Optical sheet, sheet article, polarizing plate, display device, and panel

Abstract

An optical sheet according to the present invention has a first surface and a second surface on the opposite side from the first surface. The optical sheet includes a light-diffusing layer containing: particles having a longitudinal direction; and a binder component. The standard deviation of the orientation angle of the particles is 16° to 30°. The orientation angle is the angle between the longitudinal direction and orientation direction of the particles when observed from a first direction perpendicular to the optical sheet. The orientation direction is, with respect to a reference direction, inclined at an angle that is the median of the bin having the maximum frequency in a histogram pertaining to the angle between the longitudinal direction of the particles and the reference direction when observed from the first direction.

Description

Optical sheets, sheet articles, polarizing plates, display devices, and panels

[0001] This disclosure relates to optical sheets, sheet articles, polarizing plates, display devices, and panels.

[0002] As described in Patent Documents 1 and 2, a light-diffusing layer containing particles having a longitudinal direction and a resin is known. In this light-diffusing layer, the longitudinal direction of the particles is aligned in a predetermined direction. Incident light of the light-diffusing layer is mainly diffused in a specific direction related to the orientation of the particles. The light-diffusing layer has an anisotropic light-diffusing function.

[0003] A light diffusion layer with anisotropic light diffusion function can promote light diffusion in a specific direction. This anisotropic light diffusion function can widen the viewing angle in a specific direction. Furthermore, it can suppress light diffusion in directions other than the specified direction. It can also suppress unnecessary diffusion of incident light. When this light diffusion layer is used in a display device, it can widen the viewing angle while suppressing a decrease in the efficiency of image light utilization.

[0004] When particles are oriented in the light-diffusing layer, the mechanical properties of the optical sheet including the light-diffusing layer also exhibit anisotropy. Optical sheets are prone to deformation such as curling and warping. They have low resistance to bending around an axis parallel to the particle orientation direction. When the optical sheet is bent, defects such as scratches and cracks are likely to occur. Deformation and defects are more pronounced in the light-diffusing layer, which has high mechanical strength.

[0005] Patent Document 1: Japanese Unexamined Patent Publication No. 2022-182093 Patent Document 2: International Publication 2022 / 209643

[0006] An optical sheet according to one embodiment of the present disclosure is an optical sheet having a first surface and a second surface facing the first surface, comprising a light-diffusing layer containing particles having a longitudinal direction and a binder component, wherein the standard deviation of the orientation angle of the particles is 16° or more and 30° or less, the orientation angle is the angle between the longitudinal direction and the orientation direction of the particles when observed from a first direction perpendicular to the optical sheet, and the orientation direction is a direction tilted with respect to the reference direction by an angle that is the median of the interval with the maximum frequency in a histogram of the angle between a reference direction and the longitudinal direction of each particle when observed from the first direction.

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

[0008] A polarizing plate according to one embodiment of the present disclosure comprises an optical sheet according to one embodiment of the present disclosure and a polarizer superimposed on the optical sheet.

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

[0010] A panel according to one embodiment of the present disclosure comprises an article to be bonded and any optical sheet according to one embodiment of the present disclosure.

[0011] According to this disclosure, deformation and the occurrence of defects in an optical sheet containing particles having a longitudinal direction can be suppressed.

[0012] 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 showing another example of an optical sheet. Figure 3 is a cross-sectional view showing yet another example of an optical sheet. Figure 4 is a diagram illustrating an example of the light diffusion function of a light diffusion layer that may be included in the optical sheets shown in Figures 1 to 3. Figure 5 is a diagram illustrating another example of the light diffusion function of a light diffusion layer that may be included in the optical sheets shown in Figures 1 to 3. Figure 6 is a diagram showing an example of particles that may be included in the light diffusion layer shown in Figures 4 and 5. Figure 7 is an example of a reference orientation angle and a histogram of orientation angles in a light diffusion layer that may be included in the optical sheets shown in Figures 1 to 3. Figure 8A is a side view showing an example of a method for manufacturing the light diffusion layer shown in Figures 4 and 5. Figure 8B is a top view showing an example of a method for manufacturing the light diffusion layer shown in Figures 4 and 5. Figure 9A is a diagram showing a method for evaluating the light diffusion function of the optical sheets shown in Figures 1 to 3. Figure 9B is a diagram showing a method for evaluating the light diffusion function of the optical sheets shown in Figures 1 to 3. Figure 10 is a diagram showing a method for evaluating the light diffusion function of the optical sheets shown in Figures 1 to 3. Figure 11 is a perspective view showing an example of a sheet article containing an optical sheet. Figure 12 is a cross-sectional view showing an example of a polarizing plate containing an optical sheet. Figure 13 is a cross-sectional view showing an example of a display device containing an optical sheet. Figure 14 is a cross-sectional view showing an example of a panel containing an optical sheet. Figure 15 is an example of an SEM image showing a light diffusion layer that may be included in the optical sheets shown in Figures 1 to 3.

[0013] One embodiment of the present disclosure relates to the following <1> to <28>.

[0014] <1> An optical sheet comprising a first surface and a second surface opposite to the first surface, wherein the optical sheet comprises a light-diffusing layer containing particles having a longitudinal direction and a binder component, wherein the standard deviation of the orientation angle of the particles is 16° or more and 30° or less, the orientation angle is the angle between the longitudinal direction and the orientation direction of the particles when observed from a first direction perpendicular to the optical sheet, and the orientation direction is a direction tilted with respect to the reference direction by an angle that is the median of the interval with the maximum frequency in a histogram of the angle between a reference direction and the longitudinal direction of each particle when observed from the first direction.

[0015] <2> The optical sheet described in <1>, wherein the full width at half maximum of the histogram is 38° or more and 71° or less.

[0016] <3> The optical sheet according to <1> or <2>, wherein the ratio of the luminance of the first surface in the first oblique direction to the luminance of the first surface in the second oblique direction is 1.13 or more or 0.885 or less, the first oblique direction is inclined at 60° with respect to the first direction and perpendicular to the orientation direction, and the second oblique direction is inclined at 60° with respect to the first direction and parallel to a surface parallel to both the first direction and the orientation direction.

[0017] <4> The optical sheet according to any one of <1> to <3>, wherein the weight ratio of the particles in the light diffusion layer is 5% or more and 30% or less.

[0018] <5> The optical sheet according to any one of <1> to <4>, wherein the average thickness of the light diffusing layer is 10 μm or more.

[0019] <6> An optical sheet as described in any one of items <1> to <5>, wherein the maximum lift height in the curl test is 30 mm or less.

[0020] <7> An optical sheet according to any one of <1> to <6>, which is resistant to bending tests using a cylindrical mandrel with a diameter of φ8 mm centered on an axis parallel to the orientation direction.

[0021] <8> The optical sheet according to any one of <1> to <7>, wherein the pencil hardness of the first surface is 2H or higher.

[0022] <9> The optical sheet according to any one of <1> to <8>, wherein the reflectance on the first surface is 2.0% or less.

[0023] <10> The optical sheet according to any one of <1> to <9>, wherein the particles include one or more metal oxide particles, metal compound particles, glass particles, and organic particles.

[0024] <11> The optical sheet according to any one of <1> to <10>, wherein the material of the metal oxide particles and the metal compound particles includes one or more of the following: titanium oxide, zirconium oxide, aluminum oxide, zinc oxide, calcium carbonate, strontium carbonate, barium carbonate, magnesium carbonate, zinc carbonate, zirconium carbonate, manganese carbonate, cobalt carbonate, boehmite, aluminum borate, calcium silicate, magnesium sulfate, magnesium sulfate hydrate, and potassium titanate.

[0025] <12> The optical sheet according to any one of <1> to <11>, wherein the particles are surface-treated.

[0026] <13> The optical sheet according to any one of <1> to <12>, wherein the particles may contain one or more silane coupling agents, surfactants, and oils and fats on their surface.

[0027] <14> The optical sheet according to any one of <1> to <13>, wherein the length of the particles in the longitudinal direction is 1.0 μm or more and 100 μm or less, and the length of the particles in the short direction is 0.10 μm or more and 10 μm or less.

[0028] <15> The optical sheet according to any one of <1> to <14>, wherein the ratio of the length of the particle in the longitudinal direction to the length of the particle in the short direction is 5.0 or more.

[0029] <16> The optical sheet according to any one of <1> to <15>, wherein the binder component includes a cured resin.

[0030] <17> The optical sheet according to any one of <1> to <16>, wherein the refractive index of the binder component is 1.40 or more and 1.60 or less.

[0031] <18> The optical sheet according to any one of <1> to <17>, wherein the difference between the refractive index of the particles in the short direction and the refractive index of the binder component is greater than the difference between the refractive index of the particles in the long direction and the refractive index of the binder component.

[0032] <19> Further comprising a base material, wherein the base material and the light diffusion layer are positioned in this order from the second surface toward the first surface, the optical sheet according to any one of <1> to <18>.

[0033] <20> Further comprising a functional layer, wherein the light diffusion layer and the functional layer are positioned in this order from the second surface toward the first surface, the optical sheet according to any one of <1> to <19>.

[0034] <21> The refractive index of the functional layer is 1.40 or less, the optical sheet according to <20>.

[0035] <22> Further comprising a second functional layer positioned between the light diffusion layer and the functional layer, the optical sheet according to <20> or <21>.

[0036] <23> The refractive index of the functional layer is 1.60 or more, the optical sheet according to <22>.

[0037] <24> A sheet article comprising a plurality of the optical sheets according to any one of <1> to <23>.

[0038] <25> The sheet article according to <24>, which is wound around a winding axis.

[0039] <26> Comprising a first protective sheet, a polarizer, and a second protective sheet, wherein at least one of the first protective sheet and the second protective sheet includes the optical sheet according to any one of <1> to <23>, a polarizing plate.

[0040] <27> An image forming apparatus and the optical sheet according to any one of <1> to <23> superimposed on the image forming apparatus, a display device.

[0041] <28> An article to be joined and the optical sheet according to any one of <1> to <23> joined to the article to be joined, a panel.

[0042] Hereinafter, details of an embodiment of the present disclosure will be described. In the drawings attached to this specification, for the convenience of illustration and easy understanding, the scale, the aspect ratio in the vertical and horizontal directions, etc. are appropriately changed and exaggerated from those of the actual object.

[0043] In this specification, terms such as "sheet," "film," and "plate" are not distinguished from each other solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished from components such as optical films or optical plates solely on the basis of differences in name.

[0044] In this specification, the direction perpendicular to a sheet-like (film-like, plate-like) member refers to the direction parallel to the perpendicular or normal to the sheet surface of the sheet-like (film-like, plate-like) member in question. The "sheet surface (film surface, plate surface)" refers to the surface that coincides with the sheet-like (film-like, plate-like) member in question when viewed as a whole and in a broad sense.

[0045] 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.

[0046] To clarify directional relationships between drawings, some drawings use arrows with common symbols to indicate common directions. 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, 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. Arrows pointing towards the front of the drawing, perpendicular to the plane of the drawing, are indicated by a symbol of a dot inside a circle, as shown in Figure 8A, for example.

[0047] <<<Optical Sheet>>> As shown in Figure 1, 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 first direction D1 is perpendicular to the optical sheet 10. The optical sheet 10 includes a light diffusion layer 30.

[0048] As shown in Figure 1, the optical sheet 10 may include a substrate 20 and a light diffusion layer 30 in the order from the second surface 12 to the first surface 11. In the example shown in Figure 1, the substrate 20 constitutes the second surface 12, and the light diffusion layer 30 constitutes the first surface 11.

[0049] The optical sheet 10 of this embodiment is not limited to the layer configuration shown in Figure 1. The optical sheet 10 of this embodiment may have a layer configuration other than that shown in Figure 1.

[0050] As shown in Figure 2, the optical sheet 10 may include a substrate 20, a light diffusion layer 30, and a functional layer 40 in the order from the second surface 12 to the first surface 11. The functional layer 40 is a layer expected to perform some function. In the example shown in Figure 2, the light diffusion layer 30 is located between the substrate 20 and the functional layer 40 in the first direction D1. The substrate 20 constitutes the second surface 12. The functional layer 40 constitutes the first surface 11.

[0051] As shown in Figure 3, the optical sheet 10 may include a substrate 20, a light diffusion layer 30, a second functional layer 50, and a functional layer 40 in the order from the second surface 12 to the first surface 11. The functional layer 40 and the second functional layer 50 are layers expected to perform some function. In the example shown in Figure 3, the light diffusion layer 30 is located between the substrate 20 and the second functional layer 50 in the first direction D1. The second functional layer 50 is located between the light diffusion layer 30 and the functional layer 40 in the first direction D1. The substrate 20 constitutes the second surface 12. The functional layer 40 constitutes the first surface 11.

[0052] In the examples shown in Figures 1-3, the first direction D1 is the stacking direction. In the specific examples shown in Figures 1-3, the first direction D1 is perpendicular to the first surface 11. The multiple layers 20, 30, 40, and 50 contained in the optical sheet 10 are stacked in the first direction D1. Each layer 20, 30, 40, and 50 has a perpendicular or normal line parallel to the first direction D1. Each layer 20, 30, 40, and 50 extends in the second direction D2 and the third direction D3, which are perpendicular to the first direction D1. In the illustrated examples, the second direction D2 and the third direction D3 are perpendicular to each other.

