Optical film, film article, surface light source device, and display device

Abstract

This optical film comprises a first surface and a second surface which are opposed to each other in a first direction. The optical film comprises, in order from the second surface toward the first surface, a base material, an optical functional layer, and a surface layer. The optical functional layer includes light absorption parts and light transmission parts. The light absorption parts and the light transmission parts are alternately arranged along a second direction orthogonal to the first direction. The elastic modulus of the surface layer is 0.31 MPa or less.

Description

Optical film, film article, surface light source device, and display device

[0001] This disclosure relates to optical films, film articles, surface light source devices, and display devices.

[0002] Patent Document 1 discloses a louver film as an optical film. The louver film includes an optical functional layer in which light-absorbing portions and light-transmitting portions are arranged alternately.

[0003] Cracks may occur in the louver film. In particular, when light-absorbing particles are held in the base resin to form a light-absorbing section, the louver film may be prone to cracking depending on the configuration of the light-absorbing section.

[0004] Japanese Patent Publication No. 2017-45060

[0005] This disclosure aims to make optical films less prone to cracking.

[0006] An optical film according to one embodiment of the present disclosure is an optical film having a first surface and a second surface facing each other in a first direction, comprising, in order from the second surface toward the first surface, a substrate, an optical functional layer, and a surface layer, wherein the optical functional layer includes a light absorbing portion and a light transmitting portion, the light absorbing portion and the light transmitting portion are arranged alternately along a second direction perpendicular to the first direction, and the elastic modulus of the surface layer is 0.31 MPa or less.

[0007] [Effects of the Invention] According to this disclosure, cracks are less likely to occur in the optical film.

[0008] Figure 1 is a diagram illustrating one embodiment and is a cross-sectional view showing an example of an optical film. Figure 2A is an enlarged cross-sectional view of the optical film shown in Figure 1. Figure 2B is a partial cross-sectional view showing an example of a part of the cross-section of the light-absorbing portion. Figure 2C is a partial cross-sectional view showing an example of a part of the cross-section of the light-absorbing portion. Figure 3 is a cross-sectional view illustrating a bending resistance test using the cylindrical mandrel method. Figure 4A is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 4B is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 4C is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 4D is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 5A is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 5B is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 5C is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 5D is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 6A is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 6B is a diagram illustrating an example of a method for manufacturing the optical film shown in Figure 1. Figure 7A is a plan view of the optical film shown in Figure 1. Figure 7B is an enlarged view showing a portion of the optical film shown in Figure 7A. Figure 7C is an enlarged view showing another portion of the optical film shown in Figure 7A. Figure 8 is a cross-sectional view showing an example of a display device including the optical film shown in Figure 1. Figure 9 is a diagram illustrating the shape of a mold used in the production of the optical film according to the embodiment, and is an enlarged cross-sectional view of a portion of the mold.

[0009] One embodiment of the present disclosure relates to the following <1> to <14>.

[0010] <1> An optical film having a first surface and a second surface facing each other in a first direction, comprising, in order from the second surface toward the first surface, a substrate, an optical functional layer, and a surface layer, wherein the optical functional layer includes a light absorbing portion and a light transmitting portion, the light absorbing portion and the light transmitting portion are arranged alternately along a second direction perpendicular to the first direction, and the elastic modulus of the surface layer is 0.31 MPa or less.

[0011] <2> The optical film described in <1>, which, after being stored at 25°C for four months, is resistant to bending tests using a cylindrical mandrel with a diameter of 16 mm.

[0012] <3> The optical film according to <1> or <2>, wherein the light-absorbing portion comprises a base resin and light-absorbing particles held in the base resin.

[0013] <4> The average area of ​​the light-absorbing particles appearing in the cross-section of the light-absorbing portion is 4 μm ２ The optical film described in <3> below.

[0014] <5> The optical film according to <3> or <4>, wherein the refractive index of the light-transmitting portion is higher than the refractive index of the base resin, and the light-absorbing portion has a shape that tapers from the first surface to the second surface.

[0015] <6> The surface layer is an optical film according to any one of <1> to <5> that constitutes the first surface including a matte surface.

[0016] <7> The optical film according to any one of <1> to <6>, wherein the light-absorbing portion and the light-transmitting portion extend linearly along a third direction perpendicular to the first direction and the second direction.

[0017] <8> The optical film according to any one of <1> to <7>, wherein the elastic modulus of the surface layer is 0.2 MPa or less.

[0018] <9> An optical film according to any of <1> to <8> that, after being stored at 25°C for 4 months, is resistant to a flexural resistance test using a cylindrical mandrel with a diameter of 10 mm.

[0019] <10> An optical film according to any one of <1> to <9> that, after being stored at 25°C for one day, is resistant to a bending resistance test using a cylindrical mandrel with a diameter of 6 mm.

[0020] <11> A film article comprising multiple optical films as described in any of <1> to <10>.

[0021] <12> The film article described in <11>, which is wound around a winding axis.

[0022] <13> A surface light source device comprising an optical film as described in any of <1> to <10>.

[0023] <14> A display device equipped with the surface light source device described in <13>.

[0024] An embodiment of this disclosure will be described below with reference to the drawings. In the drawings attached to this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual object for the sake of ease of understanding. Some components shown in some drawings may be omitted in other drawings. The scale and aspect ratios may differ between drawings. In cross-sectional views, hatching may be omitted for the sake of ease of understanding.

[0025] In this specification, terms such as "parallel," "orthogonal," and "identical," as well as values ​​of length and angle, which specify shapes, geometric conditions, and their degrees, shall not be limited to their strict meanings, but shall be interpreted to include a range that can be expected to function similarly.

[0026] 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, "optical film" is a concept that includes components that may also be called optical plates or optical sheets, and therefore, "optical film" cannot be distinguished from components called "optical sheets," etc., solely on the basis of differences in name.

[0027] In this specification, the normal direction of a film-like (sheet-like, plate-like) member refers to the direction parallel to the normal or perpendicular to the film surface (sheet surface, plate surface) of the film-like (sheet-like, plate-like) member in question. The "film surface (sheet surface, plate surface)" refers to the surface that coincides with the film-like (sheet-like, plate-like) member in question when viewed as a whole and in a broad sense.

[0028] To clarify the directional relationships between drawings, some drawings use arrows with common symbols to indicate a common first direction D1, second direction D2, and third direction D3. The tip of the arrow represents the first side of each direction. The opposite side of the arrow represents the second side of each direction. Arrows pointing from the drawing plane toward the viewer, along the direction perpendicular to the drawing plane, are indicated by a symbol of a dot inside a circle, as shown in Figure 1, for example.

[0029] 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.

[0030] Figure 1 is a schematic cross-sectional view showing the layer structure of the optical film 10 according to this embodiment. The optical film 10 includes a first surface 10a and a second surface 10b facing a first direction D1. The optical film 10 comprises a base material 11, an optical functional layer 12, and a surface layer 13, in the order from the second surface 10b toward the first surface 10a.

[0031] As shown in the illustrated example, the substrate 11 and the optical functional layer 12 may be in contact with each other. The substrate 11 and the optical functional layer 12 may be in contact with each other and bonded together. The surface layer 13 and the optical functional layer 12 may be in contact with each other. The surface layer 13 and the optical functional layer 12 may be in contact with each other and bonded together. The surface layer 13 covers the optical functional layer 12 from the side opposite to the substrate 11. The surface layer 13 covers the optical functional layer 12 from the first side in the first direction D1. As shown in Figure 1, the surface layer 13 may constitute the first surface 10a. The optical functional layer 12 is located between the substrate 11 and the surface layer 13. In the illustrated example, the first direction D1 is the lamination direction of the substrate 11, the optical functional layer 12, and the surface layer 13. The substrate 11, the optical functional layer 12, and the surface layer 13 are located in this order in the first direction D1 and are adjacent to each other.

[0032] As shown in the specific example in Figure 1, the optical film 10 may further include a second surface layer 14. The second surface layer 14 and the substrate 11 may be in contact with each other. The second surface layer 14 and the substrate 11 may be in contact with each other and bonded together. The second surface layer 14 covers the substrate 11 from the side opposite to the optical functional layer 12. The second surface layer 14 covers the substrate 11 from the second side in the first direction. The substrate 11 is located between the optical functional layer 12 and the second surface layer 14. As shown in Figure 1, the second surface layer 14 constitutes the second surface 10b. In the illustrated example, the first direction D1 is the lamination direction of the second surface layer 14, the substrate 11, the optical functional layer 12, and the surface layer 13. The second surface layer 14, the substrate 11, the optical functional layer 12, and the surface layer 13 are located in this order in the first direction D1 and are adjacent to each other.

