Optical film and image display device

Abstract

This optical film includes, on at least one surface of a resin base material, a primer layer and an optical functional layer, in that order. The value of a hue a* of SCE reflection light is -2.0 to +2.0, and the value of a hue b* of the SCE reflection light is -3.0 to +3.0. Preferably, the optical film has a spectral transmittance of 67.0% or less at a wavelength of 390 nm and 86.0% or less at a wavelength of 400 nm. Preferably, the optical functional layer of the optical film is a UV-blocking hard coat layer. Preferably, the film thickness of the primer layer of the optical film is 70 nm to 120 nm.

Description

Optical films and image display devices

[0001] This invention relates to an optical film and an image display device using the same.

[0002] With the increasing size of smartphones and tablet devices, the development of foldable image display devices is progressing.

[0003] For example, Patent Document 1 discloses that an optical film is provided on a resin substrate made of one or more resins selected from polyimide resins, polyamideimide resins, polyamide resins, and polyester resins, with a first optical adjustment layer of 30 nm to 200 nm on a first surface, a third optical adjustment layer of 30 nm to 1 μm on a second surface opposite to the first surface, and a functional layer further provided on the first optical adjustment layer, and that no cracks or breaks occur when the optical film is folded 10,000 times with the functional layer facing inward.

[0004] Japanese Patent Publication No. 2018-159913

[0005] When laminating an optical functional layer onto a resin substrate, a primer layer may be formed on top of the resin substrate to ensure proper adhesion. Although the primer layer is a thin film, it exhibits adhesion to both the resin substrate and the optical functional layer, effectively enhancing the performance of the optical film. For example, in the case of a foldable optical film, ensuring sufficient adhesion improves flexural durability (bending resistance).

[0006] However, the inventors have found that a substrate with a laminated primer layer has the problem that when incident light with wavelengths in the short wavelength range is passed through the primer layer, the diffusion becomes significant, and the reflected light becomes bluish.

[0007] The present invention relates to a foldable optical film and an image display device using the same, which, while having a primer layer, suppresses diffuse reflection by incident light having wavelengths in the short wavelength range and exhibits minimal hue variation in reflected light.

[0008] The present invention relates to the following [1] and [2]. [1] A primer layer and an optical functional layer are provided in this order on at least one surface of a resin substrate, and the hue a of the SCE reflected light ＊ The value of is between -2.0 and +2.0, and the hue b ＊ An optical film in which the value of is -3.0 or greater and +3.0 or less. [2] An image display device comprising the optical film described in [1].

[0009] The optical film of the present invention, while having a primer layer, exhibits excellent effects such as suppressing diffuse reflection by incident light having wavelengths in the short wavelength range and minimizing hue variation of reflected light.

[0010] Figure 1 is a schematic cross-sectional view showing an example of the optical film of the present invention. Figure 2 is a schematic cross-sectional view showing another example of the optical film of the present invention. Figure 3 is a schematic cross-sectional view showing yet another example of the optical film of the present invention. Figure 4 is an enlarged graph showing an example of the spectral transmittance of the optical film of the present invention in the range of 385 nm to 405 nm.

[0011] Figure 1 is a schematic cross-sectional view showing an example of an optical film according to the embodiment.

[0012] The optical film 10 comprises a resin substrate 1, and on one side of the resin substrate 1, a primer layer 2 and an optical functional layer 3 in that order.

[0013] The details of each layer are explained below.

[0014] The resin substrate 1 is a film that serves as the base for an optical film and is formed from a material with excellent visible light transmittance. As the material for forming the resin substrate 1, various transparent resins and inorganic glasses can be used, including polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polyamides such as nylon 6 and nylon 66, polyimide, polyarylate, polycarbonate, triacetylcellulose, polyvinyl alcohol, polyvinyl chloride, cycloolefin copolymers, norbornene-containing resins, polyethersulfone, and polysulfone. Among these, polyester resins, polyimide resins, and polyamide resins are preferred from the viewpoint of providing transparency and flexibility, and polyimide, polyamide, polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are more preferred.

[0015] The thickness of the resin substrate 1 is not particularly limited, but from the viewpoint of improving bending resistance, it is preferably 100 μm or less, more preferably 80 μm or less. The lower limit is not particularly limited, but from the viewpoint of strength, it may be 5.0 μm or more, or 10 μm or more.

[0016] Furthermore, the resin substrate 1 may be subjected to surface modification treatment from the viewpoint of improving adhesion with other layers. Examples of surface modification treatments include alkali treatment, corona treatment, plasma treatment, sputtering, application of surfactants or silane coupling agents, and Si deposition.

[0017] The primer layer 2 functions as an easy-adhesion layer that improves the adhesion between the resin substrate 1 and the optical functional layer 3, thereby further improving bending resistance.

