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

Abstract

This optical sheet includes a first surface and a second surface. The optical sheet includes a base material layer and a functional layer in the stated order from the second surface to the first surface. The base material layer includes an acrylic resin. The functional layer includes a resin cured product. Regarding an erosion depth (μm) and an erosion rate (μm / g) from the first surface, obtained as test results of an erosion test, the change gradient of the erosion rate with respect to the change in the erosion depth is defined as an erosion rate gradient ((μm / g) / (μm)). The ratio (H / W) of the maximum value H (μm / g) / (μm) of a Gaussian function fitted to the test results on a graph in which the horizontal axis represents the erosion depth and the vertical axis represents the erosion rate gradient to the full width at half maximum W (μm) of the Gaussian function is 2.0 or less.

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] Optical sheets are known, as disclosed in Patent Document 1 (JP2019-101298A). Optical sheets include a functional layer containing a cured resin. Optical sheets can be applied to display devices, for example. Examples of display devices include televisions, display devices incorporated into notebook PCs, display devices incorporated into desktop PCs, display devices incorporated into smartphones, and display devices incorporated into tablets. The functional layer has a function according to the application. Examples of functional layers include an anti-glare layer with anti-glare properties and a hard coat layer with scratch resistance.

[0003] An optical sheet includes a substrate that supports a functional layer. In the optical sheet described in Patent Document 1, a substrate made of an acrylic resin film is used.

[0004] It was confirmed that when a substrate containing acrylic resin is used, defects such as cracks, breaks, and peeling are more likely to occur in the functional layer.

[0005] This disclosure aims to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a substrate containing acrylic resin.

[0006] A first anti-glare sheet according to one embodiment of the present disclosure is an optical sheet including a first surface and a second surface, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a resin cured product, and for the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the slope of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), and the ratio (H / W) of the maximum value H (μm / g) / μm) of a Gaussian function fitted to the test results on a graph with the erosion depth on the horizontal axis and the erosion rate slope on the vertical axis to the full width at half maximum W (μm) of the Gaussian function is 2.0 or less.

[0007] A second anti-glare sheet according to one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a resin cured product, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the gradient of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), the first average erosion rate slope is 0.0050 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, and the first average erosion rate slope is the average value of the erosion rate slope after smoothing treatment. The smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis, on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), and the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions before the measurement position where the erosion rate first exceeds 0.20 μm / g, in an optical sheet.

[0008] A third anti-glare sheet according to one embodiment of the present disclosure is an optical sheet including a first surface and a second surface facing each other in a first direction, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a resin cured product, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the gradient of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), the second average erosion rate slope is 0.0035 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, and the second average erosion rate slope is the average value of the values ​​obtained by smoothing the erosion rate slope such that the absolute value is 0.10 μm / g or less. The smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis, on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), and the erosion rate slope used to calculate the second average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions before the measurement position where the erosion rate first exceeds 0.20 μm / g, in an optical sheet.

[0009] A sheet article according to one embodiment of the present disclosure comprises a plurality of anti-glare sheets according to one embodiment of the present disclosure.

[0010] A polarizing plate according to one embodiment of the present disclosure comprises an anti-glare sheet according to one embodiment of the present disclosure and a polarizer superimposed on the anti-glare sheet.

[0011] A display device according to one embodiment of the present disclosure comprises an anti-glare sheet according to one embodiment of the present disclosure and a display element superimposed on the anti-glare sheet.

[0012] A panel according to one embodiment of the present disclosure comprises an article to be bonded and any anti-glare sheet according to one embodiment of the present disclosure.

[0013] According to this disclosure, in an optical sheet using a substrate containing acrylic resin, it is possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer.

[0014] Figure 1 is a diagram illustrating one embodiment, and is a cross-sectional view showing an example of an optical sheet. Figure 2 is an enlarged view of Figure 1, and is a diagram showing the measurement area for erosion testing. Figure 3A is a diagram showing a test apparatus that can be used for erosion testing. Figure 3B is a diagram illustrating the test method for erosion testing. Figure 4 is a graph showing an example of the test results of erosion testing, showing the relationship between erosion depth and erosion rate. Figure 5 is a graph showing an example of the test results of erosion testing, showing the relationship between erosion depth and erosion rate slope. Figure 6 is a graph showing an example of the test results of erosion testing, showing a Gaussian function fitted to the test results of erosion depth and erosion rate slope. Figure 7 is a graph showing an enlarged view of the Gaussian function. Figure 8 is a graph showing the erosion rate slope of the test results shown in Figure 5 after smoothing. Figure 9 is a cross-sectional view showing another example of an optical sheet. Figure 10 is a cross-sectional view showing yet another example of an optical sheet. Figure 11 is a perspective view showing an example of a sheet article including an optical sheet. Figure 12 is a cross-sectional view showing an example of a polarizing plate including an optical sheet. Figure 13 is a cross-sectional view showing an example of a display device including an optical sheet. Figure 14 is a cross-sectional view showing an example of a panel including an optical sheet.

[0015] One embodiment of the present disclosure relates to the following <1> to <15>.

[0016] <1> An optical sheet comprising a first surface and a second surface, wherein a base layer and a functional layer are provided in order from the second surface toward the first surface, the base layer comprises an acrylic resin, and the functional layer comprises a resin cured product, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the slope of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), and the ratio (H / W) of the maximum value H (μm / g) / μm) of a Gaussian function fitted to the test results on a graph with the erosion depth on the horizontal axis and the erosion rate slope on the vertical axis to the full width at half maximum W (μm) of the Gaussian function is 2.0 or less.

[0017] <2> The optical sheet according to <1>, wherein the full width at half maximum W is 0.45 μm or more.

[0018] <3> The optical sheet according to <1> or <2>, wherein the maximum value H is 0.80 μm or less.

[0019] <4> The first average erosion rate slope is 0.0050 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, the first average erosion rate slope is the average value of the erosion rate slope after smoothing, the smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on both sides of the horizontal axis on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), the first surface and the second surface face each other in the first direction, The optical sheet according to any one of <1> to <3>, wherein the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g.

[0020] <5> An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a cured resin, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the gradient of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), the first average erosion rate slope is 0.0050 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, and the first average erosion rate slope is the average value of the erosion rate slope after smoothing, The smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis, on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), and the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions before the measurement position where the erosion rate first exceeds 0.20 μm / g, in an optical sheet.

[0021] <6> The second mean erosion rate slope is 0.0035 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, the second mean erosion rate slope is the average value of the values ​​obtained by smoothing the erosion rate slope such that the absolute value is 0.10 μm / g or less, the smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on both sides of the horizontal axis on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), the first surface and the second surface face each other in the first direction, The optical sheet according to any one of <1> to <5>, wherein the erosion rate slope used to calculate the second average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g.

[0022] <7> An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a cured resin, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the gradient of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), the second average erosion rate slope is 0.0035 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, and the second average erosion rate slope is the average value of the values ​​obtained by smoothing the erosion rate slope such that the absolute value is 0.10 μm / g or less. The smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis, on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), and the erosion rate slope used to calculate the second average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions before the measurement position where the erosion rate first exceeds 0.20 μm / g, in an optical sheet.

[0023] <8> The optical sheet according to any one of <1> to <7>, wherein the average erosion rate of the functional layer is smaller than the average erosion rate of the substrate layer, the average erosion rate of the functional layer is the arithmetic mean of the erosion rates measured at measurement positions within the functional layer measurement area, the first surface and the second surface face each other in a first direction, the functional layer measurement area is a region at least 0.50 μm away from both surfaces of the functional layer in the first direction, the average erosion rate of the substrate layer is the arithmetic mean of the erosion rates measured at measurement positions within the substrate layer measurement area, and the substrate layer measurement area is a region at least 4.0 μm away from the surface of the substrate layer facing the first surface in the first direction,

[0024] <9> The optical sheet according to any one of <1> to <8>, wherein the difference between the average erosion rate of the substrate layer and the average erosion rate of the functional layer is 0.30 μm / g or more and 0.80 μm / g or less.

[0025] <10> An optical sheet as described in any one of <1> to <9>, wherein the transmitted haze is 0.5 or more and 40 or less.

[0026] <11> A sheet article comprising multiple optical sheets as described in any one of items <1> to <10>.

[0027] <12> The sheet article described in <11>, which is wound around a winding axis.

[0028] <13> A polarizing plate comprising an optical sheet described in any one of <1> to <10>, and a polarizer superimposed on the optical sheet.

[0029] <14> A display device comprising an optical sheet described in any one of <1> to <10>, and a display element superimposed on the optical sheet.

[0030] <15> A panel comprising an article to be joined and an optical sheet according to any one of <1> to <10> joined to the article to be joined.

[0031] The following describes in detail one embodiment of the present disclosure. In the drawings attached to this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of illustration and ease of understanding. Components shown in some drawings may be omitted in other drawings. The scale and aspect ratios may differ between drawings.

[0032] In this specification, terms such as "sheet," "film," and "plate" are not distinguished from each other solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished from components called optical films or optical plates solely on the basis of differences in name.

[0033] In this specification, the normal direction of a sheet-like (film-like, plate-like) member refers to the direction parallel to the normal or perpendicular to the sheet surface (film surface, plate surface) of the sheet-like (film-like, plate-like) member in question. The "sheet surface (film surface, plate surface)" refers to the surface that coincides with the sheet-like (film-like, plate-like) member in question when viewed as a whole and in a broad sense.

[0034] 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.

[0035] To clarify the directional relationships between drawings, some drawings show a common first direction D1, second direction D2, and third direction D3 using arrows with a common reference numeral. The tip of the arrow represents the first side in each direction. The opposite side of the arrow represents the second side in each direction. Arrows pointing towards the back of the drawing along a direction perpendicular to the plane of the drawing are indicated by a symbol of an "x" inside a circle, as shown in Figure 1, for example.

[0036] <<<Optical Sheet 10>>> As shown in FIG. 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 the first direction D1. The first surface 11 faces the side opposite to the second surface 12 in the first direction D1. The optical sheet 10 includes a base material layer 40 and a functional layer 20. The base material layer 40 and the functional layer 20 are positioned in this order from the second surface 12 toward the first surface 11. The base material layer 40 includes an acrylic resin. The functional layer 20 includes a cured resin product.

[0037] The functional layer 20 can be imparted with various functions according to the use of the optical sheet 10. The functional layer may be a hard coat layer. The hard coat layer is a layer excellent in physical strength. The functional layer 20 as the hard coat layer may impart scratch resistance to the optical sheet 10.

[0038] As shown in FIG. 1, the functional layer 20 may be an antiglare layer. The antiglare layer may diffuse at least a part of the transmitted light to exhibit an antiglare function. The functional layer 20 as the antiglare layer may impart antiglare property to the optical sheet 10. By adjusting the antiglare function of the functional layer 20, the transmission haze of the optical sheet 10 can be adjusted. The functional layer 20 as the antiglare layer may function as a hard coat layer. That is, the functional layer 20 may be an antiglare layer and a hard coat layer at the same time.

[0039] In the example shown in FIG. 1, the first direction D1 is the lamination direction of the functional layer 20 and the base material layer - 40. The first direction D1 is the thickness direction of the optical sheet 10. The first direction D1 is the thickness direction of the functional layer 20 and the thickness direction of the base material layer 40. In the illustrated example, the first surface 11 is located on the first side in the first direction D1. The second surface 12 is located on the second side in the first direction D1.

[0040] In the example shown in FIG. 1, the functional layer 20 includes a first surface 21 and a second surface 22. The first surface 21 and the second surface 22 face each other in the first direction D1. The first surface 21 is located on the first side in the first direction D1. The second surface 22 is located on the second side in the first direction D1. The functional layer 20 functioning as an antiglare layer may include an uneven surface - 21X. The first surface 21 may include the uneven surface 21X. The first surface 21 may be constituted by the uneven surface 21X.

[0041] The first surface 21 and the uneven surface 21X may face the opposite side of the second surface 12 in the first direction D1. The first surface 21 and the uneven surface 21X may be farther from the second surface 12 of the optical sheet 10 in the first direction D1 than the second surface 22. The first surface 21 and the uneven surface 21X may be closer to the first surface 11 of the optical sheet 10 in the first direction D1 than the second surface 22.

[0042] The first surface 11 of the optical sheet 10 may include an uneven surface 11X. The first surface 11 of the optical sheet 10 may be constituted by the first surface 21 of the functional layer 20. The uneven surface 11X of the optical sheet 10 may be constituted by the uneven surface 21X of the functional layer 20. The uneven surface 11X of the optical sheet 10 may include unevenness corresponding to the unevenness of the uneven surface 21X of the functional layer 20. The uneven surface 11X may include a convex portion at a position facing the convex portion of the uneven surface 21X in the first direction D1. The uneven surface 11X may include a concave portion at a position facing the concave portion of the uneven surface 21X in the first direction D1. The height of the convex portion of the uneven surface 11X may be lower than the height of the convex portion of the uneven surface 21X. The depth of the concave portion of the uneven surface 11X may be shallower than the depth of the concave portion of the uneven surface 21X.

[0043] Due to the uneven surfaces 11X and 21X, the optical sheet 10 can change the traveling direction of incident light. The optical sheet 10 may have a light diffusion function of diffusing incident light due to the uneven surfaces 11X and 21X. Due to the uneven surfaces 11X and 21X, the optical sheet 10 may reflect incident light in a direction other than the specular reflection direction. Due to the uneven surfaces 11X and 21X, the optical sheet 10 may diffusely reflect at least a part of the incident light. Due to the optical action on the uneven surfaces 11X and 21X, the optical sheet 10 has anti-glare properties.

[0044] According to the anti-glare properties of the optical sheet, it is possible to suppress the reflection of the background of the environment where the optical sheet is disposed, for example, a lighting device, into the optical sheet. By suppressing the reflection of the background, the back of the optical sheet can be clearly observed. For example, when the optical sheet is located on the image forming surface of a display element, it is possible to suppress the overlapping of the reflected image on the image formed by the display element. Therefore, the image displayed by the display element can be clearly observed..

[0045] In the example shown in Figure 1, the substrate layer 40 includes a first surface 41 and a second surface 42. The first surface 41 and the second surface 42 face each other in a first direction D1. The first surface 41 is located on the first side in the first direction D1. The first surface 41 faces the first surface 11 in the first direction D1. The first surface 41 is closer to the first surface 11 than the second surface 12. The second surface 42 is located on the second side in the first direction D1. In the illustrated example, the second surface 42 of the substrate layer 40 constitutes the second surface 12 of the optical sheet 10.

[0046] In the example shown in Figure 1, the optical sheet 10 further includes an intermediate layer 30 located between the functional layer 20 and the base layer 40. The intermediate layer 30 is located between the functional layer 20 and the base layer 40 in a first direction D1. The intermediate layer 30 may be adjacent to the functional layer 20 in the first direction D1. The intermediate layer 30 may be adjacent to the base layer 40 in the first direction D1.

[0047] <<Physical properties measured by erosion testing>> In optical sheets where the base layer contains acrylic resin, it has been confirmed that defects such as cracks, fractures, and peeling are prone to occur in the functional layer containing the cured resin. Conventional technology has not taken measures against defects that may occur in the functional layer used together with the base layer containing acrylic resin. The optical sheet according to this embodiment has features related to the physical properties measured by erosion testing. According to this embodiment, the occurrence of defects that may occur in the functional layer used together with the base layer containing acrylic resin can be suppressed by the characteristic configuration related to the physical properties measured by erosion testing.

[0048] <Erosion Test> (Test Method and Apparatus) In the erosion test, particles are projected onto the sample multiple times. After each particle projection, the cross-sectional profile of the sample is checked. After each particle projection, the erosion depth (μm) is measured. The erosion depth is the depth of the depression formed in the sample along the first direction D1. The erosion depth is measured from the cross-sectional profile of the sample. The depression is formed in the region of the sample onto which the particles were projected by the particle projection.

[0049] The erosion rate is calculated from the test results of the erosion test. The erosion rate is the ratio (μm / g) of the change in erosion depth (μm) to the amount of particles projected (g). The amount of particles projected (g) is the mass (g) of particles contained in the projected test solution. The method for calculating the erosion rate will be described later.

[0050] The erosion rate obtained through erosion testing is an indicator of abrasion resistance or deformation resistance to impact. A low erosion rate indicates less abrasion or deformation due to impact. Samples with a low erosion rate have high impact resistance.

[0051] Erosion testing yields the erosion rate at each erosion depth. The graph shown in Figure 4 illustrates an example of the relationship between erosion depth and erosion rate. The distribution of erosion rates at each erosion depth allows for the evaluation of impact resistance at each location in the thickness direction of the object being measured.

[0052] Further details regarding the erosion test are provided below. The test environment for conducting the erosion test shall be a temperature of 21°C to 24°C and a relative humidity of 40% to 60%. The sample to be measured shall be placed in the test environment for 24 hours before the start of the test. Before the start of the test, it shall be confirmed that the sample to be measured is free from any abnormalities such as dust or scratches. It shall also be confirmed that no condensation has occurred on the sample to be measured.

