Resin layer, optical film, and image display device

Abstract

According to one embodiment of the present invention, a resin layer (10) used in an image display device is provided, wherein the shear storage modulus G' in the resin layer (10) at 25°C and in the frequency range of 500 Hz or higher and 1000 Hz or lower is 30 MPa or higher and 200 MPa or lower, and the glass transition temperature of the resin layer (10) is 50°C or higher.

Description

Technology 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, but currently, foldable image display devices are being developed. Typically, smartphones and tablet terminals are covered with cover glass, but since glass generally has excellent hardness but is difficult to bend, there is a high risk that cover glass will crack when folded if used in an image display device. For this reason, using an optical film made of resin instead of cover glass is being considered for foldable image display devices (see, for example, Patent Document 1). Prior art literature

[0003] Japanese Patent Publication No. 2016-125063 The problem to be solved

[0004] In optical films used in such foldable image display devices, impact resistance is required because the surface of the optical film may be subjected to impact. When the surface of the optical film is subjected to impact, the surface of the optical film may become indented. For this reason, impact resistance is currently required to suppress the indentation of the film surface when the surface of the optical film is subjected to impact.

[0005] However, regarding optical films, the current situation is that impact resistance capable of suppressing surface indentation when impact is applied to the surface of the optical film is not being achieved.

[0006] In addition, regarding image display devices, it is necessary to consider use under various environments. Specifically, it is necessary to consider use under low temperature (e.g., -40°C) environments as well as room temperature (e.g., 23°C). For this reason, regarding optical films used in image display devices, it is necessary to consider use under low temperature environments as well as room temperature environments.

[0007] However, even for optical films that do not crack during folding tests at room temperature, there is a risk of cracking if the folding test is performed at a low temperature because the flexibility is compromised.

[0008] The present invention was made to solve the above problem. Specifically, the purpose is to provide a resin layer having good impact resistance and good foldability not only in a room temperature environment but also in a low temperature environment, an optical film equipped with the same, and an image display device. means of solving the problem

[0009] The present invention includes the following inventions.

[0010] [1] A resin layer used in an image display device, wherein the shear storage modulus G' in the frequency range of 25°C and 500 Hz or higher and 1000 Hz or lower in the resin layer is 30 MPa or higher and 200 MPa or lower, and the glass transition temperature of the resin layer is 50°C or higher.

[0011] [2] A resin layer described in [1] above, having a film thickness of 20㎛ or more and 150㎛ or less.

[0012] [3] An optical film having a foldable laminated structure, and having at least the resin layer described in [1] or [2].

[0013] [4] An optical film described in [3] having a functional layer provided on one side of the resin layer.

[0014] [5] An optical film described in [3] or [4], further comprising a resin substrate provided on one side of the resin layer.

[0015] [6] An optical film described in any one of [3] to [5], wherein no cracks or fractures occur when a test of folding the optical film 180° so that the gap between opposing edges of the optical film becomes 10 mm is repeated 100,000 times in an environment of 23°.

[0016] [7] The optical film described in [6] above, in which no cracks or fractures occur when the test of folding the opposing edges of the optical film 180° so that the gap is 10 mm is repeated 100,000 times in an environment of -40°.

[0017] [8] An image display device comprising a display element and a resin layer described in [1] or [2] or an optical film described in any one of [3] to [7] disposed on the observer side rather than the display element.

[0018] [9] The image display device described in [8], wherein the above display element is an organic light-emitting diode element. Effects of the invention

[0019] According to the present invention, a resin layer having good impact resistance and good foldability not only in a room temperature environment but also in a low temperature environment, an optical film having the same, and an image display device can be provided. Brief explanation of the drawing

[0020] Figure 1 is a schematic diagram of a resin layer according to an embodiment. Figure 2 is a schematic diagram of a solid shear jig used to measure the shear storage modulus G' and the glass transition temperature Tg. Figure 3 is a schematic diagram of an optical film according to an embodiment. Figures 4 (A) to 4 (C) are schematic drawings illustrating the appearance of a continuous folding test. Figure 5 is a schematic diagram of another optical film regarding an embodiment. FIG. 6 is a schematic diagram of an image display device according to an embodiment. Specific details for implementing the invention

[0021] Hereinafter, a resin layer, an optical film, and an image display device according to embodiments of the present invention will be described with reference to the drawings. In this specification, terms such as "film" and "sheet" are not distinguished from one another solely based on differences in designation. Accordingly, for example, "film" is used in the sense that it includes a component also called a sheet. FIG. 1 is a schematic diagram of a resin layer according to the present embodiment, FIG. 2 is a schematic diagram of a solid shearing jig used when measuring the shear storage modulus G' and the glass transition temperature Tg, FIG. 3 is a schematic diagram of an optical film according to the present embodiment, FIG. 4 (A) to FIG. 4 (C) are schematic diagrams illustrating the appearance of a continuous folding test, and FIG. 5 is a schematic diagram of another optical film according to the present embodiment.

[0022] <<<Resin layer>>>

[0023] The resin layer (10) illustrated in FIG. 1 is used in an image display device. In this specification, "resin layer" refers to a single-layer structure containing resin. The resin layer (10) is a layer made of a resin having light transmittance and having shock absorption properties. The resin layer (10) may be used as a single resin layer (10), but may also be used embedded in an optical film (30) in which a functional layer (31) described later is laminated to the resin layer (10), or in an optical film (50) having a resin substrate (51) described later. Additionally, a release film may be attached to the resin layer (10).

[0024] In the resin layer (10), the shear storage modulus G' in the frequency range of 25°C and 500 Hz or higher and 1000 Hz or lower is 30 MPa or higher and 200 MPa or lower. If the shear storage modulus G' of the resin layer (10) is 30 MPa or higher, deformation of the surface of the resin layer (10) can be suppressed when an impact is applied to the surface of the resin layer (10), and at the same time, a decrease in the hardness of the resin layer (10) can be suppressed. In addition, if the shear storage modulus G' of the resin layer (10) is 200 MPa or lower, the resin layer (10) is less likely to crack when the resin layer (10) is 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, in order to further suppress deformation of the surface of the resin layer (10) when an impact is applied to the surface of the resin layer (10) and to further suppress a decrease in the 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.

[0025] 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 the dynamic viscoelasticity measuring device (DMA), first, the resin layer (10) is punched into a rectangular shape of 10 mm × 5 mm to obtain a sample S1 (see FIG. 2). Then, two of these samples S1 are prepared and installed on a solid shear jig which is an option of the dynamic viscoelasticity measuring device (e.g., product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, as illustrated in FIG. 2, the solid shearing jig (20) comprises a solid shearing plate (21) (intermediate plate) made of metal with a thickness of 1 mm and two L-shaped metal members (22) (outer plates) arranged on both sides of the solid shearing plate (21). One sample S1 is placed between the solid shearing plate (21) and one L-shaped metal member (22), and the other sample S1 is placed between the solid shearing plate (21) and the other L-shaped metal member (22). Then, the L-shaped metal members (22) are fastened together with screws (23) to secure the sample S1. Next, a tensile test chuck consisting of an upper chuck and a lower chuck is installed in a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.), and a solid shearing jig is installed between the upper chuck and the lower chuck with a chuck-to-chock distance of 20 mm. The chuck-to-chock distance is the distance between the upper chuck and the lower chuck. Then, the set temperature is set to 25°C and the temperature is increased at a rate of 2°C / min. In this state, while fixing the solid shear plate (21), a deformation amount of 1% and longitudinal vibration in the range of frequency from 500 Hz to 1000 Hz is applied to two L-shaped metal members (22), and a dynamic viscoelasticity measurement of the solid at 25°C is performed to measure the shear storage modulus G' of the resin layer (10).Here, the shear storage modulus G' in the frequency range of 500 Hz to 1000 Hz in the resin layer (10) is obtained by applying longitudinal vibrations of frequencies of 500 Hz, 750 Hz, and 950 Hz to the L-shaped metal member (22), measuring the shear storage modulus G' of the resin layer (10) at each frequency, calculating the arithmetic mean of these shear storage modulus G', repeating this measurement three times, and then taking the arithmetic mean of the three arithmetic mean values ​​obtained for each. Furthermore, the frequency range of 500 Hz to 1000 Hz is used above because the frequency in this range is the frequency at which the surface of the resin layer (10) deforms by several micrometers to several tens of micrometers when an object is free-falling from a height of several tens of centimeters.

[0026] The glass transition temperature Tg of the resin layer (10) is 50°C or higher. If the glass transition temperature Tg of the resin layer (10) is 50°C or higher, the state of the resin layer (10) does not change even at room temperature (e.g., 23°C) and low temperature (e.g., -40°C), so good foldability can be maintained. The lower limit of the glass transition temperature Tg of the resin layer (10) may be 53°C or higher, 55°C or higher, or 60°C or higher. In addition, the upper limit of the glass transition temperature Tg of the resin layer (10) may be 90°C or lower from the perspective of ensuring impact resistance.

[0027] 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 the dynamic viscoelasticity measuring device (DMA), first, the resin layer (10) is punched into a rectangular shape of 10 mm × 5 mm to obtain a sample S1. Then, two of these samples are prepared and, as with the shear storage modulus G', are installed on a solid shear jig which is an option of the dynamic viscoelasticity measuring device (e.g., product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Then, the set temperature is set to -50°C and the temperature is increased at a rate of 2°C / min. In this state, while fixing the solid shear plate, a deformation amount of 1% and longitudinal vibration in the range of frequency from 500 Hz to 1000 Hz is applied to two L-shaped metal members (22), and the dynamic viscoelasticity of the solid is measured every 0.5°C to measure the shear loss tangent tanδ (shear loss modulus G'' / shear storage modulus G') of the resin layer (10). Then, the peak of the shear loss tangent tanδ is obtained, and the temperature at which this peak is detected is called the glass transition temperature Tg. This measurement is repeated three times, and the arithmetic mean of the three values ​​obtained in each case is again arithmetic mean, and the value is called the glass transition temperature Tg.

