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] Image display devices such as smartphones and tablet terminals have been known for some time, and currently, foldable image display devices are being developed. Smartphones and tablet terminals are usually covered with cover glass. Although glass is generally excellent in hardness, it is difficult to bend, so if a cover glass is used for an image display device, there is a high possibility that the device will break when folded. For this reason, the use of an optical film made of resin instead of a cover glass for a foldable image display device is being considered (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-125063 A Summary of the Invention [Problem to be solved by the invention]

[0004] Optical films used in such foldable image display devices are required to have impact resistance because an impact may be applied to the surface of the optical film. When an impact is applied to the surface of the optical film, the surface of the optical film may be dented. Therefore, there is currently a demand for impact resistance that suppresses dents in the surface of the film when an impact is applied to the surface of the optical film.

[0005] However, in the current situation, optical films are not yet capable of providing impact resistance sufficient to prevent dents on the surface of the film when an impact is applied to the surface of the optical film.

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

[0007] However, even if an optical film does not crack in a folding test in a room temperature environment, when the folding test is performed in a low temperature environment, the flexibility is lost and cracks may occur.

[0008] The present invention has been made to solve the above problems, and aims to provide a resin layer that has good impact resistance and good foldability not only in a room temperature environment but also in a low temperature environment, and an optical film and an image display device including the same. [Means for solving the problem]

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

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

[0011] [3] An optical film having a foldable laminate structure, comprising at least the resin layer described in [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 the above [3] or [4], further comprising a resin substrate provided on one surface side of the resin layer.

[0014] [6] The optical film according to any one of [3] to [5] above, wherein the optical film does not crack or break when a test in which the optical film is folded 180° so that the distance between opposing sides of the optical film is 10 mm is repeated 100,000 times in an environment of 23°C.

[0015] [7] The optical film according to [6] above, wherein the optical film does not crack or break when a test of folding the optical film 180° so that the distance between opposing sides of the optical film is 10 mm is repeated 100,000 times in an environment of -40°C.

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

[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] According to the present invention, it is possible to provide a resin layer that has good impact resistance and good foldability not only in a room temperature environment but also in a low temperature environment, and an optical film and an image display device including the same. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a resin layer according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a solid shearing jig used for measuring the shear storage modulus G' and the glass transition temperature Tg. [Diagram 3] FIG. 3 is a schematic diagram of an optical film according to an embodiment. [Figure 4]4(A) to 4(C) are schematic diagrams showing the state of the continuous folding test. [Diagram 5] FIG. 5 is a schematic diagram of another optical film according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram of an image display device according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the resin layer, optical film, and image display device according to the embodiment of the present invention will be described with reference to the drawings. In this specification, the terms "film" and "sheet" are not distinguished from each other based only on the difference in name. Therefore, for example, "film" is used to mean a member also called a sheet. FIG. 1 is a schematic diagram of the resin layer according to this embodiment, FIG. 2 is a schematic diagram of a solid shearing jig used in measuring the shear storage modulus G' and the glass transition temperature Tg, FIG. 3 is a schematic diagram of the optical film according to this embodiment, FIG. 4(A) to FIG. 4(C) are diagrams showing the state of a continuous folding test, and FIG. 5 is a schematic diagram of another optical film according to this embodiment.

[0021] <<<Resin layer>>> The resin layer 10 shown in FIG. 1 is used in an image display device. In this specification, the term "resin layer" refers to a layer having a single layer structure containing a resin. The resin layer 10 is made of a resin having optical transparency and has impact absorption properties. The resin layer 10 may be used alone, or may be incorporated into an optical film 30 in which a functional layer 31 described later is laminated on the resin layer 10, or an optical film 50 including a resin substrate 51 described later. A release film may be attached to the resin layer 10.

[0022] In the resin layer 10, the shear storage modulus G' at 25°C in the frequency range of 500 Hz to 1000 Hz is 30 MPa or more and 200 MPa or less. If the shear storage modulus G' of the resin layer 10 is 30 MPa or more, deformation of the surface of the resin layer 10 can be suppressed when an impact is applied to the surface of the resin layer 10, and a decrease in hardness of the resin layer 10 can be suppressed. If the shear storage modulus G' of the resin layer 10 is 200 MPa or less, the resin layer 10 is unlikely to crack when folded at room temperature. The lower limit of the shear storage modulus G' of the resin layer 10 is preferably 40 MPa or more, 50 MPa or more, or 80 MPa or more, 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 a decrease in hardness of the resin layer 10. 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 by a dynamic viscoelasticity measuring device (DMA). When measuring the shear storage modulus G' of the resin layer 10 by a dynamic viscoelasticity measuring device (DMA), first, the resin layer 10 is punched out into a rectangular shape of 10 mm x 5 mm to obtain a sample S1 (see FIG. 2). Then, two sheets of the sample S1 are prepared and attached to a solid shearing jig, which is an option of a dynamic viscoelasticity measuring device (for example, product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, as shown in FIG. 2, the solid shearing jig 20 includes one metal solid shearing plate 21 (middle plate) having a thickness of 1 mm and two L-shaped metal fittings 22 (outer plates) arranged on both sides of the solid shearing plate 21, and one sample S is sandwiched between the solid shearing plate 21 and one of the L-shaped metal fittings 22, and the other sample S1 is sandwiched between the solid shearing plate 21 and the other L-shaped metal fitting 22. Then, the L-shaped metal fittings 22 are tightened with the screws 23 to fix the sample S1. Next, a tensile test chuck consisting of an upper chuck and a lower chuck is attached to a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.), and then a solid shear jig is attached between the upper chuck and the lower chuck with a chuck distance of 20 mm. The chuck distance is the distance between the upper chuck and the lower chuck. The set temperature is set to 25°C and the temperature is increased at 2°C / min. In this state, the solid shear plate 21 is fixed, and the two L-shaped metal fittings 22 are given a vertical vibration with a distortion amount of 1% and a frequency range of 500Hz to 1000Hz, while the dynamic viscoelasticity of the solid is measured at 25°C, and the shear storage modulus G' of the resin layer 10 is measured. 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 metal fitting 22, measuring the shear storage modulus G' of the resin layer 10 at each frequency, obtaining the arithmetic average of these shear storage modulus G', and then repeating this measurement three times to obtain the arithmetic average of the three arithmetic averages. Note that the frequency range of 500 Hz to 1000 Hz is set above because this frequency range is a frequency at which the surface of the resin layer 10 deforms by several microns to several tens of microns when an object is allowed to fall freely 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 at low temperatures (e.g., -40°C), so that 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. In addition, 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 by a dynamic viscoelasticity measuring device (DMA). When measuring the glass transition temperature Tg of the resin layer 10 by a dynamic viscoelasticity measuring device (DMA), first, the resin layer 10 is punched out into a rectangular shape of 10 mm x 5 mm to obtain a sample S1. Then, two sheets of this sample are prepared and attached to a solid shear jig, which is an option of a dynamic viscoelasticity measuring device (for example, product name "Rheogel-E4000", manufactured by UBM Co., Ltd.) in the same manner as the shear storage modulus G'. Then, the set temperature is set to -50°C and the temperature is increased at 2°C / min. In this state, while fixing the solid shear plate, a vertical vibration with a distortion amount of 1% and a frequency range of 500Hz to 1000Hz is applied to the two L-shaped metal fittings 22, 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. The peak of the shear loss tangent tan δ is then obtained, and the temperature at which this peak is detected is taken as the glass transition temperature Tg. This measurement is repeated three times, and the arithmetic mean of the three values ​​obtained is further calculated to take the arithmetic mean value, which is taken as the glass transition temperature Tg.