[0053] The particles are projected onto the sample by spraying a test solution containing particles onto the sample. The test solution contains pure water, a dispersant, and particles. The mass ratio of pure water, dispersant, and particles is 968:2:30. The dispersant promotes the dispersion of particles in the test solution. The dispersant is not particularly limited. An example of a dispersant is "Demol N," a product name of Wako Pure Chemical Industries, Ltd.

[0054] The particles contained in the test solution shall be spherical silica. Particles sold by particle manufacturers as "spherical" qualify as spherical silica. The average particle diameter shall be within ±8% of 5.0 μm. That is, the average particle diameter shall be between 4.6 μm and 5.4 μm. For particles used in erosion testing, the average particle diameter shall be the diameter measured as the volume average value D50 in particle size distribution measurement by laser diffraction. That is, the average particle diameter of particles used in erosion testing shall be the so-called "median diameter".

[0055] As an example of particles, the model number "MSE-BS-5-3" specified by Palmeso Co., Ltd. is given. As an example of spherical silica corresponding to the model number "MSE-BS-5-3" specified by Palmeso Co., Ltd., the product number "BS5-3" from Potters-Ballotini Co., Ltd. is given.

[0056] The test liquid is supplied to the nozzle. The temperature of the test liquid supplied to the nozzle is set to 23°C ± 2°C. Compressed air is also supplied to the nozzle. The test liquid is pressurized and accelerated by the compressed air and sprayed from the nozzle's nozzle opening toward the measurement sample. The test liquid is sprayed onto the first surface 11 of the optical sheet 10 that constitutes the measurement sample. The direction of the test liquid spray from the nozzle toward the measurement sample is parallel to the first direction D1 of the optical sheet which is the measurement sample. The cross-sectional shape of the nozzle is a 1 mm × 1 mm square. The nozzle opening located at the tip of the nozzle is also a 1 mm × 1 mm square.

[0057] Cut out a sample from the optical sheet to be evaluated. Confirm that the sample is free from any abnormalities such as dust or scratches. Position the sample facing the nozzle. Attach the sample to the test apparatus so that the first surface of the optical sheet constituting the sample faces the nozzle's nozzle opening in its first direction. The distance between the nozzle's nozzle opening and the sample along the first direction D1 is set to 4 mm.

[0058] The erosion test includes an injection step in which a predetermined amount of test solution is injected from a nozzle, and a measurement step in which the erosion depth of the sample is measured with the injection of the test solution stopped. In the erosion test, a cycle including the injection step and the measurement step is repeated. That is, in the erosion test, the injection step and the measurement step are performed repeatedly.

[0059] The erosion depth increases due to the spraying of the test liquid and the projection of particles in the projection step. That is, the depth of the recess formed in the measurement sample along the first direction D1 increases due to the projection step. The spraying step and the measurement step may be repeated until the erosion depth exceeds the position 6 μm inside the substrate layer 40 along the first direction D1 from the first surface 41 of the substrate layer 40. When evaluating the presence or absence of features (A), (B), (C), (F), and (G) described later, the spraying step and the measurement step are repeated until the erosion depth exceeds the position P4 (see Figure 2) 6 μm inside the substrate layer 40 along the first direction D1 from the first surface 41 of the substrate layer 40.

[0060] The flow rate of the test fluid supplied to the nozzle, the flow rate of the compressed air supplied to the nozzle, the pressure of the compressed air supplied to the nozzle, and the pressure of the mixed fluid of the test fluid and compressed air inside the nozzle during the injection step are determined through the following calibration. Calibration is performed using the test apparatus used for the erosion test before the erosion test is conducted.

[0061] Prepare a 2 mm thick polymethyl methacrylate (PMMA) resin plate as a calibration sample. Confirm that the calibration sample is free from any abnormalities such as dust or scratches. Attach the calibration sample to the test apparatus in the same manner as the measurement sample described above. Spray an arbitrary amount of test solution from the nozzle towards the calibration sample. Then, stop spraying the test solution and measure the erosion depth from the cross-sectional profile of the calibration sample. The method for measuring the erosion depth is the same as the method for measuring the erosion depth of the measurement sample in the measurement step.

[0062] The test apparatus conditions are calibrated so that the erosion rate of the calibration sample is between 0.1615 μm / g and 0.1785 μm / g. The conditions of the test apparatus to be adjusted are the flow rate of the test liquid supplied to the nozzle, the flow rate of the compressed air supplied to the nozzle, the pressure of the compressed air supplied to the nozzle, and the pressure of the mixed fluid of the test liquid and compressed air inside the nozzle. For example, the flow rate of the test liquid supplied to the nozzle may be between 100 mL / min and 150 mL / min. The flow rate of the compressed air supplied to the nozzle may be between 4.0 mL / min and 8.0 mL / min.

[0063] Based on the above, the test apparatus is set to conditions such that the erosion rate in the erosion test on the calibration sample is between 0.1615 (μm / g) and 0.1785 (μm / g), and the above-described injection step is performed.

[0064] In the measurement step, the cross-sectional profile of the sample is measured. The cross-sectional profile represents the surface shape of the sample in a cross-section along the first direction D1, after abrasion (or erosion) caused by particle projection in the injection step. In the measurement step, the erosion depth is measured from the acquired cross-sectional profile. The erosion depth corresponds to the abrasion depth (or erosion depth) of the sample caused by particle projection in the repeated injection steps up to the time of measurement. The erosion depth is measured in the region of the calibration sample where particles were projected into the test solution. The erosion depth is measured at the most abraded position in the cross-sectional profile. That is, the erosion depth is the maximum abrasion depth at the end of the immediately preceding injection step.

[0065] Figures 3A and 3B show an example of a test apparatus 80 used for erosion testing. In the example shown in Figure 3A, the test apparatus 80 includes a nozzle 82, a tank 84, a first pipe 86, and a second pipe 88. The tank 84 stores the test liquid 96. The tank 84 may also include a stirring mechanism for agitating the test liquid.

[0066] The first pipe 86 extends between the tank 84 and the nozzle 82. The first pipe 86 supplies the test liquid 96 from the tank 84 to the nozzle 82. A flow meter 86a is provided in the first pipe 86. The flow meter 86a measures the flow rate of the test liquid 96 supplied to the nozzle 82. Compressed air is supplied to the second pipe 88 from an air source such as a compressor.

[0067] The second pipe 88 is connected to the nozzle 82. The second pipe 88 supplies compressed air to the nozzle 82. The second pipe 88 is equipped with a flow meter 88a and a pressure gauge 88b. The flow meter 88a measures the flow rate of compressed air supplied to the nozzle 82. The pressure gauge 88b measures the pressure of compressed air supplied to the nozzle 82.

[0068] The nozzle 82 mixes the test liquid 96 supplied from the first pipe 86 with compressed air supplied from the second pipe 88. The test liquid 96 is pressurized and accelerated by the compressed air. A pressure gauge 83 is provided in the nozzle 82. The pressure gauge 83 measures the pressure of the mixed fluid of the test liquid and compressed air inside the nozzle. As shown in Figure 3B, the test liquid 96 is ejected from the nozzle 82a. In the illustrated example, the nozzle 82a opens downward in the vertical direction. The nozzle 82 sprays the test liquid 96 downward in the vertical direction.

[0069] As shown in Figure 3B, the test liquid (a mixed fluid of test liquid and compressed air) 96 sprayed from the nozzle 82 contains particles 97 and air 98. When the particles 97 are projected onto the measurement sample 99, the measurement sample 99 is abraded, and abrasion fragments 99a are generated.

[0070] The illustrated test apparatus 80 further includes a mounting base 93, a support 94, a receiving container 92, and a recovery pipe 90. The mounting base 93 faces the nozzle 82a directly. The mounting base 93 faces the nozzle 82 from below in the vertical direction. The support 94 is to which the measurement sample 99 is attached. The support 94 is attached to the mounting base 93. The positions of the mounting base 93 and the support 94 are determined such that the distance d between the measurement sample 99 and the nozzle 82a is 4 mm.

[0071] The receiving container 92 surrounds the nozzle outlet 82a of the nozzle 82. The mounting base 93, support 94, and measurement sample 99 are placed inside the receiving container 92. The receiving container 92 collects the test liquid 96 injected from the receiving container 92. A recovery pipe 90 extends between the receiving container 92 and the tank 84. The recovery pipe 90 supplies the test liquid 96 collected in the receiving container 92 to the tank 84. A pumping device 91 is provided in the recovery pipe 90. The pumping device 91 may be, for example, a pump. The pumping device 91 pumps the test liquid 96 into the tank 84.

[0072] An example of a test apparatus that can be used in the injection step is the MSE test apparatus "MSE-A" from Palmeso Co., Ltd. The test apparatus "MSE-A" has the configuration shown in Figure 3A.

[0073] The measuring device used to acquire the cross-sectional profile of the sample in the measurement step may be a stylus-type device or a non-contact device. An example of a measuring device for acquiring the cross-sectional profile of a sample is the stylus-type shape measuring instrument "PU-EU1" manufactured by Kosaka Laboratory Co., Ltd. When using the measuring instrument "PU-EU1", the measurement conditions may be set as follows: Stylus tip radius: 2 μm; Load: 100 μN; Magnification: 20,000x; Measurement length: 3 mm; Measurement speed: 0.5 mm / second

[0074] (Erosion Rate and Erosion Rate Slope) Erosion testing is performed from the first surface of the optical sheet according to the erosion test method described above. Test results for the erosion depth (μm) and the amount of particles projected in each cycle (g) are obtained from the erosion testing from the first surface. The erosion rate is calculated from the erosion depth and the amount of particles projected. The erosion rate is the ratio (μm / g) of the change in erosion depth (μm) in each cycle (one projection step) to the amount of particles projected in each cycle (one projection step) (g).

[0075] Let D(n) be the erosion depth after the nth cycle. D(0) is set to 0. Let M(n) be the total particle projection after the nth cycle. M(0) is set to 0. Let R(n) be the erosion rate after the nth cycle. n is a natural number. R(n) is calculated by the following equation: R(n) = (D(n+1) - D(n-1)) / (M(n+1) - M(n-1))

[0076] The erosion rate R(n) is defined as the erosion rate at the erosion depth D(n) after the nth cycle. Figure 4 is a graph showing an example of the relationship between the erosion rate R(n) and the erosion depth D(n). In the graph shown in Figure 4, the horizontal axis represents the erosion depth (μm), and the vertical axis represents the erosion rate (μm / g).

[0077] The slope of the erosion rate (μm / g) with respect to the change in erosion depth (μm) is defined as the erosion rate slope ((μm / g) / μm). Let S(n) be the erosion rate slope after the nth cycle. R(0) is assumed to be 0. S(n) is calculated by the following equation: S(n) = (R(n+1) - R(n-1)) / (D(n+1) - D(n-1))

[0078] The erosion rate slope S(n) is defined as the erosion rate slope at the erosion depth D(n) after the nth cycle. The erosion rate slope S(n) is the slope of the erosion rate in the graph shown in Figure 4. In other words, it is the slope of the erosion rate on a graph where the horizontal axis is erosion depth (μm) and the vertical axis is erosion rate (μm / g). Figure 5 is a graph showing an example of the relationship between the erosion rate slope S(n) and the erosion depth D(n). In the graph shown in Figure 5, the horizontal axis is erosion depth (μm) and the vertical axis is erosion rate slope ((μm / g) / (μm)).

[0079] <Feature A> As described above, it has been confirmed that in optical sheets with a base layer containing acrylic resin, defects such as cracks, fractures, and peeling are prone to occur in the functional layer containing the cured resin. The optical sheet according to this embodiment has feature (A) related to the physical properties measured by erosion testing. According to feature (A), it is possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet containing a base layer containing acrylic resin.

[0080] (A): The ratio (H / W) of the maximum value H ((μm / g) / μm) of the Gaussian curve fitted to the test results of the erosion test on a graph with the horizontal axis representing the erosion depth (μm) and the vertical axis representing the erosion rate slope ((μm / g) / μm) is 2.0 or less to the full width at half maximum W (μm) of the Gaussian curve.

[0081] Erosion tests are performed from the first surface of the optical sheet to measure the slope of the erosion rate at each erosion depth. Figure 5 shows a graph with the horizontal axis representing erosion depth (μm) and the vertical axis representing the slope of the erosion rate ((μm / g) / (μm)). The measured values ​​of the slope of the erosion rate at each erosion depth are plotted on the graph shown in Figure 5. On the graph shown in Figure 5, a Gaussian function is identified that fits the measured values ​​of the slope of the erosion rate at each erosion depth for each measurement sample.

[0082] The Gaussian function is a function expressed by the following equation in the xy coordinate system: y = a × exp(-(x-b)) ２ / (2 x c) ２ )) ...Formula (A)

[0083] The Gaussian function to fit the test results for each measurement sample is determined as follows:

[0084] Fitting method: In equation (A), x corresponds to each erosion depth, and y corresponds to the slope of the erosion rate at each erosion depth. For each x (erosion depth), calculate the square of the difference between y calculated from equation (A) and the slope of the erosion rate obtained from the test at the corresponding erosion depth. Determine a, b, and c in equation (A) so that the sum of these squares is minimized. In this calculation, use the "Solver" function of Excel®, available from Microsoft®. Select "GRG Nonlinear" for "Select Solution Method".

[0085] Figure 6 shows the test results and an example of a Gaussian function to which those test results were fitted. As shown in Figure 6, the Gaussian function to which the test results are approximated includes a bell-shaped curved portion on the graph. Figure 7 is a magnified view of the curved portion of the Gaussian function fitted to the test results.

[0086] The "maximum value H ((μm / g) / μm)" defined in feature (A) is the maximum value H of the Gaussian curve, as shown in Figure 7. The maximum value H is the same as the value of a in equation (A).

[0087] The "full width at half maximum W (μm)" defined in feature (A) is the full width at half maximum FWHM of the Gaussian function, as shown in Figure 7. In the Gaussian function, the slope of the erosion rate is half of the maximum value H (H / 2) at two erosion depths, EMX and EMY. The full width at half maximum W is calculated using c in equation (A) as W = 2.3548 × c. The full width at half maximum W corresponds to the value (μm) obtained by subtracting the smaller erosion depth EMY, where the erosion rate slope is half of the maximum value H (H / 2), from the larger erosion depth EMX, where the erosion rate slope is half of the maximum value H (H / 2). The full width at half maximum W (μm) corresponds to the range of erosion depths where an erosion rate slope of half the maximum value is obtained.

[0088] The ratio defined in feature (A) is the ratio (H / W) of the maximum value H of the Gaussian function, which reflects the test results of the erosion rate slope at each erosion depth, to the full width at half maximum W. Feature (A) sets an upper limit on this ratio H / W. Repeated experiments related to feature (A) showed that, according to feature (A), it was possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet containing a substrate layer containing acrylic resin.

[0089] The ratio of the maximum value H to the full width at half maximum W (H / W) may be 2.0 or less, 1.8 or less, 1.5 or less, 1.2 or less, 1.0 or less, 0.70 or less, or 0.40 or less.

[0090] There is no specific lower limit set for the ratio of the maximum value H to the full width at half maximum W (H / W). The ratio of the maximum value H to the full width at half maximum W (H / W) may be greater than or equal to 0, or greater than 0.

[0091] The ratio of the maximum value H to the full width at half maximum W (H / W) 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 0.70, or between 0 and 0.40. The ratio of the maximum value H to the full width at half maximum W (H / W) 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 0.70 or less, or greater than 0 and 0.40 or less.

[0092] The erosion rate (μm / g) obtained by the erosion test is an indicator of abrasion resistance or deformation resistance to impact. Samples with a low erosion rate have high impact resistance. The erosion rate slope ((μm / g) / μm) is the gradient of change in the erosion rate (μm) with respect to the change in erosion depth (μm). The erosion rate slope represents the gradient of change in the erosion rate at each position in the thickness direction of the optical sheet (i.e., the first direction D1). The erosion rate slope represents the gradient of change in the erosion rate at the erosion depth position (measurement position) where the erosion rate slope was measured.

[0093] Generally, the mechanical strength of a functional layer containing a cured resin is superior to that of a substrate layer containing acrylic resin. Therefore, as shown in Figure 4 as an example, the erosion rate of the functional layer is smaller than that of the substrate layer. Furthermore, in a graph with the horizontal axis representing erosion depth and the vertical axis representing the slope of the erosion rate, the slope of the erosion rate does not change significantly in the region corresponding to the interior of the functional layer and the region corresponding to the interior of the substrate layer. On the other hand, the slope of the erosion rate rises sharply at the position between the functional layer and the intermediate layer. The slope of the erosion rate has a convex portion at the position between the functional layer and the intermediate layer on the graph shown in Figure 5. The slope of the erosion rate has a maximum value at the position between the functional layer and the intermediate layer on the graph shown in Figure 5.

