Optical film and image display device

Abstract

The purpose of the present invention is to provide a foldable optical film in which interference fringes are less likely to be produced, and an image display device comprising the optical film. Provided is a foldable optical film that is to be used in an image display device, the optical film having a polyester film serving as a base material, a functional layer provided on a first-surface side of the base material, a resin layer A provided between the base material and the functional layer, and a resin layer B provided to the side of the base material opposite from the first surface, the film thickness of the resin layer A being 10-500 nm, and the film thickness of the resin layer B being 1-200 nm, wherein cracks and fractures do not occur when a test in which the optical film is folded by 180° such that the functional layer is on the inner side, and such that the interval between opposing side parts of the optical film is 10 mm, is repeated 10,000 times.

Description

Optical film and image display device

[0001] The present invention relates to an optical film and an image display device.

[0002] Image display devices such as smartphones and tablet terminals have been known for some time, and currently, foldable image display devices are being developed. Smartphones, tablet terminals, and the like are typically covered with a cover glass. Glass, while generally highly hard, is not flexible. Therefore, if a cover glass is used for an image display device, there is a high risk of the device breaking when the device is folded. For this reason, the use of a foldable optical film, which includes a polyester film as a bendable substrate and a hard coat layer, instead of a cover glass, for a foldable image display device has been considered (see, for example, Patent Document 1).

[0003] In such foldable optical films, the resin constituting the polyester film as a substrate, which is generally bendable, has a high refractive index, which results in a large difference in refractive index between the polyester film as a substrate and the hard coat layer, which can cause interference fringes, iridescent irregularities.

[0004] One method for suppressing the occurrence of interference fringes is to increase the thickness of the hard coat layer, but increasing the thickness of the hard coat layer causes the problem of the hard coat layer cracking when folded, and therefore, at present, no optical film has been obtained that is foldable and less likely to cause interference fringes.

[0005] Japanese Patent Application Laid-Open No. 2016-125063

[0006] The present invention has been made in view of the problems of the conventional technology. That is, an object of the present invention is to provide a foldable optical film that is less likely to produce interference fringes, and an image display device including the same.

[0007] The present inventors have conducted extensive research to achieve the above object and have arrived at the present invention. That is, the present invention has the following configuration.

[0008] [1] A foldable optical film for use in an image display device, comprising: a polyester film as a substrate; a functional layer provided on a first surface of the substrate; a resin layer A provided between the substrate and the functional layer; and a resin layer B provided on a second surface of the substrate opposite the first surface, wherein the resin layer A has a film thickness of 10 nm to 500 nm, and the resin layer B has a film thickness of 1 nm to 200 nm, and the optical film does not crack or break when subjected to a test of folding the optical film 180° with the functional layer facing inward and the distance between opposing sides of the optical film being 10 mm, repeated 10,000 times. [2] The optical film according to [1], wherein the refractive index of the resin layer A is lower than the refractive index of the substrate and higher than the refractive index of the functional layer. [3] The optical film according to [1] or [2], wherein a resin layer C is provided between the substrate and the resin layer A. [4] The optical film according to [3], wherein the resin layer C has a thickness of 30 nm or more and 200 nm or less. [5] The optical film according to any one of [1] to [4], further comprising an adhesive layer on a second surface side of the polyester film as the substrate opposite to the first surface side, wherein the adhesive layer has a thickness of 25 μm or more and 300 μm or less, the shear storage modulus G' of the optical film at 25°C in a frequency range of 500 Hz to 1000 Hz is more than 200 MPa and 1200 MPa or less, and the shear loss modulus G'' of the optical film at 25°C in a frequency range of 500 Hz to 1000 Hz is 3 MPa or more and 150 MPa or less. [6] The optical film according to any one of [1] to [5], wherein the resin layer B is provided between the substrate and the adhesive layer. [7] The optical film according to any one of [1] to [6], wherein the yellow index of the optical film is 15 or less. [8] The optical film according to any one of [1] to [7], wherein the optical film does not crack or break when a test in which the optical film is folded 180° so that the functional layer is on the outside and the distance between opposing sides of the optical film is 30 mm is repeated 10,000 times.[9] The optical film according to any one of [1] to [8], wherein the resin layer A is a cured product layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (A-1), a polyester resin (A-2), a blocked isocyanate crosslinking agent (A-3), and particles (A-4), wherein the polyester resin (A-2) has a condensed polycyclic aromatic structure.

[10] The optical film according to any one of [1] to [9], wherein the resin layer B is a cured product layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (B-1), a polyester resin (B-2), a blocked isocyanate crosslinking agent (B-3), and particles (B-4), wherein the polyester resin (B-2) has a condensed polycyclic aromatic structure.

[11] The optical film according to any one of [3] to

[10] , wherein the resin layer C is a cured layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (C-1), a polyester resin (C-2), a blocked isocyanate crosslinking agent (C-3), and particles (C-4), and the polyester resin (C-2) has a condensed polycyclic aromatic structure.

[12] The optical film according to [9],

[10] , or

[11] , wherein at least one of the polyester resins (A-2), (B-2), and (C-2) having a condensed polycyclic aromatic structure contained in the resin layer A, the resin layer B, and the resin layer C has a naphthalene skeleton in its molecule.

[13] The method for producing the optical film according to any one of [1] to

[12] , comprising producing a functional layer on the first surface side of the polyester film as the substrate by a coating step.

[14] A foldable image display device comprising a display element and the optical film according to any one of [1] to

[12] , which is disposed closer to a viewer than the display element.

[15] The image display device according to

[14] , wherein the display element is an organic light-emitting diode element.

[0009] According to one aspect of the present invention, there is provided a foldable optical film that is less likely to produce interference fringes, and according to another aspect of the present invention, there is provided an image display device that includes such an optical film.

[0010] Fig. 1 is a schematic diagram of an optical film according to one embodiment. Fig. 2 is a schematic diagram showing a state of a folding test. Fig. 3 is a schematic diagram showing a state of an optical film after a folding test in another form. Fig. 4 is a schematic diagram of an optical film according to one embodiment. Fig. 5 is a schematic diagram of an optical film according to one embodiment.

[0011] The optical film and image display device of the present invention will be described below with reference to the drawings. In this specification, terms such as "film" and "sheet" are not distinguished from each other solely based on the difference in name. Therefore, for example, "film" is used to include a member also called a sheet. FIG. 1 is a schematic diagram of an optical film according to one embodiment, FIGS. 2(A) and 2(B) are schematic views showing a folding test, and FIG. 3 is a schematic view showing the state of the optical film after the folding test.

[0012] (Optical Film) The optical film 10 shown in FIG. 1 is used in an image display device and is foldable.

[0013] The optical film 10 includes a polyester film 11 as a substrate, a functional layer 12 provided on a first surface 11A (one side) of the polyester film 11 as a substrate, a resin layer A 13 provided between the polyester film 11 as a substrate and the functional layer 12, and a resin layer B 15 provided on a second surface 11B of the substrate opposite the first surface 11A. In another embodiment, a resin layer C 14 may be further provided between the polyester film 11 as a substrate and the resin layer A (see, for example, FIG. 4). The optical film 10 may further include an adhesive layer 41 on the second surface 11B of the polyester film 11 as a substrate, as in the optical film (FIG. 4) described below. In this specification, a "functional layer" refers to a layer intended to perform some function in the optical film. Specific examples of functional layers include a hard coat layer, an antistatic layer, and an antifouling layer. Preferably, the functional layer 12 functions as a hard coat layer. Furthermore, although the functional layer 12 has a single-layer structure, the functional layer may have not only a single-layer structure but also a multi-layer structure of two or more layers (e.g., a two-layer structure, a three-layer structure, a four-layer structure, etc.). Furthermore, each resin layer in this specification may have a single-layer structure or a multi-layer structure of two or more layers (e.g., a two-layer structure, a three-layer structure, a four-layer structure, etc.). A single-layer structure is preferred. For example, the resin layer may be formed through a coating process divided into multiple stages, or may have a multi-layer structure so that particles are present near the surface of each resin layer. In one embodiment, another resin layer or the like may be further provided between the resin layer A13 and the functional layer 12.

[0014] The optical film 10 is foldable. Specifically, when a test in which the optical film 10 is folded 180° with the functional layer 12 facing inward and the distance between opposing sides of the optical film 10 being 10 mm is repeated 10,000 times, no cracks or breaks occur. It is preferable that the optical film 10 does not crack or break even when the above folding test is repeated 20,000 times, and it is even more preferable that the optical film 10 does not crack or break even when the folding test is repeated 100,000 times. If cracks or the like occur in the optical film 10 when the optical film 10 is repeatedly folded 10,000 times, the foldability of the optical film 10 is insufficient.

[0015] On the other hand, even when a test (also referred to as a continuous folding test) in which the optical film 10 is continuously folded so that the functional layer 12 faces outward and the distance between opposing sides of the optical film 10 is 30 mm is repeatedly performed 10,000 times, preferably no cracks or breaks occur in the optical film 10, more preferably no cracks or breaks occur in the optical film 10 even when the continuous folding test is repeatedly performed 20,000 times, and even more preferably no cracks or breaks occur in the optical film 10 even when the continuous folding test is repeatedly performed 100,000 times. Here, when the optical film 10 is bent so that the functional layer 12 faces outward, a stress that stretches the functional layer 12 in the longitudinal direction is applied to the optical film 10 compared to a folding test performed so that the functional layer faces inward, and therefore it is desirable to perform a test in which the optical film 10 is continuously folded so that the distance between opposing sides of the optical film 10 is 30 mm. This is because it is known that the functional layer is weaker against tensile stress applied by tension than against contraction stress applied by compression. For example, bending the functional layer so that it faces outward increases the tensile stress applied to the functional layer, so measurement conditions are applied in which the folding interval is changed. Therefore, the evaluation method may be different when bending the functional layer 12 so that it faces inward and when bending the functional layer 12 so that it faces outward. In the present invention, by having at least one layer of resin layer A to resin layer C have the composition described in this specification, good results can be obtained even in evaluations where the functional layer 12 is bent so that it faces outward.

[0016] A continuous folding test in which the optical film 10 is continuously folded so that the functional layer 12 faces inward is performed as follows. As shown in FIG. 2(A), in the continuous folding test, the optical film 10 is first fixed to parallel-arranged fixing portions 20 so that the sides of the optical film 10 face each other. While the optical film 10 may have any shape, it is preferable that the optical film 10 used in the continuous folding test be rectangular (e.g., a 30 mm × 100 mm rectangle). For example, as shown in FIG. 2(A), one fixing portion 20 may be fixed to a table or the like, and the other fixing portion may be configured to slide up and down.

[0017] 2(B), the fixing units 20 are moved closer to each other, thereby deforming the optical film 10 so that the functional layer 12 faces inward and folding the optical film 10. The fixing units 20 are then moved to a position where the distance between the two opposing sides of the optical film 10 fixed by the fixing units 20 is 10 mm, and then the fixing units 20 are moved in the opposite direction to eliminate the deformation of the optical film 10. After these steps, a test is performed in which the optical film is folded 180° so that the functional layer faces inward and the distance between the opposing sides of the optical film is 10 mm, with the test being repeated 10,000 times. The optical film of the present invention does not crack or break when the folding test is repeated 10,000 times.

[0018] In the present invention, the absence of cracks or breaks in the optical film is evaluated by checking whether there is a gap between the substrate and the functional layer, and whether there is a crack or break at the bent portion. The crack or break can be evaluated visually.

[0019] As shown in FIG. 2A , the optical film 10 can be folded 180° by moving the fixing portion 20. Furthermore, by performing a continuous folding test so that the bent portion of the optical film 10 does not protrude from the end of the fixing portion 20 and controlling the distance between the fixing portions 20 to 10 mm when they are closest to each other, the distance between the two opposing sides of the optical film 10 can be set to 10 mm. In this case, the outer diameter of the bent portion is replaced with 10 mm. Because the thickness of the optical film 10 is sufficiently small compared to the distance between the fixing portions 20 (10 mm), it is believed that the results of the continuous folding test of the optical film 10 are not affected by differences in the thickness of the optical film 10. In the present invention, the optical film 10 does not crack or break when a continuous folding test is repeatedly performed 10,000 times in which the optical film 10 is folded 180° with the functional layer 12 facing inward so that the distance between opposing sides of the optical film 10 is 10 mm, and the optical film 10 does not crack or break when a continuous folding test is repeatedly performed 10,000 times in which the optical film 10 is folded 180° with the functional layer 12 facing inward so that the distance between opposing sides of the optical film 10 is 2 mm. Preferably, at least one of the layers A to C has a composition described in this specification, which enables the optical film 10 to show good results in these continuous tests.

[0020] In another evaluation of folding, the optical film 10 is fixed to the fixing part 20 so that the distance between one end of the optical film 10 and the other opposite end is 10 mm, and the optical film 10 is held in a folded state at 70°C for 12 hours (a folding holding test is performed). After the folding holding test, the optical film 10 is unfolded, and after 30 minutes at room temperature, the opening angle θ of the optical film 10 is measured, as shown in FIG. 3 . In this evaluation test, the opening angle θ of the optical film 10 is preferably 100° or greater. Note that a larger opening angle θ indicates better restorability, and the maximum opening angle θ is 180°. The folding holding test may be performed by folding the optical film 10 so that the functional layer 12 faces inward, or may be performed so that the functional layer 12 faces outward. In either case, the opening angle θ is preferably 100° or greater.

[0021] The surface of the optical film 10 (the surface of the functional layer 12) preferably has a hardness (pencil hardness) of 3H or more, more preferably 4H or more, when measured by the pencil hardness test specified in JIS K5600-5-4:1999. The pencil hardness test is performed by fixing a 30 mm x 100 mm piece of the optical film 10 cut out onto a glass plate with Cellotape (registered trademark) manufactured by Nichiban Co., Ltd. so as to prevent folds or wrinkles, and using a pencil hardness tester (product name "Pencil Scratch Coating Hardness Tester (electric type)" manufactured by Toyo Seiki Seisaku-sho, Ltd.) to the surface of the optical film, moving a pencil (product name "Uni" manufactured by Mitsubishi Pencil Co., Ltd.) at a moving speed of 1 mm / sec while applying a load of 750 g to the pencil. The pencil hardness is defined as the highest hardness that does not scratch the surface of the optical film in the pencil hardness test. When measuring the pencil hardness, multiple pencils with different hardnesses are used, and the pencil hardness test is performed five times for each pencil. If the surface of the optical film is not scratched four or more times out of the five times, it is determined that the pencil of that hardness did not scratch the surface of the optical film. The scratches refer to those visible when the surface of the optical film that has been subjected to the pencil hardness test is observed through transmission under fluorescent light.

[0022] The optical film 10 preferably has a yellow index (YI) of 15 or less. When the YI of the optical film 10 is 15 or less, the yellowness of the optical film can be suppressed, making it suitable for applications requiring transparency. The upper limit of the yellow index (YI) of the optical film 10 is more preferably 10 or less. The yellow index (YI) is a value calculated from the transmittance of the optical film at wavelengths of 300 nm to 780 nm measured in a spectrophotometer (product name "UV-2450", manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp) cut into a size of 50 mm x 50 mm, placed with the back side facing the light source, according to the calculation formula described in JIS Z8722:2009, and then from the tristimulus values ​​X, Y, and Z according to the calculation formula described in ASTM D1925:1962. The upper limit of the yellow index (YI) of the optical film 10 is more preferably 10 or less. The yellow index (YI) is the arithmetic mean value of the three measurements taken three times for each optical film. With 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" box in the calculation items. The transmittance at wavelengths of 300 nm to 780 nm is measured under the following conditions by measuring the transmittance at at least five points within 1 nm before and after each wavelength of 300 nm to 780 nm and calculating the average value. If the spectral transmittance spectrum exhibits undulations, smoothing may be performed with a delta of 5.0 nm.

[0023] (Measurement conditions) Wavelength range: 300 nm to 780 nm Scan speed: High speed Slit width: 2.0 Sampling interval: Auto (0.5 nm intervals) Illumination: C Light source: D2 and WI Field of view: 2° Light source switching wavelength: 360 nm S / R switching: Standard Detector: PM Auto zero: Performed at 550 nm after baseline scan

[0024] 1 , a blue dye, which is the complementary color of yellow, may be contained in at least one of the polyester film 11 serving as the substrate, the functional layer 12, the resin layer A 13, and the resin layer B 15. In another embodiment, when the resin layer C is provided, the resin layer C may contain a blue dye, which is the complementary color of yellow.

