Resin layer, optical film, and image display device

Abstract

To provide a resin layer of an optical film for use in a foldable image display device, the resin layer having superior impact resistance, and having superior foldability not only in a room temperature environment but also in a low temperature environment.SOLUTION: A resin layer for use in an image display device is characterized in that the shear storage elastic modulus G' within a frequency range of 500 Hz to 1000 Hz at 25°C is 30 MPa or more and 200 MPa or less, and the glass transition temperature of the resin layer is 50°C or more.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a resin layer, an optical film, and an image display device. [Background technology]

[0002] While image display devices such as smartphones and tablet devices have been known for some time, development of foldable image display devices is currently underway. Typically, smartphones and tablet devices are covered with cover glass, but while glass is generally hard, it is not flexible. Therefore, if cover glass is used in an image display device, there is a high risk of it breaking when attempting to fold it. For this reason, the use of an optical film made of resin instead of cover glass is being considered for foldable image display devices (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-125063 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Optical films used in such foldable image display devices require impact resistance because their surfaces may be subjected to impacts. When an impact is applied to the surface of an optical film, the surface may become dented. Therefore, there is currently a need for impact resistance that suppresses denting of the film surface when an impact is applied to the optical film surface.

[0005] However, in the case of optical films, the current situation is that impact resistance that suppresses dents on the surface of the film when an impact is applied to the surface of the optical film has not been achieved.

[0006] In addition, in an image display device, it is necessary to consider use in various environments. Specifically, for example, not only in a room temperature (e.g., 23°C) environment but also in a low temperature (e.g., -40°C) environment. Therefore, for the optical film used in the image display device, it is necessary to consider use not only in a room temperature environment but also in a low temperature environment.

[0007] However, even for an optical film that does not crack in a folding test in a room temperature environment, when a folding test is performed in a low temperature environment, there is a risk of cracking because the flexibility is impaired.

[0008] The present invention has been made to solve the above problems. That is, an object of the present invention is to provide a resin layer having good impact resistance and good folding properties not only in a room temperature environment but also in a low temperature environment, an optical film provided with the same, and an image display device.

Means for Solving the Problems

[0009] The present invention includes the following inventions. [1] A resin layer used in an image display device, wherein the shear storage modulus G' in the resin layer in the frequency range of 500 Hz or more and 1000 Hz or less at 25°C is 30 MPa or more and 200 MPa or less, and the glass transition temperature of the resin layer is 50°C or more.

[0010] [2] The resin layer according to [1] above, having a film thickness of 20 μm or more and 150 μm or less.

[0011] [3] A foldable laminated optical film comprising at least the resin layer according to [1] or [2] above.

[0012] [4] The optical film according to [3] above, further comprising a functional layer provided on one surface side of the resin layer.

[0013] [5] The optical film according to [3] or [4] above, further comprising a resin substrate provided on one surface side of the resin layer.

[0014] [6] In the optical film, when a test of folding 180° is repeated 100,000 times in an environment of 23°C such that the distance between the opposing side portions of the optical film becomes 10 mm, no cracking or breakage occurs. The optical film according to any one of [3] to [5] above.

[0015] [7] In the optical film, when a test of folding 180° is repeated 100,000 times in an environment of -40°C such that the distance between the opposing side portions of the optical film becomes 10 mm, no cracking or breakage occurs. The optical film according to [6] above.

[0016] [8] An image display device including a display element and the resin layer according to [1] or [2] above disposed on the observer side of the display element, or the optical film according to any one of [3] to [7] above.

[0017] [9] The image display device according to [8] above, wherein the display element is an organic light-emitting diode element. [Effect of the Invention]

[0018] [[ID=z2]] According to the present invention, it is possible to provide a resin layer having good impact resistance and good folding properties not only in a room temperature environment but also in a low temperature environment, an optical film including the same, and an image display device. [Brief Description of the Drawings]

[0019] [Figure 1] FIG. 1 is a schematic configuration diagram of a resin layer according to an embodiment. [Figure 2] FIG. 2 is a schematic configuration diagram of a solid shear jig used when measuring the shear storage modulus G' and the glass transition temperature Tg. [Figure 3] FIG. 3 is a schematic configuration diagram of an optical film according to an embodiment. [Figure 4]Figures 4(A) to 4(C) schematically illustrate the process of a continuous folding test. [Figure 5] Figure 5 is a schematic diagram of another optical film according to the embodiment. [Figure 6] Figure 6 is a schematic diagram of the image display device according to the embodiment. [Modes for carrying out the invention]

[0020] Hereinafter, a resin layer, an optical film, and an image display device according to embodiments of the present invention will be described with reference to the drawings. In this specification, terms such as "film" and "sheet" are not distinguished from each other solely on the basis of differences in name. Therefore, for example, "film" is used to include components that may also be called sheets. Figure 1 is a schematic diagram of the resin layer according to this embodiment, Figure 2 is a schematic diagram of a solid shearing jig used when measuring the shear storage modulus G' and the glass transition temperature Tg, Figure 3 is a schematic diagram of the optical film according to this embodiment, Figures 4(A) to 4(C) are schematic diagrams showing the continuous folding test, and Figure 5 is a schematic diagram of another optical film according to this embodiment.

[0021] <<<Resin layer>>> The resin layer 10 shown in Figure 1 is used in an image display device. In this specification, "resin layer" refers to a single-layer structure containing resin. The resin layer 10 is made of a light-transmitting resin and is a shock-absorbing layer. The resin layer 10 may be used on its own, or it may be incorporated into an optical film 30 in which a functional layer 31 (described later) is laminated to the resin layer 10, or into an optical film 50 equipped with a resin substrate 51 (described later). Furthermore, a release film may be attached to the resin layer 10.

[0022] In the resin layer 10, the shear storage modulus G' in the frequency range of 500 Hz to 1000 Hz at 25°C is 30 MPa to 200 MPa. If the shear storage modulus G' of the resin layer 10 is 30 MPa or higher, deformation of the surface of the resin layer 10 when an impact is applied to the surface of the resin layer 10 can be suppressed, and the decrease in hardness of the resin layer 10 can also be suppressed. Furthermore, if the shear storage modulus G' of the resin layer 10 is 200 MPa or lower, the resin layer 10 is less likely to crack when folded at room temperature. From the viewpoint of further suppressing deformation of the surface of the resin layer 10 when an impact is applied to the surface of the resin layer 10, and further suppressing the decrease in hardness of the resin layer 10, the lower limit of the shear storage modulus G' of the resin layer 10 is preferably 40 MPa or higher, 50 MPa or higher, or 80 MPa or higher. The upper limit of the shear storage modulus G' of the resin layer 10 is preferably 190 MPa or less, 180 MPa or less, or 150 MPa or less.

[0023] The shear storage modulus G' can be measured using a dynamic viscoelasticity analyzer (DMA). When measuring the shear storage modulus G' of the resin layer 10 using a dynamic viscoelasticity analyzer (DMA), first, the resin layer 10 is punched out in a 10mm x 5mm rectangular shape to obtain a sample S1 (see Figure 2). Two of these samples S1 are then prepared and attached to a solid shearing jig, which is an option for the dynamic viscoelasticity analyzer (for example, product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, as shown in Figure 2, the solid shearing jig 20 consists of a single 1mm thick metal solid shearing plate 21 (middle plate) and two L-shaped brackets 22 (outer plates) positioned on both sides of the solid shearing plate 21. One sample S is sandwiched between the solid shearing plate 21 and one L-shaped bracket 22, and the other sample S1 is sandwiched between the solid shearing plate 21 and the other L-shaped bracket 22. Then, the L-shaped brackets 22 are tightened with screws 23 to fix the sample S1. Next, a tensile test chuck consisting of an upper chuck and a lower chuck is attached to the dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.), and then a solid shearing jig is attached between the upper and lower chucks with a distance of 20 mm between the chucks. The distance between the chucks is the distance between the upper and lower chucks. The set temperature is 25°C and the temperature is raised at 2°C / min. In this state, while fixing the solid shear plate 21, the two L-shaped brackets 22 are subjected to longitudinal vibration with a strain of 1% and a frequency in the range of 500 Hz to 1000 Hz, and the dynamic viscoelasticity measurement of the solid at 25°C is performed to measure the shear storage modulus G' of the resin layer 10. Here, the shear storage modulus G' of the resin layer 10 in the frequency range of 500 Hz to 1000 Hz is determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to the L-shaped fitting 22, measuring the shear storage modulus G' of the resin layer 10 at each frequency, calculating the arithmetic mean of these shear storage moduli G', repeating this measurement three times, and then taking the arithmetic mean of the three obtained values. The reason for specifying the frequency range of 500 Hz to 1000 Hz above is that the frequencies in this range are those at which the surface of the resin layer 10 deforms by several microns to tens of microns when an object is dropped from a height of several tens of centimeters.

[0024] The glass transition temperature Tg of the resin layer 10 is 50°C or higher. If the glass transition temperature Tg of the resin layer 10 is 50°C or higher, the state of the resin layer 10 does not change even at room temperature (e.g., 23°C) and low temperatures (e.g., -40°C), so good foldability can be maintained. The lower limit of the glass transition temperature Tg of the resin layer 10 may be 53°C or higher, 55°C or higher, or 60°C or higher. Furthermore, the upper limit of the glass transition temperature Tg of the resin layer 10 may be 90°C or lower from the viewpoint of ensuring impact resistance.