[0028] In addition, as described below, when measuring the shear storage modulus G' or glass transition temperature Tg of an optical film (30) in which a functional layer (31) is laminated onto a resin layer (10), if the resin layer (10) is more flexible than the functional layer (31), the shear storage modulus G' or glass transition temperature Tg of the optical film (30) can be considered as the shear storage modulus G' or glass transition temperature Tg of the resin layer (10). Whether the resin layer (10) is more flexible than the functional layer (31) is determined from the displacement amount described below.

[0029] In cases where another film, such as a polarizing plate, is provided on one side of the resin layer (10) through an adhesive layer or an adhesive layer, the other film is peeled off together with the adhesive layer or the adhesive layer, and then the shear storage modulus G' or the glass transition temperature is measured. The peeling of the other film can be performed, for example, as follows. First, a laminate in which another film is attached to the resin layer (10) through an adhesive layer or an adhesive layer is heated with a dryer, and the blade tip of a cutter is inserted into the area thought to be the interface between the resin layer (10) and the other film, and the peeling is performed slowly. By repeating such heating and peeling, the adhesive layer or the adhesive layer and the other film can be peeled off. Furthermore, even if such a peeling process is performed, it does not have a significant effect on the measurements.

[0030] It is preferable that the film thickness of the resin layer (10) be 20㎛ or more and 150㎛ or less. If the film thickness of the resin layer (10) is 20㎛ or more, excellent impact resistance can be obtained, and if the film thickness of the resin layer (10) is 150㎛ or less, the resin layer (10) is difficult to break in a 100,000-cycle repeated folding test, thereby exhibiting excellent performance. It is more preferable that the lower limit of the film thickness of the resin layer (10) be 40㎛ or more or 50㎛ or more, and the upper limit of the film thickness of the resin layer (10) is 120㎛ or less, 100㎛ or less, 80㎛ or less, or 60㎛ or less from the perspective of promoting thinness and improving processability.

[0031] The film thickness of the resin layer (10) is determined by using a scanning transmission electron microscope (STEM) to photograph a cross-section of the resin layer (10), measuring the film thickness of the resin layer (10) at 10 locations in the cross-sectional image, and taking the arithmetic mean value of the film thicknesses at the 10 locations.

[0032] A specific method for taking cross-sectional photographs is described below. First, a block is prepared by embedding a resin layer cut to a size of 1 mm × 10 mm in an embedding resin, and from this block, a uniform section with a thickness of 70 nm or more and 100 nm or less, free of holes, is cut using a general section preparation method. For section preparation, for example, an UltraMicrotome EM UC7 manufactured by Leika Microsystems Co., Ltd. can be used. Then, this uniform section free of holes is used as a measurement sample. After that, a cross-sectional photograph of the measurement sample is taken using a Scanning Transmission Electron Microscope (STEM). As a Scanning Transmission Electron Microscope (STEM), the S-4800 manufactured by Hitachi High Technologies Co., Ltd. can be used. When taking a cross-sectional photograph using the S-4800, the detector is set to "TE," the acceleration voltage to "30 kV," and the emission current to "10 μA" to perform cross-sectional observation. Regarding the magnification, the focus is adjusted to observe whether the contrast and brightness of each layer are distinguishable, and the magnification is appropriately adjusted to 100x to 100,000x, preferably 1,000x to 50,000x, and more preferably 5,000x to 10,000x. Additionally, when taking cross-sectional photographs using the S-4800, the beam monitor aperture may be set to "3," the objective lens aperture to "3," and the WD may be set to "8 mm." When measuring the film thickness of the resin layer, it is important to observe the interface contrast between the resin layer and another layer (e.g., embedded resin) as clearly as possible when observing the cross-section. If this interface is not clearly visible due to insufficient contrast, a staining treatment such as osmium tetroxide, ruthenium tetroxide, or phosphotungstic acid may be performed, as this makes the interface between the organic layers clearly visible. Furthermore, the interface contrast may be difficult to discern at high magnification. In that case, low magnification is also observed simultaneously.For example, observe at two magnification levels, such as 2,000x and 10,000x, or 5,000x and 20,000x, calculate the arithmetic mean value at both magnification levels, and take that average value as the film thickness of the resin layer.

[0033] As for the resin constituting the resin layer (10), it is not particularly limited as long as it is a resin in which the shear storage modulus G' and glass transition temperature Tg satisfy the above range. Examples of such a resin include a cured product (polymer) of an ionizing radiation curable compound (ionizing radiation polymerizable compound). Examples of ionizing radiation in this specification include visible light, ultraviolet rays, X-rays, electron beams, α-rays, β-rays, and γ-rays. Examples of cured products of ionizing radiation curable compounds include urethane-based resins or silicone-based resins.

[0034] (Urethane resin)

[0035] Urethane resins are resins having urethane bonds. Examples of urethane resins include cured products of ionizing radiation-curable urethane resin compositions and cured products of thermosetting urethane resin compositions. Among these, a cured product of an ionizing radiation-curable urethane resin composition is preferred from the perspective of achieving high hardness, a fast curing speed, and excellent mass producibility.

[0036] The ionizing radiation-curable urethane-based resin composition comprises urethane (meth)acrylate, and the thermosetting urethane-based resin composition comprises a polyol compound and an isocyanate compound. The urethane (meth)acrylate, the polyol compound, and the isocyanate compound may be any of monomers, oligomers, and prepolymers.

[0037] It is preferable that the number of (meth)acryloyl groups (number of functional groups) in the urethane (meth)acrylate be 2 or more and 4 or less. If the number of (meth)acryloyl groups in the urethane (meth)acrylate is less than 2, there is a risk that the pencil hardness will decrease, and if it exceeds 4, there is a risk that curing shrinkage will increase, causing the resin layer to curl, and cracks will form in the resin layer during bending. It is more preferable that the upper limit of the number of (meth)acryloyl groups in the urethane (meth)acrylate be 3 or less. Furthermore, "(meth)acrylate" means including both "acrylate" and "methacrylate," and "(meth)acryloyl group" means including both "acryloyl group" and "methacryloyl group."

[0038] The weight average molecular weight of the urethane (meth)acrylate is preferably 1,500 or more and 20,000 or less. If the weight average molecular weight of the urethane (meth)acrylate is less than 1,500, there is a risk that impact resistance will decrease, and if it exceeds 20,000, there is a risk that the viscosity of the ionizing radiation-curable urethane-based resin composition will increase, thereby worsening coating properties. It is more preferable that the lower limit of the weight average molecular weight of the urethane (meth)acrylate is 2,000 or more, and the upper limit is 15,000 or less.

[0039] In addition, repeating units having a structure derived from urethane (meth)acrylate may include, for example, structures represented by the following general formulas (1), (2), (3) or (4).

[0040]

[0041] Among the above general formula (1), R 1 represents a branched-chain alkyl group, and R 2 represents a branched-chain alkyl group or a saturated cyclic aliphatic group, and R 3 represents a hydrogen atom or a methyl group, and R 4represents a hydrogen atom, a methyl group, or an ethyl group, m represents an integer greater than or equal to 0, and x represents an integer from 0 to 3.

[0042]

[0043] Among the above general formula (2), R 1 represents a branched-chain alkyl group, and R 2 represents a branched-chain alkyl group or a saturated cyclic aliphatic group, and 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 greater than or equal to 1, and x represents an integer from 0 to 3.

[0044]

[0045] Among the above general formula (3), R 1 represents a branched-chain alkyl group, and R 2 represents a branched-chain alkyl group or a saturated cyclic aliphatic group, and 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 greater than or equal to 0, and x represents an integer from 0 to 3.

[0046]

[0047] Among the above general formula (4), R 1 represents a branched-chain alkyl group, and R 2 represents a branched-chain alkyl group or a saturated cyclic aliphatic group, and 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 greater than or equal to 1, and x represents an integer from 0 to 3.

[0048] In addition, whether the resin constituting the resin layer (10) is formed by a polymer chain (repeating unit) of a certain structure 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 monomer units included in the resin layer (10) as monomer components.

[0049] The resin layer (10) may include, in addition to the resin, an ultraviolet absorber, a spectroscopic transmittance modifier, an antifouling agent, inorganic particles and / or organic particles, etc.

[0050] <<<Optical Film>>>

[0051] The optical film (30) illustrated in FIG. 3 is a film with a laminated structure and has at least a resin layer (10). The optical film (30) has a resin layer (10) and a functional layer (31) provided on one side of the resin layer (10). In this specification, "functional layer" refers to a layer that performs a certain function. The functional layer (31) has a single-layer structure, but may have a multi-layer structure of two or more layers.

[0052] In the optical film (30), the shear storage modulus G' in the frequency range of 25°C and 500 Hz or higher and 1000 Hz or lower is 30 MPa or higher and 200 MPa or lower. If the shear storage modulus G' of the optical film (30) is 30 MPa or higher, deformation of the surface (30A) of the optical film (30) can be suppressed when an impact is applied to the surface (30A) of the optical film (30), and a decrease in the hardness of the optical film (30) can be suppressed. Additionally, if the shear storage modulus G' of the optical film (30) is 200 MPa or lower, the optical film (30) is less likely to crack when folded at room temperature. 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 perspective 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). The upper limit of the shear storage modulus G' of the optical film (30) is preferably 190 MPa or less, 180 MPa or less, or 170 MPa or less, from the perspective of further suppressing cracking during folding. The measurement of the shear storage modulus G' of the optical film (30) is performed by the same method as the measurement of the shear storage modulus G' of the resin layer (10).

