Optical film and display device

Abstract

The present disclosure provides an optical film comprising a base material and a hard coat layer disposed on one surface of the base material. The hard coat layer has, from the base material side, a first hard coat layer and a second hard coat layer. The first hard coat layer contains first particles and the second hard coat layer contains second particles. The contained amount of the first particles in the first hard coat layer is greater than the contained amount of the second particles in the second hard coat layer, and the average particle diameter of the first particles is greater than the average particle diameter of the second particles.

Description

Optical films and display devices

[0001] This disclosure relates to optical films and display devices.

[0002] On the surface of the display device, an optical film having various properties such as hard coating, abrasion resistance, anti-reflective properties, anti-glare properties, anti-static properties, and anti-fouling properties is arranged as a front panel. For example, Patent Document 1 discloses a hard coat laminated film for the purpose of improving the scratch resistance and hardness of the components of an image display device, having layers of a first hard coat, a second hard coat, and a transparent resin film in order from the surface side, wherein the first hard coat is made of a paint containing a water repellent and not inorganic particles, and the second hard coat is made of a paint containing inorganic fine particles of a predetermined average particle size, and the total light transmittance and the pencil hardness of the substrate and the surface of the first hard coat are above a predetermined value.

[0003] In recent years, there has been a great deal of activity in the development of flexible displays such as foldable displays, rollable displays, and bendable displays, with particular emphasis on the development of foldable displays, or display devices that can be folded.

[0004] Optical films placed on the surface of display devices require high surface hardness. Furthermore, flexible displays must not experience display malfunctions even after repeated bending, and the optical films placed on the surface of flexible displays must have sufficient flexibility to prevent cracking during repeated bending. However, optical films with a hard coat layer have high surface hardness, which can reduce their flexibility. Therefore, there is a need for optical films that possess sufficiently high surface hardness while also exhibiting good flexibility, suitable for use on the surface of display devices.

[0005] Patent No. 7080269

[0006] This disclosure has been made in view of the above circumstances, and its main purpose is to provide an optical film that has high surface hardness while also having good flexibility.

[0007] One embodiment of the present disclosure provides an optical film having a substrate and a hard coat layer disposed on one surface of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, the first hard coat layer contains first particles and the second hard coat layer contains second particles, the content of the first particles in the first hard coat layer is greater than the content of the second particles in the second hard coat layer, and the average particle diameter of the first particles is greater than the average particle diameter of the second particles.

[0008] One embodiment of the present disclosure provides an optical film having a substrate and a hard coat layer disposed on one side of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, and of the first and second hard coat layers, at least the first hard coat layer contains particles, and if the second hard coat layer contains the particles, the content of the particles in the second hard coat layer is less than the content of the particles in the first hard coat layer, and the optical film satisfies all of the following (a) to (c): (a) The distance from the center line in the thickness direction of the optical film to the side of the second hard coat layer opposite to the side of the first hard coat layer is 31.0 μm or more and 49.5 μm or less. (b) The distance from the center line to the side of the first hard coat layer opposite to the side of the substrate is 28.0 μm or more and 46.5 μm or less. (c) The distance from the center line to the substrate-side surface of the first hard coat layer is 15.5 μm or more and 34.0 μm or less.

[0009] Another embodiment of the present disclosure provides a display device comprising a display panel and the aforementioned optical film disposed on the observer side of the display panel.

[0010] This disclosure offers the advantage of providing an optical film that has high surface hardness while also having good flexibility.

[0011] This is a schematic cross-sectional view illustrating an optical film in this disclosure. This is a schematic cross-sectional view illustrating an optical film in this disclosure. This is a schematic diagram illustrating the elongation of an optical film in this disclosure when bent. This is a schematic cross-sectional view illustrating an optical film in this disclosure. This is a schematic cross-sectional view illustrating an optical film in this disclosure. This is a schematic diagram illustrating a dynamic bending test. This is a schematic cross-sectional view illustrating an optical film in this disclosure. This is a schematic cross-sectional view illustrating a display device in this disclosure. This is an explanatory diagram illustrating the operation procedure of the image analysis software ImageJ. This is an explanatory diagram illustrating a method for selecting and extracting a 1024 x 512 pixel image from a binarized black and white image.

[0012] Embodiments of this disclosure will be described below with reference to drawings and other figures. However, this disclosure can be implemented in many different ways and should not be interpreted as being limited to the embodiments described below. In addition, the drawings may be schematically represented in terms of width, thickness, shape, etc. of each part compared to the actual form in order to make the explanation clearer, but these are merely examples and should not limit the interpretation of this disclosure. Furthermore, in this specification and each figure, elements similar to those described above with respect to previously shown figures will be denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0013] In this specification, when describing a configuration in which one member is placed on top of another member, unless otherwise specified, the terms "on top" or "below" include both cases: one in which the other member is placed directly above or below the other member so as to be in contact with it, and another in which the other member is placed above or below the other member via yet another member. Similarly, when describing a configuration in this specification in which one member is placed on the surface of another member, unless otherwise specified, the terms "on the surface" or "on the surface" include both cases: one in which the other member is placed directly above or below the other member so as to be in contact with it, and another in which the other member is placed above or below the other member via yet another member.

[0014] The optical film and display device described herein will be explained in detail below.

[0015] A. Optical Film The optical film in this disclosure has two embodiments.

[0016] A1. Optical film (first embodiment) The optical film in this embodiment is an optical film having a substrate and a hard coat layer disposed on one side of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, the first hard coat layer contains first particles and the second hard coat layer contains second particles, the content of the first particles in the first hard coat layer is greater than the content of the second particles in the second hard coat layer, and the average particle diameter of the first particles is greater than the average particle diameter of the second particles.

[0017] Figure 1 is a schematic cross-sectional view showing an example of an optical film in this embodiment. As shown in Figure 1, the optical film 10A has a substrate 1 and a hard coat layer 2 disposed on one side of the substrate 1. The hard coat layer 2 has a first hard coat layer 21 and a second hard coat layer 22, starting from the substrate 1 side.

[0018] Figure 2 is a schematic cross-sectional view illustrating the particles contained in the hard coat layer in this embodiment. As shown in Figure 2, in the optical film 10A, the first hard coat layer 21 contains first particles P1, and the second hard coat layer 22 contains second particles P2. The content of first particles P1 in the first hard coat layer 21 is greater than the content of second particles P2 in the second hard coat layer 22, and the average particle diameter of first particles P1 is greater than the average particle diameter of second particles P2.

[0019] In the optical film of this embodiment, the first hard coat layer contains first particles, and the second hard coat layer contains second particles. The content of first particles in the first hard coat layer is greater than the content of second particles in the second hard coat layer, and the average particle diameter of the first particles is greater than the average particle diameter of the second particles. As a result, the first hard coat layer located on the inside is harder than the second hard coat layer located on the outside, thereby ensuring the surface hardness of the optical film.

[0020] On the other hand, the optical film placed on the surface of a flexible display requires flexibility to prevent cracking when repeatedly bent. Specifically, bending tests of the optical film require bending resistance that can withstand both inward and outward bending.

[0021] Figure 3 is a schematic diagram showing the state of the bent portion of an optical film when it is bent at a spacing R during a bending test. As shown in Figure 3(a), when the optical film 10A is bent with the hard coat layer 2 side S facing outward, the hard coat layer 2 side S of the optical film 10A stretches, and tensile stress is generated. On the other hand, as shown in Figure 3(b), when the optical film 10A is bent with the hard coat layer 2 side S facing inward, the hard coat layer 2 side S of the optical film 10A shrinks, and compressive stress is generated. Thus, when an optical film is bent, the surface of the optical film is either stretched or compressed. Therefore, the hard coat layer 2 side S of the optical film is most susceptible to compressive or tensile stress. If the surface hardness of the optical film is high, cracking of the hard coat layer is more likely to occur when it is bent, and the bending resistance tends to decrease.

[0022] In contrast, in this embodiment, the content of the second particles in the outer second hard coat layer is less than the content of the particles in the inner first hard coat layer, and the average particle diameter of the second particles is smaller than the average particle diameter of the first particles. Therefore, although the second hard coat layer is a layer for increasing surface hardness, it is not as hard as the first hard coat layer. As a result, cracking of the hard coat layer laminate can be suppressed during bending, and bending resistance can be improved. Furthermore, by keeping the content of the second particles in the second hard coat layer within a predetermined range, it is possible to increase the surface hardness of the optical film to an extent that does not reduce bending resistance.

[0023] In other words, the optical film of this embodiment can achieve both sufficiently high surface hardness for an optical film placed on the surface of a display device and sufficiently high bending resistance for an optical film placed on the surface of a flexible display. For example, it can simultaneously achieve a surface hardness of 6H or higher on the pencil hardness scale and, as described later, bending resistance when a dynamic bending test is performed with a spacing R = 3 mm.

[0024] Although Patent Document 1 states that the pencil hardness of the hard coat surface of the hard coat laminated film is 5H or higher, it does not mention the bending resistance required for flexible display applications.

[0025] I. Characteristics of the Hard Coat Layer The optical film in this embodiment has a hard coat layer on one side of the substrate. The hard coat layer has a first hard coat layer and a second hard coat layer, starting from the substrate side. The first hard coat layer contains first particles, and the second hard coat layer contains second particles.

[0026] In this embodiment, the hard coat layer is a component for increasing surface hardness. The presence of the hard coat layer improves scratch resistance.

[0027] In this embodiment, the pencil hardness of the hard coat layer side surface of the optical film is preferably 6H or higher, and more preferably 7H or higher. Such an optical film will have sufficient surface hardness to be placed on the surface of a display device.

[0028] Here, pencil hardness is measured using the pencil hardness test specified in JIS K5600-5-4:1999. Specifically, using a test pencil specified in JIS S6006:2020, the pencil hardness test specified in JIS K5600-5-4:1999 is performed on the hard coat layer side of the optical film, and the highest pencil hardness without scratching is evaluated. The measurement conditions are an angle of 45°, a load of 750g, a speed of 1mm / sec, and a temperature of 23±2℃. As a pencil hardness tester, a pencil scratch coating hardness tester manufactured by Toyo Seiki Co., Ltd. can be used.

[0029] 1. Content and average particle size of particles In this embodiment, the content C of the first particles P1 in the first hard coat layer 21 １ is more than the content C of the second particles P2 in the second hard coat layer 22 ２ . As a result, since the first hard coat layer 21 has a higher hardness, the surface hardness of the optical film can be ensured. On the other hand, although the second hard coat layer 22 is a layer for increasing the surface hardness, it is not harder than the first hard coat layer 21. Therefore, when the optical film is bent, it functions as a protective member that suppresses cracking of the first hard coat layer 21, and cracking of the hard coat layer can be suppressed.

[0030] The content C of the first particles P1 in the first hard coat layer 21 １ and the content C of the second particles P2 in the second hard coat layer 22 ２ will be described later.

[0031] In this embodiment, the average particle size of the first particles P1 is larger than the average particle size of the second particles P2. As a result, since the first hard coat layer 21 has a higher hardness, the surface hardness of the optical film can be ensured. On the other hand, although the second hard coat layer 22 is a layer for increasing the surface hardness, it is not harder than the first hard coat layer 21. Therefore, when the optical film is bent, it functions as a protective member that suppresses cracking of the first hard coat layer 21, and cracking of the hard coat layer can be suppressed.