[0025] The glass transition temperature Tg can be measured using a dynamic viscoelasticity analyzer (DMA). When measuring the glass transition temperature Tg of the resin layer 10 using a dynamic viscoelasticity analyzer (DMA), first, the resin layer 10 is punched out in a 10 mm x 5 mm rectangular shape to obtain a sample S1. Two of these samples are prepared and attached to a solid shearing jig, which is an option for the dynamic viscoelasticity analyzer (for example, product name "Rheogel-E4000", manufactured by UBM Co., Ltd.), in the same way as the shear storage modulus G'. The temperature is then set to -50°C and raised at a rate of 2°C / min. In this state, while fixing the solid shearing plate, longitudinal vibrations are applied to two L-shaped brackets 22 with a strain of 1% and a frequency in the range of 500 Hz to 1000 Hz, and the dynamic viscoelasticity of the solid is measured every 0.5°C, and the shear loss tangent tanδ (shear loss modulus G'' / shear storage modulus G') of the resin layer 10 is measured. Next, the peak of the shear loss tangent tanδ is determined, and the temperature at which this peak is detected is defined as the glass transition temperature Tg. This measurement is repeated three times, and the arithmetic mean of the three values ​​obtained is then arithmetic mean again to determine the glass transition temperature Tg.

[0026] Furthermore, as will be described later, even when measuring the shear storage modulus G' and glass transition temperature Tg of an optical film 30 in which a functional layer 31 is laminated on a resin layer 10, if the resin layer 10 is softer than the functional layer 31, the shear storage modulus G' and glass transition temperature Tg of the optical film 30 can be considered as the shear storage modulus G' and glass transition temperature Tg of the resin layer 10. Whether or not the resin layer 10 is softer than the functional layer 31 will be determined from the amount of displacement described later.

[0027] If another film, such as a polarizing plate, is attached to one side of the resin layer 10 via an adhesive or bonding layer, the shear storage modulus G' and glass transition temperature should be measured after peeling off the other film along with the adhesive or bonding layer. The other film can be peeled off, for example, as follows: First, the laminate with the other film attached to the resin layer 10 via an adhesive or bonding layer is heated with a dryer, and the tip of a cutter blade is inserted into the area that is thought to be the interface between the resin layer 10 and the other film, and the peeling is slowly carried out. By repeating this heating and peeling process, the adhesive or bonding layer and the other film can be peeled off. Note that even if such a peeling process is performed, it will not have a significant impact on these measurements.

[0028] The thickness of the resin layer 10 is preferably 20 μm or more and 150 μm or less. If the thickness of the resin layer 10 is 20 μm or more, excellent impact resistance can be obtained, and if the thickness of the resin layer 10 is 150 μm or less, the resin layer 10 will not easily break in a 100,000-cycle folding test and will exhibit excellent performance. The lower limit of the thickness of the resin layer 10 is more preferably 40 μm or more, or 50 μm or more, and the upper limit of the thickness of the resin layer 10 is more preferably 120 μm or less, 100 μm or less, 80 μm or less, or 60 μm or less, from the viewpoint of thinning and improving processability.

[0029] The thickness of the resin layer 10 is determined by taking a cross-sectional image of the resin layer 10 using a scanning transmission electron microscope (STEM), measuring the thickness of the resin layer 10 at 10 locations in the cross-sectional image, and taking the arithmetic mean of the thicknesses at those 10 locations.

[0030] The specific method for taking cross-sectional images is described below. First, a block is prepared by embedding a resin layer cut to a size of 1 mm x 10 mm in embedding resin. From this block, uniform sections with a thickness of 70 nm to 100 nm, free from holes or other defects, are cut using a general sectioning method. For sectioning, for example, an ultramicrotome EM UC7 manufactured by Leica Microsystems Inc. can be used. These uniform sections free from holes or other defects are then used as the measurement sample. Subsequently, a cross-sectional image of the measurement sample is taken using a scanning transmission electron microscope (STEM). An example of a scanning transmission electron microscope (STEM) is the S-4800 manufactured by Hitachi High-Technologies Corporation. When taking cross-sectional images using the S-4800, the detector is set to "TE", the acceleration voltage to "30 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, adjusting it appropriately between 100x and 100,000x, preferably 1,000x to 50,000x, and more preferably 5,000x to 10,000x. When taking cross-sectional photographs using the S-4800 described above, you may also set the beam monitor aperture to "3", the objective lens aperture to "3", and the WD to "8mm". When measuring the thickness of the resin layer, it is important that the interface contrast between the resin layer and other layers (e.g., embedding resin) can be observed as clearly as possible when observing the cross-section. If the interface is difficult to see due to insufficient contrast, staining with osmium tetroxide, ruthenium tetroxide, phosphotungstic acid, etc., can make the interface between organic layers easier to see, so staining treatment may be performed. Also, the interface contrast may be more difficult to see at high magnification. In that case, observe at low magnification simultaneously. For example, observations are made at two magnifications, such as 2000x and 10,000x, or 5000x and 20,000x. The arithmetic mean of the above-mentioned values ​​is calculated for both magnifications, and this average value is then used as the thickness of the resin layer.

[0031] The resin constituting the resin layer 10 is not particularly limited as long as the shear storage modulus G' and glass transition temperature Tg satisfy the above range. Examples of such resins include cured products (polymers) of ionizing radiation-curable compounds (ionizing radiation-polymerizable compounds). Ionizing radiation in this specification includes visible light, ultraviolet rays, X-rays, electron beams, alpha rays, beta rays, and gamma rays. Examples of cured products of ionizing radiation-curable compounds include urethane resins or silicone resins.

[0032] (Urethane resin) Urethane resins are resins that have urethane bonds. Examples of urethane resins include cured products of ionizing radiation-curable urethane resin compositions and cured products of thermosetting urethane resin compositions. Among these, cured products of ionizing radiation-curable urethane resin compositions are preferred from the viewpoint of obtaining high hardness, a fast curing speed, and excellent mass productivity.

[0033] The ionizing radiation-curable urethane resin composition contains urethane (meth)acrylate, and the thermosetting urethane resin composition contains a polyol compound and an isocyanate compound. The urethane (meth)acrylate, polyol compound, and isocyanate compound may be monomers, oligomers, or prepolymers.

[0034] The number of (meth)acryloyl groups (functional groups) in the urethane (meth)acrylate is preferably 2 or more and 4 or less. If the number of (meth)acryloyl groups in the urethane (meth)acrylate is less than 2, the pencil hardness may be low, and if it exceeds 4, curing shrinkage will be large, causing the resin layer to curl and potentially crack when bent. The upper limit of the number of (meth)acryloyl groups in the urethane (meth)acrylate is more preferably 3 or less. Note that "(meth)acrylate" includes both "acrylate" and "methacrylate," and "(meth)acryloyl group" includes both "acryloyl group" and "methacryloyl group."

[0035] The weight average molecular weight of the urethane (meth)acrylate is preferably 1,500 or more and 20,000 or less. If the weight average molecular weight of the urethane (meth)acrylate is less than 1,500, the impact resistance may decrease. If it exceeds 20,000, the viscosity of the radiation-curable urethane resin composition may increase, and the coating property may deteriorate. The lower limit of the weight average molecular weight of the urethane (meth)acrylate is more preferably 2,000 or more, and the upper limit is more preferably 15,000 or less.

[0036] Examples of the repeating unit having a structure derived from urethane (meth)acrylate include structures represented by the following general formulas (1), (2), (3), or (4).

[0037]

Chemical formula

[0038]

Chemical formula

[0039]

Chemical formula

[0040] [ka] In the above general formula (4), R 1 R represents a branched alkyl group, 2 R represents a branched alkyl group or a saturated cyclic aliphatic group. 3 R represents a hydrogen atom or a methyl group. 4 x represents a hydrogen atom, a methyl group, or an ethyl group, n is an integer greater than or equal to 1, and x is an integer between 0 and 3.

[0041] Furthermore, the structure of the polymer chains (repeating units) that make up the resin layer 10 can be determined by analyzing the resin layer 10, for example, using pyrolysis gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FT-IR). In particular, pyrolysis GC-MS is useful because it can detect monomer units contained in the resin layer 10 as monomer components.

[0042] The resin layer 10 may contain, in addition to the resin, an ultraviolet absorber, a spectral transmittance modifier, an antifouling agent, inorganic particles and / or organic particles, etc.

[0043] <<<Optical Film>>> The optical film 30 shown in Figure 3 is a laminated film and comprises at least a resin layer 10. The optical film 30 comprises the resin layer 10 and a functional layer 31 provided on one side of the resin layer 10. In this specification, a "functional layer" is a layer that performs some function. The functional layer 31 has a single-layer structure, but it may have a multilayer structure of two or more layers.

[0044] In the optical film 30, the shear storage modulus G' in the frequency range of 500 Hz to 1000 Hz at 25°C is 30 MPa to 200 MPa. If the shear storage modulus G' of the optical film 30 is 30 MPa or higher, deformation of the surface 30A of the optical film 30 can be suppressed when an impact is applied to the surface 30A of the optical film 30, and the decrease in hardness of the optical film 30 can also be suppressed. Furthermore, if the shear storage modulus G' of the optical film 30 is 200 MPa or lower, the optical film 30 is less likely to crack when folded at room temperature. From the viewpoint of further suppressing the deformation of the surface 30A of the optical film 30 when an impact is applied to the surface of the optical film 30, and further suppressing the decrease in hardness of the optical film 30, the lower limit of the shear storage modulus G' of the optical film 30 is preferably 40 MPa or higher, 50 MPa or higher, or 80 MPa or higher. The upper limit of the shear storage modulus G' of the optical film 30 is preferably 190 MPa or less, 180 MPa or less, or 170 MPa or less, from the viewpoint of further suppressing cracking during folding. The shear storage modulus G' of the optical film 30 shall be measured by the same method as the shear storage modulus G' of the resin layer 10.