[0094] In the examples shown in Figures 4 and 5, the thickness of the functional layer, i.e., the length of the functional layer along the first direction D1, is approximately 4.5 μm. In the examples shown in Figures 4 and 5, the intermediate layer is located between the functional layer and the substrate layer. The thickness of the intermediate layer, i.e., the length of the intermediate layer along the first direction D1, is approximately 2.5 μm.

[0095] The "maximum value H" defined in feature (A) is an indicator of the magnitude of the change in the erosion rate. The "full width at half maximum W" defined in feature (A) is an indicator of the thickness (μm) of the portion where the erosion rate is changing significantly, in other words, the length of that portion along the first direction D1. Therefore, by setting an upper limit on the ratio of the maximum value H to the full width at half maximum W (H / W) according to feature (A), it is possible to suppress abrupt changes in the erosion rate along the first direction D1, which is the thickness direction of the optical sheet 10. The inventors of this case have confirmed that, according to feature (A), it was possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet including a substrate layer containing acrylic resin.

[0096] The detailed reason why setting an upper limit on the ratio of the maximum value H to the full width at half maximum W (H / W) can suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer is unclear. According to the inventors' investigation, the following is presumed to be one of the reasons why the occurrence of defects in the functional layer can be suppressed. However, this disclosure is not bound by the following presumption.

[0097] Acrylic resin is stronger than other resins commonly used as substrates for optical sheets. However, the inventors of this study found that optical sheets using a substrate layer containing acrylic resin were prone to defects such as cracks, fractures, and peeling in the functional layer. Upon closer examination of the physical defects occurring in the functional layer, it was determined that they were caused by impactful external forces.

[0098] According to Feature (A), the physical properties of the optical sheet are evaluated based on the test results of an erosion test, which is suitable for evaluating impact resistance. Moreover, under the test conditions described above for the erosion test, the amount of change in erosion depth per injection step can be reduced. In other words, under the test conditions described above, the gradient of change in the impact resistance of the optical sheet can be evaluated at a large number of measurement positions located at very small intervals in the thickness direction. Therefore, according to Feature (A), it is possible to suppress large changes in the erosion rate at local locations in the thickness direction. That is, according to Feature (A), it is possible to suppress large changes in impact resistance at local locations in the thickness direction. As a result, even if an impact is applied to the optical sheet from the outside, the occurrence of a boundary (or boundary layer) where the physical behavior due to the impact changes significantly can be suppressed. Since the occurrence of such a boundary (or boundary layer) can be suppressed, it is presumed that according to Feature (A), it is possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer.

[0099] In conventional technology, the mechanical properties of the functional layer and the base layer were sometimes adjusted. However, in conventional technology, it was not possible to evaluate physical properties at multiple measurement positions along the lamination direction within a region spanning the functional layer and the base layer, particularly at multiple measurement positions with intervals of 1.0 μm or less, and even around 0.50 μm. Thus, the effect obtained from this feature (A), which was not considered in conventional technology, namely the effect of suppressing the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a base layer containing acrylic resin, is a remarkable effect that exceeds the range that could be predicted from the current level of technology.

[0100] An optical sheet that satisfies characteristic (A) is an optical sheet in which abrupt changes in the erosion rate between the functional layer and the substrate layer are suppressed. An optical sheet having characteristic (A) can be manufactured by one or more means, such as providing an intermediate layer with appropriate thickness and hardness between the functional layer and the substrate, and adjusting the manufacturing conditions of the functional layer.

[0101] The erosion rate of the intermediate layer may be greater than the erosion rate of the functional layer. The erosion rate of the intermediate layer may be greater than the erosion rate of the base material layer. The slope of the erosion rate of the intermediate layer may be greater than the slope of the erosion rate of the functional layer. The slope of the erosion rate of the intermediate layer may be greater than the slope of the erosion rate of the base material layer.

[0102] The maximum value H and full width at half maximum W of the optical sheet to be evaluated, as defined in feature (A), are determined based on the test results of three measurement samples obtained from the optical sheet. Three measurement values ​​for the maximum value H are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measurement values ​​for the maximum value H is taken as the maximum value H of the optical sheet to be evaluated. Three measurement values ​​for the full width at half maximum W are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measurement values ​​for the full width at half maximum W is taken as the full width at half maximum W of the optical sheet to be evaluated. The ratio (H / W) for the optical sheet to be evaluated is calculated by dividing the maximum value H of the optical sheet to be evaluated by the full width at half maximum W of the optical sheet to be evaluated. Whether or not feature (A) is satisfied is determined by the calculated ratio (H / W).

[0103] <Feature B> In addition to the above-described feature (A), the optical sheet may also have the following feature (B): (B): The full width at half maximum W is 0.45 μm or more.

[0104] According to feature (B), a lower limit is set for the "full width at half maximum W (μm)" defined in feature (A). By setting a lower limit for the full width at half maximum W (μm), a region where the slope of the erosion rate becomes large in the first direction D1, which is the lamination direction of the functional layer and the base layer, can be secured to a certain extent. In other words, by setting a lower limit for the full width at half maximum W (μm), the length of the region along the first direction D1 in which the erosion rate changes along the first direction D1 can be increased. Therefore, it is possible to suppress large changes in the erosion rate at local locations in the first direction D1. As a result, the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a base layer containing acrylic resin can be suppressed more effectively.

[0105] The full width at half maximum W may be 0.45 μm or greater, 0.50 μm or greater, 0.53 μm or greater, 0.57 μm or greater, 0.60 μm or greater, 0.70 μm or greater, or 0.76 μm or greater.

[0106] An upper limit may be set on the full width at half maximum (FWHM) W. By setting an upper limit on the FWHM W, the thickness of the optical sheet can be reduced. The FWHM W may be 5.0 μm or less, 3.0 μm or less, 2.0 μm or less, or 1.5 μm or less.

[0107] The full width at half maximum (FWHM) W may be 0.45 μm or more and 5.0 μm or less, 0.50 μm or more and 5.0 μm or less, 0.53 μm or more and 5.0 μm or less, 0.57 μm or more and 5.0 μm or less, 0.60 μm or more and 5.0 μm or less, 0.70 μm or more and 5.0 μm or less, or 0.76 μm or more and 5.0 μm or less. The full width at half maximum (FWHM) W may be 0.45 μm or more and 3.0 μm or less, 0.50 μm or more and 3.0 μm or less, 0.53 μm or more and 3.0 μm or less, 0.57 μm or more and 3.0 μm or less, 0.60 μm or more and 3.0 μm or less, 0.70 μm or more and 3.0 μm or less, or 0.76 μm or more and 3.0 μm or less. The full width at half maximum (FMAX) W may be 0.45 μm or more and 2.0 μm or less, 0.50 μm or more and 2.0 μm or less, 0.53 μm or more and 2.0 μm or less, 0.57 μm or more and 2.0 μm or less, 0.60 μm or more and 2.0 μm or less, 0.70 μm or more and 2.0 μm or less, or 0.76 μm or more and 2.0 μm or less. The full width at half maximum (FMAX) W may be 0.45 μm or more and 1.5 μm or less, 0.50 μm or more and 1.5 μm or less, 0.53 μm or more and 1.5 μm or less, 0.57 μm or more and 1.5 μm or less, 0.60 μm or more and 1.5 μm or less, 0.70 μm or more and 1.5 μm or less, or 0.76 μm or more and 1.5 μm or less.

[0108] The full width at half maximum W specified in feature (B) can be adjusted by the thickness and hardness of the intermediate layer located between the functional layer and the base material, the manufacturing conditions of the functional layer, and so on.

[0109] The full width at half maximum (FMAX) W specified in feature (B) is determined based on the test results of three measurement samples obtained from the optical sheet. Three measurement values ​​for the FMAX W are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measurement values ​​for the FMAX W is taken as the FMAX W of the optical sheet being evaluated. Based on the obtained FMAX W, it is determined whether or not feature (B) is satisfied.

[0110] <Feature C> In addition to the above-described feature (A), the optical sheet may also have the following feature (C): (C): The maximum value H is 0.80 μm or less.

[0111] According to feature (C), an upper limit is set on the "maximum value H (μm)" defined in feature (A). By setting an upper limit on the maximum value H (μm), the slope of the erosion rate can be reduced. That is, by setting an upper limit on the maximum value H (μm), the slope of the change in the erosion rate with respect to the change in the amount of change in the erosion depth can be reduced. Therefore, it is possible to suppress large changes in the erosion rate at local locations in the first direction D1. As a result, the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a substrate layer containing acrylic resin can be suppressed more effectively.

[0112] The maximum value H may be 0.80 μm or less, 0.68 μm or less, 0.55 μm or less, 0.53 μm or less, or 0.44 μm or less.

[0113] There is no lower limit set for the maximum value H. The maximum value H may be greater than or equal to 0 μm, or greater than 0 μm.

[0114] The maximum value H may be 0 μm or more and 0.80 μm or less, 0 μm or more and 0.68 μm or less, 0 μm or more and 0.55 μm or less, 0 μm or more and 0.53 μm or less, or 0 μm or more and 0.44 μm or less. The maximum value H may be greater than 0 μm and 0.80 μm or less, greater than 0 μm and 0.68 μm or less, greater than 0 μm and 0.55 μm or less, greater than 0 μm and 0.53 μm or less, or greater than 0 μm and 0.44 μm or less.

[0115] The maximum value H specified in feature (C) can be adjusted by the thickness and hardness of the intermediate layer located between the functional layer and the substrate, the manufacturing conditions of the functional layer, and so on.

[0116] The maximum value H specified in feature (C) is determined based on the test results of three measurement samples obtained from the optical sheet. Three measurement values ​​related to the maximum value H are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measurement values ​​related to the maximum value H is taken as the maximum value H of the optical sheet being evaluated. Based on the obtained maximum value H, it is determined whether or not feature (C) is satisfied.

[0117] <Feature D> The optical sheet may have the following feature (D) in place of or in addition to feature (A) described above: (D): The first mean erosion rate slope is 0.0050 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less.

[0118] The first mean erosion rate slope is the average value of the erosion rate slope after smoothing. The smoothing process for the erosion rate slope is a Gaussian weighted average of five points (five measurements) including two points (two measurements) located on either side of the horizontal axis on a graph where the horizontal axis is erosion depth (μm) and the vertical axis is erosion rate slope ((μm / g) / μm).

[0119] The erosion rate slope GS(i) in the i-th smoothed cycle, in other words, the Gaussian weighted mean GS(i) of the erosion rate slope S(i) in the i-th cycle, is given by the following equation: GS(i) = {S(i-2) × Gσ(D(i-2) - D(i)) + S(i-1) × Gσ(D(i-1) - D(i)) + S(i) × Gσ(0) + S(i+1) × Gσ(D(i+1) - D(i)) + S(i+2) × Gσ(D(i+2) - D(i))} / {Gσ(D(i-2) - D(i)) + Gσ(D(i-1) - D(i)) + Gσ(0) + Gσ(D(i+1) - D(i)) + Gσ(D(i+2) - D(i))}

[0120] In the formula for the Gaussian weighted average GS(i), D(i) is the erosion depth after the i-th cycle. In the formula for the Gaussian weighted average GS(i), S(i) is the slope of the erosion rate in the i-th cycle. In the formula for the Gaussian weighted average GS(i), Gσ(x) represents a Gaussian function. Gσ(x) is expressed by the following equation. In the Gaussian function in the following equation, let σ = 0.5.

[0121]

[0122] Figure 5 is a graph showing the distribution of erosion rate slopes at each erosion depth. Figure 8 is a graph showing the distribution of erosion rate slopes at each erosion depth shown in Figure 5 after smoothing. The horizontal axis of the graphs shown in Figures 5 and 8 represents erosion depth (μm). The vertical axis of the graphs shown in Figures 5 and 8 represents erosion rate slope ((μm / g) / μm).

[0123] As described above, the erosion rate slope is the gradient of change in the erosion rate (μm / g) with respect to the change in erosion depth (μm). The erosion depth and erosion rate are obtained from erosion tests on the first surface 11. Let S(n) be the erosion rate slope after the nth cycle. This erosion rate slope S(n) is calculated by the following equation: S(n) = (R(n+1) - R(n-1)) / (D(n+1) - D(n-1))

[0124] The measurement position is the position in the first direction D1. The measurement position is the deepest point of the recess formed in the measurement sample at the start of each injection step. The first measurement position is 0. The measurement position at the nth time is the position in the first direction reached by the injection step in the (n-1)th cycle. In other words, the measurement position at the nth time is the position of the erosion depth D(n-1) at the measurement position at the (n-1)th time. To put it another way, the measurement position at the nth time is the deepest point of the recess formed in the measurement sample by the (n-1)th measurement.

[0125] The erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at the measurement position within the region adjacent to the first surface (within the functional layer in the illustrated example). A region arises along the first direction D1 where the erosion rate slope increases from the functional layer toward the substrate layer in the first direction D1. The erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at the measurement position before it increases. In other words, the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at the measurement position within the region where the erosion rate is small. To put it another way, the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope that reflects the physical properties of the functional layer itself.

[0126] Specifically, the erosion rate slope used to calculate the first mean erosion rate slope is the erosion rate slope at a measurement position at least 0.50 μm away from the first surface 11 along the first direction D1. For example, suppose the erosion depth reached by the 5th injection step is 0.452 μm at the 6th measurement position, and the 7th measurement position is 0.568 μm. In this example, the erosion rate slope used to calculate the first mean erosion rate slope is the erosion rate slope at the 7th measurement position and subsequent measurement positions.

[0127] In addition, the erosion rate slope used to calculate the first mean erosion rate slope is the erosion rate slope at measurement positions up to four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g. For example, suppose the erosion rate at the 38th measurement position is 0.177 (μm / g) and the erosion rate at the 39th measurement position is 0.351 (μm / g). In this example, the erosion rate slope used to calculate the first mean erosion rate slope is the erosion rate slope up to the 35th measurement position, which is four measurement positions prior to the 39th measurement position.

[0128] As described above, the measurement position for the erosion rate slope used to calculate the first mean erosion rate slope is a measurement position located at least 0.50 μm away from the first surface 11, and is four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g. In the specific example described above, the erosion rate slope from the 7th measurement position to the 35th measurement position is used to calculate the first mean erosion rate slope.

[0129] In feature (D), a lower limit is set for the slope of the first mean erosion rate. By setting a lower limit for the slope of the first mean erosion rate, it was possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer of the optical sheet containing a substrate layer containing acrylic resin.

[0130] The erosion rate (μm / g) obtained by the erosion test is an indicator of abrasion resistance or deformation resistance to impact. Samples with a low erosion rate have high impact resistance. The erosion rate slope ((μm / g) / μm) is the gradient of change in the erosion rate (μm / g) with respect to the change in erosion depth (μm). The erosion rate slope represents the gradient of change in the erosion rate at each position in the thickness direction of the optical sheet (i.e., the first direction D1). If the erosion rate slope is greater than 0, it means that the erosion rate increases from the first surface to the second surface of the optical sheet in the first direction D1.

[0131] Generally, the mechanical strength of a functional layer containing a cured resin is superior to that of a substrate layer containing acrylic resin. Therefore, as shown in Figure 4 as an example, the erosion rate of the functional layer is smaller than that of the substrate layer. In the example shown in Figure 4, characteristic (F) described later is satisfied, and the average erosion rate of the functional layer is smaller than that of the substrate layer.

[0132] According to feature (D), a lower limit greater than 0 is set for the first mean erosion rate slope. The first mean erosion rate slope is generally the arithmetic mean of the erosion rate slopes at measurement positions within the region corresponding to the interior of the functional layer. Therefore, in an optical sheet having feature (D), the overall trend is that the erosion rate of the functional layer increases from the first surface to the second surface in the first direction D1. In an optical sheet having features (D) and (F), the overall trend is that the erosion rate of the functional layer approaches the erosion rate of the substrate layer from the first surface to the second surface in the first direction D1. As a result, the amount of change in the erosion rate between the functional layer at a position close to the substrate layer in the first direction D1 and the substrate layer at a position close to the functional layer in the first direction D1 can be reduced. At each position in the thickness direction between the functional layer and the substrate layer, abrupt changes in the erosion rate can be suppressed. In other words, it is possible to suppress abrupt changes in impact resistance at each position in the thickness direction between the functional layer and the base material layer.

[0133] In addition, according to feature (D), excellent mechanical strength can be provided to the region of the functional layer that is adjacent to the first surface in the first direction D1.

[0134] Furthermore, the aforementioned test conditions for the erosion test can significantly reduce the change in erosion depth per injection step. In other words, the amount of wear or deformation per injection step can be significantly reduced. Therefore, according to the test conditions for the erosion test, the erosion rate slope can be measured at numerous measurement positions within a very thin region, and a first mean erosion rate slope can be obtained from the measured values ​​of the numerous erosion rate slopes. This first mean erosion rate slope allows for highly accurate evaluation of the impact resistance trend within a very thin region.