[0032] The ratio (D １ of the average particle size D of the second particles to the average particle size D ２ of the first particles) (D ２ / D １ ) is, for example, 0.02 or more, and may be 0.10 or more, or may be 0.20 or more. If the above ratio (D ２ / D １ ) is within the above range, the average particle size D ２ of the second particles does not become too small, so the surface hardness of the optical film can be increased. On the other hand, the above ratio (D ２ / D １) is, for example, 0.75 or less, and may be 0.60 or less, or 0.50 or less. The above ratio (D ２ / D １ If the above range is true, then the average particle diameter D of the second particle ２ Since the ratio does not become too large, the surface hardness of the optical film can be increased to an extent that does not reduce its flexibility. The above ratio (D ２ / D １ For example, the value of ) is 0.02 or more and 0.75 or less, and may be 0.10 or more and 0.60 or less, or 0.20 or more and 0.50 or less.

[0033] Average particle diameter D of the first particle １ and the average particle diameter D of the second particle ２ The specific values ​​will be discussed later.

[0034] 2. Thickness The thickness of the hard coat layer is preferably 12 μm or more, may be 15 μm or more, or 19 μm or more. By having the hard coat layer thickness within the above range, the surface hardness of the hard coat layer side of the optical film can be further increased, and scratch resistance can be improved. On the other hand, from the viewpoint of flexibility, the thickness of the hard coat layer is, for example, 30 μm or less, may be 25 μm or less, or 22 μm or less. The thickness of the hard coat layer is, for example, 12 μm or more and 30 μm or less, may be 15 μm or more and 25 μm or less, or 19 μm or more and 22 μm or less. Note that the thickness of the hard coat layer is the total thickness of the hard coat layer, and if the hard coat layer has a third hard coat layer described later, it is the total thickness of the three layers consisting of the first hard coat layer, the second hard coat layer and the third hard coat layer.

[0035] The specific thicknesses of the first and second hard coat layers will be described later.

[0036] Here, the thickness of each layer is the arithmetic mean of the thicknesses at any 10 points obtained by measuring the cross-section in the thickness direction of the optical film observed by a scanning electron microscope (SEM). The specific method for taking cross-sectional photographs is shown below. First, the optical film is cut to a size of 2 cm x 2 cm, a block is prepared by embedding the optical film in embedding resin, and a cross-section is prepared using a polishing machine. A TegraPoll-35 manufactured by Struers can be used as the polishing machine. After that, a cross-sectional photograph of the measurement sample is taken using a scanning electron microscope. A Hitachi High-Technologies Corporation S-4800 can be used as the scanning electron microscope. When taking cross-sectional photographs using a scanning electron microscope (Hitachi High-Technologies Corporation S-4800), the detector is set to "Lower", the acceleration voltage to "3 kV", and the emission current to "10 μA" for cross-sectional observation. Regarding magnification, adjust the focus and observe whether each layer can be distinguished in terms of contrast and brightness, adjusting it appropriately within the range of 100x to 100,000x, preferably 1,000x to 50,000x, and more preferably 5,000x to 10,000x. When taking cross-sectional images using a scanning electron microscope (S-4800 manufactured by Hitachi High-Technologies Corporation), you may also set the beam monitor aperture to "1", the objective lens aperture to "3", and the W.D. to "8mm". In addition, the contrast of the interface may be difficult to discern at high magnification. In that case, observe at a low magnification simultaneously. For example, observe at two magnifications, high and low, such as 2,000x and 10,000x, or 5,000x and 20,000x. Then, calculate the arithmetic mean of the cross-sectional images at both magnifications, and use that average as the thickness of each layer. If the interface is difficult to discern, you may stain it with a stain to make the interface visible. Unless otherwise specified, the same applies to the measurement methods for the thickness of other layers of the optical film.

[0037] Thickness T of the second hard coat layer ２ The thickness T of the first hard coat layer is １ It is preferable that it be thinner than [this]. Generally, the surface hardness tends to increase as the thickness of the hard coat layer increases. Therefore, the thickness T of the second hard coat layer is [this].２ However, the thickness of the first hard coat layer T １ By being thinner, the first hard coat layer becomes harder, and the second hard coat layer becomes less hard than the first hard coat layer. Therefore, it is possible to increase the surface hardness of the optical film while improving its flexibility. Specifically, the thickness T of the first hard coat layer １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the sum of the two layers. ２ The proportion (T ２ / (T １ +T ２ )) is preferably 0.25 or less, may be 0.22 or less, or may be 0.20 or less. On the other hand, the above ratio (T ２ / (T １ +T ２ The ratio (T) is preferably 0.10 or higher, may be 0.12 or higher, or may be 0.16 or higher. ２ / (T １ +T ２ )) is greater than or equal to the above value, so that the second hard coat layer can adequately protect the first hard coat layer, and cracking of the hard coat layer laminate can be suppressed when bending. The above ratio (T ２ / (T １ +T ２ )) is preferably 0.10 or more and 0.25 or less, may be 0.12 or more and 0.22 or less, or 0.16 or more and 0.20 or less.

[0038] 3. Distance from the center line As shown in Figure 4, it is preferable that the optical film 10A in this embodiment satisfies all of the following (a) to (c): (a) Thickness direction D of the optical film 10A Ｔ (b) The distance X1 from the center line N to the surface S1 of the second hard coat layer 22 opposite to the first hard coat layer 21 is 31.0 μm or more and 49.5 μm or less. (b) The distance X2 from the center line N to the surface S2 of the first hard coat layer 21 opposite to the substrate 1 is 28.0 μm or more and 46.5 μm or less. (c) The distance X3 from the center line N to the surface S3 of the first hard coat layer 21 on the substrate 1 side is 15.5 μm or more and 34.0 μm or less.

[0039] In this specification, "center line in the thickness direction of the optical film" refers to the thickness direction D of the optical film 10A, as shown in Figure 4. Ｔ This is line N passing through the center of the region.

[0040] Figure 3 is a schematic diagram showing the state of the bent portion of an optical film when it is bent at a distance R during a bending test. As shown in Figure 3(a), in the case of outward bending, where the surface S on the hard coat layer 2 side is facing outward, the surface S of the optical film 10A facing the hard coat layer 2 stretches relative to the center line N in the thickness direction of the optical film 10A, and tensile stress is generated. On the other hand, as shown in Figure 3(b), in the case of inward bending, where the surface S on the hard coat layer 2 side is facing inward, the surface S of the optical film 10A facing the hard coat layer 2 shrinks relative to the center line N, and compressive stress is generated. Thus, when an optical film is bent, the surface of the optical film is either stretched or compressed relative to the center line in the thickness direction of the optical film. Generally, the further away from the center line, the greater the compressive and tensile stress, while the closer to the center line, the smaller the compressive and tensile stress. Therefore, the surface S of the optical film facing the hard coat layer 2 is the furthest from the center line N, and thus experiences the maximum compressive or tensile stress.

[0041] As described above, the first hard coat layer located on the inside is harder. The second hard coat layer located on the outside is a layer that increases surface hardness, but it is not as hard as the first hard coat layer. By keeping the distance X1 from the center line N to the surface S1 of the relatively less hard second hard coat layer 22 within a predetermined range, it is possible to suppress excessive compressive and tensile stress at the surface S1 of the second hard coat layer 22 during bending. Therefore, cracking of the second hard coat layer 22 becomes less likely. Furthermore, by keeping the distance X2 from the center line N to the surface S2 of the harder first hard coat layer 21 within a predetermined range, it is possible to reduce compressive and tensile stress at the surface S2 of the first hard coat layer 21 during bending. Therefore, cracking of the first hard coat layer 21 becomes less likely. Thus, cracking of the hard coat layers can be suppressed.

[0042] In this embodiment, the center line N is located inside the substrate 1. Generally, the thicker the hard coat layer, the higher the surface hardness and the lower the bending resistance tends to be. By keeping the distance X3 from the center line N to the surface S3 of the first hard coat layer 21 below a predetermined value, the center line N is located further inside the substrate 1, so the thickness of the hard coat layer 2 does not become excessively thick, and bending resistance can be improved. On the other hand, by keeping the distance X3 from the center line N to the surface S3 of the first hard coat layer 21 above a predetermined value, the thickness of the hard coat layer becomes relatively thick, making it easier to obtain high surface hardness.

[0043] Therefore, by satisfying the above conditions (a) to (c), it is possible to increase surface hardness while improving flexibility.

[0044] The distance X1 from the center line N to the surface S1 of the second hard coat layer 22 opposite to the first hard coat layer 21 is preferably 31.0 μm or more and 49.5 μm or less, may be 32.5 μm or more and 47.5 μm or less, or 34.5 μm or more and 46.0 μm or less.

[0045] The distance X2 from the center line N to the surface S2 of the first hard coat layer 21 opposite to the substrate 1 side is preferably 28.0 μm or more and 46.5 μm or less, may be 29.5 μm or more and 44.5 μm or less, or 31.5 μm or more and 43.0 μm or less.

[0046] The distance X3 from the center line N to the surface S3 of the first hard coat layer 21 on the substrate 1 side is preferably 15.5 μm or more and 34.0 μm or less, may be 17.5 μm or more and 32.5 μm or less, or 19.0 μm or more and 30.5 μm or less.

[0047] The measurement method for distances X1 to X3 described above is the same as the thickness measurement method described above.

[0048] II. Layer Structure 1. First Hard Coat Layer The optical film in this embodiment has a first hard coat layer. The first hard coat layer and the substrate may or may not be in direct contact. The first hard coat layer and the second hard coat layer may or may not be in direct contact.

[0049] (1) The first hard coat layer of the material contains first particles and a binder resin.

[0050] (a) The first particle may be either an inorganic particle or an organic particle. In particular, the first particle is preferably an inorganic particle. This is because inorganic particles provide superior hardness compared to organic particles.

[0051] Examples of inorganic particles include silica (SiO₂). ２ Examples include metal oxide particles such as aluminum oxide, zirconia, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, indium tin oxide (ITO), antimony oxide, and cerium oxide; metal fluoride particles such as magnesium fluoride and sodium fluoride; metal particles; metal sulfide particles; and metal nitride particles. Among these, metal oxide particles are preferred, at least one selected from silica particles and aluminum oxide particles is more preferred, and silica particles are even more preferred. This is because they provide excellent hardness and good dispersibility.

[0052] Furthermore, it is preferable that the inorganic particles are reactive inorganic particles having photoreactive reactive functional groups on at least a portion of the particle surface that can crosslink with other inorganic particles or with at least one polymerizable compound to form covalent bonds. By crosslinking reactive inorganic particles with other reactive inorganic particles or with at least one radical polymerizable compound and a cationic polymerizable compound, the hardness of the first hard coat layer can be further improved.

[0053] Reactive inorganic particles have at least a portion of their surface coated with an organic component, and have reactive functional groups introduced by the organic component on their surface. Suitable reactive functional groups include, for example, polymerizable unsaturated groups, and more preferably, photocurable unsaturated groups. Examples of reactive functional groups include ethylenically unsaturated bonds such as (meth)acryloyl groups, vinyl groups, and allyl groups, and epoxy groups.