[0018] The primer layer 2 can be formed, for example, by coating the surface of the resin substrate 1 with a primer layer-forming composition containing at least an active energy ray-curable compound (described later) and curing it. The primer layer-forming composition may be a prepared one or a known one (e.g., an anchor coating agent).

[0019] Furthermore, additives such as refractive index adjusters, diffusing agents, photosensitizers, conductive materials, and leveling agents may be added to the primer layer-forming composition as needed. Fine particles to prevent the layers from sticking together may also be added. In this invention, the primer layer may also have a UV-cutting function; for example, the primer layer-forming composition may contain an ultraviolet absorber.

[0020] Furthermore, as shown in Figure 2, the other side of the resin substrate 1 may have a primer layer 2 laminated on it to improve adhesion to other layers (for example, an adhesive layer for display lamination). Another example of an optical film according to the embodiment is an optical film 20 which comprises a resin substrate 1, a primer layer 2 and an optical functional layer 3 in that order on one side of the resin substrate 1, and a primer layer 2 on the other side of the resin substrate 1.

[0021] The thickness of the primer layer 2 is not particularly limited, but from the viewpoint of adhesion, it is preferably 40 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, and from the viewpoint of thinning, it is preferably 500 nm or less, and more preferably 400 nm or less.

[0022] Furthermore, the hue variation of reflected light can also be suppressed by reducing the thickness of the primer layer 2. The lower limit is preferably 40 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoint of adhesion, while the upper limit is preferably 120 nm or less, more preferably 100 nm or less, even more preferably 90 nm or less, even more preferably 80 nm or less, and even more preferably 75 nm or less. Within the above range, it is possible to reduce diffuse reflection via the primer layer while exhibiting adhesion to both the resin substrate and the optical functional layer, thereby achieving both an improved bending resistance effect and an effect of suppressing hue variation of reflected light. Note that if the thickness of the primer layer 2 is within the above range (for example, 40 nm or more and 120 nm or less), the presence or absence of ultraviolet (UV) cut function of the optical functional layer 3 is irrelevant, and if it has an ultraviolet (UV) cut function, the effects of the present invention will be synergistically achieved.

[0023] The refractive index of the primer layer 2 is not particularly limited, but it may be designed so that the optical film thickness (nd), obtained by multiplying the film thickness of the primer layer by the refractive index of the primer layer, is approximately equal to 1 / 4 of the wavelength to be suppressed (e.g., 380 to 430 nm). For example, when the film thickness is 70 nm or more and 120 nm or less, the refractive index is preferably 1.53 or more and 1.62 or less. A suitable range for the optical film thickness of the primer layer 2 is, for example, 110.6 nm or more and 189.6 nm or less.

[0024] The optical functional layer 3 is laminated on the primer layer 2 and exhibits ultraviolet (UV) cut functionality, thereby suppressing hue fluctuations of reflected light. It also improves the hardness while providing flexibility to the optical film, thereby improving bending resistance and pencil hardness. Examples of UV cut functionality include UV absorption, UV shielding, and UV scattering. In this invention, any of these functions is acceptable as long as the amount of UV reaching the primer layer is reduced, and this can be achieved by using a known UV cut agent. An example of an optical functional layer according to this embodiment is a UV-cut hard coat layer.

[0025] A UV-cut hard coat layer can be formed by applying and curing a hard coat layer-forming composition containing an active energy ray-curable compound, a UV-cutting agent, a photopolymerization initiator, and a solvent.

[0026] Active energy ray curable compounds are resins that polymerize and harden upon irradiation with active energy rays such as ultraviolet rays and electron beams. For example, monofunctional, bifunctional, or trifunctional (meth)acrylate monomers can be used. In this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

[0027] Examples of monofunctional (meth)acrylate monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfluryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isobornyl (meth)acrylate. Lilate, Isodecyl (meth)acrylate, Lauryl (meth)acrylate, Tridecyl (meth)acrylate, Cetyl (meth)acrylate, Stearyl (meth)acrylate, Benzyl (meth)acrylate, 2-Ethoxyethyl (meth)acrylate, 3-Methoxybutyl (meth)acrylate, Ethyl carbitol (meth)acrylate, Phosphate (meth)acrylate, Ethylene oxide-modified Phosphate (meth)acrylate, Phenoxy (meth)acrylate, Ethylene oxide-modified Phenoxy (meth)acrylate, Propylene oxide Phenoxy(meth)acrylate modified with ethylene oxide, nonylphenol(meth)acrylate, ethylene oxide modified nonylphenol(meth)acrylate, propylene oxide modified nonylphenol(meth)acrylate, methoxydiethylene glycol(meth)acrylate, methoxypolyethylene glycol(meth)acrylate, methoxypropylene glycol(meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, 2-(meth) Acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane,Examples include adamantane derivative mono(meth)acrylates such as adamantyl acrylate, which has a monovalent mono(meth)acrylate derived from adamantanediol.