[0045] The optical film 30 is foldable. Specifically, it is preferable that no cracks or breaks occur in the optical film 30 even when the folding test (continuous folding test) described below is repeated 100,000 times, 200,000 times, 500,000 times, or 1,000,000 times in an environment with a temperature of 23±5℃ (e.g., 23℃) and a relative humidity of 30% to 70%, and in an environment with a temperature of -40℃±5℃ (e.g., -40℃), respectively. If cracks or breaks occur in the optical film 30 when the continuous folding test is repeated 100,000 times, the foldability of the optical film 30 will be insufficient. The reason why the number of folding cycles in the above continuous folding test is evaluated at least 100,000 times is as follows. For example, if the optical film is to be incorporated into a foldable smartphone, the frequency of folding (frequency of opening and closing) will be very high. Therefore, evaluating the continuous folding test by setting the number of folds to, for example, 10,000 or 50,000 times may not allow for evaluation at a practical level. Specifically, for example, assuming a person who uses a smartphone constantly, it is expected that they will open and close their smartphone 5 to 10 times during their morning commute on trains or buses alone, meaning they will open and close their smartphone at least 30 times a day. Therefore, assuming a smartphone is opened and closed 30 times a day, a continuous folding test with 10,000 folds would result in 30 folds x 365 days = 10,950 folds, which is equivalent to a test simulating one year of use. In other words, even if the results of a continuous folding test with 10,000 folds are good, cracks or breaks may occur in the optical film after one year. Therefore, an evaluation with 10,000 folds in a continuous folding test can only confirm a level where the product is unusable, and products that are usable but insufficient may also be marked as good, making evaluation impossible. Therefore, in order to evaluate whether it is at a practical level, the number of folds in the above continuous folding test must be evaluated at least 100,000 times.The continuous folding test may be performed by folding the optical film 30 so that surface 30A is on the outside, or by folding the optical film 30 so that surface 30A is on the inside, but in either case, it is preferable that no cracks or breaks occur in the optical film 30.

[0046] The continuous folding test is performed as follows. As shown in Figure 4(A), in the continuous folding test, first, a sample S2 measuring 30 mm × 100 mm is cut from the optical film 30. If it is not possible to cut a sample S2 measuring 30 mm × 100 mm from the optical film 30, a sample S2 measuring, for example, 10 mm × 100 mm may be cut. Then, the edges S2a and S2b of the cut sample S2 are fixed to the fixing parts 40 and 45 of a folding durability testing machine (for example, product name "U-shaped stretch test machine DLDMLH-FS", manufactured by Yuasa System Equipment Co., Ltd., compliant with IEC62715-6-1) which are arranged in parallel. Fixing by the fixing parts 40 and 45 is performed by holding a portion of the sample S2 of approximately 10 mm on one side in the longitudinal direction of the sample S2. However, if the sample S2 is smaller than the above size, measurement is possible by attaching it to the fixing parts 40 and 45 with tape, provided that the portion of the sample S2 required for this fixing is approximately 20 mm or less. Also, as shown in Figure 4(A), the fixing part 40 is slidable horizontally. Furthermore, unlike conventional methods such as wrapping the sample around a rod, this apparatus is preferable because it allows for durability evaluation against bending loads without generating tension or friction in the sample.

[0047] Next, as shown in Figure 4(B), the fixing part 40 is moved closer to the fixing part 45, causing the central part of the sample S2 to be deformed by folding. Furthermore, as shown in Figure 4(C), the fixing part 40 is moved to a position where the distance φ between the two opposing sides S2a and S2b fixed by the fixing parts 40 and 45 of the sample S2 is 10 mm, and then the fixing part 40 is moved in the opposite direction to eliminate the deformation of the optical film 30.

[0048] As shown in Figures 4(A) to (C), the central part of sample S2 can be folded 180° by moving the fixing part 40. Furthermore, by ensuring that the bent part S2c of sample S2 does not protrude from the lower ends of the fixing parts 40 and 45, and by performing a continuous folding test under the following conditions, and by controlling the distance φ when the fixing parts 40 and 45 are closest together, the distance φ between the two opposing sides S2a and S2b of sample S2 can be made 10 mm. In this case, the outer diameter of the bent part S2c is considered to be 10 mm. In sample S2, it is preferable that no cracks or fractures occur when the test of folding 180° so that the distance φ between the opposing sides of sample S2 is 10 mm is repeated 100,000 times, but it is even more preferable that no cracks or fractures occur when the continuous folding test of folding 180° so that the distance φ between the opposing sides S2b and S2c of sample S2 is 8 mm or 6 mm is repeated 100,000 times. (Folding conditions) • Round-trip speed: 120 rpm (cycles per minute) • Bending angle: 180°

[0049] The surface 30A of the optical film 30 (surface 31A of the functional layer 31) preferably has a hardness (pencil hardness) of 2H or higher, and more preferably 3H or higher, as measured by the pencil hardness test specified in JIS K5600-5-4:1999. The pencil hardness test shall be performed by fixing the optical film 30, cut to a size of 30 mm x 100 mm, onto a glass plate with cellophane tape (registered trademark) manufactured by Nichiban Co., Ltd., so that there are no folds or wrinkles, and using a pencil hardness tester (for example, product name "Pencil Scratch Coating Hardness Tester (Electric Type)", manufactured by Toyo Seiki Seisakusho Co., Ltd.) on the surface 30A of the optical film 30, while applying a load of 750 g to a pencil (for example, product name "Uni", manufactured by Mitsubishi Pencil Co., Ltd.) and moving the pencil at a moving speed of 1 mm / second. Pencil hardness is defined as the highest hardness at which the optical film surface was not scratched during the pencil hardness test. While multiple pencils of different hardness levels are used for the measurement, each pencil is tested five times. If the optical film surface is not scratched in four or more of these five tests, it is determined that this hardness level of pencil did not scratch the optical film surface. The scratches mentioned above refer to those visible when the optical film surface is observed under fluorescent light after the pencil hardness test.

[0050] If another film, such as a polarizing plate, is provided on one side of the optical film 30 via an adhesive or bonding layer, the other film shall be peeled off together with the adhesive or bonding layer, as described above, before measuring the shear storage modulus G' and the glass transition temperature, and performing a folding test.

[0051] The optical film 30 may be cut to a desired size, or it may be in roll form. If the optical film 30 is cut to a desired size, the size of the optical film is not particularly limited and is appropriately determined according to the size of the display surface of the image display device. Specifically, the size of the optical film 30 may be, for example, 2.8 inches or more and 500 inches or less. In this specification, "inch" means the length of the diagonal if the optical film is rectangular, the diameter if it is circular, and the average value of the sum of the minor axis and major axis if it is elliptical. Here, if the optical film is rectangular, the aspect ratio of the optical film when determining the above inches is not particularly limited as long as it does not pose a problem as a display screen for the image display device. For example, vertical:horizontal = 1:1, 4:3, 16:10, 16:9, 2:1, etc. However, in particular, in automotive applications and digital signage where design is important, the aspect ratio is not limited to such ratios. Furthermore, if the optical film 30 is large, it shall be cut to A5 size (148 mm x 210 mm) from any position, and then cut to the size of each measurement item. For example, if the optical film 30 is in roll form, a predetermined length shall be unwound from the roll of optical film 30, and the desired size shall be cut from the effective area near the center where the quality is stable, rather than from the ineffective area including both ends that extend along the longitudinal direction of the roll.

[0052] The applications of the optical film 30 are not particularly limited, but examples of applications include image display devices such as smartphones, tablet devices, personal computers (PCs), wearable devices, digital signage, televisions, and car navigation systems. The optical film 30 is also suitable for in-vehicle applications. The above image display devices are also preferable for applications requiring flexibility, such as foldable and rollable forms.

[0053] The optical film 30 in the image display device may be placed inside the image display device, but it is preferable that it be placed near the surface of the image display device. When used near the surface of the image display device, the optical film 30 functions as a cover film (window film) used in place of a cover glass.

[0054] <<Functional Layer>> The functional layer 31 shown in Figure 3 is a layer that functions as a hard coat layer. However, the functional layer 31 may be a layer having other functions. In this specification, "hard coat layer" means a layer whose pencil hardness is "H" or higher in the pencil hardness test described above.

[0055] When the displacement of the functional layer 31 is measured by the nanoindentation method, the displacement of the functional layer 31 is preferably between 50 nm and 500 nm. If the displacement of the functional layer 31 is 50 nm or more, good hardness can be obtained, and if it is 500 nm or less, good folding performance can be obtained. The measurement of the displacement by the nanoindentation method described above can be performed on an optical film cut to a size of 30 mm x 30 mm using a "TI950 TriboIndenter" manufactured by Bruker. Specifically, under the following measurement conditions, the depth to which a Berkovich indenter (triangular pyramid, for example, TI-0039 manufactured by Bruker) is pressed perpendicularly to the cross-section of the functional layer with a force of 500 μN is measured and this is defined as the displacement. Here, in order to avoid the influence of the resin layer and the side edges of the functional layer, the Berkovich indenter should be pressed into a portion of the functional layer that is 500 nm or more away from the interface between the resin layer and the functional layer toward the center of the functional layer, and 500 nm or more away from both ends of the functional layer toward the center of the functional layer. The amount of displacement can be adjusted by the type of resin and the amount of inorganic particles contained, as described later. (Measurement conditions) • Control method: Load control (maximum load 500 μN) • Lift amount: 0nm • Preload: 0.5 μN ·Loading speed: 20μN / sec ·Holding time: 5 seconds ·Loading and unloading speed: 20μN / sec ·Measurement temperature: 23±5℃ • Relative humidity: 30%~70%

[0056] The thickness of the functional layer 31 is preferably 3 μm or more and 10 μm or less. If the thickness of the functional layer 31 is 3 μm or more, good hardness can be obtained, and if it is 10 μm or less, deterioration of processability can be suppressed. In this specification, "thickness of the functional layer" means the total thickness obtained by summing the thicknesses of each functional layer when the functional layer has a multilayer structure. The lower limit of the thickness of the functional layer 31 is more preferably 5 μm or more, and the upper limit is more preferably 8 μm or less. The thickness of the functional layer 31 can be measured by the same method as the thickness of the resin layer 10.