[0033] As shown in Figure 1, the optical film 10 may extend in a direction perpendicular to the first direction D1. The illustrated optical film 10 may also extend in the second direction D2 and the third direction D3. In the illustrated example, the first direction D1 is perpendicular to the second direction D2 and also perpendicular to the third direction D3. In the illustrated example, the optical film 10 is spread on a plane. Unlike the illustrated example, the optical film 10 may also extend on a curved surface.

[0034] Hereinafter, each layer included in the optical film 10 according to the present embodiment will be described in detail.

[0035] The base material 11 is composed of resin, glass or the like. The base material 11 may be, for example, a film mainly composed of polycarbonate, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polyolefin, polyacrylate, or polyamide. The term "main component" refers to the component that is contained in the largest amount among the plurality of components constituting a certain substance. The main component may be a component contained in a proportion of 50% or more of the entire substance among the plurality of components constituting the substance.

[0036] The thickness of the base material 11 may be 60 µm or more and 400 µm or less, may be 150 µm or more and 350 µm or less, or may be 200 µm or more and 300 µm or less. The refractive index of the base material 11 is, for example, 1.46 or more and 1.67 or less.

[0037] The optical functional layer 12 includes a light incident surface 121 and a light exit surface 122. The light incident surface 121 and the light exit surface 122 oppose each other in a first direction D1. As shown in FIG. 1, the optical functional layer 12 may be in contact with the base material 11 at the light exit surface 122. The optical functional layer 12 may be in contact with the surface layer 13 at the light incident surface 121. The light incident surface 121 is located between the first surface 10a and the light exit surface 122 in the first direction D1. The light exit surface 122 is located between the light incident surface 121 and the second surface 10b in the first direction D1.

[0038] The optical functional layer 12 includes a light absorbing portion 12a and a light transmitting portion 12b. The optical functional layer 12 functions as a louver layer that controls a viewing angle. As in the specific example shown in FIG. 1, the light absorbing portions 12a and the light transmitting portions 12b are alternately arranged in a second direction D2 orthogonal to the first direction D1. The light absorbing portions 12a and the light transmitting portions 12b may extend linearly along a third direction D3 orthogonal to the first direction D1 and the second direction D2. As another example, the light absorbing portions 12a and the light transmitting portions 12b may be alternately arranged in both the second direction D2 and the third direction D3.

[0039] In a cross-section of the optical functional layer 12 along the first direction D1 and the second direction D2, the area ratio of the light absorbing portions 12a may be 5% or more, 10% or more, or 15% or more. By providing a lower limit to the area ratio of the light absorbing portions 12a, the viewing angle can be narrowed.

[0040] In a cross-section of the optical functional layer 12 along the first direction D1 and the second direction D2, the area ratio of the light absorbing portions 12a may be 50% or less, or 45% or less. By providing an upper limit to the area ratio of the light absorbing portions 12a, image light can be made less likely to become dark.

[0041] The area ratio of the light absorbing portions 12a refers to the ratio of the total area of the light absorbing portions 12a to the sum of the areas of the light absorbing portions 12a and the light transmitting portions 12b measured in a cross-section of the optical functional layer 12 along the first direction D1 and the second direction D2. The area ratio of the light absorbing portions 12a is expressed as a percentage. The unit of the area ratio of the light absorbing portions 12a is %.

[0042] The light absorbing portions 12a may have a shape tapered toward either the first side or the second side in the first direction D1. As shown in FIG. 1, the light absorbing portions 12a may have a shape tapered from the light incident surface 121 toward the light exit surface 122. The light transmitting portions 12b may have a shape tapered from the second surface 10b toward the first surface 10a. The light transmitting portions 12b may have a shape tapered from the light exit surface 122 toward the light incident surface 121. As an example, when cut along a plane perpendicular to the extending direction of the light absorbing portions 12a, the cross-section of the light absorbing portions 12a exhibits a trapezoidal shape whose width narrows from the light incident surface 121 toward the light exit surface 122. The trapezoidal shape may be line-symmetric with respect to an axis of symmetry parallel to the first direction D1. However, the cross-sectional shapes of the light absorbing portions 12a and the light transmitting portions 12b can adopt various shapes according to required functions, and are not particularly limited. The cross-sectional shapes of the light absorbing portions 12a and the light transmitting portions 12b may be rectangular.

[0043] The light absorbing portions 12a may be exposed to the outside of the optical functional layer 12 on the light incident surface 121 side, and may form a part of the light incident surface 121. In other words, the light absorbing portions 12a may be exposed toward the surface layer 13 on the light incident surface 121 side of the optical functional layer 12, and may form a part of the light incident surface 121.

[0044] In the example shown in Figure 2A, the light-absorbing portion 12a includes a base resin 12d and light-absorbing particles 12e. The base resin 12d is the binder resin of the light-absorbing portion 12a. The light-absorbing particles 12e are held in place by the base resin 12d. As the light-absorbing particles 12e, for example, acrylic beads containing carbon black can be used. The structure of the light-absorbing portion 12a is not limited to the example shown in Figure 2A. The light-absorbing portion 12a may also be made by impregnating the binder resin with a black filler.

[0045] The morphology of the light-absorbing portion 12a when the light-absorbing portion 12a includes a base resin 12d and light-absorbing particles 12e will be further described. Figure 2B is a partial cross-sectional view showing a part of the cross-section of the light-absorbing portion 12a including the base resin 12d and light-absorbing particles 12e. Figure 2B corresponds to a part of the cross-section obtained by cutting the light-absorbing portion 12a in a plane perpendicular to the direction in which the light-absorbing portion 12a extends.

[0046] The average area of ​​the light-absorbing particles 12e appearing in the cross-section of the light-absorbing portion 12a, as shown in Figure 2B, is 4 μm². ２ The following is preferable. The average area of ​​the light-absorbing particles 12e appearing in the cross-section of the light-absorbing portion 12a is measured using the image processing software ImageJ (version 1.54g) by the following method.

[0047] First, the optical film 10 containing the light-absorbing portion 12a to be measured is cut to reveal the cross-section of the light-absorbing portion 12a as shown in Figure 2B. Next, the cross-section of the light-absorbing portion 12a is photographed using a microscope at a magnification of 1000x.

[0048] Next, we will perform image calibration. Calibration involves setting a calibration value that represents the image scale. For this setting, we can use the scale display that is applied to the image when acquiring the image using a microscope. Specifically, we will use the ImageJ Straight command to draw a straight line along the scale display in the image. Then, we will select Set Scale from the Analyze menu in the ImageJ menu bar to set the calibration value.

[0049] Next, the captured image of the cross-section of the light-absorbing part 12a is converted to 8-bit (256-level grayscale) using ImageJ. Then, the image is binarized. Specifically, the image is converted to a binary image by selecting Threshold in Adjust from Image in the Image menu bar. More specifically, the brightness values ​​in the range of 0 to 100 in the 256-level grayscale image are converted to 255, and the brightness values ​​in the other range are converted to 0. Then, morphological processing of Fill Holes and Watershed is performed by selecting Binary from Process in the ImageJ menu bar. Binarization and morphological processing result in an image in which multiple white areas are placed in the black areas. The white areas can be considered to be the parts corresponding to the light-absorbing part 12a that appeared in the cross-section.

[0050] Next, using ImageJ's functions, the area of ​​each of the multiple white areas is calculated, and among the multiple white areas, the area of ​​1 μm ２ The average area of ​​the portion that exceeds 1 μm is calculated. Specifically, this calculation is performed by the following method: Select Area in Set Measurement from Analyze in the ImageJ menu bar, and calculate the average area by setting Size to 1-Infinity and Circularity to 0-1 in Analyze Particles in the Analyze menu bar of ImageJ. The calculated average is adopted as the average area of ​​the light-absorbing particles 12e that appear in the cross-section of the light-absorbing portion 12a. Among the multiple black portions, the area of ​​1 μm ２ Parts less than 1 μm are considered noise and are excluded when calculating the average area of ​​the light-absorbing particles 12e. ２ When excluding portions that are less than a certain value, the calibration value set during image calibration can be used.

[0051] The average area of ​​the light-absorbing particles 12e is 4 μm ２The effects of the following will be explained. Figure 2C is a diagram showing an example of a cross-section of a light-absorbing section 12a where the average area of ​​the light-absorbing particles 12e is larger than that of Figure 2B. As can be seen from the comparison between Figure 2B and Figure 2C, in a light-absorbing section 12a where the average area of ​​the light-absorbing particles 12e is smaller, as in Figure 2B, the gaps between the light-absorbing particles 12e tend to be smaller as well. In particular, when the total mass of the light-absorbing particles 12e used in the light-absorbing section 12a is equal, the gaps between the light-absorbing particles 12e tend to be smaller in a light-absorbing section 12a where the average area of ​​the light-absorbing particles 12e is smaller. In particular, in the manufacturing method of the optical film 10 described later, by stirring the material of the light-absorbing section material layer 12aR so that the distribution of light-absorbing particles 12e in the light-absorbing section material layer 12aR becomes uniform, the gaps between the light-absorbing particles 12e become uniform and small. If the gaps between the light-absorbing particles 12e are small, the light-absorbing effect of the light-absorbing section 12a can be increased. The inventors of this case have set the average area of ​​the light-absorbing particle 12e to 4 μm². ２ We found that by doing the following, the gaps between the light-absorbing particles 12e can be stably reduced, and the light-absorbing effect of the light-absorbing section 12a can be sufficiently increased. Therefore, the average area of ​​the light-absorbing particles 12e is 4 μm ２ The following conditions allow the light-absorbing effect of the light-absorbing section 12a to be sufficiently large.