[0026] Incidentally, 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 as described below, 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 regarded 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 is determined from the amount of displacement, which will be described later.

[0027] In the case where another film such as a polarizing plate is provided on one side of the resin layer 10 via an adhesive layer or a bonding layer, the other film is peeled off together with the adhesive layer or the bonding layer before measuring the shear storage modulus G' and the glass transition temperature. The peeling off of the other film can be performed, for example, as follows. First, a laminate in which the other film is attached to the resin layer 10 via an adhesive layer or a bonding layer is heated with a dryer, and the tip of a cutter is inserted into the area that is thought to be the interface between the resin layer 10 and the other film, and the film is slowly peeled off. By repeating such heating and peeling, the adhesive layer, the bonding layer, and the other film can be peeled off. Even if such a peeling process is performed, it does not have a significant effect 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 is less likely to break and exhibits excellent performance in a 100,000 times repeated folding test. 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 achieving a thin film and good processability.

[0029] The thickness of the resin layer 10 is determined by photographing a cross section of the resin layer 10 using a scanning transmission electron microscope (STEM), measuring the thickness of the resin layer 10 at 10 points on the image of the cross section, and arithmetic mean value of the thicknesses at the 10 points.

[0030] A specific method for taking a cross-sectional photograph is described below. First, a resin layer cut into a size of 1 mm x 10 mm is embedded in an embedding resin to prepare a block, and a uniform slice having a thickness of 70 nm to 100 nm without holes is cut out from this block by a general slice preparation method. For example, an ultramicrotome EM UC7 manufactured by Leica Microsystems can be used to prepare the slice. Then, this uniform slice without holes is used as a measurement sample. Then, a cross-sectional photograph 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 a cross-sectional photograph using the S-4800, the detector is set to "TE", the acceleration voltage is set to "30 kV", and the emission current is set to "10 μA" to observe the cross section. The magnification is adjusted appropriately between 100x and 100,000x, preferably 1,000x and 50,000x, and more preferably 5,000x and 10,000x while observing whether the layers can be distinguished by adjusting the focus and observing the contrast and brightness. When taking a cross-sectional photograph using the S-4800, the beam monitor aperture may be set to "3", the objective lens aperture may be set to "3", and the WD may be set to "8 mm". When measuring the film 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, a staining process using osmium tetroxide, ruthenium tetroxide, phosphotungstic acid, etc. may be performed to make the interface between the organic layers easier to see. In addition, the contrast of the interface may be difficult to see at high magnification. In that case, observation is also performed at low magnification at the same time. For example, the film is observed at two magnifications, high and low, such as 2000x and 10,000x, or 5000x and 20,000x, and the arithmetic average value is calculated at both magnifications, and the average value is taken as the film thickness of the resin layer.

[0031] The resin constituting the resin layer 10 is not particularly limited as long as it is a resin whose shear storage modulus G' and glass transition temperature Tg satisfy the above ranges. Examples of such resins include cured products (polymerized products) of ionizing radiation curable compounds (ionizing radiation polymerizable compounds). Examples of ionizing radiation in this specification include visible light, ultraviolet light, X-rays, electron beams, α-rays, β-rays, and γ-rays. Examples of cured products of ionizing radiation curable compounds include urethane-based resins and silicone-based resins.

[0032] (Urethane resin) The urethane resin is a resin having a urethane bond. Examples of the urethane resin include a cured product of an ionizing radiation curable urethane resin composition and a cured product of a thermosetting urethane resin composition. Among these, a cured product of an ionizing radiation curable urethane resin composition is preferred from the viewpoints of obtaining high hardness, a fast curing speed, and excellent mass productivity.

[0033] The ionizing radiation curable urethane resin composition contains a urethane (meth)acrylate, and the thermosetting urethane resin composition contains a polyol compound and an isocyanate compound. The urethane (meth)acrylate, the polyol compound, and the isocyanate compound may be any one of a monomer, an oligomer, and a prepolymer.

[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, the curing shrinkage may be large, the resin layer may curl, and the resin layer may crack when folded. It is more preferable that the upper limit of the number of (meth)acryloyl groups in the urethane (meth)acrylate is 3 or less. Note that "(meth)acrylate" means both "acrylate" and "methacrylate", and "(meth)acryloyl group" means both "acryloyl group" and "methacryloyl group".

[0035] The weight average molecular weight of the urethane (meth)acrylate is preferably 1500 or more and 20000 or less. If the weight average molecular weight of the urethane (meth)acrylate is less than 1500, the impact resistance may decrease, and if it exceeds 20000, the viscosity of the ionizing radiation curable urethane resin composition may increase, and the coatability may deteriorate. The lower limit of the weight average molecular weight of the urethane (meth)acrylate is more preferably 2000 or more, and the upper limit is more preferably 15000 or less.

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

[0037] [ka] In the above general formula (1), R 1 represents a branched alkyl group, and R 2 represents a branched alkyl group or a saturated cyclic aliphatic group, R 3 represents a hydrogen atom or a methyl group, and R 4 represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 0 or more, and x represents an integer of 0 to 3.

[0038] [ka] In the above general formula (2), R 1 represents a branched alkyl group, and R 2 represents a branched alkyl group or a saturated cyclic aliphatic group, R 3 represents a hydrogen atom or a methyl group, and R 4 represents a hydrogen atom, a methyl group or an ethyl group, n represents an integer of 1 or more, and x represents an integer of 0 to 3.

[0039] [ka] In the above general formula (3), R 1represents a branched alkyl group, and R 2 represents a branched alkyl group or a saturated cyclic aliphatic group, R 3 represents a hydrogen atom or a methyl group, and R 4 represents a hydrogen atom, a methyl group or an ethyl group, m represents an integer of 0 or more, and x represents an integer of 0 to 3.

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

[0041] The structure of the polymer chain (repeating unit) of the resin constituting the resin layer 10 can be determined by analyzing the resin layer 10 by, for example, 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 the 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 absorbing agent, a spectral transmittance adjusting agent, an antifouling agent, inorganic particles and / or organic particles, and the like.

[0043] <<<Optical films>>> The optical film 30 shown in Fig. 3 is a film with a laminated structure, and includes at least a resin layer 10. The optical film 30 includes the resin layer 10 and a functional layer 31 provided on one surface of the resin layer 10. In this specification, the "functional layer" is a layer that exhibits some function. The functional layer 31 has a single-layer structure, but may also have a multi-layer structure of two or more layers.