[0054] The reactive silica particles are not particularly limited and conventionally known ones can be used, for example, the reactive silica particles described in Japanese Patent Application Publication No. 2008-165040. Commercially available reactive silica particles include, for example, MIBK-SD, MIBK-SDMS, MIBK-SDL, MIBK-SDZL from Nissan Chemical Industries, Ltd., and V8802 and V8803 from JGC Catalysts & Chemicals Ltd.

[0055] The shape of the first particles is not particularly limited. The first particles may be, for example, spherical particles or irregularly shaped particles. Irregularly shaped particles are preferred. Spherical particles and irregularly shaped particles may be mixed. In this specification, irregularly shaped particles refer to particles with a potato-like, random uneven surface. Since irregularly shaped particles have a larger surface area compared to spherical particles, including such irregularly shaped particles increases the contact area with the binder resin, thereby improving the hardness of the first hard coat layer. Whether or not irregularly shaped silica particles are present can be confirmed by cross-sectional observation of the first hard coat layer using an electron microscope.

[0056] The hardness of the first hard coat layer can be controlled by adjusting the average particle size and content of the first particles.

[0057] Average particle diameter D of the first particle １ The average particle diameter D of the second particle is ２ It is sufficient if it is larger than the average particle diameter D of the first particle mentioned above. １ The average particle diameter D of the second particle relative to ２ The proportion (D ２ / D １ It is preferable that the following conditions are met. Average particle diameter D of the first particle １From the viewpoint of improving the surface hardness of the optical film, the particle size is preferably 20 nm or more, may be 25 nm or more, or may be 30 nm or more. Average particle size D of the first particle １ If it is within the above range, then the above proportion (D ２ / D １ This makes it easier to satisfy the condition D of the first particle. １ From the viewpoint of transparency, the particle size is preferably 50 nm or less, but may also be 45 nm or less, or 40 nm or less. Average particle size D of the first particle １ If the particle size is too large, it may lead to the formation of large irregularities in the first hard coat layer or increase haze. Average particle size D of the first particle １ The wavelength is preferably 20 nm or more and 50 nm or less, but may also be 25 nm or more and 45 nm or less, or 30 nm or more and 40 nm or less.

[0058] Here, the average particle diameter of the first particle is measured by cross-sectional observation of the first hard coat layer using an electron microscope. The average particle diameter of the first particle is the average of the particle diameters of 10 arbitrarily selected first particles. The average particle size of the irregularly shaped particle is the average of the maximum (major axis) and minimum (minor axis) distances between two points on the outer circumference of the irregularly shaped particle observed by cross-sectional microscopy of the hard coat layer.

[0059] The content C1 of the first particles in the first hard coat layer is not particularly limited, as long as it is greater than the content C2 of the second particles in the second hard coat layer. The content C1 of the first particles in the first hard coat layer is preferably 20% by mass, more preferably 25% by mass or more, and even more preferably 35% by mass or more. If the content of the first particles is within the above range, the hardness of the first hard coat layer can be increased. On the other hand, the content C1 of the second particles in the first hard coat layer is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. If the content of the first particles is within the above range, good flexibility can be obtained. For example, the content C1 of the first particles in the first hard coat layer is preferably 20% by mass or more and 60% by mass or less, more preferably 25% by mass or more and 50% by mass or less, and even more preferably 35% by mass or more and 45% by mass or less.

[0060] Here, the content C of the first particle in the first hard coat layer １ This value (mass%) is calculated from the area ratio of particles in the first hard coat layer and the weight ratio per unit area of ​​the first particles and the binder resin, as shown below.

[0061] (Calculation of the area ratio of the first particle) First, the area ratio of the first particle in the first hard coat layer is measured by observing a thin film section of the optical film with a scanning transmission electron microscope (STEM) and performing image analysis. The measurement method is shown below.

[0062] (A) First, a 70 nm thick thin film section is cut from the optical film using a microtome. The method for cutting the thin film section is as follows: (A1) First, a cut sample is cut from the optical film to be measured. The cut sample should be in the shape of a strip. The size of the cut sample should be 3 mm wide and 10 mm long when observed from the direction normal to the optical film. (A2) Next, the cut sample is embedded with embedding resin. Specifically, first, the cut sample is placed in an embedding plate. Then, the embedding resin is poured into the embedding plate on which the cut sample is placed. After that, the embedding resin is allowed to harden by leaving it at room temperature for 12 hours. This creates an embedded sample containing the cut sample and the hardened embedding resin. By removing the embedded sample from the embedding plate, an embedded sample is obtained in which the cut sample is embedded in the embedding resin. (A3) Next, a thin film section is cut from the embedded sample using a microtome. Specifically, first, the block-shaped embedded sample is roughly cut with a glass knife to create a surface approximately 100 μm long and 20 μm wide that includes the cross-section of the optical film (rough trimming). Next, the obtained surface is cut with a diamond knife to cut a thin film section with a thickness of 70 nm onto the water. The thin film section floating on the water is collected with a mesh to obtain a thin film section.

[0063] (B) Next, a cross-sectional image of the optical film is obtained by STEM observation. Specifically, (B1) First, the thin film section is subjected to electron staining. This makes it easier to distinguish between particles and binder resin (usually a cured product of a curable component). For example, in the case of osmium staining, the osmium compound reacts with the double bonds in the binder resin and stains it. (B2) Next, a photograph of the thin film section is taken using STEM. As the STEM, a scanning electron microscope "S-4800" manufactured by Hitachi High-Technologies Corporation can be used. When taking a photograph using a scanning electron microscope (S-4800 manufactured by Hitachi High-Technologies Corporation), the detector is set to "TE", the acceleration voltage to "30kV", and the emission current to "10μA" for observation. Regarding magnification, the focus is adjusted, and the contrast and brightness are adjusted as appropriate while observing whether the particles and binder resin (usually a cured product of a curable component) can be distinguished and whether the shape of the particles is clear. Furthermore, when taking photographs using a scanning electron microscope (S-4800 manufactured by Hitachi High-Technologies Corporation), you may also set the beam monitor aperture to "3", the objective lens aperture to "3", and the W.D. to "8 mm".

[0064] (C) Next, using the image analysis software ImageJ Version 1.54g, the particles and binder resin (usually a cured product of a curable component) in the cross-sectional image of the optical film are binarized to extract a black and white image and calculate the area ratio of the particles. (C1) Specifically, first, the baseline is adjusted using the Rolling Ball method. At this time, as illustrated in Figure 9(a), select Process → Subtract Background. Next, set "Rolling ball radius" in the dialog box. At this time, adjust the value according to the image size and features. Then, check "Preview". After that, click "OK" to finish the Background subtraction process. (C2) Next, binarization is determined using the Otsu method. At this point, select Image → Adjust → Threhold, as illustrated in Figure 9(b). Next, set the "Method" in the "Threshold" window to Otsu, as illustrated in Figure 9(c). Then, click "Apply" to generate the binarized image. (C3) Next, check whether the particles are represented as black areas and the binder resin as white areas in the binarized black and white image. If, due to electron staining, the particles are represented as white areas and the binder resin as black areas in the binarized black and white image, uncheck "Dark background" in the "Threshold" window when generating the binarized image to perform black and white inversion. (C4) Next, select and extract a 1024 × 512 pixel image from the black and white image. In this process, as shown in Figures 10(a) and 10(b), a 1024 × 512 pixel image 52a is selected and extracted from the black and white image 51 from the interface of the first hard coat layer 21 on the substrate 1 side, and a 1024 × 512 pixel image 52b is selected and extracted from the interface of the first hard coat layer 21 on the second hard coat layer 22 side. Furthermore, in the black and white image 51 shown in Figures 10(a) and 10(b), when the vertical direction is the thickness direction of the optical film and the horizontal direction is the surface direction of the optical film, images 52a and 52b of 1024 × 512 pixels are selected and extracted symmetrically with respect to the center line 53 in the surface direction of the optical film. In other words, two 1024 × 512 pixel images are selected and extracted from one black and white image.In Figures 10(a) and 10(b), reference numeral 110 denotes the embedding resin. (C5) Next, in a 1024 × 512 pixel image, the area is measured using Analyze → Measure, as illustrated in Figure 9(d). As described above, in a 1024 × 512 pixel image, particles are represented as black areas and binder resin as white areas. (C6) Finally, the sum of the area of ​​the black areas and the area of ​​the white areas (area of ​​the target region) A. ０ Black area A Ｂ A ratio (A Ｂ / A ０ ) is calculated. For each 1024 x 512 pixel image, A Ｂ / A ０ The arithmetic mean of this is used as the particle area ratio.

[0065] (Content of the first particle C) １ (Calculation of mass %) The weight ratio per unit area of ​​the binder resin and the first particle (weight per unit area of ​​binder resin : weight per unit area of ​​the first particle = Wr:Wp) is determined. The weight ratio per unit area of ​​the binder resin and the first particle corresponds to the density ratio. For the density of the first particle, the composition of the first particle is analyzed by SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy) to identify the type of first particle, and the density of that particle (g / cm³) which is generally known is determined. ３ ) will be adopted. For SEM-EDX, the Oxford X-MaxN 80 can be used. Regarding the density of the binder resin, after confirming the type of resin with NMR (nuclear magnetic resonance spectrometer) or IR (infrared spectrometer), the density (g / cm³) of the resin that is generally known will be used. ３) will be adopted. For NMR, the AVANCE III HD400 manufactured by Bruker BioSpin can be used. For IR, the Nicolet 6700 manufactured by Thermo Fisher Scientific can be used. Particle density and binder resin density can be found in the literature. For density, first refer to the 3rd edition of the CRC Materials Science and Engineering Handbook (CRC Publishing). Next, if it is not listed there, refer to the 4th edition, 5th edition, ..., and the latest edition of the CRC Materials Science and Engineering Handbook in that order. Furthermore, if it is not listed in these, refer to the CRC Handbook of Chemistry and Physics. Furthermore, acrylic resins, which are cured products of compounds containing (meth)acryloyl groups such as acrylates, epoxy acrylates, and urethane acrylates, have a density of 1.1 g / cm³ in both aliphatic and aromatic cases. ３ 1.2g / cm or more ３ The following is often the case. The ratio of these density values ​​is taken as the weight ratio per unit area of ​​the binder resin and the first particle. The weight ratio per unit area of ​​the binder resin (cured urethane acrylate) and silica particles is 1.2:2.0. The weight ratio per unit area of ​​the binder resin and alumina particles is 1.2:3.7. The weight ratio per unit area of ​​the binder resin and zirconia particles is 1.2:6.1. Based on the above area ratio A calculated from image processing, a weight conversion is performed and the content (mass %) of the first particle is calculated from the following calculation. Content C of the first particle １ (Mass %) = {Weight of the first particle / (Weight of binder resin + Weight of the first particle)} × 100 = [(Wp × A) / {Wr × (1 - A) + (Wp × A)}] × 100

[0066] (b) Binder resin The first hard coat layer contains a binder resin. Examples of the binder resin include cured resin products. Specifically, the first hard coat layer preferably contains a cured resin product of a resin composition containing a polymerizable compound as the binder resin. A cured resin product of a resin composition containing a polymerizable compound can be obtained by polymerizing the polymerizable compound using a polymerization initiator as needed and using a known method.