[0052] The material constituting the base resin 12d in the light-absorbing section 12a is not particularly limited. The base resin 12d may include a cured resin product. The cured resin product is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may also be a cured product of an ionizing radiation-curable resin composition. The ionizing radiation-curable resin composition may be an ultraviolet-curable resin composition or an electron beam-curable resin composition. The base resin 12d may include a solvent-drying resin. A solvent-drying resin is a resin that forms a film simply by drying the solvent added to adjust the solid content during coating. The base resin 12d may include a mixture of a cured resin product and a solvent-drying resin.

[0053] The refractive index of the base resin 12d in the light-absorbing section 12a may be between 1.47 and 1.65, or between 1.49 and 1.57. By setting the refractive index of the base resin 12d within this range, the refractive index difference between the base resin 12d and the light-transmitting section 12b can be reduced, making it less likely for interfacial reflection to occur at the interface between the light-absorbing section 12a and the light-transmitting section 12b. By making interfacial reflection between the light-absorbing section 12a and the light-transmitting section 12b less likely, light incident on the light-absorbing section 12a can be absorbed efficiently. By setting an upper limit on the refractive index of the base resin 12d in the light-absorbing section 12a, the material of the base resin 12d can be made more resistant to cracking. The refractive index of the base resin 12d in the light-absorbing section 12a may be equal to the refractive index of the light-transmitting section 12b.

[0054] The tensile modulus of the light-absorbing portion 12a may be 200 MPa or less, 190 MPa or less, or 180 MPa or less. By setting an upper limit on the tensile modulus of the light-absorbing portion 12a, the optical film 10 has sufficient flexibility and is less prone to cracking. No lower limit is set for the tensile modulus of the light-absorbing portion 12a. The tensile modulus of the light-absorbing portion 12a may be 1 MPa or more.

[0055] The elongation at break of the light-absorbing portion 12a may be 15% or more, 20% or more, or 25% or more. By setting a lower limit for the elongation at break of the light-absorbing portion 12a, the optical film 10 has sufficient flexibility and is less prone to cracking. There is no particular upper limit set for the elongation at break of the light-absorbing portion 12a. The elongation at break of the light-absorbing portion 12a may be 100% or less.

[0056] The tensile modulus and elongation at break (tensile fracture strain, nominal tensile fracture strain) of the light-absorbing portion 12a are measured using a test method in accordance with JIS K 7127:1999. Details of the measurement method for the tensile modulus and elongation at break of the light-absorbing portion 12a are described below.

[0057] The tensile modulus and elongation at break of the light-absorbing portion 12a will be tested using a Type 2 sample according to JIS K 7127:1999. The sample will be prepared as follows: A resin composition containing light-absorbing particles 12e in an uncured curable resin composition used to form the base resin 12d will be sandwiched between PET films and cured in a laminated state. The laminated resin piece will be cut into 10 mm x 70 mm pieces to prepare the sample. The thickness of the sample will be 30 μm.

[0058] After preparing the sample, clamp both ends of the short side of the sample. The distance between the clamps should be 50 mm. Pull the sample at a test speed of 10 mm / min until it breaks. The modulus of elasticity obtained when the sample is pulled is defined as the tensile modulus. The elongation at which the sample breaks is defined as the elongation at break. The arithmetic mean of the tensile modulus and elongation at break for five samples is adopted as the measured values ​​for the tensile modulus and elongation at break.

[0059] The test environment will be set to a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The samples to be evaluated will be placed in the test environment for 16 hours before the start of the test.

[0060] The light-transmitting portion 12b may contain a material different from the material contained in the light-absorbing portion 12a. The light-transmitting portion 12b may contain the same material as the material contained in the light-absorbing portion 12a. The material constituting the light-transmitting portion 12b is not particularly limited. The light-transmitting portion 12b may contain a cured resin. The cured resin 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 a cured product of an ionizing radiation curable resin composition. The ionizing radiation curable resin composition may be an ultraviolet curable resin composition or an electron beam curable resin composition. The light-transmitting portion 12b may contain a solvent-drying resin. A solvent-drying resin is a resin that forms a film simply by drying the solvent added to adjust the solid content during coating. The light-transmitting portion 12b may be a mixture of the cured resin and the solvent-drying resin.

[0061] The refractive index of the light-transmitting portion 12b may be between 1.47 and 1.65, or between 1.49 and 1.57. By setting the refractive index of the light-transmitting portion 12b within this range, the refractive index difference between the base resin 12d and the light-transmitting portion 12b can be reduced, making it less likely for interfacial reflection to occur at the interface between the light-absorbing portion 12a and the light-transmitting portion 12b. By making interfacial reflection between the light-absorbing portion 12a and the light-transmitting portion 12b less likely, light incident on the light-absorbing portion 12a can be absorbed efficiently. By setting an upper limit on the refractive index of the light-transmitting portion 12b, the material of the light-transmitting portion 12b can be made more resistant to cracking.

[0062] The refractive index of the light-transmitting portion 12b may be higher than or the same as the refractive index of the base resin 12d of the light-absorbing portion 12a. If the refractive index of the light-transmitting portion 12b is higher than the refractive index of the base resin 12d of the light-absorbing portion 12a, it becomes possible to use optical design that utilizes total internal reflection of light traveling from the light-transmitting portion 12b to the light-absorbing portion 12a, thereby increasing the efficiency of light utilization, for example. Also, if the refractive index of the light-transmitting portion 12b is the same as the refractive index of the base resin 12d of the light-absorbing portion 12a, total internal reflection and refraction of light do not occur, so even if the distance from the surface of the display device to the optical film 10 is large, for example, it becomes possible to prevent the occurrence of a double image of transmitted light and total internal reflection or refracted light.

[0063] The pitch of the arrangement of the light-absorbing portion 12a and the light-transmitting portion 12b in the optical functional layer 12 is not particularly limited, but from the viewpoint of effectively exhibiting the function of the louver film, it may be 30 μm or more and 100 μm or less.

[0064] In the example shown in Figure 2A, the light-absorbing portion 12a and the light-transmitting portion 12b are located in the same region in the first direction D1. The height D (thickness) of the light-absorbing portion 12a and the light-transmitting portion 12b, that is, the length of the light-absorbing portion 12a and the light-transmitting portion 12b along the first direction D1, are the same. The height D (thickness) of the light-absorbing portion 12a and the light-transmitting portion 12b, that is, the length of the light-absorbing portion 12a along the first direction D1, may be 60 μm or more and 150 μm or less.

[0065] The optical functional layer 12 may include a light-absorbing portion 12a and a light-transmitting portion 12b, as well as a land portion 12c facing the first direction D1. The land portion 12c is in the form of a film. The land portion 12c may support a plurality of light-absorbing portions 12a and a plurality of light-transmitting portions 12b. The land portion 12c may be integrally molded with the light-transmitting portion 12b. The land portion 12c may be connected to the light-transmitting portion 12b without a joint. The thickness of the land portion 12c may be 10 μm or more and 50 μm or less.

[0066] The surface layer 13 covers the optical functional layer 12 from the light-receiving surface 121 side. The surface layer 13 protects the optical functional layer 12.

[0067] The elastic modulus of the surface layer 13 is 0.31 MPa or less. The elastic modulus of the surface layer 13 may be 0.2 MPa or less. The elastic modulus of the surface layer 13 is measured by the following method. First, a measuring sheet containing the surface layer 13 is prepared. At least one side of the measuring sheet is composed of the surface layer 13. In the optical film 10 shown in Figure 1, the surface layer 13 constitutes the first surface 10a. In this case, the optical film 10 can be used as a measuring sheet. In the measuring sheet, the influence of elements other than the surface layer 13 included in the measuring sheet on the measurement of the elastic modulus of the surface layer 13 is sufficiently suppressed. When measuring the elastic modulus of the surface layer 13 by nanoindentation using a microhardness tester described later, if the depth to which the indenter used by the microhardness tester is pressed into the measuring sheet does not exceed the thickness of the surface layer 13, it can be considered that the influence of elements other than the surface layer 13 included in the measuring sheet is sufficiently suppressed.

[0068] Next, the side of the measuring sheet opposite to the side formed by the surface layer 13 is adhered to the slide glass. Then, the measuring sheet and slide glass are placed on the measuring stage with the side formed by the surface layer 13 of the measuring sheet facing upwards. Next, the measuring sheet and slide glass are fixed to the measuring stage using adhesive tape.