[0135] Feature (D) makes it possible to reduce the amount of change in the erosion rate in the region where the erosion rate between the functional layer and the substrate layer increases rapidly. As a result, even if an external impact is applied to the optical sheet, the occurrence of a boundary (or boundary layer) where the physical behavior due to the impact changes significantly can be suppressed. Since the occurrence of such a boundary (or boundary layer) can be suppressed, it is presumed that, according to feature (D), it is possible to suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer. However, this disclosure is not bound by this presumption.

[0136] From the viewpoint of suppressing the occurrence of defects in the functional layer, the first mean erosion rate slope may be 0.0050 ((μm / g) / μm) or higher, 0.0060 ((μm / g) / μm) or higher, 0.0070 ((μm / g) / μm) or higher, 0.0080 ((μm / g) / μm) or higher, 0.0090 ((μm / g) / μm) or higher, 0.010 ((μm / g) / μm) or higher, or 0.014 ((μm / g) / μm) or higher.

[0137] From the viewpoint of suppressing large changes in the erosion rate within the functional layer, the first mean erosion rate slope may be 0.030 ((μm / g) / μm) or less, 0.025 ((μm / g) / μm) or less, or 0.020 ((μm / g) / μm) or less.

[0138] The first mean erosion rate slope, expressed in units of "(μm / g) / μm", may be 0.0050 or more and 0.030 or less, 0.0060 or more and 0.030 or less, 0.0070 or more and 0.030 or less, 0.0080 or more and 0.030 or less, 0.0090 or more and 0.030 or less, 0.010 or more and 0.030 or less, or 0.014 or more and 0.030 or less. The first mean erosion rate slope, expressed in units of "(μm / g) / μm", may be 0.0050 or more and 0.025 or less, 0.0060 or more and 0.025 or less, 0.0070 or more and 0.025 or less, 0.0080 or more and 0.025 or less, 0.0090 or more and 0.025 or less, 0.010 or more and 0.025 or less, or 0.014 or more and 0.025 or less. The first mean erosion rate slope, expressed in units of "(μm / g) / μm", may be 0.0050 or more and 0.020 or less, 0.0060 or more and 0.020 or less, 0.0070 or more and 0.020 or less, 0.0080 or more and 0.020 or less, 0.0090 or more and 0.020 or less, 0.010 or more and 0.020 or less, or 0.014 or more and 0.020 or less.

[0139] In conventional technology, the mechanical properties of the functional layer and the base layer were sometimes adjusted. However, the evaluation of physical properties at multiple measurement positions along the lamination direction within the functional layer, particularly at intervals of 0.20 μm or less, and even around 0.15 μm, was not performed in conventional technology. The effect obtained by this feature (D), which was not considered in conventional technology, namely the effect of suppressing the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a base layer containing acrylic resin, is a remarkable effect that exceeds the range predicted by the current level of technology.

[0140] An optical sheet that satisfies characteristic (D) is one in which the erosion rate tends to gradually increase in the region between the substrate layer and the first surface, and in which there is little abrupt change in the erosion rate in that region. An optical sheet that satisfies characteristic (D) can be manufactured by containing curable resins with different numbers of functional groups and adjusting the solvent and drying conditions. An optical sheet that satisfies characteristic (D) becomes easier to manufacture by containing curable resins with four or more different numbers of functional groups.

[0141] An optical sheet that satisfies characteristic (D) is an optical sheet in which abrupt changes in the erosion rate between the functional layer and the substrate layer are suppressed. An optical sheet having characteristic (D) can be manufactured by providing an intermediate layer with appropriate thickness and hardness between the functional layer and the substrate, or by adjusting the manufacturing conditions of the functional layer.

[0142] The erosion rate of the intermediate layer may be greater than the erosion rate of the functional layer. The erosion rate of the intermediate layer may be greater than the erosion rate of the base material layer. The slope of the erosion rate of the intermediate layer may be greater than the slope of the erosion rate of the functional layer. The slope of the erosion rate of the intermediate layer may be greater than the slope of the erosion rate of the base material layer.

[0143] The first mean erosion rate slope specified in feature (D) is determined based on the test results of three measurement samples obtained from the optical sheet. Three measurements related to the first mean erosion rate slope are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measurements related to the first mean erosion rate slope is taken as the first mean erosion rate slope of the optical sheet being evaluated. Based on the obtained first mean erosion rate slope, it is determined whether or not feature (D) is satisfied.

[0144] <Feature E> The optical sheet may have the following feature (E) in place of or in addition to feature (A) described above: (E): The second mean erosion rate slope is 0.0035 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less.

[0145] The second mean erosion rate slope is the average value of the erosion rate slope after smoothing, where the absolute value is 0.10 (μm / g) / μm or less. According to the erosion test conditions described above, the erosion rate and erosion rate slope of the functional layer are measured at measurement positions located at very small intervals along the first direction D1. However, under these measurement conditions, erosion rate slopes with large absolute values ​​can be measured in a hyperlocal manner. Measurement positions where such erosion rate slopes are measured cannot, on their own, have a significant impact on the occurrence of defects in the functional layer. On the other hand, when such erosion rate slopes are measured in a hyperlocal manner, it is difficult to grasp the trend of erosion rate slopes within the functional layer. The second mean erosion rate slope is an arithmetic mean calculated by excluding values ​​with an absolute value exceeding 0.10 (μm / g) / μm from the smoothed erosion rate slope values, from the viewpoint of more clearly evaluating the trend of erosion rate slopes within the functional layer.

[0146] The second mean erosion rate slope differs from the first mean erosion rate slope in that it is the arithmetic mean obtained by smoothing the erosion rate slope and excluding values ​​with an absolute value exceeding 0.10 (μm / g) / μm. In other respects, the second mean erosion rate slope is calculated in the same way as the first mean erosion rate slope. For example, the smoothing process used to calculate the second mean erosion rate slope is the same as the smoothing process used to calculate the second mean erosion rate slope. The measurement location of the erosion rate slope used to calculate the second mean erosion rate slope is the same as the measurement location of the erosion rate slope used to calculate the first mean erosion rate slope.

[0147] In other words, the second mean erosion rate slope is the average value of the values ​​obtained by smoothing the erosion rate slope, where the absolute value is 0.10 (μm / g) / μm or less. The smoothing process is a Gaussian weight averaging of a total of five points. The erosion rate slope used to calculate the second mean erosion rate slope is the erosion rate slope at measurement positions from a measurement position at least 0.50 μm away from the first surface in the first direction D1 to four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g.

[0148] The second mean erosion rate slope differs from the first mean erosion rate slope in that it does not take into account the erosion rate slope after smoothing treatment with an absolute value greater than 0.10 (μm / g) / μm. Otherwise, the second mean erosion rate slope is calculated in the same manner as the first mean erosion rate slope.

[0149] Feature (E) sets a lower limit greater than 0 for the second mean erosion rate slope. The second mean erosion rate slope is generally the arithmetic mean of the erosion rate slopes at measurement locations within the region corresponding to the interior of the functional layer. Therefore, in an optical sheet having feature (E), the overall trend is that the erosion rate of the functional layer increases from the first surface to the second surface in the first direction D1. In an optical sheet having features (E) and (F), the overall trend is that the erosion rate of the functional layer approaches the erosion rate of the substrate layer from the first surface to the second surface in the first direction D1. As a result, the amount of change in the erosion rate between the functional layer at a location close to the substrate layer in the first direction D1 and the substrate layer at a location close to the functional layer in the first direction D1 can be reduced. At each location in the thickness direction between the functional layer and the substrate layer, abrupt changes in the erosion rate can be suppressed. In other words, it is possible to suppress abrupt changes in impact resistance at each position in the thickness direction between the functional layer and the base material layer.

[0150] In addition, according to feature (E), excellent mechanical strength can be provided to the region of the functional layer that is adjacent to the first surface in the first direction D1.

[0151] Furthermore, the aforementioned test conditions for the erosion test can significantly reduce the change in erosion depth per injection step. In other words, the amount of wear or deformation per injection step can be significantly reduced. Therefore, according to the test conditions for the erosion test, the erosion rate slope can be measured at numerous measurement positions within a very thin region, and a second mean erosion rate slope can be obtained from the measured values ​​of the numerous erosion rate slopes. This second mean erosion rate slope allows for highly accurate evaluation of the impact resistance trend within a very thin region.

[0152] Feature (E) makes it possible to reduce the amount of change in the erosion rate in the region where the erosion rate between the functional layer and the substrate layer increases rapidly. As a result, even if an external impact is applied to the optical sheet, the occurrence of a boundary (or boundary layer) where the physical behavior due to the impact changes significantly can be suppressed. Since the occurrence of such a boundary (or boundary layer) can be suppressed, it is presumed that, according to feature (E), the occurrence of defects such as cracks, fractures, and peeling in the functional layer can be suppressed. However, this disclosure is not bound by this presumption.

[0153] From the viewpoint of suppressing the occurrence of defects in the functional layer, the second mean erosion rate slope may be 0.0035 ((μm / g) / μm) or higher, 0.0040 ((μm / g) / μm) or higher, 0.0045 ((μm / g) / μm) or higher, 0.0050 ((μm / g) / μm) or higher, or 0.0060 ((μm / g) / μm) or higher.

[0154] From the viewpoint of suppressing large changes in the erosion rate within the functional layer, the second mean erosion rate slope may be 0.030 ((μm / g) / μm) or less, 0.025 ((μm / g) / μm) or less, or 0.020 ((μm / g) / μm) or less.

[0155] The second mean erosion rate slope, expressed in units of "(μm / g) / μm", may be 0.0035 or more and 0.030 or less, 0.0040 or more and 0.030 or less, 0.0045 or more and 0.030 or less, 0.0050 or more and 0.030 or less, or 0.0060 or more and 0.030 or less. The second mean erosion rate slope, expressed in units of "(μm / g) / μm", may be 0.0035 or more and 0.025 or less, 0.0040 or more and 0.025 or less, 0.0050 or more and 0.025 or less, or 0.0060 or more and 0.025 or less. The second mean erosion rate slope, expressed in units of "(μm / g) / μm", may be 0.0035 or more and 0.020 or less, 0.0040 or more and 0.020 or less, 0.0045 or more and 0.020 or less, 0.0050 or more and 0.020 or less, or 0.0060 or more and 0.020 or less.

[0156] In conventional technology, the mechanical properties of the functional layer and the base layer were sometimes adjusted. However, evaluating the physical properties at multiple measurement positions along the lamination direction within the functional layer, particularly at intervals of 0.20 μm or less, and even around 0.15 μm, was not performed in conventional technology. The effect obtained from this feature (E), which was not considered in conventional technology, namely the effect of suppressing the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a base layer containing acrylic resin, is a remarkable effect that exceeds the range predicted by the current level of technology.

[0157] An optical sheet that satisfies characteristic (E) is one in which the erosion rate tends to gradually increase in the region between the substrate layer and the first surface, and in which there is little abrupt change in the erosion rate in that region. An optical sheet that satisfies characteristic (E) can be manufactured by containing a curable resin having various numbers of functional groups and adjusting the solvent and drying conditions. An optical sheet that satisfies characteristic (E) becomes easier to manufacture by containing a curable resin with four or more different numbers of functional groups.

[0158] An optical sheet that satisfies characteristic (E) is an optical sheet in which abrupt changes in the erosion rate between the functional layer and the substrate layer are suppressed. An optical sheet having characteristic (E) can be manufactured by providing an intermediate layer with appropriate thickness and hardness between the functional layer and the substrate, or by adjusting the manufacturing conditions of the functional layer.

[0159] The erosion rate of the intermediate layer may be greater than the erosion rate of the functional layer. The erosion rate of the intermediate layer may be greater than the erosion rate of the base material layer. The slope of the erosion rate of the intermediate layer may be greater than the slope of the erosion rate of the functional layer. The slope of the erosion rate of the intermediate layer may be greater than the slope of the erosion rate of the base material layer.

[0160] The second mean erosion rate slope specified in feature (E) is determined based on the test results of three measurement samples obtained from the optical sheet. Three measurements related to the second mean erosion rate slope are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measurements related to the second mean erosion rate slope is taken as the second mean erosion rate slope of the optical sheet being evaluated. Based on the obtained second mean erosion rate slope, it is determined whether or not feature (E) is satisfied.

[0161] <Feature F> In addition to the above-described features (A), (D), or (E), the optical sheet may also have the following feature (F): (F): The average erosion rate of the functional layer is smaller than the average erosion rate of the substrate layer.

[0162] By combining one or more of features (A) to (E) with feature (F), it is possible to effectively suppress the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a substrate layer containing acrylic resin.

[0163] The average erosion rate of the functional layer 20 is the arithmetic mean of the erosion rates measured at measurement positions located within the functional layer measurement area R20. As shown in Figure 2, the functional layer measurement area R20 is a region at least 0.50 μm away from both surfaces 21 and 22 of the functional layer 20 facing the first direction D1, along the first direction D1. That is, the functional layer measurement area R20 is the region between the first position P1 and the second position P2 in the first direction D1. The first position P1 is a position 0.50 μm away from the first surface 21 of the functional layer 20 toward the second surface 22 along the first direction D1. The second position P2 is a position 0.50 μm away from the second surface 22 of the functional layer 20 toward the first surface 21 along the first direction D1.

[0164] The average erosion rate of the substrate layer 40 is the arithmetic mean of the erosion rates measured at measurement positions located within the substrate layer measurement area R40. The substrate layer measurement area R40 is a region located 4.0 μm to 6.0 μm away from the first surface 41 of the substrate layer 40 facing the first surface 11, along the first direction D1 toward the second surface 42 of the substrate layer 40. That is, the substrate layer measurement area R40 is the region between the third position P3 and the fourth position P4 in the first direction D1. The third position P3 is located 4.0 μm away from the first surface 41 of the substrate layer 40 toward the second surface 42, along the first direction D1. The fourth position P4 is located 6.0 μm away from the first surface 41 of the substrate layer 40 toward the second surface 42, along the first direction D1.

[0165] <Feature G> In addition to the above-described feature (F), the optical sheet may also have the following feature (G): (G): The difference between the average erosion rate of the substrate layer and the average erosion rate of the functional layer is 0.30 μm / g or more and 0.80 μm / g or less.

[0166] As described above, according to features (A) to (E), the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a substrate layer containing acrylic resin can be suppressed. Therefore, even if the difference between the average erosion rate of the substrate layer and the average erosion rate of the functional layer is 0.30 (μm / g) or more, the occurrence of defects in the functional layer can be suppressed.

[0167] According to feature (G), a lower limit is set on the difference between the average erosion rate of the base layer and the average erosion rate of the functional layer. Therefore, according to feature (G), excellent mechanical strength can be imparted to the functional layer. The difference between the average erosion rate of the base layer and the average erosion rate of the functional layer may be 0.30 (μm / g) or more, 0.35 (μm / g) or more, or 0.40 (μm / g) or more.

[0168] According to feature (G), an upper limit is set on the difference between the average erosion rate of the base layer and the average erosion rate of the functional layer. Therefore, according to feature (G), the occurrence of defects such as cracks, fractures, and peeling in the functional layer of an optical sheet using a base layer containing acrylic resin can be more effectively suppressed. The difference between the average erosion rate of the base layer and the average erosion rate of the functional layer may be 0.80 (μm / g) or less, 0.60 (μm / g) or less, or 0.50 (μm / g) or less.

[0169] The difference between the average erosion rate of the base layer and the average erosion rate of the functional layer may be 0.30 (μm / g) or more and 0.80 (μm / g) or less, or 0.35 (μm / g) or more and 0.80 (μm / g) or less, or 0.40 (μm / g) or more and 0.80 (μm / g) or less. The difference between the average erosion rate of the base layer and the average erosion rate of the functional layer may be 0.30 (μm / g) or more and 0.60 (μm / g) or less, or 0.35 (μm / g) or more and 0.60 (μm / g) or less, or 0.40 (μm / g) or more and 0.60 (μm / g) or less. The difference between the average erosion rate of the substrate layer and the average erosion rate of the functional layer may be 0.30 (μm / g) or more and 0.50 (μm / g) or less, 0.35 (μm / g) or more and 0.50 (μm / g) or less, or 0.40 (μm / g) or more and 0.50 (μm / g) or less.

[0170] The average erosion rate of the functional layer specified in features (F) and (G) is determined based on the test results of three measurement samples obtained from the optical sheet. Three measured values ​​for the average erosion rate of the functional layer are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measured values ​​for the average erosion rate of the functional layer is taken as the average erosion rate of the functional layer of the optical sheet being evaluated.

[0171] The average erosion rate of the substrate layer as defined in features (F) and (G) is determined based on the test results of three measurement samples obtained from the optical sheet. Three measured values ​​for the average erosion rate of the substrate layer are obtained from the experimental results of each measurement sample. The arithmetic mean of the three measured values ​​for the average erosion rate of the substrate layer is taken as the average erosion rate of the substrate layer of the optical sheet being evaluated.

[0172] Based on the average erosion rate of the functional layer as the arithmetic mean of the three measured values, and the average erosion rate of the substrate layer as the arithmetic mean of the three measured values, it is determined whether or not features (F) and (G) are met.