[0067] A polymerizable compound is one that has at least one polymerizable functional group in its molecule. Examples of polymerizable compounds include at least one radical polymerizable compound and a cationic polymerizable compound.

[0068] A radical polymerizable compound is a compound that has a radical polymerizable group. The radical polymerizable group of a radical polymerizable compound can be any functional group capable of undergoing a radical polymerization reaction, and is not particularly limited, but examples include groups containing a carbon-carbon unsaturated double bond, and specifically, vinyl groups and (meth)acryloyl groups. If a radical polymerizable compound has two or more radical polymerizable groups, these radical polymerizable groups may be the same or different.

[0069] The number of radical polymerizable groups in one molecule of a radical polymerizable compound is preferably two or more, and more preferably three or more, from the viewpoint of improving the hardness of the first hard coat layer.

[0070] As radical polymerizable compounds, compounds having (meth)acryloyl groups are preferred due to their high reactivity. For example, polyfunctional (meth)acrylate monomers and oligomers with molecular weights of several hundred to several thousand and containing several (meth)acryloyl groups in the molecule, such as urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, melamine (meth)acrylate, polyfluoroalkyl (meth)acrylate, and silicone (meth)acrylate, can be preferably used. Polyfunctional (meth)acrylate polymers having two or more (meth)acryloyl groups in the side chain of the acrylate polymer can also be preferably used. In particular, polyfunctional (meth)acrylate monomers having two or more (meth)acryloyl groups in one molecule can be preferably used. By including a cured product of the polyfunctional (meth)acrylate monomer in the first hard coat layer, the hardness of the first hard coat layer can be improved, and the adhesion can be further improved. Furthermore, polyfunctional (meth)acrylate oligomers or polymers having two or more (meth)acryloyl groups in one molecule can also be preferably used. By including a cured product of the polyfunctional (meth)acrylate oligomer or polymer in the first hard coat layer, the hardness and flexibility of the first hard coat layer can be improved, and the adhesion can be further improved.

[0071] In this specification, (meth)acryloyl refers to acryloyl and methacryloyl respectively, and (meth)acrylate refers to acrylate and methacrylate respectively.

[0072] Specific examples of polyfunctional (meth)acrylate monomers can be found in, for example, Japanese Patent Publication No. 2019-132930. In particular, those having 3 to 6 (meth)acryloyl groups per molecule are preferred due to their high reactivity, improved hardness of the first hard coat layer, and adhesion. For example, pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPPA), trimethylolpropane tri(meth)acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, etc. are preferred, and at least one selected from pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexaacrylate, as well as those modified with PO, EO, or caprolactone, is preferred.

[0073] The resin composition may contain monofunctional (meth)acrylate monomers as radical polymerizable compounds for purposes such as adjusting hardness and viscosity, and improving adhesion. Specific examples of monofunctional (meth)acrylate monomers can be found in, for example, Japanese Patent Application Publication No. 2019-132930.

[0074] A cationic polymerizable compound is a compound having a cationic polymerizable group. The cationic polymerizable group of a cationic polymerizable compound can be any functional group capable of undergoing a cationic polymerization reaction, and is not particularly limited, but examples include epoxy groups, oxetanyl groups, and vinyl ether groups. If a cationic polymerizable compound has two or more cationic polymerizable groups, these cationic polymerizable groups may be the same or different.

[0075] The number of cationic polymerizable groups in one molecule of a cationic polymerizable compound is preferably two or more, and more preferably three or more, from the viewpoint of improving the hardness of the first hard coat layer.

[0076] Furthermore, among cationic polymerizable compounds, compounds having at least one of epoxy groups and oxetanyl groups as cationic polymerizable groups are preferred, and compounds having two or more of at least one of epoxy groups and oxetanyl groups in one molecule are more preferred. Cyclic ether groups such as epoxy groups and oxetanyl groups are preferred because they exhibit less shrinkage during polymerization. In addition, compounds having epoxy groups among cyclic ether groups are readily available in a variety of structures, do not adversely affect the durability of the resulting first hard coat layer, and have the advantage of being easy to control in terms of compatibility with radical polymerizable compounds. Moreover, among cyclic ether groups, oxetanyl groups have a higher degree of polymerization and lower toxicity compared to epoxy groups, and when the resulting first hard coat layer is combined with a compound having epoxy groups, they accelerate the network formation rate obtained from cationic polymerizable compounds in the coating film, and have the advantage of forming an independent network without leaving unreacted monomers in the film even in regions where they are mixed with radical polymerizable compounds.

[0077] Examples of cationic polymerizable compounds having epoxy groups include alicyclic epoxy resins obtained by epoxidizing polyglycidyl ethers of polyhydric alcohols having alicyclic rings, or compounds containing cyclohexene rings or cyclopentene rings, with a suitable oxidizing agent such as hydrogen peroxide or peracid; aliphatic epoxy resins such as polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts, polyglycidyl esters of aliphatic long-chain polybasic acids, and homopolymers and copolymers of glycidyl (meth)acrylates; glycidyl ethers produced by the reaction of bisphenols such as bisphenol A, bisphenol F, and hydrogenated bisphenol A, or derivatives thereof such as alkylene oxide adducts and caprolactone adducts, with epichlorohydrin, and novolac epoxy resins, as well as glycidyl ether-type epoxy resins derived from bisphenols.

[0078] Specific examples of alicyclic epoxy resins, glycidyl ether type epoxy resins, and cationic polymerizable compounds having an oxetanyl group can be found in, for example, Japanese Patent Application Publication No. 2018-104682. The cured product of the resin composition containing the polymerizable compound in the first hard coat layer can be analyzed using a Fourier transform infrared spectrophotometer (FTIR), a gas chromatography-mass chromatograph (GC-MS), and for the decomposition products of the polymer, a combination of high-performance liquid chromatography, gas chromatography-mass spectrometry, NMR, elemental analysis, XPS / ESCA, and TOF-SIMS.

[0079] The resin composition may contain a polymerization initiator as needed. As the polymerization initiator, radical polymerization initiators, cationic polymerization initiators, radical and cationic polymerization initiators, etc., can be appropriately selected and used. These polymerization initiators are decomposed by at least one of light irradiation and heating, generating radicals or cations to promote radical polymerization and cationic polymerization. Note that in some cases, the polymerization initiator may be completely decomposed and not remain in the first hard coat layer.

[0080] Specific examples of radical polymerization initiators and cationic polymerization initiators can be found, for example, in Japanese Patent Application Publication No. 2018-104682.

[0081] (c) Other additives The first hard coat layer may further contain additives as needed. Additives are selected appropriately according to the function to be imparted to the first hard coat layer and are not particularly limited, but examples include inorganic or organic particles for adjusting the refractive index, ultraviolet absorbers, infrared absorbers, anti-glare agents, anti-fouling agents, antistatic agents, colorants such as blue or purple pigments, leveling agents, surfactants, lubricants, various sensitizers, flame retardants, adhesion promoters, polymerization inhibitors, antioxidants, light stabilizers, and surface modifiers.

[0082] (2) Thickness of the first hard coat layer T １ The thickness T of the second hard coat layer is ２ A thickness greater than the specified amount is preferable. Specifically, the thickness T of the first hard coat layer. １The thickness T of the first hard coat layer described above is... １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the sum of the two layers. ２ The proportion (T ２ / (T １ +T ２ It is preferable that the following conditions be met. Also, the thickness T of the first hard coat layer is preferable. １ Preferably, the distance from the center line in the thickness direction of the optical film to each surface is such that the thickness satisfies (a) to (c) above.

[0083] Thickness T of the first hard coat layer １ For example, the thickness of the first hard coat layer is 5 μm or more, may be 10 μm or more, or may be 15 μm or more. By having the thickness of the first hard coat layer within the above range, the surface hardness of the optical film can be increased and scratch resistance can be improved. On the other hand, the thickness T of the first hard coat layer １ For example, the thickness of the first hard coat layer is 30 μm or less, but may also be 25 μm or less, or 20 μm or less. By having the thickness of the first hard coat layer within the above range, good flexibility can be obtained. Thickness T of the first hard coat layer １ For example, it may be 5 μm or more and 30 μm or less, and may also be 10 μm or more and 25 μm or less, or 15 μm or more and 20 μm or less.

[0084] (3) Formation Method The method for forming the first hard coat layer may be appropriately applied depending on the material of the first hard coat layer, for example, by applying a curable resin composition for hard coat layers containing the polymerizable compound to one side of the substrate and curing it. The curable resin composition for hard coat layers may further contain a solvent as needed.

[0085] The method for applying the curable resin composition for the hard coat layer to the substrate is not particularly limited as long as it can be applied to the desired thickness, and common application methods include gravure coating, gravure reverse coating, gravure offset coating, spin coating, roll coating, reverse roll coating, blade coating, dip coating, and screen printing. Furthermore, a transfer method can also be used to form the coating film of the resin composition for the hard coat layer.

[0086] The coating film of the curable resin composition for the hard coat layer is dried to remove the solvent as needed. Drying methods include, for example, vacuum drying, heat drying, or a combination of these methods. For example, drying can be achieved by heating at a temperature of 30°C to 120°C for 10 to 180 seconds.

[0087] The method for curing the coating film of the hard coat layer curable resin composition can be appropriately selected depending on the polymerizable group of the polymerizable compound, and for example, at least one of light irradiation and heating can be used.

[0088] Light irradiation primarily uses ultraviolet light, visible light, electron beams, and ionizing radiation. For ultraviolet curing, for example, ultraviolet light emitted from ultra-high pressure mercury lamps, high-pressure mercury lamps, low-pressure mercury lamps, carbon arcs, xenon arcs, and metal halide lamps can be used. The irradiation dose from the energy source is, for example, 50 mJ / cm² as the integrated exposure dose at an ultraviolet wavelength of 365 nm. ２ More than 5000mJ / cm ２ It is approximately as follows.

[0089] If heating is required, the reaction can be carried out at a temperature of, for example, 40°C to 120°C. Alternatively, the reaction may be carried out by leaving it at room temperature (25°C) for 24 hours or more.

[0090] (4) Indentation hardness The first hard court layer is harder than the second hard court layer. That is, the indentation hardness of the first hard court layer is greater than that of the second hard court layer. The indentation hardness of the first hard court layer is, for example, 600 MPa or more and 900 MPa or less.

[0091] The indentation hardness of the first hard coat layer was measured using the following method: (Preparation of measurement sample) An optical film was cut into 1 mm x 10 mm sections, and a block was prepared by embedding the cut optical film in embedding resin. Next, using an ultramicrotome (Leica Microsystems' "Ultramicrotome EM UC7"), uniform sections with no holes, etc., and a thickness of 50 nm to 100 nm were cut from this block. The remaining block from which the sections were cut was then used as the measurement sample.