[0025] The blue pigment may be either a pigment or a dye. However, for example, when the optical film 10 is used in an organic light-emitting diode display device, a pigment that combines light resistance and heat resistance is preferred. Polycyclic organic pigments and metal complex organic pigments, etc., are preferred as blue pigments for applications requiring light resistance, as they are less susceptible to molecular cleavage by ultraviolet rays and have significantly better light resistance than molecularly dispersed dyes. More specifically, phthalocyanine organic pigments are preferred. However, since pigments are dispersed in a solvent, transparency is hindered by particle scattering. Therefore, it is preferable to set the particle size of the pigment dispersion within the Rayleigh scattering region. On the other hand, when the transparency of the optical film is important, it is preferable to use a dye that molecularly disperses in a solvent as the blue pigment. Alternatively, an inorganic pigment such as cobalt blue may be used as the blue pigment.

[0026] The optical film 10 is irradiated with light having a continuous spectrum in the wavelength range of 300 nm to 780 nm from the resin layer B15 side at an incident angle of 0°, and the L * a * b * Color coordinate a of the color system * , b * When we search for a * is -3.0 or more and 2.0 or less, and b * is preferably -2.0 or more and 8.0 or less. * and b * When each of these is within the above range, the yellow index can be set to 15 or less. * and b *The measurement of can be carried out using a spectrophotometer (product name "UV-2450", manufactured by Shimadzu Corporation). Examples of the light source include a tungsten halogen (WI) lamp alone, or a combination of a deuterium (D2) lamp and a tungsten halogen (WI) lamp. In this specification, "light at an incident angle of 0°" means light in the normal direction when the normal direction to the first surface of the optical film is set to 0°. * a * b * "Color system", "a * " and "b * " conforms to JIS Z8729:2004.

[0027] The optical film 10 preferably has a spectral transmittance of 8% or less at a wavelength of 380 nm. If the spectral transmittance of the optical film exceeds 8%, when the optical film is used in a mobile terminal, the polarizer may be exposed to ultraviolet light and easily deteriorate. The transmittance can be measured using a spectrophotometer (product name "UV-2450" manufactured by Shimadzu Corporation). The measurement conditions for the spectral transmittance are the same as those for the spectral transmittance at wavelengths of 300 nm to 780 nm. The transmittance is measured three times on an optical film cut into a size of 50 mm x 100 mm, and the arithmetic mean value of the three measurements is used. The upper limit of the transmittance of the optical film 10 is more preferably 5%. The transmittance of the optical film 10 can be achieved by, for example, adjusting the amount of ultraviolet absorber added, as described below.

[0028] The total light transmittance of the optical film 10 is preferably 85% or more. If the total light transmittance of the optical film 10 is 85% or more, sufficient image visibility can be obtained when the optical film 10 is used in a mobile terminal. The total light transmittance of the optical film 10 is more preferably 87% or more, and most preferably 90% or more.

[0029] The total light transmittance can be measured using a haze meter (product name "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.) according to a method in accordance with JIS K7361-1:1997. The optical film is cut into pieces measuring 50 mm x 100 mm, and then placed in a state free of curls, wrinkles, fingerprints, dust, etc., and measured three times per optical film. The total light transmittance is the arithmetic mean value of the three measurements. In this specification, "measured three times" does not mean measuring the same location three times, but rather measuring three different locations. In the optical film 10, the surface 10A when visually observed is flat, and the layers laminated thereon, such as the functional layer 12, are also flat, and the film thickness variation is within a range of ±10%. Therefore, it is believed that measuring the total light transmittance at three different locations on the cut optical film will roughly provide an average value for the total light transmittance throughout the entire in-plane of the optical film. The variation in total light transmittance is within ±10%, even when the measurement target is as long as 1 m x 3000 m, or as small as a 5-inch smartphone. If the optical film cannot be cut to the above size, for example, the entrance opening for measurement of the HM-150 is 20 mmφ, so a sample size with a diameter of 21 mm or more is required. Therefore, the optical film may be appropriately cut to a size of 22 mm x 22 mm or more. If the optical film is small, measurement points are set at three locations by gradually shifting the light source spot or changing the angle within a range that does not miss the light source spot.

[0030] The haze value (total haze value) of the optical film 10 is preferably 2.5% or less. If the haze value of the optical film is 2.5% or less, whitening of the image display surface can be suppressed when the optical film is used in a mobile terminal. The haze value is more preferably 1.5% or less, and even more preferably 1.0% or less.

[0031] The haze value can be measured using a haze meter (product name "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.) according to a method in accordance with JIS K7136:2000. The optical film is cut into pieces measuring 50 mm x 100 mm, and then placed in a state free of curls, wrinkles, fingerprints, dust, etc., and the haze value is measured three times per optical film. The arithmetic mean value of the three measurements is taken as the haze value. In the optical film 10, the visually observed surface 10A is flat, and the layers laminated thereon, such as the functional layer 12, are also flat, and the film thickness variation is within a range of ±10%. Therefore, it is believed that measuring the haze value at three different locations on the cut optical film will provide an approximate average value of the haze value throughout the entire in-plane of the optical film. The variation in haze value is within ±10%, even when the measurement target is as long as 1 m x 3000 m or as small as a 5-inch smartphone. If the optical film cannot be cut to the above size, for example, the HM-150 has an entrance opening of 20 mmφ for measurement, so a sample size of 21 mm or more is required. Therefore, the optical film may be cut to a size of 22 mm x 22 mm or more as appropriate. If the optical film is small, the measurement points are set to three by shifting the light source spot slightly or by changing the angle within the range where the light source spot does not shift.

[0032] If another film, such as a polarizing plate, is provided on the first surface of the optical film 10 via a pressure-sensitive adhesive layer or adhesive layer, the other film is peeled off together with the pressure-sensitive adhesive layer before performing the folding test, folding retention test, yellow index measurement, total light transmittance measurement, and haze measurement. The peeling of the other film can be performed, for example, as follows: First, a laminate in which the other film is attached to the optical film via a pressure-sensitive adhesive layer or adhesive layer is heated with a dryer, and the edge of a cutter is inserted into the area believed to be the interface between the optical film and the other film, and the film is slowly peeled off. By repeating this heating and peeling process, the pressure-sensitive adhesive layer, adhesive layer, and other film can be peeled off. Note that even if such a peeling step is performed, it does not significantly affect these tests or measurements. The haze measurement is performed after the pressure-sensitive adhesive layer or adhesive layer has been peeled off and any dirt on the pressure-sensitive adhesive layer or adhesive layer has been thoroughly wiped off with alcohol.

[0033] In recent years, light-emitting diodes (LEDs) have been widely adopted as light sources for backlights in image display devices such as personal computers and tablet terminals. However, these LEDs emit a strong light called blue light. This blue light has wavelengths of 380 nm to 495 nm and has properties similar to ultraviolet light. Because it has strong energy, it is believed that if it reaches the retina without being absorbed by the cornea or lens, it can cause retinal damage, eye fatigue, and adverse effects on sleep. For this reason, when applied to an image display device, an optical film preferably has excellent blue light blocking properties without affecting the color of the display screen. Therefore, from the perspective of blocking blue light, the optical film 10 preferably has a spectral transmittance of less than 1% at a wavelength of 380 nm, a spectral transmittance of less than 10% at a wavelength of 410 nm, and a spectral transmittance of 70% or more at a wavelength of 440 nm. If the spectral transmittance at a wavelength of 380 nm is 1% or more, or if the spectral transmittance at a wavelength of 410 nm is 10% or more, problems caused by blue light may not be resolved, and if the spectral transmittance at a wavelength of 440 nm is less than 70%, the color of the display screen of an image display device using the optical film may be affected. The optical film 10 sufficiently absorbs light in the wavelength range of 410 nm or less among blue light wavelengths, while sufficiently transmitting light with a wavelength of 440 nm or more, thereby achieving excellent blue light blocking properties without affecting the color of the display screen. Furthermore, when such optical film 10 having excellent blue light blocking properties is applied to an organic light-emitting diode (OLED) display device as an image display device, it is also effective in suppressing deterioration of the organic light-emitting diode elements.

[0034] The optical film 10 preferably has a light transmittance of almost 0% up to a wavelength of 380 nm, gradually increasing from a wavelength of 410 nm, and rapidly increasing near a wavelength of 440 nm. Specifically, for example, the spectral transmittance preferably varies along a sigmoid curve between wavelengths of 410 nm and 440 nm. The spectral transmittance at a wavelength of 380 nm is more preferably less than 0.5%, even more preferably less than 0.2%; the spectral transmittance at a wavelength of 410 nm is more preferably less than 7%, even more preferably less than 5%; and the spectral transmittance at a wavelength of 440 nm is more preferably 75% or more, even more preferably 80% or more. The optical film 10 preferably has a spectral transmittance at a wavelength of 420 nm of less than 50%. By satisfying these spectral transmittance relationships, the optical film 10 exhibits a rapidly increasing transmittance near a wavelength of 440 nm, thereby achieving excellent blue light blocking properties without affecting the color of the display screen.

[0035] The optical film 10 more preferably has a spectral transmittance of less than 0.1% at a wavelength of 380 nm, a spectral transmittance of less than 7% at a wavelength of 410 nm, and a spectral transmittance of 80% or more at a wavelength of 440 nm.

[0036] The optical film 10 preferably has a transmission spectrum slope of greater than 2.0 in the wavelength range of 415 to 435 nm, obtained using the least squares method. If the slope is less than 2.0, blue light wavelengths, such as those in the 415 to 435 nm wavelength range, may not be sufficiently blocked, resulting in a weak blue light blocking effect. It is also possible that the blue light wavelength range (415 to 435 nm) is blocked too much, which could result in interference with the backlight or emission wavelength range of the image display device (e.g., OLED emission at a wavelength of 430 nm), potentially resulting in poor color reproduction. The slope can be calculated, for example, by measuring transmittance data for at least five points between 415 and 435 nm, within a 1 nm range, using a spectrophotometer (product name "UV-2450" manufactured by Shimadzu Corporation) capable of measuring in 0.5 nm increments.

[0037] The optical film 10 preferably has a blue light blocking rate of 40% or more. If the blue light blocking rate is less than 40%, the problems caused by blue light described above may not be sufficiently resolved. The blue light blocking rate is, for example, a value calculated according to JIS T7333:2005. Note that such a blue light blocking rate can be achieved, for example, by including a sesamol-type benzotriazole-based monomer described below in the functional layer 12.

[0038] The use of the optical film 10 is not particularly limited, and examples of uses of the optical film 10 include image display devices such as smartphones, tablet terminals, personal computers (PCs), wearable terminals, digital signage, televisions, and car navigation systems. The optical film 10 is also suitable for in-vehicle use. The form of each of the above image display devices is also preferred for uses requiring flexibility, such as foldability and rollability.

[0039] The optical film 10 may be cut to a desired size or may be in a roll form. When the optical film 10 is cut to a desired size, the size of the optical film is not particularly limited and is appropriately determined depending on the size of the display surface of the image display device. Specifically, the size of the optical film 10 may be, for example, 2.8 inches or more and 500 inches or less. In this specification, "inches" refers to the length of the diagonal when the optical film is rectangular, the diameter when the optical film is circular, and the average value of the sum of the minor axis and the major axis when the optical film is elliptical. Here, when the optical film is rectangular, the aspect ratio of the optical film used to calculate the above-mentioned inches is not particularly limited as long as it does not cause any problems as a display screen for an image display device. Examples include length:width = 1:1, 4:3, 16:10, 16:9, and 2:1. However, such aspect ratios are not limited, particularly for in-vehicle applications and digital signage, which require sophisticated design. Furthermore, if the optical film 10 is large, it is cut out from an arbitrary position to an A5 size (148 mm×210 mm) and then cut out to the size of each measurement item.

[0040] The optical film 10 may be disposed inside the image display device, but is preferably disposed near the surface of the image display device. When used near the surface of the image display device, the optical film 10 functions as a cover film used in place of a cover glass.

[0041] (Polyester Film as Substrate) The polyester film 11 as the substrate has optical transparency. In this specification, "optical transparency" means the property of transmitting light, and includes, for example, a total light transmittance of 50% or more, preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. Optical transparency does not necessarily mean transparency, and may also be translucent.

[0042] The polyester film 11 serving as the substrate is a substrate made of a polyester-based resin (for example, a polyethylene terephthalate resin or a polyethylene naphthalate resin).

[0043] The polyester film is not only resistant to cracking or breaking in a continuous folding test, but also has excellent hardness and transparency, and is excellent in adhesion to the resin layer of the present invention.

[0044] The polyester resin material is not particularly limited, but a copolymer formed by polycondensation of a dicarboxylic acid component and a diol component, or a blend resin thereof can be used. Examples of dicarboxylic acid components constituting the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

[0045] Examples of diol components constituting the polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.

[0046] The dicarboxylic acid component and the diol component may each be used alone or in combination of two or more kinds. In addition, other polycarboxylic acid components such as trimellitic acid and other polyol components such as trimethylolpropane may also be added as appropriate.

[0047] Specific examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Among these, polyethylene terephthalate is preferred in terms of the balance between physical properties and cost. In addition, it is also a preferred embodiment to contain other copolymerization components or other polymers in order to control optical properties such as polarization. From the viewpoint of controlling the optical properties of the polyester film, preferred copolymerization components include diethylene glycol and copolymerization components having norbornene in the side chain.

[0048] The intrinsic viscosity of the polyester resin (solvent: phenol / tetrachloroethane=60:40) is, for example, 0.50 to 1.0 dl / g.

[0049] The polyester film is a film mainly composed of the polyester resin. Here, "a film mainly composed of a polyester resin" means a film formed from a resin composition containing 50% by mass or more of polyester resin. When blended with other polymers (e.g., polycarbonate resin, polyimide resin, etc.), this means that the polyester resin is contained in an amount of 50% by mass or more, and when copolymerized with other monomers, this means that the polyester structural unit is contained in an amount of 50 mol% or more. Preferably, the polyester film contains 90% by mass or more of polyester resin, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0050] In order to improve the handling properties of polyester films, such as slipperiness and windability, inert particles can be incorporated into the film. Examples of inert particles include inorganic particles such as silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, titanium dioxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, magnesium carbonate, and magnesium hydroxide. The average particle diameter of the inert particles is, for example, 200 to 5000 nm, and preferably 250 to 4500 nm. This average particle diameter is measured using the method described in the Examples (number-based average particle diameter using SEM). To maintain high transparency, it is preferable to minimize the content of inert particles in the film. Therefore, it is preferable to use a multilayer structure in which particles are incorporated only in the surface layer of the film, or to incorporate fine particles only in the resin layer laminated on at least one side of the polyester film, with substantially no particles incorporated in the film.

[0051] The phrase "substantially free of particles" means, for example, in the case of inorganic particles, that the content of elements derived from the particles is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit when quantitatively analyzed by fluorescent X-ray analysis. This is because even if particles are not intentionally added to the substrate film, contaminants derived from foreign matter or dirt adhering to the raw material resin or the production line or equipment in the film manufacturing process may peel off and be inevitably mixed into the film.

[0052] Furthermore, when the polyester film has a multi-layer structure, it may have a two-kind three-layer structure in which the inner layer does not substantially contain inert particles and only the outermost layer (second layer) contains inert particles, which is preferable because it can achieve both transparency and processability.

[0053] The polyester film serving as the substrate may be a single layer or a laminate of two or more layers. Furthermore, various additives may be incorporated into the film as needed, as long as the effects of the present invention are achieved. Examples of additives include antioxidants, light-resistant agents, antigelling agents, organic wetting agents, antistatic agents, UV absorbers, surfactants, and the like. When the film has a laminated structure, it is also preferable to incorporate additives into each layer as needed, depending on the function of each layer. For example, adding a UV absorber or the like to an inner layer is a preferred embodiment to prevent photodegradation of the polarizer.