[0057] The functional layer 31 preferably further contains a resin and inorganic particles dispersed in the resin.

[0058] <Resin> The resin contains polymers (cured products) of polymerizable compounds (curable compounds). Polymerizable compounds have at least one polymerizable functional group in their molecule. Examples of polymerizable functional groups include ethylenically unsaturated groups such as (meth)acryloyl groups, vinyl groups, and allyl groups.

[0059] As polymerizable compounds, polyfunctional (meth)acrylates are preferred. Examples of the above polyfunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Examples include methylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, isocyanuric acid tri(meth)acrylate, isocyanuric acid di(meth)acrylate, polyester tri(meth)acrylate, polyester di(meth)acrylate, bisphenol di(meth)acrylate, diglycerin tetra(meth)acrylate, adamantyl di(meth)acrylate, isoboronyl di(meth)acrylate, dicyclopentane di(meth)acrylate, tricyclodecane di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and modified versions of these with PO, EO, caprolactone, etc.

[0060] Among these, those with 3 to 6 functionalities are preferred because they can suitably satisfy the displacement amounts mentioned above. 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.

[0061] Furthermore, monofunctional (meth)acrylate monomers may be included to adjust hardness, viscosity, and adhesion. Examples of the above monofunctional (meth)acrylate monomers include hydroxyethyl acrylate (HEA), glycidyl methacrylate, methoxypolyethylene glycol (meth)acrylate, isostearyl (meth)acrylate, 2-acryloyloxyethyl succinate, acryloylmorpholine, N-acryloyloxyethyl hexahydrophthalimide, cyclohexyl acrylate, tetrahydrofuryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and adamantyl acrylate.

[0062] The weight-average molecular weight of the above monomer is preferably less than 1000, and more preferably between 200 and 800, from the viewpoint of improving the hardness of the resin layer. Furthermore, the weight-average molecular weight of the above polymerizable oligomer is preferably between 1000 and 20,000, more preferably between 1000 and 10,000, and even more preferably between 2000 and 7000.

[0063] <Inorganic particles> The inorganic particles are not particularly limited as long as they can improve hardness, but silica particles are preferred from the viewpoint of obtaining excellent hardness. Among silica particles, reactive silica particles are preferred. The above reactive silica particles are silica particles that can form a crosslinking structure with the above polyfunctional (meth)acrylate, and by including these reactive silica particles, the hardness of the functional layer 31 can be sufficiently increased.

[0064] The above-mentioned reactive silica particles preferably have reactive functional groups on their surface, and for example, the polymerizable functional groups described above are preferably used as such reactive functional groups.

[0065] The reactive silica particles mentioned above are not particularly limited and conventionally known particles can be used, for example, the reactive silica particles described in Japanese Patent Application Publication No. 2008-165040. Examples of commercially available reactive silica particles include MIBK-SD, MIBK-SD-MS, MIBK-SD-L, MIBK-SD-ZL (all manufactured by Nissan Chemical Industries, Ltd.) and V8802, V8803 (both manufactured by JGC Catalysts & Chemicals Ltd.).

[0066] Furthermore, the silica particles may be spherical silica particles, but irregularly shaped silica particles are preferred. Spherical silica particles and irregularly shaped silica particles may be mixed. In this specification, "spherical silica particles" refers to silica particles that are, for example, perfectly spherical or ellipsoidal, and "irregularly shaped silica particles" refers to silica particles that have a potato-like shape (aspect ratio of 1.2 to 40 when observed in cross-section) with random irregularities on their surface. Since the surface area of ​​the irregularly shaped silica particles is larger than that of spherical silica particles, including such irregularly shaped silica particles increases the contact area with the polyfunctional (meth)acrylate, etc., and can improve the hardness of the functional layer 31. Whether or not the silica particles contained in the functional layer 31 are irregularly shaped silica particles can be confirmed by observing a cross-section of the functional layer 31 with a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM).

[0067] The average particle diameter of the silica particles is preferably between 5 nm and 200 nm. If the average particle diameter of the silica particles is 5 nm or more, the manufacturing of the particles themselves will not be difficult, aggregation of particles can be suppressed, and it will not be difficult to make them irregular in shape. On the other hand, if the average particle diameter of the irregularly shaped silica particles is 200 nm or less, the formation of large irregularities in the functional layer can be suppressed, and the increase in haze can also be suppressed. In the case of spherical silica particles, the average particle diameter of the silica particles is determined by measuring the particle diameters of 20 particles from cross-sectional images of the particles taken using a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM), and taking the arithmetic mean of the particle diameters of the 20 particles. Furthermore, if the silica particles are irregularly shaped silica particles, the average particle diameter of the silica particles is determined by measuring the maximum (major axis) and minimum (minor axis) distances between two points on the outer circumference of the particle from a cross-sectional image of the functional layer taken using a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM), averaging these values, and using the arithmetic mean of the particle diameters of 20 particles.

[0068] The hardness (displacement) of the functional layer 31 can be controlled by controlling the size and amount of the inorganic particles. For example, when forming the functional layer 31, the silica particles are preferably 25 to 60 parts by mass per 100 parts by mass of the polymerizable compound, with a diameter of 5 nm to 200 nm.

[0069] The functional layer 31 may contain materials other than those described above, to the extent that it satisfies the above-mentioned displacement. For example, the resin component may include polymerizable monomers or polymerizable oligomers that form a cured product upon irradiation with ionizing radiation. Examples of the polymerizable monomers or polymerizable oligomers include (meth)acrylate monomers having radical polymerizable unsaturated groups in the molecule, or (meth)acrylate oligomers having radical polymerizable unsaturated groups in the molecule. Examples of (meth)acrylate monomers or (meth)acrylate oligomers having radical polymerizable unsaturated groups in the molecule include urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, melamine (meth)acrylate, polyfluoroalkyl (meth)acrylate, and silicone (meth)acrylate monomers or oligomers. These polymerizable monomers or polymerizable oligomers may be used individually or in combination of two or more. Among these, polyfunctional (6 or more functional) urethane (meth)acrylates with a weight-average molecular weight of 1,000 to 10,000 are preferred.

[0070] The functional layer 31 may further contain an ultraviolet absorber, a spectral transmittance modifier, and / or an antifouling agent.

[0071] <<<Other optical films>>> The optical film 30 shown in Figure 3 does not have a substrate, but it may have a substrate, as shown in the optical film 50 in Figure 5. The optical film 50 comprises a resin layer 10, a resin substrate 51, and a functional layer 52 in that order, as shown in Figure 5. The resin substrate 51 may be adjacent to the resin layer 10. In the optical film 50, the resin layer 10 is adjacent to the resin substrate 51, but it may also be attached to the resin substrate via an adhesive layer.

[0072] The surface 50A of the optical film 50 is the surface 52A of the functional layer 52. In this specification, the surface of the optical film is used to mean one side of the optical film, so the side opposite to the surface of the optical film is referred to as the back surface to distinguish it from the surface of the optical film. The back surface 50B of the optical film 50 is the side of the resin layer 10 opposite to the side facing the resin substrate 51.

[0073] The optical film 50 is foldable in environments with a temperature of 23±5°C and a relative humidity of 30% to 70%, and in environments with a temperature of -40°C. The preferred number of folds, the preferred distance φ between opposing edges, and the conditions for the continuous folding test are the same as for the optical film 30, so a detailed explanation is omitted here.

[0074] The surface 50A of the optical film 50 (surface 52A of the functional layer 52) preferably has a hardness (pencil hardness) of 2H or higher, and more preferably 3H or higher, as measured by the pencil hardness test specified in JIS K5600-5-4:1999. The pencil hardness of the optical film 50 shall be measured by the same method as that used for the pencil hardness of the optical film 30.

[0075] The optical film 50 preferably has a yellow index (YI) of 15 or less. If the YI of the optical film 50 is 15 or less, the yellowing of the optical film can be suppressed, and it can be applied to applications where transparency is required. The upper limit of the yellow index (YI) of the optical film 50 is more preferably 10 or less, 5 or less, or 1.5 or less. The Yellow Index (YI) is calculated by measuring the transmittance of an optical film cut to a size of 50 mm x 100 mm in a spectrophotometer (e.g., product name "UV-2450", manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp) at a temperature of 23 ± 5°C and a relative humidity of 30% to 70%, with the resin layer side of the optical film facing the light source. The chromaticity tristimulus values ​​X, Y, and Z are calculated from the transmittance of the optical film at wavelengths of 300 nm to 780 nm according to the calculation formula described in JIS Z8722:2009, and the value is calculated from the tristimulus values ​​X, Y, and Z according to the calculation formula described in ASTM D1925:1962. It is more preferable that the upper limit of the Yellow Index (YI) of optical film 50 is 10 or less. The above Yellow Index (YI) is the arithmetic mean of the values ​​obtained from three measurements of one optical film. In the case of UV-2450, the yellow index is calculated by reading the above transmittance measurement data on the monitor connected to the UV-2450 and checking the "YI" item in the calculation items. Transmittance measurement at wavelengths of 300nm to 780nm shall be performed under the following conditions, by measuring the transmittance for at least 5 points within 1nm before and after each wavelength in the range of 300nm to 780nm, and calculating the average value. If the spectral transmittance spectrum shows fluctuations, smoothing may be performed with a delta of 5.0nm. (Measurement conditions) ·Wavelength range: 300nm~780nm • Scan speed: High Slit width: 2.0 • Sampling interval: Auto (0.5nm intervals) ·Lighting:C • Light source: D2 and WI ·Field of view: 2° • Light source switching wavelength: 360nm S / R switching: Standard • Pixel: PM • Auto-zero: Performed at 550nm after baseline scan.