[0092] The indentation hardness of each layer is measured by using the following nanoindenter to press a Berkovich indenter perpendicularly into the center of the cross-section of the layer being measured, in the cross-section obtained by cutting out the above section from the measurement sample. Here, the Berkovich indenter is pressed into the center of the thickness of the layer being measured, at a distance of 300 nm or more from the interface between the layer being measured and the adjacent layer toward the center of the layer being measured. After holding it for a certain period to relax the residual stress, the load is removed and the maximum load after relaxation is measured. Then the maximum load P ｍａｘ and contact projected area A ｐ Using P ｍａｘ / A ｐ Therefore, indentation hardness (H ＩＴ The indentation hardness (H) is calculated. The above contact projection area is the contact projection area obtained by correcting the indenter tip curvature using the Oliver-Pharr method with a standard sample of fused silica (BRUKER's "5-0098"). ＩＴ For each layer, 10 measurements are taken, and the arithmetic mean of these 10 measurements is used. If any of the measurements deviate by more than ±20% from the arithmetic mean, those measurements are excluded and remeasured.

[0093] (Measurement Conditions) ・Apparatus Used: Nanoindenter (Hysitron TI950 TriboIndenter, manufactured by Bruker) ・Indenter Used: Berkovich indenter (triangular pyramid, "TI-0039" manufactured by Bruker) ・Indentation Control Method: Displacement Control Method ・Indentation Depth: 100 nm ・Indentation Speed: 10 nm / second ・Loading Time: 20 seconds ・Holding Time: 5 seconds ・Load Unloading Speed: 10 nm / second ・Unloading Time: 20 seconds ・Measurement Temperature: 25°C

[0094] 2. Second Hard Coat Layer The optical film in this embodiment has a second hard coat layer. The surface of the second hard coat layer on the side opposite to the first hard coat layer side is usually the outermost surface of the optical film.

[0095] (1) Materials The second hard coat layer contains second particles and a binder resin.

[0096] (a) Second Particles The second particles may be either inorganic particles or organic particles. Among them, the second particles are preferably inorganic particles. This is because inorganic particles can provide excellent hardness compared to organic particles.

[0097] The types of inorganic particles used as the second particles are the same as the inorganic particles exemplified for the first particles, so the description here is omitted.

[0098] The average particle diameter D of the second particles ２ may be smaller than the average particle diameter D of the first particles, but it is preferable to satisfy the ratio (D １ / D １ ) of the average particle diameter D of the second particles to the average particle diameter D of the first particles as described above. From the viewpoint of improving hardness, the average particle diameter D of the second particles is preferably 1 nm or more, may be 5 nm or more, may be 7 nm or more, or may be 10 nm or more. If the average particle diameter of the second particles is too small, it is difficult to manufacture the particles, and there is a risk that the particles will easily aggregate. On the other hand, the average particle diameter D of the second particles ２ <0 ２ <0 １ ) of the average particle diameter D of the second particles to the average particle diameter D of the first particles as described above. From the viewpoint of improving hardness, the average particle diameter D of the second particles is preferably 1 nm or more, may be 5 nm or more, may be 7 nm or more, or may be 10 nm or more. If the average particle diameter of the second particles is too small, it is difficult to manufacture the particles, and there is a risk that the particles will easily aggregate. On the other hand, the average particle diameter D of the second particles ２ is preferably 1 nm or more, may be 5 nm or more, may be 7 nm or more, or may be 10 nm or more from the point of view of improving hardness. If the average particle diameter of the second particles is too small, it is difficult to manufacture the particles, and there is a risk that the particles will easily aggregate. On the other hand, the average particle diameter D of the second particles ２From the viewpoint of obtaining flexibility, the particle diameter is, for example, 20 nm or less, preferably 18 nm or less, and may also be 15 nm or less. Average particle diameter D of the second particle ２ If it is within the above range, then the above proportion (D ２ / D １ This makes it easier to satisfy the condition D of the second particle. ２ The wavelength is preferably 1 nm or more and 20 nm or less, preferably 5 nm or more and 20 nm or less, may be 7 nm or more and 18 nm or less, or 10 nm or more and 15 nm or less.

[0099] Here, the average particle diameter of the second particle is measured by cross-sectional observation of the second hard coat layer using an electron microscope. The average particle diameter of the second particle is the average of the particle diameters of 10 arbitrarily selected second particles. The average particle size of the irregularly shaped particle is the average of the maximum (major axis) and minimum (minor axis) distances between two points on the outer circumference of the irregularly shaped particle observed by cross-sectional microscopy of the hard coat layer.

[0100] Content C of the second particle in the second hard coat layer ２ This is the content of the first particle in the first hard coat layer. １ If it is less than that, it is not particularly limited.

[0101] Content C of the second particle in the second hard coat layer ２ The content of the second particle C is preferably 10% by mass or less, may be 7% by mass or less, or 6% by mass or less. ２ If it falls within the above range, good flexibility resistance is likely to be obtained. On the other hand, the content of the second particle in the second hard coat layer C ２ The content of the second particle C is preferably 1% by mass or more, may be 3% by mass or more, or may be 4% by mass or more. ２ If the above range is maintained, the surface hardness of the optical film can be increased even if the substrate thickness is thin to ensure flexibility, compared to the case where particles are contained only in the first hard coat layer. Content C of the second particles in the second hard coat layer ２ The amount is preferably 1% by mass or more and 10% by mass or less, but may also be 3% by mass or more and 7% by mass or less, or 4% by mass or more and 6% by mass or less.

[0102] Content C of the second particle in the second hard coat layer ２ The measurement method is the content of the first particle in the first hard coat layer C １ This is the same measurement method as [another method].

[0103] In calculating the area ratio of the second particle, when selecting and extracting a 1024 x 512 pixel image from the black and white image, although not shown in the diagram, a 1024 x 512 pixel image is selected and extracted from the black and white image from the interface of the second hard coat layer on the first hard coat layer side, and a 1024 x 512 pixel image is also selected and extracted from the interface of the second hard coat layer on the opposite side from the first hard coat layer.

[0104] (b) Binder resin The second hard coat layer includes, for example, a binder resin. Examples of binder resins included in the second hard coat layer include the resins exemplified as binder resins included in the first hard coat layer.

[0105] (c) Additives The second hard coat layer may contain additional additives as needed. Examples of additives include those listed as additives that the first hard coat layer may contain.

[0106] (2) Thickness of the second hard coat layer T ２ The thickness T of the first hard coat layer is １ It is preferable that it be thinner than the second hard coat layer T. ２ The thickness T of the first hard coat layer described above is... １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the sum of the two layers. ２ The proportion (T ２ / (T １ +T ２ It is preferable that the following conditions be met. Also, the thickness T of the second hard coat layer is preferable. ２ Preferably, the distance from the center line in the thickness direction of the optical film to each surface is such that the thickness satisfies (a) to (c) above.

[0107] The thickness of the second hard coat layer is, for example, 1 μm or more, and may be 3 μm or more. On the other hand, the thickness of the second hard coat layer is, for example, 7 μm or less, and may be 5 μm or less, and may be 4 μm or less. The thickness of the second hard coat layer is, for example, 1 μm or more and 7 μm or less, and may be 3 μm or more and 5 μm or less, and may be 3 μm or more and 4 μm or less.

[0108] (3) Formation method The method for forming the second hard coat layer is the same as the method for forming the first hard coat layer.

[0109] (4) Indentation hardness The second hard court layer is less hard than the first hard court layer. That is, the indentation hardness of the second hard court layer is less than that of the first hard court layer. The indentation hardness of the second hard court layer is, for example, 300 MPa or more and 600 MPa or less. The method for measuring the indentation hardness of the second hard court layer is the same as the method for measuring the indentation hardness of the first hard court layer.

[0110] 3. Substrate The substrate in this embodiment is a member that supports the hard coat layer. The substrate is not particularly limited as long as it has flexibility and transparency, and examples include resin substrates and glass substrates.

[0111] (1) Resin base material Examples of resins constituting the resin base material include polyamide resins, polyester resins, cellulose resins, acrylic resins, polyimide resins, and polycarbonate resins. Examples of polyester resins include polyethylene terephthalate (PET), polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate (PEN). Examples of cellulose resins include triacetylcellulose (TAC). Examples of acrylic resins include poly(meth)acrylate and poly(meth)acrylate. Examples of polyimide resins include polyimide, polyamideimide, polyetherimide, and polyesterimide. The base material may be a single layer or a multilayer such as a co-extruded film. Among these, polyimide resins, polyamide resins, polyester resins, and cellulose resins are preferred because they have flexibility and excellent hardness and transparency.

[0112] (2) Glass substrate Examples of glass constituting the glass substrate include silicate glass and silica glass. Among these, borosilicate glass, aluminosilicate glass and aluminoborosilicate glass are preferred, and alkali-free glass is more preferred. Examples of commercially available glass substrates include G-Leaf ultra-thin glass from Nippon Electric Glass Co., Ltd. and ultra-thin glass from Matsunami Glass Industry Co., Ltd.

[0113] Furthermore, it is preferable that the glass constituting the glass substrate is chemically strengthened glass. Chemically strengthened glass is preferable because it has excellent mechanical strength and can be made thinner. Chemically strengthened glass is typically glass whose mechanical properties have been strengthened by a chemical method, such as by partially exchanging ionic species near the surface of the glass, such as replacing sodium with potassium, and has a compressive stress layer on its surface.

[0114] Examples of glass materials that make up chemically strengthened glass substrates include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkali barium glass, and aluminoborosilicate glass.

[0115] Examples of commercially available chemically strengthened glass substrates include Corning's Gorilla Glass, AGC's Dragontrail, and Schott's chemically strengthened glass.

[0116] (3) Thickness The thickness of the substrate is not particularly limited, but it is preferable that the distance from the center line in the thickness direction of the optical film to each surface is such that all of (a) to (c) above are satisfied. The thickness of the substrate may be, for example, 25 μm or more, and may be 50 μm or more. On the other hand, the thickness of the substrate may be, for example, 150 μm or less, and may be 100 μm or less. The thickness of the substrate may be, for example, 25 μm or more, 150 μm or less, 50 μm or more, and 100 μm or less.

[0117] (4) Characteristics When the optical film in this embodiment is used, for example, in a display device, the substrate is preferably transparent. Specifically, the total light transmittance of the substrate is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more. The total light transmittance is measured in accordance with JIS K7361-1:1997. Specifically, the total light transmittance can be measured using a haze meter HM150 manufactured by Murakami Color Technology Laboratory.

[0118] Furthermore, the haze of the substrate is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. The haze is measured in accordance with JIS K-7136:2000. Specifically, the haze can be measured using a haze meter HM150 manufactured by Murakami Color Technology Laboratory.

[0119] 4. Other Layers The optical film in this embodiment may have other layers in addition to the above-described layers, as needed.

[0120] (1) Primer layer As shown in Figure 5(a), the optical film 10A may have a primer layer 3 between the substrate 1 and the hard coat layer 2.

[0121] The material for the primer layer is not particularly limited as long as it can improve the adhesion between the substrate and the hard coat layer, and resins are an example. Examples of resins include (meth)acrylic resins, urethane resins, (meth)acrylic urethane copolymers, vinyl chloride-vinyl acetate copolymer resins, polyesters, butyral resins, chlorinated polypropylene, chlorinated polyethylene, epoxy resins, and silicone resins. These resins may be used individually or in combination of two or more.