[0053] In this embodiment, as shown in Figures 4 and 5, the light diffusion layer 30 includes a binder component 36 and particles 37. As shown in Figure 6, the particles 37 have a longitudinal direction DL and a transverse direction DS. The longitudinal direction DL is the direction in which the length of the particle 37 is longest. The transverse direction DS is the direction perpendicular to the longitudinal direction DL.

[0054] As can be seen from Figures 4 and 5, the particles 37 are arranged such that their longitudinal direction DL is parallel to the orientation direction DX. Alternatively, the particles 37 are arranged such that their longitudinal direction DL is not significantly inclined with respect to the orientation direction DX. In other words, the particles 37 are arranged such that the orientation angle θX is 0° or small. As described above, the particles 37 are oriented in the light diffusion layer 30.

[0055] As shown in Figure 6, the orientation angle θX of particle 37 is the angle between the longitudinal direction DL and the orientation direction DX of particle 37 when observed from the first direction D1. The unit of the orientation angle is degrees (°). The orientation angle is between 0° and 90°.

[0056] By orienting particles 37 having a longitudinal direction DL in the light diffusion layer 30, an anisotropic light diffusion function can be imparted to the light diffusion layer 30. Anisotropic light diffusion function means a light diffusion function in which the light diffusion ability differs depending on the direction.

[0057] In the light diffusion layer 30 and optical sheet 10 shown in Figures 4 and 5, the light diffusion ability to spread light in the orientation direction DX is low. In the light diffusion layer 30 and optical sheet 10 shown in Figures 4 and 5, the light diffusion ability to spread light in the direction DY perpendicular to the orientation direction DX is high.

[0058] In the examples shown in Figures 4 and 5, the orientation direction DX is parallel to the third direction D3. The light diffusion direction DY, perpendicular to the orientation direction DX, is parallel to the second direction D2. In the examples shown in Figures 4 and 5, the optical sheet 10 can diffuse incident light mainly in the second direction D2. When observing the image on the back of the optical sheet 10, the field of view in the second direction D2 becomes wider. When observing the image on the back of the optical sheet 10, the field of view in the third direction D3 becomes narrower. If the observation position in the third direction D3 does not change significantly, the optical sheet 10 and the light diffusion layer 30 can effectively expand the field of view in the desired direction while avoiding unnecessary light diffusion.

[0059] As will be described later with reference to Figure 13, the optical sheet 10 can be applied to the display element 66. In this application example, the optical sheet 10 and the light diffusion layer 30 can expand the viewing angle in a desired direction (e.g., the horizontal direction) without excessively diffusing the image light. The energy efficiency of the display element 66 can be improved. That is, the viewing angle in a specific direction can be expanded using a low-energy-consuming display element 66.

[0060] Incidentally, in a light-diffusing layer in which particles having a longitudinal direction are oriented, not only the light-diffusing function but also the mechanical properties exhibit anisotropy. Light-diffusing layers and optical sheets in which particles having a longitudinal direction are oriented are easily bent around an axis parallel to the orientation direction DX. On the other hand, the light-diffusing layer and optical sheet 10 are resistant to bending around an axis perpendicular to the orientation direction DX.

[0061] Therefore, optical sheets containing a light-diffusing layer in which particles with a longitudinal orientation are oriented are prone to deformation such as curling and warping. Furthermore, optical sheets containing a light-diffusing layer in which particles with a longitudinal orientation are prone to defects such as cracks and scratches when deformed. In other words, conventional optical sheets had problems such as deformation and defects.

[0062] Furthermore, as described in Patent Document 1 (JP2022-182093A) and Patent Document 2 (WO2022 / 209643A1), deformation and defects are less likely to occur in light diffusion layers with low mechanical strength. For example, in light diffusion layers that function as adhesive layers, as described in Patent Document 1 (JP2022-182093A) and Patent Document 2 (WO2022 / 209643A1), deformation and defects are less likely to occur. On the other hand, in optical sheets that include a light diffusion layer containing a cured resin, problems such as deformation and defects become more pronounced.

[0063] The optical sheet according to this embodiment incorporates features to suppress deformation and defect formation, as described below. According to the optical sheet of this embodiment, deformation and defect formation in the light diffusion layer containing the cured resin can also be suppressed.

[0064] <<Standard deviation of orientation angle>> The optical sheet 10 according to this embodiment has the following feature (A): (A) The standard deviation of the particle orientation angle is 16° or more and 30° or less.

[0065] According to feature (A), by setting an upper limit on the orientation angle θX, particles can be sufficiently oriented within the light diffusion layer. By sufficiently oriented particles with a longitudinal direction, sufficient anisotropic light diffusion function can be imparted to the optical sheet.

[0066] From the viewpoint of imparting sufficient anisotropic light diffusion function to the optical sheet, the upper limit of the standard deviation of the particle orientation angle may be set as follows: The standard deviation of the particle orientation angle may be 30° or less, 28° or less, 26° or less, or 25° or less.

[0067] According to feature (A), by setting a lower limit on the standard deviation of the orientation angle θX, it is possible to suppress the excessive alignment of particle orientations within the light diffusion layer. The slight variation in the longitudinal direction of particles within the light diffusion layer provides the optical sheet with resistance to bending around an axis parallel to the orientation direction DX. Therefore, the occurrence of defects such as cracks and scratches in the optical sheet can be suppressed.

[0068] From the viewpoint of suppressing the occurrence of defects in the optical sheet, the lower limit of the standard deviation of the particle orientation angle may be set as follows: The standard deviation of the particle orientation angle may be 16° or more, 18° or more, 19° or more, 20° or more, or 22° or more.

[0069] The standard deviation of the particle orientation angle may be 16° to 30°, 18° to 30°, 19° to 30°, 20° to 30°, or 22° to 30°. The standard deviation of the particle orientation angle may be 16° to 28°, 18° to 28°, 19° to 28°, 20° to 28°, or 22° to 28°. The standard deviation of the particle orientation angle may be 16° to 26°, 18° to 26°, 19° to 26°, 20° to 26°, or 22° or more. The standard deviation of the particle orientation angle may be between 16° and 25°, between 18° and 25°, between 19° and 25°, between 20° and 25°, or between 22° and 25°.

[0070] The orientation angle θX is the angle (°) between the longitudinal direction DL of the particle 37 and the orientation direction DX when observed from a first direction D1 perpendicular to the optical sheet, as shown in Figure 6. The orientation direction DX is determined using a histogram of the orientation reference angle θZ of the particle 37. The orientation reference angle θZ is the angle (°) between the reference direction DZ and the longitudinal direction DL of each particle 37 when observed from the first direction D1. The orientation direction DX is the direction tilted relative to the reference direction DZ by an angle that is the median of the interval with the highest frequency in the histogram of the orientation reference angle θZ. The orientation direction DX is the direction corresponding to the center of the interval with the highest frequency in the histogram of the orientation reference angle θZ. The angle between the orientation direction DX and the reference direction DZ is the median (°) of the interval with the highest frequency in the histogram of the orientation reference angle θZ.

[0071] It is conceivable that the histogram for the reference orientation angle θZ may contain multiple intervals with the highest frequency. If multiple intervals with the highest frequency exist, the orientation direction DX is defined as the direction tilted relative to the reference direction DZ by the angle equal to the arithmetic mean of the medians of each of the intervals with the highest frequency.

[0072] Figure 7 shows an example of a histogram for the reference orientation angle θZ.

[0073] The reference direction DZ is not particularly limited. The reference direction DZ may be determined arbitrarily. For example, the reference direction DZ may be parallel to any one of the side edges of the optical sheet 10.

[0074] When the light diffusion layer 30 is manufactured using the manufacturing method described later with reference to Figures 8A and 8B, the reference direction DZ may be the flow direction of the substrate 20. The reference direction DZ may also be parallel to the longitudinal direction of the sheet article 5 described later. The reference direction DZ may also be parallel to one side edge of the rectangular optical sheet 10. In these examples, as shown in Figure 7, the orientation direction DX tends to coincide with the reference direction DZ. When the orientation direction DX and the reference direction DZ coincide, the orientation angle θX and the reference orientation angle θZ coincide. Therefore, as shown in Figure 7, the histogram for the orientation angle θX coincides with the histogram for the reference orientation angle θZ.

[0075] In the histogram for the reference orientation angle θZ, an interval is provided where the reference orientation angle θZ is between -1° and less than 1°. In the histogram for the reference orientation angle θZ, the width of the interval is 2°. In the histogram for the reference orientation angle θZ, there is no particular limit to the number of intervals.

[0076] The reference orientation angle θZ is an angle value between -90° and less than 90°. When observed from the first direction D1, if the longitudinal direction DL of particle 37 is tilted clockwise with respect to the reference direction DZ, the reference orientation angle θZ of particle 37 is a positive angle value. When observed from the first direction D1, if the longitudinal direction DL of particle 37 is rotated counterclockwise with respect to the reference direction DZ, the reference orientation angle θZ of particle 37 is a negative angle value.

[0077] The orientation angle θX is an angle value between -90° and less than 90°. When observed from the first direction D1, if the longitudinal direction DL of particle 37 is tilted clockwise with respect to the orientation direction DX, the orientation angle θX of particle 37 is a positive angle value. When observed from the first direction D1, if the longitudinal direction DL of particle 37 is rotated counterclockwise with respect to the reference direction DZ, the orientation angle θX of particle 37 is a negative angle value.

[0078] <Method for measuring orientation direction DX and orientation angle θX> The reference orientation angle θZ, the histogram for the reference orientation angle θZ, the orientation direction DX, and the orientation angle θX are measured and determined by the following procedure. The following method includes the steps of acquiring an image of the light diffusion layer, measuring the reference orientation angle θZ from the observed image, and identifying the orientation direction DX and orientation angle θX from the histogram for the reference orientation angle θZ.

[0079] (Step to acquire observation image) The step to acquire an observation image of the light diffusion layer is carried out as follows: A sample measuring 1 cm x 1 cm is cut from the optical sheet to be evaluated. If the optical sheet is rectangular, each side edge of the sample is made parallel to one of the side edges of the optical sheet. Conductive double-sided tape is attached to the entire surface of the sample corresponding to the second surface of the optical sheet. Furthermore, the conductive double-sided tape attached to the sample is attached to the flat sample stage. In this way, the sample is fixed to the flat sample stage using conductive double-sided tape. The flat sample stage is an accessory of the scanning electron microscope (SEM) used for observing the sample. The conductive double-sided tape is not particularly limited. The conductive double-sided tape may be SEM carbon tape with an aluminum base manufactured by Nissin EM Co., Ltd.

[0080] Apply carbon paste to the four corners of the sample fixed to the flat sample stage. The carbon paste is not particularly limited. The carbon paste may be colloidal graphite No. 7141 (solvent: isopropanol) manufactured by Nisshin EM Co., Ltd.

[0081] Next, a PtPd vapor-deposited film is formed on the sample using an ion sputtering apparatus. The ion sputtering conditions are as follows: Ar gas is introduced into the chamber containing the sample. Target: PtPd Vacuum level: 8 Pa Discharge current: 15 mA Deposition time: 30 seconds

[0082] After forming the vapor-deposited film, the standard sample stage with the sample fixed is mounted in the standard sample holder of a scanning electron microscope. Using the scanning electron microscope, an image of the light diffusion layer of the optical sheet is acquired from the first surface along the first direction. The observation conditions of the scanning electron microscope are set to allow observation of particles located within the total thickness of the light diffusion layer.

[0083] As a scanning electron microscope, Hitachi High-Technologies Corporation's field emission scanning electron microscope S4800 may be used. When using the scanning electron microscope S4800, the observation conditions may be set as follows. Figure 15 shows an example of an observed image. • Measurement mode: SE (Upper detector, HA mode) • Acceleration voltage: 30 kV • Emission current: 20 μA • WD (working distance): 10.0 mm or more and 10.5 mm or less • Lens mode: High • Magnification: 500x • Data size: 2560 pixels × 1920 pixels • Pixel size: 99.21875 nm

[0084] (Step to measure the reference orientation angle θZ from the observed image) The step of measuring the reference orientation angle θZ from the observed image obtained above is carried out as follows: Remove only the unnecessary parts, such as scale bars, that are not part of the sample image from the observed image. By removing the unnecessary parts, image data for image processing is obtained.

[0085] The longitudinal direction of each particle is determined from the image data. The angle between the reference direction DZ and the longitudinal direction of each particle is measured as the reference orientation angle θZ. The reference direction DZ is set to be parallel to one side of a 1 cm × 1 cm sample. ImageJ and Fiji are used as image processing software to measure the reference orientation angle θZ. The version of ImageJ used is 1.52e. ImageJ is open-source, public-domain image processing software whose development began at the National Institutes of Health in the United States. The Directionality analysis command (Method: Fourier Components) from the Analyze menu of Fiji is used to measure the reference orientation angle θZ.