[0053] The optical film (30) is foldable. Specifically, it is desirable that no cracks or fractures occur in the optical film (30) even when the folding test (continuous folding test) described below is repeated 100,000 times, 200,000 times, 500,000 times, or 1,000,000 times for each optical film (30) under an environment with a temperature of 23±5℃ (e.g., 23℃) and a relative humidity of 30% or more and 70% or less, and under an environment with a temperature of -40℃±5℃ (e.g., -40℃). If cracks or fractures occur in the optical film (30) when the continuous folding test is repeated 100,000 times for the optical film (30), the foldability of the optical film (30) becomes insufficient. Furthermore, the reason the number of folds in the above continuous folding test is evaluated to be at least 100,000 times is due to the following reasons. For example, if we assume that an optical film is embedded in a foldable smartphone, the frequency of folding (the frequency of opening and closing) becomes very high. For this reason, there is a concern that an evaluation cannot be conducted at a practical level when the number of folds in the continuous folding test is set to, for example, 10,000 or 50,000 times. Specifically, for example, assuming a person who uses a smartphone constantly, it is assumed that the smartphone is opened and closed 5 to 10 times during the morning commute on trains or buses alone, so it is assumed that the smartphone is opened and closed at least 30 times a day. Therefore, assuming that the smartphone is opened and closed 30 times a day, a continuous folding test with 10,000 folds results in 30 times × 365 days = 10,950 times, which is a test simulating one year of use. In other words, even if the results of the continuous folding test with 10,000 folds are satisfactory, there is a concern that cracks or breakage may occur in the optical film after one year. Therefore, an evaluation with 10,000 folds in the continuous folding test can only confirm a level where the product cannot be used, and even if it is usable but insufficient, it is considered good and cannot be evaluated.For this reason, in order to evaluate whether it is at a practical level, the number of folds in the continuous folding test must be evaluated as at least 100,000 times. The continuous folding test may be performed by folding the optical film (30) so that the surface (30A) becomes the outer side, or by folding the optical film (30) so that the surface (30A) becomes the inner side, but in either case, it is desirable that no cracks or fractures occur in the optical film (30).

[0054] The continuous folding test is performed as follows. In the continuous folding test as illustrated in (A) of FIG. 4, first, a sample S2 with a size of 30 mm × 100 mm is cut from the optical film (30). Also, if it is not possible to cut a sample S2 with a size of 30 mm × 100 mm from the optical film (30), the sample S2 may be cut with a size of, for example, 10 mm × 100 mm. Then, the edge S2a of the cut sample S2 and the edge S2b opposite to edge S2a are each fixed to the fixing parts (40, 45) of a folding endurance tester (e.g., product name “U-shaped Stretch Tester DLDMLH-FS”, manufactured by Yuasa System Machinery Co., Ltd., compliant with IEC 62715-6-1) arranged in parallel. Fixing by the fixing part (40, 45) is performed by holding and supporting a portion of sample S2 of approximately 10 mm on one side in the longitudinal direction of sample S2. However, if sample S2 is smaller than the above size, and the portion requiring this fixing in sample S2 is up to approximately 20 mm, measurement is possible by attaching it to the fixing part (40, 45) with tape. In addition, as shown in FIG. 4 (A), the fixing part (40) is movable horizontally. Furthermore, the above device is desirable because, unlike conventional methods such as winding a sample onto a rod, it is possible to evaluate durability against bending load without generating tension or friction on the sample.

[0055] Next, as shown in Fig. 4 (B), the central part of sample S2 is deformed to be folded by moving the fixing part (40) close to the fixing part (45), and as shown in Fig. 4 (C), the fixing part (40) is moved to a position where the gap φ between the two opposing edges S2a and S2b, which are fixed by the fixing parts (40, 45) of sample S2, becomes 10 mm, and then the fixing part (40) is moved in the reverse direction to relieve the deformation of the optical film (30).

[0056] As illustrated in FIG. 4 (A) to (C), the central part of sample S2 can be folded 180° by moving the fixed part (40). Additionally, the bending part S2c of sample S2 can be prevented from protruding from the bottom of the fixed part (40, 45), and a continuous folding test is performed under the following conditions. Furthermore, by controlling the gap φ when the fixed part (40, 45) is closest, the gap φ of the two opposing edges S2a and S2b of sample S2 can be set to 10 mm. In this case, the outer diameter of the bending part S2c is considered to be 10 mm. In the case of sample S2, it is desirable that no crack or fracture occurs when a test of folding 180° so that the gap φ of the opposing edges of sample S2 becomes 10 mm is repeated 100,000 times, but it is even more desirable that no crack or fracture occurs when a continuous folding test of folding 180° so that the gap φ of the opposing edges S2b and S2c of sample S2 becomes 8 mm or 6 mm is repeated 100,000 times.

[0057] (Folding condition)

[0058] · Reciprocating speed: 120 rpm (per rotation)

[0059] · Bending angle: 180°

[0060] The surface (30A) of the optical film (30) (the surface (31A) of the functional layer (31)) preferably has a hardness (pencil hardness) of 2H or higher when measured in a pencil hardness test specified in JIS K5600-5-4:1999, and more preferably 3H or higher. The pencil hardness test is performed by fixing an optical film (30) cut to a size of 30 mm × 100 mm onto a glass plate with cellophane tape (registered trademark) manufactured by Nichiban Co., Ltd. so as not to bend or wrinkle, and, under an environment with a temperature of 23 ± 5°C and a relative humidity of 30% or more and 70% or less, using a pencil hardness tester (e.g., product name "Pencil Scratch Coating Hardness Tester (Electric Type)," manufactured by Toyo Seiki Seisakusho Co., Ltd.) and moving the pencil at a speed of 1 mm / second while applying a load of 750 g to the pencil (e.g., product name "Uni," manufactured by Mitsubishi Enpits Co., Ltd.). The pencil hardness is defined as the highest hardness that does not cause scratches on the surface of the optical film during the pencil hardness test. In addition, when measuring pencil hardness, multiple pencils of different hardness are used, but a pencil hardness test is performed five times for one pencil, and if no scratches are made on the surface of the optical film in four or more of the five tests, it is determined that no scratches are made on the surface of the optical film for that pencil of hardness. The above scratches refer to those that are visible when the surface of the optical film subjected to the pencil hardness test is observed through transmission under a fluorescent light.

[0061] In the case where an adhesive layer or another film such as a polarizing plate is provided on one side of the optical film (30) through the adhesive layer, the other film is peeled off together with the adhesive layer or adhesive layer as described above, and then the shear storage modulus G' and glass transition temperature are measured and a folding test is performed.

[0062] The optical film (30) may be cut to a desired size, or it may be in the form of a roll. 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" refers to the length of the diagonal when the optical film is rectangular, the diameter when it is circular, and the average value of the sum of the short diameter and the long diameter when it is elliptical. Here, when the optical film is rectangular, the aspect ratio of the optical film when calculating the inch is not particularly limited as long as there is no problem with the display screen of the image display device. For example, vertical:horizontal = 1:1, 4:3, 16:10, 16:9, 2:1, etc. However, particularly for applications such as vehicle mounting or digital signage with excellent design quality, this aspect ratio is not limited. In addition, if the optical film (30) is large, it is cut to an A5 size (148 mm × 210 mm) from any position and then cut to the size of each measurement item. In addition, for example, if the optical film (30) is in the form of a roll, a predetermined length is drawn from the roll of the optical film (30), and instead of the non-effective area including both ends extending along the long direction of the roll, it is cut to a desired size from the effective area near the center where quality is stable.

[0063] The use of the optical film (30) is not particularly limited, but examples of uses for 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. Additionally, the optical film (30) is also suitable for vehicle mounting applications. As for the form of each of the above image display devices, applications requiring flexibility, such as foldable and rollable displays, are also desirable.

[0064] The placement location of the optical film (30) in the image display device may be inside the image display device, but it is preferable that it be 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 instead of a cover glass.

[0065] <<Functional Layer>>

[0066] The functional layer (31) illustrated 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, "hard coat layer" refers to a layer in which the pencil hardness is "H" or higher in the pencil hardness test described above.

[0067] When the displacement amount of the functional layer (31) is measured by the nanoindentation method, it is preferable that the displacement amount of the functional layer (31) be 50 nm or more and 500 nm or less. If the displacement amount of the functional layer (31) is 50 nm or more, good hardness can be obtained, and if it is 500 nm or less, good folding performance can be obtained. The measurement of the displacement amount by the nanoindentation method can be performed using a Bruker "TI950 TriboIndenter" on an optical film cut to a size of 30 mm × 30 mm. Specifically, under the following measurement conditions, the depth is measured when a Berkovitch indenter (triangular pyramid, e.g., Bruker TI-0039) is pressed perpendicularly into the cross-section of the functional layer with 500 μN as the indenter, and this is taken as the displacement amount. Here, the Berkovitch indenter is pressed into a portion of the functional layer that is spaced at least 500 nm toward the center of the functional layer from the interface between the resin layer and the functional layer, and spaced at least 500 nm toward the center of the functional layer from each of the two side ends of the functional layer, in order to avoid the influence of the side edges of the resin layer or the functional layer. The amount of displacement can be adjusted by the type of resin or the content of inorganic particles, etc., described later.

[0068] (Measurement conditions)

[0069] · Control method: Load control (maximum load 500μN)

[0070] · Lift amount: 0 nm

[0071] · Preload: 0.5μN

[0072] · Load rate: 20μN / sec

[0073] · Duration: 5 seconds

[0074] · Unloading rate: 20μN / sec

[0075] · Measured temperature: 23±5℃

[0076] · Relative humidity: 30% to 70%

[0077] It is preferable that the film thickness of the functional layer (31) be 3㎛ or more and 10㎛ or less. If the film thickness of the functional layer (31) is 3㎛ or more, good hardness can be obtained, and if it is 10㎛ or less, the deterioration of processability can be suppressed. In this specification, "film thickness of the functional layer" refers to the film thickness (total thickness) obtained by summing the film thicknesses of each functional layer when the functional layer has a multilayer structure. It is more preferable that the lower limit of the film thickness of the functional layer (31) be 5㎛ or more, and it is more preferable that the upper limit be 8㎛ or less. The film thickness of the functional layer (31) can be measured by the same method as the film thickness of the resin layer (10).

[0078] The functional layer (31) preferably further contains resin and inorganic particles dispersed in the resin.