[0122] One method for forming the primer layer is to apply the primer layer composition to one side of the substrate. Common application methods include gravure coating, gravure reverse coating, gravure offset coating, spin coating, roll coating, reverse roll coating, blade coating, dip coating, and screen printing. Transfer methods can also be used to form the primer layer.

[0123] The thickness of the primer layer is not particularly limited as long as it is thick enough to improve adhesion between the substrate and the hard coat layer. For example, it may be 0.01 μm or more and 0.5 μm or less, 0.02 μm or more and 0.2 μm or less, or 0.05 μm or more and 0.15 μm or less.

[0124] When the optical film has a primer layer, the "distance from the center line to the substrate-side surface of the first hard coat layer" in condition (c) described above is the distance X3 from the center line N to the interface between the first hard coat layer 21 and the primer layer 3, as shown in Figure 5(a).

[0125] (2) Third hard coat layer As shown in Figure 5(b), the hard coat layer 2 in the optical film 10A may have a third hard coat layer 23 between the first hard coat layer 21 and the second hard coat layer 22.

[0126] The third hard coat layer comprises, for example, third particles and a binder resin. The content of the third particles in the third hard coat layer is C ３ This is the content of the first particle P1 in the first hard coat layer 21.１ It is preferable that the amount is less than the amount of the second particle P2 in the second hard coat layer 22 and greater than the amount of C2. Furthermore, it is preferable that the average particle diameter of the third particle is smaller than the average particle diameter of the first particle and larger than the average particle diameter of the second particle.

[0127] The third particle may be either an inorganic or organic particle. The types of inorganic particles are the same as those exemplified for the first particle, so their explanation is omitted here.

[0128] Examples of binder resins included in the third hard coat layer include those exemplified in the example of binder resins included in the first hard coat layer.

[0129] The thickness of the third hard court layer is preferably thinner than the thickness of the first hard court layer and thicker than the thickness of the second hard court layer.

[0130] When the hard coat layer 2 in the optical film 10A has a third hard coat layer 23, the "distance from the center line to the surface of the first hard coat layer opposite to the substrate side" in the above-described condition (b) is the distance X2 from the center line N to the interface between the third hard coat layer 23 and the first hard coat layer 21, as shown in Figure 5(b).

[0131] III. Characteristics of the Optical Film 1. Flexural Resistance The optical film in this embodiment has flexural resistance. Specifically, in the optical film of this embodiment, it is preferable that no cracks occur in the optical film when a dynamic bending test is performed with a spacing R of 3 mm and the hard coat layer side of the optical film facing inward, and when a dynamic bending test is performed with the hard coat layer side of the optical film facing outward, as described below.

[0132] A dynamic bending test with a spacing R = 3 mm is performed as follows. First, a test piece of optical film measuring 20 mm x 100 mm is prepared. Next, as shown in Figure 6(a), the short side portion 10P of the optical film 10A and the short side portion 10Q opposite to the short side portion 10P are fixed with parallel fixing portions 100A and 100B, respectively. As shown in Figure 6(a), fixing portions 100A and 100B are slidable horizontally. Next, as shown in Figures 6(b) to 6(c), the optical film 10A is bent into a U-shape by moving fixing portions 100A and 100B closer together, and the optical film 10A is folded 180° so that the spacing R between the opposing short sides 10P and 10Q of the optical film 10A is 3 mm. This operation is repeated 200,000 times. After the test, the optical film is observed to check for any cracks. For inward bending, the optical film should be fixed so that the hard coat layer side faces inward when bent, and the above test should be performed. For outward bending, the optical film should be fixed so that the hard coat layer side faces outward when bent, and the above test should be performed.

[0133] <Measurement Conditions> Equipment: DLDMLH-FS manufactured by Yuasa System Equipment Co., Ltd. Test speed: 120 r / min Number of flexions: 200,000 times

[0134] In dynamic bending tests, "cracking" refers to the phenomenon of cracks occurring in the optical film.

[0135] 2. Total Light Transmittance and Haze When the optical film in this embodiment is used in a display device, it is preferable that it be transparent. The total light transmittance of the optical film in this embodiment is preferably 80% or more, more preferably 85% or more, and even more preferably 87% or more. By having such a high total light transmittance, an optical film with good transparency can be made. The total light transmittance is measured in accordance with JIS K7361-1:1997. Specifically, the total light transmittance can be measured using a haze meter HM150 manufactured by Murakami Color Technology Laboratory.

[0136] In this embodiment, the haze of the optical film is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. A low haze level allows for an optical film with good transparency. The haze is measured in accordance with JIS K-7136:2000. Specifically, the haze can be measured using a haze meter HM150 manufactured by Murakami Color Technology Laboratory.

[0137] 3. Warping In this embodiment, it is preferable that the optical film is less warped. Specifically, the amount of warping of the optical film is preferably ±3.0 mm or less, and more preferably ±1.0 mm or less. The amount of warping of the optical film when it warps towards the hard coat layer is represented by "+", and the amount of warping of the optical film when it warps towards the substrate layer is represented by "-".

[0138] The amount of warping is measured by the following method. First, cut the optical film to a size of 50 mm x 50 mm to obtain a test specimen. Next, place the test specimen on a horizontal table with the hard coat layer side facing upwards. Then, measure the amount of warping at each of the four corners of the test specimen. The amount of warping is the distance between the surface of the horizontal table and the corner of the test specimen. The average value of the amount of warping at the four corners of the test specimen is taken as the amount of warping (+) of the optical film. Also, if the test specimen is placed on a horizontal table with the hard coat layer side facing downwards and the same measurement is performed, the average value of the amount of warping at the four corners of the test specimen is taken as the amount of warping (-) of the optical film.

[0139] 4. Yellowness (YI) In this embodiment, it is preferable that the optical film has a yellowness (YI) of less than 3.0. This improves the transparency of the optical film.

[0140] The yellowness (YI) is calculated according to JIS K7373:2006 using a UV-Vis-Near-Infrared spectrophotometer. The transmittance is measured at 1 nm intervals in the range from 250 nm to 800 nm using an auxiliary illuminant C and a 2-degree field of view. The tristimulus values ​​X, Y, and Z in the XYZ color system are determined from these values, and the YI is calculated using the following formula. A JASCO V-7100 can be used as the UV-Vis-Near-Infrared spectrophotometer. YI = 100(1.2769X - 1.0592Z) / Y

[0141] IV. Applications The optical film in this embodiment is used in a display device. In the display device, the optical film is positioned on the observer side of the display panel.

[0142] A2. Optical Film (Second Embodiment) The optical film in this embodiment is an optical film having a substrate and a hard coat layer disposed on one side of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, and of the first hard coat layer and the second hard coat layer, at least the first hard coat layer contains particles, and if the second hard coat layer contains particles, the content of particles in the second hard coat layer is less than the content of particles in the first hard coat layer, and all of the following (a) to (c) are satisfied. (a) The distance from the center line in the thickness direction of the optical film to the side of the second hard coat layer opposite to the side of the first hard coat layer is 31.0 μm or more and 49.5 μm or less. (b) The distance from the center line to the side of the first hard coat layer opposite to the side of the substrate is 28.0 μm or more and 46.5 μm or less. (c) The distance from the center line to the substrate-side surface of the first hard coat layer is 15.5 μm or more and 34.0 μm or less.

[0143] Hereinafter, in this embodiment, particles contained in the first hard coat layer may be referred to as first particles, and particles contained in the second hard coat layer may be referred to as second particles.

[0144] Figure 1 is a schematic cross-sectional view showing an example of an optical film in this embodiment. As shown in Figure 1, the optical film 10B has a substrate 1 and a hard coat layer 2 disposed on one side of the substrate 1. The hard coat layer 2 has a first hard coat layer 21 and a second hard coat layer 22, starting from the substrate 1 side.

[0145] Figures 2 and 7 are schematic cross-sectional views illustrating the particles in the hard coat layer 2 in this embodiment. In the optical film 10B of this embodiment, as shown in Figure 2, the first hard coat layer 21 may contain first particles P1 and the second hard coat layer 22 may contain second particles P2, and as shown in Figure 7, the first hard coat layer 21 may contain first particles P1 and the second hard coat layer 22 may not contain second particles P2. In Figure 2, the content of first particles P1 in the first hard coat layer 21 is greater than the content of second particles P2 in the second hard coat layer 22. In Figure 7, since the particle content in the second hard coat layer 22 is zero, it can be said that the particle content in the first hard coat layer 21 is greater than the particle content in the second hard coat layer 22.

[0146] In the optical film of this embodiment, of the first and second hard coat layers, at least the first hard coat layer contains particles. On the other hand, the second hard coat layer does not contain particles, or if the second hard coat layer contains particles, the particle content in the second hard coat layer is less than the particle content in the first hard coat layer. As a result, the first hard coat layer located on the inside is harder than the second hard coat layer located on the outside, thereby ensuring the surface hardness of the optical film.

[0147] On the other hand, the optical film placed on the surface of a flexible display requires flexibility to prevent cracking when repeatedly bent. Specifically, bending tests of the optical film require bending resistance that can withstand both inward and outward bending. If the surface hardness of the optical film is high, cracking of the hard coat layer is more likely to occur when bent, and the flexibility tends to decrease.

[0148] In contrast, in this embodiment, the outer second hard coat layer does not contain particles, or if the second hard coat layer contains particles, the amount of second particles in the second hard coat layer is less than the amount of particles in the inner first hard coat layer. Therefore, the second hard coat layer is less hard than the first hard coat layer. As a result, cracking of the hard coat layer lamination can be suppressed during bending, and bending resistance can be improved.

[0149] Figure 3 is a schematic diagram showing the state of the bent portion of an optical film when it is bent at a distance R during a bending test. As shown in Figure 3(a), in the case of outward bending, where the surface S on the hard coat layer 2 side is facing outward, the surface S of the optical film 10A facing the hard coat layer 2 stretches relative to the center line N in the thickness direction of the optical film 10A, and tensile stress is generated. On the other hand, as shown in Figure 3(b), in the case of inward bending, where the surface S on the hard coat layer 2 side is facing inward, the surface S of the optical film 10A facing the hard coat layer 2 shrinks relative to the center line N, and compressive stress is generated. Thus, when an optical film is bent, the surface of the optical film is either stretched or compressed relative to the center line in the thickness direction of the optical film. Generally, the further away from the center line, the greater the compressive and tensile stress, while the closer to the center line, the smaller the compressive and tensile stress. Therefore, the surface S of the optical film facing the hard coat layer 2 is the furthest from the center line N, and thus experiences the maximum compressive or tensile stress.

[0150] As described above, the first hard coat layer located on the inside is harder. The second hard coat layer located on the outside is less hard than the first hard coat layer. By keeping the distance X1 from the center line N to the surface S1 of the relatively less hard second hard coat layer 22 within a predetermined range, it is possible to suppress excessive compressive and tensile stress at surface S1 of the second hard coat layer 22 during bending. Therefore, cracking of the second hard coat layer 22 becomes less likely. Furthermore, by keeping the distance X2 from the center line N to the surface S2 of the harder first hard coat layer 21 within a predetermined range, it is possible to reduce compressive and tensile stress at surface S2 of the first hard coat layer 21 during bending. Therefore, cracking of the first hard coat layer 21 becomes less likely. Thus, cracking of the hard coat layers can be suppressed.