[0069] The elastic modulus of the surface layer 13 of the measurement sheet, fixed to the measurement stage by the method described above, is measured by the nanoindentation method using a microhardness tester (product name "PICODETOR HM500", manufactured by Fischer Instruments). For measurement using the nanoindentation method, the PICO012 (Vickers) indenter (manufactured by Helmut Fischer) was used. During measurement, the load was applied, held, and unloaded in the following order: load control (maximum indentation load 1 mN), load application time 10 seconds, holding time 5 seconds at the maximum indentation load, and load removal time 10 seconds. The atmosphere during elastic modulus measurement was adjusted to a temperature of 23°C ± 5°C and a relative humidity of 40% to 65%.

[0070] In addition to the elastic modulus of the surface layer 13, the Martens hardness, creep, elastic deformation work rate, and indentation hardness on the surface of the surface layer 13 may be measured using the nanoindentation method with the microhardness tester described above. The Martens hardness on the surface of the surface layer 13 measured in this way is, for example, 10.0 MPa or less. The creep on the surface of the surface layer 13 is, for example, 10.0% or less. The elastic deformation work rate on the surface of the surface layer 13 is, for example, 50.0% or less. The indentation hardness on the surface of the surface layer 13 is, for example, 11.0 MPa or less.

[0071] The thickness of the surface layer 13 may be between 5 μm and 50 μm. The refractive index of the surface layer 13 may be between 1.47 and 1.65.

[0072] The material of the surface layer 13 is not particularly limited. The surface layer 13 may contain a cured resin product. The cured resin product is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may also be a cured product of an ionizing radiation curable resin composition. The ionizing radiation curable resin composition may be an ultraviolet curable resin composition or an electron beam curable resin composition. The surface layer 13 may contain a solvent-drying resin. A solvent-drying resin is a resin that forms a film simply by drying the solvent added to adjust the solid content during coating. The surface layer 13 may contain a mixture of the cured resin product and the solvent-drying resin.

[0073] When the optical film 10 is incorporated into the surface light source device 70, it is assumed that the first surface 10a may come into surface contact with other optical components. If the optical film 10 comes into surface contact with other optical components on the first surface 10a, appearance defects such as interference fringes may occur. From the viewpoint of minimizing appearance defects, the first surface 10a may include a matte surface. A matte surface is a rough surface.

[0074] In the illustrated example, the surface layer 13 constitutes the first surface 10a of the optical film 10. The surface layer 13 may include the first surface 10a. The surface layer 13 may constitute the first surface 10a including a matte surface. That is, the surface layer 13 may be formed as a matte layer.

[0075] The second surface layer 14 is provided to protect the substrate 11. The thickness of the second surface layer 14 may be 5 μm or more and 50 μm or less. The refractive index of the second surface layer 14 may be 1.47 or more and 1.65 or less.

[0076] The material of the second surface layer 14 is not particularly limited. The second surface layer 14 may contain a cured resin product. The cured resin product is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may also be a cured product of an ionizing radiation curable resin composition. The ionizing radiation curable resin composition may be an ultraviolet curable resin composition or an electron beam curable resin composition. The second surface layer 14 may contain a solvent-drying resin. A solvent-drying resin is a resin that forms a film simply by drying the solvent added to adjust the solid content during coating. The second surface layer 14 may contain a mixture of the cured resin product and the solvent-drying resin.

[0077] The second surface layer 14 may contain the same material as the surface layer 13. In this example, the difference between the coefficient of thermal expansion of the second surface layer 14 and the surface layer 13 can be reduced. By reducing the difference between the coefficient of thermal expansion of the second surface layer 14 and the surface layer 13, defects such as curling can be made less likely to occur in the optical film 10. Manufacturing costs can also be kept low by manufacturing the surface layer 13 and the second surface layer 14 from the same material. The second surface layer 14 may contain a different material than the material contained in the surface layer 13. The second surface layer 14 may have the same physical properties as the surface layer 13.

[0078] Next, the flexibility of the optical film 10 will be described. The optical film 10 according to this embodiment is provided with the flexibility described below.

[0079] The optical film 10 may withstand a flexural resistance test using a cylindrical mandrel with a diameter of 16 mm after being stored at 25°C for four months. The inventors confirmed that the optical film 10 manufactured by the manufacturing method described later gradually decreased in flexural resistance from immediately after manufacture until a certain period of time had elapsed. The flexural resistance of the optical film 10 after being stored at 25°C for four months is the flexural resistance evaluated after four months have elapsed in a 25°C environment from immediately after manufacture, and is generally the lowest flexural resistance among those evaluated. The inventors confirmed that the optical film 10 that withstands a flexural resistance test using a cylindrical mandrel with a diameter of 16 mm after being stored at 25°C for four months makes it less likely for the optical film 10 to crack when cut from the film article (long optical film) 100 described later. From the results of this flexural resistance test, it can be understood that the optical film 10 according to this embodiment is less prone to a decrease in flexural resistance over time.

[0080] The flexural resistance test using the cylindrical mandrel method is performed as follows:

[0081] A sample measuring 100 mm x 50 mm is cut from the optical film to be evaluated. The pair of sides of the sample that are 50 mm long are parallel to the third direction D3 of the optical film 10.

[0082] A 180° bending test will be performed using a Type 1 test apparatus as specified in "6.2.1." of JIS K 5600-1:1999. As shown in Figure 3, the sample will be mounted on the test apparatus so that the second surface 10b is in contact with the mandrel 300. The bending of the sample using the test apparatus will be performed over 2 seconds. The mandrel 300 will be made of stainless steel with a diameter of 16 mm.

[0083] After bending is complete, check the sample surface for defects such as scratches or cracks without removing the sample from the test apparatus. Observe the sample surface under indoor lighting. The observation distance should be approximately 30 cm. The illuminance on the sample surface should be between 800 Lx and 1200 Lx. Check for defects visually or using a 10x magnifying glass.

[0084] Three samples are cut from the optical film to be evaluated. If no defects are found in two or more samples, the film is evaluated as having resistance to the bending resistance test.

[0085] The test environment will be set to a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Samples cut from the optical film to be evaluated will be placed in the test environment for 16 hours before the start of the test.

[0086] Other conditions for conducting the flexural resistance test using a 16 mm diameter cylindrical mandrel shall conform to JIS K 5600-5-1:1999.

[0087] JIS K 5600-5-1:1999 specifies that the diameter of the mandrel 300 should be reduced until a defect occurs, and the smallest mandrel diameter that is deemed to withstand the bending resistance test should be identified. Diameters of mandrel 300 smaller than the 16 mm diameter specified in JIS K 5600-5-1:1999 are specified as 12 mm, 10 mm, 8 mm, 6 mm, 5 mm, 4 mm, 3 mm, and 2 mm. The optical film 10 may withstand a bending resistance test using a cylindrical mandrel with a diameter of 12 mm after being stored at 25°C for 4 months, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 10 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 8 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 6 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 5 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 4 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 3 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 2 mm.

[0088] The optical film 10 may withstand a bending resistance test using a cylindrical mandrel with a diameter of 16 mm after being stored at 25°C for one day, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 12 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 10 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 8 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 6 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 5 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 4 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 3 mm, or it may withstand a bending resistance test using a cylindrical mandrel with a diameter of 2 mm. The inventors confirmed that, with an optical film 10 that withstands a bending resistance test using a 16 mm diameter cylindrical mandrel after being stored at 25°C for one day, cracking of the optical film 10 is less likely to occur when cutting it from a long optical film (film article) 100, as described later.

[0089] Next, the method for manufacturing the optical film 10 will be described with reference to Figures 4A to 4D, 5A to 5D, 6A, and 6B.

[0090] In the example described here, a film article (a long optical film) 100 (see Figure 6A) containing a base material 11 and an optical functional layer 12 is first manufactured. The film article 100 includes a plurality of optical films 10 before cutting. The optical films 10 are obtained by cutting them from the film article 100. As shown in Figure 6A, the film article 100 may be wound around a winding axis.

[0091] First, as shown in Figure 4A, a light-transmitting material layer 12bR is provided on the substrate 11. The light-transmitting material layer 12bR is a coating film of, for example, a curable resin composition before curing. The light-transmitting material layer 12bR is obtained by continuously coating the curable resin composition onto the substrate 11, which is being conveyed by a roll (not shown). In this example, a second surface layer 14 is already provided on the substrate 11, but the timing of the formation of the second surface layer 14 is not particularly limited.