[0086] (Step to identify orientation direction DX and orientation angle θX from a histogram of the reference orientation angle θZ) From the obtained reference orientation angle θZ, a histogram as shown in Figure 7 as an example is generated. The direction tilted from the reference direction DZ by the angle of the median of the interval with the highest frequency in the obtained histogram is identified as the orientation direction DX. If the histogram contains multiple intervals with the highest frequency, the direction tilted from the reference direction DZ by the average of the medians of the multiple intervals with the highest frequency is identified as the orientation direction DX.

[0087] The frequency in a histogram may also be expressed as a count. The count represents the number of particles contained within an interval. The unit of the count is "particles". The frequency in a histogram may also be expressed as a percentage. The percentage represents the ratio of the number of particles contained within an interval to the total number of particles measured at the reference orientation angle θZ. The unit of the percentage may be "%", or it may be a unitless value as shown in the histogram in Figure 7.

[0088] In the histogram shown in Figure 7, the interval with the highest frequency is the interval between -1° and less than 1°. In the example shown in Figure 7, the median of the interval with the highest frequency is 0°, which is the average of -1° and 1°. The orientation direction DX is the direction rotated 0° clockwise from the reference direction DZ. In the example shown in Figure 7, the orientation direction DX is parallel to the reference direction DZ.

[0089] The orientation angle θX of each particle is calculated by subtracting the angle of the median of the interval of maximum frequency in the histogram of the reference orientation angle θZ from the reference orientation angle θZ of that particle. The standard deviation (°) of the orientation angle θX is equal to the standard deviation (°) of the reference orientation angle θZ. The standard deviation of the reference orientation angle θZ is determined using the coefficients of a Gaussian function fitted to the histogram of the reference orientation angle θZ. Fiji is used for fitting. The standard deviation (°) of the orientation angle θX is taken as the value of the standard deviation of the reference orientation angle θZ determined in this way. Based on the obtained standard deviation (°) of the orientation angle θX, the characteristics (A) of the optical sheet in question can be evaluated. By determining the standard deviation (°) of the orientation angle θX using the method described above, instead of calculating the standard deviation (°) from the measured values ​​of the orientation angle θX, the influence of measurement anomalies of the orientation angle θX can be suppressed.

[0090] As shown in Figures 8A and 8B, the light-diffusing layer 30 can be formed using a coating solution for a light-diffusing layer containing a binder component 36 and particles 37. In the example shown in Figures 8A and 8B, the coating solution for a light-diffusing layer is applied onto the substrate 20 from a coater 83. A coating film 30F of the coating solution for a light-diffusing layer is formed on the substrate 20. By solidifying or curing the coating film 30F, the light-diffusing layer 30 is obtained from the coating film 30F.

[0091] In the example shown in Figure 8A, a long substrate 20 is conveyed by a support roll 81. A coater 83 applies a light-diffusing layer coating solution onto the substrate 20. The light-diffusing layer coating solution on the substrate 20 is flattened by a flattening roll 82. As a result, a coating film 30F of approximately constant thickness is obtained on the substrate 20.

[0092] In this forming method, the particles 37 dispersed in the coating liquid for the light diffusion layer are oriented by the shear force from the flattening roll 82. As shown in Figure 8B, the longitudinal direction DL of the particles 37 is aligned with the rotational direction of the flattening roll 82, that is, the conveying direction of the long substrate 20, or in other words, the mechanical direction of the apparatus.

[0093] In the light diffusion layer 30 formed by the methods shown in Figures 8A and 8B, the standard deviation of the orientation angle θX can be increased by weakening the orientation force from the flattening roll 82. The standard deviation of the orientation angle θX can be decreased by strengthening the orientation force from the flattening roll 82.

[0094] The shear force depends on the product of the viscosity of the coating solution for the light diffusion layer and the shear speed. By increasing the viscosity of the coating solution for the light diffusion layer, the standard deviation of the orientation angle θX can be reduced. By decreasing the viscosity of the coating solution for the light diffusion layer, the standard deviation of the orientation angle θX can be increased. By increasing the transport speed of the substrate 20, the standard deviation of the orientation angle θX can be reduced. By decreasing the transport speed of the substrate 20, the standard deviation of the orientation angle θX can be increased.

[0095] By increasing the size of the particles 37, the standard deviation of the orientation angle θX can be reduced. By decreasing the size of the particles 37, the standard deviation of the orientation angle θX can be increased. By reducing the thickness of the coating film, the standard deviation of the orientation angle θX can be reduced. By increasing the thickness of the coating film, the standard deviation of the orientation angle θX can be increased.

[0096] The methods for fabricating the light-diffusing layer shown in Figures 8A and 8B are merely illustrative. In the examples shown in Figures 8A and 8B, comma coating is used. Particle orientation can also be achieved by coating equipment other than comma coating if shear stress is generated in a certain direction. Reverse coating, gap coating, comma coating, die coating, lip coating, wire bar coating, dip coating, microgravure coating, or roll coating may also be used to fabricate the light-diffusing layer.

[0097] <<Histogram Full Width at Half Maximum>> In addition to feature (A), the optical sheet may also have feature (B). (B) The full width at half maximum of the histogram for the reference orientation angle is 38° or more and 71° or less.

[0098] Feature (B) specifies upper and lower limits for the full width at half maximum (FWHM) of the histogram for the reference orientation angle θZ. The full width at half maximum of the histogram for the reference orientation angle is the angular range in which more than half of the maximum frequency is obtained.

[0099] The full width at half maximum (FMAX) of the histogram for the reference orientation angle θZ is the same as the full width at half maximum of the histogram for the orientation angle θX. The full width at half maximum of the orientation angle θX may be set in the same manner as the full width at half maximum of the reference orientation angle θZ. The full width at half maximum of the reference orientation angle θZ is determined from the standard deviation σ of the reference orientation angle θZ. The full width at half maximum is given by "2σ × (2ln²) １／２ It is identified as "[ ]". The full width at half maximum of the reference orientation angle θZ is approximately 2.35 times the standard deviation of the reference orientation angle θZ.

[0100] According to feature (B), by setting an upper limit on the full width at half maximum of the histogram for the reference orientation angle, particles can be sufficiently oriented within the light diffusion layer. By sufficiently oriented particles with a longitudinal direction, sufficient anisotropic light diffusion function can be stably imparted to the optical sheet.

[0101] From the viewpoint of imparting a more effective anisotropic light diffusion function to the optical sheet, the upper limit of the full width at half maximum of the histogram for the reference orientation angle may be set as follows: The standard deviation of the particle orientation angle may be 71° or less, 65° or less, 60° or less, or 59° or less.

[0102] According to feature (B), by setting a lower limit on the full width at half maximum of the histogram for the reference orientation angle, the excessive alignment of particle orientations within the light diffusion layer can be more effectively suppressed. The slight variation in the longitudinal direction of particles within the light diffusion layer allows for more stable resistance to bending around an axis parallel to the orientation direction DX in the optical sheet. Therefore, the occurrence of defects such as cracks and scratches in the optical sheet can be more effectively suppressed.

[0103] From the viewpoint of suppressing the occurrence of defects in the optical sheet, the lower limit of the full width at half maximum of the histogram for the reference orientation angle may be set as follows: The standard deviation of the particle orientation angle may be 38° or greater, 40° or greater, 45° or greater, 50° or greater, or 52° or greater.

[0104] The full width at half maximum of the histogram for the reference orientation angle may be 38° or more and 71° or less, 40° or more and 71° or less, 45° or more and 71° or less, 50° or more and 71° or less, or 52° or more and 71° or less. The full width at half maximum of the histogram for the reference orientation angle may be 38° or more and 65° or less, 40° or more and 65° or less, 45° or more and 65° or less, 50° or more and 65° or less, or 52° or more and 65° or less. The full width at half maximum of the histogram for the reference orientation angle may be 38° or more and 60° or less, 40° or more and 60° or less, 45° or more and 60° or less, 50° or more and 60° or less, or 52° or more and 60° or less. The full width at half maximum of the histogram for the reference orientation angle may be 38° or more and 59° or less, 40° or more and 59° or less, 45° or more and 59° or less, 50° or more and 59° or less, or 52° or more and 59° or less.

[0105] The full width at half maximum of the histogram for the reference orientation angle θZ depends on the viscosity of the coating solution for the light diffusion layer, the transport speed of the substrate 20, the size of the particles 37, and the thickness of the coating film of the light diffusion layer.

[0106] Increasing the viscosity of the coating solution for the light diffusion layer tends to decrease the total width at half maximum. Decreasing the viscosity of the coating solution for the light diffusion layer tends to increase the total width at half maximum. Increasing the transport speed of the substrate 20 tends to decrease the total width at half maximum. Decreasing the transport speed of the substrate 20 tends to increase the total width at half maximum.

[0107] By increasing the size of particle 37, the total width at half maximum tends to decrease. By decreasing the size of particle 37, the total width at half maximum tends to increase. By decreasing the thickness of the coating film, the total width at half maximum tends to decrease. By increasing the thickness of the coating film, the total width at half maximum tends to increase.

[0108] <<Brightness Ratio>> In addition to feature (A), the optical sheet may also have feature (C). (C) The ratio of the brightness of the first surface in the first oblique direction to the brightness of the first surface in the second oblique direction is 1.13 or more, or 0.885 or less.

[0109] The ratio of luminances defined in feature (C) is also simply called the luminance ratio. The luminance ratio is the ratio of the first oblique luminance to the second oblique luminance. The luminance ratio has no units. The first oblique luminance is the luminance (cd / m²) on the first surface 11 in the first oblique direction DI1. ２ The first oblique direction DI1 is the direction in which diffusion is promoted or suppressed. The second oblique luminance is the luminance (cd / m²) on the first surface 11 in the second oblique direction DI2. ２ The second oblique direction DI2 is the direction in which diffusion is suppressed or the direction in which diffusion is promoted.

[0110] The first oblique direction DI1 is inclined at 60° with respect to the first direction D1, which is perpendicular to the optical sheet 10, as shown in Figure 9A. The first oblique direction DI1 is perpendicular to the orientation direction DX. That is, the first oblique direction DI1 is parallel to the plane perpendicular to the orientation direction DX and is inclined at 60° with respect to the first direction D1.

[0111] The second oblique direction DI2 is inclined at 60° with respect to the first direction D1, which is perpendicular to the optical sheet 10, as shown in Figure 9B. The second oblique direction DI2 is parallel to a plane that is parallel to both the first direction D1 and the orientation direction DX.

[0112] The luminance ratio is an indicator of the degree of anisotropy in the light diffusion function of the light diffusion layer 30. When the luminance ratio is far from 1, the light diffusion function of the light diffusion layer 30 exhibits strong anisotropy. When the luminance ratio is 1 or close to 1, the light diffusion function of the light diffusion layer 30 exhibits weak anisotropy.

[0113] By setting a lower limit greater than 1 for the luminance ratio, the optical sheet's light diffusion function has sufficient anisotropy. From the viewpoint of providing the optical sheet with a sufficiently effective anisotropic light diffusion function, a luminance ratio greater than 1 may be 1.13 or higher, 1.15 or higher, 1.20 or higher, 1.24 or higher, or 1.28 or higher.

[0114] There is no specific upper limit set for luminance ratios greater than 1. However, as the luminance ratio greater than 1 increases, the standard deviation of the orientation angle θX may fall below the lower limit defined in feature (A). Therefore, a luminance ratio greater than 1 may be 3.00 or less, 1.60 or less, or 1.57 or less.

[0115] A luminance ratio greater than 1 may be 1.13 or more and 3.00 or less, 1.15 or more and 3.00 or less, 1.20 or more and 3.00 or less, 1.24 or more and 3.00 or less, or 1.28 or more and 3.00 or less. A luminance ratio greater than 1 may be 1.13 or more and 1.60 or less, 1.15 or more and 1.60 or less, 1.20 or more and 1.60 or less, 1.24 or more and 1.60 or less, or 1.28 or more and 1.60 or less. A luminance ratio greater than 1 may be 1.13 or more and 1.57 or less, 1.15 or more and 1.57 or less, 1.20 or more and 1.57 or less, 1.24 or more and 1.57 or less, or 1.28 or more and 1.57 or less.

[0116] By setting an upper limit less than 1 for the luminance ratio, the light diffusion function of the optical sheet has sufficient anisotropy. From the viewpoint of providing the optical sheet with a sufficiently effective anisotropic light diffusion function, the luminance ratio less than 1 may be 0.885 or less, 0.870 or less, 0.833 or less, 0.806 or less, or 0.781 or less.

[0117] There is no specific lower limit set for luminance ratios less than 1. However, if the luminance ratio less than 1 becomes too small, the standard deviation of the orientation angle θX may fall below the lower limit defined in feature (A). Therefore, the luminance ratio less than 1 may be 0.333 or greater, 0.625 or greater, or 0.637 or greater.

[0118] A luminance ratio less than 1 may be 0.333 or more and 0.885 or less, 0.333 or more and 0.870 or less, 0.333 or more and 0.833 or less, 0.333 or more and 0.806 or less, or 0.333 or more and 0.781 or less. A luminance ratio less than 1 may be 0.625 or more and 0.885 or less, 0.625 or more and 0.870 or less, 0.625 or more and 0.833 or less, 0.625 or more and 0.806 or less, or 0.625 or more and 0.781 or less. A luminance ratio less than 1 may be between 0.637 and 0.885, between 0.637 and 0.870, between 0.637 and 0.833, between 0.637 and 0.806, or between 0.637 and 0.781.