[0028] Examples of difunctional (meth)acrylate monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, and other di(meth)acrylates.

[0029] Examples of trifunctional (meth)acrylate monomers include trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, glycerin tri(meth)acrylate, and other trifunctional (meth)acrylate monomers such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate. Examples include polyfunctional (meth)acrylate monomers with three or more functions, such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate, as well as polyfunctional (meth)acrylate monomers in which some of these (meth)acrylates are substituted with alkyl groups or ε-caprolactone.

[0030] Furthermore, urethane (meth)acrylates can also be used as polyfunctional monomers. Examples of urethane (meth)acrylates include those obtained by reacting a product obtained by reacting a polyester polyol with an isocyanate monomer or prepolymer with a hydroxyl group (meth)acrylate monomer.

[0031] Examples of urethane (meth) acrylates include pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, and the like.

[0032] The above-mentioned active energy ray-curable compound may be used alone or in combination of two or more. Further, the active energy ray-curable compound may be a monomer or an oligomer in which a part is polymerized in the coating liquid.

[0033] The content of the active energy ray-curable compound is not particularly limited. For example, it is 10% by mass or more and 90% by mass or less of the total solid content. In this specification, the total solid content indicates the total content of all components other than the solvent of the composition.

[0034] The UV cut agent is added to reduce the amount of ultraviolet rays reaching the primer layer, suppress diffuse reflection caused by the primer layer, particularly suppress diffuse reflection by incident light having a wavelength in the short wavelength range, and suppress the reflected light from becoming bluish. Further, since the light resistance is exhibited, a decrease in the adhesion between the primer layer and the optical functional layer is suppressed, so that the bending resistance can also be improved. Examples of the UV cut agent include a UV absorber, a UV shielding agent, a UV scattering agent, etc. From the viewpoint of reducing the amount of ultraviolet rays reaching the primer layer, a UV absorber is preferable.

[0035] The UV absorber is not particularly limited as long as it can absorb ultraviolet rays. For example, those having a maximum absorption wavelength of 280 nm or more and 330 nm or less, or those capable of absorbing in the long wavelength region of the ultraviolet region, for example, up to around 390 nm, can be used. Examples of the UV absorber include benzotriazole-based compounds, indole-based compounds, benzophenone-based compounds, triazine-based compounds, etc., and known ones may be used alone or in combination of two or more.

[0036] The content of the UV absorber is not particularly limited as long as it can reduce the amount of ultraviolet rays reaching the primer layer, and is, for example, 3% by mass or more and 7% by mass or less based on the total amount of the solid components. If it is 3% by mass or more, the UV absorption ability in the optical functional layer becomes good, and the suppression effect of diffuse reflection through the primer layer becomes good. Also, if it is 7% by mass or less, the curing inhibition of the active energy ray-curable compound is suppressed, so that the hard coat layer becomes flexible and the bending resistance is improved.

[0037] Further, when adjusting the thickness of the primer layer to suppress the hue variation of the reflected light, the optical functional layer 3 does not necessarily have to have the above-described UV cut function. In that case, an active energy ray-curable compound, a photoinitiator, and a solvent are appropriately selected from materials that can be used in the UV cut hard coat layer, and a hard coat layer-forming composition containing them is applied and cured to form it.

[0038] The photoinitiator may be any one that triggers a polymerization reaction upon irradiation with ultraviolet rays, electron beams, etc. Examples include 2,2-ethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, Michler's ketone, acetophenone, 2-chlorothioxanthone, etc. From the viewpoint of avoiding curing inhibition by the UV absorber, it may be appropriately selected in consideration of the maximum absorption wavelength of the UV absorber. These may be used alone or in combination of two or more.

[0039] The content of the photopolymerization initiator is not particularly limited, but is, for example, 0.010% by mass or more and 20% by mass or less of the total amount of solid components.

[0040] Examples of solvents include ketone solvents such as acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK); alcohol solvents such as ethanol, methanol, isopropyl alcohol (IPA), and isobutanol; ether solvents such as ethylene glycol dimethyl ether and propylene glycol monomethyl ether (PGME); ester solvents such as ethyl acetate, propylene glycol monomethyl ether acetate (PGMEA), and 2-ethoxyethyl acetate; and aromatic hydrocarbon solvents such as toluene. These may be used individually or in combination of two or more.

[0041] The hard coat layer forming composition may contain various additives as needed, such as antistatic agents, defoamers, antioxidants, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, photosensitizers, and surface modifiers. The amounts of these additives can be adjusted as appropriate according to known technology.

[0042] The thickness of the UV-cut hard coat layer is not particularly limited. For example, the lower limit can be 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more, while the upper limit can be 10.0 μm or less, or 8.0 μm or less. Hard coat layers without UV-cut functionality can also be set to a similar thickness.