[0079] Suzy

[0080] The resin comprises a polymer (cured product) of a polymerizable compound (curable compound). The polymerizable compound has at least one polymerizable functional group within its molecule. Examples of polymerizable functional groups include ethylenically unsaturated groups such as (meth)acryloyl groups, vinyl groups, and allyl groups.

[0081] As a polymerizable compound, polyfunctional (meth)acrylates are preferred. As the above-mentioned polyfunctional (meth)acrylates, for example, 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, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, isocyanuric acid tri(meth)acrylate, Examples include 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, isobornel di(meth)acrylate, dicyclopentane di(meth)acrylate, tricyclodecane di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, or these modified with PO, EO, caprolactone, etc.

[0082] Among these, since the above-mentioned displacement amount can be suitably satisfied, those with 3 to 6 functionalities are preferred, 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.

[0083] In addition, monofunctional (meth)acrylate monomers may also be included to adjust hardness or viscosity of the composition, or to improve adhesion. Examples of the monofunctional (meth)acrylate monomers include hydroxyethyl acrylate (HEA), glycidyl methacrylate, methoxypolyethylene glycol (meth)acrylate, isostearyl (meth)acrylate, 2-acryloyloxyethylsuccinate, acryloylmorpholine, N-acryloyloxyethylhexahydrophthalimide, cyclohexyl acrylate, tetrahydrofuryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and adamantyl acrylate.

[0084] The weight-average molecular weight of the monomer is preferably less than 1,000 and more than 200 and less than 800 from the perspective of improving the hardness of the resin layer. In addition, the weight-average molecular weight of the polymerizable oligomer is preferably 1,000 and more than 20,000 and less than 10,000 and more than 10,000 and more than 2,000 and less than 7,000.

[0085] Weapon Particles

[0086] As for the inorganic particles, they are not particularly limited as long as they can improve hardness, but silica particles are preferred from the perspective of obtaining excellent hardness. Among silica particles, reactive silica particles are preferred. The reactive silica particles are silica particles capable of forming a cross-linked structure with the polyfunctional (meth)acrylate, and by including these reactive silica particles, the hardness of the functional layer (31) can be sufficiently increased.

[0087] The above-mentioned reactive silica particles preferably have reactive functional groups on their surface, and as the reactive functional groups, for example, the above-mentioned polymerizable functional groups are suitably used.

[0088] The above-mentioned reactive silica particles are not particularly limited and conventionally known ones may be used, such as the reactive silica particles described in Japanese Patent Publication No. 2008-165040. In addition, commercially available products of the above-mentioned reactive silica particles include, for example, MIBK-SD, MIBK-SD-MS, MIBK-SD-L, MIBK-SD-ZL (all manufactured by Nissan Kagaku Kogyo Co., Ltd.) and V8802, V8803 (both manufactured by Nikki Shokubai Kasei Co., Ltd.).

[0089] In addition, the silica particles may be spherical silica particles, but it is preferable that they be heteromorphic silica particles. Spherical silica particles and heteromorphic silica particles may be mixed. Furthermore, in this specification, "spherical silica particles" refers to silica particles such as true spherical or elliptical spherical shapes, and "heterologous silica particles" refers to silica particles having a shape with random irregularities on the surface (an aspect ratio of 1.2 or more and 40 or less when observing the cross-section). Since the surface area of ​​the heteromorphic silica particles is larger compared to that of spherical silica particles, by including such heteromorphic silica particles, the contact area with the polyfunctional (meth)acrylate, etc. is increased, and the hardness of the functional layer (31) can be improved. Whether the silica particles included in the functional layer (31) are heteromorphic 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).

[0090] It is preferable that the average particle size of the above silica particles be 5 nm or larger and 200 nm or smaller. If the average particle size of the silica particles is 5 nm or larger, the manufacturing of the particles themselves is not difficult, so aggregation between particles can be suppressed, and it is not difficult to form them. On the other hand, if the average particle size of the above-mentioned silica particles is 200 nm or smaller, the formation of large irregularities in the functional layer can be suppressed, and the rise of haze can also be suppressed. In the case where the silica particles are spherical silica particles, the average particle size of the silica particles is determined by measuring the particle sizes of 20 particles from a cross-sectional image of the particles taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), and taking the arithmetic mean value of the particle sizes of the 20 particles. In addition, if the silica particles are heterogeneous silica particles, the average particle size of the silica particles is determined by measuring the maximum value (long diameter) and minimum value (short diameter) of the distance between two points on the outer circumference of the particles from an image of the cross-section of the functional layer taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), averaging them to obtain the particle size, and taking the arithmetic mean value of the particle sizes of 20 particles.

[0091] The hardness (displacement amount) of the functional layer (31) can be controlled by controlling the size and amount of the inorganic particles. For example, when forming the functional layer (31), the silica particles have a diameter of 5 nm or more and 200 nm or less, and it is preferable that the amount is 25 to 60 parts by mass with respect to 100 parts by mass of the polymerizable compound.

[0092] The functional layer (31) may include materials other than the materials described above within the range satisfying the displacement amount described above, and for example, as a resin component material, may include polymerizable monomers or polymerizable oligomers that form a cured product upon irradiation with ionizing radiation. Examples of the polymerizable monomers or polymerizable oligomers include (meth)acrylate monomers having radical polymerizable unsaturated groups in their molecules, or (meth)acrylate oligomers having radical polymerizable unsaturated groups in their molecules. Examples of monomers or oligomers having radical polymerizable unsaturated groups in the above molecules, or having radical polymerizable unsaturated groups in the above molecules, include urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, melamine (meth)acrylate, polyfluoroalkyl (meth)acrylate, silicone (meth)acrylate, etc. One or more of these polymerizable monomers or polymerizable oligomers may be used. Among these, urethane (meth)acrylate is polyfunctional (6 or more functions) and has a weight average molecular weight of 1,000 to 10,000.

[0093] The functional layer (31) may further include an ultraviolet absorber, a spectroscopic transmittance modifier, and / or an antifouling agent.

[0094] <<<Other Optical Films>>>

[0095] The optical film (30) shown in FIG. 3 does not have a substrate, but may have a substrate as shown in FIG. 5. The optical film (50) has a resin layer (10), a resin substrate (51), and a functional layer (52) in that order, as shown in FIG. 5. The resin substrate (51) may be adjacent to the resin layer (10). In addition, in the optical film (50), the resin layer (10) may be adjacent to the resin substrate (51) but may be attached to the resin substrate through an adhesive layer.

[0096] The surface (50A) of the optical film (50) is the surface (52A) of the functional layer (52). In this specification, the surface of the optical film is used to mean one side of the optical film, so the side opposite to the surface of the optical film is referred to as the back side to distinguish it from the surface of the optical film. The back side (50B) of the optical film (50) is the side opposite to the side of the resin substrate (51) in the resin layer (10).

[0097] The optical film (50) is foldable under an environment with a temperature of 23±5℃ and a relative humidity of 30% or more and 70% or less, and under an environment with a temperature of -40℃, respectively. The preferred number of folds, the preferred gap φ between opposing edges, and the conditions for the continuous folding test are the same as those for the optical film (30), so they are omitted from explanation here.

[0098] The surface (50A) of the optical film (50) (the surface (52A) of the functional layer (52)) preferably has a hardness (pencil hardness) of 2H or higher when measured in a pencil hardness test specified in JIS K5600-5-4:1999, and more preferably 3H or higher. The pencil hardness of the optical film (50) is measured by the same method as the pencil hardness of the optical film (30).

[0099] It is preferable that the optical film (50) has a yellow index (YI) of 15 or less. If the YI of the optical film (50) is 15 or less, the yellowish appearance of the optical film can be suppressed, so it can be applied to applications requiring transparency. It is more preferable that the upper limit of the yellow index (YI) of the optical film (50) is 10 or less, 5 or less, or 1.5 or less. The yellow index (YI) is a value calculated by determining the chromaticity tristimulus values ​​X, Y, and Z according to the formula described in JIS Z8722:2009 from the transmittance of an optical film with a wavelength of 300 nm to 780 nm, measured in a spectrophotometer (e.g., product name "UV-2450", manufactured by Shimadzu Seisakusho Co., Ltd., light source: tungsten lamp and deuterium lamp) with the resin layer side facing the light source, under conditions of an environment with a temperature of 23±5℃ and a relative humidity of 30% or more and 70% or less, and calculating the tristimulus values ​​X, Y, and Z according to the formula described in ASTM D1925:1962 from the tristimulus values ​​X, Y, and Z. It is more preferable that the upper limit of the yellow index (YI) of the optical film (50) be 10 or less. The above Yellow Index (YI) is the arithmetic mean of the values ​​obtained from three measurements taken for one optical film. In addition, for the UV-2450, the Yellow Index is calculated by reading the transmittance measurement data on a monitor connected to the UV-2450 and checking the "YI" item in the calculation items. The measurement of transmittance for wavelengths from 300 nm to 780 nm is determined by measuring the transmittance for at least 5 points within a range of 1 nm before and after each wavelength from 300 nm to 780 nm under the following conditions, and calculating the average value. In addition, if a bend occurs in the spectrum of the spectral transmittance, smoothing treatment may be performed with a delta of 5.0 nm.

[0100] (Measurement conditions)

[0101] · Wavelength range: 300 nm to 780 nm

[0102] · Scan speed: High speed

[0103] · Slit width: 2.0

[0104] · Sampling interval: Auto (0.5 nm interval)

[0105] ·Lighting: C

[0106] · Light source: D2 and WI

[0107] · Field of view: 2°

[0108] · Light source switching wavelength: 360 nm

[0109] · S / R Conversion: Standard

[0110] · Detector: PM

[0111] · Auto Zero: Performed at 550 nm after baseline scan

[0112] It is preferable that the total light transmittance of the optical film (50) be 85% or higher. If the total light transmittance of the optical film (50) is 85% or higher, sufficient image visibility can be obtained when the optical film (50) is used in a mobile terminal. It is preferable that the total light transmittance of the optical film (50) be 87% or higher, or 90% or higher.