[0119] When the luminance ratio is greater than 1, diffusion to the first diagonal direction DI1 is promoted, and diffusion to the second diagonal direction DI2 is suppressed. When the luminance ratio is less than 1, diffusion to the first diagonal direction DI1 is suppressed, and diffusion to the second diagonal direction DI2 is promoted.

[0120] The first and second oblique brightness are measured as follows: A 5 cm x 5 cm sample is cut from the optical sheet to be evaluated. One side of the sample is parallel to the orientation direction DX of the optical sheet. An optically transparent adhesive is applied to the entire surface corresponding to the second surface of the sample. A triacetylcellulose substrate is bonded to the optical sheet using the optically transparent adhesive. The thickness of the optically transparent adhesive layer is 10 μm to 40 μm. The thickness of the triacetylcellulose substrate is 80 μm. As a result, an evaluation sample 90 (see Figure 10) is obtained, which includes the optical sheet 10, the optically transparent adhesive layer 91, and the triacetylcellulose substrate 92 in this order, as shown in Figure 10.

[0121] Prepare a display element held on a rotating platform. The rotating platform holds the display element so that it can rotate around an axis A66 (see Figures 9A and 9B) parallel to the vertical direction. The display element is a Samsung Neo QLED KQ43QNB90AFXKR 43-inch display.

[0122] Prepare a luminance meter for the display element. Display a white image across the entire image-forming surface of the display element. Adjust the focus of the luminance meter to the image-forming surface of the display element. Measure the luminance of the image-forming surface (front luminance) from a direction perpendicular to the image-forming surface. Measure the luminance of the image-forming surface (oblique luminance) from a direction tilted 60° horizontally relative to the front direction. Front luminance is 400 cd / m². ２ More than 550cd / m ２ Please confirm the following: The oblique brightness is 50 cd / m². ２ 150cd / m or more ２ Please confirm the following:

[0123] As shown in Figure 10, the evaluation sample 90 is attached to the image forming surface 66a of the display element 66 using a small amount of water W. Care is taken to prevent air bubbles from forming in the water W.

[0124] Figure 9A shows the method for measuring the first oblique luminance. When measuring the first oblique luminance, the evaluation sample 90 is attached to the image forming surface 66a such that the rotation axis A66 of the support base and the orientation direction DX are parallel. By rotating the display element 66 to which the evaluation sample 90 is attached using the support base, the luminance meter is positioned to face the evaluation sample 90 from the first oblique direction DI1. The luminance of the surface corresponding to the first surface of the evaluation sample 90 is measured from the first oblique direction DI1 to obtain the first oblique luminance.

[0125] Figure 9B shows the method for measuring the second oblique luminance. When measuring the second oblique luminance, the evaluation sample 90 is attached to the image forming surface 66a such that the rotation axis R66 of the support base and the orientation direction DX are perpendicular. By rotating the display element 66 to which the evaluation sample 90 is attached using the support base, the luminance meter is positioned to face the evaluation sample 90 from the second oblique direction DI2. The luminance of the surface corresponding to the first surface of the evaluation sample 90 is measured from the second oblique direction DI2 to obtain the second oblique luminance. The position on the first surface 11 where the second oblique luminance is measured coincides with the position on the first surface where the first oblique luminance is measured.

[0126] The first oblique luminance, second oblique luminance, and frontal luminance are measured in a darkroom. The first oblique luminance, second oblique luminance, and frontal luminance are measured with the display element 66 displaying white across its entire surface. The test environment for measuring the first oblique luminance, second oblique luminance, and frontal luminance is set to a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample cut from the optical sheet is placed in the test environment for 16 hours before the start of the test.

[0127] Three samples are taken from the optical sheet to be evaluated. For each of the three samples, the ratio of the first oblique brightness to the second oblique brightness is calculated. The average of the three calculated ratios is taken as the brightness ratio for the optical sheet.

[0128] <<Weight Ratio of Particles>> In addition to feature (A), the optical sheet may also have feature (D). (D) The weight ratio of particles in the light diffusion layer is 5% or more and 30% or less.

[0129] Light diffusion in the light diffusion layer is due to the interface between the binder component and the particles, which has a refractive index difference. When the weight proportion of particles in the light diffusion layer is large, the area of ​​the refractive index interface increases. In other words, by increasing the weight proportion of particles in the light diffusion layer, a strong light diffusion function can be imparted to the optical sheet. On the other hand, when the weight proportion of particles in the light diffusion layer is small, the area of ​​the refractive index interface decreases. In other words, by decreasing the weight proportion of particles in the light diffusion layer, the light diffusion function of the optical sheet can be weakened.

[0130] The weight percentage of particles in the light diffusion layer serves as an indicator of the degree of light diffusion function of the light diffusion layer 30. Feature (D) specifies the upper and lower limits of the weight percentage of particles in the light diffusion layer. By setting a lower limit for the weight percentage of particles in the light diffusion layer, a sufficiently strong diffusion function can be imparted to the optical sheet. From the viewpoint of imparting a sufficiently strong diffusion function to the optical sheet, the weight percentage of particles in the light diffusion layer may be 5% or more, 10% or more, 15% or more, or 20% or more.

[0131] If the weight proportion of particles in the light diffusion layer becomes too high, the binder component may no longer be able to adequately hold the particles. When the binder component can no longer adequately hold the particles, particle detachment may occur. When the binder component can no longer adequately hold the particles, defects such as cracks and scratches are more likely to occur. From the viewpoint of suppressing particle detachment and the occurrence of defects, the weight proportion of particles in the light diffusion layer may be 30% or less.

[0132] The weight percentage of particles in the light diffusion layer may be 5% to 30%, 10% to 30%, 15% to 30%, or 20% to 30%.

[0133] The importance of the particles is determined by the following method: First, a sample is cut from the optical sheet. Layers other than the light-diffusing layer are removed from the sample to prepare a sample consisting only of the light-diffusing layer.

[0134] The sample is placed in a metal container, and the total weight (g) of the sample and the metal container is measured. This total weight (g) of the sample and the metal container is called the first weight. The metal container should be one that opens at the top. The weight (g) of the container alone is measured beforehand. This weight (g) of the container alone is called the container weight.

[0135] The metal container holding the sample is placed in an electric furnace heated to 450°C for 12 hours. After that, the container is removed from the electric furnace and cooled. After cooling, the total weight (g) of the container and the residual substance remaining inside the container is measured. This total weight (g) of the container and residual substance is called the second weight.

[0136] By holding the sample in a 450°C environment for 12 hours, the binder components of the light-diffusing layer are burned off. The residual substance will be the substance associated with the particles. The weight percentage of the particles is obtained by dividing the weight of the particles by the weight of the light-diffusing layer. The weight of the particles (g) is calculated as (((second weight) - (container weight))). The weight of the light-diffusing layer (g) is calculated as ((first weight) - (container weight))).

[0137] However, depending on the material constituting the particles, a part of the particles may vaporize and detach. When detachment due to vaporization occurs, the weight of the particles represented by "((Second weight) - (Container weight))" is not the weight of the particles but the weight of the residual substance after detachment. The product of the ratio of the molecular weight of the particles to the molecular weight of the residual substance after detachment (Molecular weight of particles / Molecular weight of residual substance) and the weight of the residual substance after detachment ((Second weight) - (Container weight)) is the weight of the particles. By dividing this weight of the particles by the weight (g) of the light diffusion layer ((First weight) - (Container weight)), the weight ratio of the particles can be obtained.

[0138] As an example, from calcium carbonate particles, CO2 detaches at high temperatures. The particles change from calcium carbonate represented by CaCO ３ to a residual substance represented by CaO and remain in the container. The molecular weight of calcium carbonate represented by CaCO ３ is 100.1, and the molecular weight of the residual substance represented by CaO is 56.1. The weight of the particles is specified as "(Second weight - Container weight) × 1.78".

[0139] The test environment for measuring the first weight, second weight, and container weight shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The measurement object for measuring the first weight, second weight, and container weight shall be placed in the test environment for 16 hours.

[0140] Take out three samples from the optical sheet to be evaluated. For each of the three samples, calculate the weight ratio of the particles. The average value of the three calculated weight ratios (%) shall be taken as the weight ratio (%) of the light diffusion layer.

[0141] <<Birefringence of Particles>> In addition to feature (A), the optical sheet may have feature (E). (E) The difference between the refractive index n37y of the particles in the short-axis direction and the refractive index n36 of the binder component is different from the difference between the refractive index n37x of the particles in the long-axis direction and the refractive index n36 of the binder component.

[0142] According to characteristic (E), particle 37 is birefringent. The refractive index n37y in the short direction of the particle, the refractive index n37x in the long direction of the particle, and the refractive index n36 of the binder component satisfy either of the following two relationships (X) and (Y). If (X) is satisfied, diffusion to the first oblique direction DI1 is promoted and diffusion to the second oblique direction DI2 is suppressed. If (Y) is satisfied, diffusion to the first oblique direction DI1 is suppressed and diffusion to the second oblique direction DI2 is promoted. (X) |n37x-n36| < |n37y-n36| (Y) |n37x-n36| > |n37y-n36|

[0143] <<Average thickness of the light-diffusing layer>> In addition to feature (A), the optical sheet may also have feature (F). (F) The average thickness of the light-diffusing layer is 10 μm or more.

[0144] Feature (F) specifies the lower limit of the average thickness of the light diffusion layer. By setting a lower limit of the average thickness of the light diffusion layer, the light diffusion layer can contain a sufficient amount of particles. By setting a lower limit of the average thickness of the light diffusion layer, a sufficiently strong diffusion function can be imparted to the optical sheet. From the viewpoint of imparting a sufficiently strong diffusion function to the optical sheet, the average thickness of the light diffusion layer may be 10 μm or more, 15 μm or more, 19 μm or more, 20 μm or more, or 24 μm or more.

[0145] There is no specific upper limit set for the average thickness of the light diffusion layer. From the viewpoint of suppressing the enlargement of the optical sheet, it may be 30 μm or less, or 26 μm or less.

[0146] The average thickness of the light-diffusing layer may be 10 μm or more and 30 μm or less, 15 μm or more and 30 μm or less, 19 μm or more and 30 μm or less, 20 μm or more and 30 μm or less, or 24 μm or more and 30 μm or less. The average thickness of the light-diffusing layer may be 10 μm or more and 26 μm or less, 15 μm or more and 26 μm or less, 19 μm or more and 26 μm or less, 20 μm or more and 26 μm or less, or 24 μm or more and 26 μm or less.

[0147] The "average thickness" used for each layer contained in the optical sheet shall be the value specified by (A1) to (A3) below. (A1) Observe an image by imaging the cross-section of the optical sheet with a scanning transmission electron microscope (STEM). Determine the imaging area so that the thickness direction (first direction) of the layer to be measured is aligned with the short side of the rectangular imaging area. The magnification during imaging shall be an appropriate magnification such that the thickness of the layer to be measured is between 1 / 3 and 2 / 3 of the length of the short side of the imaging area. (A2) Measure the thickness of the layer to be measured at the center position along the direction perpendicular to the first direction in the captured image, and the thickness of the layer to be measured at positions shifted 50 μm on both sides from the center position along the direction perpendicular to the first direction. The thickness shall be the length (μm) of the layer to be measured along the first direction. (A3) Perform the above steps (A1) and (A2) five times for the layer to be measured, and measure the thickness of the layer to be measured at a total of 15 positions. The average of the 15 thickness measurements will be taken as the average thickness (μm) of the layer being measured.

[0148] <<Deformation Resistance>> An optical sheet having characteristic (A) has excellent deformation resistance. An optical sheet having characteristic (A) may also have the deformation resistance described below.

[0149] <Curl Test Resistance> In addition to characteristic (A), the optical sheet may also have characteristic (G). (G) The maximum lift height in the curl test is 30 mm or less.

[0150] The curl test is performed as follows: A 10 cm x 10 cm sample is cut from the optical sheet to be evaluated. One side of the sample is parallel to the orientation direction DX of the optical sheet. The sample is placed on the mounting surface of a surface plate, and the height of the sample that is highest above the mounting surface of the surface plate is measured. The mounting surface of the surface plate is parallel to the horizontal plane. The height of the sample is the maximum height that is vertically lifted from the mounting surface.

[0151] A total of five samples were cut from the optical sheet. For the five samples cut from the optical sheet to be evaluated, the optical sheet was placed on the mounting surface from the second side. The average of the maximum heights measured for the five samples was taken as the maximum lift height in the curl test for the optical sheet to be evaluated.

[0152] The test environment for the curl test will be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The optical sheet to be evaluated will be placed in the test environment for 16 hours before the start of the test. Immediately before the test, a 10 cm x 10 cm sample will be cut from the optical sheet.

[0153] In light-diffusing layers containing cured resin as a binder component, defects such as deformation are prone to occur. As demonstrated in the examples described later, in optical sheets having characteristic (A), even when the light-diffusing layer contains cured resin, the maximum lift height in the curl test could be reduced to 30 mm or less.

[0154] The maximum lift height in the curl test may be 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, or 10 mm or less. There is no specific lower limit set for the maximum lift height in the curl test. The maximum lift height in the curl test may be 0 mm or more, or greater than 0 mm.