[0044] In the optical film 30, the shear storage modulus G' at 25°C in the frequency range of 500 Hz to 1000 Hz is 30 MPa or more and 200 MPa or less. If the shear storage modulus G' of the optical film 30 is 30 MPa or more, 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 a decrease in hardness of the optical film 30 can be suppressed. If the shear storage modulus G' of the optical film 30 is 200 MPa or less, the optical film 30 is less likely to break when folded at room temperature. The lower limit of the shear storage modulus G' of the optical film 30 is preferably 40 MPa or more, 50 MPa or more, or 80 MPa or more, from the viewpoint of further suppressing 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 a decrease in hardness of the optical film 30. From the viewpoint of further suppressing cracking during folding, 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. The shear storage modulus G' of the optical film 30 is measured by the same method as that for measuring the shear storage modulus G' of the resin layer 10.

[0045] The optical film 30 is foldable. Specifically, even if the folding test (continuous folding test) described below is repeatedly performed on the optical film 30 100,000 times, 200,000 times, 500,000 times, or 1 million times under an environment with a temperature of 23±5°C (for example, 23°C) and a relative humidity of 30% to 70%, and an environment with a temperature of -40°C±5°C (for example, -40°C), it is preferable that the optical film 30 does not crack or break in any of the cases. If the optical film 30 cracks or breaks when the continuous folding test is repeatedly performed on the optical film 30 100,000 times, the foldability of the optical film 30 is insufficient. The reason why the number of folding times in the continuous folding test is evaluated at least 100,000 times is as follows. For example, assuming that the optical film is incorporated into a foldable smartphone, the frequency of folding (frequency of opening and closing) becomes very high. For this reason, in the evaluation of the number of folding times in the continuous folding test, for example, 10,000 times or 50,000 times, there is a possibility that evaluation at a practical level cannot be performed. Specifically, for example, assuming a person who always uses a smartphone, it is assumed that the smartphone is opened and closed 5 to 10 times just during the morning commute on a train or bus, and therefore it is assumed that the smartphone is opened and closed at least 30 times just in one day. Therefore, assuming that the smartphone is opened and closed 30 times a day, the continuous folding test with the number of folding times of 10,000 times is 30 times x 365 days = 10950 times, which is a test assuming one year of use. That is, even if the result of the continuous folding test with the number of folding times of 10,000 times is good, after one year has passed, there is a possibility that the optical film will crack or break. Therefore, the evaluation of the number of folding times of 10,000 times in the continuous folding test is only a level that cannot be used as a product, and even if it is usable but insufficient, it will be good and cannot be evaluated. For this reason, in order to evaluate whether or not the product is at a practical level, the number of folds in the above-mentioned continuous folding test needs to be at least 100,000.The continuous folding test may be performed by folding the optical film 30 so that surface 30A is on the outside, or may be performed by folding the optical film 30 so that surface 30A is on the inside, but in either case, it is preferable that the optical film 30 does not crack or break.

[0046] The continuous folding test is carried out as follows. As shown in FIG. 4(A), in the continuous folding test, first, a sample S2 having a size of 30 mm×100 mm is cut out from the optical film 30. If a sample S2 having a size of 30 mm×100 mm cannot be cut out from the optical film 30, the sample S2 may be cut out to a size of, for example, 10 mm×100 mm. Then, the side portion S2a of the cut-out sample S2 and the side portion S2b opposite to the side portion S2a are fixed by fixing parts 40 and 45 of a folding durability tester (for example, product name "U-shaped stretch tester DLDMLH-FS", manufactured by Yuasa System Devices Co., Ltd., compliant with IEC62715-6-1) arranged in parallel. Fixing by the fixing parts 40 and 45 is carried out by holding a portion of the sample S2 of about 10 mm on one side in the longitudinal direction of the sample S2. However, if sample S2 is smaller than the above size, and the portion of sample S2 required for fixing is up to about 20 mm, it can be measured by attaching it to fixing parts 40, 45 with tape. Also, as shown in Fig. 4(A), fixing part 40 is slidable in the horizontal direction. The above device is preferable because it makes it possible to evaluate the durability against bending load without generating tension or friction in the sample, unlike the conventional method of winding a sample around a rod.

[0047] Next, as shown in FIG. 4(B), fixing portion 40 is moved closer to fixing portion 45, thereby deforming the central portion of sample S2 by folding it, and further, as shown in FIG. 4(C), fixing portion 40 is moved to a position where the distance φ between the two opposing sides S2a, S2b of sample S2 fixed by fixing portions 40, 45 is 10 mm, and then fixing portion 40 is moved in the opposite direction to eliminate the deformation of optical film 30.

[0048] As shown in Figs. 4(A) to (C), the central portion of the sample S2 can be folded 180° by moving the fixing portion 40. The interval φ between the two opposing sides S2a, S2b of the sample S2 can be set to 10 mm by performing a continuous folding test under the following conditions so that the bent portion S2c of the sample S2 does not protrude from the lower ends of the fixing portions 40, 45, and controlling the interval φ when the fixing portions 40, 45 are closest to each other. In this case, the outer diameter of the bent portion S2c is considered to be 10 mm. It is preferable that the sample S2 does not crack or break when a continuous folding test is performed 100,000 times in which the sample S2 is folded 180° so that the interval φ between the opposing sides S2b, S2c of the sample S2 is 10 mm. However, it is more preferable that the sample S2 does not crack or break when a continuous folding test is performed 100,000 times in which the sample S2 is folded 180° so that the interval φ between the opposing sides S2b, S2c of the sample S2 is 8 mm or 6 mm. (Folding conditions) Reciprocating speed: 120 rpm (revolutions 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 more, more preferably 3H or more, when measured by a pencil hardness test specified in JIS K5600-5-4:1999. The pencil hardness test is performed by fixing the optical film 30 cut into a size of 30 mm x 100 mm on a glass plate with Cellotape (registered trademark) manufactured by Nichiban Co., Ltd. so as not to cause any folds or wrinkles, and by moving a pencil (for example, product name "Uni", manufactured by Mitsubishi Pencil Co., Ltd.) at a moving speed of 1 mm / sec while applying a load of 750 g to the surface 30A of the optical film 30 using a pencil hardness tester (for example, product name "Pencil Scratch Coating Hardness Tester (Electric)" manufactured by Toyo Seiki Seisakusho Co., Ltd.) in an environment of a temperature of 23±5°C and a relative humidity of 30% to 70%. The pencil hardness is defined as the highest hardness that does not scratch the surface of the optical film in the pencil hardness test. When measuring the pencil hardness, multiple pencils with different hardnesses are used, and the pencil hardness test is performed five times for each pencil. If the surface of the optical film is not scratched four or more times out of the five, it is determined that the pencil of this hardness did not scratch the surface of the optical film. The above scratches refer to those that are visually observed when the surface of the optical film that has been subjected to the pencil hardness test is observed through a fluorescent lamp.