[0173] <<Transmission Haze>> A lower limit may be set for the transmission haze of the optical sheet. By setting a lower limit for the transmission haze of the optical sheet, anti-glare properties can be imparted to the optical sheet. The transmission haze of the optical sheet may be 0.5% or more, 1.0% or more, 5.0% or more, 10% or more, 14.6% or more, or 15% or more.

[0174] An upper limit may be set on the transmission haze of the optical sheet. By setting an upper limit on the transmission haze of the optical sheet, the area behind the optical sheet can be clearly observed. The transmission haze of the optical sheet may be 40% or less, 30% or less, 25% or less, or 24.7% or less.

[0175] The transmitted haze of the optical sheet may be 0.5% to 40%, 1.0% to 40%, 5.0% to 40%, 10% to 40%, 14.6% to 40%, or 15% to 40%. The transmitted haze of the optical sheet may be 0.5% to 30%, 1.0% to 30%, 5.0% to 30%, 10% to 30%, 14.6% to 30%, or 15% to 30%. The transmitted haze of the optical sheet may be 0.5% to 25%, 1.0% to 25%, 5.0% to 25%, 10% to 25%, 14.6% to 25%, or 15% to 25%. The transmission haze of the optical sheet may be 0.5% or more and 24.7% or less, 1.0% or more and 24.7% or less, 5.0% or more and 24.7% or less, 10% or more and 24.7% or less, 14.6% or more and 24.7% or less, or 15% or more and 24.7% or less.

[0176] Before measuring the transmitted haze of the sample, the light source lamp is lit for 15 minutes to stabilize its output. The incident surface when measuring the transmitted haze of the optical sheet is the second surface 12 of the optical sheet. The overall spectral characteristics are a combination of the photopic standard luminous efficiency V(λ) (IEC 60050-845) and the CIE standard optics D65. The test environment when measuring the transmitted haze is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before the start of the test. Other measurement conditions when measuring the transmitted haze follow JIS K7136:2000.

[0177] The transmitted haze is defined as the arithmetic mean of five measurements. The five measurements are taken at five measurement locations within the evaluation area. The five measurement locations are located at least 10 mm apart from each other.

[0178] <<Internal Haze>> The internal haze of the optical sheet may be 0% to 20%, 0% to 15%, 0% to 12.1%, 0% to 10%, 0% to 5.0%, or 0% to 3.2%.

[0179] A measurement sample for measuring internal haze is prepared by attaching a triacetylcellulose film to the first surface 11 that forms the uneven surface 11X of the optical sheet 10 using a transparent adhesive. The transparent adhesive is "PD-S1" manufactured by Panac Corporation. The thickness of the transparent adhesive is 25 μm. The triacetylcellulose film is "TD80UL" manufactured by Fujifilm Corporation. The thickness of the triacetylcellulose film is 80 μm.

[0180] The preparation environment for preparing the measurement samples shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The optical sheet, transparent adhesive, and triacetylcellulose film used in the preparation of the measurement samples shall be placed in the preparation environment for 16 hours before preparation begins.

[0181] The transmitted haze of the measurement sample, measured according to the transmitted haze measurement method described above, becomes the internal haze (%) of the optical sheet 10. The incident surface when measuring the internal haze of the optical sheet 10 is the second surface 12 of the optical sheet 10.

[0182] Internal haze is defined as the arithmetic mean of five measurements. The five measurements are taken at five measurement locations within the evaluation area. The five measurement locations are located at least 10 mm apart from each other.

[0183] <<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%. The total light transmittance of the optical sheet may be 50% or more and 100% or less, 70% or more and 100% or less, 80% or more and 100% or less, or 90% or more and 100% or less. 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%.

[0184] Before measuring the total light transmittance of the sample, the light source lamp is lit for 15 minutes to stabilize its output. The incident surface when measuring the total light transmittance of the optical sheet is the second surface 12 of the optical sheet. The overall spectral characteristics are a combination of the photopic standard luminous efficiency V(λ) (IEC 60050-845) and the CIE standard optics D65. The test environment when measuring the total light transmittance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before the start of the test. Other measurement conditions when measuring the total light transmittance follow JIS K7361-1:1997.

[0185] The total light transmittance is the arithmetic mean of five measured values. The five measured values ​​are taken at five measurement locations on the subject of evaluation. The five measurement locations are located at least 10 mm apart from each other.

[0186] <<Layers included in the optical sheet>> Referring to the illustrated optical sheet 10, each layer included in the optical sheet 10 will be described in more detail. The optical sheet 10 shown in Figure 1 includes a base layer 40, an intermediate layer 30, and a functional layer 20 in the order from the second surface 12 to the first surface 11 in the first direction D1.

[0187] The optical sheet 10 may further include other layers. In the example shown in Figure 9, the optical sheet 10 includes a base layer 40, an intermediate layer 30, a functional layer (first functional layer) 20, and a second functional layer 51 in this order. The second functional layer 51 may include a binder resin and particles. The particles may be low refractive index particles. The refractive index of the particles may be lower than the refractive index of the binder resin. In the example shown in Figure 9, the second functional layer 51 may be configured as a layer with a lower refractive index than the functional layer 20 adjacent to the first direction D1. The second functional layer 51 may be a low-reflection layer or reflection-suppressing layer having the function of suppressing reflection.

[0188] The optical sheet 10 may further include two or more layers. In the example shown in Figure 10, the optical sheet 10 includes a base layer 40, an intermediate layer 30, a functional layer (first functional layer) 20, a third functional layer 52, and a second functional layer 51 in this order. The third functional layer 52 may include a binder resin and particles. The particles may be high refractive index particles. The refractive index of the particles may be higher than the refractive index of the binder resin. In the example shown in Figure 10, the second functional layer 51 may be configured as a layer with a lower refractive index than the third functional layer 52 adjacent to the first functional layer D1. The third functional layer 52 may be configured as a layer with a higher refractive index than the functional layer 20 adjacent to the first functional layer D1. The second functional layer 51 and the third functional layer 52 may be low-reflection layers or reflection-suppressing layers having the function of suppressing reflection.

[0189] The optical sheet 10 may include other functional layers, unlike the illustrated example. Examples of other functional layers include a hard coat layer, an antistatic layer, an ultraviolet absorbing layer, an adhesive layer, and the like.

[0190] In the illustrated example, the first direction D1 is the stacking direction. The first direction D1 is the thickness direction. Each layer 20, 30, 40, 51, 52 contained in the optical sheet 10 is stacked in the first direction D1. Each layer 20, 30, 40, 51, 52 has a normal direction or perpendicular direction parallel to the first direction D1. Each layer 20, 30, 40, 51, 52 extends in the second direction D2 and the third direction D3 which are perpendicular to the first direction D1. In the illustrated example, the second direction D2 and the third direction D3 are perpendicular to each other. Not limited to the illustrated example, each layer 20, 30, 40, 51, 52 may be curved.

[0191] In the example shown in Figure 1, the first surface 11 is composed of a functional layer 20. In the examples shown in Figures 9 and 10, the first surface 11 is composed of a second functional layer 51. The second functional layer 51 and the third functional layer 52 are thin layers that extend along the uneven surface 21X of the functional layer 20. In the examples shown in Figures 9 and 10, the first surface 11 is an uneven surface 11X having irregularities corresponding to the uneven surface 21X of the functional layer 20.

[0192] The following describes the base layer 40, the functional layer 20, the intermediate layer 30, the second functional layer 51, and the third functional layer 52.

[0193] <Base Layer> The base layer 40 supports the functional layer 20 and the intermediate layer 30. As shown in Figures 1, 2, 9, and 10, the base layer 40 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 first direction D1.

[0194] The substrate layer may be transparent. Transparency means that the total light transmittance is 50% or more, but it may also be 70% or more, 80% or more, or 90% or more.

[0195] The base layer may contain acrylic resin. "Acrylic resin" includes both acrylic resins and methacrylic resins. The base layer may contain acrylic resin as its main component. The main component means the material contained in the layer (e.g., the base layer) in the largest mass percentage (wt%). The base layer may contain acrylic resin in a mass percentage of 50% or more.

[0196] The acrylic resin contained in the substrate layer may be any suitable (meth)acrylic resin. Examples of (meth)acrylic resins include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, methyl (meth)acrylic acid-styrene copolymers (MS resin, etc.), and polymers having alicyclic hydrocarbon groups (e.g., methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylic acid copolymer, etc.). The resin used in the substrate layer is poly(meth)acrylic acid C such as poly(meth)acrylate. １－６ Alkyl compounds may be included. The base layer may contain methyl methacrylate as its main component. The base layer may contain methyl methacrylate in an amount of 50% to 100% by mass, or 70% to 100% by mass.

[0197] A lower limit may be set for the average thickness T40 of the base layer 40 (see Figure 2). By setting a lower limit for the average thickness T40, deformation of the base layer 40 and the overall deformation of the optical sheet can be suppressed. The base layer 40 may be the thickest layer included in the optical sheet 10. The average thickness T40 of the base layer 40 may be 10 μm or more, 20 μm or more, or 35 μm or more.

[0198] An upper limit may be set on the average thickness T40 of the base layer 40. By setting an upper limit on the average thickness T40 of the base layer 40, the optical sheet 10 can be made thinner. The average thickness T40 of the base layer 40 may be 150 μm or less, 110 μm or less, or 90 μm or less.

[0199] The average thickness T40 of the base layer 40 may be 10 μm or more and 150 μm or less, 20 μm or more and 150 μm or less, or 35 μm or more and 150 μm or less. The average thickness T40 of the base layer 40 may be 10 μm or more and 110 μm or less, 20 μm or more and 110 μm or less, or 35 μm or more and 110 μm or less. The average thickness T40 of the base layer 40 may be 10 μm or more and 90 μm or less, 20 μm or more and 90 μm or less, or 35 μm or more and 90 μm or less.

[0200] The "average thickness" used for each layer 20, 30, and 40 contained in the optical sheet shall be the value specified by (A1) to (A3) below.

[0201] (A1) Observe an image of the cross-section of the optical sheet using a scanning transmission electron microscope (STEM). Determine the imaging area so that the first direction, which is the thickness direction of the layer to be measured, is aligned with the short side of the rectangular imaging area. The magnification during imaging should 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.

[0202] (A2) The thickness of the target layer at the center of the captured image along the direction perpendicular to the first direction, and the thickness of the target layer at positions shifted 50 μm to both sides from the center along the direction perpendicular to the first direction are measured. The thickness is defined as the length (μm) of the target layer along the first direction.

[0203] (A3) Perform the above steps (A1) and (A2) five times on the layer to be measured, and measure the thickness of the layer to be measured at a total of 15 locations. The average of the 15 thickness measurements will be taken as the average thickness (μm) of the layer to be measured.

[0204] In the application of optical sheets to foldable applications, the substrate layer may be flexible. In this example, the average thickness of the substrate layer may be between 10 μm and 40 μm.

[0205] The base layer may be prepared as a base film. This base film may contain only a single layer or multiple layers. The base layer may contain an acrylic resin film. The base layer may contain a primer layer such as an easy-adhesion layer. One or more etching treatments such as sputtering, corona discharge, ultraviolet irradiation, electron beam irradiation, chemical conversion, oxidation, and undercoating treatments may be applied to the surface of the base film. These treatments can improve the adhesion between the base film and layers adjacent to the base film. The surface of the base film may be cleaned using a solvent cleaning or ultrasonic cleaning treatment.

[0206] <Functional Layer> This layer is expected to perform some function. As shown in Figures 1 and 2, the functional layer 20 includes a first surface 21 and a second surface 22. The first surface 21 faces the first side in the first direction D1. The second surface 22 faces the second side in the first direction D1.

[0207] The functional layer contains a cured resin. The functional layer may contain a cured resin as its main component. The functional layer may contain a cured resin in a mass proportion of 50% or more.

[0208] The functional layer may include a base portion containing a cured resin and additives. The base portion may function as a binder component that holds the additives. Examples of additives include organic particles and inorganic fine particles, refractive index modifiers, antistatic agents, antifouling agents, ultraviolet absorbers, light stabilizers, antioxidants, viscosity modifiers, and thermal polymerization initiators.

[0209] The cured resin product is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may also be an ionizing radiation-curable resin composition. The functional layer may contain at least one of the cured product of the thermosetting resin composition and the cured product of the ionizing radiation-curable resin composition. The cured resin product imparts high strength and high hardness to the functional layer. The ionizing radiation-curable resin composition is particularly useful from the viewpoint of improving scratch resistance.

[0210] The functional layer containing the cured resin may be manufactured by a wet process. The functional layer may also be manufactured using a functional layer coating solution for forming the functional layer. The functional layer may also be manufactured by drying and curing the coating film of the functional layer coating solution. The functional layer coating solution may contain the resin composition that constitutes the functional layer.

[0211] A thermosetting resin composition contains a thermosetting resin. The thermosetting resin composition hardens upon heating. Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, unsaturated polyester resins, and silicone resins. The thermosetting resin composition may also contain a curing agent.

[0212] The ionizing radiation-curable resin composition contains a compound having an ionizing radiation-curable functional group. Hereinafter, the compound having an ionizing radiation-curable functional group will also be referred to as the "ionizing radiation-curable compound." Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups. The ionizing radiation-curable compound may contain ethylenically unsaturated bonding groups. The ionizing radiation-curable compound may contain two or more ethylenically unsaturated bonding groups. The ionizing radiation-curable compound may also be a polyfunctional (meth)acrylate compound containing two or more ethylenically unsaturated bonding groups. The polyfunctional (meth)acrylate compound may contain either monomers or oligomers. The ionizing radiation may be electromagnetic waves or charged particle beams. The ionizing radiation has energy quanta that can polymerize or crosslink molecules. Examples of ionizing radiation include ultraviolet (UV) rays, electron beams (EB), X-rays, gamma rays, alpha rays, and ion beams.

[0213] Examples of polyfunctional (meth)acrylate compounds include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxydiaacrylate, bisphenol A tetrapropoxydiaacrylate, and 1,6-hexanediol diacrylate as bifunctional (meth)acrylate monomers. Examples of trifunctional or more (meth)acrylate monomers include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and isocyanuric acid-modified tri(meth)acrylate. (Meth)acrylate monomers may have a modified molecular skeleton. The above (meth)acrylate monomers may have part of their molecular skeleton modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc.

[0214] Examples of polyfunctional (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.

[0215] For purposes such as adjusting the viscosity of a coating solution for a functional layer to form a functional layer, monofunctional (meth)acrylates may be used as ionizing radiation-curable compounds. Examples of monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isobornyl (meth)acrylate.

[0216] One type of ionizing radiation-curable compound may be used alone, or two or more types of ionizing radiation-curable compounds may be used in combination.

[0217] The weight-average molecular weight of the monomer may be greater than 0 and less than 1000, greater than 0 and 800 or less, or greater than 0 and 600 or less. The weight-average molecular weight of the oligomer may be between 1500 and 20000, between 2000 and 15000, or between 3000 and 12000. The weight-average molecular weight is the average molecular weight measured by GPC analysis and converted to standard polystyrene.

[0218] When the ionizing radiation-curable compound is an ultraviolet-curable compound, the coating solution for the functional layer, which includes the curable resin composition that forms the functional layer, may contain additives such as photopolymerization initiators and photopolymerization accelerators. Examples of photopolymerization initiators include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler ketone, benzoin, benzyldimethyl ketal, benzoyl benzoate, α-acyloxime ester, α-aminoalkylphenone, thioxanthones, etc. Photopolymerization accelerators reduce polymerization inhibition by air during curing and accelerate the curing rate. Examples of photopolymerization accelerators include one or more selected from p-dimethylaminobenzoate isoamyl ester, p-dimethylaminobenzoate ethyl ester, etc.

[0219] If the functional layer contains a cured product of an ionizing radiation-curable resin composition, it may have the following configuration (C1) or (C2).

[0220] (C1) The functional layer comprises a cured product of an ionizing radiation-curable resin composition and a thermoplastic resin. (C2) The functional layer comprises substantially only a cured product of an ionizing radiation-curable resin composition as a resin component, and contains 70% by mass or more of monomer components as ionizing radiation-curable compounds contained in the ionizing radiation-curable resin composition.

[0221] When the above configuration (C1) is adopted, the viscosity of the coating liquid for the functional layer is increased by the thermoplastic resin. Additives such as particles become less likely to settle in the coating liquid for the functional layer.

[0222] Examples of thermoplastic resins include polystyrene resin, polyolefin resin, ABS resin (including heat-resistant ABS resin), AS resin, AN resin, polyphenylene oxide resin, polycarbonate resin, polyacetal resin, acrylic resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polysulfone resin, and polyphenylene sulfide resin.

[0223] The mass-average molecular weight of the thermoplastic resin may be between 20,000 and 200,000, between 30,000 and 150,000, or between 50,000 and 100,000. The mass-average molecular weight is the average molecular weight measured by GPC analysis and converted to standard polystyrene.