[0092] Next, as shown in Figure 4B, voids 15 for filling the light-absorbing portion 12a are formed in the light-transmitting portion material layer 12bR using a mold. Specifically, in the light-transmitting portion material layer 12bR having a pair of main surfaces, a plurality of voids 15 are formed in a second direction D2 parallel to each of the main surfaces, indenting from one main surface toward the other. The voids 15 may be formed using a roll mold. Then, as the light-transmitting portion material layer 12bR hardens, the light-transmitting portion 12b is formed between adjacent voids 15.

[0093] Next, as shown in Figure 4C, a light-absorbing material layer 12aR is provided so as to cover the multiple light-transmitting portions 12b and the void 15. Here, the light-absorbing material layer 12aR is filled into the void 15. The light-absorbing material layer 12aR is formed from a material that includes, for example, a curable resin composition before curing as a base resin 12d, and also contains light-absorbing particles 12e.

[0094] Next, as shown in Figure 4D, the light-absorbing material layer 12aR is scraped off by the squeegee 120 so that the light-absorbing material layer 12aR fills the void 15 and any excess light-absorbing material layer 12aR is removed. Then, as the light-absorbing material layer 12aR hardens, the light-absorbing portion 12a is formed as shown in Figure 5A. Thus, the optical functional layer 12 is formed.

[0095] Next, as shown in Figure 5B, a surface layer material layer 13R is provided so as to cover the light-transmitting portion 12b and the light-absorbing portion 12a. Then, the surface layer material layer 13R is cured. At this point, the surface layer material layer 13R is in a semi-cured state, not completely cured.

[0096] Next, as shown in Figure 5C, a laminate consisting of a base material 11, a second surface layer 14, an optical functional layer 12, and a surface layer material layer 13R is passed between a pair of embossing rollers 140, 140. Here, the surface of one of the pair of embossing rollers 140, 140 is matte with fine irregularities, and this surface comes into contact with the surface layer 13 to give the surface layer 13 a matte finish, in other words, a textured or embossed finish. As a result, as shown in Figure 5D, fine irregularities are formed on the surface of the surface layer material layer 13R, and the surface layer 13 is formed. By completely curing the surface layer 13, a film article 100 is manufactured. The longitudinal direction of the manufactured film article 100 may be parallel to the third direction D3, or it may be inclined with respect to the third direction D3.

[0097] The manufactured film article 100 is wound around the winding axis A to form a winding body 101. Then, as shown in Figure 6A, the film article 100 is unwound to cut out a rectangular optical film 10. For example, from the unwound film article 100, a rectangular optical film 10 is cut out by a die 200 (see Figure 6B) along the dashed line in the figure. The directions parallel to the four sides of the rectangular optical film 10 may be different from the second direction D2 and the third direction D3.

[0098] The length of the short side of the cut rectangular optical film 10 may be 30 mm or more, 50 mm or more, 80 mm or more, or 100 mm or more. The length of the short side of the cut rectangular optical film 10 may be 400 mm or less, 300 mm or less, 200 mm or less, or 150 mm or less. The length of the long side of the cut rectangular optical film 10 may be 100 mm or more, 150 mm or more, 200 mm or more, or 250 mm or more. The length of the long side of the cut rectangular optical film 10 may be 600 mm or less, 500 mm or less, 400 mm or less, or 350 mm or less.

[0099] As shown in Figure 6B, the die 200 cuts out the optical film 10 from the first surface 10a toward the second surface 10b.

[0100] The shape of the optical film 10 is not limited to a rectangular shape. For example, as shown in Figure 7A, the optical film 10 may have tab portions 16A and 16B that are divided into very small sections relative to the overall shape. Figure 7B shows a magnified view of tab portion 16A. Figure 7C shows a magnified view of tab portion 16B.

[0101] Incidentally, cracks can occur in optical films. In particular, cracks can occur in optical films when cutting the optical film 10 from the film article 100 using a die or the like. Also, if the optical film has tabs, stress concentrates in the tabs, making them prone to cracking.

[0102] Cracking is particularly likely to occur in the tab portions 16A and 16B shown in Figures 7B and 7C. In the example shown in Figure 7B, where the light-transmitting portion and the light-absorbing portion extend in the third direction, cracking is likely to occur at the position indicated by the dotted line in Figure 7B. In the example shown in Figure 7C, where the light-transmitting portion and the light-absorbing portion extend in the third direction, cracking is likely to occur at the position indicated by the dotted line in Figure 7C.

[0103] To address these issues, the optical film 10 according to this embodiment withstands a flexural resistance test using a cylindrical mandrel with a diameter of 16 mm after being stored at 25°C for four months. The optical film 10 gradually hardens from the time of manufacture and stabilizes after four months. The inventors confirmed that the optical film 10, which has sufficient flexural resistance even after being stored at 25°C for four months, makes it less likely for cracks to occur when cutting the film article 100 with the die 200.

[0104] The bending resistance test using the cylindrical mandrel method can be easily performed. By performing the bending resistance test, the ease with which the optical film 10 breaks can be easily evaluated. By evaluating the bending resistance in advance using the bending resistance test, it is possible to accurately determine whether or not there are cracks in the cut optical film 10.

[0105] An example of how to use the optical film 10 will be explained with reference to Figure 8. Figure 8 is a schematic diagram showing a display device 1 including the optical film 10. The display device 1 shown in Figure 8 includes a surface light source device 70. The display device 1 includes the surface light source device 70, a liquid crystal panel 50, and a visibility adjustment sheet 60 in that order. The surface light source device 70 shown in Figure 8 includes the optical film 10. The surface light source device 70 includes a light source 20, a prism sheet 30, a reflective polarization separation sheet 40, and the optical film 10 in that order. In this example, the surface layer 13 may come into contact with the reflective polarization separation sheet 40, but if the surface layer 13 is a matte surface, close contact with the reflective polarization separation sheet 40 is avoided.

[0106] The optical film 10 according to the embodiment described above is an optical film having a first surface 10a and a second surface 10b facing a first direction D1, and comprising a substrate 11, an optical functional layer 12, and a surface layer 13 in the order from the second surface 10b toward the first surface. The optical functional layer 12 has a light absorbing portion 12a and a light transmitting portion 12b. The light absorbing portion 12a and the light transmitting portion 12b are arranged alternately along a second direction D2 perpendicular to the first direction D1.

[0107] In particular, the inventors of this invention found that in the optical film 10 described above, cracks tend to occur in the portion of the surface layer 13 that overlaps with the light-absorbing portion 12a when observed from the first direction D1. In particular, they found that when the light-absorbing particles 12e are held in the base resin 12d to form the light-absorbing portion 12a, cracks tend to occur in the optical film 10 depending on the configuration of the light-absorbing portion 12a. In addition, the inventors of this invention found that cracks are less likely to occur in the optical film 10 by setting the elastic modulus of the surface layer 13 to 0.31 MPa or less. The inventors of this invention found that cracks are less likely to occur in the optical film 10 in particular by setting the elastic modulus of the surface layer 13 to 0.2 MPa or less. In particular, they found that cracks are less likely to occur in the optical film 10 when it is subjected to stress. In particular, they found that cracks are less likely to occur in the optical film 10 when it is cut from the film article 100. Furthermore, assuming that the optical film 10 will be used in automotive components and the like, it was found that even when the optical film 10 is subjected to rigorous vibration testing, cracks are less likely to occur in the optical film 10. Based on the above, the inventors of this invention have completed the invention of the optical film 10 according to this embodiment.

[0108] In the optical film 10, the following reasons are considered to be the reason why cracks are likely to occur in the portion of the surface layer 13 that overlaps with the light-absorbing portion 12a when observed from a first direction D1. The region of the optical functional layer 12 where the light-absorbing portion 12a is located and the region where only the light-transmitting portion 12b is located, when observed from a first direction D1, are thought to have different physical properties such as hardness. Due to this difference in physical properties, the portion of the surface layer 13 that overlaps with the light-absorbing portion 12a may have less adhesion to the optical functional layer 12 than the portion of the surface layer 13 that does not overlap with the light-absorbing portion 12a. In this case, the surface layer 13 may peel off from the optical functional layer 12 in the portion that overlaps with the light-absorbing portion 12a, and cracks may occur in the optical film 10 starting from the peeled portion. For the above reasons, it is considered that cracks are likely to occur in the portion of the surface layer 13 that overlaps with the light-absorbing portion 12a when observed from a first direction D1.

[0109] In particular, when the light absorbing particles 12e are held in the base resin 12d to form the light absorbing portion 12a, there may be cases where it is required to reduce the average area of the light absorbing particles 12e appearing in the cross-section of the light absorbing portion 12a. For example, as described above, there may be cases where it is required to reduce the average area of the light absorbing particles 12e appearing in the cross-section of the light absorbing portion 12a for the purpose of increasing the light absorbing effect of the light absorbing portion 12a. In particular, the average area of the light absorbing particles 12e is set to 4 μm ２ or less in some cases. In this case, due to the increased light absorbing effect of the light absorbing portion 12a, the difference in physical properties between the region where the light absorbing portion 12a is located and the region where the light absorbing portion 12a is not located in the optical functional layer 12 when observed from the first direction D1 tends to become larger. In this case, it is considered that the portion of the surface layer 13 overlapping with the light absorbing portion 12a becomes particularly difficult to maintain adhesion to the optical functional layer 12.