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

[0051] The optical film 30 may be cut to a desired size, or may be in a roll shape. When 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 line when the optical film is rectangular, the diameter when the optical film is circular, and the average value of the sum of the short diameter and the long diameter when the optical film is elliptical. Here, when the optical film is rectangular, the aspect ratio of the optical film when calculating the above inch is not particularly limited as long as it does not cause any problem as a display screen of the image display device. For example, length:width = 1:1, 4:3, 16:10, 16:9, 2:1, etc. can be mentioned. However, in particular, in-vehicle applications and digital signage that are rich in design, such aspect ratios are not limited. Furthermore, when the size of the optical film 30 is large, it is cut into A5 size (148 mm x 210 mm) from an arbitrary position, and then cut into the size of each measurement item. For example, when the optical film 30 is in a roll, a predetermined length is unwound from the roll of the optical film 30, and the desired size is cut from the effective area near the center where the quality is stable, not from the non-effective area including both ends extending along the longitudinal direction of the roll.

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

[0053] The optical film 30 may be disposed inside the image display device, but is preferably disposed 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 Fig. 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, the "hard coat layer" means a layer that has a pencil hardness of "H" or more in the above-mentioned pencil hardness test.

[0055] When the displacement of the functional layer 31 is measured by the nanoindentation method, the displacement of the functional layer 31 is preferably 50 nm or more and 500 nm or less. 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 displacement measurement by the nanoindentation method 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, a Berkovich indenter (triangular pyramid, for example, TI-0039 manufactured by Bruker) is pressed perpendicularly into the cross section of the functional layer with 500 μN to measure the depth, which is the displacement amount. Here, in order to avoid the influence of the resin layer and the side edges of the functional layer, the Berkovich indenter is pressed into a part 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 each of the two 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 content of inorganic particles, which will be described later. (Measurement conditions) Control method: Load control (maximum load 500μN) Lift amount: 0nm Preload: 0.5μN ·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, the "thickness of the functional layer" means the thickness (total thickness) of the functional layer when the functional layer has a multi-layer 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 that 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 a polymer (cured product) of a polymerizable compound (curable compound). The polymerizable compound has at least one polymerizable functional group in the molecule. Examples of the polymerizable functional group include ethylenically unsaturated groups such as (meth)acryloyl group, vinyl group, and allyl group.

[0059] The polymerizable compound is preferably a polyfunctional (meth)acrylate. Examples of the polyfunctional (meth)acrylate 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, dipentaerythritol penta(meth)acrylate, and the like. acrylate, 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, isobornyl di(meth)acrylate, dicyclopentane di(meth)acrylate, tricyclodecane di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and those modified with PO, EO, caprolactone, etc.

[0060] Among these, those having three to six functionalities are preferred since they can suitably satisfy the above-mentioned displacement amount. 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] In addition, the composition may further contain a monofunctional (meth)acrylate monomer in order to adjust the hardness or viscosity of the composition, improve adhesion, etc. Examples of the monofunctional (meth)acrylate monomer include hydroxyethyl acrylate (HEA), glycidyl methacrylate, methoxypolyethylene glycol (meth)acrylate, isostearyl (meth)acrylate, 2-acryloyloxyethyl succinate, acryloylmorpholine, N-acryloyloxyethylhexahydrophthalimide, cyclohexyl acrylate, tetrahydrofuryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and adamantyl acrylate.

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

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

[0064] The reactive silica particles preferably have a reactive functional group on the surface thereof, and as the reactive functional group, for example, the above-mentioned polymerizable functional group is preferably used.

[0065] The reactive silica particles are not particularly limited, and conventionally known ones can be used, for example, the reactive silica particles described in JP-A-2008-165040, etc. In addition, commercially available reactive silica particles include, for example, MIBK-SD, MIBK-SD-MS, MIBK-SD-L, MIBK-SD-ZL (all manufactured by Nissan Chemical Industries, Ltd.), V8802, V8803 (all manufactured by JGC Catalysts and Chemicals, Ltd.), etc.

[0066] The silica particles may be spherical silica particles, but are preferably irregular silica particles. Spherical silica particles and irregular silica particles may be mixed. In this specification, the term "spherical silica particles" refers to silica particles having, for example, a perfect sphere, an elliptical sphere, or the like, and the term "irregular silica particles" refers to silica particles having a potato-like shape (aspect ratio when observed in cross section is 1.2 or more and 40 or less) with random irregularities on the surface. The irregular silica particles have a larger surface area than spherical silica particles, so that the inclusion of such irregular silica particles increases the contact area with the polyfunctional (meth)acrylate, etc., and can improve the hardness of the functional layer 31. Whether the silica particles contained in the functional layer 31 are irregular silica particles can be confirmed by observing the 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 5 nm or more and 200 nm or less. If the average particle diameter of the silica particles is 5 nm or more, the particles themselves are not difficult to manufacture, the aggregation of the particles can be suppressed, and it is not difficult to make them into irregular shapes. 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. When the silica particles are spherical silica particles, the average particle diameter of the silica particles is determined by measuring the particle diameters of 20 particles from an image of the cross section of the particles taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), and the arithmetic average value of the particle diameters of the 20 particles is used. In addition, when the silica particles are irregularly shaped silica particles, the average particle diameter of the silica particles is determined by measuring the maximum (long axis) and minimum (short axis) distance between two points on the outer periphery of the particles from an image of a cross-section of the functional layer taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), averaging them to determine the particle diameter, and using this as the arithmetic mean of the particle diameters of 20 particles.

[0068] By controlling the size and amount of the inorganic particles, it is possible to control the hardness (displacement amount) of the functional layer 31. For example, when forming the functional layer 31, it is preferable that the silica particles have a diameter of 5 nm or more and 200 nm or less, and are present in an amount of 25 to 60 parts by mass relative to 100 parts by mass of the polymerizable compound.

[0069] The functional layer 31 may contain materials other than the above-mentioned materials within a range that satisfies the above-mentioned displacement amount. For example, the resin component may contain a polymerizable monomer or a polymerizable oligomer that forms a cured product by irradiation with ionizing radiation. Examples of the above-mentioned polymerizable monomer or polymerizable oligomer include a (meth)acrylate monomer having a radical polymerizable unsaturated group in the molecule, or a (meth)acrylate oligomer having a radical polymerizable unsaturated group in the molecule. Examples of the above-mentioned (meth)acrylate monomer having a radical polymerizable unsaturated group in the molecule or a (meth)acrylate oligomer having a radical polymerizable unsaturated group in the molecule include monomers or oligomers such as urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, melamine (meth)acrylate, polyfluoroalkyl (meth)acrylate, and silicone (meth)acrylate. These polymerizable monomers or polymerizable oligomers may be used alone or in combination of two or more. Among these, polyfunctional (six or more functional) urethane (meth)acrylates having a weight average molecular weight of 1,000 to 10,000 are preferred.

[0070] The functional layer 31 may further include an ultraviolet absorbing agent, a spectral transmittance adjusting agent, and / or an antifouling agent.

[0071] <<<Other optical films>>> The optical film 30 shown in Fig. 3 does not include a substrate, but may include a substrate like the optical film 50 shown in Fig. 5. As shown in Fig. 5, the optical film 50 includes a resin layer 10, a resin substrate 51, and a functional layer 52 in this order. The resin substrate 51 may be adjacent to the resin layer 10. Note that in the optical film 50, the resin layer 10 is adjacent to the resin substrate 51, but may be attached to the resin substrate via an adhesive layer.