[0113] The above total light transmittance can be measured in accordance with JIS K7361-1:1997 using a haze meter (e.g., product name “HM-150”, manufactured by Kijutsu Genkyujo, Murakami Kishisai Co., Ltd.) under an environment with a temperature of 23±5℃ and a relative humidity of 30% or more and 70% or less. The above total light transmittance is determined by cutting an optical film to a size of 50mm × 100mm, installing it in a state free of curls or wrinkles, and free of fingerprints or dust, and measuring it three times for one sheet of optical film, and taking the arithmetic mean of the values ​​obtained from the three measurements. In this specification, “measuring three times” means measuring three different locations, not measuring the same location three times. In the case of the optical film (50), the surface (50A) as seen by the eye is flat, and the laminated layer such as the resin layer (10) is also flat, and the variation in film thickness converges within a range of ±10%. Therefore, it is believed that by measuring the total light transmittance at three different locations on the cut optical film, the average value of the total light transmittance of the entire surface of the optical film is obtained. The variation in total light transmittance is within ±10%, whether the measurement target is long (1m × 3000m) or the size of a 5-inch smartphone. In addition, if the optical film cannot be cut to the above size, for example, since the entrance opening of the HM-150 when measuring is 20mmφ, 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 × 22mm or larger. When the size of the optical film is small, the measurement points are set to three locations by slightly shifting the light source spot or changing the angle so that the light source spot does not deviate.

[0114] It is preferable that the haze value of the optical film (50) be 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. It is more preferable that the haze value be 1.5% or less, 1.0% or less, or 0.5% or less.

[0115] The above haze value can be measured in accordance with JIS K7136:2000 using a haze meter (e.g., product name “HM-150”, manufactured by Kijutsu Genkyujo, Murakami Kishisai Co., Ltd.) under an environment with a temperature of 23±5℃ and a relative humidity of 30% or more and 70% or less. Specifically, the haze value is measured by the same method as the method for measuring total light transmittance.

[0116] In cases where another film, such as a polarizing plate, is provided on the surface (50A) or back side (50B) of the optical film (50) through an adhesive layer or adhesive layer, the other film is peeled off together with the adhesive layer or adhesive layer, and then a folding test, yellow index measurement, total light transmittance measurement, haze value measurement, etc. are performed. Furthermore, even if such a peeling process is performed, it does not have a significant effect on these tests or measurements. The haze value measurement is performed after peeling off the adhesive layer or adhesive layer, and after thoroughly wiping off any contamination from the adhesive layer or adhesive layer with alcohol.

[0117] The uses of the optical film (50) are not particularly limited and may include uses similar to those described in the section on the optical film (30).

[0118] <<Recorded by Suji>>

[0119] The resin substrate (51) has light transmittance. In this specification, "light transmittance" 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. Light transmittance does not necessarily have to be transparent and may be translucent.

[0120] The resin substrate (51) preferably comprises one or more resins selected from the group consisting of, for example, polyimide resin, polyamideimide resin, polyamide resin, and polyester resin (for example, polyethylene terephthalate resin or polyethylene naphthalate resin).

[0121] Among these resins, polyimide-based resins, polyamide-based resins, or mixtures thereof are preferred from the perspective that they not only have a low likelihood of cracking or breaking during a continuous folding test but also possess excellent hardness and transparency, and also have excellent heat resistance, and further excellent hardness and transparency can be imparted by firing.

[0122] Polyimide resins are obtained by reacting a tetracarboxylic acid component with a diamine component. Polyimide resins are not particularly limited, but, for example, in terms of having excellent light transmittance and excellent rigidity, it is preferable to have at least one structure selected from the group consisting of structures represented by the following general formula (5) and the following general formula (7).

[0123]

[0124] In the above general formula (5), R 5 is a tetravalent group that is a tetracarboxylic acid residue, R 6...represents at least one divalent group selected from the group consisting of a trans-cyclohexanediamine residue, a trans-1,4-bismethylenecyclohexanediamine residue, a 4,4'-diaminodiphenylsulfone residue, a 3,4'-diaminodiphenylsulfone residue, and a divalent group represented by the following general formula (6). n represents the number of repeating units and is 1 or more. In this specification, "tetracarboxylic acid residue" refers to a residue from a tetracarboxylic acid excluding four carboxyl groups, and represents the same structure as a residue from a tetracarboxylic acid dianhydride excluding the acid dianhydride structure. Also, "diamine residue" refers to a residue from a diamine excluding two amino groups.

[0125]

[0126] In the above general formula (6), R 7 and R 8 Each represents, independently, a hydrogen atom, an alkyl group, or a perfluoroalkyl group.

[0127]

[0128] In the above general formula (7), R 9 is at least one tetravalent group selected from the group consisting of a cyclohexane tetracarboxylic acid residue, a cyclopentane tetracarboxylic acid residue, a dicyclohexane-3,4,3',4'-tetracarboxylic acid residue, and a 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, R 10 represents a divalent group, which is a diamine residue. n' represents the number of repeating units and is 1 or greater.

[0129] In the above general formula (5), R 5 is a tetracarboxylic acid residue and can be a residue obtained by excluding the acid dianhydride structure from a tetracarboxylic acid dianhydride as exemplified above. R in the general formula (5) above 5Among these, in order to improve light transmittance and also improve rigidity, it is preferable to include at least one selected from the group consisting of a 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, a 3,3',4,4'-biphenyltetracarboxylic acid residue, a pyromellitic acid residue, a 2,3',3,4'-biphenyltetracarboxylic acid residue, a 3,3',4,4'-benzophenonetetracarboxylic acid residue, a 3,3',4,4'-diphenylsulfonetetracarboxylic acid residue, a 4,4'-oxydiphthalic acid residue, a cyclohexanetetracarboxylic acid residue, and a cyclopentanetetracarboxylic acid residue. Additionally, the 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, the 4,4'-oxydiphthalic acid residue, and It is preferable to include at least one selected from the group consisting of 3,3',4,4'-diphenylsulfonetetracarboxylic acid residues.

[0130] R 5 In this regard, it is preferable to include at least 50 mol% of these suitable residues in total, more preferable to include at least 70 mol%, and even more preferable to include at least 90 mol%.

[0131] Also, R 5 As such, it is also preferable to use a mixture of a group of tetracarboxylic acid residues suitable for improving rigidity (Group A), such as at least one selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic acid residues, 3,3',4,4'-benzophenonetetracarboxylic acid residues, and pyromellitic acid residues, and a group of tetracarboxylic acid residues suitable for improving transparency (Group B), such as at least one selected from the group consisting of 4,4'-(hexafluoroisopropylidene)diphthalic acid residues, 2,3',3,4'-biphenyltetracarboxylic acid residues, 3,3',4,4'-diphenylsulfonetetracarboxylic acid residues, 4,4'-oxydiphthalic acid residues, cyclohexanetetracarboxylic acid residues, and cyclopentanetetracarboxylic acid residues.

[0132] In this case, the content ratio of the tetracarboxylic acid residue group (Group A) suitable for improving rigidity and the tetracarboxylic acid residue group (Group B) suitable for improving transparency is preferably such that, for every 1 mole of the tetracarboxylic acid residue group (Group B) suitable for improving transparency, the tetracarboxylic acid residue group (Group A) suitable for improving rigidity is 0.05 moles or more and 9 moles or less, more preferably 0.1 moles or more and 5 moles or less, and even more preferably 0.3 moles or more and 4 moles or less.

[0133] R in the above general formula (5) 6 Among these, in order to improve light transmittance and also improve rigidity, it is preferable that at least one divalent group selected from the group consisting of a 4,4'-diaminodiphenylsulfone residue, a 3,4'-diaminodiphenylsulfone residue, and a divalent group represented by the general formula (6), and also, a 4,4'-diaminodiphenylsulfone residue, a 3,4'-diaminodiphenylsulfone residue, and R 7 and R 8 It is preferable that this perfluoroalkyl group be at least one divalent group selected from the group consisting of divalent groups represented by the general formula (6) above.

[0134] R in the above general formula (7) 9 Among these, it is preferable to include a 4,4'-(hexafluoroisopropylidene)diphthalic acid residue, a 3,3',4,4'-diphenylsulfonetetracarboxylic acid residue, and an oxydiphthalic acid residue in order to improve light transmittance and also improve rigidity.

[0135] R 9 In this regard, it is preferable to include 50 mol% or more of these suitable residues, more preferable to include 70 mol% or more, and even more preferable to include 90 mol% or more.

[0136] R in the above general formula (7) 10is a diamine residue, and can be a residue obtained by removing two amino groups from a diamine as exemplified above. R in the general formula (5) above 6 As for, among others, in terms of improving light transmittance and also improving rigidity, 2,2'-bis(trifluoromethyl)benzidine residue, bis[4-(4-aminophenoxy)phenyl]sulfone residue, 4,4'-diaminodiphenylsulfone residue, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residue, bis[4-(3-aminophenoxy)phenyl]sulfone residue, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenylether 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)diphenylether residue, 4,4'-diaminobenzanilide It is preferable to include at least one divalent group selected from the group consisting of a residue, an N,N'-bis(4-aminophenyl)terephthalamide residue, and a 9,9-bis(4-aminophenyl)fluorene residue, and also preferable to include 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'-diaminodiphenylsulfone residue.

[0137] R 10 In this regard, it is preferable to include at least 50 mol% of these suitable residues in total, more preferable to include at least 70 mol%, and even more preferable to include at least 90 mol%.

[0138] Also, R 10As, a group of diamine residues suitable for improving rigidity (Group C), such as at least one selected from the group consisting of a bis[4-(4-aminophenoxy)phenyl]sulfone residue, a 4,4'-diaminobenzanilide residue, an N,N'-bis(4-aminophenyl)terephthalamide residue, a paraphenylenediamine residue, a metaphenylenediamine residue, and a 4,4'-diaminodiphenylmethane residue, and a 2,2'-bis(trifluoromethyl)benzidine residue, a 4,4'-diaminodiphenylsulfone residue, a 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residue, a bis[4-(3-aminophenoxy)phenyl]sulfone residue, and a 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether residue. It is also preferable to use a mixture of diamine residues (Group D) suitable for improving transparency, such as at least one selected from the group consisting of 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.