[0054] The polyester film can be produced by a conventional method. For example, it can be obtained by melt-extruding a material containing the above-mentioned polyester resin into a film shape, and then cooling and solidifying it on a casting drum to form a film. As the polyester film in the present invention, either a non-stretched film or a stretched film can be used, but a stretched film is preferred from the viewpoint of durability such as mechanical strength and chemical resistance.

[0055] When the polyester film is a stretched film, the stretching method is not particularly limited, and may be a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, a longitudinal and transverse simultaneous biaxial stretching method, or the like. When stretching a polyester film, the stretching may be carried out before laminating an easy-adhesion resin layer described later, or may be carried out after laminating an easy-adhesion resin layer. It is also possible to uniaxially stretch the polyester film in the longitudinal or transverse direction before laminating an easy-adhesion resin layer, and then stretch the polyester film in the other direction after laminating the resin layer.

[0056] For example, a polyimide film, polyamide film, polyamideimide film, polycarbonate film, acrylic film, triacetyl cellulose film, cycloolefin polymer film, polyphenylene sulfide film, polymethylpentene film, or the like may be laminated on at least one surface of a polyester film as a substrate.

[0057] The refractive index of the polyester film 11 as the substrate is desirably higher than the refractive index of the functional layer 12. The refractive index of the polyester film 11 as the substrate can be measured, for example, by the Becke method. When measuring the refractive index of the polyester film 11 as the substrate using the Becke method, ten pieces of the polyester film 11 as the substrate are cut out, and the refractive index of each of the ten cut pieces is measured by the Becke method using a refractive index standard solution. The average value of the ten measured refractive indices of the pieces is taken as the refractive index of the polyester film 11 as the substrate. The refractive index of the polyester film 11 as the substrate may be 1.500 or more and 1.800 or less. Alternatively, the refractive index of the polyester film 11 as the substrate may be calculated by measuring the average reflectance at wavelengths of 380 to 780 nm using a spectrophotometer (product name "UV-2450" manufactured by Shimadzu Corporation) and using the obtained average reflectance, according to the following formula (1): The average reflectance (R) of the polyester film 11 as the substrate is measured after attaching a black vinyl tape (for example, product name "Yamato Vinyl Tape No. 200-38-21" manufactured by Yamato Co., Ltd., 38 mm width) having a width larger than the measurement spot area to the back surface of the polyester film 11 as the substrate in order to prevent back surface reflection.

[0058] R1 = (1 - n1) 2 / (1+n1) 2 ...(1)

[0059] In the above formula (1), R1 represents the average reflectance (%) of the polyester film as the substrate in the wavelength range of 380 to 780 nm, and n1 represents the refractive index of the polyester film as the substrate.

[0060] The thickness of the polyester film 11 as the substrate is preferably 10 μm or more and 100 μm or less. When the thickness of the polyester film as the substrate is 10 μm or more, curling of the optical film can be suppressed, sufficient hardness can be obtained, and even when the optical film is produced by roll-to-roll, wrinkles are less likely to occur, and there is no risk of deterioration in appearance. On the other hand, when the thickness of the polyester film as the substrate is 100 μm or less, the folding performance of the optical film is good, the requirements of the continuous folding test can be satisfied, and it is also preferable in terms of reducing the weight of the optical film. The thickness of the polyester film 11 as the substrate is determined by photographing a cross section of the polyester film 11 as the substrate using a scanning electron microscope (SEM), measuring the film thickness of the polyester film 11 as the substrate at 10 points on the image of the cross section, and calculating the arithmetic average of the film thicknesses at the 10 points. It is more preferable that the lower limit of the polyester film 11 as the substrate is 25 μm or more, and it is more preferable that the upper limit of the polyester film 11 as the substrate is 80 μm or less.

[0061] (Functional Layer) The optical film of the present invention has a functional layer 12 provided on the first surface 11A side of the substrate 11. The functional layer 12 is, for example, a layer that functions as a hard coat layer. The functional layer 12 may have a function other than hard coat properties in addition to hard coat properties. In this specification, the term "hard coat layer" refers to a layer having a Martens hardness of 375 MPa or more at the center of the cross section of the hard coat layer. In this specification, the term "Martens hardness" refers to the hardness measured by the nanoindentation method when an indenter is pressed 500 nm deep. The Martens hardness measurement by the nanoindentation method is performed on a measurement sample using a "TI950 TriboIndenter" manufactured by HYSITRON. Specifically, first, a block is prepared by embedding an optical film cut into a size of 1 mm x 10 mm in an embedding resin, and then a uniform slice without holes or the like, with a thickness of 70 nm to 100 nm, is cut out from this block using a general slice preparation method. An "Ultramicrotome EM UC7" (Leica Microsystems) or the like can be used to prepare the slices. The remaining block from which the uniform slice without holes or the like has been cut out is used as the measurement sample. Next, in the cross section obtained by cutting out the slices of such a measurement sample, a Berkovich indenter (triangular pyramid) is pressed 500 nm into the center of the cross section of the functional layer under the following measurement conditions, and the indenter is held constant to allow the residual stress to relax. The load is then released, and the maximum load after relaxation is measured. The maximum load P max (μN) and the area A of the 500 nm deep depression (nm 2 ) and P max The Martens hardness is calculated from the following equation: / A The Martens hardness is the arithmetic mean value of the values ​​measured at 10 locations.

[0062] (Measurement conditions) ・Loading speed: 10 nm / sec ・Holding time: 5 seconds ・Unloading speed: 10 nm / sec ・Measurement temperature: 25°C

[0063] The functional layer 12 preferably has a Martens hardness of 500 MPa or more and 2000 MPa or less at the center of the cross section of the functional layer 12. If the Martens hardness of the functional layer 12 is 500 MPa or more, sufficient hardness as a hard coat layer can be obtained, and if it is 2000 MPa or less, good folding performance of the optical film can be obtained. The lower limit of the Martens hardness at the center of the cross section of the functional layer 12 is preferably 600 MPa or more, and the upper limit is preferably 1500 MPa or less.

[0064] The refractive index of the functional layer 12 may be 1.400 or more and 1.800 or less. The refractive index of the functional layer 12 can be determined by measuring the average reflectance at wavelengths of 380 to 780 nm using a spectrophotometer (product name "UV-2450", manufactured by Shimadzu Corporation), and using the obtained average reflectance, using the following formula (2). The average reflectance of the functional layer 12 is measured after applying a functional layer composition to a 50 μm thick polyethylene terephthalate (PET) substrate that has not been subjected to an easy-adhesion treatment, curing it to form a functional layer with a thickness of 1 to 10 μm, and then attaching black vinyl tape (for example, product name "Yamato Vinyl Tape NO200-38-21", manufactured by Yamato Co., Ltd., 38 mm wide) with a width larger than the measurement spot area to prevent backside reflection on the surface (backside) of the PET substrate opposite the surface on which the functional layer is located.

[0065] R2 = (1 - n2) 2 / (1+n2) 2 …(2)

[0066] In the above formula (2), R2 represents the average reflectance (%) of the functional layer in the wavelength range of 380 to 780 nm, and n2 represents the refractive index of the functional layer.

[0067] The thickness of the functional layer 12 is preferably 2 μm or more and 40 μm or less. If the thickness of the functional layer 12 is 2 μm or more, sufficient hardness as a hard coat layer can be obtained, and if it is 40 μm or less, deterioration of processability can be suppressed. In this specification, the "thickness of the functional layer" means the thickness (total thickness) of the functional layer when the functional layer has a multilayer structure. The upper limit of the thickness of the functional layer 12 is more preferably 30 μm or less, and even more preferably 20 μm or less. The thickness of the functional layer 12 can be 2 μm or more and 30 μm or less, or 2 μm or more and 20 μm or less.

[0068] The film thickness of the functional layer 12 is determined by photographing a cross section of the functional layer 12 using a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM), measuring the film thickness of the functional layer 12 at 20 locations on the cross section image, and calculating the arithmetic mean value of the film thicknesses at those 20 locations. A specific method for photographing the cross section is described below. First, a block is prepared by embedding an optical film cut into a size of 1 mm x 10 mm in an embedding resin. A uniform slice with a thickness of 70 nm to 100 nm and no holes is cut from this block using a general slice preparation method. An "Ultramicrotome EM UC7" (Leica Microsystems) or the like can be used to prepare the slice. This uniform slice without holes is then used as the measurement sample. A cross-sectional photograph of the measurement sample is then taken using a scanning transmission electron microscope (STEM) (product name "S-4800" manufactured by Hitachi High-Technologies Corporation). When taking a cross-sectional photograph using the S-4800, the detector is set to "TE," the acceleration voltage is set to "30 kV," and the emission current is set to "10 μA" to observe the cross section. The magnification is adjusted appropriately between 5,000x and 200,000x while adjusting the focus and observing whether the contrast and brightness of each layer can be distinguished. A preferred magnification is 10,000x to 100,000x, a more preferred magnification is 10,000x to 50,000x, and a most preferred magnification is 25,000x to 50,000x. When taking a cross-sectional photograph using the S-4800, the aperture may be set to "beam monitor aperture 3," the objective lens aperture to "3," and the WD to "8 mm." When measuring the film thickness of the hard coat layer, it is important that the interfacial contrast between the functional layer and other layers (e.g., a polyester film as a substrate) can be observed as clearly as possible during cross-sectional observation. If the interface is difficult to see due to insufficient contrast, dyeing with osmium tetroxide, ruthenium tetroxide, phosphotungstic acid, or the like can be performed to make the interface between the organic layers more visible. Furthermore, the contrast of the interface may be more difficult to see at higher magnifications. In such cases, observations at lower magnifications are also performed. For example, observations are performed at two magnifications, such as 25,000x and 50,000x, or 50,000x and 100,000x, and the arithmetic average value described above is calculated at both magnifications. This average value is then used as the film thickness value of the functional layer.

[0069] The functional layer 12 may be an antistatic hard coat layer, and may contain a binder resin and an antistatic agent present in the binder resin. In addition to the binder resin, the functional layer 12 may contain additives such as inorganic particles, organic particles, ultraviolet absorbers, adhesion improvers, leveling agents, thixotropy-imparting agents, coupling agents, plasticizers, antifoaming agents, bulking agents, colorants, and fillers, as needed, within the scope of the present invention.

[0070] (Binder Resin) The binder resin contains a polymer (cured product) of a polymerizable compound (curable compound). The polymerizable compound has at least one polymerizable functional group in the molecule. Examples of the polymerizable functional group include ethylenically unsaturated groups such as a (meth)acryloyl group, a vinyl group, and an allyl group. The term "(meth)acryloyl group" includes both an "acryloyl group" and a "methacryloyl group."

[0071] The polymerizable compound is preferably a polyfunctional (meth)acrylate. Examples of the polyfunctional (meth)acrylate include trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, isocyanuric acid tri(meth)acrylate, isocyanuric acid di(meth)acrylate, polyester tri(meth)acrylate, polyester di(meth)acrylate, bisphenol di(meth)acrylate, diglycerin tetra(meth)acrylate, adamantyl di(meth)acrylate, isoboronyl di(meth)acrylate, dicyclopentane di(meth)acrylate, tricyclodecane di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and those modified with PO, EO, caprolactone, etc.

[0072] Among these, tri- to hexa-functional compounds are preferred because they can suitably satisfy the above-mentioned Martens hardness, and examples thereof include 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. In this specification, "(meth)acrylate" means "acrylate" and "methacrylate".

[0073] The composition may further contain a monofunctional (meth)acrylate monomer in order to adjust the hardness or viscosity of the composition, improve adhesion, etc. Examples of the monofunctional (meth)acrylate monomer include hydroxyethyl acrylate (HEA), glycidyl methacrylate, methoxypolyethylene glycol (meth)acrylate, isostearyl (meth)acrylate, 2-acryloyloxyethyl succinate, acryloylmorpholine, N-acryloyloxyethyl hexahydrophthalimide, cyclohexyl acrylate, tetrahydrofuryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and adamantyl acrylate.

[0074] From the viewpoint of improving the hardness of the functional layer, the mass average molecular weight of the monomer is preferably less than 1,000, and more preferably from 200 to 800. The mass average molecular weight of the polymerizable oligomer is preferably from 1,000 to 20,000, more preferably from 1,000 to 10,000, and even more preferably from 2,000 to 7,000.

[0075] (Antistatic Agent) The antistatic agent used in the functional layer 12 is not particularly limited as long as it has good compatibility with the binder resin. Antistatic agents include ion-conductive antistatic agents and electron-conductive antistatic agents, and ion-conductive antistatic agents are preferred from the viewpoint of compatibility with the binder resin.

[0076] The functional layer 12 may further include an ultraviolet absorber, a spectral transmittance adjuster, and / or an antifouling agent.

[0077] (Ultraviolet absorber) Optical films are particularly suitable for use in mobile devices such as foldable smartphones and tablet devices. However, such mobile devices are often used outdoors, which poses a problem of the polarizer disposed on the display element side of the optical film being easily exposed to ultraviolet light and degraded. However, since the functional layer 12 is disposed on the viewer side of the polarizer, if the functional layer 12 contains an ultraviolet absorber, it is possible to effectively prevent the polarizer from degrading due to exposure to ultraviolet light. The ultraviolet absorber (UVA) may be contained in the polyester film 11 serving as the substrate, rather than in the functional layer 12.

[0078] Examples of the ultraviolet absorber include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers.

[0079] Examples of the triazine-based ultraviolet absorber include 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, and 2,4-bis[2-hydroxy-4-butoxyphenyl]-6 -(2,4-dibutoxyphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, and 2-[4-[(2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine. Commercially available triazine-based ultraviolet absorbers include TINUVIN 460 and TINUVIN 477 (both manufactured by BASF), and LA-46 (manufactured by ADEKA).

[0080] Examples of the benzophenone-based ultraviolet absorbers include 2-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, hydroxymethoxybenzophenone sulfonic acid and its trihydrate, sodium hydroxymethoxybenzophenone sulfonate, etc. Examples of commercially available benzophenone-based ultraviolet absorbers include CHMASSORB81 / FL (manufactured by BASF).

[0081] Examples of the benzotriazole-based ultraviolet absorbers include 2-ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate, 2-(2H-benzotriazol-2-yl)-6-(linear and branched chain dodecyl)-4-methylphenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5',5'-di-tert-butyl ... 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-(3'',4'',5'',6''-tetrahydrophthalimidomethyl)-5'-methylphenyl)benzotriazole, 2,2-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol), and 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole. Examples of commercially available benzotriazole-based ultraviolet absorbers include KEMISORB71D and KEMISORB79 (both manufactured by Chemipro Chemical Co., Ltd.), JF-80 and JAST-500 (both manufactured by Johoku Chemical Co., Ltd.), ULS-1933D (manufactured by Ippo), and RUVA-93 (manufactured by Otsuka Chemical Co., Ltd.).

[0082] Among the ultraviolet absorbers, triazine-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are preferably used. The ultraviolet absorber preferably has high solubility in the resin components constituting the functional layer, and preferably exhibits little bleed-out after the above-mentioned continuous folding test. The ultraviolet absorber is preferably polymerized or oligomerized. The ultraviolet absorber is preferably a polymer or oligomer having a benzotriazole, triazine, or benzophenone skeleton, and more preferably a thermal copolymerization of a (meth)acrylate having a benzotriazole or benzophenone skeleton with methyl methacrylate (MMA) in any ratio. When the optical film is applied to an organic light-emitting diode (OLED) display device, the ultraviolet absorber can also protect the OLED from ultraviolet rays.

[0083] The content of the ultraviolet absorber is not particularly limited, but is preferably 1 part by mass or more and 6 parts by mass or less per 100 parts by mass of the solid content of the functional layer composition. If it is 1 part by mass or more, the effect of including the ultraviolet absorber in the functional layer can be fully obtained, and if it is 6 parts by mass or less, the functional layer will not suffer from significant coloration or a decrease in strength. The lower limit of the content of the ultraviolet absorber is more preferably 2 parts by mass or more, and the upper limit is more preferably 5 parts by mass or less. The content of the ultraviolet absorber may be 2 parts by mass or more and 6 parts by mass or less, or 2 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the solid content of the functional layer composition.