[0110] As an example, consider the case where the base resin 12d is an ultraviolet-curable resin composition. In this case, by irradiating the light absorbing portion material layer 12aR containing the base resin 12d and the light absorbing particles 12e with ultraviolet rays, the light absorbing portion material layer 12aR can be cured to form the light absorbing portion 12a. In this case, if the average area of the light absorbing particles 12e appearing in the cross-section of the light absorbing portion 12a is reduced to increase the light absorbing effect of the light absorbing portion 12a, it becomes difficult for ultraviolet rays to reach the base resin 12d, and the base resin 12d becomes difficult to cure. Therefore, when reducing the average area of the light absorbing particles 12e, it may be necessary to add a large amount of initiator to the base resin 12d in order to sufficiently cure the base resin 12d. When a large amount of initiator is added to the base resin 12d, the formed light absorbing portion 12a becomes particularly hard, and it may become difficult to maintain the adhesion of the portion of the surface layer 13 overlapping with the light absorbing portion 12a to the optical functional layer 12.

[0111] In particular, in the examples shown in Figures 1 and 2A, the optical functional layer 12 is in contact with the surface layer 13 on the light-receiving surface 121. The light-absorbing portion 12a constitutes a part of the light-receiving surface 121. As a result, the light-absorbing portion 12a and the surface layer 13 are in contact. When the light-absorbing portion 12a and the surface layer 13 are in contact, the decrease in adhesion between the portion of the surface layer 13 that overlaps with the light-absorbing portion 12a and the optical functional layer 12 tends to become more pronounced.

[0112] The following reasons can be considered for why cracking of the optical film 10 is less likely to occur by setting the elastic modulus of the surface layer 13 to 0.31 MPa or less. It is thought that by setting the elastic modulus of the surface layer 13 to 0.31 MPa or less, the surface layer 13 does not resist the deformation of the optical functional layer 12, but instead follows it smoothly. Therefore, even in the portion of the surface layer 13 that overlaps with the light-absorbing portion 12a, where adhesion to the optical functional layer 12 is difficult to maintain, it is possible to maintain adhesion between the surface layer 13 and the optical functional layer 12, making cracking of the optical film 10 less likely. In particular, by setting the elastic modulus of the surface layer 13 to 0.31 MPa or less, even when the light-absorbing particles 12e are held in the base resin 12d to form the light-absorbing portion 12a, it is possible to maintain adhesion between the surface layer 13 and the optical functional layer 12, making cracking of the optical film 10 less likely. Specifically, by setting the elastic modulus of the surface layer 13 to 0.31 MPa or less, the average area of ​​the light-absorbing particles 12e is 4 μm ２ Even in the following cases, the adhesion of the surface layer 13 to the optical functional layer 12 can be maintained, making it less likely for cracks to occur in the optical film 10. For the same reason, by setting the elastic modulus of the surface layer 13 to 0.2 MPa or less, cracks are particularly less likely to occur in the optical film 10.

[0113] If the elastic modulus of the surface layer 13 is 0.31 MPa or less, as described above, the surface layer 13 is thought to be able to smoothly follow the deformation of the optical functional layer 12 without resisting it. For this reason, cracking in the portion of the surface layer 13 that does not overlap with the light-absorbing portion 12a is less likely to occur. For the same reason, if the elastic modulus of the surface layer 13 is 0.2 MPa or less, cracking in the portion of the surface layer 13 that does not overlap with the light-absorbing portion 12a is particularly less likely to occur. Furthermore, if the elastic modulus of the surface layer 13 is 0.31 MPa or less, the adhesion of the surface layer 13 to the optical functional layer 12 is stably maintained, and the optical functional layer 12 can be stably protected by the surface layer 13. For this reason, if the elastic modulus of the surface layer 13 is 0.31 MPa or less, cracking in the optical functional layer 12 is also less likely to occur due to the surface layer 13. For example, it is conceivable that cracking may occur at the interface between the light-absorbing portion 12a and the light-transmitting portion 12b of the optical functional layer 12. If the elastic modulus of the surface layer 13 is 0.31 MPa or less, the surface layer 13 can make it less likely for cracks to occur at the interface between the light-absorbing portion 12a and the light-transmitting portion 12b of the optical functional layer 12. For the same reason, if the elastic modulus of the surface layer 13 is 0.2 MPa or less, the surface layer 13 can make it particularly less likely for cracks to occur in the optical functional layer 12.

[0114] In particular, according to this embodiment, when cutting the optical film 10 from a film article (long optical film), cracking of the optical film 10 is less likely to occur. Furthermore, even when the optical film 10 is subjected to rigorous vibration testing, assuming its use in automotive components or the like, cracking of the optical film 10 is less likely to occur.

[0115] In one specific example of this embodiment, the optical film 10 withstands a flexural resistance test using a cylindrical mandrel with a diameter of 16 mm after being stored at 25°C for four months from the date of manufacture. Such an optical film 10 is less likely to experience a decrease in flexural resistance over time. In particular, an optical film 10 in which the average area of ​​the light-absorbing particles 12e is small, making it difficult to maintain adhesion between the light-absorbing portion 12a of the surface layer 13 and the optical functional layer 12, is considered to be at a disadvantage in terms of flexural resistance. In particular, if the optical film 10 is stored at 25°C for four months from the date of manufacture, the hardening of the optical film 10, including the light-absorbing portion 12a, will proceed sufficiently, and in the flexural resistance test after such storage, it is possible to evaluate the flexural resistance at the point when the flexural resistance of the target for evaluation is at its lowest. According to this embodiment, by setting the elastic modulus of the surface layer 13 to 0.31 MPa or less, even an optical film 10 with a small average area of ​​light-absorbing particles 12e can be given resistance to a flexural resistance test after being stored at 25°C for four months from the date of manufacture. In particular, the average area of ​​the light-absorbing particles 12e is 4 μm ２ The following optical film 10 can also be given resistance to the bending resistance test after being stored at 25°C for 4 months from the date of manufacture. According to this embodiment, by setting the elastic modulus of the surface layer 13 to 0.2 MPa or less, even optical film 10 with a small average area of ​​light-absorbing particles 12e can have particularly high resistance to the bending resistance test after being stored at 25°C for 4 months from the date of manufacture.

[0116] In the specific example shown in Figure 2A, the light-absorbing portion 12a may include a base resin 12d and light-absorbing particles 12e held in the base resin 12d. The light-absorbing particles 12e absorb the light incident on the light-absorbing portion 12a, making it difficult for the light to spread over a wide area. Therefore, the optical film 10 can control the viewing angle.

[0117] The average area of ​​the light-absorbing particles 12e appearing in the cross-section of the light-absorbing portion 12a is 4 μm². ２ The following may also be true: The average area of ​​the light-absorbing particles 12e is 4 μm. ２ The following conditions allow the light-absorbing effect of the light-absorbing portion 12a to be sufficiently large. Furthermore, according to the optical film 10 in one specific example of this embodiment, the average area of ​​the light-absorbing particles 12e is 4 μm ２Even in the following cases, the adhesion of the surface layer 13 to the optical functional layer 12 can be maintained, making it less likely for cracks to occur in the optical film 10.

[0118] In one specific example of this embodiment, the refractive index of the light-transmitting portion 12b may be higher than that of the base resin 12d. The light-absorbing portion 12a may have a tapered shape from the first surface 10a to the second surface 10b. By having a refractive index of the light-transmitting portion 12b higher than that of the base resin 12d of the light-absorbing portion 12a, the total internal reflection of light traveling from the light-transmitting portion 12b to the light-absorbing portion 12a can be utilized. Furthermore, by having a tapered shape for the light-absorbing portion 12a, the viewing angle can be controlled by adjusting the cross-sectional shape of the light-absorbing portion 12a.

[0119] In one specific example of this embodiment, the surface layer 13 may constitute a first surface 10a including a matte surface. Therefore, when the optical film 10 is incorporated into the display device, it is prevented from coming into close contact with other optical components.

[0120] In one specific example of this embodiment, the light-absorbing portion 12a and the light-transmitting portion 12b may extend linearly along a third direction D3 that is perpendicular to the first direction D1 and the second direction D2. Therefore, the viewing angle characteristics of the optical film 10 can be controlled depending on its orientation when incorporated into the display device 1.

[0121] This disclosure will be further described in detail by examples. This disclosure is not limited to the following examples.

[0122] <<<1. Preparation of Optical Films>>> Optical films according to Example 1 and Comparative Example 1 were prepared using the method described above.

[0123] <<Example 1>> An optical film according to Example 1 was manufactured using the following materials and dimensions.