[0155] <Flexural Resistance (Cylindrical Mandrel Method)> In addition to characteristic (A), the optical sheet may also have characteristic (H). Optical sheets having characteristic (H) are less prone to defects such as cracks and scratches. (H) It is resistant to flexural resistance testing using a φ8 mm cylindrical mandrel method centered on an axis parallel to the orientation direction.

[0156] The bending resistance test using the cylindrical mandrel method is performed as follows: A sample measuring 100 mm x 50 mm is cut from the optical sheet to be evaluated. A pair of sides of the sample with a length of 50 mm are made parallel to the orientation direction DX of the optical sheet.

[0157] A 180° bending test will be performed using a Type 1 test apparatus as specified in "6.2.1." of JIS K 5600-5-1:1999. The sample will be mounted in the test apparatus so that the side facing the second surface is in contact with the mandrel. The bending of the sample using the test apparatus will be performed over 2 seconds. The mandrel will be made of stainless steel with a diameter of 8 mm.

[0158] After bending is complete, check the sample surface for defects such as scratches or cracks without removing the sample from the test apparatus. Observe the sample surface under indoor lighting. The observation distance should be approximately 30 cm. The illuminance on the sample surface should be between 800 Lx and 1200 Lx. Check for defects visually or using a 10x magnifying glass.

[0159] Three samples are cut from the optical sheet to be evaluated. If no defects are found in two or more samples, the sheet is evaluated as having resistance to the bending resistance test.

[0160] The test environment for the curl test will be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Samples cut from the optical sheet to be evaluated will be placed in the test environment for 16 hours before the start of the test.

[0161] Other conditions for conducting the flexural resistance test using the φ8 mm cylindrical mandrel method shall conform to JIS K 5600-5-1:1999.

[0162] Furthermore, JIS K 5600-5-1:1999 stipulates that the mandrel diameter should be reduced until a defect occurs, and the smallest mandrel diameter deemed to be resistant to the flexural resistance test should be identified. Mandrel diameters smaller than the 8 mm diameter specified in JIS K 5600-5-1:1999 are specified as 6 mm, 5 mm, 4 mm, 3 mm, and 2 mm. In a flexural resistance test using the cylindrical mandrel method centered on an axis parallel to the orientation direction, the optical sheet may be resistant to testing with a 6 mm diameter mandrel. In a flexural resistance test using the cylindrical mandrel method centered on an axis parallel to the orientation direction, the optical sheet may be resistant to testing with a 5 mm diameter mandrel.

[0163] In light-diffusing layers containing cured resin as a binder component, defects such as cracks and scratches are more likely to occur. As demonstrated in the examples described later, optical sheets having characteristic (A) can withstand bending resistance tests using mandrels with a diameter of 5 mm or less, even when the light-diffusing layer contains cured resin.

[0164] <<Pencil Hardness>> Defects such as cracks and scratches, as well as deformation, were more likely to occur in the light-diffusing layer, which has high mechanical strength. However, as demonstrated in the examples described later, according to feature (A), the occurrence of defects and deformation can be effectively suppressed even in optical sheets with high mechanical strength.

[0165] The optical sheet may have feature (J) in addition to feature (A). (J) The pencil hardness of the first surface is 2H or higher.

[0166] Pencil hardness is an index that indicates the resistance to defects such as scratches that occur when a pencil lead is pressed against and moved over a sample being evaluated. By having feature (J) in addition to feature (A) in the optical sheet, the scratch resistance of the first surface can be improved in an optical sheet in which the occurrence of defects and deformation is suppressed.

[0167] The pencil hardness on the first surface is measured as follows:

[0168] The optical sheet sample to be evaluated shall be rectangular in shape. The shorter side of the rectangle shall be 50 mm and the longer side shall be 100 mm. The test environment shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample shall be placed in the test environment for 16 hours before the start of the test. The rectangular sample shall be spread out on the pencil hardness tester so as not to wrinkle or warp. The two shorter sides of the spread-out sample shall be fixed to the electric pencil hardness tester using mending tape along the entire length of those shorter sides. The mending tape is not particularly limited. For example, the mending tape may be 3M's product name "810-3-18".

[0169] The load applied to the pencil during the test shall be 500g. The pencil's movement speed shall be 1.4 mm / second. The length of the pencil's movement shall be 10 mm. The direction of the pencil's movement shall be parallel to the long side of the sample. The pencil shall be a MITSU-BISHI uni. Five tests shall be performed on the same sample using pencils of the same hardness. The five tests shall be conducted at locations within the same sample that are at least 10 mm apart. A pencil with a resharpened lead shall be used for each of the five tests.

[0170] If no defects were found on the first surface during four or more tests, the sample is considered to have passed the evaluation. A defect is defined as a scratch of 3 mm or larger. The presence or absence of defects is confirmed by visual inspection of the surface of the sample after it has been removed from the pencil hardness tester. The observation of the sample surface is performed under indoor lighting. The observation distance is approximately 30 cm. The illuminance on the surface of the sample being observed is between 800 Lx and 1200 Lx.

[0171] The hardness of the pencil used in the tests that were judged to pass shall be the highest hardness among those used. The pencil hardness of the sample to be evaluated shall be the highest hardness. Other conditions for the pencil hardness test shall be in accordance with JIS K 5600-5-4:1999.

[0172] <<Total Light Transmittance>> The total light transmittance of the optical sheet may be 50% or more, 70% or more, 80% or more, or 90% 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%.

[0173] 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%, or 90% 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%, or 90% or more and less than 100%.

[0174] 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.

[0175] 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.

[0176] <<Transmission Haze>> The transmission haze of the optical sheet may be 30% or more, 35% or more, 38% or more, or 42% or more. The transmission haze of the optical sheet may be 60% or less, 55% or less, 50% or less, 48% or less, or 46% or less.

[0177] The transmitted haze of the optical sheet may be 30% to 60%, 35% to 60%, 38% to 60%, or 42% to 60%. The transmitted haze of the optical sheet may be 30% to 55%, 35% to 55%, 38% to 55%, or 42% to 55%. The transmitted haze of the optical sheet may be 30% to 50%, 35% to 50%, 38% to 50%, or 42% to 50%. The transmitted haze of the optical sheet may be 30% to 50%, 35% to 50%, 38% to 50%, or 42% to 50%. The transmitted haze of the optical sheet may be 30% to 48%, 35% to 48%, 38% to 48%, or 42% to 48%. The transmission haze of the optical sheet may be 30% to 46%, 35% to 46%, 38% to 46%, or 42% to 46%.

[0178] 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.

[0179] The transmitted haze is the arithmetic mean of five measurements. The five measurements are taken at five different measurement locations on the optical sheet being evaluated. The five measurement locations are located at least 10 mm apart from each other.

[0180] <<Luminous Reflectance>> The optical sheet may have a reflection suppression function that suppresses the reflection of light incident on the first surface. If the optical sheet has a reflection suppression function, the luminous reflectance Y value at the first surface measured at an incident angle of 5° may be 2.0% or less, 1.8% or less, 1.5% or less, 1.2% or less, 1.0% or less, 0.8% or less, 0.7% or less, 0.6% or less, or 0.5% or less.

[0181] There is no specific lower limit set for luminous reflectance. The luminous reflectance Y value at the first surface 11, measured at an incident angle of 5°, may be 0% or greater, or it may be greater than 0%.

[0182] The luminous reflectance Y value on the first surface, measured at an incident angle of 5°, may be between 0% and 2.0%, between 0% and 1.8%, between 0% and 1.5%, between 0% and 1.2%, between 0% and 1.0%, between 0% and 0.8%, between 0% and 0.7%, between 0% and 0.6%, or between 0% and 0.5%. The luminous reflectance Y value on the first surface, measured at an incident angle of 5°, may be greater than 0% and 2.0% or less, greater than 0% and 1.8% or less, 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, greater than 0% and 0.7% or less, greater than 0% and 0.6% or less, and greater than 0% and 0.5% or less.

[0183] The luminous reflectance Y value refers to the luminous reflectance Y value in the CIE 1931 standard color system. The luminous reflectance Y value (%) is measured using a spectrophotometer as follows:

[0184] A sample is cut from the optical sheet to be evaluated. A black plate is attached to the surface of the sample, which is formed by the second surface of the optical sheet, via an optically transparent adhesive sheet. The optically transparent adhesive sheet is "Panaclean PD-S1" manufactured by Panac 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 1% or less. Based on the above, evaluation sample A including the optical sheet, optically transparent adhesive sheet, and black plate is prepared.

[0185] Light is shone onto the surface of evaluation sample A, which is composed of the first surface of the optical sheet, at an incident angle of 5°. Based on the specular reflected light from evaluation sample A, the reflectance (luminous reflectance 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 based on the specular reflectance measured at 0.5 nm intervals in the range from 380 nm to 780 nm. Before measuring the luminous reflectance Y value of optical sheet 10, the auxiliary illuminant C is lit for 15 minutes to stabilize its output. The test environment for measuring luminous reflectance is set to a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before the start of the test.

[0186] Other measurement conditions when measuring luminous reflectance shall conform to JIS Z 8722:2009.

[0187] The luminous reflectance is the arithmetic mean of five measurements. The five measurements are taken at five different measurement locations on the optical sheet being evaluated. The five measurement locations are located at least 10 mm apart from each other.

[0188] <<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 substrate 20 and a light diffusion layer 30 from the second surface 12 toward the first surface 11. The optical sheet 10 shown in Figure 2 includes a substrate 20, a light diffusion layer 30, and a functional layer 40 from the second surface 12 toward the first surface 11. The optical sheet 10 shown in Figure 3 includes a substrate 20, a light diffusion layer 30, a second functional layer 50, and a functional layer 40 from the second surface 12 toward the first surface 11.

[0189] In the example shown in Figure 2, a low refractive index layer having a refractive index lower than that of the adjacent layer is exemplified as the functional layer 40 constituting the first surface 11. The functional layer 40 as a low refractive index layer can exhibit a low reflection function or reflection suppression function that suppresses reflection on the first surface 11. The functional layer 40 may be an antifouling layer or an antistatic layer.

[0190] In the example shown in Figure 3, a low-refractive-index layer having a refractive index lower than that of the adjacent layer is exemplified as the functional layer 40 constituting the first surface 11. In the example shown in Figure 3, a high-refractive-index layer having a refractive index higher than that of the two adjacent layers is exemplified as the second functional layer 50. The functional layer 40 and the second functional layer 50 can exhibit a low-reflection function or reflection suppression function that suppresses reflection on the first surface 11.

[0191] The optical sheet 10 may have a different layer configuration than those shown in Figures 1 to 3. The optical sheet 10 may include one or more antistatic layers and antifouling layers.

[0192] <Substrate> The substrate supports the light diffusion layer. As shown in Figures 1 to 3, the substrate 20 may constitute the second surface 12 of the optical sheet 10. The second surface 12 may be a flat surface. The second surface 12 may be a surface perpendicular to the lamination direction of the layers included in the optical sheet 10.

[0193] The substrate may be transparent. Transparency means that the total light transmittance is 50% or more. The total light transmittance of the substrate may be 70% or more, 80% or more, or 90% or more. The total light transmittance of the substrate may be 100% or less, or less than 100%. The total light transmittance of the substrate may be 70% or more and 100% or less, 80% or more and 100% or less, or 90% or more and 100% or less. The total light transmittance of the substrate may be 70% or more and less than 100%, 80% or more and less than 100%, or 90% or more and less than 100%.

[0194] 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.

[0195] The resin used for the base material may be an olefin resin such as polyethylene or polypropylene. The resin used for the base material may be a vinyl resin such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, or ethylene-vinyl alcohol copolymer. The resin used for the base material may be an ester 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.

[0196] The thickness of the resin substrate is not particularly limited. From the viewpoint of handling, the thickness of the resin substrate may be 10 μm or more, 20 μm or more, or 50 μm or more. The thickness of the resin substrate may be 500 μm or less, 400 μm or less, or 300 μm or less. The thickness of the 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. The thickness of the glass substrate may be 5 mm or less, or 500 μm or more.

[0197] In the application of optical sheets to foldable applications, the substrate may be flexible. In this example, the thickness of the resin substrate 20 may be 10 μm or more and 40 μm or less. When the optical sheet is used laminated with glass, the thickness of the resin substrate may be 40 μm or more and 100 μm or less from the viewpoint of preventing glass from shattering.

[0198] 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.

[0199] <Light Diffusing Layer> The light diffusing layer contains a binder component and particles. The particles have a longitudinal direction. The particles may also be birefringent. The light diffusing layer can exhibit anisotropic light diffusing function through reflection or refraction at the interface between the longitudinally oriented particles and the binder component.

[0200] ((Binder component)) The binder component is an element that holds particles. The binder component may also function as a binder for forming a coating film. The functional layer may maintain its film shape by holding the particles contained in the light diffusion layer with the binder component. The binder component may contain a resin. The resin contained in the binder component may be a natural resin or a synthetic resin. The binder component may completely surround each particle contained in the functional layer, or it may partially expose at least some of the particles contained in the functional layer.