[0151] In this embodiment, the center line N is located inside the substrate 1. Generally, the thicker the hard coat layer, the higher the surface hardness and the lower the bending resistance tends to be. By keeping the distance X3 from the center line N to the surface S3 of the first hard coat layer 21 below a predetermined value, the center line N is located further inside the substrate 1, so the thickness of the hard coat layer 2 does not become excessively thick, and bending resistance can be improved. On the other hand, by keeping the distance X3 from the center line N to the surface S3 of the first hard coat layer 21 above a predetermined value, the thickness of the hard coat layer becomes relatively thick, making it easier to obtain high surface hardness.

[0152] Therefore, in this embodiment, it is possible to improve both surface hardness and flexibility. In other words, the optical film in this embodiment can achieve both sufficiently high surface hardness for an optical film placed on the surface of a display device and sufficiently high flexibility for an optical film placed on the surface of a flexible display. For example, it is possible to simultaneously achieve a surface hardness of 6H or higher on the pencil hardness scale and flexibility when a dynamic bending test is performed with a spacing R = 3 mm, as will be described later.

[0153] I. Characteristics of the Hard Coat Layer The optical film in this embodiment has a hard coat layer on one side of the substrate. The hard coat layer 2 has a first hard coat layer 21 and a second hard coat layer 22, starting from the substrate 1 side. Of the first and second hard coat layers, at least the first hard coat layer contains particles.

[0154] In this embodiment, the hard coat layer is a component for increasing surface hardness. The presence of the hard coat layer improves scratch resistance.

[0155] In this embodiment, the pencil hardness of the hard coat layer side surface of the optical film is preferably 6H or higher, and more preferably 7H or higher. Such an optical film will have sufficient surface hardness to be placed on the surface of a display device.

[0156] 1. Particle Content In this embodiment, of the first hard coat layer and the second hard coat layer, at least the first hard coat layer contains particles. The first hard coat layer may contain first particles and the second hard coat layer may contain second particles, or the first hard coat layer may contain first particles and the second hard coat layer may not contain second particles.

[0157] If the second hard coat layer contains particles, the particle content in the second hard coat layer is less than the particle content in the first hard coat layer. As a result, the first hard coat layer 21 becomes harder, thus ensuring the surface hardness of the optical film. On the other hand, the second hard coat layer 22 is less hard than the first hard coat layer 21, so when the optical film is bent, it functions as a protective member that suppresses cracking of the first hard coat layer 21, thereby suppressing cracking of the hard coat layer.

[0158] Content C of the first particle P1 in the first hard coat layer 21 １ and the content of the second particle P2 in the second hard coat layer 22 ２ The specific values ​​will be discussed later.

[0159] 2. Distance from the center line As shown in Figure 4, the optical film 10B in this embodiment satisfies all of the following (a) to (c): (a) Thickness direction D of the optical film 10B Ｔ (b) The distance X1 from the center line N to the surface S1 of the second hard coat layer 22 opposite to the first hard coat layer 21 is 31.0 μm or more and 49.5 μm or less. (b) The distance X2 from the center line N to the surface S2 of the first hard coat layer 21 opposite to the substrate 1 is 28.0 μm or more and 46.5 μm or less. (c) The distance X3 from the center line N to the surface S3 of the first hard coat layer 21 on the substrate side 3 is 15.5 μm or more and 34.0 μm or less.

[0160] The distances X1 to X3 described above are the same as those described in the first embodiment.

[0161] 3. Average particle diameter In this embodiment, when the first hard coat layer contains first particles and the second hard coat layer contains second particles, it is preferable that the average particle diameter of the first particles P1 is larger than the average particle diameter of the second particles P2. This makes the first hard coat layer 21 harder, thus ensuring the surface hardness of the optical film. On the other hand, although the second hard coat layer 22 is a layer for increasing surface hardness, it is not as hard as the first hard coat layer 21. Therefore, when the optical film is bent, it functions as a protective member that suppresses cracking of the first hard coat layer 21, thereby suppressing cracking of the hard coat layer.

[0162] Average particle diameter D of the first particle １ The average particle diameter D of the second particle relative to ２ The proportion (D ２ / D １ ), and the average particle diameter D of the first particle １ and the average particle diameter D of the second particle ２ The specific values ​​are the same as those described in the first embodiment above.

[0163] II. Layer Structure 1. First Hard Coat Layer The first hard coat layer contains first particles and a binder resin. The material, thickness, and formation method of the first hard coat layer are the same as those of the first hard coat layer in the first embodiment described above, so a detailed explanation is omitted here.

[0164] 2. Second Hard Coat Layer The second hard coat layer contains a binder resin. The second hard coat layer may or may not contain particles. In particular, it is preferable that the second hard coat layer contains particles. Compared to the case where particles are contained only in the first hard coat layer, the surface hardness of the optical film can be increased even if the thickness of the substrate is thin in order to ensure flexibility.

[0165] The material, thickness, and formation method of the second hard coat layer are the same as those of the second hard coat layer in the first embodiment described above, so a detailed explanation is omitted here.

[0166] Here, "the second hard coat layer does not contain particles" means that the particle content in the second hard coat layer is 0.5% by mass or less. If the second hard coat layer does not contain particles, the particle content in the second hard coat layer may be 0.3% by mass or less, or it may be 0% by mass.

[0167] Content C of the second particle in the second hard coat layer ２ The content of the second particle C is preferably 10% by mass or less, and may be 7% by mass or less. ２ If it falls within the above range, good flexibility resistance is likely to be obtained. On the other hand, the content of the second particle in the second hard coat layer C ２ It is 0% by mass or more. In particular, the content of the second particle in the second hard coat layer is C ２ The content of the second particle C is preferably 1% by mass or more, may be 3% by mass or more, or may be 5% by mass or more. ２ If the above range is maintained, the surface hardness of the optical film can be increased even if the substrate thickness is thin to ensure flexibility, compared to the case where particles are contained only in the first hard coat layer. Content C of the second particles in the second hard coat layer ２ The amount is 0% by mass or more and 10% by mass or less, preferably 1% by mass or more and 10% by mass or less, and may be 3% by mass or more and 10% by mass or less, or 5% by mass or more and 7% by mass or less.

[0168] 3. Substrate The substrate in this embodiment is the same as the substrate in the first embodiment described above, so its explanation is omitted here.

[0169] 4. Other Layers The optical film in this embodiment may have other layers in addition to the above-described layers, as needed.

[0170] As shown in Figure 5(a), the optical film 10B may have a primer layer 3 between the substrate 1 and the hard coat layer 2. The primer layer is the same as the primer layer in the first embodiment described above, so its explanation is omitted here.

[0171] As shown in Figure 5(b), the hard coat layer 2 in the optical film 10B may have a third hard coat layer 23 between the first hard coat layer 21 and the second hard coat layer 22. The third hard coat layer is the same as the third hard coat layer in the first embodiment described above, so its explanation is omitted here.

[0172] III. Characteristics and Applications of the Optical Film The characteristics and applications of the optical film in this embodiment are the same as those of the optical film in the first embodiment described above, so a detailed explanation is omitted here.

[0173] B. Display device The display device in this disclosure comprises a display panel and the optical film described above, which is positioned on the observer side of the display panel.

[0174] Figure 8 is a schematic cross-sectional view showing an example of a display device in this disclosure. As shown in Figure 8, the display device 30 comprises a display panel 31 and an optical film 10 disposed on the observer side of the display panel 31. The optical film 10 is either the optical film 10A of the first embodiment or the optical film 10B of the second embodiment described above. In the display device 30, the optical film 10 is used as a component disposed on the surface of the display device 30, and an adhesive layer 32 is disposed between the optical film 10 and the display panel 31. As the adhesive layer, a known adhesive layer used for bonding optical films can be used.

[0175] The optical film in this disclosure is the same as the optical film described above. The optical film is arranged so that the substrate-side surface faces the display panel. The method of arranging the optical film on the surface of the display device is not particularly limited and includes, for example, a method using an adhesive layer.

[0176] Examples of display panels in this disclosure include display panels used in display devices such as liquid crystal displays, organic EL displays, and LED displays.

[0177] The display device in this disclosure may have a touch panel member between the display panel and the optical film.

[0178] Furthermore, the display device in this disclosure may have a second optical film disposed on the display panel side of the optical film or on the side of the optical film opposite to the display panel. The second optical film has a second substrate and a functional layer disposed on one side of the second substrate. The functional layer may be a single layer or may have multiple layers. The functional layer may also be a layer having a single function or may have multiple layers having different functions. Examples of functional layers constituting the second optical film disposed on the display panel side of the optical film include a shatterproof layer and an impact-absorbing layer. Examples of functional layers constituting the second optical film disposed on the side of the optical film opposite to the display panel include an anti-glare layer, a protective layer and an anti-fouling layer.

[0179] The display device in this disclosure is preferably a flexible display such as a foldable display, a rollable display, or a bendable display. Among these, the display device in this disclosure is more preferably a foldable display. Because the display device in this disclosure has the optical film described above, it has excellent surface hardness and bending resistance, making it suitable as a flexible display, and even more so as a foldable display.

[0180] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure.

[0181] The present disclosure will be further explained below with reference to examples and comparative examples.

[0182] [Example 1] A polyimide film with a thickness of 80 μm was prepared as a substrate. The following primer layer composition was applied to one side of the substrate so that the film thickness after drying was 0.1 μm, and it was dried at 120°C for 30 seconds to form a primer layer with a thickness of 0.1 μm.

[0183] <Composition for Primer Layer> - Amorphous polyester (product name "Byron 63SS", manufactured by Toyobo Co., Ltd.): 3.85 parts by mass (calculated as 100% solids) - Zirconium oxide (average particle size 20 nm, manufactured by CIK Nanotech): 1.15 parts by mass (calculated as 100% solids) - Methyl isobutyl ketone: 95 parts by mass The above "calculated as 100% solids" refers to the value when the solids content in the solvent-diluted product is considered to be 100%.

[0184] On the above primer layer, the following curable resin composition for the first hard coat layer is applied, with a cured thickness T １ The mixture was applied to the thickness shown in Table 1, dried at 70°C for 1 minute, and then irradiated at a dose of 200 mJ / cm². ２ The material was cured by irradiation with ultraviolet light to form the first hard coat layer. The average particle size and particle content in the first hard coat layer were prepared to the values ​​shown in Table 1 below.

[0185] <Curable resin composition for the first hard coat layer> - 40% by mass methyl isobutyl ketone solution of a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate: 75 parts by mass of solids - Silica fine particles (manufactured by Nissan Chemical, MIBK-SD-L, methyl isobutyl ketone dispersed silica sol, SiO ２ 30% by mass: 20 parts by mass of solids; 1-hydroxycyclohexylphenyl ketone (BASF, Irgacure 184): 5 parts by mass of solids

[0186] Next, the following curable resin composition for the second hard coat layer is applied to the obtained first hard coat layer, with a cured thickness T. ２ The mixture was applied to the thickness shown in Table 1, dried at 70°C for 1 minute, and then irradiated at a dose of 200 mJ / cm². ２ The material was cured by irradiation with ultraviolet light to form a second hard coat layer. The average particle size and particle content in the second hard coat layer were prepared to match the values ​​shown in Table 1 below.