[0072] A surface 50A of the optical film 50 is a 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, and the surface opposite to the surface of the optical film is referred to as a back surface to distinguish it from the front surface of the optical film. A back surface 50B of the optical film 50 is a surface opposite to the surface of the resin layer 10 on the resin substrate 51 side.

[0073] The optical film 50 can be folded in an environment with a temperature of 23±5° C. and a relative humidity of 30% to 70%, and in an environment with a temperature of −40° C. The preferred number of foldings, the preferred distance φ between opposing sides, and the conditions for the continuous folding test are similar to those of the optical film 30, and therefore will not be described 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 more, and more preferably 3H or more, when measured by the pencil hardness test specified in JIS K5600-5-4: 1999. The pencil hardness of the optical film 50 is measured by the same method as that 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 yellowish tinge of the optical film can be suppressed, and the optical film can be applied to applications requiring transparency. 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 a value calculated from the chromaticity tristimulus values ​​X, Y, and Z of the optical film cut to a size of 50 mm x 100 mm, measured in a spectrophotometer (e.g., product name "UV-2450" manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp) in an environment of temperature 23 ± 5 ° C. and relative humidity 30% to 70%, with the resin layer side of the optical film being placed on the light source side, according to the calculation formula described in JIS Z8722: 2009. The tristimulus values ​​X, Y, and Z are calculated according to the calculation formula described in ASTM D1925: 1962. The upper limit of the yellow index (YI) of the optical film 50 is more preferably 10 or less. The yellow index (YI) is the arithmetic average value of the values ​​obtained by measuring three times for one optical film. In addition, in 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. The transmittance at wavelengths of 300nm to 780nm is measured under the following conditions by measuring the transmittance at at least 5 points within 1nm before and after each wavelength of 300nm to 780nm and calculating the average value. If the spectrum of the spectral transmittance appears to be wavy, smoothing processing may be performed with a delta of 5.0nm. (Measurement conditions) ·Wavelength range: 300nm~780nm Scan speed: Fast Slit width: 2.0 Sampling interval: Auto (0.5 nm interval) ·Lighting:C Light source: D2 and WI ·Field of view: 2° Light source switching wavelength: 360nm S / R Switching: Standard Detector: PM Autozero: Performed at 550 nm after baseline scan

[0076] The total light transmittance of the optical film 50 is preferably 85% or more. If the total light transmittance of the optical film 50 is 85% or more, 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 more, or 90% or more.

[0077] The total light transmittance can be measured in an environment of 23±5°C temperature and 30% to 70% relative humidity using a haze meter (for example, product name "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.) according to a method conforming to JIS K7361-1:1997. The total light transmittance is measured three times for each optical film after cutting the optical film into a size of 50 mm x 100 mm, placing the optical film in a state free of curls and wrinkles and free of fingerprints and dust, and the arithmetic average value of the values ​​obtained by the three measurements is taken as the total light transmittance. In this specification, "measured three times" does not mean measuring the same place three times, but measuring three different places. In the optical film 50, the surface 50A when visually observed is flat, and the laminated layers such as the resin layer 10 are also flat, and the variation in film thickness is within the range of ±10%. Therefore, it is considered that the average value of the total light transmittance of the entire in-plane of the optical film can be obtained by measuring the total light transmittance at three different points of the cut optical film. The variation of the total light transmittance is within ±10%, even if the measurement target is as long as 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 entrance opening of the HM-150 is 20mmφ when measuring, so a sample size with a diameter of 21mm or more is required. For this reason, the optical film may be appropriately cut to a size of 22mm x 22mm or more. If the size of the optical film is small, the measurement points are set to three points by shifting the light source spot little by little or changing the angle within the range where the light source spot does not move.

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

[0080] In the case where another film such as a polarizing plate is provided on the front surface 50A side or the back surface 50B side of the optical film 50 via an adhesive layer or a bonding layer, the other film is peeled off together with the adhesive layer or the bonding layer before carrying out the folding test, the yellow index measurement, the total light transmittance measurement, the haze value measurement, etc. Even if such a peeling step is performed, it does not have a significant effect on these tests and measurements. The haze value is measured after the adhesive layer or the bonding layer is peeled off and dirt on the adhesive layer or the bonding layer is thoroughly wiped off with alcohol.

[0081] The use of the optical film 50 is not particularly limited, and may be the same as the uses described in the section of the optical film 30.

[0082] <<Resin substrate>> The resin base material 51 has optical transparency. In this specification, "optical transparency" means a 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. Optical transparency does not necessarily mean transparency, and may be translucent.

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

[0084] Among these resins, polyimide-based resins, polyamide-based resins, or mixtures thereof are preferred, since they are not only less likely to crack or break in a continuous folding test, but also have excellent hardness and transparency, and are also excellent in heat resistance, and can be imparted with even greater hardness and transparency by baking.

[0085] The polyimide resin is obtained by reacting a tetracarboxylic acid component with a diamine component. The polyimide resin is not particularly limited, but it is preferable that the polyimide resin has at least one structure selected from the group consisting of structures represented by the following general formula (5) and the following general formula (7) in terms of excellent light transmittance and excellent rigidity.

[0086] [ka] In the above general formula (5), R 5 is a tetravalent group which is a tetracarboxylic acid residue, R 6 represents at least one divalent group selected from the group consisting of trans-cyclohexanediamine residue, trans-1,4-bismethylenecyclohexanediamine residue, 4,4'-diaminodiphenylsulfone residue, 3,4'-diaminodiphenylsulfone residue, and divalent groups represented by the following general formula (6). n represents the number of repeating units and is 1 or more. In this specification, the term "tetracarboxylic acid residue" refers to a residue obtained by removing four carboxyl groups from a tetracarboxylic acid, and represents the same structure as the residue obtained by removing an acid dianhydride structure from a tetracarboxylic dianhydride. In addition, the term "diamine residue" refers to 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 independently represents a hydrogen atom, an alkyl group, or a perfluoroalkyl group.

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

[0089] In the above general formula (5), R 5 R in the above general formula (5) is a tetracarboxylic acid residue, and can be a residue obtained by removing the acid dianhydride structure from the tetracarboxylic acid dianhydride as exemplified above. 5 Among them, from the viewpoint of improving light transmittance and improving 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, and it is further 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 the present invention, the total amount of these suitable residues is preferably 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 a tetracarboxylic acid residue group (Group A) suitable for improving rigidity, 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 a tetracarboxylic acid residue group (Group B) suitable for improving transparency, 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 the rigidity (Group A) to the tetracarboxylic acid residue group suitable for improving the transparency (Group B) is preferably such that the tetracarboxylic acid residue group suitable for improving the rigidity (Group A) is 0.05 mol or more and 9 mol or less, more preferably 0.1 mol or more and 5 mol or less, and even more preferably 0.3 mol or more and 4 mol or less, per 1 mol of the tetracarboxylic acid residue group suitable for improving the transparency (Group B).