[0043] The optical film of the present invention may have one or more other functional layers laminated on it, such as an anti-reflective layer, an anti-glare layer, an anti-static layer, an electromagnetic wave shielding layer, an infrared absorption layer, or a color correction layer, as long as the effects of the present invention are not impaired.

[0044] For example, as shown in Figure 3, as yet another example of an optical film according to the embodiment, the optical film 30 comprises a resin substrate 1, a primer layer 2, an optical functional layer 3, and an anti-reflective layer 4 on one side of the resin substrate 1 in that order, and a primer layer 2 on the other side of the resin substrate 1. The primer layers provided on both sides of the resin substrate 1 may be of the same thickness or of different thicknesses.

[0045] The anti-reflective layer 4 is laminated on the optical functional layer 3 to reduce surface reflection of the optical film. Examples of anti-reflective layers include a low refractive index layer, a medium refractive index layer, and a high refractive index layer, and depending on the application, they may be used as a single layer or in combination of multiple layers. For example, an embodiment consisting only of a low refractive index layer, an embodiment in which a low refractive index layer and a high refractive index layer are laminated, and an embodiment in which a low refractive index layer, a high refractive index layer, and a medium refractive index layer are laminated.

[0046] A low refractive index layer has a refractive index lower than that of the underlying layer, which can suppress reflection through optical interference and improve visibility. Examples of refractive indices include those between 1.25 and 1.45.

[0047] A low refractive index layer can be formed by applying a composition containing an active energy ray-curable compound to the surface of a lower layer and curing the coating film. The low refractive index layer may also contain a refractive index adjusting agent for refractive index adjustment.

[0048] Examples of refractive index modifiers include LiF, MgF, 3NaF·AlF or AlF (all with a refractive index of 1.4), or Na ３ AlF ６ Fine particles such as cryolite (refractive index 1.33) and silica fine particles having internal voids can be suitably used. Silica fine particles having internal voids are advantageous for lowering the refractive index of the low refractive index layer because the void portion can have the refractive index of air (approximately 1). Specifically, porous silica particles and silica particles with a shell structure can be used. The content of the refractive index adjusting agent is not particularly limited, but is, for example, 1.0% by mass or more and 60% by mass or less of the total amount of solid components.

[0049] As the active energy ray curable compound, the polymerizable compound described in the section on the optical functional layer can be used. In addition, the polymerization initiator, solvent, additives, etc. mentioned above may be added to the composition for forming the low refractive index layer as appropriate.

[0050] The thickness of the low refractive index layer is not particularly limited; for example, the lower limit can be 50 nm or more and 75 nm or more, while the upper limit can be 200 nm or less and 150 nm or less. From the viewpoint of thinning and suppressing reflectivity, the optical film thickness (nd), obtained by multiplying the film thickness of the low refractive index layer by the refractive index of the low refractive index layer, may be designed to be approximately equal to 1 / 4 of the wavelength of visible light (the wavelength to be suppressed).

[0051] High-refractive-index and medium-refractive-index layers, like low-refractive-index layers, suppress reflection through optical interference. Depending on the layering configuration, the refractive index adjusting agent used can be appropriately adjusted to form them in the same manner as the low-refractive-index layer. When using a low-refractive-index layer in combination with a high-refractive-index layer and / or a medium-refractive-index layer, their refractive indices are not particularly limited and can be used based on relative evaluation.

[0052] The coating method for each of the above-mentioned layer compositions is not particularly limited, and can be used, for example, with a spin coater, roll coater, reverse roll coater, gravure coater, microgravure coater, knife coater, bar coater, wire bar coater, die coater, dip coater, spray coater, applicator, etc.

[0053] The coated composition can be photocured by heating and drying, followed by irradiation with ultraviolet light using a known light source such as a halogen lamp.

[0054] Thus, the optical film of the present invention is obtained. Preferred embodiments of the optical film of the present invention include, for example, those laminated in any of the following configurations selected from (1) to (8): (1) Resin substrate / primer layer / optical functional layer (2) Resin substrate / primer layer / optical functional layer / high refractive index layer / low refractive index layer (3) Resin substrate / primer layer / optical functional layer / medium refractive index layer / high refractive index layer / low refractive index layer (4) Primer layer / resin substrate / primer layer / optical functional layer (5) Primer layer / resin substrate / primer layer / optical functional layer / low refractive index layer (6) Primer layer / resin substrate / primer layer / optical functional layer / high refractive index layer / low refractive index layer (7) Primer layer / resin substrate / primer layer / optical functional layer / medium refractive index layer / high refractive index layer / low refractive index layer (8)

[0055] The thickness of the optical film of the present invention is not particularly limited and may be, for example, 50 μm or more and 120 μm or less.