[0224] In the above configuration (C1), the mass ratio of the cured product of the ionizing radiation-curable resin composition to the thermoplastic resin may be 60:40 to 90:10, or 70:30 to 80:20. By using 10 parts by mass or more of thermoplastic resin for every 90 parts by mass of the cured product of the ionizing radiation-curable resin composition, the effect of increasing the viscosity of the coating liquid for the functional layer can be effectively obtained. By using 40 parts by mass or less of thermoplastic resin for every 60 parts by mass of the cured product of the ionizing radiation-curable resin composition, the mechanical strength of the functional layer can be improved.

[0225] When the functional layer having the above configuration (C2) contains particles, the particles are packed into the bottom of the functional layer, and in some areas, the particles are more easily stacked. Furthermore, a very thin resin acting as a binder component covers the particles.

[0226] In the above configuration (C2), the ratio of the cured product of the ionizing radiation-curable resin composition to the total amount of resin 36 may be 90% by mass or more, 95% by mass or more, or 100% by mass. In the above configuration (C2), the ratio of the monomer component to the total amount of the ionizing radiation-curable compound may be 70% by mass or more, or 75% by mass or more. When the above configuration (C2) is adopted, the monomer component may be a polyfunctional (meth)acrylate compound.

[0227] As mentioned above, the functional layer may be a hard coat layer. The functional layer may also be an anti-glare layer, as shown in Figures 1, 9, and 10.

[0228] The average thickness T20 (see Figure 2) of the functional layer 20, which functions as a hard coat layer or anti-glare layer, may be 1.0 μm or more, 2.0 μm or more, 3.0 μm or more, or 3.5 μm or more. The average thickness T20 (see Figure 2) of the functional layer 20, which functions as a hard coat layer or anti-glare layer, may be 15.0 μm or less, 10.0 μm or less, 8.0 μm or less, or 6.0 μm or less.

[0229] The average thickness T20 (see Figure 2) of the functional layer 20, which functions as a hard coat layer or anti-glare layer, may be 1.0 μm or more and 15.0 μm or less, 2.0 μm or more and 15.0 μm or less, 3.0 μm or more and 15.0 μm or less, or 3.5 μm or more and 15.0 μm or less. The average thickness T20 (see Figure 2) of the functional layer 20, which functions as a hard coat layer or anti-glare layer, may be 1.0 μm or more and 10.0 μm or less, 2.0 μm or more and 10.0 μm or less, 3.0 μm or more and 10.0 μm or less, or 3.5 μm or more and 10.0 μm or less. The average thickness T20 (see Figure 2) of the functional layer 20, which functions as a hard coat layer or anti-glare layer, may be 1.0 μm or more and 8.0 μm or less, 2.0 μm or more and 8.0 μm or less, 3.0 μm or more and 8.0 μm or less, or 3.5 μm or more and 8.0 μm or less. The average thickness T20 (see Figure 2) of the functional layer 20, which functions as a hard coat layer or anti-glare layer, may be 1.0 μm or more and 6.0 μm or less, 2.0 μm or more and 6.0 μm or less, 3.0 μm or more and 6.0 μm or less, or 3.5 μm or more and 6.0 μm or less.

[0230] In the functional layer which is an anti-glare layer, the first surface 21 may be an uneven surface 21X having irregularities. The second surface 22 may be a flat surface. The functional layer 20 may be in contact with the intermediate layer 30 at the second surface 22. The functional layer 20 may be bonded to the intermediate layer 30 at the second surface 22.

[0231] In the example shown in Figure 1, the first surface 21 of the functional layer 20 constitutes the first surface 11 of the optical sheet 10. The first surface 11 is an uneven surface 11X composed of uneven surfaces 21X. On the first surface 11 as an uneven surface 11X, ambient light in the environment in which the optical sheet 10 is installed is diffusely reflected. Due to this diffuse reflection, the background image in the environment in which the optical sheet 10 is installed is suppressed from being reflected on the optical sheet 10. In this way, the functional layer 20 and the optical sheet 10 exhibit anti-glare properties.

[0232] In the examples shown in Figures 9 and 10, the second functional layer 51 constitutes the first surface 11 of the optical sheet 10. The second functional layer 51 is a very thin layer and extends along the uneven surface 21X. The first surface 11 is an uneven surface 11X that includes irregularities corresponding to the irregularities of the uneven surface 21X. On the first surface 11 as the uneven surface 11X, ambient light in the environment in which the optical sheet 10 is installed is diffusely reflected. Due to this diffuse reflection, the background image in the environment in which the optical sheet 10 is installed is suppressed from being reflected on the optical sheet 10. In this way, the functional layer 20 and the optical sheet 10 exhibit anti-glare properties.

[0233] As shown in Figures 1, 9, and 10, the functional layer 20, which is an anti-glare layer, may include a base portion 26 and particles 27. The base portion 26 includes a cured resin. The base portion 26 may include a cured resin as its main component. The base portion 26 may contain a cured resin in a mass proportion of 50% or more. As described above, the base portion 26 may include a cured resin and a thermoplastic resin.

[0234] The base portion 26 may function as a binder component that holds the particles 27. The base portion 26 may also function as a binder for forming a functional layer containing the particles 27. The functional layer may maintain its film shape by holding the particles contained in the functional layer with the base portion. The base portion may enclose the particles contained in the functional layer. The base portion may completely enclose each particle contained in the functional layer, or it may partially expose at least some of the particles contained in the functional layer.

[0235] The particles 27 may be organic particles. The particles 27 may be inorganic particles. The functional layer 20 may contain both organic and inorganic particles as particles 27.

[0236] Examples of materials for organic particles include polymethyl methacrylate, polyacrylic-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone, fluororesins, and polyester resins. Examples of materials for inorganic particles include silica, alumina, zirconia, and titania.

[0237] Examples of materials for inorganic particles include silica, alumina, zirconia, and titania. The average particle size of the inorganic particles may be between 1 nm and 200 nm, between 2 nm and 100 nm, or between 5 nm and 50 nm. The average particle size of the inorganic particles can be measured in the same way as the average particle size of the particles described above.

[0238] By including inorganic particles in the functional layer, particle aggregation and dispersion become easier to control, making it easier to achieve desired light diffusion characteristics. Therefore, the functional layer can be given an effective anti-glare function through light diffusion.

[0239] The inorganic particles may be amorphous inorganic particles. Amorphous silica is an example of amorphous inorganic particles.

[0240] When the average particle diameter is increased relative to the average thickness of the functional layer, the first surface 21 tends to contain relatively large inclined surfaces. When the average particle diameter is decreased relative to the average thickness of the functional layer, the first surface 21 tends to contain relatively small inclined surfaces. The average particle diameter of the particles 27 may be between 1.0 μm and 7.0 μm, between 1.5 μm and 6.0 μm, or between 1.7 μm and 5.0 μm.

[0241] The "average particle diameter" used for organic and inorganic particles shall be the value specified by (B1) to (B3) below. Although particles may aggregate, the average particle diameter is the average primary particle diameter.

[0242] (B1) A cross-section of an optical sheet containing particles is observed using a transmission electron microscope (TEM), and an image is obtained by imaging.

[0243] (B2) Ten arbitrary particles are extracted from the observation image, and the particle diameter of each particle is measured. The particle diameter (μm) is defined as the distance between two parallel lines that maximize the distance between the two lines when the cross-section of the particle is enclosed by those two lines. In other words, the particle diameter is the maximum length of the particle in question in the observation image. The particle diameter is identified as the particle diameter (maximum length) of each individual particle. That is, the particle diameter is the primary particle diameter.

[0244] (B3) Perform the above steps (B1) and (B2) five times on the same optical sheet to be measured, and measure the particle diameter of a total of 50 particles. The average of the 50 particle diameter measurements will be taken as the average particle diameter (μm) of the particle.

[0245] The ratio of the average particle diameter D of the particles 27 to the average thickness T20 of the functional layer 20 (D / T20) may be 0.10 or more and 3.5 or less, 0.20 or more and 2.0 or less, 0.30 or more and 1.0 or less, or 0.50 or more and 0.70 or less.

[0246] Increasing the particle content in the base makes it easier for the first surface of the functional layer to densely contain inclined surfaces. Decreasing the particle content in the base makes it easier for the first surface of the functional layer to sparsely contain inclined surfaces.

[0247] The content of organic particles, inorganic particles, etc. may be 10 parts by mass or more and 200 parts by mass or 15 parts by mass or 170 parts by mass or 20 parts by mass or 150 parts by mass per 100 parts by mass of the base portion.

[0248] (Coating liquid for functional layer) As described above, the functional layer may be produced by drying and curing a coating film of the coating liquid for the functional layer. The coating liquid for the functional layer may contain a curable resin composition. The coating liquid for the functional layer may contain additives such as particles, antistatic agents, antioxidants, surfactants, dispersants, and ultraviolet absorbers.

[0249] The coating solution for the functional layer may contain a silicone-based leveling agent (silicone-based compound) as an additive. By including a silicone-based leveling agent in the coating solution for the functional layer, it is possible to suppress the particles from protruding significantly from the first surface of the functional layer.

[0250] 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.

[0251] The coating solution for the functional layer may contain a solvent. The viscosity of the coating solution for the functional layer can be adjusted by the solvent. The dispersion of each component can be controlled by the solvent. The surface properties of the resulting functional 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 penetration of the solvent into the transparent substrate. 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 functional layer may contain one or more solvents.

[0252] The coating solution for the functional layer may contain a solvent with a fast evaporation rate. By increasing the evaporation rate of the solvent, it is possible to suppress the settling of particles at the bottom of the functional layer.

[0253] A solvent with a fast evaporation rate is defined as a solvent whose evaporation rate is 100 or higher, with the evaporation rate of butyl acetate set to 100. The evaporation rate of a fast-evaporating solvent may be between 120 and 300, or between 150 and 220. Examples of fast-evaporating solvents include methyl isobutyl ketone (evaporation rate 160), toluene (evaporation rate 200), and methyl ethyl ketone (evaporation rate 370).

[0254] The coating solution for the functional layer may contain a small amount of a slow-evaporating solvent in addition to a fast-evaporating solvent. A slow-evaporating solvent is defined as a solvent whose evaporation rate is less than 100 when the evaporation rate of butyl acetate is set to 100. The evaporation rate of the slow-evaporating solvent may be between 20 and 60, or between 25 and 40. Examples of slow-evaporating solvents include cyclohexanone (evaporation rate 32) and propylene glycol monomethyl ether acetate (evaporation rate 44).

[0255] When preparing a functional layer from a coating solution for the functional layer, the drying conditions of the coating film of the functional layer coating solution may be adjusted. The drying conditions can be adjusted by the drying temperature and the air velocity in the dryer. The drying temperature may be between 30°C and 120°C. The drying air velocity may be between 0.2 m / s and 50 m / s. In order to adjust the surface properties of the functional layer by drying, the coating film may be irradiated with ionizing radiation after drying.

[0256] <Intermediate Layer> As shown in Figures 1, 9, and 10, the intermediate layer 30 is located between the functional layer 20 and the base material layer 40. The intermediate layer 30 is not particularly limited.

[0257] The intermediate layer may contain a resin. The intermediate layer may contain a thermoplastic resin. Examples of thermoplastic resins include polystyrene resin, polyolefin resin, ABS resin (including heat-resistant ABS resin), AS resin, AN resin, polyphenylene oxide resin, polycarbonate resin, polyacetal resin, acrylic resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polysulfone resin, and polyphenylene sulfide resin.

[0258] The intermediate layer may contain a cured resin product. The cured resin product is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may be an ionizing radiation curable resin composition. The intermediate layer may contain one or more cured products of a thermosetting resin composition and a cured product of an ionizing radiation curable resin composition. The intermediate layer may contain the above-mentioned cured resin products and curable resin compositions that can be used in the functional layer.

[0259] The intermediate layer may be manufactured by a wet process, similar to the functional layer. The intermediate layer may be manufactured using an intermediate layer coating solution for forming the intermediate layer. The intermediate layer may also be manufactured by drying and curing the coating film of the intermediate layer coating solution. The intermediate layer coating solution may contain a resin composition that constitutes the intermediate layer. The intermediate layer coating solution may contain additives that can be applied to the functional layer coating solution.

[0260] The intermediate layer may be a layer with high adhesion to the substrate layer. The intermediate layer may be a layer with high adhesion to the functional layer. The intermediate layer may contain the same resin components as at least some of the resin components contained in the functional layer. The intermediate layer may contain acrylic resin. The intermediate layer may contain the same resin components as at least some of the resin components contained in the functional layer. The intermediate layer may contain monomers. The intermediate layer may contain at least some of the monomers contained in the coating solution for the functional layer used to produce the functional layer.

[0261] The intermediate layer may be a mixed layer of the resin component of the functional layer and the resin component of the base layer. The intermediate layer as a mixed layer may also be a permeable layer in which a coating solution for the functional layer used to create the functional layer has been impregnated into the base film. Both the base layer and the intermediate layer may be composed of a base film. The base film is coated with a coating solution for the functional layer used to create the functional layer. The intermediate layer may be composed of the portion of the base film in which the coating solution for the functional layer has been impregnated (permeable layer). The base layer 40 may be composed of the portion of the base film in which the coating solution for the functional layer has not been impregnated.

[0262] The solvent contained in the coating solution for the functional layer easily penetrates the base film, allowing for the stable formation of an intermediate layer as a penetrating layer. Using a base film with high water absorption (liquid absorption) facilitates the penetration of the solvent into the base film. The solvent easily penetrates the acrylic resin. Therefore, by using a base film containing acrylic resin, an intermediate layer adjacent to both the base layer and the functional layer can be stably produced. The produced intermediate layer contains acrylic resin.

[0263] The ease with which a permeable layer is formed depends on the relationship between the curable resin composition, curable resin compound, and solvent contained in the functional layer coating solution and the substrate film. Furthermore, the ease with which a permeable layer is formed also depends on the viscosity of the functional layer coating solution, the drying conditions of the coating film, and the curing conditions of the coating film. Therefore, the thickness of the intermediate layer, which acts as a permeable layer, can be adjusted by controlling the materials contained in the functional layer coating solution, the materials of the substrate film, the preparation conditions of the functional layer coating solution, the drying conditions of the coating film, and the curing conditions of the coating film.

[0264] The average thickness T30 of the intermediate layer 30 (see Figure 2) may be 0.3 μm or more, 0.5 μm or more, 1.0 μm or more, or 2.0 μm or more. The average thickness T30 of the intermediate layer 30 (see Figure 2) may be 7.0 μm or less, 6.0 μm or less, 4.0 μm or less, or 3.0 μm or less.

[0265] The average thickness T30 of the intermediate layer 30 (see Figure 2) may be 0.3 μm or more and 7.0 μm or less, 0.5 μm or more and 7.0 μm or less, 1.0 μm or more and 7.0 μm or less, or 2.0 μm or more and 7.0 μm or less. The average thickness T30 of the intermediate layer 30 (see Figure 2) may be 0.3 μm or more and 6.0 μm or less, 0.5 μm or more and 6.0 μm or less, 1.0 μm or more and 6.0 μm or less, or 2.0 μm or more and 6.0 μm or less. The average thickness T30 of the intermediate layer 30 (see Figure 2) may be 0.3 μm or more and 4.0 μm or less, 0.5 μm or more and 4.0 μm or less, 1.0 μm or more and 4.0 μm or less, or 2.0 μm or more and 4.0 μm or less. The average thickness T30 of the intermediate layer 30 (see Figure 2) may be 0.3 μm or more and 3.0 μm or less, 0.5 μm or more and 3.0 μm or less, 1.0 μm or more and 3.0 μm or less, or 2.0 μm or more and 3.0 μm or less.

[0266] <Second Functional Layer> The optical sheet 10 shown in Figure 9 further includes a second functional layer 51. The second functional layer 51 constitutes the first surface 11 of the optical sheet 10. The illustrated second functional layer 51 is a low refractive index layer. A low refractive index layer has a refractive index lower than that of adjacent layers. As a low refractive index layer, the second functional layer 51 is a low-reflection layer or reflection-suppressing layer that has the function of suppressing reflection.

[0267] 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 functional layer (first functional layer).

[0268] The second 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 second functional layer is based on the interference of light reflected from both sides of the second functional layer. From the viewpoint of making this reflection suppression function effective, the refractive index of the second functional layer may be between the refractive indices of two regions adjacent to the second functional layer from both sides (in the illustrated example, the functional layer and the air layer). 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.

[0269] From the viewpoint of reflection suppression function, the refractive index and average thickness of the second functional layer can be set as follows: The refractive index of the second 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 second 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.

[0270] The refractive index of the second 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 second 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 second 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 second functional layer may be 1.10 or more and 1.38 or less, 1.20 or more and 1.38 or less, 1.26 or more and 1.38 or less, 1.28 or more and 1.38 or less, or 1.30 or more and 1.38 or less. The refractive index of the second 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.