[0076] The total light transmittance of the optical film 50 is preferably 85% or higher. If the total light transmittance of the optical film 50 is 85% or higher, sufficient image visibility can be obtained when the optical film 50 is used in a mobile terminal. The total light transmittance of the optical film 50 is preferably 87% or higher, or 90% or higher.

[0077] The above total light transmittance can be measured in an environment with a temperature of 23±5℃ and a relative humidity of 30% to 70% using a haze meter (for example, product name "HM-150", manufactured by Murakami Color Technology Laboratory Co., Ltd.) in accordance with the method compliant with JIS K7361-1:1997. The above total light transmittance is measured three times for each optical film after cutting the optical film to a size of 50mm × 100mm, ensuring that it is free from curling, wrinkles, fingerprints, dust, etc., and the arithmetic mean of the values ​​obtained from the three measurements is taken. In this specification, "measure three times" means measuring at three different locations, not measuring at the same location three times. In the optical film 50, the visually observed surface 50A is flat, and the laminated layers such as the resin layer 10 are also flat, and the variation in film thickness is within ±10%. Therefore, by measuring the total light transmittance at three different locations on the cut optical film, it is thought that an approximate average value of the total light transmittance across the entire surface of the optical film can be obtained. The variation in total light transmittance is within ±10%, whether the measurement target is a long length of 1m x 3000m or the size of a 5-inch smartphone. If the optical film cannot be cut to the above size, for example, the HM-150 has an entrance opening of 20mmφ for measurement, so a sample size of 21mm or larger in diameter is required. For this reason, the optical film may be appropriately cut to a size of 22mm x 22mm or larger. If the optical film is small, the measurement points can be made into three locations by slightly shifting them or changing the angle while keeping the light source spot within the range where it does not stray.

[0078] The haze value of the optical film 50 is preferably 2.0% or less. If the haze value of the optical film 50 is 2.0% or less, whitening of the image display surface can be suppressed when the optical film 50 is used in a mobile terminal. The haze value is more preferably 1.5% or less, 1.0% or less, or 0.5% or less.

[0079] The above haze value can be measured in an environment with a temperature of 23±5℃ and a relative humidity of 30% to 70% using a haze meter (for example, product name "HM-150," manufactured by Murakami Color Technology Laboratory Co., Ltd.) in accordance with JIS K7136:2000. Specifically, the haze value is measured using the same method as for measuring total light transmittance.

[0080] If other films, such as polarizing plates, are provided on the front surface 50A or back surface 50B of the optical film 50 via an adhesive or bonding layer, the other films shall be peeled off along with the adhesive or bonding layer before performing the folding test, yellow index measurement, total light transmittance measurement, haze value measurement, etc. However, such a peeling process does not significantly affect these tests or measurements. The haze value measurement shall be performed after the adhesive or bonding layer has been peeled off and any remaining dirt on the adhesive or bonding layer has been thoroughly wiped off with alcohol.

[0081] The uses of optical film 50 are not particularly limited and include the same uses as those described in the section on optical film 30.

[0082] <<Resin base material>> The resin substrate 51 is light-transmitting. In this specification, "light-transmitting" means the property of transmitting light, and includes, for example, a total light transmittance of 50% or more, preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. Light-transmitting does not necessarily mean that it is transparent; it may be semi-transparent.

[0083] The resin substrate 51 preferably contains one or more resins selected from the group consisting of, for example, polyimide resins, polyamideimide resins, polyamide resins, and polyester resins (for example, polyethylene terephthalate resins and polyethylene naphthalate resins).

[0084] Among these resins, polyimide resins, polyamide resins, or mixtures thereof are preferred because they are less prone to cracking or fracturing in continuous folding tests, possess excellent hardness and transparency, have excellent heat resistance, and can be further enhanced in hardness and transparency by firing.

[0085] Polyimide resins are obtained by reacting a tetracarboxylic acid component with a diamine component. While polyimide resins are not particularly limited, it is preferable that they have at least one structure selected from the group consisting of structures represented by the following general formulas (5) and (7), for example, in terms of having excellent light transmittance and excellent rigidity.

[0086] [ka] In the above general formula (5), R 5 R is a tetravalent group which is a tetracarboxylic acid residue. 6 n represents at least one divalent group selected from the group consisting of trans-cyclohexanediamine residues, trans-1,4-bismethylenecyclohexanediamine residues, 4,4'-diaminodiphenylsulfone residues, 3,4'-diaminodiphenylsulfone residues, and divalent groups represented by the following general formula (6). n represents the number of repeating units and is 1 or greater. In this specification, "tetracarboxylic acid residue" means a residue obtained by removing four carboxyl groups from a tetracarboxylic acid, and represents the same structure as a residue obtained by removing the acid dianhydride structure from a tetracarboxylic dianhydride. Also, "diamine residue" means a residue obtained by removing two amino groups from a diamine.

[0087] [ka] In the above general formula (6), R 7 and R 8 Each of these independently represents a hydrogen atom, an alkyl group, or a perfluoroalkyl group.

[0088] [ka] In the above general formula (7), R 9 R is at least one tetravalent group selected from the group consisting of cyclohexanetetracarboxylic acid residues, cyclopentanetetracarboxylic acid residues, dicyclohexane-3,4,3',4'-tetracarboxylic acid residues, and 4,4'-(hexafluoroisopropylidene)diphthalic acid residues. 10 represents a divalent group, which is a diamine residue. n' represents the number of repeating units, which is 1 or greater.

[0089] In the above general formula (5), R 5 R is a tetracarboxylic acid residue, and can be a residue obtained by removing the acid dianhydride structure from a tetracarboxylic dianhydride as exemplified above. 5 In particular, from the viewpoint of improving light transmittance and rigidity, it is preferable to include at least one selected from the group consisting of 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, 3,3',4,4'-biphenyltetracarboxylic acid residue, pyromellitic acid residue, 2,3',3,4'-biphenyltetracarboxylic acid residue, 3,3',4,4'-benzophenonetetracarboxylic acid residue, 3,3',4,4'-diphenylsulfonetetracarboxylic acid residue, 4,4'-oxydiphthalic acid residue, cyclohexanetetracarboxylic acid residue, and cyclopentanetetracarboxylic acid residue. Furthermore, it is preferable to include at least one selected from the group consisting of 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, 4,4'-oxydiphthalic acid residue, and 3,3',4,4'-diphenylsulfonetetracarboxylic acid residue.

[0090] R 5In this mixture, it is preferable that these preferred residues are present in a total of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more.

[0091] Also, R 5 It is also preferable to use a mixture of tetracarboxylic acid residues suitable for improving rigidity (Group A), such as at least one selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic acid residues, 3,3',4,4'-benzophenonetetracarboxylic acid residues, and pyromellitic acid residues, and tetracarboxylic acid residues suitable for improving transparency (Group B), such as at least one selected from the group consisting of 4,4'-(hexafluoroisopropylidene)diphthalic acid residues, 2,3',3,4'-biphenyltetracarboxylic acid residues, 3,3',4,4'-diphenylsulfonetetracarboxylic acid residues, 4,4'-oxydiphthalic acid residues, cyclohexanetetracarboxylic acid residues, and cyclopentanetetracarboxylic acid residues.

[0092] In this case, the content ratio of the tetracarboxylic acid residue group suitable for improving rigidity (group A) and the tetracarboxylic acid residue group suitable for improving transparency (group B) is preferably 0.05 moles or more and 9 moles or less of the tetracarboxylic acid residue group suitable for improving rigidity (group A) per mole of the tetracarboxylic acid residue group suitable for improving transparency (group B), more preferably 0.1 moles or more and 5 moles or less, and even more preferably 0.3 moles or more and 4 moles or less.

[0093] In the above general formula (5), R 6 In particular, from the viewpoint of improving light transmittance and rigidity, it is preferable that the group consists of a 4,4'-diaminodiphenylsulfone residue, a 3,4'-diaminodiphenylsulfone residue, and at least one divalent group selected from the group consisting of a divalent group represented by the general formula (6) above, and further, the 4,4'-diaminodiphenylsulfone residue, the 3,4'-diaminodiphenylsulfone residue, and R 7 and R8 Preferably, is at least one divalent group selected from the group consisting of divalent groups represented by the above general formula (6), wherein is a perfluoroalkyl group.

[0094] In the above general formula (7), R 9 In particular, it is preferable to include a 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, a 3,3',4,4'-diphenylsulfonetetracarboxylic acid residue, and an oxydiphthalic acid residue, as these improve light transmittance and rigidity.

[0095] R 9 In this mixture, it is preferable that these preferred residues are present in an amount of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more.

[0096] In the above general formula (7), R 10R6 is a diamine residue, and can be a residue obtained by removing two amino groups from a diamine as exemplified above. Among the R6s in the above general formula (3), in terms of improving light transmittance and rigidity, 2,2'-bis(trifluoromethyl)benzidine residue, bis[4-(4-aminophenoxy)phenyl]sulfone residue, 4,4'-diaminodiphenylsulfone residue, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residue, bis[4-(3-aminophenoxy)phenyl]sulfone residue, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residue, 1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene residue, 2,2-bis[4-(4-amino-2-triphenyl It is preferable to include at least one divalent group selected from the group consisting of [ruoromethylphenoxy)phenyl]hexafluoropropane residue, 4,4'-diamino-2-(trifluoromethyl)diphenyl ether residue, 4,4'-diaminobenzanilide residue, N,N'-bis(4-aminophenyl)terephthalamide residue, and 9,9-bis(4-aminophenyl)fluorene residue, and it is even more preferable to include at least one divalent group selected from the group consisting of 2,2'-bis(trifluoromethyl)benzidine residue, bis[4-(4-aminophenoxy)phenyl]sulfone residue, and 4,4'-diaminodiphenylsulfone residue.

[0097] R 10 In this mixture, it is preferable that these preferred residues are present in a total of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more.