[0056] The optical film of the present invention, from the viewpoint of suppressing the bluish tint of reflected light, has a spectral transmittance of approximately 4 to 10% lower in the wavelength range of 390 nm to 400 nm compared to an optical film with the same configuration except for the absence of a UV-cut function. Specifically, for example, the spectral transmittance at wavelengths of 390 nm or less is preferably 67.0% or less, more preferably 66.0% or less. The spectral transmittance at wavelengths of 400 nm or less is preferably 86.0% or less, more preferably 85.0% or less. If the spectral transmittance at wavelengths of 390 nm to 400 nm is reduced to this extent, the reflected light will not have a bluish tint, diffuse reflection will be suppressed, transparency will be ensured, and visibility will be good. Therefore, in the present invention, it is preferable to maintain a UV-cut function in the optical functional layer so that the spectral transmittance in the above wavelength range is achieved, and for example, the content can be adjusted according to known technology depending on the type of UV absorber used. In this specification, spectral transmittance is measured using a spectrophotometer (Hitachi High-Tech U-4100) under the conditions of a C light source and a 2-degree field of view. The thickness of the primer layer may also be adjusted in advance so that the spectral transmittance at wavelengths of 390 nm to 400 nm falls within the aforementioned range.

[0057] The optical film of the present invention has a hue a of the reflected light SCE (Special Component Exclude). ＊ The value of is preferably between -2.0 and +2.0, and more preferably between -0.80 and +0.80. Also, hue b ＊ The value of is preferably -3.0 or greater and +3.0 or less, and more preferably -2.0 or greater and +2.0 or less. Generally, when a primer layer is present, diffusion by incident light having wavelengths in the short wavelength range becomes significant, so the hue is prone to change, and in particular hue b ＊ When the absolute value of is large, for example, a value smaller than -3.0 such as -3.1 or -3.3, the color becomes more bluish. However, in this invention, because the optical functional layer has a UV-cutting function, diffuse reflection is suppressed, resulting in a smaller hue change. Furthermore, when the thickness of the primer layer is thin, diffuse reflection itself is suppressed, resulting in a smaller hue change. Note that the above a ＊ and b＊ is the coordinate value in the La ＊ b ＊ color space (CIELAB).

[0058] Also, it is preferable that the reflectance (SCE reflectance) at wavelengths from 390 nm to 400 nm measured by the SCE method is 0.50% or less. If the SCE reflectance is 0.50% or less, diffusion on the outermost surface is sufficiently suppressed, excellent low reflectivity is achieved, and whitening of the appearance due to diffused light can be suppressed. In this specification, the hue a ＊ and b ＊ values and reflectance are measured under the conditions of a D65 light source using a spectrophotometer (CM-2600d, manufactured by Konica Minolta).

[0059] The optical film of the present invention preferably has a visual reflectance of 1.6% or less. If the visual reflectance is 1.6% or less, high antireflection properties can be confirmed visually, which is preferable, and 1.0% or less is more preferable. In this specification, the visual reflectance of the film can be evaluated using a spectrophotometer (U-4100, manufactured by Hitachi, Ltd.).

[0060] The optical film of the present invention preferably has a transmitted YI value (in accordance with JIS K 7373) of 3.5 or less, and more preferably 2.5 or less. If the transmitted YI value is 3.5 or less, the yellowness is good (less yellowish).

[0061] The optical film of the present invention preferably has a total haze (in accordance with JIS K 7136) of 1.0% or less. If the total haze is 1.0% or less, diffuse reflection is suppressed, transparency can be ensured, and visibility is good.

[0062] The optical film of the present invention preferably has a stretch ratio (tensile elongation, elongation at break) of 10.0% or more, and more preferably 11.0% or more. A stretch ratio of 10.0% or more results in excellent stretchability and good repeated bending properties. A higher value indicates better repeated bending properties. In this specification, the stretch ratio of the film is determined by stretching a test piece cut to 100 x 10 mm using a tensile testing machine (chuck distance 50 mm, tensile speed 10 mm / min (usually within the range of 5 to 10 mm / min)), measuring the amount of film stretch when a crack appears visually, and calculating the rate of change from before stretching.

[0063] The optical film of the present invention, when a surface-type unloaded U-shaped stretch test fixture (DMX-FS) is attached to a benchtop durability test machine (manufactured by Yuasa System Equipment), a sample is attached so that it is flat, and the optical functional layer is facing inward while the distance between opposing surfaces is 10 mm, is continuously folded 180°. Even after 300,000 continuous folding operations, no cracks or fractures can be visually confirmed at the bent portion. A higher number of folds without cracking or fracturing indicates higher bending resistance.

[0064] The optical film of the present invention exhibits good adhesion both before and after the lightfastness test. The lightfastness test was conducted using an iSuper UV tester (metal halide lamp type weather meter, manufactured by Iwasaki Electric) under conditions of a temperature of 62°C and a relative humidity of 45%, with an irradiation dose of 75 mW / cm². ２ The test is performed by irradiating the optical functional layer surface with ultraviolet light for 3 hours. Adhesion can be evaluated by performing a cross-cut test in accordance with JIS K 5600 and determining the percentage of the area of ​​the optical functional layer that remains without peeling, thereby representing the adhesion of the optical functional layer to the resin substrate. The peeling state is classified into 6 stages from 0 to 5, with classification 0 to 1 indicating good adhesion. The optical film of the present invention preferably has no change in adhesion before and after the lightfastness test, preferably has adhesion corresponding to classification 0 to 1, and more preferably has adhesion corresponding to classification 0.