[0139] In this case, the content ratio of the diamine residue group (Group C) suitable for improving rigidity and the diamine residue group (Group D) suitable for improving transparency is preferably such that, for every 1 mole of the diamine residue group (Group D) suitable for improving transparency, the diamine residue group (Group C) suitable for improving rigidity is 0.05 moles or more and 9 moles or less, more preferably 0.1 moles or more and 5 moles or less, and even more preferably 0.3 moles or more and 4 moles or less.

[0140] In the structure 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 greater. The number of repeating units n in the polyimide can be appropriately selected according to the structure to represent the preferred glass transition temperature described later, and is not particularly limited. The average number of repeating units is typically 10 to 2000, and more preferably 15 to 1000.

[0141] In addition, the polyimide resin may include a polyamide structure in part. Examples of polyamide structures that may be included include 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.

[0142] For polyimide resins, in terms of heat resistance, it is preferable that the glass transition temperature be 250°C or higher, and also preferable that it be 270°C or higher. On the other hand, in terms of ease of stretching or reduction of bake temperature, it is preferable that the glass transition temperature be 400°C or lower, and also preferable that it be 380°C or lower.

[0143] Examples of polyimide resins include compounds 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.

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161] Among the above polyimide resins, a polyimide resin or a polyamide resin having a structure in which charge transfer within or between molecules is difficult to occur is preferred because it has excellent transparency. Specifically, examples include a fluorinated polyimide resin of formulas (8) to (15) and a polyimide resin having a ring structure of formulas (15) to (19).

[0162] In addition, the fluorinated polyimide resins of the above chemical formulas (8) to (15) have a fluorinated structure, so they have high heat resistance and do not get colored by the heat during the manufacture of the polyimide film made of the polyimide resin, thus having excellent transparency.

[0163] Polyamide resins are a concept that includes not only aliphatic polyamides but also aromatic polyamides (aramids). Examples of polyamide resins include compounds having a backbone represented by the following chemical formulas (25) to (27). In addition, in the following formulas, n is a repeating unit and represents an integer of 2 or more.

[0164]

[0165]

[0166]

[0167] The substrate made of a polyimide resin or a polyamide resin represented by the above chemical formulas (8) to (24) and (27) may be a commercially available product. Examples of commercially available polyimide resins include Neopulim (registered trademark) manufactured by Mitsubishi Gas Chemical Co., Ltd., and examples of commercially available substrates containing the above polyamide resin include Micron (registered trademark) manufactured by Toray Co., Ltd.

[0168] In addition, the polyimide resin or polyamide resin 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 resin represented by the above chemical formula (8) is described in Japanese Patent Publication No. 2009-132091, and specifically, it can be obtained by reacting 4,4'-hexafluoropropylidene bisphthalic dianhydride (FPA) represented by the following chemical formula (28) with 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB).

[0169]

[0170] The weight average molecular weight of the above polyimide-based resin or polyamide-based resin is preferably in the range of 3,000 to 500,000, more preferably in the range of 5,000 to 300,000, and even more preferably in the range of 10,000 to 200,000. If the weight average molecular weight is less than 3,000, sufficient strength may not be obtained, and if it exceeds 500,000, viscosity increases and solubility decreases, so a substrate with a smooth surface and uniform film thickness may not be obtained. In addition, in this specification, "weight average molecular weight" refers to a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0171] In order to improve hardness, the resin substrate (51) preferably uses a fluorinated polyimide resin represented by the above chemical formulas (8) to (15), etc., or a polyamide resin having a halogen group represented by the above chemical formula (27). Among these, in order to further improve hardness, it is more preferable to use a substrate containing a polyimide resin represented by the above chemical formula (8).

[0172] Examples of polyester resins include resins having at least one of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a component.

[0173] It is preferable that the thickness of the resin substrate (51) be 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 and sufficient hardness can be obtained, and even when manufacturing the optical film (50) by roll-to-roll, wrinkles are less likely to occur, so there is no risk of 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, so the requirements for a continuous folding test can be satisfied, and it is also desirable in terms of making the optical film (50) lighter. The thickness of the resin substrate (51) can be measured by the same method as the film thickness of the resin layer (10). It is more preferable that the lower limit of the resin substrate (51) be 20㎛ or more, 30㎛ or more, or 40㎛ or more, and the upper limit of the resin substrate (51) be 80㎛ or less or 50㎛ or less.

[0174] <<Functional Layer>>

[0175] The functional layer (52) is similar to the functional layer (31), so the explanation here is omitted.

[0176] <<<Method for manufacturing resin layer and optical film>>>

[0177] The resin layer (10) and optical film (30, 50) can be manufactured as follows. First, a composition for the resin layer is applied to one side of a release film using a coating device such as a bar coater to form a coating film.

[0178] <<Composition for Resin Layers>>

[0179] The composition for the resin layer includes an ionizing radiation-curable compound. In addition to the ionizing radiation-curable compound, the composition for the resin layer may further include a solvent and a polymerization initiator. Since the ionizing radiation-curable compound has been described in the section on the resin layer (10), it will be omitted from the description here.

[0180] (menstruum)

[0181] As the above solvent, alcohols (e.g., methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol, t-butanol, benzyl alcohol, PGME, ethylene glycol, diacetone alcohol), ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone, diethyl ketone, diacetone alcohol), esters (methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, methyl formate, 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., Examples include dimethylformamide, dimethylacetamide, n-methylpyrrolidone), ethers (e.g., diethyl ether, dioxane, tetrahydrofuran), ether alcohols (e.g., 1-methoxy-2-propanol), and carbonates (dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate). These solvents may be used alone or in combination of two or more types. Among them, methyl isobutyl ketone and methyl ethyl ketone are preferred as the solvents because they can dissolve or disperse components such as urethane (meth)acrylate and other additives, thereby suitably coating the composition for the resin layer.

[0182] (Polymer initiator)

[0183] A polymerization initiator is a component that decomposes upon ionizing radiation irradiation to generate radicals, thereby initiating or promoting the polymerization (crosslinking) of polymerizable compounds.

[0184] The polymerization initiator is not particularly limited as long as it is capable of releasing a substance that initiates radical polymerization upon ionizing radiation. As a polymerization initiator, any known substance may be used without being particularly limited, and specific examples include, for instance, acetophenones, benzophenones, myeler benzoyl benzoate, α-amyloxime esters, thioxantones, propiophenones, benzyls, benzoins, and acylphosphine oxides. In addition, it is preferable to use a photosensitizer mixed in, and specific examples include, for instance, n-butylamine, triethylamine, poly-n-butylphosphine, etc.

[0185] After forming a coating film of a composition for a resin layer, if the composition for the resin layer contains a solvent, the coating film is dried by heating it at a temperature of, for example, 30°C or higher and 120°C or lower for 10 to 120 seconds using various known methods to evaporate the solvent.

[0186] After drying the coating film, the coating film is irradiated with ionizing radiation such as ultraviolet rays to cure it. Then, the release film is peeled off to obtain a resin layer (10).

[0187] In addition, when forming an optical film (30), after drying the coating film of the composition for the resin layer, the coating film is irradiated with ionizing radiation such as ultraviolet rays to partially cure it. In this specification, "partially cured" means that curing proceeds substantially when further ionizing radiation is irradiated.

[0188] After that, a composition for a functional layer for forming a functional layer (31) is applied to the semi-cured coating film using a coating device such as a bar coater, thereby forming a coating film of the composition for a functional layer.

[0189] Composition for Functional Layer

[0190] The composition for the functional layer comprises a polymerizable compound. Additionally, the composition for the functional layer may, if necessary, comprise an ultraviolet absorber, a spectroscopic transmittance modifier, an antifouling agent, inorganic particles, a leveling agent, a solvent, and a polymerization initiator. Since the solvent and the polymerization initiator are the same as those in the composition for the resin layer, they will be omitted from this description.

[0191] After forming a coating film of the composition for the functional layer, the coating film is dried by heating it by various known methods, for example, at a temperature of 30°C or higher and 120°C or lower for 10 to 120 seconds, thereby evaporating the solvent.

[0192] After drying the coating film of the composition for the functional layer, ionizing radiation such as ultraviolet rays is irradiated to completely cure the coating film, thereby forming a functional layer (31). However, "complete curing" in this specification means that curing does not substantially proceed even if ionizing radiation is irradiated further. After that, the release film is peeled off to obtain an optical film (30).

[0193] When forming an optical film (50), a functional layer (52) is formed on one side of the resin substrate (51). The functional layer (52) can be formed by the same method as the functional layer (31). Then, a resin layer (10) is formed on the side opposite to the side of the resin substrate (51) where the functional layer (52) is formed, in the same manner as above. By doing so, an optical film (50) can be obtained.

[0194] According to the present embodiment, since the shear storage modulus G' in the resin layer (10) at 25°C and in the frequency range of 500 Hz or higher and 1000 Hz or lower is 30 MPa or higher and 200 MPa or lower, good impact resistance can be obtained.

[0195] Typically, resins with a low shear storage modulus G' have a low glass transition temperature, so even if they have good flexibility under room temperature conditions, they become hard and brittle when subjected to low temperature conditions below the glass transition temperature. According to the present embodiment, since the glass transition temperature of the resin layer (10) is 50°C or higher, the change in the state of the resin layer (10) under room temperature conditions and low temperature conditions can be suppressed. Therefore, the flexibility of the resin layer (10) can be maintained not only under room temperature conditions but also under low temperature conditions. As a result, good folding properties can be obtained.