[0124] A 250 μm thick polycarbonate film (Opcon PC#250KM20D, manufactured by Keiwa Co., Ltd.) was used as the base material.

[0125] The light-transmitting portion and the land portion were integrally molded by curing ultraviolet-curable urethane acrylate. As shown in Figure 9, the mold 400 that forms the void is a roll mold in which projections 401 having a trapezoidal cross-section with an upper base width W1 of 7 μm, a lower base width W2 of 28 μm, a height L of 120 μm, and a slope angle θ of 5.0° are arranged with a pitch P of 39 μm. The projections 401 of the mold 400 form the void. The roll mold has a cylindrical outer shape. The projections 401 are provided on the side surface of the cylindrical outer shape. The projections 401 extend along the circumference on the side surface.

[0126] The land portion had a thickness of 25 μm. The refractive index of both the light-transmitting portion and the land portion was 1.57. The light-transmitting portion had a tapered shape as it moved away from the land portion. The light-transmitting portion extended linearly along the third direction.

[0127] As the base resin for the light-absorbing portion, an ultraviolet-curable resin composition containing a urethane oligomer, an acrylate monomer, and an initiator was used. The light-absorbing particles were obtained by incorporating carbon black into acrylic beads with an average particle size of 4 μm. The ratio of the mass of the light-absorbing particles to the total mass of the light-absorbing portion material, which includes the ultraviolet-curable resin composition and the light-absorbing particles, was set to 20% by mass. More specifically, 100 g of the base resin and 25 g of the light-absorbing particles were used.

[0128] A void for filling the light-absorbing portion was formed in the light-transmitting material layer provided on the substrate using the mold 400 described above. Subsequently, the light-absorbing material was coated onto the light-transmitting material layer so that the material for the light-absorbing portion filled the void. Next, excess material from the light-absorbing portion was scraped off using a doctor blade (corresponding to the squeegee 120 in Figure 4D). Then, the UV-curable resin composition, which was the base resin, was irradiated with ultraviolet light and cured. This formed a light-absorbing portion containing a UV-curable urethane acrylate base resin and light-absorbing particles. The refractive index of the base resin was 1.54.

[0129] A UV-curable resin composition was used as the material for the surface layer. In particular, a UV-curable urethane acrylate resin (EBECRYL 4265 N=1.508, manufactured by Daicel Ornex Co., Ltd.) was used as the material for the surface layer. The UV-curable resin composition was molded on the light-transmitting and light-absorbing parts, and the surface layer was formed by demolding. The thickness of the surface layer was 25 μm.

[0130] As the material for the second surface layer, the same ultraviolet-curable resin composition as the surface layer was used. The second surface layer was formed by molding the ultraviolet-curable resin composition on a substrate and then releasing it from the mold. The thickness of the second surface layer was 25 μm.

[0131] <<Example 2>> The optical film according to Example 2 was prepared in the same manner as in Example 1, except for the points described below.

[0132] As the UV-curable urethane acrylate resin used as the material for the surface layer, a mixture of "EBECRYL 4265" and "EBECRYL 230" manufactured by Daicel Ornex Co., Ltd. was used. The ratio of "EBECRYL 4265" to "EBECRYL 230" in the mixture was 30% by mass and 70% by mass. The exposure amount when curing the UV-curable resin composition, which is the base resin, by irradiating it with ultraviolet light was adjusted to 80% when the exposure in Example 1 was set to 100%. This adjustment made the degree of curing of the base resin more flexible than in Example 1.

[0133] <<Example 3>> The optical film according to Example 3 was prepared in the same manner as in Example 1, except for the points described below.

[0134] As the UV-curable urethane acrylate resin used as the material for the surface layer, a mixture of "EBECRYL 4265" and "EBECRYL 230" manufactured by Daicel Ornex Co., Ltd. was used. The ratio of "EBECRYL 4265" to "EBECRYL 230" in the mixture was 20% by mass and 80% by mass. The exposure amount when curing the UV-curable resin composition, which is the base resin, by irradiating it with ultraviolet light was adjusted to 90% when the exposure in Example 1 was set to 100%. This adjustment resulted in a degree of curing of the base resin that was more flexible than in Example 1 but less flexible than in Example 2.

[0135] <<Example 4>> The optical film according to Example 4 was prepared in the same manner as in Example 1, except for the points described below.

[0136] The exposure level when curing the UV-curable resin composition, which is the base resin, by irradiating it with ultraviolet light was adjusted to 120% compared to 100% in Example 1. This adjustment increased the crosslinking density of the base resin and raised its elastic modulus.

[0137] <<Comparative Example 1>> The optical film according to Comparative Example 1 was identical to that of Example 1, except for the points described later. In the optical film according to Comparative Example 1, ultraviolet-curable urethane acrylate resin (manufactured by Sanyo Chemical Industries, Ltd., BCP-34 N=1.503) was used as the material for the surface layer and the second surface layer.

[0138] <<Comparative Example 2>> The optical film according to Comparative Example 2 was prepared in the same manner as in Example 1, except for the points described below.

[0139] The exposure amount when curing the base resin, an ultraviolet-curable resin composition, by irradiating it with ultraviolet light was adjusted to 140% when the exposure amount in Example 1 was set to 100%.

[0140] <<Comparative Example 3>> The optical film according to Comparative Example 3 was prepared in the same manner as in Example 1, except for the points described below.

[0141] As the UV-curable urethane acrylate resin used as the material for the surface layer, "EBECRYL 1290" manufactured by Daicel Ornex was used. The exposure amount when curing the UV-curable resin composition, which is the base resin, by irradiating it with ultraviolet light was adjusted to 140% when the exposure in Example 1 was set to 100%.

[0142] <<Comparative Example 4>> The optical film according to Comparative Example 4 was prepared in the same manner as in Example 1, except for the points described below.

[0143] As the UV-curable urethane acrylate resin used as the material for the surface layer, "EBECRYL 1290" manufactured by Daicel Ornex was used. The exposure amount when curing the UV-curable resin composition, which is the base resin, by irradiating it with ultraviolet light was adjusted to 160% when the exposure in Example 1 was set to 100%.

[0144] <<<2. Measurement and Evaluation>>> Next, the optical films according to the examples and comparative examples were measured and evaluated. The test environment for measurement and evaluation was set to a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Before starting the measurement and evaluation, the target samples were placed in the above-mentioned test environment for 16 hours. In addition, the samples used for measurement and evaluation were visually inspected to ensure that there were no abnormalities such as dust or scratches. The measurement and evaluation results for Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1. In addition, the exposure amount when curing the urethane acrylate resin used as the material for the surface layer and the UV-curable resin composition, which is the base resin, by irradiating them with ultraviolet light is also shown in Table 1.

[0145] <<2-1. Flexural Resistance Test using Cylindrical Mandrel Method>> The optical films according to the examples and comparative examples were subjected to flexural resistance tests using the method described above. Mandrels with diameters of 40 mm, 32 mm, 25 mm, 20 mm, 16 mm, 12 mm, 10 mm, 8 mm, 6 mm, 5 mm, 4 mm, and 3 mm were used in the flexural resistance tests. The flexural resistance tests were continued by decreasing the diameter of the mandrel until the flexural resistance of the optical film was ruled out. The smallest mandrel diameter that was judged to be resistant to the flexural resistance test was identified. The flexural resistance tests were performed on optical films stored at 25°C for 1 day after manufacture and on optical films stored at 25°C for 4 months after manufacture.

[0146] The evaluation results of the flexural resistance test after storage at 25°C for one day are shown in the "After 1 Day" column of Table 1. The evaluation results of the flexural resistance test after storage at 25°C for four months are shown in the "After 4 Months" column of Table 1. The "After 1 Day" and "After 4 Months" columns of Table 1 show the smallest mandrel diameter that was judged to be resistant.

[0147] <<2-2. Evaluation of Surface Layer Properties>> The elastic modulus of the surface layer of the optical films in the examples and comparative examples was measured using the method described above. In addition, the Martens hardness, creep, work rate of elastic deformation, and indentation hardness were measured on the surface of the optical films in the examples and comparative examples. The optical films themselves in the examples and comparative examples were used as measurement sheets. The elastic modulus of the surface layer, as well as the Martens hardness, creep, work rate of elastic deformation, and indentation hardness on the surface of the surface layer, were measured using the nanoindentation method with a microhardness tester (product name "PICODETOR HM500", manufactured by Fischer Instruments). The measurement results for the elastic modulus of the surface layer are shown in the "Elastic Modulus" column of Table 1. The measurement results for Martens hardness, creep, work rate of elastic deformation, and indentation hardness on the surface of the surface layer are shown in the "Martens Hardness", "Creep", "Work Rate of Elastic Deformation", and "Indentation Hardness" columns of Table 1, respectively.