[0098] Also, R 10As such, a group of diamine residues suitable for improving rigidity (Group C) consisting of at least one selected from the group consisting of bis[4-(4-aminophenoxy)phenyl]sulfone residues, 4,4'-diaminobenzanilide residues, N,N'-bis(4-aminophenyl)terephthalamide residues, paraphenylenediamine residues, metaphenylenediamine residues, and 4,4'-diaminodiphenylmethane residues, and a group of diamine residues suitable for improving rigidity (Group C), and a group consisting of 2,2'-bis(trifluoromethyl)benzidine residues, 4,4'-diaminodiphenylsulfone residues, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residues, bis[4-(3-A It is also preferable to use a mixture of diamine residues suitable for improving transparency (Group D), such as at least one selected from the group consisting of minophenoxy)phenyl]sulfone residues, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residues, 1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene residues, 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane residues, 4,4'-diamino-2-(trifluoromethyl)diphenyl ether residues, and 9,9-bis(4-aminophenyl)fluorene residues.

[0099] In this case, the content ratio of the diamine residue group suitable for improving rigidity (group C) and the diamine residue group suitable for improving transparency (group D) is preferably 0.05 moles to 9 moles of the diamine residue group suitable for improving rigidity (group C) per mole of the diamine residue group suitable for improving transparency (group D), more preferably 0.1 moles to 5 moles, and more preferably 0.3 moles to 4 moles.

[0100] In the structures represented by the above general formulas (5) and (7), n and n' each independently represent the number of repeating units and are 1 or greater. The number of repeating units n in polyimide can be appropriately selected according to the structure so as to exhibit a preferred glass transition temperature, as described later, and is not particularly limited. The average number of repeating units is usually 10 to 2000, and more preferably 15 to 1000.

[0101] Furthermore, polyimide resins may contain a polyamide structure as part of their composition. Examples of polyamide structures that may be included include polyamide-imide structures containing tricarboxylic acid residues, such as trimellitic anhydride, and polyamide structures containing dicarboxylic acid residues, such as terephthalic acid.

[0102] From the viewpoint of heat resistance, polyimide resins are preferably given a glass transition temperature of 250°C or higher, and more preferably 270°C or higher. On the other hand, from the viewpoint of ease of stretching and reduction of bake temperature, the glass transition temperature is preferably 400°C or lower, and more preferably 380°C or lower.

[0103] Examples of polyimide resins include compounds having the structure represented by the following chemical formula. In the following chemical formula, n is a repeating unit and represents an integer of 2 or more.

[0104] [ka]

[0105] [ka]

[0106] [ka]

[0107] [ka]

[0108]

change

[0109]

change

[0110]

change

[0111]

change

[0112]

change

[0113]

change

[0114]

change

[0115]

change

[0116]

change

[0117]

change

[0118] [ka]

[0119] [ka]

[0120] [ka]

[0121] Among the polyimide resins mentioned above, polyimide resins or polyamide resins having a structure that makes intramolecular or intermolecular charge transfer less likely are preferred because they have excellent transparency. Specifically, examples include fluorinated polyimide resins such as those of chemical formulas (8) to (15) and polyimide resins having an alicyclic structure such as those of formulas (15) to (19).

[0122] Furthermore, fluorinated polyimide resins such as those represented by chemical formulas (8) to (15) above have a fluorinated structure, thus possessing high heat resistance and excellent transparency, as they are not discolored by the heat generated during the manufacturing of polyimide films made from these polyimide resins.

[0123] Polyamide resins are a concept that includes not only aliphatic polyamides but also aromatic polyamides (aramids). Examples of polyamide resins include compounds having the skeletons represented by the following chemical formulas (25) to (27). In the following formulas, n is a repeating unit and represents an integer of 2 or more.

[0124] [ka]

[0125] [ka]

[0126] [ka]

[0127] The substrate made of polyimide resin or polyamide resin represented by the above chemical formulas (8) to (24) and (27) may be a commercially available product. Examples of commercially available polyimide resins include NeoPrim® manufactured by Mitsubishi Gas Chemical Company, and examples of commercially available substrates containing polyamide resin include Miktron® manufactured by Toray Industries, Inc.

[0128] Furthermore, the polyimide resins or polyamide resins represented by the above chemical formulas (8) to (24) and (27) may be those synthesized by known methods. For example, a method for synthesizing the polyimide resin represented by the above chemical formula (8) is described in Japanese Patent Application Publication No. 2009-132091, and specifically, it can be obtained by reacting 4,4'-hexafluoropropylene bisphthalic acid dianhydride (FPA), represented by the following chemical formula (28), with 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB).

[0129] [ka]

[0130] The weight-average molecular weight of the above-mentioned polyimide resin or polyamide resin is preferably in the range of 3,000 to 500,000, more preferably in the range of 5,000 to 300,000, and even more preferably in the range of 10,000 to 200,000. If the weight-average molecular weight is less than 3,000, sufficient strength may not be obtained, and if it exceeds 500,000, viscosity increases and solubility decreases, so a substrate with a smooth surface and uniform film thickness may not be obtained. In this specification, "weight-average molecular weight" is the polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0131] From the viewpoint of improving hardness, it is preferable to use a resin substrate 51 made of a fluorinated polyimide resin represented by the above chemical formulas (8) to (15), etc., or a polyamide resin having a halogen group such as the above chemical formula (27). In particular, from the viewpoint of further improving hardness, it is more preferable to use a substrate containing the polyimide resin represented by the above chemical formula (8).

[0132] Examples of polyester resins include resins that contain at least one of the following as constituent components: polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

[0133] The thickness of the resin substrate 51 is preferably 10 μm or more and 100 μm or less. If the thickness of the resin substrate 51 is 10 μm or more, curling of the optical film 50 can be suppressed, sufficient hardness can be obtained, and even when the optical film 50 is manufactured by roll to roll, wrinkles are less likely to occur, and there is no risk of deterioration of appearance. On the other hand, if the thickness of the resin substrate 51 is 100 μm or less, the folding performance of the optical film 50 is good, the requirements of the continuous folding test can be satisfied, and it is also preferable in terms of reducing the weight of the optical film 50. The thickness of the resin substrate 51 can be measured by the same method as the film thickness of the resin layer 10. The lower limit of the resin substrate 51 is more preferably 20 μm or more, 30 μm or more, or 40 μm or more, and the upper limit of the resin substrate 51 is more preferably 80 μm or less or 50 μm or less.

[0134] <<Functional Layer>> Since functional layer 52 is the same as functional layer 31, its explanation will be omitted here.

[0135] <<<Method for manufacturing resin layers and optical films>>> The resin layer 10 and optical films 30 and 50 can be manufactured as follows. First, a resin layer composition is applied to one side of a release film using a coating device such as a bar coater to form a coating film.

[0136] <<Composition for resin layer>> The resin layer composition contains an ionizing radiation-curable compound. In addition to the ionizing radiation-curable compound, the resin layer composition may further contain a solvent and a polymerization initiator. The ionizing radiation-curable compound was explained in the section on resin layer 10, so its explanation is omitted here.

[0137] (solvent) The solvents mentioned above include alcohols (e.g., methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol, t-butanol, benzyl alcohol, PGME, ethylene glycol, diacetone alcohol), ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone, diethyl ketone, diacetone alcohol), and esters (methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, formic acid). Examples of solvents include chlorohydrate (PGMEA), aliphatic hydrocarbons (e.g., hexane, cyclohexane), halogenated hydrocarbons (e.g., methylene chloride, chloroform, carbon tetrachloride), aromatic hydrocarbons (e.g., benzene, toluene, xylene), amides (e.g., dimethylformamide, dimethylacetamide, n-methylpyrrolidone), ethers (e.g., diethyl ether, dioxane, tetrahydrofuran), ether alcohols (e.g., 1-methoxy-2-propanol), and carbonates (dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate). These solvents may be used individually or in combination of two or more. Among these, methyl isobutyl ketone and methyl ethyl ketone are preferred as solvents because they can dissolve or disperse components such as urethane (meth)acrylate and other additives, and allow for suitable coating of the resin layer composition.

[0138] (Polymerization initiator) Polymerization initiators are components that decompose upon irradiation with ionizing radiation, generating radicals that initiate or accelerate the polymerization (crosslinking) of polymerizable compounds.

[0139] The polymerization initiator is not particularly limited as long as it is capable of releasing a substance that initiates radical polymerization upon irradiation with ionizing radiation. The polymerization initiator is not particularly limited and known substances can be used. Specific examples include acetophenones, benzophenones, Michler-benzoyl benzoates, α-amyloxime esters, thioxanthones, propiophenones, benzyls, benzoins, and acylphosphine oxides. It is also preferable to use a photosensitizer in combination. Specific examples of such photosensitizers include n-butylamine, triethylamine, and poly-n-butylphosphine.

[0140] After forming a coating film of the resin layer composition, if the resin layer composition contains a solvent, the coating film is dried by various known methods, for example, by heating it at a temperature of 30°C to 120°C for 10 to 120 seconds, to evaporate the solvent.

[0141] After the coating film has dried, it is cured by irradiating it with ionizing radiation such as ultraviolet light. Then, the release film is peeled off to obtain the resin layer 10.

[0142] Furthermore, when forming the optical film 30, after drying the coating of the resin layer composition, the coating is irradiated with ionizing radiation such as ultraviolet light to partially cure it. In this specification, "partially cured" means that further irradiation with ionizing radiation will substantially advance the curing process.

[0143] Subsequently, a functional layer composition for forming the functional layer 31 is applied to the semi-cured coating using a coating device such as a bar coater to form a coating film of the functional layer composition.