[0084] The sesamol-type benzotriazole monomer is not particularly limited, but specific substance names include 2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]ethyl methacrylate, 2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]ethyl acrylate, 3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propyl methacrylate, 3- [2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propyl acrylate, 4-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]butyl methacrylate, 4-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]butyl acrylate, 2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yloxol hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yloxy]ethyl acrylate, 2-[3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propanoyloxy]ethyl methacrylate, 2-[3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propanoyloxy]ethyl acrylate, 4-[3-[2-(6 -hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propanoyloxy]butyl methacrylate, 4-[3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propanoyloxy]butyl acrylate, 2-[3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazol-5-yl]propanoyloxy]ethyl methacrylate, 2-[3-[2-(6-hydroxybenzo[1,Examples of suitable sesamol-type benzotriazole monomers include 2-(methacryloyloxy)ethyl 2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]propanoyloxy]ethyl acrylate, 2-(methacryloyloxy)ethyl 2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate, 2-(acryloyloxy)ethyl 2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate, 4-(methacryloyloxy)butyl 2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate, and 4-(acryloyloxy)butyl 2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate. These sesamol-type benzotriazole monomers may be used alone or in combination of two or more.

[0085] (Anti-fouling agent) The anti-fouling agent is not particularly limited, and examples thereof include silicone-based anti-fouling agents, fluorine-based anti-fouling agents, and silicone-based and fluorine-based anti-fouling agents, which may be used alone or in combination. The anti-fouling agent may also be an acrylic-based anti-fouling agent.

[0086] The content of the antifouling agent is preferably 0.01 to 3.0 parts by mass relative to 100 parts by mass of the polymerizable compound. If the content is 0.01 part by mass or more, sufficient antifouling performance can be imparted to the functional layer, and if the content is 3.0 parts by mass or less, there is no risk of a decrease in the hardness of the functional layer.

[0087] The antifouling agent preferably has a weight-average molecular weight of 5,000 or less, and is a compound having preferably one or more, more preferably two or more reactive functional groups in order to improve the durability of the antifouling performance. In particular, the use of an antifouling agent having two or more reactive functional groups can impart excellent scratch resistance.

[0088] If the antifouling agent does not have a reactive functional group, the antifouling agent will be transferred to the back surface of the optical film when the optical film is stacked, whether the optical film is in roll form or sheet form, and when an attempt is made to attach or apply another layer to the back surface of the optical film, the other layer may peel off. Furthermore, the other layer may easily peel off when a multiple consecutive folding test is performed.

[0089] Furthermore, the antifouling agent having the reactive functional group has good antifouling performance durability (durability), and in particular, the functional layer containing the above-mentioned fluorine-based antifouling agent is less susceptible to fingerprints (less noticeable) and has good wiping properties. Furthermore, since the surface tension of the functional layer composition can be reduced during application, the leveling properties are good and the appearance of the functional layer formed is good.

[0090] A functional layer containing a silicone-based antifouling agent has good slipperiness and good steel wool resistance. A touch sensor incorporating an optical film containing such a silicone-based antifouling agent in its functional layer has good slipperiness when touched with a finger or pen, resulting in a good tactile feel. Furthermore, fingerprints are less likely to be left on the functional layer (are less noticeable), and the layer can be easily wiped off. Furthermore, the surface tension of the functional layer composition can be reduced during application, resulting in good leveling properties and a good appearance for the functional layer formed.

[0091] Commercially available silicone-based antifouling agents include, for example, SUA1900L10 (manufactured by Shin-Nakamura Chemical Co., Ltd.), SUA1900L6 (manufactured by Shin-Nakamura Chemical Co., Ltd.), Ebecryl 1360 (manufactured by Daicel-Cytec Co., Ltd.), UT3971 (manufactured by Nippon Synthetic Co., Ltd.), BYKUV3500 (manufactured by BYK-Chemie Co., Ltd.), BYKUV3510 (manufactured by BYK-Chemie Co., Ltd.), BYKUV3570 (manufactured by BYK-Chemie Co., Ltd.), X22-164E, X Examples of suitable acrylic resins include 22-174BX, X22-2426, KBM503, and KBM5103 (manufactured by Shin-Etsu Chemical Co., Ltd.), TEGO-RAD2250, TEGO-RAD2300, TEGO-RAD2200N, TEGO-RAD2010, TEGO-RAD2500, TEGO-RAD2600, and TEGO-RAD2700 (manufactured by Evonik Japan Co., Ltd.), and Megafac RS854 (manufactured by DIC Corporation).

[0092] Commercially available fluorine-based antifouling agents include, for example, Optool DAC and Optool DSX (manufactured by Daikin Industries, Ltd.), Megafac RS71 and Megafac RS74 (manufactured by DIC Corporation), LINC152EPA, LINC151EPA, and LINC182UA (manufactured by Kyoeisha Chemical Co., Ltd.), Ftergent 650A, Ftergent 601AD, and Ftergent 602.

[0093] Commercially available fluorine-based and silicone-based antifouling agents having reactive functional groups include, for example, Megafac RS851, Megafac RS852, Megafac RS853, Megafac RS854 (manufactured by DIC Corporation), Opstar TU2225, Opstar TU2224 (manufactured by JSR Corporation), and X71-1203M (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0094] (Resin Layer A) The optical film of the present invention has a resin layer A13 provided between the substrate 11 and the functional layer 12. The resin layer A13 is, for example, a layer for suppressing the occurrence of interference fringes. From the viewpoint of suppressing the occurrence of interference fringes, the refractive index of the resin layer A13 is preferably lower than the refractive index of the polyester film 11 serving as the substrate and higher than the refractive index of the functional layer 12. The refractive index of the resin layer A13 can be measured by the same method as that for the refractive index of the functional layer.

[0095] The refractive index difference between the resin layer A13 and the functional layer 12 (e.g., the refractive index of the resin layer A minus the refractive index of the functional layer) is preferably 0.005 or more and 0.100 or less. If this refractive index difference is 0.005 or more, interfacial reflection occurs between the resin layer A13 and the functional layer 12, but interference fringes can be made invisible. If this refractive index difference is 0.100 or less, interference fringes can be slightly observed, but can be made to a level that does not cause problems in practical use. The lower limit of this refractive index difference is more preferably 0.007 or more, and the upper limit is more preferably 0.090 or less. The refractive index of the resin layer A13 may be 0.010 or more and 0.080 or less, 0.007 or more and 0.100 or less, 0.007 or more and 0.090 or less, 0.007 or more and 0.080 or less, etc.

[0096] The film thickness of the resin layer A13 is preferably 10 nm or more and 500 nm or less, for example, 30 nm or more and 200 nm or less. If the film thickness of the resin layer A13 is 10 nm or more, sufficient adhesion between the functional layer 12 and the resin layer A13 can be ensured, and if it is 500 nm or less, interference fringes can be further suppressed and foldability can be improved. The film thickness of the resin layer A13 can be determined in the same manner as for the functional layer 12. The resin layer A (13) is more preferably 50 nm or more, for example, more preferably 150 nm or less. The film thickness of the resin layer A13 may be 50 nm or more and 500 nm or less, 50 nm or more and 200 nm or less, or 50 nm or more and 150 nm or less.

[0097] The resin layer A13 may be composed solely of resin, but preferably contains a binder resin and particles (A-4) for adjusting the refractive index. The binder resin of the resin layer A13 is preferably at least one resin selected from the group consisting of (meth)acrylic resin, cellulose resin, urethane resin, vinyl chloride resin, polyester resin, polyolefin resin, polycarbonate, nylon, polystyrene, and ABS resin. The particles contained in the resin layer A13 include inorganic particles, organic polymer particles, and the like. Examples of inorganic particles include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, zirconia, talc, kaolin, clay, and mixtures thereof. Furthermore, other common inorganic particles, such as calcium phosphate, mica, hectorite, tungsten oxide, lithium fluoride, calcium fluoride, and the like, can also be used in combination. Examples of organic polymer particles include styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based polymer particles. In one embodiment, it is preferably at least one selected from the group consisting of low refractive index particles such as silica and magnesium fluoride, metal oxide particles such as titanium oxide and zirconium oxide, inorganic pigments such as cobalt blue, etc. Among these, from the viewpoints of adhesion and adjusting the refractive index difference, a combination of a polyester resin and metal oxide particles such as titanium oxide and zirconium oxide may be used.

[0098] The binder resin constituting the resin layer A13 is a resin with high adhesive properties, and includes a polycarbonate polyurethane resin, which is a urethane resin having a polycarbonate structure, and a polyester resin. Using a resin layer made from a combination of these significantly improves adhesion between the polyester film substrate and the functional layer. In one embodiment, the resin layer A is a cured product layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (A-1), a polyester resin (A-2), a blocked isocyanate crosslinking agent (A-3), and particles (A-4), where the polyester resin (A-2) has a condensed polycyclic aromatic structure. The inclusion of these components in the resin layer A can suppress the generation of interference light, and furthermore, can produce an optical film that does not crack or break even when subjected to a 180° folding test repeated 10,000 times. In particular, in the present invention, the presence of the resin layer A dramatically improves the adhesion between the polyester film substrate and the functional layer, so that when an impact is applied to the surface of the optical film, not only deformation of the optical film itself but also plastic deformation of the adhesive layer can be suppressed even when the adhesive layer is disposed inside the image display device rather than the optical film. Furthermore, cracking of the optical film when folded can be suppressed. Furthermore, good restorability can be obtained when the optical film is folded, held, and then opened again.

[0099] In particular, it has been confirmed that the resin layer A is a cured product layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (A-1), a polyester resin (A-2), a blocked isocyanate crosslinking agent (A-3), and particles (A-4), and therefore can ensure stable adhesion to the functional layer. Here, "stable" refers to long-term adhesion stability, stability in a humid and hot environment, and adhesion stability after bending tests, etc., and can achieve the effect of maintaining adhesion without peeling of the functional layer before and after treatment.

[0100] The resin layer A of the present invention has good compatibility with the composition of the functional layer described below. Furthermore, the functional layer is obtained by UV curing through UV irradiation and has a crosslinked network structure. The polycarbonate polyurethane resin and polyester resin of the resin layer interact with each other, making the resins more compatible and entangled. Furthermore, it is believed that this entangled resin becomes entangled in the network structure of the functional layer formed thereon, resulting in a resin layer with superior adhesion compared to conventional resins. Furthermore, since the resin layer contains a polyester resin, adhesion to the polyester film substrate is also improved, resulting in a resin layer with superior adhesion.

[0101] The polycarbonate polyurethane resin is not particularly limited as long as it is a urethane resin having a polycarbonate structure in the molecule, and is obtained by addition reaction of a polycarbonate diol component, a diisocyanate component, and, if necessary, a diol component as a chain extender.

[0102] Examples of diol components necessary for preparing polycarbonate polyurethane resins include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. Among these, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, and 1,6-hexadiol are particularly preferred. These diol components can be used alone or in combination of two or more. When combining two or more diols, the ratio is not particularly limited and can be adjusted to obtain a polycarbonate polyurethane that exhibits the required properties.

[0103] Examples of diisocyanate components necessary for preparing polycarbonate polyurethane resins include toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 4,4-methylenebiscyclohexyldiisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, and 1,4-bis(isocyanatomethyl)cyclohexane. Among these, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 4,4-methylenebiscyclohexyldiisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, etc. are particularly preferred because they have the above-mentioned structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group. These isocyanate components can be used alone or in combination of two or more. When combining two or more, the ratio is not particularly limited, and can be adjusted so as to obtain a polycarbonate polyurethane that has the required properties.

[0104] The polyester resin is a copolymer of a dicarboxylic acid component and a diol component, and is not particularly limited as long as it is a copolymer polyester composed of a dicarboxylic acid component and a diol component, and one or more dicarboxylic acid components and two or more diol components may be used. In the present invention, it is particularly preferred that the dicarboxylic acid component has a structure containing a naphthalene ring.

[0105] Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, cyclohexylmethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, cyclohexylmethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and 1,1-cyclohexanediacetic acid. Among these, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and the like are particularly preferred because they have the above-mentioned structure containing a naphthalene ring.

[0106] Examples of the diol component include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.

[0107] The ratio of the dicarboxylic acid component and the diol component when combined is not particularly limited and can be adjusted to obtain a polyester with the required properties. In particular, in the present invention, it is preferable that the polyester resin (A-2) has a condensed polycyclic aromatic structure. The presence of a condensed polycyclic aromatic structure in the polyester resin (A-2) improves interaction with the functional layer, dramatically improving adhesion to the functional layer. It has been confirmed that this ensures stable adhesion to the functional layer. "Stable" here refers to long-term adhesion stability, stability in a humid and hot environment, and adhesion stability after bending tests, etc., and provides the effect of ensuring adhesion without peeling of the functional layer before and after treatment. For example, at least one of the polyesters (A-2), (B-2), and (C-2) having a condensed polycyclic aromatic structure contained in resin layer A, resin layer B, and resin layer C, respectively, has a naphthalene skeleton in its molecule. The presence of a naphthalene skeleton in its molecule improves interaction with the functional layer, dramatically improving adhesion to the functional layer. This has been confirmed to ensure stable adhesion to the functional layer. "Stable" here refers to long-term adhesion stability, stability in a humid and hot environment, and adhesion stability after bending tests, etc., and provides the effect of ensuring that the functional layer remains tightly adhered without peeling before and after treatment.

[0108] Although the exact mechanism by which the polycarbonate polyurethane resin and polyester resin used in the resin layer exhibit the effects of the present invention is not clear, the resin layer of the present invention can maintain the rigidity of the resin while improving the flexibility of the resin, and therefore functions optimally as a resin layer. In other words, not only does it have excellent adhesion to the substrate, such as the polyester film substrate and the functional layer, but it also greatly improves adhesion over time. This makes it possible to obtain a film that maintains its quality for a long period of time.

[0109] In the present invention, it is important that the binder resin contains a polycarbonate polyurethane resin and a polyester resin. The ratio of the two is not particularly limited as long as the physical properties of the resulting resin layer can be ensured. When the total amount of the binder resin is taken as 100% by mass, the polycarbonate polyurethane resin is typically 40% by mass or more and 85% by mass or less, more preferably 45% by mass or more and 80% by mass or less, and even more preferably 50% by mass or more and 75% by mass or less. By ensuring that the polycarbonate polyurethane resin is 40% by mass or more, the balance between flexibility and hardness of the urethane resin can be ensured, and adhesion over time can be ensured. Furthermore, by ensuring that the ratio is 85% by mass or less, the balance between hardness and softness of the resin layer can be maintained and flexibility can be improved, thereby functioning optimally as a resin layer.

[0110] (Crosslinking Agent) In the present invention, the composition used to form the resin layer may contain a crosslinking agent to form a crosslinked structure between resins in the resin layer. By including a crosslinking agent, it becomes possible to further improve adhesion under high temperature and high humidity conditions. Specific examples of crosslinking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred from the viewpoint of the stability of the coating liquid over time and the effect of improving adhesion under high temperature and high humidity treatment. Furthermore, a catalyst or the like can be used as needed to promote the crosslinking reaction.

[0111] When the resin layer-forming composition contains a binder resin and a crosslinking agent, the binder resin content is preferably 50 to 95% by weight, more preferably 55 to 90% by weight, even more preferably 60 to 90% by weight, and most preferably 80 to 90% by weight, based on 100% by weight of the total weight of the binder resin and crosslinking agent. A binder resin content of 95% by weight or less maintains the strength of the resin layer coating and provides good adhesion under high temperature and high humidity conditions. A binder resin content of 50% by weight or more maintains the flexibility of the resin layer and provides good adhesion under normal temperature and high temperature and high humidity conditions. Furthermore, when the total weight of the binder resin and crosslinking agent is taken as 100% by weight, the crosslinking agent content is preferably 5 to 50% by weight, more preferably 10 to 45% by weight, even more preferably 10 to 40% by weight, and most preferably 10 to 20% by weight.

[0112] When an isocyanate-based crosslinking agent is used as the crosslinking agent, it is preferable to use a blocking agent to control the reactivity of the isocyanate. Examples of types of blocking agents include bisulfite compounds such as sodium bisulfite; pyrazole compounds such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 4-nitro-3,5-dimethylpyrazole; phenols such as phenol and cresol; aliphatic alcohols such as methanol and ethanol; active methylene compounds such as dimethyl malonate and acetylacetone; mercaptans such as butyl mercaptan and dodecyl mercaptan; acid amides such as acetanilide and acetic acid amide; lactams such as ε-caprolactam and δ-valerolactam; acid imides such as succinimide and maleimide; oximes such as acetaldoxime, acetone oxime, and methyl ethyl ketone oxime; and amines such as diphenylaniline, aniline, and ethyleneimine. From the viewpoint of reactivity, a blocking agent having a pyrazole skeleton is suitable for this system.