[0148] <<2-3. Average Area of ​​Light-Absorbing Particles Appearing in the Cross-Section of the Light-Absorbing Section>> The average area of ​​light-absorbing particles appearing in the cross-section of the light-absorbing section of the optical film according to Example 1 was measured using the method described above. Since Examples 1 to 4 and Comparative Examples 1 to 4 share the same method for creating the optical functional layer including the light-absorbing section, the average area of ​​light-absorbing particles appearing in the cross-section of the light-absorbing section of the optical film according to Examples 2 to 4 and Comparative Examples 1 to 4 is considered to be the same as that of Example 1. The measurement results of the average area of ​​light-absorbing particles appearing in the cross-section of the light-absorbing section are shown in the "Average Area of ​​Light-Absorbing Particles" column of Table 1.

[0149] <<2-4. Evaluation of cracking during cutting>> The presence or absence of cracking was evaluated when cutting the optical films according to the examples and comparative examples from the film article using a die. Twenty samples of 300 mm x 120 mm were cut from the optical film. The presence or absence of cracks in the cut samples was visually checked. The evaluation results are shown in the "Cracking" column of Table 1. The evaluation criteria were as follows: A: No cracks were found in any of the samples. B: At least one crack was found in one of the samples.

[0150]

[0151] The following was confirmed from the results of the examples and comparative examples. Comparative Example 1, in which the elastic modulus of the surface layer exceeded 0.31 MPa, and in particular exceeded 0.2 MPa, received a "B" rating for cracking during cutting and did not withstand the flexural resistance test using a 16 mm diameter cylindrical mandrel after 4 months at 25°C from the date of manufacture. On the other hand, Example 1, in which the elastic modulus of the surface layer was 0.31 MPa or less, and in particular 0.2 MPa or less, received an "A" rating for cracking during cutting and did withstand the flexural resistance test using a 16 mm diameter cylindrical mandrel after 4 months at 25°C from the date of manufacture. The average area of ​​light-absorbing particles appearing in the cross-section of the light-absorbing part was 4 μm. ２ In Comparative Example 1, described below, the resistance after 4 months at 25°C from the date of manufacture was significantly lower than the resistance after 1 day at 25°C from the date of manufacture. On the other hand, in Example 1, similar to Comparative Example 1, the average area of ​​light-absorbing particles appearing in the cross-section of the light-absorbing part was 4 μm. ２Despite the following, the evaluation of cracking during cutting resulted in an "A" rating, and after 4 months at 25°C from the date of manufacture, it withstood the flexural resistance test using a 16 mm diameter cylindrical mandrel.

[0152] In Comparative Example 2, the elastic modulus of the surface layer was 0.33 MPa, and was not 0.31 MPa or less. Comparative Example 2 was evaluated as having resistance in the bending resistance test using a 16 mm diameter cylindrical mandrel after being stored at 25°C for 4 months from the time of manufacture. However, the result of the crack evaluation during cutting in Comparative Example 2 was "B". The result of the crack evaluation during cutting in Comparative Example 2 supports the inventors' finding that cracks are likely to occur in the part that overlaps with the light-absorbing part, as described above. The result of the crack evaluation during cutting in Comparative Example 2 supports the inventors' finding that cracks are less likely to occur in the optical film by setting the elastic modulus of the surface layer to 0.31 MPa or less, as described above. In Comparative Example 2, since the elastic modulus of the surface layer exceeds 0.31 MPa, it is thought that in the crack evaluation test, stress relaxation on the light-absorbing part was insufficient, and the local stress during cutting could not be absorbed, making it prone to cracking.

[0153] On the other hand, in Examples 1 to 4, the elastic modulus of the surface layer was 0.31 MPa or less. In all of Examples 1 to 4, the evaluation result for cracking during cutting was "A". Furthermore, it was confirmed that cracking can be made particularly effective when the elastic modulus of the surface layer is 0.2 MPa or less.

[0154] Examples 1 to 4 demonstrated that, in a flexural resistance test after storage at 25°C for 4 months from manufacture, stable flexural resistance was observed without cracking when the mandrel diameter was 10 mm or more. From these results, it was understood that a preferred optical film configuration can be clearly identified by specifying that the elastic modulus of the surface layer is 0.31 MPa or less and that the film is resistant to the flexural resistance test using a 16 mm diameter cylindrical mandrel after storage at 25°C for 4 months. In particular, it was understood that a more preferred optical film configuration can be clearly identified by specifying that the elastic modulus of the surface layer is 0.31 MPa or less and that the film is resistant to the flexural resistance test using a 10 mm diameter cylindrical mandrel after storage at 25°C for 4 months. Examples 1 to 4 were confirmed to not exhibit cracking or whitening even when the mandrel diameter was 6 mm, in a flexural resistance test after storage at 25°C for 1 day from manufacture. From these results, it was understood that a more preferable form of optical film can be identified by specifying that the elastic modulus of the surface layer is 0.31 MPa or less, and that it can withstand the bending resistance test using a 6 mm diameter cylindrical mandrel after storage at 25°C for one day.

[0155] In particular, the results from Comparative Example 2 showed that, in order to reduce the likelihood of cracking in optical films, it is insufficient for the optical film to simply have the characteristic of "being able to withstand a flexural resistance test using a 16 mm diameter cylindrical mandrel after being stored at 25°C for 4 months." From the results from the Examples and Comparative Examples, it was understood that, in order to reduce the likelihood of cracking in optical films, it is rather important to set the elastic modulus of the surface layer to 0.31 MPa or less. From the results from the Examples and Comparative Examples, it was understood that by setting the elastic modulus of the surface layer to 0.31 MPa or less, cracking on the light-absorbing part can be suppressed, and processing reliability during cutting of optical films can be ensured.

[0156] Comparative Example 2 does not possess the characteristic of "having resistance to the flexural resistance test using a 10 mm diameter cylindrical mandrel after storage at 25°C for 4 months." Furthermore, Comparative Example 2 does not possess the characteristic of "having resistance to the flexural resistance test using a 6 mm diameter cylindrical mandrel after storage at 25°C for 1 day." It was found that the optical films in Examples 1 to 4 are less prone to cracking than those in Comparative Example 2. From this, it was found that by further specifying the characteristics of "having resistance to the flexural resistance test using a 10 mm diameter cylindrical mandrel after storage at 25°C for 4 months" and "having resistance to the flexural resistance test using a 6 mm diameter cylindrical mandrel after storage at 25°C for 1 day," a more preferable form of optical film in terms of both flexural resistance and crack resistance will become clear.

[0157] 1…Display device 10…Optical film 10a…First surface 10b…Second surface 11…Substrate 12…Optical functional layer 121…Light receiving surface 122…Light emitting surface 12a…Light absorbing part 12aR…Light absorbing part material layer 12b…Light transmitting part 12bR…Light transmitting part material layer 12c…Land part 12d…Base resin 12e…Light absorbing particles 13…Surface layer 13R…Surface layer material layer 14…Second surface layer 15…Void 70…Surface light source device 100…Film article 120…Squeegee 140…Embossing roller 200…Die 300…Mandrel D1…First direction D2…Second direction D3…Third direction

Claims

1. An optical film having a first surface and a second surface facing each other in a first direction, comprising, in order from the second surface toward the first surface, a substrate, an optical functional layer, and a surface layer, wherein the optical functional layer includes a light absorbing portion and a light transmitting portion, the light absorbing portion and the light transmitting portion are arranged alternately along a second direction perpendicular to the first direction, and the elastic modulus of the surface layer is 0.31 MPa or less.

2. The optical film according to claim 1, which, after being stored at 25°C for four months, is resistant to a flexural resistance test using a cylindrical mandrel with a diameter of 16 mm.

3. The optical film according to claim 1, wherein the light-absorbing portion comprises a base resin and light-absorbing particles held in the base resin.

4. The average area of ​​the light-absorbing particles appearing in the cross-section of the light-absorbing portion is 4 μm². ２ The optical film according to claim 3, which is as follows:

5. The optical film according to claim 3, wherein the refractive index of the light-transmitting portion is higher than that of the base resin, and the light-absorbing portion has a shape that tapers from the first surface to the second surface.

6. The optical film according to claim 1, wherein the surface layer constitutes the first surface including a matte surface.

7. The optical film according to claim 1, wherein the light-absorbing portion and the light-transmitting portion extend linearly along a third direction perpendicular to the first and second directions.

8. The optical film according to claim 1, wherein the elastic modulus of the surface layer is 0.2 MPa or less.

9. The optical film according to claim 1, which, after being stored at 25°C for four months, is resistant to a flexural resistance test using a cylindrical mandrel with a diameter of 10 mm.

10. The optical film according to claim 1, which, after being stored at 25°C for one day, is resistant to a flexural resistance test using a cylindrical mandrel with a diameter of 6 mm.

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

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

13. A surface light source device comprising an optical film according to any one of claims 1 to 10.

14. A display device comprising the surface light source device described in claim 13.

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