[0093] R in the above general formula (5) 6 Among them, from the viewpoint of improving light transmittance and improving rigidity, it is preferable that R is at least one divalent group selected from the group consisting of 4,4'-diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, and divalent groups represented by the above general formula (6), and further, 4,4'-diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, and R 7 and R8 is preferably at least one divalent group selected from the group consisting of divalent groups represented by the above general formula (6), which is a perfluoroalkyl group.

[0094] R in the above general formula (7) 9 Among these, from the viewpoints of improving light transmittance and improving rigidity, it is preferable that the diphthalic acid residue contains 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, 3,3',4,4'-diphenylsulfonetetracarboxylic acid residue, and oxydiphthalic acid residue.

[0095] R 9 In the above, these suitable residues are preferably contained in an amount of 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more.

[0096] R in the above general formula (7) 10is a diamine residue, and may be a residue obtained by removing two amino groups from the diamines exemplified above. In terms of improving light transmittance and rigidity, R6 in the above general formula (3) may be, among others, 2,2'-bis(trifluoromethyl)benzidine residue, bis[4-(4-aminophenoxy)phenyl]sulfone residue, 4,4'-diaminodiphenyl sulfone 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-trifluoromethyl ...4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residue, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residue, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residue, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residue, It is preferable that the aryl group contains at least one divalent group selected from the group consisting of a 2,2'-bis(trifluoromethyl)benzidine residue, a bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residue, a 4,4'-diamino-2-(trifluoromethyl)diphenyl ether residue, a 4,4'-diaminobenzanilide residue, an N,N'-bis(4-aminophenyl)terephthalamide residue, and a 9,9-bis(4-aminophenyl)fluorene residue, and it is further preferable that the aryl group contains at least one divalent group selected from the group consisting of a 2,2'-bis(trifluoromethyl)benzidine residue, a bis[4-(4-aminophenoxy)phenyl]sulfone residue, and a 4,4'-diaminodiphenyl sulfone residue.

[0097] R 10 In the present invention, the total amount of these suitable residues is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more.

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

[0099] In this case, the content ratio of the diamine residue group suitable for improving rigidity (Group C) to the diamine residue group suitable for improving transparency (Group D) is preferably 0.05 mol or more and 9 mol or less of the diamine residue group suitable for improving rigidity (Group C) per 1 mol of the diamine residue group suitable for improving transparency (Group D), more preferably 0.1 mol or more and 5 mol or less, and even more preferably 0.3 mol or more and 4 mol or less.

[0100] In the structures represented by the above general formula (5) and the above general formula (7), n and n' each independently represent the number of repeating units and are 1 or more. The number of repeating units in the polyimide, n, may be appropriately selected according to the structure so as to show a preferred glass transition temperature 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] The polyimide resin may contain a polyamide structure in part thereof, for example, a polyamideimide structure containing a tricarboxylic acid residue such as trimellitic anhydride, or a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid.

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

[0103] An example of a polyimide resin is a compound having a 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 above polyimide-based resins, polyimide-based resins or polyamide-based resins having a structure in which intramolecular or intermolecular charge transfer is unlikely to occur are preferred because they have excellent transparency. Specific examples thereof include fluorinated polyimide-based resins such as those represented by the above chemical formulas (8) to (15), and polyimide-based resins having an alicyclic structure such as those represented by the above formulas (15) to (19).

[0122] In addition, the fluorinated polyimide resins such as those represented by the above chemical formulas (8) to (15) have high heat resistance due to their fluorinated structure, and are not discolored by heat during the production of a polyimide film made of the polyimide resin, and therefore have excellent transparency.

[0123] The polyamide resin is a concept including not only aliphatic polyamides but also aromatic polyamides (aramids). Examples of polyamide resins include compounds having 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 the polyimide-based resin or polyamide-based resin represented by the above chemical formulas (8) to (24) and (27) may be commercially available. Examples of commercially available polyimide-based resins include Neoprim (registered trademark) manufactured by Mitsubishi Gas Chemical Company, Inc., and examples of commercially available substrates containing the polyamide-based resins include Miktron (registered trademark) manufactured by Toray Industries, Inc.

[0128] The polyimide-based resins or polyamide-based resins represented by the above chemical formulas (8) to (24) and (27) may be synthesized by a known method. For example, a method for synthesizing the polyimide-based resin represented by the above chemical formula (8) is described in JP-A-2009-132091, and specifically, the polyimide-based resin can be obtained by reacting 4,4'-hexafluoropropylidenebisphthalic 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 polyimide resin or polyamide resin is preferably in the range of 3000 to 500,000, more preferably in the range of 5000 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 3000, sufficient strength may not be obtained, and if it exceeds 500,000, the viscosity increases and the solubility decreases, so that a substrate with a smooth surface and a uniform film thickness may not be obtained. In this specification, the "weight average molecular weight" is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0131] From the viewpoint of being able to improve the hardness, it is preferable to use a substrate made of a fluorinated polyimide resin represented by the above chemical formulas (8) to (15) or a polyamide resin having a halogen group represented by the above chemical formula (27), etc., for the resin substrate 51. Among them, from the viewpoint of being able to further improve the hardness, it is more preferable to use a substrate containing a polyimide resin represented by the above chemical formula (8).

[0132] Examples of polyester-based resins include resins containing at least one of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component.

[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 if the optical film 50 is manufactured by roll to roll, wrinkles are unlikely to occur, and there is no risk of causing deterioration of the 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 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>> The functional layer 52 is similar to the functional layer 31, and therefore a description thereof will be omitted here.

[0135] <<<Method of manufacturing resin layer and optical film>>> The resin layer 10 and the optical films 30, 50 can be produced as follows: First, a resin layer composition is applied onto one surface 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. The resin layer composition may further contain a solvent and a polymerization initiator in addition to the ionizing radiation curable compound. The ionizing radiation curable compound has been described in the section on the resin layer 10, and therefore will not be described here.

[0137] (solvent) Examples of the solvent include alcohols (e.g., methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol, t-butanol, benzyl alcohol, PGME, ethylene glycol, and diacetone alcohol), ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone, diethyl ketone, and diacetone alcohol), esters (methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, and methyl formate), and Examples of the solvent include ethyl, 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), carbonates (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate), and the like. These solvents may be used alone or in combination of two or more. Among them, methyl isobutyl ketone and methyl ethyl ketone are preferred as the solvent, in that they can dissolve or disperse components such as urethane (meth)acrylate and other additives and can suitably coat the resin layer composition.

[0138] (Polymerization initiator) The polymerization initiator is a component that is decomposed by irradiation with ionizing radiation to generate radicals and initiate or advance the polymerization (crosslinking) of a polymerizable compound.

[0139] The polymerization initiator is not particularly limited as long as it can release a substance that initiates radical polymerization by irradiation with ionizing radiation. The polymerization initiator is not particularly limited, and known initiators can be used, and specific examples thereof include acetophenones, benzophenones, Michler's benzoyl benzoate, α-amyloxime ester, thioxanthones, propiophenones, benzils, benzoins, and acylphosphine oxides. It is also preferable to use a photosensitizer in combination, and specific examples thereof 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 at a temperature of 30°C or higher and 120°C or lower for 10 to 120 seconds, to evaporate the solvent.