[0113] It is preferable to introduce a hydrophilic group into the blocked isocyanate crosslinking agent from the viewpoint of imparting water dispersibility in aqueous solvents. Furthermore, the hydrophilic group is preferably an anionic group such as a carboxyl group or a sulfonic acid group, or a nonionic group such as an oxyalkyl group. Crosslinking agents having these hydrophilic groups can be prepared by previously reacting a polyisocyanate, which serves as the base of the blocked isocyanate, with a compound having a hydrophilic group and a reactive group such as a hydroxyl group.

[0114] (Additives) The resin layer in the present invention may contain known additives, such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc., within the range that does not impair the effects of the present invention. However, it is preferable not to use substances that are undesirable from an environmental perspective, etc.

[0115] In order to further improve the blocking resistance of the resin layer, it is also a preferred embodiment to add inactive particles to the resin layer. Examples of particles to be contained in the resin layer include inorganic particles and organic polymer particles. Examples of inorganic particles include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, and mixtures thereof. Furthermore, other common inorganic particles such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, and the like can also be used in combination. Examples of organic polymer particles include styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based polymer particles.

[0116] The average particle size of the inactive particles in the resin layer (average particle size based on the number of particles measured by SEM; the same applies hereinafter) is preferably 0.01 to 20 μm, more preferably 0.04 to 2.0 μm, and even more preferably 0.1 to 1.0 μm. When the average particle size of the inactive particles is 0.04 μm or more, it is easy to form irregularities on the surface of the resin layer, which improves the handling properties of the highly adhesive polyester film, such as slipperiness and winding ability, and provides good processability during lamination, which is preferred. On the other hand, when the average particle size of the inactive particles is 2.0 μm or less, particle detachment is less likely to occur, which is preferred. The particle concentration in the resin layer is preferably 1 to 20% by mass relative to the resin content.

[0117] The resin layer A13 may contain an antistatic agent to obtain antistatic properties. When the resin layer A13 contains an antistatic agent, the resin layer A13 also functions as an antistatic layer. When the resin layer A13 contains an antistatic agent, the surface resistance value of the surface 10A of the optical film 10 can be further stabilized. When the resin layer A13 contains an antistatic agent, if the functional layer 12 also contains an antistatic agent, the surface resistance value of the surface 10A of the optical film 10 can be further stabilized. As the antistatic agent contained in the resin layer A13, the same antistatic agent as described in the section on the functional layer 12 can be used, and therefore, description thereof will be omitted here.

[0118] (Composition for Resin Layer A) The composition for resin layer A may contain known materials as long as the problems to be solved and the effects of the present invention are not impaired.

[0119] (Resin Layer B) The optical film of the present invention may have a resin layer B15 provided on the second surface 11B of the substrate 11, opposite the first surface 11A. The resin layer B15 is a layer that improves the light transmittance of the optical film 10. The refractive index of the resin layer B15 is higher than the refractive index of air, 1.000, and lower than the refractive index of the polyester film 11 serving as the substrate. The refractive index of the resin layer B15 can be measured by the same method as that of the functional layer 12, and therefore, description thereof will be omitted here.

[0120] The refractive index difference between the polyester film 11 as the substrate and the resin layer B15 (refractive index of the polyester film as the substrate - refractive index of the resin layer B) is preferably 0.005 or more and 0.700 or less. If this refractive index difference is 0.005 or more, the light transmittance of the optical film 10 can be improved, and if it is 0.700 or less, the transparency of the optical film 10 is not impaired. The lower limit of this refractive index difference is more preferably 0.010 or more, and the upper limit is more preferably 0.600 or less. The refractive index of the resin layer B15 may be 0.050 or more and 0.500 or less.

[0121] The film thickness of the resin layer B15 is 1 nm or more and 200 nm or less, preferably 10 nm or more and 180 nm or less, for example, 30 nm or more and 150 nm or less. If the film thickness of the resin layer B15 is 1 nm or more and 200 nm or less, the light transmittance of the optical film 10 can be further improved. For example, if the film thickness is 200 nm or less, deterioration of processability can be suppressed. The film thickness of the resin layer B15 can be determined by the same method as that of the functional layer 12.

[0122] The configuration of the resin layer B15 is not particularly limited as long as it has a refractive index higher than 1.000 and lower than the refractive index of the polyester film 11 used as the base material. The resin layer B15 can be composed of a resin. In addition to the resin, the resin layer B15 may contain low-refractive-index particles having a refractive index lower than that of the resin to further reduce the refractive index. The resin layer B15 may also contain an antistatic agent to achieve antistatic properties. When the resin layer B15 contains an antistatic agent, the resin layer B15 also functions as an antistatic layer. Furthermore, the resin layer B15 may contain a color adjuster such as a spectral transmittance adjuster to adjust the color of the optical film 10.

[0123] The spectral transmittance adjuster adjusts the spectral transmittance of the optical film. For example, when the resin layer C contains a sesamol-type benzotriazole monomer, the spectral transmittance can be suitably adjusted.

[0124] Resin layer B is a cured product layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (B-1), a polyester resin (B-2), a blocked isocyanate crosslinking agent (B-3), and particles (B-4). In resin layer B, the polyester resin (B-2) may have a condensed polycyclic aromatic structure. For details of these components, the description of resin layer A13 can be cited. The various components contained in resin layer A and resin layer B may be the same or different.

[0125] The binder resin constituting the resin layer B15 is a resin having high adhesiveness, and contains a polycarbonate polyurethane resin, which is a urethane resin having a polycarbonate structure, and a polyester resin. By using a resin layer made of these resins, the adhesion between the polyester film substrate and the resin layer B is dramatically improved.

[0126] The reason for this is the good compatibility between the resin layer and the composition of the functional layer described below. The functional layer is obtained by UV curing through UV irradiation and has a crosslinked network structure. The polycarbonate polyurethane resin and polyester resin of the resin layer interact with each other, making the resins more compatible and entangled. It is believed that this entangled resin becomes entangled in the network structure of the functional layer formed thereon, resulting in a resin layer with superior adhesion compared to conventional resins. Furthermore, since the resin layer contains a polyester resin, adhesion to the polyester film substrate is also improved, resulting in a resin layer with superior adhesion.

[0127] Furthermore, it has been found that by including a dicarboxylic acid component having a structure containing a naphthalene ring in the polyester resin used, not only can the light transmittance be improved, but it has also been confirmed that the adhesion to the adhesive layer placed on the opposite side of the substrate is improved.

[0128] The resin layer B15 may be composed of only a resin, but preferably contains a binder resin and particles for adjusting the refractive index. The resin layer B15 can be prepared by the same method as the resin layer A13, and can be obtained by preparing a composition for resin layer B in the same manner as the composition for resin layer A.

[0129] (Resin Layer C) In one embodiment, for example, as shown in Fig. 4, the resin layer C14 is provided between the substrate 11 and the resin layer A13. The resin layer C14 is a layer mainly for improving the adhesion between the polyester film 11 as the substrate and the resin layer A13 without generating interference fringes. A more detailed explanation of Fig. 4 will be given later. By providing the resin layer C14 between the polyester film 11 as the substrate and the resin layer A13, the adhesion can be improved compared to when the polyester film 11 as the substrate and the resin layer A13 are in direct contact.

[0130] From the viewpoint of interference fringes, the refractive index of the resin layer C14 is preferably lower than that of the polyester film 11 as the substrate and higher than that of the resin layer A 13. The refractive index of the resin layer C14 can be measured by the same method as that of the functional layer 12.

[0131] The refractive index difference between the resin layer C14 and the resin layer A13 (refractive index of resin layer C - refractive index of resin layer A) is preferably 0.005 or more and 0.100 or less. If this refractive index difference is 0.005 or more, interfacial reflection occurs between the resin layer C14 and the resin layer A13, but interference fringes can be made invisible, and if it is 0.100 or less, interference fringes can be slightly observed, but can be made to a level that does not cause problems in practical use. The lower limit of this refractive index difference is more preferably 0.007 or more, and the upper limit is more preferably 0.090 or less. The refractive index of the resin layer A13 may be 0.010 or more and 0.080 or less.

[0132] The film thickness of the resin layer C14 is preferably 30 nm or more and 200 nm or less. If the film thickness of the resin layer C14 is 30 nm or more, sufficient adhesion between the resin layer A13 and the resin layer C14 and between the polyester film 11 as the substrate and the resin layer C14 can be ensured. If the film thickness is 200 nm or less, interference fringes will not occur due to the refractive index difference between the resin layer C14 and the resin layer A13, and foldability can be improved. The film thickness of the resin layer C14 is determined in the same manner as the functional layer 12. The lower limit of the resin layer C14 is more preferably 50 nm or more, and the upper limit is more preferably 150 nm or less. The film thickness of the resin layer C14 may be 50 nm or more and 200 nm or less, 30 nm or more and 150 nm or less, 50 nm or more and 150 nm or less, etc.

[0133] The resin layer C14 may be composed of only a resin, but preferably contains a binder resin and particles for adjusting the refractive index. The composition of the resin layer C14 can be prepared by the same method as the composition of the resin layer A13, and can be obtained by preparing a composition for the resin layer C in the same way as the composition for the resin layer A. The various components contained in the resin layer A, the resin layer B, and the resin layer C may be the same or different.

[0134] (Method for Producing Optical Film) As an example, a method for producing an optical film having a resin layer C will be described. The optical film 10 can be produced, for example, as follows. First, a composition for the resin layer C is applied to the first surface 11A of the polyester film 11 serving as a substrate using a coating device such as a bar coater to form a coating film of the composition for the resin layer C, in order to form the resin layer C14.

[0135] After forming a coating film of the composition for resin layer C, the coating film is dried by various known methods, for example, by heating at a temperature of 40°C or higher and 200°C or lower for 10 to 120 seconds to evaporate the solvent or harden the coating film, and if necessary, the coating film is irradiated with ionizing radiation such as ultraviolet light to form a resin layer C14 on the polyester film 11 as the substrate.

[0136] Next, a resin layer A composition for forming the resin layer A13 is applied onto the resin layer C14 using a coating device such as a bar coater to form a coating film of the resin layer A composition.

[0137] After forming a coating film of the composition for resin layer A, the coating film is dried by various known methods, for example, by heating at a temperature of 40°C or higher and 200°C or lower for 10 to 120 seconds, to evaporate the solvent or cure the coating film, and if necessary, the coating film is irradiated with ionizing radiation such as ultraviolet light to form resin layer A13.

[0138] After forming the resin layer A13, a functional layer composition for forming the functional layer 12 is applied onto the resin layer A13 using a coating device such as a bar coater to form a coating film of the functional layer composition. In this way, the method for producing an optical film of the present invention includes producing the functional layer 12 on the first surface 11A side of the polyester film 11 as a substrate by a coating step.

[0139] <Composition for Functional Layer> The composition for functional layer contains a polymerizable compound that becomes a binder resin after curing. The composition for functional layer may also contain, as necessary, an antistatic agent, an ultraviolet absorber, a spectral transmittance adjuster, an antifouling agent, inorganic particles, a leveling agent, a solvent, and a polymerization initiator.

[0140] (solvent) Examples of the solvent include alcohols (e.g., methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol, t-butanol, benzyl alcohol, PGME, ethylene glycol, diacetone alcohol), ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone, diethyl ketone, diacetone alcohol), 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., 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, ethyl methyl carbonate). These solvents may be used alone or in combination of two or more thereof. Among them, methyl isobutyl ketone and methyl ethyl ketone are preferred as the solvents, since they can dissolve or disperse components such as urethane (meth)acrylate and other additives and allow the functional layer composition to be suitably applied.

[0141] (Polymerization Initiator) The polymerization initiator is a component that is decomposed by irradiation with ionizing radiation to generate radicals and initiate or advance polymerization (crosslinking) of a polymerizable compound.

[0142] The polymerization initiator is not particularly limited as long as it is capable of releasing a substance that initiates radical polymerization upon irradiation with ionizing radiation. The polymerization initiator is not particularly limited, and known initiators can be used, specific examples of which include acetophenones, benzophenones, Michler's benzoyl benzoate, α-amyloxime ester, thioxanthones, propiophenones, benzils, benzoins, and acylphosphine oxides. It is also preferable to use a photosensitizer in combination, specific examples of which include n-butylamine, triethylamine, and poly-n-butylphosphine.

[0143] After forming a coating film of the composition for the functional layer, the coating film is dried by various known methods, for example, by heating at a temperature of 30°C or higher and 120°C or lower for 10 to 120 seconds, to evaporate the solvent.

[0144] After drying the coating film, the coating film is irradiated with ionizing radiation such as ultraviolet light to harden the coating film, thereby forming the functional layer 12 adjacent to the resin layer A13.

[0145] After forming the functional layer 12, a composition for resin layer B for forming resin layer B15 is applied to the second surface 11B of the polyester film 11 as the base material using an application device such as a bar coater to form a coating film of the composition for resin layer B.

[0146] After forming a coating film of the composition for resin layer B, the coating film is dried by various known methods, for example, by heating at a temperature of 40° C. or higher and 200° C. or lower for 10 to 120 seconds to evaporate the solvent or cure the coating film, and if necessary, the coating film is irradiated with ionizing radiation such as ultraviolet light to form resin layer B 15. In this way, an optical film 10 according to one embodiment is obtained.

[0147] An example of an optical film used in an image display device may be the optical film shown in FIG. 4. Even in the case of FIG. 4, the optical film is foldable. In one embodiment, the optical film of the present invention may further include an adhesive layer. For example, an adhesive layer 41 may be further included on the second surface 11B side of the polyester film 11 serving as a substrate, the second surface 11B being opposite to the first surface 11A side. Alternatively, the optical film may include the polyester film 11 serving as a substrate, a resin layer B15, and an adhesive layer 41 in this order. By providing the resin layer B between the substrate 11 and the adhesive layer 41 in this manner, the effects of the present invention can be more effectively exhibited.

[0148] 4 includes a polyester film 11 as a substrate, and a resin layer C14, a resin layer A13, and a functional layer 12, in this order, on a first surface 11A side of the polyester film 11 as a substrate. Also, a resin layer B15 and an adhesive layer 41, in this order, on a second surface 11B side of the polyester film 11 as a substrate.

[0149] As another embodiment, an optical film (FIG. 5) having a configuration in which the resin layer C14 is removed from the configuration in FIG. 4 is also used as an image display device and is foldable.

[0150] In an optical film having an adhesive layer, the shear storage modulus G' at 25°C in the frequency range of 500 Hz to 1000 Hz can be greater than 200 MPa and less than 1200 MPa. When the shear storage modulus G' of the film exceeds 200 MPa, not only deformation of the optical film itself can be suppressed when an impact is applied to the surface of the optical film, but also plastic deformation of the adhesive layer can be suppressed even when the adhesive layer is disposed further inside the image display device than the optical film. Furthermore, when the shear storage modulus G' of an optical film having an adhesive layer is 1200 MPa or less, cracking of the optical film when folded can be suppressed. The lower limit of the shear storage modulus G' of the optical film is preferably 400 MPa or more, and more preferably 500 MPa or more. By setting such a lower limit, better impact resistance can be obtained. The upper limit of the shear storage modulus G' of the optical film is preferably less than 800 MPa. By setting such an upper limit, good restorability can be obtained when the optical film is folded, held, and then opened again. The shear storage modulus G' of the optical film may be 400 MPa or more and 1200 MPa or less, 400 MPa or more and 800 MPa or less, 500 MPa or more and 1200 MPa or less, or 500 MPa or more and 800 MPa or less.