[0065] The present invention also provides an image display device comprising the optical film of the present invention. The image display device is not particularly limited as long as it is a foldable display device, and examples of foldable devices include smartphones, tablets, portable game consoles and other personal information terminals. It may also be a rollable display device, for example, it may be applied to a rollable television. On the other hand, it may also be applied to non-foldable devices, such as televisions, monitors, mobile phones, portable game consoles, personal information terminals, personal computers, e-books, video cameras, digital still cameras, head-mounted displays and navigation systems.

[0066] The following embodiments are preferred examples of the optical film of the present invention: [1] A primer layer and an optical functional layer are provided in this order on at least one surface of a resin substrate, the optical functional layer has an ultraviolet (UV) cut function, and the hue a of the SCE reflected light ＊ The value of is between -2.0 and +2.0, and the hue b ＊ An optical film in which the value of is -3.0 or greater and +3.0 or less. [2] An optical film comprising a primer layer and an optical functional layer in this order on at least one surface of a resin substrate, wherein the optical functional layer does not have an ultraviolet (UV) cut function, the primer layer has a thickness of 120 nm or less, and the hue a of the SCE reflected light ＊ The value of is between -2.0 and +2.0, and the hue b ＊ An optical film in which the value is between -3.0 and +3.0.

[0067] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples.

[0068] Examples 1-9 and Comparative Examples 1-2 <Substrate> Polyethylene terephthalate film (U40, with easy-adhesion layer on both sides, manufactured by Toray), polyethylene terephthalate film (U40, with easy-adhesion layer on one side, manufactured by Toray), or polyimide film (developed product, with easy-adhesion layer on both sides, manufactured by Kolon) with the thicknesses shown in Tables 1 and 2 were used.

[0069] <Hard Coat Layer> A composition for forming a hard coat layer was prepared by diluting 99.9 parts by mass of a photocurable resin (hard coat agent containing quaternary ammonium salt, manufactured by Arakawa Chemical Industries) and 0.10 parts by mass of an acrylic polymer (TEGO® Flow 300, manufactured by Evonik), or by diluting 96.4 parts by mass of a photocurable resin (hard coat agent containing quaternary ammonium salt, manufactured by Arakawa Chemical Industries), 0.10 parts by mass of an acrylic polymer (TEGO® Flow 300, manufactured by Evonik), and 3.5 parts by mass of a triazine-based ultraviolet absorber (Tinuvin® 477, manufactured by BASF Japan) in a mixed solvent of propylene glycol monomethyl ether / methyl ethyl ketone / isopropyl alcohol (mass ratio 25 / 50 / 20) and stirring.

[0070] The obtained hard coat layer forming composition is applied to one side of the substrate (or the side with the primer layer if the substrate has a primer layer on one side) using a wire bar coater to form a coating film. After drying at 60°C for 60 seconds, it is cured in a nitrogen atmosphere using a conveyor-type ultraviolet curing device with an exposure of 200 mJ / cm². ２ By irradiating with ultraviolet light, hard coat layers of the thicknesses shown in Tables 1 and 2 were fabricated.

[0071] <Low refractive index layer> A composition for forming a low refractive index layer was prepared by diluting 30.0 parts by mass of hollow silica fine particles (Thru-Ria 5320, manufactured by JGC Catalysts & Chemicals), 62.0 parts by mass of acrylic monomer (pentaerythritol triacrylate, Viscoat #300, manufactured by Osaka Organic Chemical Industry), 5.0 parts by mass of fluorine-based antifouling agent (KY-1203, manufactured by Shin-Etsu Chemical Co., Ltd.), and 3.0 parts by mass of photopolymerization initiator (Omnirad® 184, manufactured by IGM Resins) in a methyl isobutyl ketone / propylene glycol monomethyl ether acetate (mass ratio 50 / 50) mixed solvent and stirring.

[0072] The obtained low refractive index layer-forming composition was applied to the upper surface of the hard coat layer obtained above using a wire bar coater to form a coating film. After drying at 60°C for 60 seconds, it was cured in a nitrogen atmosphere using a conveyor-type ultraviolet curing device with an exposure of 200 mJ / cm². ２ By irradiating with ultraviolet light, a low refractive index layer with a thickness of 100 nm was fabricated, and an optical film was obtained.

[0073] In Example 10 and Comparative Example 3, an optical film was obtained in the same manner as in Example 1, except that a low refractive index layer was not laminated.