[0141] After drying the coating, the coating is irradiated with ionizing radiation such as ultraviolet light to harden it, and the release film is peeled off to obtain the resin layer 10.

[0142] In addition, when forming the optical film 30, after drying the coating film of the composition for resin layer, the coating film is irradiated with ionizing radiation such as ultraviolet light to semi-cure it. In this specification, "semi-cure" means that curing substantially proceeds when further irradiated with ionizing radiation.

[0143] Thereafter, a functional layer composition for forming the functional layer 31 is applied onto the semi-cured coating film 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 composition for the functional layer contains a polymerizable compound. The composition for the functional layer may further contain an ultraviolet absorber, a spectral transmittance adjuster, an antifouling agent, inorganic particles, a leveling agent, a solvent, and a polymerization initiator, as necessary. The solvent and the polymerization initiator are the same as those in the composition for the resin layer, and therefore the description thereof will be omitted here.

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

[0146] After drying the coating of the functional layer composition, the coating is fully cured by irradiating it with ionizing radiation such as ultraviolet light to form the functional layer 31. In this specification, however, "fully cured" means that the curing does not substantially proceed even if the coating is further irradiated with ionizing radiation. Thereafter, the release film is peeled off to obtain the optical film 30.

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

[0148] According to this embodiment, the resin layer 10 has a shear storage modulus G' of 30 MPa or more and 200 MPa or less at 25° C. in a frequency range of 500 Hz or more and 1000 Hz or less, and therefore good impact resistance can be obtained.

[0149] Normally, a resin with a low shear storage modulus G' has a low glass transition temperature, and therefore, even if it has good flexibility in a room temperature environment, it becomes hard and brittle in a low temperature environment 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 state of the resin layer 10 in a room temperature environment and a low temperature environment can be suppressed. Therefore, the flexibility of the resin layer 10 can be maintained not only in a room temperature environment but also in a low temperature environment. As a result, good foldability can be obtained.

[0150] <<<Image display devices>>> The optical films 30 and 50 can be incorporated into a foldable image display device for use. FIG. 6 is a schematic diagram of the image display device according to this embodiment. As shown in FIG. 6, the image display device 60 is mainly composed of a housing 61 in which a battery or the like is stored, a display element 62, a circular polarizing plate 63, a touch sensor 64, and an optical film 30, which are laminated in this order toward the observer side. An adhesive layer 65 or an adhesive layer having optical transparency is arranged 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 members are fixed to each other by the adhesive layer 65 or the adhesive layer. The adhesive layer 65 is arranged 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 location 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 disposed so that the functional layer 31 is closer to the viewer than 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 or the like. The touch sensor 64 is disposed closer to the observer than the circular polarizer 63, but may be disposed between the display element 62 and the circular polarizer 63. The touch sensor 64 may be of an on-cell type or an in-cell type. For example, an OCA (Optical Clear Adhesive) may be used as the adhesive layer 65. EXAMPLES

[0153] In order to explain the present invention in detail, examples are given below, but the present invention is not limited to these descriptions.

[0154] <Preparation of composition for hard coat layer> First, the components were mixed so as to obtain the composition shown below, thereby obtaining a composition 1 for a hard coat layer. (Hard Coat Layer Composition 1) Mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (product name "M403", manufactured by Toa Gosei Co., Ltd.): 25 parts by mass Dipentaerythritol EO modified hexaacrylate (product name "A-DPH-6E", manufactured by Shin-Nakamura Chemical Co., Ltd.): 25 parts by weight - Irregularly shaped silica particles (average particle size 25 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.): 50 parts by weight (based on 100% solids) 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 weight (based on 100% solids) Methyl isobutyl ketone (MIBK): 150 parts by weight

[0155] <Composition for resin layer> The components were mixed so as to obtain the composition shown below, thereby obtaining a composition for a resin layer. (Composition 1 for resin layer) Urethane acrylate (product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 90 parts by weight Phenoxyethyl acrylate (product name: Viscoat #200, manufactured by Osaka Organic Chemical Industry Co., Ltd.): 10 parts by weight Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 5 parts by mass Methyl isobutyl ketone: 10 parts by weight

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

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

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

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

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

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

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

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

[0164] <Example 1> A polyethylene terephthalate substrate (product name "Cosmoshine (registered trademark) A4100", manufactured by Toyobo Co., Ltd.) having a thickness of 50 μm was prepared as a release film, and the composition for resin layer 1 was applied to the untreated surface 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 light was irradiated in air using an ultraviolet irradiator (light source H bulb, manufactured by Fusion UV Systems Japan Co., Ltd.) until an accumulated light amount of 100 mJ / cm was reached. 2 The coating was half-cured by irradiating the light so as to form a resin layer made of a urethane resin having a thickness of 100 μm.

[0165] Next, the 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. The formed coating film was then heated at 70°C for 1 minute to evaporate the solvent in the coating film, and ultraviolet rays were irradiated using an ultraviolet irradiator (manufactured by Fusion UV Systems Japan, light source H bulb) at an accumulated light amount of 300 mJ / cm under conditions of an oxygen concentration of 200 ppm or less. 2 The coating was completely cured (fully cured) by irradiating the coating with light so as to obtain a hard coat layer having a thickness of 5 μm.

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

[0167] The thickness of each layer was measured by photographing the cross section of the optical film using a scanning transmission electron microscope (STEM) (product name "S-4800", manufactured by Hitachi High-Technologies Corporation), measuring the thickness of each layer at 10 points on the cross section image, and taking the arithmetic average value of the thicknesses at the 10 points. The cross-sectional photograph of the optical film was taken as follows. First, the optical film cut to 1 mm x 10 mm was embedded in an embedding resin to prepare a block, and a uniform slice with a thickness of 70 nm to 100 nm without holes was cut from this block by a general slice preparation method. An ultramicrotome EM UC7 made by Leica Microsystems was used to prepare the slices. The uniform slice without holes was used as the measurement sample. Then, a cross-sectional photograph of the measurement sample was taken using a scanning transmission electron microscope (STEM). When taking the cross-sectional photograph of each layer, the detector was set to "TE", the acceleration voltage was set to "30 kV", and the emission current was set to "10 μA" for STEM observation. The magnification was adjusted appropriately from 100x to 100,000x while observing whether the layers could be distinguished in terms of contrast and brightness by adjusting the focus. The magnification was adjusted appropriately from 5,000x to 200,000x while observing whether the layers could be distinguished in terms of contrast and brightness by adjusting the focus. During STEM observation, the beam monitor aperture was set to "3", the objective lens aperture was set to "3", and the WD was set to "8mm". In Examples 2 to 10 and Comparative Examples 1 to 4, the film thickness of each layer was measured by 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 the composition 2 for resin layer was used instead of the composition 1 for resin layer.

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

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

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

[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 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 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 composition 6 for resin layer was used instead of composition 1 for resin layer.