[0151] In an optical film having an adhesive layer, the shear loss modulus G" at 25°C in a frequency range of 500 Hz to 1000 Hz can be 3 MPa or more and 150 MPa or less. If the shear loss modulus G" of the optical film is 3 MPa or more, a decrease in impact absorption performance can be suppressed. Furthermore, if the shear loss modulus G" of the optical film having an adhesive layer is 150 MPa or less, a decrease in hardness of the adhesive layer 41 can be suppressed. The lower limit of the shear loss modulus G" of the optical film having an adhesive layer is preferably 20 MPa or more, and from the viewpoint of thinning the optical film, the upper limit of the shear loss modulus G" of the optical film is preferably 130 MPa or less, more preferably 100 MPa or less. The shear loss modulus G" of the optical film can be 20 MPa or more and 150 MPa or less, 20 MPa or more and 130 MPa or less, 20 MPa or more and 100 MPa or less, etc.

[0152] The shear storage modulus G' and shear loss modulus G" can be measured using a dynamic viscoelasticity measuring apparatus (DMA). When measuring the shear storage modulus G' and shear loss modulus G" of an optical film using a dynamic viscoelasticity measuring apparatus (DMA), first, a sample is obtained by punching out an optical film having an adhesive layer into a rectangular shape of 10 mm x 5 mm. Two such samples are then prepared and attached to a solid shearing jig, which is an option for a dynamic viscoelasticity measuring apparatus (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, the solid shearing jig includes a 1 mm-thick metal solid shearing plate (middle plate) and two L-shaped metal fittings (outer plates) arranged on either side of the solid shearing plate. One sample is sandwiched between the solid shearing plate and one of the L-shaped metal fittings, and the other sample is sandwiched between the solid shearing plate and the other L-shaped metal fitting. In this case, the sample was sandwiched so that the resin layer faced the solid shear plate and the functional layer faced the L-shaped metal fitting. The L-shaped metal fittings were then tightened with screws to secure the sample. Next, a tensile test chuck consisting of an upper chuck and a lower chuck was attached to a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.), and a solid shear jig was attached between the upper and lower chucks with a chuck distance of 20 mm. The chuck distance was the distance between the upper and lower chucks. The temperature was set to 25°C and increased at a rate of 2°C / min. In this state, while the solid shear plate was fixed, a dynamic viscoelasticity measurement of the solid was performed at 25°C while applying a 1% strain to the two L-shaped metal fittings and a longitudinal vibration with a frequency ranging from 500 Hz to 1000 Hz. The shear storage modulus G' and shear loss modulus G'' of the optical film were measured. Here, the shear storage modulus G' and shear loss modulus G'' of the optical film in the frequency range of 500 Hz or more and 1000 Hz or less are determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to the L-shaped metal fitting, measuring the shear storage modulus G' and shear loss modulus G'' of the optical film at each frequency, determining the arithmetic mean value of these shear storage modulus G' and shear loss modulus G'', and further repeating this measurement three times to obtain the arithmetic mean value of the three arithmetic mean values ​​obtained respectively.The reason why the frequency range is set to 500 Hz or more and 1000 Hz or less in the above description is that this frequency range is a frequency at which the surface of the optical film deforms by several microns to several tens of microns when an object is allowed to fall freely from a height of several centimeters, and is a frequency at which the optical film can damage a display panel or the like inside the image display device.

[0153] Other than the above, the physical properties of the optical film having the adhesive layer are the same as those of the optical film 10, and may vary depending on the physical properties of the adhesive layer.

[0154] (Adhesive Layer) The adhesive layer 41 is a layer made of a resin having optical transparency. The adhesive layer 41 is a layer having impact absorption properties. The adhesive layer may have a multi-layer structure made of two or more resin layers (e.g., a two-layer structure, a three-layer structure, a four-layer structure, etc.).

[0155] The thickness of the adhesive layer 41 can be 25 μm or more and 300 μm or less. If the thickness of the adhesive layer 41 is 25 μm or more, a decrease in the hardness of the adhesive layer 41 can be suppressed, and if the thickness is 300 μm or less, the adhesive layer 41 can be made thinner without deteriorating processability. The thickness of the adhesive layer 41 is determined by photographing a cross section of the adhesive layer 41 using a scanning electron microscope (SEM), measuring the thickness of the adhesive layer 41 at 20 points on the image of the cross section, and calculating the arithmetic mean value of the thicknesses at the 20 points. The lower limit of the adhesive layer 41 is more preferably 60 μm or more, and the upper limit of the adhesive layer 41 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. The thickness of the adhesive layer may be 25 μm or more and 200 μm or less, 25 μm or more and 150 μm or less, 25 μm or more and 100 μm or less, 50 μm or more and 300 μm or less, 50 μm or more and 200 μm or less, 50 μm or more and 150 μm or less, 50 μm or more and 100 μm or less, etc.

[0156] The resin constituting the adhesive layer 41 is not particularly limited as long as it is a resin that has a shear storage modulus G' and a shear loss modulus G'' within the above-mentioned ranges at 25°C in the frequency range of 500 Hz to 1000 Hz in an optical film having the adhesive layer. Examples of such resins include acrylic gels, urethane gels, silicone gels, urethane resins, and epoxy resins. Among these, urethane gels are preferred. "Gel" generally refers to a dispersion system that is highly viscous and has lost fluidity. In addition to acrylic gels and urethane resins, the adhesive layer 41 may also contain rubber or a thermoplastic elastomer.

[0157] The urethane resin is a resin having a urethane bond. Examples of the urethane resin include a cured product of an ionizing radiation-curable urethane resin composition and a cured product of a thermosetting urethane resin composition. Among these, a cured product of an ionizing radiation-curable urethane resin composition is preferred from the viewpoints of obtaining high hardness, a fast curing rate, and excellent mass productivity.

[0158] The ionizing radiation-curable urethane resin composition contains a urethane (meth)acrylate, and the thermosetting urethane resin contains a polyol compound and an isocyanate compound. The urethane (meth)acrylate, the polyol compound, and the isocyanate compound may be any of a monomer, an oligomer, and a prepolymer.

[0159] The number of (meth)acryloyl groups (number of functional groups) in the urethane (meth)acrylate is preferably 2 or more and 4 or less. If the number of (meth)acryloyl groups in the urethane (meth)acrylate is less than 2, the pencil hardness may be reduced, and if it exceeds 4, the cure shrinkage may be large, causing the optical film to curl and the resin layer to crack when bent. It is more preferable that the upper limit of the number of (meth)acryloyl groups in the urethane (meth)acrylate is 3 or less. The term "(meth)acryloyl group" includes both "acryloyl group" and "methacryloyl group".

[0160] The weight-average molecular weight of the urethane (meth)acrylate is preferably 1,500 or more and 20,000 or less. If the weight-average molecular weight of the urethane (meth)acrylate is less than 1,500, the impact resistance may decrease, and if it exceeds 20,000, the viscosity of the ionizing radiation-curable urethane resin composition may increase, resulting in poor coatability. The lower limit of the weight-average molecular weight of the urethane (meth)acrylate is more preferably 2,000 or more, and the upper limit is more preferably 15,000 or less.

[0161] The structure of the polymer chains (repeating units) of the resin constituting the adhesive layer 41 can be determined by analyzing the adhesive layer 41 using, for example, pyrolysis GC-MS and FT-IR. Pyrolysis GC-MS is particularly useful because it can detect the monomer units contained in the adhesive layer 41 as monomer components.

[0162] The adhesive layer 41 may contain an ultraviolet absorber, a spectral transmittance adjuster, an antifouling agent, inorganic particles and / or organic particles, etc., as long as the shear storage modulus G' and shear loss modulus G'' of the optical film having the adhesive layer at 25°C in the frequency range of 500 Hz to 1000 Hz are within the above-mentioned ranges. The ultraviolet absorber, etc. may be the same as the ultraviolet absorber, etc. described in the section on the functional layer 12, and therefore further description thereof will be omitted here.

[0163] (Image display device) The optical film can be incorporated into a foldable image display device. The image display device mainly includes a housing containing a battery and other components, a protective film, a display element, a circular polarizer, a touch sensor, and an optical film stacked in this order facing the viewer. Optically transparent adhesive layers are arranged between the display element and the circular polarizer, between the circular polarizer and the touch sensor, and between the touch sensor and the optical film, and these components are fixed to each other by the adhesive layers. Note that the adhesive layers are arranged between the display element and the circular polarizer, between the circular polarizer and the touch sensor, and between the touch sensor and the optical film, but the location of the adhesive layer is not particularly limited as long as it is between the optical film and the display element.

[0164] The optical film may be arranged so that the functional layer 12 is closer to the viewer than the polyester film 11 serving as the substrate. In an image display device, the functional layer 12 in the optical film 10 may form the surface of the image display device. In another aspect, a foldable image display device is provided, comprising a display element and the optical film of the present invention arranged closer to the viewer than the display element. The optical film of the present invention may be an optical film having an adhesive layer, or may be an optical film not having an adhesive layer. When an optical film not having an adhesive layer is used, the display element and the optical film not having an adhesive layer may be bonded together via a known adhesive layer or the like.

[0165] In the image display device, the display element is preferably an organic light-emitting diode element including an organic light-emitting diode or the like. The touch sensor may be disposed closer to the viewer than the circular polarizer, or may be disposed between the display element and the circular polarizer. The touch sensor may be an on-cell type or an in-cell type. For example, an OCA (Optical Clear Adhesive) may be used as the adhesive layer.

[0166] According to this embodiment, a polyester film 11 made of polyester-based resin is used as a base material, and a resin layer A13 is provided between the polyester film 11 as a base material and the functional layer 12, so that the occurrence of interference fringes can be suppressed while the product is foldable.

[0167] When the back surface of an optical film is a polyester film substrate, the polyester film substrate is in contact with an air layer, which can increase reflection at the interface between the polyester film substrate and the air layer, potentially reducing light transmittance. In particular, when a polyester film substrate made of a polyester-based resin is used, the refractive index of these polyester films is relatively high, making interfacial reflection more likely to occur. In contrast, in this embodiment, a resin layer B15 having a refractive index greater than 1.000 and lower than the refractive index of the polyester film substrate 11 is provided on the second surface 11B of the polyester film substrate 11. This reduces interfacial reflection and light reflectance compared to when the polyester film substrate is in contact with an air layer. This can improve the light transmittance of an optical film having an adhesive layer, for example.

[0168] Furthermore, when the resin layer B15 contains an antistatic agent, the optical film has a functional layer 12, which is an antistatic hard coat layer, on the first surface 11A side of the polyester film 11 as the substrate, and a resin layer B15 containing an antistatic agent on the second surface 11B side of the polyester film 11 as the substrate, so that adhesion of dust and the like to the optical film can be suppressed. Furthermore, in this case, even if protective films are attached to both surfaces of the optical film and the protective films are peeled off from the optical film, charging of the optical film can be suppressed. This can improve the yield of the assembly process of image display devices.

[0169] Optical films used in foldable image display devices are sometimes required to have impact resistance because their surfaces may be subjected to impact. When an impact is applied to the surface of the optical film, the surface of the optical film may become dented, and components of the image display device, such as a display panel (e.g., an organic light-emitting diode panel), located further inside the optical film may be damaged. The dents on the surface of the optical film can be classified into dents caused by the optical film itself and dents caused by a soft layer, such as an adhesive layer, located further inside the image display device than the optical film. The term "dents caused by the optical film itself" refers to dents caused by deformation of the optical film itself due to impact applied to the surface of the optical film. The term "dents caused by a soft layer" refers to dents caused by plastic deformation of a soft layer located further inside the image display device than the optical film, resulting in the optical film following the plastic deformation of the soft layer due to the softness of this layer. For this reason, it is currently desirable for optical films to have excellent impact resistance such that, when an impact is applied to the surface of the optical film, dents caused by the optical film itself and dents caused by the soft layer are suppressed, and components located inside the image display device are not damaged more than the optical film. Here, the shear loss tangent tanδ has traditionally been known as an index of impact absorption performance. Therefore, it has been considered possible to express the impact resistance of an optical film having a structure in which a functional layer is provided on the first surface side of a polyester film as a substrate and a resin layer on the second surface side using the shear loss tangent tanδ. However, the shear loss tangent tanδ has not been able to suppress surface dents caused by the optical film itself and the soft layer, and damage to components located inside the image display device more than the optical film, when an impact is applied to the surface of the optical film (the surface of the functional layer). This is thought to be because the shear loss tangent tanδ is the ratio (G" / G') of the shear loss modulus G" to the shear storage modulus G'.As a result of further intensive research, the present inventors have found that in order to suppress surface depressions caused by the optical film itself and the soft layer when an impact is applied to the surface of the optical film, and to suppress damage to components located more internally than the optical film, it is important to balance the film thickness, shear storage modulus G', and shear loss modulus G" of the resin layer. Such characteristics can be achieved by the configuration in which the resin layer in the present invention is a cured layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin, a polyester resin, a blocked isocyanate crosslinking agent, and particles, and the polyester resin has a condensed polycyclic aromatic structure.

[0170] According to this embodiment, in an optical film having a structure in which a functional layer 12 is provided on the first surface 11A side of a polyester film 11 as a substrate and an adhesive layer 41 is provided on the second surface 11B side, the adhesive layer 41 has a thin thickness of 25 μm or more and 300 μm or less, the shear storage modulus G' of the optical film is greater than 200 MPa and less than 1200 MPa, and the shear loss modulus G'' of the optical film is greater than 3 MPa and less than 150 MPa. Therefore, even though the optical film is foldable, when an impact is applied to the surface of the optical film, it is possible to suppress surface depressions caused by the optical film itself and by layers softer than the optical film present inside the image display device, and it is also possible to suppress damage to components such as display elements located inside the image display device. This allows for excellent impact resistance.

[0171] In order to explain the present invention in detail, the following examples are given, but the present invention is not limited to these examples. Note that the "value calculated based on 100% solids content" below refers to a value when the solids content in the solvent-diluted product is taken as 100%.

[0172] <Refractive Index> The refractive indexes of the functional layer and various resin layers were determined based on the above formula (2) by applying a functional layer composition and a resin layer composition to a 50 μm-thick PET sheet that had not been subjected to an easy-adhesion treatment, respectively, to form a cured film having a thickness of 1 to 10 μm, attaching black vinyl tape (for example, Yamato Vinyl Tape No. 200-38-21 (38 mm width)) having a width greater than the measurement spot area to the side of the PET that had not been coated with the functional layer composition or the resin layer composition (rear surface) to prevent rear surface reflection, and measuring the average reflectance at wavelengths of 380 to 780 nm using a spectrophotometer (product name "UV-2450" manufactured by Shimadzu Corporation).

[0173] <Film Thickness> 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 Corporation), measuring the film thickness of each layer at 20 locations on the image of the cross section, and calculating the arithmetic average of the film thicknesses at those 20 locations. The cross-sectional photograph of the optical film was taken as follows. First, a 1 mm x 10 mm piece of optical film was cut out and embedded in an embedding resin to prepare a block. From this block, a uniform slice with a thickness of 70 nm to 100 nm and no holes was cut using a general slice preparation method. An "Ultramicrotome EM UC7" (Leica Microsystems) or the like was used to prepare the slice. This uniform slice with no holes was used as the measurement sample. Then, a cross-sectional photograph of the measurement sample was taken using a scanning transmission electron microscope (STEM). When taking this cross-sectional photograph, STEM observation was performed with the detector set to "TE," the acceleration voltage set to "30 kV," and the emission current set to "10 μA." The magnification was adjusted appropriately from 5,000x to 200,000x while adjusting the focus and observing whether the contrast and brightness of each layer could be distinguished. Furthermore, when taking the cross-sectional photograph, the aperture was set to "Beam monitor aperture 3," the objective lens aperture to "3," and the WD to "8 mm."

[0174] <Evaluation of Interference Fringes> The optical films according to the examples and comparative examples were evaluated for the presence or absence of interference fringes. Specifically, a black acrylic plate was attached to the back surface of each optical film via a transparent adhesive to prevent back surface reflection, and light was irradiated onto each optical film from the front surface side, and the optical film was visually observed for the presence or absence of interference fringes. A three-wavelength fluorescent lamp was used as the light source. The occurrence of interference fringes was evaluated according to the following criteria: ◯: No interference fringes were observed. Δ: Some interference fringes were observed, but at a level that was not problematic in practical use. ×: Interference fringes were clearly observed.