[0074] The obtained optical films were evaluated as follows. The results are shown in Tables 1 and 2.

[0075] Test Example 1 [Transmittance] Spectral transmittance at wavelengths of 390 nm and 400 nm was measured using a spectrophotometer (U-4100, Hitachi High-Tech) under the conditions of a C light source and a 2-degree field of view. A transmittance of 67% or less at 390 nm and 86% or less at 400 nm were considered good.

[0076] Test Example 2 [Diffuse Reflectance SCE Hue] An optical film was prepared by attaching a PET film (Kikkiri Mieru, manufactured by TOMOEGAWA) to the back surface, and the hue a was measured using the SCE method with a spectrophotometer (CM2600-d, manufactured by Konica Minolta, measurement diameter 3 mm, 2-degree field of view). ＊ and b ＊ The value of hue a was measured. ＊ The value of is between -2.0 and +2.0, and the hue b ＊ A value between -3.0 and +3.0 was considered a pass.

[0077] Test Example 3 [Diffuse Reflectance SCE Reflectance] An optical film with a PET film attached was prepared in the same manner as in Test Example 2, and the reflectance at wavelengths of 390 nm and 400 nm was measured using the SCE method with a spectrophotometer (CM2600-d, Konica Minolta, measurement diameter 3 mm, 2-degree field of view). If the reflectance is 0.50% or less at either wavelength, it indicates excellent low reflectivity (diffuse reflection suppression).

[0078] Test Example 4 [Luminous Reflectance] The spectral reflectance on the film surface on the side of the optical film where the hard coat layer is formed was measured using an automatic spectrophotometer (U-4100, Hitachi, Ltd.). For spectral reflectance measurement, a matte black tape (#302 black, Teraoka vinyl tape) was applied to the back surface of the optical film (the side opposite to the side with the hard coat layer) to prevent reflection, and specular reflection was measured at an incident angle of 5°. From the obtained spectral reflectance curve, the lumenable reflectance (Y value) was calculated in accordance with JIS R 3106. A lumenable reflectance of 1.6% or less was considered acceptable.

[0079] Test Example 5 [Transmitted YI] The transmitted YI value was measured using a spectrophotometer (U-4100, Hitachi High-Tech) in accordance with JIS K 7373. A transmitted YI value of 3.5 or less was evaluated as having good yellowness (low yellowness).

[0080] Test Example 6 [Haze] Using a haze meter (NDH2000, manufactured by Nippon Denshoku Industries), the total haze was measured in accordance with JIS K 7105. If the total haze was 1.0% or less, it was evaluated that diffuse reflectance was suppressed.

[0081] Test Example 7 [Stretchability] A test piece cut to 100 x 10 mm was set in a tensile testing machine (STB-1225L, manufactured by A&D Manufacturing) (chuck distance 50 mm) and stretched. The length of the film when a crack appeared was measured visually, and the stretch rate (%) was calculated from the change in length from before stretching. A stretch rate of 10.0% or higher was considered acceptable. Stretch rate (%) = 100 x (film length at break - film length before test) / film length before test

[0082] Test Example 8 [Repeated Folding Resistance] The optical functional layer was folded 180° so that the optical film had an inner surface and a distance of 10 mm between opposing edges. This test was repeated 300,000 times. If no cracking or breakage occurred, it was marked as "○", and if cracking or breakage occurred, it was marked as "×".

[0083] Test Example 9 [Adhesion] Using an iSuper UV tester (metal halide lamp type weather meter, manufactured by Iwasaki Electric), under conditions of a temperature of 62°C and relative humidity of 45%, the irradiation dose was 75 mW / cm².２ A cross-cut test was performed in accordance with JIS K5600 before and after irradiating the optical functional layer surface with ultraviolet light for 3 hours. Specifically, the adhesion of the optical functional layer to the substrate was investigated by determining the area ratio of the optical functional layer surface that remained without peeling. The peeling state was classified into six stages from 0 to 5, with the least peeling being the most severe. A peeling state corresponding to category 0 was marked with "◎", category 1 with "〇", category 2 with "△", and category 3 or higher with "×".

[0084] Test Example 10 [Visual Evaluation of Display] Each optical film was attached to the observer's side image display device of a foldable smartphone [Samsung Galaxy Z Flip 6 (manufactured by Samsung Electronics)] using optical adhesive. In a bright place (illuminance around the LCD monitor: 400 lux), the displayed image was observed visually from the front and at an oblique angle (approximately 45 degrees), and the anti-reflective properties and the presence or absence of reflective color were evaluated according to the following criteria. The observation was performed by 10 people, and the evaluation with the most votes was taken as the observation result. <Anti-reflective properties> ○: The observer's face was not reflected and observed. This was at a level that did not cause problems in actual use. ×: The observer's face was clearly reflected and observed. <Reflective color> ○: The reflective color of the image display screen was colorless and not noticeable. This was at a level that did not cause problems in actual use. ×: The reflective color of the image display screen was colored and noticeable.