[0271] The average thickness of the second functional layer may be 80 nm or more, 85 nm or more, or 90 nm or more. The average thickness of the second functional layer may be 150 nm or less, 110 nm or less, or 105 nm or less.

[0272] The average thickness of the second functional layer may be 80 nm to 150 nm, 85 nm to 150 nm, or 90 nm to 150 nm. The average thickness of the second functional layer may be 80 nm to 110 nm, 85 nm to 110 nm, or 90 nm to 110 nm. The average thickness of the second functional layer may be 80 nm to 105 nm, 85 nm to 105 nm, or 90 nm to 105 nm.

[0273] The binder component included in the second functional layer may be the same as the binder component included in the functional layer. The binder component included in the second functional layer may include a cured resin product, i.e., 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. The cured resin product and curable resin composition used in the second functional layer may include the above-mentioned cured resin product and curable resin composition that can be used in the functional layer.

[0274] The particles included in the second functional layer may be the same as the particles included in the functional layer. The second functional layer may contain one or more organic particles and inorganic particles. The second functional layer may contain one or more hollow silica, solid silica, and magnesium fluoride particles as inorganic particles.

[0275] 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 second functional layer.

[0276] The second functional layer may be manufactured by a wet process, similar to the functional layer. The second functional layer may also be manufactured using a coating solution for the second functional layer. The functional layer may also be manufactured by drying and curing the coating film of the coating solution for the second functional layer. The coating solution for the second functional layer may contain resin compositions and particles that constitute 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 functional layer.

[0277] <Third Functional Layer> The optical sheet 10 shown in Figure 10 includes a second functional layer 51 and a third functional layer 52. In the example shown in Figure 10, the second functional layer 51 may be configured in the same way as the second functional layer 51 described above included in the optical sheet 10 shown in Figure 9. That is, the second functional layer 51 constitutes the first surface 11 of the optical sheet 10. The second functional layer 51 is a low refractive index layer. The low refractive index layer has a refractive index lower than that of the adjacent third functional layer 52.

[0278] The third functional layer 52 is located between the second functional layer 51 and the functional layer 20 in the first direction D1, which is the stacking direction. The third functional layer 52 has a refractive index higher than that of the functional layer 20 and the second functional layer 51. The second functional layer 51 as a low refractive index layer and the third functional layer 52 as a high refractive index layer function as a low reflection layer or reflection suppression layer, suppressing reflection on the first surface 11 of the optical sheet 10.

[0279] In terms of specific configuration, the third functional layer may include 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 third functional layer is increased by including high refractive index particles. The refractive index of the third functional layer is greater than that of the two regions adjacent to the third functional layer from both sides (the functional layer and the second functional layer in the illustrated example).

[0280] From the viewpoint of reflection suppression function, the refractive index and average thickness of the third functional layer may be set as follows: The refractive index of the third functional layer may be 1.55 or higher, or 1.56 or higher. The refractive index of the third functional layer may be 1.85 or lower, or 1.75 or lower. The refractive index of the third functional layer may be 1.55 or higher and 1.85 or lower, 1.56 or higher and 1.85 or lower, 1.55 or higher and 1.75 or lower, or 1.56 or higher and 1.75 or lower.

[0281] The average thickness of the third functional layer 52 may be 50 nm or more. The average thickness of the second functional layer may be 200 nm or less, or 180 nm or less. The average thickness of the third functional layer may be 50 nm or more and 200 nm or less, or 50 nm or more and 180 nm or less.

[0282] The binder component included in the third functional layer may be the same as the binder component included in the functional layer. The binder component included in the third functional layer may include a cured resin product, i.e., 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. The cured resin product and curable resin composition used in the third functional layer may include the above-mentioned cured resin product and curable resin composition that can be used in the functional layer.

[0283] The particles included in the third functional layer may be the same as those included in the functional layer. The third functional layer 52 may contain one or more organic and inorganic particles. Examples of particles included in the third functional layer include antimony pentoxide, zinc oxide, titanium oxide, cerium oxide, tin-doped indium oxide, antimony-doped tin oxide, yttrium oxide, and zirconium oxide.

[0284] The third functional layer may be manufactured by a wet process, similar to the functional layer. The third functional layer may also be manufactured using a coating solution for the third functional layer. The third functional layer may also be manufactured by drying and curing the coating film of the coating solution for the third functional layer. The coating solution for the third functional layer may contain resin compositions and particles that constitute the third functional layer. The coating solution for the third functional layer may contain additives that can be applied to the third layer coating solution.

[0285] <<<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.

[0286] <<<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 sandwich the polarizer 62 and cover the polarizer 62 from both sides. 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.

[0287] 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.

[0288] <<<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.

[0289] The observer observes the image displayed by the display element 66 through the optical sheet 10. In a display device 65 to which an anti-glare optical sheet 10 is applied, it is possible to suppress the reflection of background images located in the environment in which the display device 65 is placed, such as lighting equipment, onto the optical sheet 10.

[0290] <<<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 functional article having various properties (for example, anti-glare properties and hard coat properties) due to the optical sheet 10. For example, the panel 70 as an anti-glare article suppresses the reflection of external images due to its anti-glare function. The optical sheet 10 is superimposed on the article to be bonded 71 such that its second surface 12 faces 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 adhesive or tack. Examples of the article to be bonded 71 include instrument panels, clocks, showcases, shop windows, windows, and front panels for display devices. The article to be bonded 71 may also be a transparent substrate such as glass or a resin film.

[0291] This disclosure will be further described in detail by examples. This disclosure is not limited to the following examples.

[0292] <<<1. Preparation of Optical Sheets>>> Optical sheets according to Examples 1 to 3 and Comparative Example 1 were prepared.

[0293] <<Example 1>> (Production of base material) A copolymer of methyl methacrylate and methyl acrylate was kneaded at 260°C using a twin-screw extruder to obtain a pelletized composition (glass transition temperature: 128°C). The obtained pelletized composition was formed into a film by melt extrusion using a T-die (T-die temperature: 250°C), and the formed film was discharged onto a cooling roll at 130°C. Next, the obtained film was sequentially biaxially stretched in the longitudinal and transverse directions at a stretching ratio of 1.3 times at a stretching temperature of 145°C. After that, the stretched film was cooled to obtain a base material film made of acrylic resin with a thickness of 40 μm.

[0294] The intermediate layer coating solution 1, according to the following formulation, was applied to the base film to form a coating film of the intermediate layer coating solution 1. The amount of intermediate layer coating solution 1 applied was 1.0 g / m². ２ Next, the coating film was dried at 50°C and a wind speed of 5 m / s for 30 seconds, and then dried again at 70°C and a wind speed of 5 m / s for 30 seconds. After that, it was dried in a nitrogen atmosphere with an oxygen concentration of 200 ppm or less, with an integrated light intensity of 100 mJ / cm². ２ The coated film was irradiated with ultraviolet light to form an intermediate layer.

[0295] <Intermediate Coating Solution 1> Difunctional monomer (tetraethylene diacrylate) 80 parts by mass Monofunctional monomer (acryloyl morpholine) 20 parts by mass Photopolymerization initiator (IGM Resins BV's product name "Omnirad 184") 5 parts by mass Leveling agent (silicone-based leveling agent) 0.1 parts by mass Solvent (methyl isobutyl ketone) 105 parts by mass Solvent (cyclohexanone) 45 parts by mass

[0296] Next, the functional layer coating solution 1 with the following formulation was applied to the intermediate layer to form a coating film of the functional layer coating solution 1. The amount of functional layer coating solution 1 applied was 5.5 g / m². ２ Next, the coating film was dried at 70°C and a wind speed of 5 m / s for 60 seconds. After that, it was exposed to a nitrogen atmosphere with an oxygen concentration of 200 ppm or less, with an integrated light intensity of 500 mJ / cm². ２ The coated film was irradiated with ultraviolet light. A functional layer consisting of the cured coated film was formed on the intermediate layer.

[0297] <Coating Liquid 1 for Functional Layer>Organic particles (spherical polyacrylic styrene copolymer, average particle diameter 2.0 μm, particle refractive index n = 1.55) 12 parts by mass Inorganic particles (dry silica particles, average primary particle diameter 12 nm) 2 parts by mass Urethane acrylate (Kyoeisha UA-510H) 60 parts by mass Tetrafunctional monomer (pentaerythritol tetraacrylate) 20 parts by mass Trifunctional monomer (pentaerythritol triacrylate) 15 parts by mass Bifunctional monomer (tetraethylene diacrylate) 5 parts by mass Photoinitiator (trade name “Omnirad 184” of IGM Resins B.V.) 5 parts by mass Leveling agent (silicone-based leveling agent) 0.1 part by mass Solvent (toluene) 105 parts by mass Solvent (isopropanol) 15 parts by mass Solvent (methyl isobutyl ketone) 30 parts by mass

[0298] Thus, an optical sheet according to Example 1 including a base material layer made of a base material film, an intermediate layer, and a functional layer in this order from the second surface toward the first surface was obtained.

[0299] <<Example 2>>In Example 2, the coating amount of the coating liquid 1 for the intermediate layer was 3.0 g / m ２ and the coating liquid 1 for the functional layer was changed to the coating liquid 2 for the functional layer with the following formulation, and the coating amount of the coating liquid 2 for the functional layer was 5.0 g / m ２ which was different from Example 1 above, and an antiglare sheet according to Example - 2 was obtained in the same manner as Example 1 in other respects.

[0300] <Coating Solution for Functional Layer 2> Organic fine particles (spherical polyacrylic styrene copolymer, average particle size 2.0 μm, particle refractive index n = 1.55) 12 parts by mass Inorganic particles (dry silica particles, average primary particle size 12 nm) 2 parts by mass Urethane acrylate (Kyoeisha UA-510H) 65 parts by mass Tetrafunctional monomer (pentaerythritol tetraacrylate) 15 parts by mass Trifunctional monomer (pentaerythritol triacrylate) 15 parts by mass Difunctional monomer (tetraethylene diacrylate) 5 parts by mass Photopolymerization initiator (IGM Resins BV product name "Omnirad 184") 5 parts by mass Leveling agent (silicone-based leveling agent) 0.1 parts by mass Solvent (toluene) 105 parts by mass Solvent (isopropanol) 15 parts by mass Solvent (methyl isobutyl ketone) 30 parts by mass

[0301] <<Example 3>> Example 3 is characterized in that the intermediate layer coating solution 1 is changed to the intermediate layer coating solution 2 of the following formulation, and the amount of intermediate layer coating solution 2 applied is 3.0 g / m ２ The points mentioned above, the functional layer coating solution 1 was changed to the functional layer coating solution 3 in the following formulation, and the application amount of the functional layer coating solution 3 was set to 5.0 g / m². ２ In this respect, it differs from Example 1 described above, but in other respects, the anti-glare sheet according to Example 3 was obtained in the same manner as Example 1.

[0302] <Intermediate Coating Solution 2> Difunctional monomer (tetraethylene diacrylate) 85 parts by mass Monofunctional monomer (acryloyl morpholine) 15 parts by mass Photopolymerization initiator (IGM Resins BV's product name "Omnirad 184") 5 parts by mass Leveling agent (silicone-based leveling agent) 0.1 parts by mass Solvent (methyl isobutyl ketone) 105 parts by mass Solvent (cyclohexanone) 45 parts by mass

[0303] <Functional Layer Coating Solution 3> Organic particles (spherical polyacrylic styrene copolymer, average particle size 2.0 μm, particle refractive index n = 1.55) 12 parts by mass Inorganic particles (dry silica particles, average primary particle size 12 nm) 2 parts by mass Urethane acrylate (Kyoeisha UA-510H) 65 parts by mass Tetrafunctional monomer (pentaerythritol tetraacrylate) 10 parts by mass Trifunctional monomer (pentaerythritol triacrylate) 20 parts by mass Difunctional monomer (tetraethylene diacrylate) 5 parts by mass Photopolymerization initiator (IGM Resins BV product name "Omnirad 184") 5 parts by mass Leveling agent (silicone-based leveling agent) 0.1 parts by mass Solvent (toluene) 105 parts by mass Solvent (isopropanol) 15 parts by mass Solvent (methyl isobutyl ketone) 30 parts by mass

[0304] <<Comparative Example 1>> Comparative Example 1 differs from Example 1 in that the intermediate layer coating solution 1 is changed to the intermediate layer coating solution 3 of the following formulation, the drying conditions for the coating film of the intermediate layer coating solution 3 are 70°C and a wind speed of 10 m / s for 30 seconds, and the functional layer coating solution 1 is changed to the functional layer coating solution 4 of the following formulation, and otherwise the anti-glare sheet according to Example 3 is obtained in the same manner as Example 1.

[0305] <Intermediate Coating Solution 3> 80 parts by mass of bifunctional monomer (tetraethylene diacrylate) 20 parts by mass of monofunctional monomer (acryloyl morpholine) 5 parts by mass of photopolymerization initiator (IGM Resins BV's product name "Omnirad 184") 0.1 parts by mass of leveling agent (silicone-based leveling agent) 120 parts by mass of solvent (methyl isobutyl ketone) 30 parts by mass of solvent (cyclohexanone)

[0306] <Functional Layer Coating Solution 4> Organic particles (spherical polyacrylic styrene copolymer, average particle size 2.0 μm, particle refractive index n = 1.55) 12 parts by mass Inorganic particles (dry silica particles, average primary particle size 12 nm) 2 parts by mass Urethane acrylate (Kyoeisha UA-510H) 60 parts by mass Tetrafunctional monomer (pentaerythritol tetraacrylate) 15 parts by mass Trifunctional monomer (pentaerythritol triacrylate) 20 parts by mass Difunctional monomer (tetraethylene diacrylate) 5 parts by mass Photopolymerization initiator (IGM Resins BV product name "Omnirad 184") 5 parts by mass Leveling agent (silicone-based leveling agent) 0.1 parts by mass Solvent (toluene) 105 parts by mass Solvent (isopropanol) 15 parts by mass Solvent (methyl isobutyl ketone) 30 parts by mass

[0307] <<<2. Measurement and Evaluation>>> The optical sheets of the examples and comparative examples were measured and evaluated as described below.

[0308] <<2-1. Transmitted Haze>> A 10 cm x 10 cm measurement sample was cut from the optical sheet relating to the examples and comparative examples. The measurement sample was visually inspected to ensure there were no abnormalities such as dust or scratches. The transmitted haze (%) 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 transmitted haze. The measurement results of the transmitted haze are shown in the "Hz" column of Table 1.

[0309] <<2-2. Internal Haze>> A 10 cm x 10 cm sample was cut from the anti-glare sheet relating to the examples and comparative examples. The sample was visually inspected to ensure there were no abnormalities such as dust or scratches. Measurement samples for measuring internal haze were prepared using the method described above with a transparent adhesive and triacetylcellulose film. The transmitted haze was measured for each measurement sample. A haze meter "HM-150" manufactured by Murakami Color Technology Laboratory was used to measure the internal haze. The measurement results for internal haze are shown in the "I Hz" column of Table 1.

[0310] <<2-3. Erosion Test>> Measurement samples measuring 3 cm x 4 cm were cut from the optical sheets relating to the examples and comparative examples. Three measurement samples were prepared from each example. The measurement samples were visually inspected to ensure there were no abnormalities such as dust or scratches. Erosion tests were performed on the measurement samples under the conditions and methods described above. For conditions and methods other than those described above, the tests were performed as follows.

[0311] The test solution was prepared as follows: In a beaker, pure water, a dispersant, and spherical silica with an average particle size (median diameter) of 5 μm were mixed in a mass ratio of 968:2:30 to obtain the test solution. The dispersant was "Demol N," a product of Wako Pure Chemical Industries, Ltd. The spherical silica was "MSE-BS-5-3," a model specified by Palmeso Co., Ltd. The test solution was stirred in the beaker using a glass rod. The prepared test solution and stirring bar were placed in a container (pot). The lid was then secured to the pot with a clamp.

[0312] Next, a dummy sample was fixed to the mounting base of the test apparatus. The test apparatus was used to spray the test solution onto the dummy sample under predetermined conditions. After the spraying of the test solution onto the dummy sample was completed, the apparatus was calibrated.

[0313] For calibration, a calibration sample was first prepared. The calibration sample was a 2 mm thick polymethyl methacrylate (PMMA) resin plate (product name: MSE standard test piece (PMMA), model: HPMMA-C20-50). The calibration sample was fixed to the mounting base of the test apparatus using double-sided tape. The double-sided tape used was "Kapton double-stick tape" (product number: P-223 1-6299-01) manufactured by Nitto Denko America, Inc. The position of the mounting base was adjusted so that the distance d (see Figure 3A) between the calibration sample and the tip of the nozzle was 4 mm. The test liquid was sprayed from the nozzle towards the calibration sample. The cross-sectional profile of the calibration sample onto which the particles were projected was measured. From the cross-sectional profile, the erosion depth due to a single particle projection was measured. The erosion rate was measured from the amount of particles projected in a single particle projection (g) and the erosion depth due to a single particle projection (μm).