[0175] <Continuous foldability and adhesion of optical film before durability test> An optical film was cut into a 30 mm x 100 mm rectangle to prepare a sample. This sample was attached to a durability tester (product name "DLDMLH-FS", manufactured by Yuasa System Equipment Co., Ltd.) with the short sides (30 mm) of the sample fixed with fixing parts, and the minimum distance between the two opposing sides was 10 mm as shown in FIG. 2 (B). A continuous folding test (a test in which the hard coat layer was folded on the inside and the substrate, resin layer B, or adhesive layer was folded on the outside) was performed 10,000 times to check for any gaps between the substrate and the functional layer, and to check for any cracks or breaks in the bent portions. The results of the continuous folding test were divided into continuous foldability and adhesion and evaluated according to the following criteria. The samples used in the continuous folding test were cut from the optical film before the durability test described below was performed. (Continuous folding property) ◯: In the continuous folding test, no cracks or breaks occurred at the bent portions. △: In the continuous folding test, some cracks or breaks occurred at the bent portions, but at a level that does not pose a problem in practical use. ×: In the continuous folding test, cracks or breaks clearly occurred at the bent portions. (Adhesion) ◯: In the continuous folding test, no lifting occurred between the substrate and the hard coat layer. △: In the continuous folding test, some lifting occurred between the substrate and the hard coat layer, but at a level that does not pose a problem in practical use. ×: In the continuous folding test, lifting clearly occurred between the substrate and the hard coat layer.

[0176] <Continuous foldability and adhesion of optical film after durability test> A durability test was performed in which the optical film was left in an environment of 60 ° C. and 90% relative humidity for 12 hours. After the durability test, the optical film was cut into a 30 mm x 100 mm rectangle to prepare a sample. The sample was attached to a durability tester (product name "DLDMLH-FS", manufactured by Yuasa System Equipment Co., Ltd.) with the short sides (30 mm) of the sample fixed with the fixing parts, and attached so that the minimum distance between the two opposing sides was 10 mm as shown in FIG. 2 (B). A continuous folding test (a test in which the surface side of the sample was folded 180 ° with the functional layer on the inside and the substrate, resin layer B, or adhesive layer on the outside) was performed 10,000 times, and the occurrence of any lift (gaps) between the substrate and the functional layer was examined, as well as the occurrence of any cracks or breaks in the bent portions. The results of the continuous folding test were divided into continuous foldability and adhesion and evaluated according to the following criteria. (Continuous folding property) ◯: In the continuous folding test, no cracks or breaks occurred at the bent portions. △: In the continuous folding test, some cracks or breaks occurred at the bent portions, but at a level that does not pose a problem in practical use. ×: In the continuous folding test, cracks or breaks clearly occurred at the bent portions. (Adhesion) ◯: In the continuous folding test, no lifting occurred between the substrate and the hard coat layer. △: In the continuous folding test, some lifting occurred between the substrate and the hard coat layer, but at a level that does not pose a problem in practical use. ×: In the continuous folding test, lifting clearly occurred between the substrate and the hard coat layer.

[0177] <Pencil Hardness> The pencil hardness of the surface of the optical film was measured according to JIS K5600-5-4:1999. The pencil hardness test was performed by fixing an optical film cut into a size of 30 mm x 100 mm on a glass plate with Cellotape (registered trademark) manufactured by Nichiban Co., Ltd. so as to prevent folds or wrinkles, and using a pencil hardness tester (product name "Pencil Scratch Coating Hardness Tester (electric type)" manufactured by Toyo Seiki Seisaku-sho, Ltd.) to the surface of the optical film, moving a pencil (product name "Uni" manufactured by Mitsubishi Pencil Co., Ltd.) at a moving speed of 1 mm / sec while applying a load of 750 g to the pencil. The pencil hardness was defined as the highest hardness that did not scratch the surface of the optical film in the pencil hardness test. When measuring the pencil hardness, a plurality of pencils with different hardnesses are used, and the pencil hardness test is performed five times for each pencil. If no scratches are visually observed on the surface of the optical film when the surface of the optical film is observed through a fluorescent lamp four or more times out of the five times, it is determined that the pencil of that hardness did not scratch the surface of the optical film. Note that the optical film used was the optical film before the durability test.

[0178] <Peel Charging Resistance> A protective film was attached to the surface of the optical film, and the amount of peeling charge was measured when the protective film was peeled from the surface of the optical film to evaluate the magnitude of the peeling charge. Specifically, a protective film with an adhesive layer (product name "SAT2038T-JSL", manufactured by San-A Kaken Co., Ltd.) was attached to the surface of the optical film, and the protective film was peeled at an angle of 180° from the surface of the optical film at a peeling rate of 300 mm / min under an environment of 23°C and 50% relative humidity. The potential of the surface of the optical film was measured from a distance of 50 mm from the surface using a static meter (product name "KSD-0103", manufactured by Kasuga Electric Co., Ltd.), thereby measuring the amount of peeling charge. The amount of peeling charge was measured 10 times on the surface of the optical film, and the arithmetic mean value of the 10 measurements was used. The evaluation criteria were as follows. Note that the optical film used was an optical film before the durability test. ○: The amount of peeling charge on the surface of the optical film was within the range of -10 kV to 10 kV. x: The amount of charge on the surface of the optical film after peeling exceeded ±10 kV.

[0179] <Yellow Index (YI)> The yellow index of each optical film was measured. Specifically, an optical film cut into a size of 50 mm x 50 mm was placed in a spectrophotometer (product name "UV-2450," manufactured by Shimadzu Corporation; light source: tungsten lamp and deuterium lamp) with the substrate side of the optical film facing the light source. The optical film was free of defects (contamination of foreign matter), cracks, wrinkles, and stains, and was held in the spectrophotometer in a flat, curled state. In this state, transmittance was measured at wavelengths of 300 nm to 780 nm at least five points within 1 nm before and after each point under the following measurement conditions, and the average value was calculated to determine the yellow index. The transmittance measurement data was then read on a monitor connected to the UV-2450, and the YI was obtained by checking "YI" in the calculation item. The optical film used was the optical film before the durability test. (Measurement conditions) Wavelength range: 300 nm to 780 nm Scan speed: High speed Slit width: 2.0 Sampling interval: Auto (0.5 nm intervals) Illumination: C Light source: D2 and WI Field of view: 2° Light source switching wavelength: 360 nm S / R switching: Standard Detector: PM Auto zero: Performed at 550 nm after baseline scan

[0180] <Measurement of Total Light Transmittance> The total light transmittance of the optical film was measured using a haze meter (product name "HM-150", manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K7361-1:1997. The optical film was cut into a size of 50 mm x 100 mm, and then placed in a state free of curls, wrinkles, fingerprints, dust, etc., with the hard coat layer side facing away from the light source. The total light transmittance was measured three times for each optical film, and the arithmetic mean value of the values ​​obtained from the three measurements was used. Note that the optical film used was an optical film before the durability test.

[0181] <Measurement of G', G" and tanδ> The shear storage modulus G', shear loss modulus G", and shear loss tangent tanδ of the optical film were measured. Specifically, the optical film was first punched into a rectangular shape measuring 10 mm x 5 mm to prepare a sample. Two of these samples were then prepared and attached to the measurement jig of a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.). Specifically, the solid shearing jig included a 1 mm-thick metal solid shearing plate and two L-shaped metal fittings arranged on either side of the solid shearing plate. One sample was sandwiched between the solid shearing plate and the L-shaped metal fitting, and the other sample was sandwiched between the solid shearing plate and the other L-shaped metal fitting. In this case, the sample was sandwiched so that the resin layer was facing the solid shearing plate and the hard coat layer was facing the L-shaped metal fitting. The L-shaped metal fittings were then tightened with screws to fix the sample. Next, a dynamic viscoelasticity measuring device (product name "Rheogel-E4000", manufactured by UBM Co., Ltd.) was fitted with a tensile test chuck consisting of an upper chuck and a lower chuck, and a solid shearing jig was placed between the upper and lower chucks with a chuck distance of 20 mm. The temperature was set to 25°C and increased at a rate of 2°C / min. In this state, while the solid shearing plates were fixed, dynamic viscoelasticity measurement of the solid was performed at 25°C while applying longitudinal vibration to the two L-shaped metal fittings with a strain of 1% and a frequency in the range of 500 Hz to 1000 Hz, and the shear storage modulus G', shear loss modulus G'', and shear loss tangent tanδ of the optical film were measured. Here, the shear storage modulus G', shear loss modulus G", and shear loss tangent tanδ of the optical film in the frequency range of 500 Hz to 1000 Hz were determined by applying longitudinal vibrations of 500 Hz, 750 Hz, and 950 Hz to the L-shaped metal fitting, measuring the shear storage modulus G', shear loss modulus G", and shear loss tangent tanδ of the optical film at each frequency, determining the arithmetic mean values ​​of the shear storage modulus G', shear loss modulus G", and shear loss tangent tanδ, and repeating this measurement three times to obtain the arithmetic mean value of the three arithmetic mean values. Note that the optical film used was the optical film before the durability test.

[0182] <Impact Resistance Test> An optical film was placed directly on the surface of a 0.7 mm thick soda glass with the soda glass facing the resin layer, and an impact resistance test A was performed three times. An optical film was placed on the 0.7 mm thick soda glass with the soda glass facing the adhesive layer, via a 200 μm thick adhesive sheet (product name "High Transparency Double-Sided Tape 8146-2", manufactured by 3M). An impact resistance test B was performed three times. The position from which the iron ball was dropped was changed each time. After impact resistance test A, the optical film was visually evaluated for the presence of dents on the surface of the functional layer, and for the presence of cracks in the soda glass. Further, after impact resistance test B, the optical film was visually evaluated for the presence of dents on the surface of the functional layer. (Evaluation of dents on the surface of the hard coat layer) ○: No dents were observed on the surface of the hard coat layer when the hard coat layer was observed from the front and at an angle. △: No dents were observed on the surface of the hard coat layer when the hard coat layer was observed from the front, but dents were observed on the surface of the hard coat layer when observed at an angle. ×: Clear dents were observed on the surface of the hard coat layer when the hard coat layer was observed from the front and at an angle. (Evaluation of cracks in soda glass) ○: The soda glass did not crack. △: The soda glass was scratched but did not crack. ×: Cracks occurred in the soda glass all three times.

[0183] [Polycarbonate polyurethane resin] Synthesis of polycarbonate polyurethane resin (PCPU-1): 29.4 parts by mass of dicyclohexylmethane-4,4'-diisocyanate, 63.6 parts by mass of polycarbonate diol with a melting point of 33°C, mainly composed of 1,5-pentanediol / 1,6-hexanediol (=45 / 55) (molar ratio) having a number average molecular weight of 1000, 7 parts by mass of dimethylolpropionic acid, and 200 parts by mass of ethyl methyl ketone as a solvent, were placed in a four-neck flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, and the mixture was stirred for 3 hours at 75°C under a nitrogen atmosphere. The infrared spectrum of the reaction solution was measured, and the disappearance of the isocyanate groups in the reaction solution was confirmed. Next, the solution was cooled to room temperature, and then 8.2 parts by mass of triethylamine was added to obtain a polycarbonate polyurethane resin (PCPU-1) solution with a solid content of 50.0% by mass.

[0184] Preparation of water dispersion (PCPU-1WD) of polycarbonate polyurethane resin (PCPU-1): A predetermined amount of water was added to a reaction vessel equipped with a homodisperser capable of high speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred for 2000 min. -1 While stirring and mixing at 50°C, the polycarbonate polyurethane resin (PCPU-1) solution was gradually added to disperse it in water. The solvent, ethyl methyl ketone, was then removed under reduced pressure. The concentration was adjusted with water to prepare an aqueous dispersion (PCPU-1WD) of polycarbonate polyurethane resin (PCPU-1) with a solids content of 35.0% by mass.

[0185] <Reduced Viscosity ηsp / c (unit: dl / g) of Polyester Resin> 0.10 g of polyester resin was dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4), and the viscosity was measured at 30° C. using an Ubbelohde viscometer.

[0186] <Polyester Resin Composition> A polyester resin was dissolved in deuterated chloroform, and the resulting solution was analyzed using a Varian Gemini-200 nuclear magnetic resonance analyzer (NMR). 1 H-NMR analysis was carried out and the molar percentage of each component was determined from the integral ratio.

[0187] <Viscosity of Polyester Resin Dispersion> A polyester resin aqueous dispersion was placed in a 140 cc glass bottle, and the bottle was placed in a thermostatic bath at 25° C. using a viscometer model BL (TOKIMEC INC.) with a No. 1 or No. 2 rotor. Measurement was carried out at a rotation speed of 60 rpm for 1 minute to measure the viscosity of the polyester resin aqueous dispersion.

[0188] [Polyester Resin] Production of Polyester Resin (PEs-1): Polyester resin (PEs-1) was polymerized according to a known polymerization method. The composition of the obtained polymer was: 1 H-NMR analysis was performed, and the mole percentage ratio of each component was determined from the integral ratio. The results are shown in Table 4. The reduced viscosity of the resulting polyester resin was 0.493 dl / g. The abbreviations shown in Table 4 are as follows: TPA: terephthalic acid IPA: isophthalic acid NDC: naphthalenedicarboxylic acid SA: sebacic acid DSS: dimethyl-5-sodium sulfoisophthalate EG: ethylene glycol HD: hexanediol DEG: diethylene glycol NPG: neopentyl glycol

[0189] Preparation of polyester aqueous dispersion (PEs-1WD): 30 parts by mass of copolymer polyester resin (PEs-1) and 15 parts by mass of ethylene glycol-n-butyl ether were placed in a reactor equipped with a stirrer, thermometer, and reflux device, and the mixture was heated to 110°C and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to produce a milky white polyester resin (PEs-1) aqueous dispersion (PEs-1WD) with a solids content of 25.1% by mass. The liquid viscosity of the resulting aqueous dispersion was 32 mPa s.

[0190] [Crosslinking Agent] Preparation of Water Dispersion (C-1WD) of Blocked Isocyanate Crosslinking Agent (C-1): 125.2 parts by mass of a polyisocyanate compound having a biuret structure made from hexamethylene diisocyanate (Asahi Kasei Chemicals Corporation, Duranate 24A-100, NCO concentration 23.1%), 50.0 parts by mass of dipropylene glycol dimethyl ether, and 68.8 parts by mass of 3,5-dimethylpyrazole were added to a flask equipped with a stirrer, thermometer, and reflux condenser, and the mixture was stirred at 70°C for 2 hours under a nitrogen atmosphere. The reaction solution was then subjected to infrared spectroscopy to confirm that the absorption of the isocyanate group had disappeared. After cooling to room temperature, 6 parts by mass of polyethylene glycol (n = 12) monolaurate was added, and the mixture was stirred for 2000 min. -1 Water was added while stirring and mixing at 80°C. The concentration was adjusted with water to prepare an aqueous dispersion (C-1WD) of the blocked isocyanate crosslinking agent (C-1) having a solids content of 30.0% by mass.

[0191] <Average particle size of particles> [Measurement method using a scanning electron microscope] The average particle size of particles present in the resin layer in the present invention can be measured by the following method: Particles are photographed using a scanning electron microscope (SEM), and the maximum diameters (the distance between the two most distant points) of 300 to 500 particles are measured at a magnification such that the size of the smallest particle is 2 to 5 mm, and the arithmetic mean of these is taken as the average particle size.

[0192] [Dynamic Light Scattering Method] The average particle size of particles can also be determined by dynamic light scattering during the production of particles or films. The sol is diluted with a dispersion medium, and the average particle size is measured using a submicron particle analyzer N4 PLUS (manufactured by Beckman Coulter) using the parameters of the dispersion medium, and the average particle size is calculated using the cumulant method. In dynamic light scattering, the average particle size of particles in the sol is observed, and if particles aggregate, the average particle size of the aggregated particles is observed.

[0193] <Refractive Index of Particles> The refractive index of particles can be measured by the following method. After inorganic particles are dried at 150°C and pulverized in a mortar, the resulting fine particles are immersed in solvent 1 (having a lower refractive index than the particles), and then solvent 2 (having a higher refractive index than the particles) is added in small amounts until the fine particles become almost transparent. The refractive index of this liquid is measured using an Abbe refractometer (Abbe refractometer manufactured by Atago Co., Ltd.). The measurement was performed at 23°C using D-line (wavelength 589 nm). Solvents 1 and 2 are selected to be mutually miscible, and examples of solvents that can be used depending on the refractive index include 1,1,1,3,3,3-hexafluoro-2-propanol, 2-propanol, chloroform, carbon tetrachloride, toluene, and glycerin.