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

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

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

[0181] <Shear storage modulus G´ measurement> The shear storage modulus G' of the optical films according to the examples and comparative examples was measured. Specifically, first, the optical film was punched out into a rectangular shape of 10 mm x 5 mm to prepare a sample. Then, two of these samples were prepared and attached to a solid shearing jig, which is an option of a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, the solid shearing jig includes a metal solid shearing plate having a thickness of 1 mm and two L-shaped metal fittings arranged on both sides of the solid shearing plate, and one sample was sandwiched between the solid shearing plate and one of the L-shaped metal fittings, and the other sample was sandwiched between the solid shearing plate and the other L-shaped metal fitting. In this case, the sample was sandwiched so that the resin layer was on the solid shearing plate side and the hard coat layer was on the L-shaped metal fitting side. Then, the L-shaped metal fittings were tightened with a screw to fix the sample. 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.), and then a solid shearing jig was placed between the upper chuck and the lower chuck with a chuck distance of 20 mm. The temperature was set to 25°C and increased at a rate of 2°C / min. In this state, while the solid shear plate was fixed, a vertical vibration with a distortion amount of 1% and a frequency range of 500Hz to 1000Hz was applied to the two L-shaped metal fittings, while dynamic viscoelasticity of the solid was measured at 25°C, and the shear storage modulus G' of the optical film was measured. Here, the shear storage modulus G' of the optical film in the frequency range of 500 Hz to 1000 Hz was measured by applying longitudinal vibrations of frequencies 500 Hz, 750 Hz, and 950 Hz to the L-shaped metal fitting, measuring the shear storage modulus G' of the optical film at each frequency, determining the arithmetic mean value of these shear storage modulus G', and further repeating this measurement three times to obtain the arithmetic mean value of the three arithmetic mean values ​​obtained. Note that in the optical film, since the resin layer is softer than the hard coat layer, the shear storage modulus G' of the optical film can be regarded 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 according to the examples and comparative examples was measured. Specifically, first, a sample of the same size as the sample used in the shear storage modulus G' measurement was obtained from the optical film, and the sample was attached to a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.) in the same manner as in the shear storage modulus G' measurement. Then, the set temperature was set to -50°C and the temperature was raised at 2°C / min. In this state, the solid shear plate was fixed, and a vertical vibration with a distortion amount of 1% and a frequency range of 500Hz to 1000Hz was applied to the two L-shaped metal fittings, while the dynamic viscoelasticity of the solid was measured, 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 measured by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to the L-shaped metal fitting, measuring the shear loss tangent tanδ of the optical film at each frequency, and determining the peak temperatures from these shear loss tangents tanδ to obtain the arithmetic mean value of the glass transition temperature. Furthermore, this measurement was repeated three times, and the three arithmetic mean values ​​obtained were further arithmetically averaged to obtain the value. In addition, since the resin layer is softer than the hard coat layer in the optical film, the glass transition temperature Tg of the optical film can be regarded as the glass transition temperature Tg of the resin layer.

[0183] <Impact resistance test> Impact resistance tests were performed using the optical films according to the examples and the comparative examples. Specifically, the optical films according to the examples and the comparative examples were placed directly on the surface of a 0.7 mm thick soda glass with the hard coat layer facing up, and an impact resistance test was performed three times each in which an iron ball weighing 100 g and having a diameter of 30 mm was dropped on the surface of the hard coat layer of the optical film from a position 30 cm high. In the impact resistance test, the position where the iron ball was dropped was changed each time. Then, the optical films after the impact resistance test were visually evaluated for whether the surface of the hard coat layer was dented. The evaluation results were as follows. A: When the hard coat layer was observed from the front and from an oblique direction, no depressions were found on the surface of the hard coat layer. B: When the hard coat layer was observed either from the front or from an oblique direction, dents were found on the surface of the hard coat layer, but were not of a level that would cause any problems in practical use. C: When the hard coat layer was observed from the front, no dents were observed on the surface of the hard coat layer, but when observed obliquely, dents were confirmed on the surface of the hard coat layer. D: When the hard coat layer was observed from the front and from an oblique angle, obvious depressions were observed on the surface of the hard coat layer.

[0184] <Foldability> A continuous folding test was performed on the optical films according to the examples and comparative examples to evaluate the foldability. Specifically, first, a sample having a size of 30 mm x 100 mm was cut out from the optical film. Then, the two opposing sides of the cut out sample were fixed by the fixing parts of a folding durability tester (for example, product name "U-shaped stretch tester DLDMLH-FS", manufactured by Yuasa System Devices Co., Ltd., compliant with IEC62715-6-1) arranged in parallel. Thereafter, a continuous folding test was performed in which the optical film was folded 100,000 times at 180° under the following conditions so that the minimum interval φ between the two opposing sides was 10 mm and the front side (hard coat layer side) of the optical film was on the outside as shown in FIG. 4(C), and the bending part was examined for deformation, cracks, or breakage. The continuous folding test was performed in a room temperature environment of room temperature (23°C) and relative humidity of 50% and in a low temperature environment of low temperature (-40°C). The evaluation criteria were as follows. A: During the continuous folding test, no deformation, cracks or breaks occurred in the bent parts. B: In the continuous folding test, deformation at the bent portion was confirmed to a level that did not cause practical problems, but no cracks or breaks occurred. C: In the continuous folding test, deformation was clearly observed at the bent portion, but no cracks or breaks occurred. D: During the continuous folding test, cracks or breaks occurred at the bent portion.

[0185] <Pencil hardness> The pencil hardness of the surface (surface of the hard coat layer) of the optical film according to the examples and comparative examples was measured based on JIS K5600-5-4:1999. Specifically, the optical film cut to a size of 30 mm x 100 mm was fixed on a glass plate having a thickness of 2 mm with Cellotape (registered trademark) manufactured by Nichiban Co., Ltd. so as not to bend or wrinkle. Then, using a pencil hardness tester (product name "Pencil Scratch Coating Hardness Tester (Electric)" manufactured by Toyo Seiki Seisakusho Co., Ltd.), a pencil (product name "Uni", manufactured by Mitsubishi Pencil Co., Ltd.) was moved at a speed of 1 mm / sec under an environment of a temperature of 23°C and a relative humidity of 50% while applying a load of 750 g to the pencil. The pencil hardness was determined as the highest hardness at which the surface of the optical film (surface of the hard coat layer) was not scratched in the pencil hardness test. When measuring the pencil hardness, multiple pencils with different hardnesses were used. The pencil hardness test was performed five times for each pencil. If no scratches were visible on the surface of the optical film when the surface was observed through a fluorescent light four or more times out of the five, it was determined that the pencil of that hardness 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. The optical films according to Comparative Examples 1 and 4 had good foldability in a room temperature environment because the glass transition temperature of the resin layer was too low, but poor foldability in a low temperature environment. In contrast, the optical films according to Examples 1 to 10 had good impact resistance because the shear storage modulus G' was 30 MPa or more and 200 MPa or less, and good foldability not only in a room temperature environment but also in a low temperature environment because the glass transition temperature of the resin layer was 50°C or more. [Explanation of symbols]

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

Claims

[Claim 1] A resin layer for use in an image display device, The resin layer has a shear storage modulus G' of 30 MPa or more and 200 MPa or less at 25°C and in a frequency range of 500 Hz or more and 1000 Hz or less, The resin layer has a glass transition temperature of 50° C. or higher.

Images