[0196] <<<Image Display Device>>>

[0197] The optical film (30, 50) can be embedded in a foldable image display device. FIG. 6 is a schematic diagram of an image display device according to the present embodiment. As shown in FIG. 6, the image display device (60) is stacked in the order of a housing (61) in which a battery, etc. is housed, mainly, a display element (62), a circular polarizer (63), a touch sensor (64), and an optical film (30) facing the observer. Between the housing (61) and the display element (62), between the display element (62) and the circular polarizer (63), between the circular polarizer (63) and the touch sensor (64), and between the touch sensor (64) and the optical film (30), a light-transmitting adhesive layer (65) or an adhesive layer is disposed, and these components are fixed to each other by the adhesive layer (65) or the adhesive layer. Additionally, the adhesive layer (65) is positioned between the housing (61) and the display element (62), between the display element (62) and the circular polarizer (63), between the circular polarizer (63) and the touch sensor (64), and between the touch sensor (64) and the optical film (30), but the position of the adhesive layer is not particularly limited as long as it is between the optical film and the display element.

[0198] The optical film (30) is arranged so that the functional layer (31) is on the observer side rather 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).

[0199] In the image display device (60), the display element (62) is an organic light-emitting diode element including an organic light-emitting diode. The touch sensor (64) is positioned on the observer side rather than the circular polarizer (63), but may also be positioned between the display element (62) and the circular polarizer (63). Additionally, the touch sensor (64) may be an on-cell or in-cell type. For example, an OCA (Optical Clear Adhesive) may be used as the adhesive layer (65).

[0200] Examples

[0201] To explain the present invention in detail, examples are described below, but the present invention is not limited to these descriptions.

[0202] <Preparation of a composition for a hard coat layer>

[0203] First, each component was mixed to obtain the composition shown below, thereby obtaining composition 1 for a hard coat layer.

[0204] (Composition for hard coat layer 1)

[0205] · Mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (Product name "M403", manufactured by Doa Kose Co., Ltd.): 25 parts by mass

[0206] · Dipentaerythritol EO-modified hexaacrylate (Product name "A-DPH-6E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 25 parts by mass

[0207] · Irregular silica particles (average particle size 25 nm, manufactured by Nikki Shokubai Kasei Co., Ltd.): 50 parts by mass (value converted to 100% solid content)

[0208] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 4 parts by mass

[0209] · Fluorine-based leveling agent (Product name "F568", manufactured by DIC Co., Ltd.): 0.2 parts by mass (value converted to 100% solid content)

[0210] · Methyl isobutyl ketone (MIBK): 150 parts by mass

[0211] Composition for Resin Layers

[0212] A composition for a resin layer was obtained by mixing each component to obtain the composition shown below.

[0213] (Composition for resin layer 1)

[0214] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 90 parts by mass

[0215] · Cyclic trimethylolpropane formal acrylate (Product name "Viscot #200", manufactured by Osaka Yuki Kagaku High School): 10 parts by mass

[0216] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0217] ·Methyl isobutyl ketone: 10 parts by mass

[0218] (Composition for resin layer 2)

[0219] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 40 parts by mass

[0220] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 5 parts by mass

[0221] · Phenoxyethyl acrylate (Product name "Viscot #192", manufactured by Osaka Yuki Kagaku High School): 5 parts by mass

[0222] · Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (Product name "KAYARAD PET-30", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass

[0223] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0224] ·Methyl isobutyl ketone: 10 parts by mass

[0225] (Composition for resin layer 3)

[0226] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 35 parts by mass

[0227] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 10 parts by mass

[0228] · Phenoxyethyl acrylate (Product name "Viscot #192", manufactured by Osaka Yuki Kagaku High School): 5 parts by mass

[0229] · Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (Product name "KAYARAD PET-30", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass

[0230] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0231] ·Methyl isobutyl ketone: 10 parts by mass

[0232] (Composition for resin layer 4)

[0233] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 25 parts by mass

[0234] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 20 parts by mass

[0235] · Phenoxyethyl acrylate (Product name "Viscot #192", manufactured by Osaka Yuki Kagaku High School): 5 parts by mass

[0236] · Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (Product name "KAYARAD PET-30", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass

[0237] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0238] ·Methyl isobutyl ketone: 10 parts by mass

[0239] (Composition for resin layer 5)

[0240] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 15 parts by mass

[0241] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 30 parts by mass

[0242] · Dicyclofentanyl acrylate (Product name "FA-513AS", manufactured by Hitachi Kasei Co., Ltd.): 5 parts by mass

[0243] · Dipentaerythritol hexaacrylate (Product name "KAYARAD DPHA", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass

[0244] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0245] ·Methyl isobutyl ketone: 10 parts by mass

[0246] (Composition for resin layer 6)

[0247] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 90 parts by mass

[0248] · Tetrahydrofurfuryl alcohol acrylic acid polymer ester (product name "Viscot #150D", manufactured by Osaka Yuki Kagaku High School): 10 parts by mass

[0249] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0250] ·Methyl isobutyl ketone: 10 parts by mass

[0251] (Composition for resin layer 7)

[0252] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 40 parts by mass

[0253] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 5 parts by mass

[0254] · Phenoxyethyl acrylate (Product name "Viscot #192", manufactured by Osaka Yuki Kagaku High School): 5 parts by mass

[0255] · Dipentaerythritol hexaacrylate (Product name "KAYARAD DPHA", manufactured by Nippon Kayaku Co., Ltd.): 50 parts by mass

[0256] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0257] ·Methyl isobutyl ketone: 10 parts by mass

[0258] (Composition for resin layer 8)

[0259] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 30 parts by mass

[0260] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 60 parts by mass

[0261] · Dicyclofentanyl acrylate (Product name "FA-513AS", manufactured by Hitachi Kasei Co., Ltd.): 10 parts by mass

[0262] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0263] ·Methyl isobutyl ketone: 10 parts by mass

[0264] (Composition for resin layer 9)

[0265] · Urethane acrylate (Product name "UV-3310B", manufactured by Mitsubishi Chemical Corporation): 80 parts by mass

[0266] · Ethoxylated pentaerythritol tetraacrylate (Product name "ATM-35E", manufactured by Shin-Nakamura Kagaku Kogyo Co., Ltd.): 10 parts by mass

[0267] · Phenoxyethyl acrylate (Product name "Viscot #192", manufactured by Osaka Yuki Kagaku High School): 10 parts by mass

[0268] · Polymerization initiator (1-hydroxycyclohexylphenyl ketone, product name "Omnirad 184", manufactured by IGM Resins BV): 5 parts by mass

[0269] ·Methyl isobutyl ketone: 10 parts by mass

[0270] <Example 1>

[0271] As a release film, a polyethylene terephthalate substrate with a thickness of 50 μm (product name "Cosmo Shine (registered trademark) A4100", manufactured by Toyobo Co., Ltd.) was prepared, and composition 1 for a resin layer was applied to the untreated side of the polyethylene terephthalate substrate using a bar coater to form a film. Then, the solvent in the film was evaporated by heating the formed film at 70°C for 1 minute, and the film was partially cured (half-cured) by using an ultraviolet irradiation device (manufactured by Fusion UV Systems Japan, light source H bulb) to irradiate ultraviolet light in air such that the integrated light amount was 100 mJ / cm², thereby forming a resin layer made of a urethane-based resin with a film thickness of 100 μm.

[0272] Next, composition 1 for a hard coat layer was applied to the surface of the semi-cured film using a bar coater to form a film. After that, the solvent in the film was evaporated by heating the formed film at 70°C for 1 minute, and the film was fully cured (full cure) by irradiating it with ultraviolet light using an ultraviolet irradiation device (manufactured by Fusion UV Systems Japan, light source H bulb) so that the integrated light intensity was 300 mJ / cm² under conditions where the oxygen concentration was 200 ppm or less. By doing so, a hard coat layer with a film thickness of 5 μm was formed.

[0273] Subsequently, 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.

[0274] The film thickness of each layer was determined by photographing a cross-section of the optical film using a scanning transmission electron microscope (STEM) (product name "S-4800", manufactured by Hitachi High Technologies Co., Ltd.), measuring the film thickness of each layer at 10 locations in the cross-sectional image, and taking the arithmetic mean of the film thicknesses at those 10 locations. The cross-sectional photograph of the optical film was taken as follows. First, a block was prepared by embedding the optical film, cut to 1 mm × 10 mm, in an embedding resin. From this block, a uniform section with a thickness of 70 nm or more and 100 nm or less, free of holes, was cut using a general section preparation method. An UltraMicrotome EM UC7 from Leika Microsystems Co., Ltd. was used for section preparation. Then, this uniform section free of holes was used as the measurement sample. Subsequently, a cross-sectional photograph of the measurement sample was taken using a scanning transmission electron microscope (STEM). When taking cross-sectional photographs of each layer, STEM observation was performed by setting the detector to "TE," the acceleration voltage to "30 kV," and the emission current to "10 μA." Regarding magnification, the focus was adjusted to appropriately adjust the contrast and brightness to 100 to 100,000 times while observing whether each layer could be distinguished. Regarding magnification, the focus was adjusted to appropriately adjust the contrast and brightness to 5,000 to 200,000 times while observing whether each layer could be distinguished. In addition, 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 "8 mm." 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.

[0275] <Example 2>

[0276] In Example 2, an optical film was obtained in the same manner as in Example 1, except that composition 2 for a resin layer was used instead of composition 1 for a resin layer.

[0277] <Example 3>

[0278] In Example 3, an optical film was obtained in the same manner as in Example 1, except that composition 3 for a resin layer was used instead of composition 1 for a resin layer.

[0279] <Example 4>

[0280] In Example 4, an optical film was obtained in the same manner as in Example 1, except that composition 4 for a resin layer was used instead of composition 1 for a resin layer.

[0281] <Example 5>

[0282] In Example 5, an optical film was obtained in the same manner as in Example 1, except that composition 5 for a resin layer was used instead of composition 1 for a resin layer.

[0283] <Example 6>

[0284] 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.

[0285] <Example 7>

[0286] 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.

[0287] <Example 8>

[0288] 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.

[0289] <Example 9>

[0290] 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.

[0291] <Example 10>

[0292] 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.

[0293] <Comparative Example 1>

[0294] In Comparative Example 1, an optical film was obtained in the same manner as in Example 1, except that composition 6 for a resin layer was used instead of composition 1 for a resin layer.