[0194] (Zirconia Particles) 2,283.6 g of pure water and 403.4 g of oxalic acid dihydrate were added to a 3-liter glass container and heated to 40°C to prepare a 10.72 wt% oxalic acid aqueous solution. While stirring this aqueous solution, 495.8 g of zirconium oxycarbonate powder (ZrOCO3, manufactured by AMR International Corp., containing 39.76 wt% ZrO2) was gradually added and mixed for 30 minutes, followed by heating at 90°C for 30 minutes. Next, 1,747.2 g of a 25.0 wt% aqueous tetramethylammonium hydroxide solution (manufactured by Tama Chemicals Co., Ltd.) was gradually added over 1 hour. At this point, the mixture was in a slurry state and contained 4.0 wt% ZrO2. This slurry was transferred to a stainless steel autoclave container and subjected to hydrothermal treatment at 145°C for 5 hours. The product after this hydrothermal treatment was completely solated with no undissolved matter. The resulting sol contained 4.0% by mass of ZrO2, had a pH of 6.8, and had an average particle size of 19 nm as measured by dynamic light scattering. The sol was adjusted to a ZrO2 concentration of 2.0% by mass with pure water, and the transmittance measured was 88%. Observation of the particles using a transmission electron microscope revealed that most of the particles were aggregates of ZrO2 primary particles of approximately 7 nm. 4,000 g of the zirconia sol with a ZrO2 concentration of 4.0% by mass obtained by the above hydrothermal treatment was washed and concentrated using an ultrafiltration device while gradually adding pure water, yielding 953 g of zirconia sol with a ZrO2 concentration of 13.1% by mass and a transmittance of 76% at a pH of 4.9. The refractive index of the resulting zirconia-based microparticles was 1.75.

[0195] (Zirconia Sol) 3.93 g of 20 wt% citric acid aqueous solution and 11.0 g of 25 wt% tetramethylammonium hydroxide aqueous solution were added to 300 g of zirconia sol with a ZrO concentration of 13.1 wt% obtained by the above washing and concentration, and the mixture was further concentrated using an ultrafiltration device to obtain 129 g of a high-concentration zirconia sol with a ZrO concentration of 30.5 wt%. The obtained high-concentration zirconia sol had a pH of 9.3 and an average particle size of 19 nm as measured by dynamic light scattering. Furthermore, this zirconia sol was free of sediment and stable for more than one month at 50 °C.

[0196] <Composition 1 for Resin Layer A> A coating liquid having the following composition was prepared: Water 42.38 parts by mass Isopropyl alcohol 29.79 parts by mass Zirconia sol 4.50 parts by mass (zirconia sol having an average particle size of 20 nm, solid content concentration 30% by mass) Silica sol 0.87 parts by mass (silica sol having an average particle size of 450 nm, solid content concentration 4% by mass) PCPU-1WD 5.62 parts by mass (solid content concentration 35.0% by mass) PEs-1WD 11.08 parts by mass (solid content concentration 25.1% by mass) C-1WD 5.20 parts by mass (solid content concentration 30.0% by mass) Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10.0% by mass) High-boiling-point solvent 0.26 parts by mass

[0197] <Composition 2 for Resin Layer A> A coating liquid having the following composition was prepared: Water 40.30 parts by mass Isopropyl alcohol 29.79 parts by mass Zirconia sol 4.50 parts by mass (zirconia sol having an average particle size of 20 nm, solid content concentration 30% by mass) Silica sol 0.87 parts by mass (silica sol having an average particle size of 450 nm, solid content concentration 4% by mass) PCPU-1WD 1.31 parts by mass (solid content concentration 35.0% by mass) PEs-1WD 17.46 parts by mass (solid content concentration 25.1% by mass) C-1WD 5.20 parts by mass (solid content concentration 30.0% by mass) Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10.0% by mass) High-boiling-point solvent 0.26 parts by mass

[0198] <Composition 1 for Resin Layer B> A coating liquid having the following composition was prepared: Water 52.75 parts by mass Isopropyl alcohol 30.95 parts by mass Zirconia sol 2.60 parts by mass (zirconia sol having an average particle size of 20 nm, solid content concentration 30% by mass) Silica sol 0.50 parts by mass (silica sol having an average particle size of 450 nm, solid content concentration 4% by mass) PCPU-1WD 3.25 parts by mass (solid content concentration 35.0% by mass) PEs-1WD 6.40 parts by mass (solid content concentration 25.1% by mass) C-1WD 3.00 parts by mass (solid content concentration 30.0% by mass) Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10.0% by mass) High-boiling-point solvent 0.26 parts by mass

[0199] <Composition 2 for Resin Layer B> A coating liquid having the following composition was prepared: Water 51.56 parts by mass Isopropyl alcohol 30.95 parts by mass Zirconia sol 2.60 parts by mass (zirconia sol having an average particle size of 20 nm, solid content concentration 30% by mass) Silica sol 0.50 parts by mass (silica sol having an average particle size of 450 nm, solid content concentration 4% by mass) PCPU-1WD 0.76 parts by mass (solid content concentration 35.0% by mass) PEs-1WD 10.08 parts by mass (solid content concentration 25.1% by mass) C-1WD 3.00 parts by mass (solid content concentration 30.0% by mass) Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10.0% by mass) High-boiling-point solvent 0.26 parts by mass

[0200] <Composition 1 for Functional Layer> A coating liquid having the following composition was prepared: Isopropanol 21.00 parts by mass Toluene 49.00 parts by mass Pentaerythritol triacrylate 21.38 parts by mass (A-TMM-3 manufactured by Shin-Nakamura Chemical Co., Ltd.) Urethane acrylate 7.12 parts by mass (Shikou UV-7600B manufactured by Mitsubishi Chemical Corporation) Photopolymerization initiator 1.50 parts by mass (Omnirad 184 manufactured by IGM Resins B.V.)

[0201] <Composition 2 for Functional Layer> A coating liquid having the following composition was prepared: 64.40 parts by mass of methyl ethyl ketone, 27.20 parts by mass of dipentaerythritol hexaacrylate (A-DPH manufactured by Shin-Nakamura Chemical Co., Ltd.), 3.40 parts by mass of polyethylene glycol diacrylate (Light Acrylate 9EG-A manufactured by Kyoeisha Chemical Co., Ltd.), 4.00 parts by mass of bisphenol A diacrylate (Light Acrylate BP-4PA manufactured by Kyoeisha Chemical Co., Ltd.), 1.00 parts by mass of photopolymerization initiator (Omnirad 184 manufactured by IGM Resins B.V.).

[0202] <Composition for adhesive layer> A coating liquid having the following composition was prepared: 10.00 parts by mass of methyl isobutyl ketone, 72.25 parts by mass of urethane acrylate (UV3310B manufactured by Nippon Synthetic Chemical Industry), 12.75 parts by mass of phenoxyethyl acrylate (Viscoat #192 manufactured by Osaka Organic Chemical Industry), 5.00 parts by mass of photopolymerization initiator (Omnirad 184 manufactured by IGM Resins B.V.).

[0203] Example 1 A polyester-based substrate having a refractive index of 1.650 and a thickness of 50 μm was prepared as a polyester film substrate. Resin layer A composition 1 was applied to one side (a first surface) of the polyester-based substrate using a bar coater to form a coating film. The formed coating film was then heated at 90°C for 1 minute to evaporate the solvent in the coating film, and then heated at 230°C for 1 minute to cure the coating film, thereby forming a resin layer A-1 having a refractive index of 1.57 and a thickness of 100 nm. Functional layer composition 1 was applied to the surface of resin layer A-1 using a bar coater to form a coating film. The formed coating film was then heated at 70°C for 1 minute to evaporate the solvent in the coating film, and then ultraviolet light was applied to the surface of resin layer A-1 using an ultraviolet irradiation device (manufactured by Fusion UV Systems Japan, light source H bulb) at an integrated light intensity of 200 mJ / cm in air. 2 The coating film was cured by irradiating the resin layer B with light at a refractive index of 1.52, forming a functional layer-1 with a thickness of 5 μm. Subsequently, resin layer B composition 1 was applied to the surface opposite to the applied functional layer-1, i.e., the second surface of the polyester substrate, using a bar coater to form a coating film. The formed coating film was then heated at 90°C for 1 minute to evaporate the solvent in the coating film, and then heated at 230°C for 1 minute to cure the coating film, forming a resin layer B-1 with a refractive index of 1.57 and a thickness of 50 nm. Furthermore, a pressure-sensitive adhesive layer composition was applied to the surface of resin layer B-1 with a bar coater to form a coating film. The formed coating film was then heated at 70°C for 1 minute to evaporate the solvent in the coating film, and then irradiated with ultraviolet light in air at an integrated light intensity of 1200 mJ / cm using an ultraviolet irradiation device (Fusion UV Systems Japan, light source H bulb). 2 The coating was cured by irradiating the coating with light so that the refractive index was 1.50 and the thickness was 50 μm, forming a resin layer made of a urethane resin. This resulted in an optical film in which resin layer A was adjacent to the functional layer and resin layer B was adjacent to the adhesive layer, separated by a polyester film as a substrate. The various evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0204] Example 2, Example 3, Comparative Example 2 Optical films were produced in the same manner as in Example 1, except that the thickness of the resin layer A to be formed was changed to the thickness shown in Table 1. The results of various evaluations of the obtained optical films are as shown in Tables 2 and 3.

[0205] Example 4 An optical film was produced in the same manner as in Example 1, except that the thickness of the resin layer B to be formed was changed to the thickness shown in Table 1. The various evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0206] Example 5 An optical film was produced in the same manner as in Example 1, except that resin layer B was not formed and an adhesive layer was provided directly on the second surface of the polyester-based substrate. The evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0207] Example 6 Before forming the resin layer A-1, the resin layer A composition 2 was applied adjacently to the first surface of the polyester substrate using a bar coater to form a coating film. The formed coating film was then heated at 90°C for 1 minute to evaporate the solvent in the coating film, and then heated at 230°C for 1 minute to cure the coating film, thereby forming a resin layer C having a refractive index of 1.60 and a film thickness of 100 nm. A resin layer A-1 was formed on the surface of the resin layer C in the same manner as in Example 1. Thereafter, an optical film was produced in the same manner as in Example 1. The various evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0208] Example 7 An optical film was produced in the same manner as in Example 1, except that resin layer A-2 was formed instead of resin layer A-1 using resin layer A-composition 2 instead of resin layer A-composition 1 in the same manner as in Example 1. The evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0209] Example 8 An optical film was produced in the same manner as in Example 1, except that resin layer B-2 was formed instead of resin layer B-1 using composition 2 for resin layer B instead of composition 1 for resin layer B in the same manner as in Example 1. The evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0210] Examples 9 and 10 Optical films were produced in the same manner as in Example 1, except that the thickness of the functional layer was changed to the film thickness shown in Table 1. The evaluation results of the obtained optical films are as shown in Tables 2 and 3.

[0211] Examples 11 and 12 Optical films were produced in the same manner as in Example 1, except that the thickness of the formed adhesive layer was changed to the film thickness shown in Table 1. The evaluation results of the obtained optical films are as shown in Tables 2 and 3.

[0212] Example 13 An optical film was produced in the same manner as in Example 1, except that functional layer composition 2 was used instead of functional layer composition 1, the film thickness was adjusted to the value shown in Table 1, and functional layer 2 was formed instead of functional layer 1 in the same manner as in Example 1. The various evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0213] Example 14 An optical film was produced in the same manner as in Example 13, except that resin layer A-2 was formed instead of resin layer A-1 using resin layer A-composition 2 instead of resin layer A-composition 1 in the same manner as in Example 13. The evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0214] Comparative Example 1 An optical film was produced in the same manner as in Example 1, except that a functional layer was provided directly on the first surface of the polyester-based substrate without forming resin layer A, and that an adhesive layer was provided directly on the second surface of the polyester-based substrate without forming resin layer B. The evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0215] Comparative Example 3 An optical film was produced in the same manner as in Example 1, except that a functional layer was provided directly on the first surface of the polyester-based substrate without forming resin layer A. The evaluation results of the obtained optical film are as shown in Tables 2 and 3.

[0216] Comparative Example 4 An optical film was produced in the same manner as in Example 1, except that the thickness of the resin layer B was set to 350 nm. The evaluation results of the obtained optical film are shown in Tables 2 and 3.

[0217]

[0218]

[0219]

[0220]

[0221] The optical film of the present invention is suitable for use as a foldable optical film, has high adhesion reliability between the functional layer and the substrate, and is excellent in optical interference. It also has excellent reliability as an image display device, and can be widely used in optical applications, etc.

[0222] REFERENCE SIGNS LIST 10 Optical film 11 Polyester film 11A First surface of substrate 11B Second surface of substrate 12 Functional layer 13 Resin layer A 14 Resin layer C 15 Resin layer B 20 Fixing portion 41 Adhesive layer

Claims

1. A foldable optical film for use in an image display device, comprising: a polyester film as a substrate; a functional layer provided on a first surface of the substrate; a resin layer A provided between the substrate and the functional layer; and a resin layer B provided on a second surface of the substrate opposite the first surface, wherein the resin layer A has a film thickness of 10 nm or more and 500 nm or less, and the resin layer B has a film thickness of 1 nm or more and 200 nm or less, and wherein the optical film does not crack or break when a test in which the optical film is folded 180 degrees so that the functional layer is on the inside and the distance between opposing sides of the optical film is 10 mm is repeated 10,000 times.

2. The optical film according to claim 1, wherein the refractive index of the resin layer A is lower than the refractive index of the substrate and higher than the refractive index of the functional layer.

3. The optical film according to claim 1, wherein a resin layer C is provided between the substrate and the resin layer A.

4. The optical film according to claim 3, wherein the thickness of the resin layer C is 30 nm or more and 200 nm or less.

5. The optical film according to claim 1, further comprising an adhesive layer on a second surface of the polyester film as the substrate opposite to the first surface, wherein the adhesive layer has a thickness of 25 μm or more and 300 μm or less, wherein the optical film has a shear storage modulus G' of more than 200 MPa and 1200 MPa or less at 25°C and in a frequency range of 500 Hz or more and 1000 Hz or less, and wherein the optical film has a shear loss modulus G'' of 3 MPa or more and 150 MPa or less at 25°C and in a frequency range of 500 Hz or more and 1000 Hz or less.

6. The optical film according to claim 5, wherein the resin layer B is provided between the substrate and the adhesive layer.

7. The optical film according to claim 1, wherein the yellow index of the optical film is 15 or less.

8. The optical film according to claim 1, wherein the optical film does not crack or break when a test in which the optical film is folded 180° so that the functional layer is on the outside and the distance between opposing sides of the optical film is 30 mm is repeated 10,000 times.

9. The optical film according to claim 1, wherein the resin layer A is a cured layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (A-1), a polyester resin (A-2), a blocked isocyanate crosslinking agent (A-3), and particles (A-4), and the polyester resin (A-2) has a condensed polycyclic aromatic structure.

10. The optical film according to claim 1, wherein the resin layer B is a cured layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (B-1), a polyester resin (B-2), a blocked isocyanate crosslinking agent (B-3), and particles (B-4), and the polyester resin (B-2) has a condensed polycyclic aromatic structure.

11. The optical film according to claim 3, wherein the resin layer C is a cured layer of a cured resin composition formed from a composition containing a polycarbonate polyurethane resin (C-1), a polyester resin (C-2), a blocked isocyanate crosslinking agent (C-3), and particles (C-4), and the polyester resin (C-2) has a condensed polycyclic aromatic structure.

12. The optical film according to claim 9, 10 or 11, wherein at least one of the polyester resins (A-2), (B-2) and (C-2) having a condensed polycyclic aromatic structure contained in the resin layer A, resin layer B and resin layer C has a naphthalene skeleton in the molecule.

13. A method for producing an optical film according to claim 1, comprising producing a functional layer on the first surface side of the polyester film as the substrate by a coating process.

14. A foldable image display device comprising: a display element; and the optical film according to claim 1, which is disposed closer to a viewer than the display element.

15. The image display device according to claim 14, wherein the display element is an organic light-emitting diode element.