[0201] The binder component may contain a resin. The binder component may contain a thermoplastic resin. Examples of thermoplastic resins include polystyrene resins, polyolefin resins, ABS resins (including heat-resistant ABS resins), AS resins, AN resins, polyphenylene oxide resins, polycarbonate resins, polyacetal resins, acrylic resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polysulfone resins, and polyphenylene sulfide resins.

[0202] The binder component may include a cured resin product. The light-diffusing layer containing the cured resin product as a binder component can also function as a hard coat layer. 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 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 light-diffusing 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.

[0203] A thermosetting resin composition contains a thermosetting compound. The thermosetting compound is a resin that hardens upon heating. The thermosetting compound is not particularly limited. Examples of thermosetting compounds include phenolic resins, urea resins, diallyl phthalate resins, melamine resins, guanamine resins, unsaturated polyester resins, polyurethane resins, epoxy resins, amino alkyd resins, melamine-urea cocondensation resins, silicon resins, and the like. The thermosetting resin composition may contain one or more of these thermosetting compounds.

[0204] Ionizing radiation-curable resin compositions contain compounds having ionizing radiation-curable functional groups. Hereinafter, compounds having ionizing radiation-curable functional groups will also be referred to as "ionizing radiation-curable compounds." Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups.

[0205] Ionizing radiation-curable compounds may contain two or more ionizing radiation-curable functional groups. Ionizing radiation-curable compounds may also be compounds having ethylenically unsaturated bonding groups. Ionizing radiation-curable compounds may also be (meth)acrylate compounds having (meth)acryloyl groups. Ionizing radiation-curable compounds may also be siloxane compounds containing siloxane bonds.

[0206] (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."

[0207] The (meth)acrylate compound may be a monomer or an oligomer. An ionizing radiation-curable compound containing a low-functionality (meth)acrylate compound can suppress uneven shrinkage during curing and smooth the surface of the functional layer 40.

[0208] The proportion of low-functional (meth)acrylate compounds in the ionizing radiation-curable compound may be 5% by mass or more, 10% by mass or more, 20% by mass or more, or 40% by mass or more. From the viewpoint of suppressing uneven shrinkage during curing and smoothing the uneven surface shape of the functional layer 40, the low-functional (meth)acrylate compound may be a (meth)acrylate compound containing two ethylenically unsaturated bonding groups. When the ionizing radiation-curable compound contains a large amount of polyfunctional (meth)acrylate compounds, the surface of the functional layer can be smoothed by appropriately adjusting the type of solvent and drying conditions, as described later.

[0209] 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.

[0210] 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.

[0211] (Particles) As shown in Figure 6, the particles have a longitudinal direction DL. The particles have a transverse direction DS perpendicular to the longitudinal direction DL. The particles are oriented in the light diffusion layer as defined in feature (A). The particles are arranged such that the orientation angle θX, which is the angle between the longitudinal direction of the particle and the orientation direction DX, is small. Due to the birefringence of the particles, the optical sheet and the light diffusion layer have anisotropic light diffusion function.

[0212] In the example shown in Figure 6, the width of the particle along the short direction DS decreases as it approaches both ends in the longitudinal direction DL. The particle shape is not limited to the example shown in Figure 6. The particle shape may have a constant width at each position along the longitudinal direction DL.

[0213] As shown in Figure 6, the particles may have a solid-of-revolution shape. The particles may have an ellipsoidal shape. The particles may have a rectangular parallelepiped shape. The particles may be isotropic even in a cross section perpendicular to the longitudinal direction DL. The particles may be anisotropic even in a cross section perpendicular to the longitudinal direction DL. The width of the particles may not be constant in a cross section perpendicular to the longitudinal direction DL.

[0214] The particles may have dimensions within the numerical range described below. By using particles having the following dimensions, the particles can be oriented in the light diffusion layer to satisfy feature (A).

[0215] The length of the particle along its longitudinal direction DL may be 1.0 μm or more and 100 μm or less, 10 μm or more and 60 μm or less, or 20 μm or more and 40 μm or less. The length of the particle along its short direction DS may be 0.10 μm or more and 10 μm or less, 0.20 μm or more and 5.0 μm or less, or 0.50 μm or more and 2.0 μm or less.

[0216] The aspect ratio of the particle shape is defined as the ratio of the length of the particle along its longitudinal direction DL to the length along its short direction DS. The aspect ratio of the particle shape may be 5.0 or greater, 10 or greater, or 20 or greater. There is no specific upper limit set for the aspect ratio of the particle shape. The aspect ratio of the particle shape may be 100 or less. The aspect ratio of the particle shape may be 5.0 or greater and 100 or less, 10 or greater and 100 or less, or 20 or greater and 100 or less.

[0217] When calculating the aspect ratio of the particle shape, the length along the shorter side is the dimension at the position where the area of ​​the cross-section perpendicular to the longer side DL is maximized. As described above, if the width at the cross-section is not constant, the length of the particle in the shorter side DS is the average of the maximum width at the cross-section and the width along the direction DS1 (see Figure 6) where the maximum width is obtained and the direction DS2 (see Figure 6) which is perpendicular to both the direction DS1 (see Figure 6) and the longer side DL.

[0218] As described above in Feature (E), the particles may have birefringence. That is, the refractive index of the particles may change depending on the polarization component of the incident light. In particles having a longitudinal direction DL and a transverse direction DS, the refractive index in the longitudinal direction DL and the refractive index in the transverse direction DS may be different.

[0219] As described in feature (E), the difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component may be greater than the difference between the refractive index n37x in the long direction of the particle and the refractive index n36 of the binder component. That is, particle 37 is birefringent. Furthermore, the refractive index n37y in the short direction of the particle, the refractive index n37x in the long direction of the particle, and the refractive index n36 of the binder component may satisfy either of the following two relationships (X) and (Y): (X) |n37x - n36| < |n37y - n36| (Y) |n37x - n36| > |n37y - n36|

[0220] When (X) is satisfied, the refractive index difference of the interface between the particle and the binder component extending in the orientation direction DX is greater than the refractive index difference of the interface extending in the direction DY perpendicular to the orientation direction DX. Incident light to the light diffusion layer is more easily diffused in the direction DY perpendicular to the orientation direction DX than in the orientation direction DX.

[0221] When (Y) is satisfied, the refractive index difference of the interface between the particle and the binder component extending in the orientation direction DX is smaller than the refractive index difference of the interface extending in the direction DY perpendicular to the orientation direction DX. Incident light to the light diffusion layer is more easily diffused in the orientation direction DX than in the direction DY perpendicular to the orientation direction DX.

[0222] If (X) is satisfied, the difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component (|n37y - n36|) may be 0.10 or greater, 0.12 or greater, or 0.14 or greater. Setting a lower limit on the difference (|n37y - n36|) can promote diffusion in the direction DY perpendicular to the orientation direction DX. No upper limit is set for the difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component. The difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component may be 0.40 or less. The difference between the refractive index n37y of the particle in the short direction and the refractive index n36 of the binder component (|n37y - n36|) may be between 0.10 and 0.40, between 0.12 and 0.40, or between 0.14 and 0.40.

[0223] If (X) is satisfied, the difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component (|n37x - n36|) may be 0.14 or less, 0.12 or less, or 0.10 or less. By setting an upper limit on the difference (|n37x - n36|), diffusion in the orientation direction DX can be suppressed. No lower limit is set for the difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component. The difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component may be 0 or greater, or greater than 0. The difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component (|n37x - n36|) may be 0 or more and 0.14 or less, 0 or more and 0.12 or less, or 0 or more and 0.10 or less. The difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component (|n37x - n36|) may be greater than 0 and 0.14 or less, greater than 0 and 0.12 or less, or greater than 0 and 0.10 or less.

[0224] If (Y) is satisfied, the difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component (|n37x - n36|) may be 0.10 or greater, 0.12 or greater, or 0.14 or greater. Setting a lower limit on the difference (|n37x - n36|) can promote diffusion in the orientation direction DX. No upper limit is set for the difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component. The difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component may be 0.40 or less. The difference between the refractive index n37x in the longitudinal direction of the particle and the refractive index n36 of the binder component (|n37x - n36|) may be 0.10 or greater and 0.40 or less, 0.12 or greater and 0.40 or less, or 0.14 or greater and 0.40 or less.

[0225] If (Y) is satisfied, the difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component (|n37y - n36|) may be 0.14 or less, 0.12 or less, or 0.10 or less. By setting an upper limit on the difference (|n37y - n36|), diffusion in the direction DY perpendicular to the orientation direction DX can be suppressed. No lower limit is set for the difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component. The difference between the refractive index n37y in the long direction of the particle and the refractive index n36 of the binder component may be 0 or greater, or greater than 0. The difference between the refractive index n37y in the short direction of the particle and the refractive index n36 of the binder component (|n37y - n36|) may be 0 or more and 0.14 or less, 0 or more and 0.12 or less, or 0 or more and 0.10 or less. The difference between the refractive index n37y of the particle in the short direction and the refractive index n36 of the binder component (|n37y - n36|) may be greater than 0 and 0.14 or less, greater than 0 and 0.12 or less, or greater than 0 and 0.10 or less.

[0226] Note that the refractive index in each direction DS in a cross section perpendicular to the longitudinal direction DL does not have to be constant. The refractive index may change in each direction along the cross section perpendicular to the longitudinal direction DL. In this example, the refractive index in the short direction DS of the particle is defined as the average of the maximum refractive index in the direction DY perpendicular to the longitudinal direction DL (maximum refractive index) and the refractive index in the direction perpendicular to the direction in which the maximum refractive index is obtained.

[0227] The absolute value of the difference between the refractive index n37x along the longitudinal direction of the particle and the refractive index n37y along the short direction of the particle (|n37x - n37y|) may be 0.10 or greater, 0.12 or greater, or 0.15 or greater. By setting a lower limit for the absolute value of the difference (|n37x - n37y|), strong anisotropy in the light diffusion function can be imparted to the light diffusion layer. No upper limit is particularly set for the absolute value of the difference (|n37x - n37y|). The absolute value of the difference (|n37x - n37y|) may be 0.35 or less. The absolute value of the difference between the refractive index n37x along the longitudinal direction of the particle and the refractive index n37y along the short direction of the particle (|n37x - n37y|) may be 0.10 or greater and 0.35 or less, 0.12 or greater and 0.35 or less, or 0.15 or greater and 0.35 or less.

[0228] The refractive index of the binder component may be between 1.40 and 1.70. By using readily available resins for the binder component, the refractive index of the binder component can be set to between 1.40 and 1.70.

[0229] The particles may include one or more metal oxide particles, metal compound particles, glass particles, and organic particles. The materials for the metal oxide particles and metal compound particles may include one or more of the following: titanium oxide, zirconium oxide, aluminum oxide, zinc oxide, calcium carbonate, strontium carbonate, barium carbonate, magnesium carbonate, zinc carbonate, zirconium carbonate, manganese carbonate, cobalt carbonate, boehmite, aluminum borate, calcium silicate, magnesium sulfate, magnesium sulfate hydrate, and potassium titanate.

[0230] The particles may be surface-treated. The particles may be surface-modified. When forming a light-diffusing layer from a coating film of a coating solution for a light-diffusing layer, the compatibility and dispersibility of the particles can be improved by surface treatment or surface modification. Surface treatment or surface modification suppresses the aggregation of particles within the light-diffusing layer.

[0231] The particles may include a layer formed by surface treatment on their surface. The particles may also include one or more silane coupling agents, surfactants, and oils and fats on their surface. The particles may be coated with one or more silane coupling agents, surfactants, and oils and fats.

[0232] The silane coupling agent may contain one or more (meth)acryloyl groups, epoxy groups, vinyl groups, allyl groups, and styryl groups. Surface treatment of particles with a silane coupling agent improves the affinity between the particles and the binder component, making the particles less likely to aggregate. Because the particles are less likely to aggregate, they are dispersed more uniformly within the binder component.

[0233] 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.

[0234] As explained in feature (D), the weight percentage of particles in the light diffusion layer may be between 5% and 30%.

[0235] <Method for producing a light-diffusing layer> As shown in Figures 8A and 8B, the light-diffusing layer may be produced using a coating solution for a light-diffusing layer that contains a curable resin composition and particles. The light-diffusing layer may also be obtained by curing the coating film of the coating solution for a light-diffusing layer. In this example, the coating solution for a light-diffusing layer to produce the light-diffusing layer may contain additives such as an antistatic agent, an antioxidant, a surfactant, and a dispersant.

[0236] When UV-curable compounds are used to form the binder component, the coating solution for the light-diffusing layer may contain additives such as photopolymerization initiators and photopolymerization accelerators. Examples of photopolymerization initiators include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler ketone, benzoin, 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.

[0237] The coating solution for the light diffusion layer may contain a leveling agent as an additive. The leveling agent may be a fluorine-based leveling agent or a silicone-based leveling agent (silicone compound). By including a silicone-based leveling agent in the coating solution for the light diffusion layer, the protrusion of particles from the surface of the light diffusion layer can be suppressed, and the first surface can be smoothed. Therefore, the slipperiness of the first surface is improved, and the scratch resistance of the first surface can be enhanced. With a silicone-based leveling agent, excellent slipperiness and excellent antifouling properties (fingerprint wiping ability, large contact angle with pure water and hexadecane) can be imparted to the first surface formed by the light diffusion layer.