[0295] <Comparative Example 2>

[0296] In Comparative Example 2, an optical film was obtained in the same manner as in Example 1, except that composition 7 for a resin layer was used instead of composition 1 for a resin layer.

[0297] <Comparative Example 3>

[0298] In Comparative Example 3, an optical film was obtained in the same manner as in Example 1, except that composition 8 for a resin layer was used instead of composition 1 for a resin layer.

[0299] <Comparative Example 4>

[0300] In Comparative Example 4, an optical film was obtained in the same manner as in Example 1, except that composition 9 for the resin layer was used instead of composition 1 for the resin layer.

[0301] <Measurement of Shear Storage Modulus G'>

[0302] 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 into a rectangular shape of 10 mm × 5 mm to form a sample. Then, two of these samples were prepared and installed on 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 is equipped with a single metal solid shearing plate with a thickness of 1 mm and two L-shaped metal members positioned on both sides of the solid shearing plate. One sample was placed between the solid shearing plate and one L-shaped metal member, and the other sample was placed between the solid shearing plate and the other L-shaped metal member. In this case, the samples were placed such that the resin layer was on the solid shearing plate side and the hard coat layer was on the L-shaped metal member side. Then, the L-shaped metal members were fastened together with screws to secure the samples. Next, a tensile test chuck consisting of an upper chuck and a lower chuck was installed in a dynamic viscoelasticity measuring device (product name “Rheogel-E4000”, manufactured by UBM Co., Ltd.), and a solid shearing jig was installed between the upper chuck and the lower chuck with a chuck-to-chock distance of 20 mm. Then, the set temperature was set to 25°C and the temperature was increased at a rate of 2°C / min. In this state, while fixing the solid shear plate, a deformation amount of 1% and longitudinal vibration in the range of frequency from 500 Hz to 1000 Hz was applied to two L-shaped metal members, and the dynamic viscoelasticity of the solid was measured at 25°C to measure the shear storage modulus G' of the optical film. Here, the shear storage modulus G' in the frequency range of 500 Hz to 1000 Hz for the optical film was determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to an L-shaped metal member, measuring the shear storage modulus G' of the optical film at each frequency, calculating the arithmetic mean of these shear storage modulus G', repeating this measurement three times, and taking the arithmetic mean of the three arithmetic mean values ​​obtained for each time.In addition, in the case of an optical film, since the resin layer is more flexible than the hard coat layer, the shear storage modulus G' of the optical film can be considered as the shear storage modulus G' of the resin layer.

[0303] <Measurement of Glass Transition Temperature Tg>

[0304] The glass transition temperature Tg of the optical film for the examples and comparative examples was measured. Specifically, first, a sample of the same size as the sample used in the measurement of the shear storage modulus G' was obtained from the optical film, and the sample was installed in a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.) in the same way as in the measurement of the shear storage modulus G'. Then, the set temperature was set to -50°C and the temperature was increased at a rate of 2°C / min. In this state, while fixing the solid shear plate, a deformation amount of 1% and longitudinal vibration in the range of frequency from 500 Hz to 1000 Hz was applied to two L-shaped metal members, and the dynamic viscoelasticity of the solid was measured to measure the shear loss loss tangent tanδ of the optical film. Here, the shear loss tangent tanδ in the frequency range of 500 Hz to 1000 Hz for the optical film was determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to an L-shaped metal member, measuring the shear loss tangent tanδ of the optical film at each frequency, determining the peak temperature from these shear loss tangent tanδs, and calculating the arithmetic mean of the glass transition temperature. In addition, this measurement was repeated three times, and the arithmetic mean of the three obtained values ​​was calculated again. Furthermore, since the resin layer is more flexible than the hard coat layer in the optical film, the glass transition temperature Tg of the optical film can be considered as the glass transition temperature Tg of the resin layer.

[0305] Impact Resistance Test

[0306] Impact resistance tests were performed using optical films according to the examples and comparative examples. Specifically, the optical films according to the examples and comparative examples were placed directly on the surface of 0.7 mm thick soda glass with the hard coat layer side facing upward, and an impact resistance test was performed three times for each by dropping an iron ball weighing 100 g and with a diameter of 30 mm from a height of 30 cm onto the surface of the hard coat layer of the optical film. In addition, the position from which the iron ball was dropped was varied each time during the impact resistance test. After the impact resistance test, the optical films were evaluated to see if the surface of the hard coat layer was indented by visual inspection. The evaluation results are as follows.

[0307] A: When observing the hard coat layer from both the front and the angle, no indentations were confirmed on the surface of the hard coat layer.

[0308] B: When observing the hard coat layer from the front or from an angle, indentations were observed on the surface of the hard coat layer, but the level was not problematic for actual use.

[0309] C: When the hard coat layer was observed from the front, no indentations were observed on the surface of the hard coat layer, but when observed at an angle, indentations were confirmed on the surface of the hard coat layer.

[0310] D: When the hard coat layer was observed from both the front and the angle, a clear indentation was observed on the surface of the hard coat layer.

[0311] Foldability

[0312] A continuous folding test was performed on the optical films of the examples and comparative examples to evaluate the folding ability. Specifically, first, a sample of 30 mm × 100 mm was cut from the optical film. Then, two opposing edges of the cut sample were each fixed to a fixing part of a folding endurance tester (e.g., product name "U-shaped stretching tester DLDMLH-FS", manufactured by Yuasa System Machinery Co., Ltd., compliant with IEC 62715-6-1) arranged in parallel. After that, as shown in Fig. 4 (C), a continuous folding test was performed by folding 100,000 times at 180° under the following conditions, such that the minimum gap φ between the two opposing edges was 10 mm and the surface side (hard coat layer side) of the optical film was on the outside, and it was investigated whether deformation, cracks, or fractures occurred in the folded part. The continuous folding test was performed under a room temperature environment of 23°C and 50% relative humidity, and under a low temperature environment of -40°C, respectively. The evaluation criteria were as follows.

[0313] A: In the continuous folding test, no deformation, cracks, or fractures occurred in the bends.

[0314] B: In the continuous folding test, deformation at a level not causing practical problems was confirmed in the bends, but no cracks or fractures occurred.

[0315] C: In the continuous folding test, deformation was clearly observed in the bending section, but no cracks or fractures occurred.

[0316] D: In the continuous folding test, cracks or fractures occurred in the bent portion.

[0317] Pencil Hardness

[0318] The pencil hardness of the surface of the optical film (the surface of the hard coat layer) for the examples and comparative examples was measured, respectively, based on JIS K5600-5-4:1999. Specifically, first, an optical film cut to a size of 30 mm × 100 mm was fixed onto a glass plate with a thickness of 2 mm using cellophane tape (registered trademark) manufactured by Nichiban Corporation so as not to bend or wrinkle. Then, using a pencil hardness tester (product name "Pencil Scratch Coating Hardness Tester (Electric Type)", manufactured by Toyo Seiki Seisakusho Corporation), a load of 750 g was applied to a pencil (product name "Uni", manufactured by Mitsubishi Enpis Co., Ltd.) under an environment of a temperature of 23°C and a relative humidity of 50%, and the pencil was moved at a speed of 1 mm / second. Pencil hardness was defined as the highest hardness that did not cause scratches on the surface of the optical film (the surface of the hard coat layer) during the pencil hardness test. Additionally, when measuring pencil hardness, multiple pencils of different hardness levels were used, but a pencil hardness test was performed five times on one pencil. If no scratches were observed on the surface of the optical film when the surface of the optical film was observed through a fluorescent light at least four times out of the five tests, it was determined that the surface of the optical film was not scratched by the pencil of that hardness.

[0319] The results are shown in Table 1 below.

[0320]

[0321] The results are explained below. The optical film according to Comparative Example 2 had poor foldability at room temperature because the shear storage modulus G' of the resin layer was too high, and the optical film according to Comparative Example 3 had poor impact resistance because the shear storage modulus G' of the resin layer was too low. In addition, the optical films according to Comparative Examples 1 and 4 had good foldability in a room temperature environment, but poor foldability in a low temperature environment because the glass transition temperature of the resin layer was too low. In contrast, the optical films according to Examples 1 to 10 had good impact resistance because the shear storage modulus G' was 30 MPa or higher and 200 MPa or lower, and also had good foldability in a low temperature environment as well as in a room temperature environment because the glass transition temperature of the resin layer was 50°C or higher. Explanation of the symbols

[0322] 10: Resin layer 30, 50: Optical film 31: Functional layer 51: Suji entry 52: Functional layer 60: Image display device 62: Display element

Claims

Claim 1 A resin layer having shock-absorbing properties used in an image display device, wherein the resin layer comprises a urethane-based resin, the film thickness of the resin layer is 20 μm or more and 150 μm or less, the shear storage modulus G' in the frequency range of 25°C and 500 Hz or more and 1000 Hz or less in the resin layer is 30 MPa or more and 200 MPa or less, and the glass transition temperature of the resin layer is 50°C or more and 90°C or less. Claim 2 An optical film having a foldable laminated structure, and comprising at least the resin layer described in claim 1. Claim 3 An optical film according to paragraph 2, further comprising a functional layer provided on one side of the resin layer. Claim 4 An optical film according to paragraph 2, further comprising a resin substrate provided on one side of the resin layer. Claim 5 In paragraph 2, the optical film does not crack or break when a test of folding the optical film 180° so that the gap between opposing edges becomes 10 mm is repeated 100,000 times in an environment of 23°. Claim 6 In claim 5, the optical film does not crack or break when a test of folding the optical film 180° so that the gap between opposing edges becomes 10 mm is repeated 100,000 times in an environment of -40℃. Claim 7 An image display device comprising a display element and an optical film having a foldable laminated structure, wherein the resin layer described in claim 1 or the resin layer disposed on the observer side rather than the display element, and at least the optical film having the resin layer. Claim 8 In claim 7, the image display device wherein the display element is an organic light-emitting diode element. Claim 9 delete

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