[0144] <Composition for functional layer> The functional layer composition contains polymerizable compounds. The functional layer composition may also, as necessary, contain ultraviolet absorbers, spectral transmittance modifiers, antifouling agents, inorganic particles, leveling agents, solvents, and polymerization initiators. Since the solvents and polymerization initiators are the same as those used in the resin layer composition, their explanation is omitted here.

[0145] After forming a coating film of the functional layer composition, the coating film is dried by various known methods, for example, by heating it at a temperature of 30°C to 120°C for 10 to 120 seconds, thereby evaporating the solvent.

[0146] After drying the coating film of the functional layer composition, the coating film is irradiated with ionizing radiation such as ultraviolet light to fully cure it and form the functional layer 31. However, "fully cured" as used herein means that further irradiation with ionizing radiation will not substantially advance the curing process. Thereafter, the release film is peeled off to obtain the optical film 30.

[0147] When forming the optical film 50, a functional layer 52 is formed on one side of the resin substrate 51. The functional layer 52 can be formed in the same manner as the functional layer 31. Then, a resin layer 10 is formed on the side of the resin substrate 51 opposite to the side on which the functional layer 52 is formed, in the same manner as described above. This allows the optical film 50 to be obtained.

[0148] According to this embodiment, the shear storage modulus G' of the resin layer 10 at 25°C and a frequency range of 500 Hz to 1000 Hz is 30 MPa to 200 MPa, thus providing good impact resistance.

[0149] Typically, resins with a low shear storage modulus G' have a low glass transition temperature. Therefore, even if they exhibit good flexibility at room temperature, they become hard and brittle at temperatures below the glass transition temperature. According to this embodiment, since the glass transition temperature of the resin layer 10 is 50°C or higher, the change in the state of the resin layer 10 between room temperature and low-temperature environments can be suppressed. As a result, the flexibility of the resin layer 10 can be maintained not only at room temperature but also at low temperatures. This allows for good foldability.

[0150] <<<Image display device>>> The optical films 30 and 50 can be incorporated into a foldable image display device. Figure 6 is a schematic diagram of the image display device according to this embodiment. As shown in Figure 6, the image display device 60 is mainly constructed with a housing 61 containing batteries, etc., a display element 62, a circular polarizing plate 63, a touch sensor 64, and the optical film 30 stacked in this order, facing the observer. Light-transmitting adhesive layers 65 or bonding layers are placed between the housing 61 and the display element 62, between the display element 62 and the circular polarizing plate 63, between the circular polarizing plate 63 and the touch sensor 64, and between the touch sensor 64 and the optical film 30, and these components are fixed to each other by the adhesive layers 65 or bonding layers. The adhesive layer 65 is placed between the housing 61 and the display element 62, between the display element 62 and the circular polarizing plate 63, between the circular polarizing plate 63 and the touch sensor 64, and between the touch sensor 64 and the optical film 30, but the placement of the adhesive layer is not particularly limited as long as it is between the optical film and the display element.

[0151] The optical film 30 is arranged such that the functional layer 31 is on the observer side of the resin layer 10. In the image display device 60, the surface 30A of the optical film 30 constitutes the surface 60A of the image display device 60.

[0152] In the image display device 60, the display element 62 is an organic light-emitting diode element, including an organic light-emitting diode. The touch sensor 64 is positioned on the observer side of the circular polarizer 63, but it may also be positioned between the display element 62 and the circular polarizer 63. The touch sensor 64 may also be an on-cell or in-cell type. For example, OCA (Optical Clear Adhesive) can be used as the adhesive layer 65. [Examples]

[0153] To illustrate the present invention in detail, examples are given below, but the present invention is not limited to these examples.

[0154] <Preparation of compositions for hard coat layers> First, the components were blended to obtain hard coat layer composition 1, as shown below. (Composition for hard coat layer 1) • Mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (product name "M403", manufactured by Toagosei Co., Ltd.): 25 parts by mass • Dipentaerythritol EO-modified hexaacrylate (product name "A-DPH-6E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 25 parts by mass • Irregularly shaped silica particles (average particle size 25 nm, manufactured by JGC Catalysts & Chemicals Co., Ltd.): 50 parts by mass (calculated based on 100% solid content) • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 4 parts by mass • Fluorine-based leveling agent (product name "F568", manufactured by DIC Corporation): 0.2 parts by mass (calculated based on 100% solid content) Methyl isobutyl ketone (MIBK): 150 parts by mass

[0155] <Composition for resin layer> A resin layer composition was obtained by blending each component to achieve the composition shown below. (Composition 1 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 90 parts by mass Phenoxyethyl acrylate (product name "Viscoat #200", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 10 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0156] (Composition 2 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 40 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 5 parts by mass Phenoxyethyl acrylate (product name "Viscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 5 parts by mass • Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (product name "KAYARAD PET-30", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0157] (Composition 3 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 35 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 10 parts by mass Phenoxyethyl acrylate (product name "Viscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 5 parts by mass • Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (product name "KAYARAD PET-30", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0158] (Composition 4 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 25 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 20 parts by mass Phenoxyethyl acrylate (product name "Viscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 5 parts by mass • Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (product name "KAYARAD PET-30", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0159] (Composition for resin layer 5) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 15 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 30 parts by mass • Dicyclopentanyl acrylate (product name "FA-513AS", manufactured by Hitachi Chemical Co., Ltd.): 5 parts by mass • Dipentaerythritol hexaacrylate (product name "KAYARAD DPHA", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0160] (Composition 6 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 90 parts by mass · Tetrahydrofurfuryl alcohol acrylic acid polymer ester (Product name "Viscote #150D", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 10 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0161] (Composition 7 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 40 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 5 parts by mass Phenoxyethyl acrylate (product name "Viscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 5 parts by mass • Dipentaerythritol hexaacrylate (product name "KAYARAD DPHA", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0162] (Composition for resin layer 8) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 30 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 60 parts by mass • Dicyclopentanyl acrylate (product name "FA-513AS", manufactured by Hitachi Chemical Co., Ltd.): 10 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0163] (Composition 9 for resin layer) • Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 80 parts by mass • Ethoxylated pentaerythritol tetraacrylate (product name "ATM-35E", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.): 10 parts by mass Phenoxyethyl acrylate (product name "Viscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 10 parts by mass • Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by mass

[0164] <Example 1> A polyethylene terephthalate substrate with a thickness of 50 μm (product name "Cosmoshine® A4100", manufactured by Toyobo Co., Ltd.) was prepared as a release film. Composition 1 for the resin layer was applied to the untreated side of the polyethylene terephthalate substrate using a bar coater to form a coating film. The formed coating film was then heated at 70°C for 1 minute to evaporate the solvent in the coating film, and ultraviolet irradiation was performed using an ultraviolet irradiation device (Fusion UV Systems Japan, light source H bulb) to an integrated light intensity of 100 mJ / cm² in the air. 2 The coating was partially cured by irradiating it in such a way that a resin layer made of urethane resin with a thickness of 100 μm was formed.

[0165] Next, hard coat layer composition 1 was applied to the surface of the semi-cured coating film using a bar coater to form a coating film. Subsequently, the formed coating film was heated at 70°C for 1 minute to evaporate the solvent in the coating film, and ultraviolet irradiation was performed using an ultraviolet irradiation device (Fusion UV Systems Japan, light source H bulb) under conditions of an oxygen concentration of 200 ppm or less, with an integrated light intensity of 300 mJ / cm². 2 The coating was irradiated to achieve a certain degree of curing, resulting in the formation of a 5 μm thick hard coat layer.

[0166] Subsequently, the resin layer was peeled off from the polyethylene terephthalate substrate, thereby obtaining an optical film consisting of a resin layer made of urethane resin and a hard coat layer.

[0167] The film thickness of each layer was measured by taking cross-sectional images of the optical film using a scanning transmission electron microscope (STEM) (product name "S-4800", manufactured by Hitachi High-Technologies Corporation). The film thickness of each layer was measured at 10 points on the cross-sectional image, and the arithmetic mean of these 10 measurements was taken. Cross-sectional images of the optical film were taken as follows: First, a block was prepared by embedding a 1 mm × 10 mm piece of optical film in embedding resin. From this block, uniform sections with a thickness of 70 nm to 100 nm, free from holes or other defects, were cut using a general sectioning method. A Leica Microsystems EM UC7 ultramicrotome was used to prepare the sections. These uniform sections, free from holes or other defects, were then used as the measurement samples. Subsequently, cross-sectional images of the measurement samples were taken using a scanning transmission electron microscope (STEM). When taking cross-sectional images of each layer, the detector was set to "TE", the acceleration voltage to "30 kV", and the emission current to "10 μA" for STEM observation. For magnification, the focus was adjusted and the contrast and brightness were observed to ensure that each layer could be distinguished, with the magnification being adjusted appropriately between 100x and 100,000x. For magnification, the focus was adjusted and the contrast and brightness were observed to ensure that each layer could be distinguished, with the magnification being adjusted appropriately between 5,000x and 200,000x. In addition, during STEM observation, the beam monitor aperture was set to "3", the objective lens aperture to "3", and the WD was set to "8mm". In Examples 2-10 and Comparative Examples 1-4, the film thickness of each layer was measured using the same method as in Example 1.

[0168] <Example 2> In Example 2, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 2 was used instead of resin layer composition 1.

[0169] <Example 3> In Example 3, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 3 was used instead of resin layer composition 1.

[0170] <Example 4> In Example 4, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 4 was used instead of resin layer composition 1.

[0171] <Example 5> In Example 5, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 5 was used instead of resin layer composition 1.

[0172] <Example 6> In Example 6, an optical film was obtained in the same manner as in Example 2, except that the thickness of the resin layer was 40 μm.

[0173] <Example 7> In Example 7, an optical film was obtained in the same manner as in Example 2, except that the thickness of the resin layer was set to 25 μm.

[0174] <Example 8> In Example 8, an optical film was obtained in the same manner as in Example 2, except that the thickness of the resin layer was set to 75 μm.