[0238] 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.

[0239] The coating solution for the light-diffusing layer may contain a solvent. The viscosity of the coating solution for the light-diffusing layer can be adjusted by the solvent. The dispersion of each component contained in the coating solution for the light-diffusing layer can be controlled by the solvent. The surface properties of the resulting light-diffusing layer will change depending on the type of solvent. The type of solvent may be selected considering factors such as the saturated vapor pressure and the permeability of the solvent to the transparent substrate.

[0240] Examples of solvents include ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), 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 (isopropanol, butanol, cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), glycol ethers (propylene glycol monomethyl ether acetate, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), amides (dimethylformamide, dimethylacetamide, etc.), etc. The coating solution for the light diffusion layer may contain one or more solvents.

[0241] <Functional Layer> The optical sheet 10 shown in Figure 2 further includes a functional layer 40. The functional layer 40 constitutes the first surface 11. The illustrated functional layer 40 is a low refractive index layer. The low refractive index layer has a refractive index lower than that of the adjacent layer. As a low refractive index layer, the functional layer 40 is a low reflection layer or reflection suppression layer that has the function of suppressing reflection.

[0242] In terms of specific configuration, the functional layer may contain a binder component and particles. The particles may be low refractive index particles. The refractive index of the particles may be lower than that of the binder component. The refractive index of the functional layer is reduced by including low refractive index particles. The refractive index of the functional layer is lower than that of the light diffusion layer.

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

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

[0245] The refractive index of the functional layer may be 1.10 or more and 1.48 or less, 1.20 or more and 1.48 or less, 1.26 or more and 1.48 or less, 1.28 or more and 1.48 or less, or 1.30 or more and 1.48 or less. The refractive index of the functional layer may be 1.10 or more and 1.45 or less, 1.20 or more and 1.45 or less, 1.26 or more and 1.45 or less, 1.28 or more and 1.45 or less, or 1.30 or more and 1.45 or less. The refractive index of the functional layer may be 1.10 or more and 1.40 or less, 1.20 or more and 1.40 or less, 1.26 or more and 1.40 or less, 1.28 or more and 1.40 or less, or 1.30 or more and 1.40 or less. The refractive index of the functional layer may be 1.10 or more and 1.38 or less, 1.20 or more and 1.38 or less, 1.26 or more and 1.38 or less, 1.28 or more and 1.38 or less, or 1.30 or more. The refractive index of the functional layer may be 1.10 or more and 1.35 or less, 1.20 or more and 1.35 or less, 1.26 or more and 1.35 or less, 1.28 or more and 1.35 or less, or 1.30 or more and 1.35 or less.

[0246] The thickness of the functional layer may be 80 nm or more, 85 nm or more, or 90 nm or more. The thickness of the functional layer may be 150 nm or less, 110 nm or less, or 105 nm or less. The thickness of the functional layer may be 80 nm or more and 150 nm or less, 85 nm or more and 150 nm or less, or 90 nm or more and 150 nm or less. The thickness of the functional layer may be 80 nm or more and 110 nm or less, 85 nm or more and 110 nm or less, or 90 nm or more and 110 nm or less. The thickness of the functional layer may be 80 nm or more and 105 nm or less, 85 nm or more and 105 nm or less, or 90 nm or more and 105 nm or less.

[0247] The binder component in the functional layer may be the same as the binder component in the light diffusion layer. The binder component in the functional layer may also include a cured product of a curable resin composition. The curable resin composition may include one or more thermosetting resin compositions and ionizing radiation curable resin compositions.

[0248] The functional layer may contain one or more organic particles and inorganic particles. The functional layer may contain one or more hollow silica, solid silica, and magnesium fluoride particles as inorganic particles.

[0249] Hollow silica particles have an outer shell layer made of silica. In hollow silica particles, the inside of the particle surrounded by the outer shell layer is hollow. Air may be contained within the hollow space. Due to the presence of the internal hollow space, hollow silica particles have a refractive index lower than that of silica. The refractive index of hollow silica particles decreases as the volume of the internal hollow space increases. Hollow silica particles reduce the refractive index of the entire functional layer 40.

[0250] The functional layer may be fabricated by a wet process, similar to the light-diffusing layer. The functional layer may also be fabricated using a functional layer coating solution for forming the functional layer. The functional layer may be formed by drying and curing the coating film of the functional layer coating solution. The functional layer coating solution for forming the functional layer may contain additives and solvents that can be applied to the light-diffusing layer coating solution.

[0251] <Second Functional Layer> The optical sheet 10 shown in Figure 3 includes a functional layer 40 and a second functional layer 50. In the example shown in Figure 3, the functional layer 40 may be configured in the same way as the functional layer 40 described above included in the optical sheet 10 shown in Figure 2. That is, the functional layer 40 constitutes the first surface 11. The functional layer 40 is a low refractive index layer. The low refractive index layer has a refractive index lower than that of the adjacent second functional layer 50.

[0252] The second functional layer 50 is located between the functional layer 40 and the light diffusion layer 30 in the first direction D1, which is the stacking direction. The second functional layer 50 has a refractive index higher than that of the light diffusion layer 30 and the functional layer 40. The functional layer 40 as a low refractive index layer and the second functional layer 50 as a high refractive index layer function as a low reflection layer or reflection suppression layer, suppressing reflection at the first surface 11.

[0253] In terms of specific configuration, the second functional layer may contain a binder component and particles. The particles may be high refractive index particles. The refractive index of the particles may be higher than that of the binder component. The refractive index of the second functional layer is increased by containing high refractive index particles. The refractive index of the second functional layer is greater than that of the functional layer. The refractive index of the second functional layer is greater than that of the light diffusion layer.

[0254] From the viewpoint of reflection suppression function, the refractive index of the second functional layer and the average thickness of the functional layer may be set as follows: The refractive index of the second functional layer may be 1.55 or higher, or 1.56 or higher. The refractive index of the second functional layer may be 1.85 or lower, or 1.75 or lower. The refractive index of the second functional layer may be 1.55 or higher and 1.85 or lower, or 1.56 or higher and 1.85 or lower. The refractive index of the second functional layer may be 1.55 or higher and 1.75 or lower, or 1.56 or higher and 1.75 or lower. The thickness of the second functional layer may be 50 nm or higher and 250 nm or lower, or 50 nm or higher and 200 nm or lower.

[0255] The binder component included in the second functional layer may be the same as the binder component included in the light diffusion layer. The binder component included in the second functional layer may also include a cured product of a curable resin composition. The curable resin composition may include one or more thermosetting resin compositions and ionizing radiation curable resin compositions.

[0256] The second functional layer may contain one or more organic and inorganic particles. Examples of particles included in the second functional layer include antimony pentoxide, zinc oxide, titanium oxide, cerium oxide, tin-doped indium oxide, antimony-doped tin oxide, yttrium oxide, zirconium oxide, and aluminum oxide.

[0257] The second functional layer may be fabricated by a wet process, similar to the light-diffusing layer. The second functional layer may also be fabricated using a coating solution for the second functional layer. The second functional layer may also be fabricated by drying and curing the coating film of the coating solution for the second functional layer. The coating solution for the second functional layer may contain additives that can be applied to the coating solution for the light-diffusing layer.

[0258] <<<Sheet Articles>>> According to the manufacturing method of optical sheets 10 by the wet method, as shown in Figure 11, 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 11, 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.

[0259] <<<Polarizing Plate>>> The optical sheet 10 according to this embodiment may be applied to a polarizing plate 60. In the example shown in Figure 12, 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.

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

[0261] <<<Image Display Device>>> The optical sheet 10 according to this embodiment may be applied to a display device 65. In the example shown in Figure 13, the display device 65 includes a display element 66 and an optical sheet 10. The display element 66 has an image forming surface 66a for displaying an image. The optical sheet 10 is superimposed on the display element 66 such that its second surface 12 faces the image forming surface 66a. The optical sheet 10 may be bonded to the display element 66 via a bonding layer containing an adhesive or tack. The display element 66 is not particularly limited. Examples of the display element 66 include liquid crystal display elements, EL display elements, plasma display elements, electronic paper elements, and the like.

[0262] The observer observes the image displayed by the display element 66 through the optical sheet 10. As described above, the optical sheet 10 has an anisotropic light diffusion function. Therefore, it can diffuse the image light emitted from the image forming surface 66a in one direction along the image forming surface 66a. Thus, the viewing angle in one direction can be expanded. On the other hand, it can suppress image light in the direction perpendicular to that direction. Therefore, by suppressing the diffusion of image light in unnecessary directions, the image light can be used efficiently. In other words, the display element 66 can display an image that can be observed from a desired viewing angle without unnecessarily increasing the output of the display element 66.

[0263] As described above, the optical sheet 10 is designed to suppress deformation and the occurrence of defects. Therefore, it is possible to suppress the occurrence of defects such as cracks and scratches on the optical sheet 10 during handling. For example, even if the optical sheet 10 is bent when it is bonded to the image forming surface 66a of the display element 66, it is possible to suppress bending of the optical sheet 10 and the occurrence of defects on the optical sheet.

[0264] <<<Panel>>> The optical sheet 10 according to this embodiment is applicable to various uses. Figure 14 shows a panel 70 to which the optical sheet 10 is applied. The panel 70 includes the optical sheet 10 and the article to be bonded 71 to which the optical sheet 10 is bonded. The panel 70 constitutes a light-diffusing member that diffuses incident light with respect to the optical sheet 10. 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, display windows, and windows.

[0265] This disclosure will be further described in detail by examples. This disclosure is not limited to the following examples.

[0266] <<<1. Preparation of Optical Sheets>>> Optical sheets according to Examples 1 to 5 and Comparative Examples 1 to 4 were prepared.

[0267] <<Example 1>> A light-diffusing layer coating solution 1 with the following formulation was applied to a polyethylene terephthalate substrate with a thickness of 100 μm using an applicator. The viscosity of the light-diffusing layer coating solution 1 was 880 mPa·s. Next, the coating film of the light-diffusing layer coating solution 1 was dried at 70°C for 1 minute (drying air velocity of 10 m / s) to evaporate the solvent. After that, the coating film of the light-diffusing layer coating solution 1 was exposed to an integrated light intensity of 100 mJ / cm². ２ The material was then irradiated with ultraviolet light. As a result, a light-diffusing layer with a dry thickness of 19 μm was fabricated on the substrate. The particle content (by weight) in the light-diffusing layer was 20%.

[0268] Next, the functional layer coating solution 1 (low refractive index layer coating solution 1) with the following formulation was applied to the light diffusion layer using a wire bar. The solid content of the functional layer coating solution 1 was 3%. Subsequently, the coating film of the functional layer coating solution 1 was dried at 70°C for 1 minute (drying air velocity of 10 m / s) to evaporate the solvent. Next, the coating film of the functional layer coating solution 1 was exposed to an integrated light intensity of 300 mJ / cm². ２ Ultraviolet light was irradiated onto the sheet. As a result, a functional layer (low refractive index layer) with a dry thickness of 100 nm was formed, and the optical sheet of Example 1 was obtained.

[0269] <Coating Solution A1 for Light Diffusion Layer> ・UV-curable acrylate-containing composition 100 parts by weight (acrylic polymer having acryloyl groups) ・Aragonite-type calcium carbonate particles 20 parts by weight (manufactured by Maruo Calcium Co., Ltd., trade name "Wiscal", length in the longitudinal direction is 20 μm or more and 30 μm or less, length in the short direction is 0.5 μm or more and 1.0 μm or less) ・Photopolymerization initiator 5 parts by weight (IGM Resins, trade name "Omnirad 184", 1-hydroxycyclohexyl phenyl ketone) ・Fluorine-based leveling agent 0.5 parts by weight (DIC Corporation, trade name "Megafac F-568") ・Solvent (methyl isobutyl ketone)

[0270] <Coating Solution 1 for Functional Layer (Coating Solution 1 for Low Refractive Index Layer)> ・UV-curable acrylate-containing composition 100 parts by weight (acrylic polymer having acryloyl groups) ・Hollow silica particles 130 parts by weight (particles with an average primary particle diameter of 80 nm, surface-treated with a silane coupling agent having methacryloyl groups) ・Solid silica particles 20 parts by weight (particles with an average primary particle diameter of 10 nm, surface-treated with a silane coupling agent having methacryloyl groups) ・Photopolymerization initiator 7 parts by weight (IGM Resins, trade name "Omnirad 184", 1-hydroxycyclohexyl phenyl ketone) ・Fluorine-based leveling agent 2 parts by weight (DIC Corporation, trade name "Megafac RS-78") ・Solvent (methyl isobutyl ketone)

[0271] <<Example 2>> Example 2 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the coating solution A1 for the light diffusion layer is 10 parts by weight, the viscosity of the coating solution for the light diffusion layer is 610 mPa·s, and the dry thickness of the light diffusion layer is 24 μm. Otherwise, the optical sheet according to Example 2 was obtained in the same manner as in Example 1.

[0272] <<Example 3>> Example 3 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the coating solution A1 for the light diffusion layer was 15 parts by weight, the viscosity of the coating solution for the light diffusion layer was 720 mPa·s, and the dry thickness of the light diffusion layer was 15 μm. Otherwise, the optical sheet according to Example 3 was obtained in the same manner as in Example 1.