[0085]

[0086]

[0087] From the above results, it can be seen that Examples 1 to 5 exhibit lower reflectivity and suppressed hue changes caused by the primer layer compared to Comparative Examples 1 and 2. Furthermore, the transmittance at wavelengths of 390 nm to 400 nm was also suppressed (see Figure 4), and because it has a UV-cutting function, no reduction in adhesion was observed even after the lightfastness test, and consequently, repeated bending and other properties can be improved. It can also be seen that these effects are exhibited regardless of the material of the resin substrate (Examples 1 and 5). In addition, from a comparison between Example 1 and Example 4, it can be seen that even when the primer layer is placed on both sides of the substrate, the same level of hue change suppression is observed as when the primer layer is placed on only one side of the substrate.

[0088] On the other hand, in Comparative Examples 1 and 2, the amount of ultraviolet light reaching the primer layer was not suppressed, diffuse reflection was not suppressed, and there was a large change in reflected hue. Furthermore, because the amount of ultraviolet light reaching the primer layer was not suppressed, not only did the adhesion of the primer layer deteriorate after the lightfastness test, but even in the initial state, if no UV-blocking agent was included, flexibility was poor, and stretchability and repeated bending resistance were also inferior.

[0089] Furthermore, although the primer layer thickness in Examples 6-9 is thinner than in Examples 1-5, it exhibits low reflectivity and is less prone to hue changes caused by the primer layer, similar to Examples 1-5. In particular, Examples 6, 7, and 9 show that even when the hard coat layer does not have UV-cutting properties, a primer layer thickness of approximately 45 nm to 100 nm suppresses the decrease in adhesion after the lightfastness test. Also, a comparison between Example 7 and Example 8 shows that when the primer layer is the same thickness of 100 nm, the hard coat layer having UV-cutting properties further suppresses fluctuations in the intensity of redness and blueness in the reflected hue, and also maintains adhesion after the lightfastness test.

[0090] Comparative Example 3 lacked a UV-cutting function in the hard coat layer, resulting in unrestricted UV penetration into the primer layer, unrestricted diffuse reflection, and significant changes in reflected hue. Furthermore, the absence of an anti-reflective layer resulted in high luminous reflectance and poor visibility (anti-reflective properties).

[0091] The optical film of the present invention is suitably used as a protective film for foldable display devices.

[0092] 1. Resin substrate 2. Primer layer 3. Optical functional layer 4. Anti-reflective layer 10. Optical film 20. Optical film 30. Optical film

Claims

1. A primer layer and an optical functional layer are provided on at least one surface of the resin substrate in this order, and the hue of the SCE reflected light a ＊ The value of is between -2.0 and +2.0, and the hue b ＊ An optical film in which the value is between -3.0 and +3.

0.

2. The optical film according to claim 1, wherein the optical functional layer has an ultraviolet (UV) cut function.

3. The optical film according to claim 1, wherein the spectral transmittance is 67.0% or less at a wavelength of 390 nm and 86.0% or less at a wavelength of 400 nm.

4. The optical film according to claim 1, wherein the optical functional layer is a UV-cut hard coat layer.

5. The optical film according to claim 4, wherein the UV-cut hard coat layer contains a UV absorber.

6. The optical film according to claim 4, wherein the thickness of the UV-cut hard coat layer is 1.0 μm or more and 10.0 μm or less.

7. The optical film according to claim 1, wherein the thickness of the primer layer is 70 nm or more and 120 nm or less.

8. The optical film according to claim 1, further comprising an anti-reflective layer on the optical functional layer.

9. The optical film according to claim 8, wherein the anti-reflective layer is a layer consisting of a low refractive index layer, a layer in which a high refractive index layer and a low refractive index layer are laminated, or a layer in which a medium refractive index layer, a high refractive index layer and a low refractive index layer are laminated.

10. The optical film according to claim 1, wherein the resin substrate consists of one or more selected from the group consisting of polyimide, polyamide, polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

11. The optical film according to claim 1, wherein a primer layer is provided on the other side of the resin substrate.

12. The optical film according to claim 1, wherein the reflectance at wavelengths of 390 nm or more and 400 nm or less, as measured by the SCE method, is 0.50% or less.

13. The optical film according to claim 1, wherein the haze value measured in accordance with JIS K 7136 is 1.0% or less.

14. The optical film according to claim 1, wherein the transmitted YI value measured in accordance with JIS K 7373 is 3.5 or less.

15. The optical film according to claim 1, wherein the elongation rate is 10.0% or more.

16. The optical film according to claim 1, which, when folded 180° with the optical functional layer facing inward so that the distance between opposing edges of the optical film is 10 mm, does not crack or break when subjected to a test repeated 300,000 times.

17. An image display device comprising an optical film according to any one of claims 1 to 16.

Images