[0187] <Curable resin composition for the second hard coat layer> - 40% by mass methyl isobutyl ketone solution of a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (manufactured by Toagosei): 94 parts by mass of solids - Silica fine particles (manufactured by Nissan Chemical, MIBK-AC-2140Z, methyl isobutyl ketone dispersed silica sol, SiO ２ 40% by mass: 1 part by mass of solids; 1-hydroxycyclohexylphenyl ketone (BASF, Irgacure 184): 5 parts by mass of solids

[0188] This resulted in an optical film having a substrate, a primer layer, a first hard coat layer, and a second hard coat layer in that order. Average particle size D of the first particle. １ The average particle diameter D of the second particle relative to ２ The proportion (D ２ / D １ ) and the thickness T of the first hard coat layer １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the sum of the two layers. ２ The proportion (T ２ / (T １ +T ２ Table 1 shows the distances X1 to X3 from the center line to each surface in the thickness direction of the optical film.

[0189] [Examples 2-24] Curable resin compositions for the first hard coat layer and the second hard coat layer were prepared such that the average particle diameter and content of the first particles in the first hard coat layer, and the average particle diameter and content of the second particles in the second hard coat layer, were as shown in Table 1. The curable resin composition for the first hard coat layer was then cured to a thickness T. １ The coating is applied to the thickness shown in Table 1, and the curable resin composition for the second hard coat layer is cured to a thickness T. ２ An optical film was manufactured in the same manner as in Example 1, except that the coating was applied to the thickness shown in Table 1.

[0190] [Examples 25-48] Curable resin compositions for the first hard coat layer and the second hard coat layer were prepared such that the average particle size and content of the first particles in the first hard coat layer, and the average particle size and content of the second particles in the second hard coat layer, were as shown in Table 2. A polyimide film with a thickness of 50 μm was used as the substrate, and the curable resin composition for the first hard coat layer was cured to a thickness T １ The coating is applied to the thickness shown in Table 2, and the curable resin composition for the second hard coat layer is cured to a thickness T. ２ An optical film was manufactured in the same manner as in Example 1, except that the coating was applied to the thickness shown in Table 2.

[0191] [Comparative Examples 1-20] Curable resin compositions for the first hard coat layer and the second hard coat layer were prepared such that the average particle diameter and content of the first particles in the first hard coat layer, and the average particle diameter and content of the second particles in the second hard coat layer, were as shown in Table 3. The curable resin composition for the first hard coat layer was then cured to a thickness T. １ The coating is applied to the thickness shown in Table 3, and the curable resin composition for the second hard coat layer is cured to a thickness T. ２ An optical film was manufactured in the same manner as in Example 1, except that the coating was applied to the thickness shown in Table 3.

[0192] [Comparative Examples 21-40] Curable resin compositions for the first hard coat layer and the second hard coat layer were prepared such that the average particle diameter and content of the first particles in the first hard coat layer, and the average particle diameter and content of the second particles in the second hard coat layer, were as shown in Table 4. The curable resin composition for the first hard coat layer was then cured to a thickness T. １ The coating is applied to the thickness shown in Table 4, and the curable resin composition for the second hard coat layer is cured to a thickness T. ２ An optical film was manufactured in the same manner as in Example 25, except that the coating was applied to the thickness shown in Table 4.

[0193]

[0194]

[0195]

[0196]

[0197] [Evaluation] (1) Pencil hardness In accordance with JIS K5600-5-4:1999, the pencil hardness of the surface on the hard coat layer side of the optical film was measured using a pencil hardness tester (Toyo Seiki Seisakusho Co., Ltd. "Pencil scratch coating hardness tester (electric type)"). The measurement conditions were an angle of 45°, a load of 750g, a speed of 1 mm / sec, and a temperature of 23±2℃. The results are shown in Tables 5 to 8.

[0198] (2) Dynamic bending test The bending resistance of the optical film was evaluated by performing the dynamic bending test described above on the obtained optical film. For inward bending, the optical film was bent at an interval of R = 3 mm so that the hard coat layer side was on the inside and the substrate side was on the outside, and the test of folding the optical film 200,000 times was repeated. Similarly, for outward bending, the optical film was bent at an interval of R = 3 mm so that the hard coat layer side was on the outside and the substrate side was on the inside, and the test of folding the optical film 200,000 times was repeated. The evaluation was "A" if no cracking occurred and "B" if cracking occurred. The results are shown in Tables 5 to 8.

[0199]

[0200]

[0201]

[0202]

[0203] As shown in Tables 5 and 6, the optical films in this disclosure (Examples 1 to 48) were confirmed to simultaneously achieve a surface hardness of 6H or higher on the pencil hardness scale, and a bending resistance of 200,000 cycles in dynamic bending tests with an R=3 mm gap for both inward and outward bending. On the other hand, as shown in Tables 7 and 8, the comparative examples were found not to be able to simultaneously achieve the above surface hardness and bending resistance.

[0204] In other words, the present disclosure provides the following inventions.

[0205] [1] An optical film having a substrate and a hard coat layer disposed on one surface of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, the first hard coat layer contains first particles, the second hard coat layer contains second particles, the content of the first particles in the first hard coat layer is greater than the content of the second particles in the second hard coat layer, and the average particle diameter of the first particles is greater than the average particle diameter of the second particles.

[0206] [2] Thickness T of the second hard coat layer ２ However, the thickness T of the first hard coat layer mentioned above １ A thinner optical film than the one described in [1].

[0207] [3] Thickness T of the first hard coat layer １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the sum of the above. ２ The proportion (T ２ / (T １ +T ２ The optical film according to [1] or [2], wherein the ratio is 0.10 or more and 0.25 or less.

[0208] [4] Average particle diameter D of the first particle described above １The average particle diameter D of the second particle mentioned above ２ The proportion (D ２ / D １ An optical film according to any of [1] to [3], wherein the coefficient of the ion is 0.02 or greater and 0.75 or less.

[0209] [5] The optical film according to any one of [1] to [4], wherein the content of the first particles in the first hard coat layer is 20% by mass or more and 45% by mass or less, and the content of the second particles in the second hard coat layer is 1.0% by mass or more and 10% by mass or less.

[0210] [6] An optical film according to any of [1] to [5] that satisfies all of the following (a) to (c): (a) The distance from the center line in the thickness direction of the optical film to the side of the second hard coat layer opposite to the side of the first hard coat layer is 31.0 μm or more and 49.5 μm or less. (b) The distance from the center line to the side of the first hard coat layer opposite to the side of the substrate is 28.0 μm or more and 46.5 μm or less. (c) The distance from the center line to the side of the first hard coat layer on the substrate is 15.5 μm or more and 34.0 μm or less.

[0211] [7] An optical film having a substrate and a hard coat layer disposed on one side of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, and of the first hard coat layer and the second hard coat layer, at least the first hard coat layer contains particles, and if the second hard coat layer contains the particles, the content of the particles in the second hard coat layer is less than the content of the particles in the first hard coat layer, and all of the following (a) to (c) are satisfied. (a) The distance from the center line in the thickness direction of the optical film to the side of the second hard coat layer opposite to the side of the first hard coat layer is 31.0 μm or more and 49.5 μm or less. (b) The distance from the center line to the side of the first hard coat layer opposite to the side of the substrate is 28.0 μm or more and 46.5 μm or less. (c) The distance from the center line to the substrate-side surface of the first hard coat layer is 15.5 μm or more and 34.0 μm or less.

[0212] [8] Thickness T of the first hard coat layer １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the sum of the above. ２ The proportion (T ２ / (T １ +T ２ The optical film described in [7], wherein the ratio is 0.10 or more and 0.25 or less.

[0213] [9] An optical film used in a flexible display, as described in any of [1] to [8].

[0214]

[10] A display device comprising a display panel and an optical film according to any one of [1] to [9], which is positioned on the observer side of the display panel.

[0215] 1… Substrate 2… Hard coat layer 21… First hard coat layer 22… Second hard coat layer 3… Primer layer 10… Optical film 30… Display device 31… Display panel

Claims

1. An optical film having a substrate and a hard coat layer disposed on one surface of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, the first hard coat layer contains first particles, the second hard coat layer contains second particles, the content of the first particles in the first hard coat layer is greater than the content of the second particles in the second hard coat layer, and the average particle diameter of the first particles is greater than the average particle diameter of the second particles.

2. Thickness T of the second hard coat layer ２ However, the thickness T of the first hard coat layer １ The optical film according to claim 1, which is thinner than the optical film described in claim 1.

3. Thickness T of the first hard coat layer １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the total ２ The proportion (T ２ / (T １ +T ２ The optical film according to claim 1, wherein the coefficient of 4. The average particle diameter D of the first particles １ with respect to the average particle diameter D of the second particles ２ ratio (D ２ / D １ ) is 0.02 or more and 0.75 or less. The optical film according to claim 1.

5. The optical film according to claim 1, wherein the content of the first particles in the first hard coat layer is 20% by mass or more and 45% by mass or less, and the content of the second particles in the second hard coat layer is 1.0% by mass or more and 10% by mass or less.

6. The optical film according to claim 1, satisfying all of the following (a) to (c): (a) The distance from the center line in the thickness direction of the optical film to the surface of the second hard coat layer opposite to the first hard coat layer is 31.0 μm or more and 49.5 μm or less. (b) The distance from the center line to the surface of the first hard coat layer opposite to the substrate side is 28.0 μm or more and 46.5 μm or less. (c) The distance from the center line to the substrate side surface of the first hard coat layer is 15.5 μm or more and 34.0 μm or less.

7. An optical film having a substrate and a hard coat layer disposed on one side of the substrate, wherein the hard coat layer has a first hard coat layer and a second hard coat layer from the substrate side, and of the first and second hard coat layers, at least the first hard coat layer contains particles, and if the second hard coat layer contains particles, the content of particles in the second hard coat layer is less than the content of particles in the first hard coat layer, and all of the following (a) to (c) are satisfied: (a) The distance from the center line in the thickness direction of the optical film to the side of the second hard coat layer opposite to the side of the first hard coat layer is 31.0 μm or more and 49.5 μm or less. (b) The distance from the center line to the side of the first hard coat layer opposite to the side of the substrate is 28.0 μm or more and 46.5 μm or less. (c) The distance from the center line to the substrate-side surface of the first hard coat layer is 15.5 μm or more and 34.0 μm or less.

8. Thickness T of the first hard coat layer １ and the thickness T of the second hard coat layer ２ The thickness T of the second hard coat layer relative to the total ２ The proportion (T ２ / (T １ +T ２ The optical film according to claim 7, wherein the coefficient of 9. The optical film according to claim 1, used in a flexible display.

10. A display device comprising: a display panel; and an optical film according to any one of claims 1 to 9, disposed on the observer side of the display panel.

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