[0273] <<Example 4>> Example 4 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the light diffusion layer coating solution A1 is 5 parts by weight, the viscosity of the light diffusion layer coating solution is 1000 mPa·s, and the dry thickness of the light diffusion layer is 10 μm. Otherwise, the optical sheet according to Example 4 was obtained in the same manner as Example 1.

[0274] <<Example 5>> Example 5 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the light diffusion layer coating solution A1 is 30 parts by weight, the viscosity of the light diffusion layer coating solution is 500 mPa·s, and the dry thickness of the light diffusion layer is 26 μm. Otherwise, the optical sheet according to Example 5 was obtained in the same manner as in Example 1.

[0275] <<Comparative Example 1>> Comparative Example 1 differs from Example 1 in that it uses 15 parts by weight of non-hydrophilic treated acrylic-styrene copolymer organic particles (average particle size 3.5 μm, refractive index 1.55, manufactured by Sekisui Chemical Co., Ltd.) instead of aragonite-type calcium carbonate particles in the coating solution A1 for the light diffusion layer, the viscosity of the coating solution for the light diffusion layer is set to 750 mPa·s, and the dry thickness of the light diffusion layer is set to 20 μm. In all other respects, the optical sheet according to Comparative Example 1 was obtained in the same manner as in Example 1. The non-hydrophilic treated acrylic-styrene copolymer organic particles contained in the coating solution for the light diffusion layer used in Comparative Example 1 were spherical in shape and did not have a longitudinal direction.

[0276] <<Comparative Example 2>> Comparative Example 2 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the light diffusion layer coating solution A1 is 15 parts by weight, the viscosity of the light diffusion layer coating solution is 1450 mPa·s, and the dry thickness of the light diffusion layer is 16 μm. In all other respects, the optical sheet according to Comparative Example 2 was obtained in the same manner as in Example 1.

[0277] <<Comparative Example 3>> Comparative Example 3 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the light diffusion layer coating solution A1 is 10 parts by weight, the viscosity of the light diffusion layer coating solution is 240 mPa·s, and the dry thickness of the light diffusion layer is 27 μm. In all other respects, the optical sheet according to Comparative Example 3 was obtained in the same manner as in Example 1.

[0278] <<Comparative Example 4>> Comparative Example 4 differs from Example 1 in that the content of aragonite-type calcium carbonate particles in the light diffusion layer coating solution A1 is 40 parts by weight, the viscosity of the light diffusion layer coating solution is 690 mPa·s, and the dry thickness of the light diffusion layer is 47 μm. In all other respects, the optical sheet according to Comparative Example 4 was obtained in the same manner as in Example 1.

[0279] <<<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.

[0280] <<2-1. Standard deviation of orientation angle and full width at half maximum of histogram>> Using the method described above, the standard deviation of the orientation angle and the full width at half maximum of the histogram were measured for each optical sheet.

[0281] First, a 1 mm x 1 mm 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.

[0282] First, an image of the light diffusion layer was acquired using a scanning electron microscope (SEM). A Hitachi High-Technologies S4800 field emission scanning electron microscope was used as the scanning electron microscope. As an example, Figure 15 shows an image of the light diffusion layer for Example 3.

[0283] Subsequently, the orientation reference angle θZ was measured for each particle present in the image using the image processing software "ImageJ (version: 1.52e)" and "Fiji". The orientation reference angle θZ is the angle (°) between the reference direction DZ and the longitudinal direction DL of each particle. The reference direction DZ was set to be parallel to one side of the sample. A histogram of the measured reference orientation angles θZ was created. As an example, Figure 7 shows the histogram of the reference orientation angles θZ for Example 3.

[0284] The orientation direction DX and orientation angle θX were determined from the histogram of the reference orientation angle θZ. The orientation direction is the direction corresponding to the center of the interval with the highest frequency in the histogram for the reference orientation angle θZ. The orientation direction DX was defined as the direction tilted from the reference direction DZ by the angle of the median of the interval with the highest frequency in the histogram. The orientation angle θX is the angle (°) between the orientation direction DX and the longitudinal direction DL of each particle 37. The orientation angle θX of each particle was obtained by subtracting the angle of the median of the interval with the highest frequency in the histogram for the reference orientation angle θZ from the reference orientation angle θZ of that particle.

[0285] Based on the generated histograms, the standard deviation and full width at half maximum (FMAX) of the reference orientation angle θZ for each example were determined using the method described above. The standard deviation σ (°) of the orientation angle θX for each example is shown in the "Standard Deviation" column of Table 1. The full width at half maximum (°) of the histogram of the reference orientation angle θZ for each example is shown in the "FWHM" column of Table 1.

[0286] <<2-2. Brightness Ratio>> A 5cm x 5cm sample was cut from the optical sheets of the examples and comparative examples. One side of the sample was made parallel to the orientation direction DX of the optical sheet. The sample was visually inspected to ensure there were no abnormalities such as dust or scratches.

[0287] An optically transparent adhesive was applied to the entire surface corresponding to the second surface of the sample, and a triacetylcellulose substrate was attached to the sample. The thickness of the optically transparent adhesive layer was 25 μm. The thickness of the substrate was 80 μm. Thus, an evaluation sample 90 (see Figure 10) was obtained, containing an optical sheet, an optically transparent adhesive layer, and a triacetylcellulose substrate in this order. The evaluation sample 90 was attached to the display element 66 by interposing water W between the substrate 92 and the image forming surface 66a of the evaluation sample 90. The display element was a Samsung Neo QLED KQ43QNB90AFXKR 43-inch.

[0288] Using the method described above, the first oblique luminance, which is the luminance on the first surface in the first oblique direction, was measured for each example of the evaluation sample of the optical sheet. Using the method described above, the second oblique luminance, which is the luminance on the first surface in the second oblique direction, was measured for each example of the evaluation sample of the optical sheet.

[0289] A luminance meter BM-5A manufactured by Topcon Techno House Corporation was used to measure the first and second oblique luminances.

[0290] For each example, three samples were prepared, and the first and second oblique luminances were measured for each of the three samples. The luminance ratio of the first oblique luminance to the second oblique luminance was calculated for each of the three samples. The average of the luminance ratios of the three samples taken from the optical sheet for each example was taken as the luminance ratio for that example. The luminance ratios for each example are shown in the "Luminance Ratio" column of Table 1.

[0291] <<2-3. Curl Test>> A 10 cm x 10 cm sample was cut from the optical sheet relating to the examples and comparative examples. The sample was visually inspected to ensure there were no abnormalities such as dust or scratches. The curl test was performed on the optical sheet relating to each example using the method described above. The results of the curl test were evaluated according to the following evaluation criteria. The evaluation results are shown in the "Curl" column of Table 1.

[0292] <Evaluation Criteria> A: Maximum buoyancy height was 15 mm or less. B: Maximum buoyancy height was greater than 15 mm and 30 mm or less. C: Maximum buoyancy height was greater than 30 mm.

[0293] <<2-4. Cylindrical Mandrel Method Flexural Resistance Test>> A 100 mm x 50 mm 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. For the flexural resistance test, mandrels with diameters of 10 mm, 8 mm, 6 mm, 5 mm, 4 mm, 3 mm, and 2 mm were used. The diameter of the mandrel was reduced until a defect occurred, and the smallest mandrel diameter deemed to be resistant to the flexural resistance test was identified. For each example of optical sheet, a flexural resistance test was performed, bending around an axis parallel to the orientation direction DX, and bending around an axis perpendicular to the orientation direction DX. Other test methods and methods for inspecting the sample after testing were as described above.

[0294] The evaluation results of the bending resistance test, in which the mandrel is bent around an axis parallel to the orientation direction DX, are shown in the "DX" column of Table 1. The evaluation results of the bending resistance test, in which the mandrel is bent around an axis perpendicular to the orientation direction and DX, are shown in the "DY" column of Table 1. The "DX" and "DY" columns in Table 1 indicate the smallest mandrel diameter that was judged to be resistant.

[0295] <<2-5. Pencil Hardness>> A 50 mm x 100 mm sample was cut from the optical sheet relating to the examples and comparative examples. The sample was visually inspected to ensure there were no abnormalities such as dust or scratches. The pencil hardness of the optical sheet relating to each example was measured using the method described above. 3M's product name "810-3-18" was used as the mending tape to fix the sample to the pencil hardness tester. An electric pencil hardness tester manufactured by Toyo Seiki Seisakusho Co., Ltd. was used to measure the pencil hardness. The pencil hardness evaluated according to the evaluation criteria described above is shown in the "Pencil Hardness" column of Table 1.

[0296] <<2-6. Transmitted Haze>> A 10 cm x 10 cm sample was cut from the optical sheets of the examples and comparative examples. The samples were visually inspected to ensure there were no abnormalities such as dust or scratches. The transmitted haze (%) of the optical sheets of each example was measured using the method described above. A haze meter "HM-150" manufactured by Murakami Color Technology Laboratory was used to measure the transmitted haze. The measurement results of the transmitted haze are shown in the "Hz" column of Table 1.

[0297] <<2-7. Total Light Transmittance>> A 10 cm x 10 cm sample was cut from the optical sheet relating to the examples and comparative examples. The sample was visually inspected to ensure there were no abnormalities such as dust or scratches. The total light transmittance (%) of the optical sheet relating to each example was measured using the method described above. A haze meter "HM-150" manufactured by Murakami Color Technology Laboratory was used to measure the total light transmittance. The measurement results of the total light transmittance are shown in the "Tt" column of Table 1.

[0298] <<2-8. Luminous Reflectance Y>> 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 second side of the sample using 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 luminous reflectance Y (%) of the optical sheet relating to each example was measured using the method described above. A UV-2600 ultraviolet-visible spectrophotometer manufactured by Shimadzu Corporation was used to measure the luminous reflectance Y. The measurement results of the luminous reflectance Y are shown in the "Y" column of Table 1.

[0299]

[0300] D1: First direction, D2: Second direction, D3: Third direction, DX: Orientation direction, DY: Diffusion direction, DZ: Reference direction, θX: Orientation angle, θZ: Reference orientation angle, DI1: First oblique direction, D12: Second oblique direction, RA: Winding axis, W: Water, DL: Longitudinal direction, DS: Shortitudinal direction, 5: Sheet article, 6: Winding core, 7: Winding, 10: Optical sheet, 11: First surface, 12: Second surface, 20: Substrate, 30: Light diffusion layer, 30F: Coating film, 36: Binder component, 37: Particles, 40: Functional layer, 50: Second functional layer, 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: Article to be bonded, 81: Support roll, 82: Planarizing roll, 83: Coater, 90: Evaluation sample, 91: Optical transparent adhesive layer, 92: Substrate

Claims

1. An optical sheet comprising a first surface and a second surface opposite to the first surface, wherein the optical sheet comprises a light-diffusing layer containing particles having a longitudinal direction and a binder component, wherein the standard deviation of the orientation angle of the particles is 16° or more and 30° or less, the orientation angle is the angle between the longitudinal direction and the orientation direction of the particles when observed from a first direction perpendicular to the optical sheet, and the orientation direction is a direction tilted with respect to the reference direction by an angle that is the median of the interval with the maximum frequency in a histogram of the angle between a reference direction and the longitudinal direction of each particle when observed from the first direction.

2. The optical sheet according to claim 1, wherein the full width at half maximum of the histogram is 38° or more and 71° or less.

3. The optical sheet according to claim 1, wherein the ratio of the luminance of the first surface in the first oblique direction to the luminance of the first surface in the second oblique direction is 1.13 or more and 0.885 or less, the first oblique direction is inclined at 60° with respect to the first direction and perpendicular to the orientation direction, and the second oblique direction is inclined at 60° with respect to the first direction and parallel to a surface parallel to both the first direction and the orientation direction.

4. The optical sheet according to claim 1, wherein the weight ratio of the particles in the light diffusion layer is 5% or more and 30% or less.

5. The optical sheet according to claim 1, wherein the average thickness of the light diffusing layer is 10 μm or more.

6. The optical sheet according to claim 1, wherein the maximum lift height in the curl test is 30 mm or less.

7. The optical sheet according to claim 1, which is resistant to bending resistance testing using a cylindrical mandrel with a diameter of φ8 mm centered on an axis parallel to the orientation direction.

8. The optical sheet according to claim 1, wherein the reflectance on the first surface is 2.0% or less.

9. The optical sheet according to claim 1, wherein the particles include one or more metal oxide particles, metal compound particles, glass particles, and organic particles.

10. The optical sheet according to claim 1, wherein the binder component includes a cured resin.

11. A sheet article comprising a plurality of optical sheets as described in any one of claims 1 to 10.

12. The sheet article according to claim 11, which is wound around a winding axis.

13. A polarizing plate comprising a first protective sheet, a polarizer, and a second protective sheet, wherein at least one of the first protective sheet and the second protective sheet includes an optical sheet as described in any one of claims 1 to 10.

14. A display device comprising an image forming apparatus and an optical sheet according to any one of claims 1 to 10 superimposed on the image forming apparatus.

15. A panel comprising an article to be joined and an optical sheet according to any one of claims 1 to 10 joined to the article to be joined.

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