensity of element Si to the fluorescence X-ray intensity of element C at a second position in the functional layer, the first position is a position 50 nm closer to the second surface from the first surface along the first direction, and the second position is a position 140 nm closer to the second surface from the first surface along the first direction.

11. The optical sheet according to any one of claims 1 to 4 and 6, wherein the difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 380 nm to 480 nm is 0.60% or less.

12. The optical sheet according to any one of claims 1 to 5, wherein the difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 680 nm to 780 nm is 0.30% or less.

13. The optical sheet according to any one of claims 1 to 6, wherein the difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 380 nm to 780 nm is 1.0% or less.

14. The optical sheet according to any one of claims 1 to 6, wherein the maximum spectral reflectance of the first surface at wavelengths of 380 nm to 780 nm is 1.5% or less.

15. The optical sheet according to any one of claims 1 to 6, wherein the reflection Y value on the first surface is 2.5% or less.

16. The optical sheet according to any one of claims 1 to 6, wherein the difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 300 nm to 380 nm is 1.3% or less, and the difference between the maximum and minimum spectral reflectance values ​​on the first surface at wavelengths of 780 nm to 900 nm is 0.60% or less.

17. The absolute value of the difference between the first a ＊ value and the second a ＊ value is 2.0 or less, and the absolute value of the difference between the first b ＊ value and the second b ＊ value is 4.0 or less. The first a ＊ value is the a ＊ a ＊ b ＊ value in the L ＊ a-b color system measured by the reflected light on the first surface with an incident angle of 5°. The second a ＊ value is the a ＊ a ＊ b ＊ value in the L ＊ a-b color system measured by the reflected light on the first surface with an incident angle of 60°. The first b ＊ value is the b ＊ a ＊ b ＊ value in the L ＊ a-b color system measured by the reflected light on the first surface with an incident angle of 5°. The second b ＊ value is the b ＊ a ＊ b ＊ value in the L ＊ a-b color system measured by the reflected light on the first surface with an incident angle of 60°. The optical sheet according to any one of claims 1 to 6.

18. The optical sheet according to any one of claims 1 to 6, wherein the thickness of the functional layer is 140 nm or more and 280 nm or less.

19. The optical sheet according to any one of claims 1 to 6, further comprising a resin layer located between the functional layer and the substrate in the first direction, wherein the resin layer is adjacent to the functional layer, and the resin layer includes a cured resin product.

20. A sheet article comprising a plurality of optical sheets as described in any one of claims 1 to 6.

21. The sheet article according to claim 20, which is wound around a winding axis.

22. A polarizing plate comprising an optical sheet as described in any one of claims 1 to 6, and a polarizer superimposed on the optical sheet.

23. A touch panel member comprising an optical sheet as described in any one of claims 1 to 6, and an electrode layer superimposed on the optical sheet.

24. A display device comprising an optical sheet as described in any one of claims 1 to 6, and a display element superimposed on the optical sheet.

25. A lens member comprising an optical sheet as described in any one of claims 1 to 6, and a lens superimposed on the optical sheet.

26. A sensor device comprising an optical sheet as described in any one of claims 1 to 6, and a sensor superimposed on the optical sheet.

Images