[0314] Calibration was completed if the erosion rate was between 0.1615 μm / g and 0.1785 μm / g. If the erosion rate fell outside this range, the flow rate of the test liquid supplied to the nozzle, the flow rate of the compressed air supplied to the nozzle, the pressure of the compressed air supplied to the nozzle, and the pressure of the mixed fluid of the test liquid and compressed air inside the nozzle were adjusted to change the spraying conditions of the test liquid directed towards the calibration sample. The nozzle system used had a 1 mm × 1 mm square cross-section. The supply rate of the test liquid to the nozzle was changed within the range of 100 mL / min to 150 mL / min. The supply rate of compressed air to the nozzle was changed within the range of 4.0 mL / min to 8.0 mL / min. The test liquid was projected onto an unused calibration sample under the changed spraying conditions. The erosion rate due to the test liquid spraying under the changed spraying conditions was measured. Calibration was repeated until the erosion rate was between 0.1615 μm / g and 0.1785 μm / g. The injection conditions that resulted in an erosion rate between 0.1615 μm / g and 0.1785 μm / g during calibration were used as the injection conditions for the erosion test on each sample.

[0315] After calibration was completed, erosion tests were performed on each sample. First, the sample was fixed to the mounting base of the test apparatus using double-sided tape. The double-sided tape used was "Kapton double-stick tape" part number: P-223 1-6299-01, manufactured by Nitto Denko America. The position of the mounting base was adjusted so that the distance d (see Figure 3A) between the sample and the tip of the nozzle was 4 mm.

[0316] Next, the projection step, in which particles were projected onto the measurement sample, and the measurement step, in which the erosion depth of the measurement sample onto which the particles were projected, were repeatedly performed. In other words, one projection step and one measurement step constituted one cycle, and this cycle was repeated.

[0317] In the projection step, the test liquid was sprayed from the nozzle of the test apparatus toward the measurement sample. The spraying conditions for the erosion test were those which resulted in an erosion rate of 0.1615 (μm / g) or more and 0.1785 (μm / g) or less during calibration. The target amount of particles projected in a single projection step was 1.0 g.

[0318] The test apparatus used for projecting particles onto dummy samples, calibration samples, and measurement samples was the MSE-A test apparatus from Palmeso Co., Ltd.

[0319] In the measurement step, the cross-sectional profile of the sample onto which particles were projected in the projection step was measured. The stylus-type shape measuring instrument "PU-EU1" manufactured by Kosaka Laboratory Co., Ltd. was used as the measuring device to acquire the cross-sectional profile of the sample. The measurement conditions for the "PU-EU1" instrument were as follows: Stylus tip radius: 2 μm; Load: 100 μN; Magnification: 20,000x; Measurement length: 3 mm; Measurement speed: 0.5 mm / second

[0320] The cycle, including the projection step and the measurement step, was carried out until the erosion depth reached the fourth position P4 (see Figure 2). The fourth position P4 is located 6.0 μm away from the first surface of the substrate layer towards the second surface along the first direction D1.

[0321] Based on the above, data regarding the particle projection amount (g) at each projection step of each cycle and the erosion depth (μm) after the completion of each cycle were obtained as test results for each measurement sample. From the obtained data, the erosion rate R(n) and the erosion rate slope S(n) for each cycle were calculated. The erosion rate R(n) and the erosion rate slope S(n) for each cycle were calculated according to the following formula.

[0322] Let n be a natural number, and let D(n) be the erosion depth after the nth cycle. D(0) is set to 0. Also, let M(n) be the total particle projection after the nth cycle. M(0) is set to 0. The erosion rate at the nth cycle, R(n), and the slope of the erosion rate after the nth cycle, S(n), were calculated using the following formulas: R(n) = (D(n+1) - D(n-1)) / (M(n+1) - M(n-1)) S(n) = (R(n+1) - R(n-1)) / (D(n+1) - D(n-1))

[0323] Figure 4 is a graph showing the relationship between erosion depth and erosion rate. Figure 4 shows data for one measurement sample in Example 1, data for one measurement sample in Example 2, and data for one measurement sample in Comparative Example 1.

[0324] Figure 5 is a graph showing the relationship between erosion depth and erosion rate slope. Figure 5 shows the data for the measurement sample shown in Figure 4.

[0325] <Maximum value H ((μm / g) / μm), full width at half maximum W (μm), ratio (H / W)> Using the test results of the measurement sample, the maximum value H ((μm / g) / μm), full width at half maximum W (μm), and the ratio (H / W) of the maximum value H ((μm / g) / μm) to the full width at half maximum W (μm) were measured using the method described above.

[0326] First, on a graph with the horizontal axis representing erosion depth (μm) and the vertical axis representing the erosion rate slope ((μm / g) / μm), a Gaussian function that fits the test results of the erosion test for each measurement sample was identified using the method described above.

[0327] The maximum value H ((μm / g) / μm) and the full width at half maximum W (μm) were calculated from the identified Gaussian function. The measurement results for the maximum value H ((μm / g) / μm), the full width at half maximum W (μm), and the ratio of the maximum value H to the full width at half maximum W (H / W) are shown in Table 1 under "Gaussian function" as "H", "W", and "H / W", respectively.

[0328] Three measurement samples were obtained from each example's optical sheet. For each of the three measurement samples from each example's optical sheet, the maximum value H, the full width at half maximum W, and the ratio of the maximum value H to the full width at half maximum W (H / W) were calculated. The value of "H" listed in Table 1 is the arithmetic mean of the three maximum values ​​H calculated for each example. The value of "W" listed in Table 1 is the arithmetic mean of the three full widths W calculated for each example. The value of "H / W" listed in Table 1 is calculated by dividing the arithmetic mean of the three maximum values ​​H calculated for each example by the arithmetic mean of the three maximum values ​​W calculated for each example.

[0329] <First Mean Erosion Rate Slope and Second Mean Erosion Rate Slope> The first mean erosion rate slope and the second mean erosion rate slope were calculated using the method described above, based on the test results of the measurement samples.

[0330] First, the test results of each measurement sample were smoothed on a graph with the horizontal axis representing erosion depth (μm) and the vertical axis representing the erosion rate slope ((μm / g) / μm). The smoothing process involved Gaussian weighting of a total of five points (five measurement values), including two points (two measurement values) located on either side of the horizontal axis.

[0331] Figure 8 is a graph showing the relationship between erosion depth and erosion rate slope after smoothing. Figure 8 shows the data for the measurement sample shown in Figure 4.

[0332] The first average erosion rate slope ((μm / g) / μm) was calculated as the average value of the smoothed erosion rate slope. The erosion rate slope used to calculate the first average erosion rate slope was the erosion rate slope at measurement positions located at least 0.50 μm away from the first surface 11 along the first direction D1. The erosion rate slope used to calculate the first average erosion rate slope was the erosion rate slope at measurement positions up to four measurement positions prior to the measurement position where the erosion rate first exceeded 0.20 μm / g.

[0333] The second mean erosion rate slope ((μm / g) / μm) was calculated as the average value of the smoothed erosion rate slopes. The erosion rate slopes used to calculate the second mean erosion rate slope were those excluding those with an absolute value exceeding 0.10 μm / g from the erosion rate slopes used to calculate the first mean erosion rate slope.

[0334] The measurement results for the first mean erosion rate slope are shown in "S1" of Table 1. The measurement results for the second mean erosion rate slope are shown in "S2" of Table 1.

[0335] Three measurement samples were obtained from each example's optical sheet. For each of the three measurement samples from each example's optical sheet, the first mean erosion rate slope and the second mean erosion rate slope were calculated. The value "S1" listed in Table 1 is the arithmetic mean of the three first mean erosion rate slopes calculated for each example. The value "S2" listed in Table 1 is the arithmetic mean of the three second mean erosion rate slopes calculated for each example.

[0336] <Average Erosion Rate of Functional Layer and Average Erosion Rate of Base Layer> Using the test results of the measurement samples, the average erosion rate of the functional layer and the average erosion rate of the base layer were calculated using the method described above.

[0337] The average erosion rate of the functional layer was defined as the arithmetic mean of the erosion rates measured at measurement positions located within the functional layer measurement area. As shown in Figure 2, the functional layer measurement area R20 was defined as the region between the first position P1 and the second position P2 in the first direction D1. The first position P1 was located 0.50 μm away from the first surface 21 of the functional layer 20 toward the second surface 22 along the first direction D1. The second position P2 was located 0.50 μm away from the second surface 22 of the functional layer 20 toward the first surface 21 along the first direction D1.

[0338] The average erosion rate of the substrate layer is the arithmetic mean of the erosion rates measured at measurement positions located within the substrate layer measurement region R40. As shown in Figure 2, the substrate layer measurement region R40 was defined as the region between the third position P3 and the fourth position P4 in the first direction D1. The third position P3 was located 4.0 μm away from the first surface 41 of the substrate layer 40 towards the second surface 42 along the first direction D1. The fourth position P4 was located 6.0 μm away from the first surface 41 of the substrate layer 40 towards the second surface 42 along the first direction D1.

[0339] The measurement results for the average erosion rate (μm / g) of the substrate layer are shown in "AVR40" of Table 1. The measurement results for the average erosion rate (μm / g) of the functional layer are shown in "AVR20" of Table 1. The value obtained by subtracting the average erosion rate (μm / g) of the functional layer from the average erosion rate (μm / g) of the substrate layer is shown in "Difference" of Table 1.

[0340] Three measurement samples were obtained from each example's optical sheet. For each of the three measurement samples from each example's optical sheet, the average erosion rate of the base layer and the average erosion rate of the functional layer were calculated. The "AVR40" value listed in Table 1 is the arithmetic mean of the average erosion rates of the three base layers calculated for each example. The "AVR20" value listed in Table 1 is the arithmetic mean of the average erosion rates of the three functional layers calculated for each example. The "Difference" listed in Table 1 is the difference between the arithmetic mean of the average erosion rate of the base layer and the arithmetic mean of the average erosion rate of the functional layer.

[0341] <<2-4. Tensile Test>> Measurement samples for tensile testing were cut from the optical sheets relating to the examples and comparative examples. Three measurement samples were prepared from each example. The measurement samples were visually inspected to ensure there were no abnormalities such as dust or scratches. Tensile testing was performed on each measurement sample using a tensile testing machine. The test environment for the tensile testing was set to a temperature of 23°C ± 5°C and a relative humidity of 50% ± 20%. Before starting the tensile testing, the measurement samples were placed in the above test environment for 16 hours.

[0342] The measurement sample was shaped to be 3 mm wide and 100 mm long. The clamping distance (distance between grips) was set to 50 mm to prevent any bending of the measurement sample, and the measurement sample was placed on the tensile testing machine. The tensile speed was set to 10 mm / min. The tensile testing machine used was the Tensilon universal testing machine "STA-1150" manufactured by Orientec Co., Ltd.

[0343] In the tensile test, the test sample was pulled until a crack occurred. The tensile length at the point of cracking was measured. The presence or absence of a crack was visually determined by shining light from an LED onto the test piece. The elongation at the time of cracking was calculated using the following formula: Elongation (%) = (Tensile length (mm) / Distance between grips (mm)) × 100

[0344] The elongation measurements of the measurement samples when cracks occur in the functional layer are shown in "Elongation" in Table 1. Three measurement samples were obtained from each example's optical sheet. The elongation (%) was measured for each of the three measurement samples for each example's optical sheet. The "Elongation" values ​​listed in Table 1 are the arithmetic mean of the three elongation (%) values ​​calculated for each example.

[0345]

[0346] D1: First direction, D2: Second direction, D3: Third direction, R20: Functional layer measurement area, R40: Substrate layer measurement area, RA: Winding axis, 5: Sheet article, 6: Winding core, 7: Winding, 10: Optical sheet, 11: First surface, 11X: Uneven surface, 12: Second surface, 20: Functional layer, 21: First surface, 21X: Uneven surface, 22: Second surface, 26: Base part, 27: Particles, 30: Intermediate layer, 40: Substrate layer, 51: Second functional layer, 52: Third functional layer, 60: Polarizing plate, 61: First protective sheet, 62: Polarization Child, 63: Second protective sheet, 65: Display device, 66: Display element, 66a: Image forming surface, 70: Panel, 71: Article to be bonded, 80: Test device, 82: Nozzle, 82a: Spray outlet, 83: Pressure gauge, 84: Tank, 86: First piping, 86a: Flow meter, 88: Second piping, 88a: Flow meter, 88b: Pressure gauge, 90: Recovery piping, 91: Pumping device, 92: Receiving container, 93: Mounting base, 94: Support, 96: Test liquid, 97: Particles, 98: Air, 99: Measurement sample, 99a: Abrasion piece

Claims

1. An optical sheet comprising a first surface and a second surface, wherein a base layer and a functional layer are provided in order from the second surface toward the first surface, the base layer comprises an acrylic resin, and the functional layer comprises a cured resin, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the slope of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), and the ratio (H / W) of the maximum value of a Gaussian function H (μm / g) / μm) fitted to the test results on a graph with the erosion depth on the horizontal axis and the erosion rate slope on the vertical axis to the full width at half maximum W (μm) of the Gaussian function is 2.0 or less.

2. The optical sheet according to claim 1, wherein the total width at half maximum W is 0.45 μm or more.

3. The optical sheet according to claim 1, wherein the maximum value H is 0.80 μm or less.

4. The first mean erosion rate slope is 0.0050 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, the first mean erosion rate slope is the average value of the erosion rate slope after smoothing, the smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), the first surface and the second surface face each other in the first direction, The optical sheet according to claim 1, wherein the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at measurement positions from a measurement position located 0.50 μm or more away from the first surface in the first direction to four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g.

5. The second mean erosion rate slope is 0.0035 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, the second mean erosion rate slope is the average value of the values ​​obtained by smoothing the erosion rate slope such that the absolute value is 0.10 ((μm / g) / μm) or less, the smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on both sides of the horizontal axis on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), the first surface and the second surface face each other in the first direction, The optical sheet according to claim 1, wherein the erosion rate slope used in calculating the second average erosion rate slope is the erosion rate slope at measurement positions from a measurement position located 0.50 μm or more away from the first surface in the first direction to four measurement positions prior to the measurement position where the erosion rate first exceeds 0.20 μm / g.

6. The optical sheet according to claim 1, wherein the average erosion rate of the functional layer is less than the average erosion rate of the substrate layer, the average erosion rate of the functional layer is the arithmetic mean of the erosion rates measured at measurement positions within the functional layer measurement area, the first surface and the second surface face each other in a first direction, the functional layer measurement area is a region at least 0.50 μm away from both surfaces of the functional layer in the first direction, the average erosion rate of the substrate layer is the arithmetic mean of the erosion rates measured at measurement positions within the substrate layer measurement area, and the substrate layer measurement area is a region at least 4.0 μm and at most 6.0 μm away in the first direction from the surface of the substrate layer facing the first surface.

7. The optical sheet according to claim 6, wherein the difference between the average erosion rate of the substrate layer and the average erosion rate of the functional layer is 0.30 μm / g or more and 0.80 μm / g or less.

8. The optical sheet according to claim 1, wherein the transmitted haze is 0.5 or more and 40 or less.

9. An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a cured resin, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the gradient of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), the first average erosion rate slope is 0.0050 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, and the first average erosion rate slope is the average value of the erosion rate slope after smoothing, The smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis, on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), and the erosion rate slope used to calculate the first average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions before the measurement position where the erosion rate first exceeds 0.20 μm / g, in an optical sheet.

10. An optical sheet comprising a first surface and a second surface facing each other in a first direction, comprising a base layer and a functional layer in the order from the second surface toward the first surface, wherein the base layer comprises an acrylic resin, and the functional layer comprises a cured resin, and with respect to the erosion depth (μm) and erosion rate (μm / g) obtained as test results of an erosion test from the first surface, the gradient of the change in the erosion rate with respect to the change in the erosion depth is defined as the erosion rate slope ((μm / g) / μm), the second average erosion rate slope is 0.0035 ((μm / g) / μm) or more and 0.030 ((μm / g) / μm) or less, and the second average erosion rate slope is the average value of the values ​​obtained by smoothing the erosion rate slope such that the absolute value is 0.10 ((μm / g) / μm) or less. The smoothing process of the erosion rate slope is a Gaussian weight averaging process of a total of five points, including two points located on each side of the horizontal axis, on a graph where the horizontal axis is the erosion depth (μm) and the vertical axis is the erosion rate slope ((μm / g) / μm), and the erosion rate slope used to calculate the second average erosion rate slope is the erosion rate slope at measurement positions from a measurement position 0.50 μm or more away from the first surface in the first direction to four measurement positions before the measurement position where the erosion rate first exceeds 0.20 μm / g, in an optical sheet.

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 an optical sheet as described in any one of claims 1 to 10, and a polarizer superimposed on the optical sheet.

14. A display device comprising an optical sheet as described in any one of claims 1 to 10, and a display element superimposed on the optical sheet.

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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