[0175] <Example 9> In Example 9, an optical film was obtained in the same manner as in Example 2, except that the thickness of the resin layer was 140 μm.

[0176] <Example 10> In Example 10, an optical film was obtained in the same manner as in Example 2, except that the thickness of the resin layer was 160 μm.

[0177] <Comparative Example 1> In Comparative Example 1, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 6 was used instead of resin layer composition 1.

[0178] <Comparative Example 2> In Comparative Example 2, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 7 was used instead of resin layer composition 1.

[0179] <Comparative Example 3> In Comparative Example 3, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 8 was used instead of resin layer composition 1.

[0180] <Comparative Example 4> In Comparative Example 4, an optical film was obtained in the same manner as in Example 1, except that resin layer composition 9 was used instead of resin layer composition 1.

[0181] <Measurement of shear storage modulus G'> The shear storage modulus G' of the optical films in the examples and comparative examples was measured. Specifically, first, the optical film was punched out into a 10 mm x 5 mm rectangle to create a sample. Two of these samples were prepared and attached to a solid shearing jig, an option for the dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, the solid shearing jig consists of a single 1 mm thick metal solid shearing plate and two L-shaped brackets positioned on either side of this plate. One sample was sandwiched between the solid shearing plate and one L-shaped bracket, and the other sample was sandwiched between the solid shearing plate and the other L-shaped bracket. In this case, the resin layer was on the solid shearing plate side and the hard coat layer was on the L-shaped bracket side. The samples were then secured by tightening screws between the L-shaped brackets. Next, a tensile test chuck consisting of an upper chuck and a lower chuck was attached to a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Then, a solid shearing jig was placed between the upper and lower chucks with a distance of 20 mm between the chucks. The temperature was set to 25°C and increased at a rate of 2°C / min. In this state, while fixing the solid shear plate, a longitudinal vibration of 1% strain and a frequency in the range of 500 Hz to 1000 Hz was applied to two L-shaped brackets, and the dynamic viscoelasticity measurement of the solid was performed at 25°C to measure the shear storage modulus G' of the optical film. Here, the shear storage modulus G' of the optical film in the frequency range of 500 Hz to 1000 Hz was determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to an L-shaped bracket, measuring the shear storage modulus G' of the optical film at each frequency, calculating the arithmetic mean of these shear storage moduli G', repeating this measurement three times, and then taking the arithmetic mean of the three obtained values. Note that in the optical film, the resin layer is softer than the hard coat layer, so the shear storage modulus G' of the optical film can be considered as the shear storage modulus G' of the resin layer.

[0182] <Glass transition temperature (Tg) measurement> The glass transition temperature Tg of the optical films in the examples and comparative examples was measured. Specifically, first, a sample of the same size as the sample used for the shear storage modulus G' measurement was obtained from the optical film, and the sample was mounted on a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.) in the same manner as for the shear storage modulus G' measurement. The temperature was set to -50°C and raised at a rate of 2°C / min. In this state, while fixing the solid shear plate, a longitudinal vibration of 1% strain and a frequency in the range of 500Hz to 1000Hz was applied to two L-shaped brackets, and the dynamic viscoelasticity measurement of the solid was performed, and the shear loss tangent tanδ of the optical film was measured. Here, the shear loss tangent tanδ of the optical film in the frequency range of 500 Hz to 1000 Hz was determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to an L-shaped bracket, measuring the shear loss tangent tanδ of the optical film at each frequency, determining the peak temperature from these shear loss tangents tanδ, and calculating the arithmetic mean of the glass transition temperature. Furthermore, this measurement was repeated three times, and the arithmetic mean of the three obtained values ​​was taken as the value. Note that in the optical film, the resin layer is softer than the hard coat layer, so the glass transition temperature Tg of the optical film can be considered as the glass transition temperature Tg of the resin layer.

[0183] <Impact Resistance Test> Impact resistance tests were conducted using the optical films according to the examples and comparative examples. Specifically, the optical films according to the examples and comparative examples were placed directly on the surface of 0.7 mm thick soda glass with the hard coat layer facing upwards, and an impact resistance test was performed three times for each optical film by dropping a 100 g, 30 mm diameter steel ball onto the hard coat layer of the optical film from a height of 30 cm. The position from which the steel ball was dropped was changed each time during the impact resistance test. After the impact resistance test, the surface of the hard coat layer of the optical film was visually evaluated to see if it was indented. The evaluation results are as follows. A: No indentations were observed on the surface of the hard coat layer when it was viewed from both the front and at an angle. B: When the hard coat layer was observed from either the front or an oblique angle, indentations were found on the surface of the hard coat layer, but these were at a level that did not pose a problem in practical use. C: When the hard coat layer was observed from the front, no indentations were observed on the surface of the hard coat layer, but when it was observed at an angle, indentations were confirmed on the surface of the hard coat layer. D: When the hard coat layer was observed both from the front and from an oblique angle, clear indentations were observed on the surface of the hard coat layer.

[0184] <Foldability> The optical films of the examples and comparative examples were subjected to continuous folding tests to evaluate their foldability. Specifically, a 30mm x 100mm sample was first cut from the optical film. Then, the two opposing sides of the cut sample were fixed to the fixing parts of a folding durability tester (for example, product name "U-shaped stretch tester DLDMLH-FS", manufactured by Yuasa System Equipment Co., Ltd., compliant with IEC62715-6-1) which was arranged in parallel. Subsequently, as shown in Figure 4(C), a continuous folding test was performed by folding the sample 180° 100,000 times under the following conditions, such that the minimum distance φ between the two opposing sides was 10mm and the surface side (hard coat layer side) of the optical film was facing outwards, and it was checked whether deformation, cracking, or breakage occurred at the bend. The continuous folding test was performed in a room temperature environment (23°C, 50% relative humidity) and in a low temperature environment (-40°C). The evaluation criteria were as follows. A: In the continuous folding test, no deformation, cracking, or breakage occurred in the bent area. B: In the continuous folding test, deformation at the bending point was observed at a level that does not pose a practical problem, but no cracks or fractures occurred. C: In the continuous folding test, deformation was clearly observed at the bending point, but no cracks or fractures occurred. D: During the continuous folding test, cracks or fractures occurred at the bending point.

[0185] <Pencil hardness> The pencil hardness of the optical film surface (hard coat layer surface) in the examples and comparative examples was measured according to JIS K5600-5-4:1999. Specifically, first, an optical film cut to a size of 30 mm x 100 mm was fixed onto a 2 mm thick glass plate with cellophane tape (registered trademark) manufactured by Nichiban Co., Ltd., ensuring there were no folds or wrinkles. Then, using a pencil hardness tester (product name "Pencil Scratch Coating Hardness Tester (Electric Type)", manufactured by Toyo Seiki Seisakusho Co., Ltd.), a 750 g load was applied to a pencil (product name "Uni", manufactured by Mitsubishi Pencil Co., Ltd.) under conditions of 23°C and 50% relative humidity, while the pencil was moved at a speed of 1 mm / second. The pencil hardness was defined as the highest hardness at which the surface of the optical film (hard coat layer surface) was not scratched during the pencil hardness test. When measuring pencil hardness, multiple pencils with different hardness levels are used. Each pencil undergoes five hardness tests, and if no scratches are visible on the surface of the optical film when observed under fluorescent light in four or more of the five tests, it is determined that pencils of that hardness level did not scratch the surface of the optical film.

[0186] The results are shown in Table 1 below.

[0187] [Table 1]

[0188] The results are described below. The optical film according to Comparative Example 2 had poor foldability at room temperature because the shear storage modulus G' of the resin layer was too high, and the optical film according to Comparative Example 3 had poor impact resistance because the shear storage modulus G' of the resin layer was too low. In addition, the optical films according to Comparative Examples 1 and 4 had poor foldability at low temperatures, although they had good foldability at room temperature, because the glass transition temperature of the resin layer was too low. In contrast, the optical films according to Examples 1 to 10 had good impact resistance because the shear storage modulus G' was between 30 MPa and 200 MPa, and the glass transition temperature of the resin layer was 50°C or higher, so they had good foldability not only at room temperature but also at low temperatures. [Explanation of Symbols]

[0189] 10…Resin layer 30, 50… Optical film 31… Functional Layer 51…Resin base material 52… Functional Layer 60…Image display device 62…Display element

Claims

1. A resin layer used in an image display device, The aforementioned resin layer is a single-layer structure containing resin, The aforementioned resin layer contains a cured product of an ionizing radiation-curable compound, The thickness of the resin layer is 20 μm or more and 120 μm or less. The shear storage modulus G' of the resin layer at 25°C and a frequency range of 500 Hz to 1000 Hz is 30 MPa to 200 MPa. A resin layer having a glass transition temperature of 50°C or higher and 90°C or lower.

2. A foldable laminated optical film, An optical film comprising at least the resin layer described in claim 1.

3. The optical film according to claim 2, wherein the haze value is 2.0% or less.

4. The optical film according to claim 2 or claim 3, further comprising a functional layer provided on one side of the resin layer.

5. The optical film according to any one of claims 2 to 4, further comprising a resin substrate provided on one side of the resin layer.

6. The optical film according to any one of claims 2 to 5, wherein no cracks or breaks occur when the optical film is folded 180° so that the distance between opposing sides of the optical film is 10 mm, and this test is repeated 100,000 times in an environment of 23°C.

7. The optical film according to claim 6, wherein no cracks or breaks occur when the optical film is folded 180° so that the distance between opposing sides of the optical film is 10 mm, and this test is repeated 100,000 times in an environment of -40°C.

8. Display element and A resin layer according to claim 1, or an optical film according to any one of claims 2 to 7, which is positioned on the observer side of the display element, An image display device equipped with the following features.

9. The image display device according to claim 8, wherein the display element is an organic light-emitting diode element.

Images