Low–refractive index layer formation composition, optical film, and image display device

Abstract

A low–refractive index layer formation composition according to the present invention contains a binder resin (A), a photopolymerization initiator (B), inorganic oxide particles (C) that have internal voids, inorganic oxide particles (D) that do not have internal voids, and a surface modifier (E). The binder resin (A) is at least 10 mass% a (meth)acryloyl-modified compound that has at least one of a silsesquioxane structure and a hydroxyl group in the molecule thereof. Of the total solid content, the photopolymerization initiator (B) is 1–9 mass%, the inorganic oxide particles (C) are 20–55 mass%, and the inorganic oxide particles (D) are 4–20 mass%.

Description

Composition for forming a low refractive index layer, optical film, and image display device

[0001] The present invention relates to a composition for forming a low refractive index layer used in the production of an optical film, an optical film, and an image display device.

[0002] Many displays require low reflectivity because external light is reflected on the display surface and the reflected image is mixed with the display light, deteriorating the display quality. Generally, an optical film having low reflectivity can be obtained by providing a low refractive index layer containing inorganic fine particles or the like on the surface of a transparent plastic film substrate. On the other hand, in recent years, low-reflection films for devices such as tablets also require abrasion resistance. However, the low refractive index materials used in the low refractive index layer (for example, silica having voids inside) are inferior in strength and the film thickness of the low refractive index layer itself is also thin, so there is a trade-off relationship between low reflectivity and abrasion resistance.

[0003] Regarding the compatibility of low reflectivity and abrasion resistance, for example, Patent Document 1 discloses a composition containing a photopolymerizable compound; inorganic fine particles containing hollow silica particles; polysilsesquioxane substituted with one or more reactive functional groups; a fluorine-based compound containing a photoreactive functional group; and a photopolymerization initiator, and containing 0.5 to 25 parts by weight of the polysilsesquioxane with respect to 100 parts by weight of the photopolymerizable compound, which provides a low refractive index layer that simultaneously realizes high alkali resistance and scratch resistance while having a low reflectivity and a high transmittance.

[0004] Patent Document 2 discloses that a low refractive index layer formed of a composition containing a photocurable resin, two or more types of hollow inorganic fine particles having different particle sizes, a fluorine-based compound, and a polymerization initiator has a small difference in reflectivity before and after a steel wool test of 0.2% or less, and an antireflection film containing such a low refractive index layer not only effectively suppresses an increase in reflectivity and a change in color of a damaged or deformed portion due to external rubbing or friction, but also has mechanical physical properties such as high abrasion resistance and scratch resistance and excellent optical properties.

[0005] Patent Document 3 discloses a binder resin, hollow silica fine particles with an average particle size of 5 to 100 nm, alumina fine particles with an average particle size of 1 to 100 nm, and a surface modifier such as a fluorine-based silicone compound, which includes a low refractive index layer in which the amount of alumina fine particles is 0.7 to 14.0% by weight of the total amount of solid matter. This results in less reflection from external light sources and excellent visibility, as well as high water and oil repellency, making it resistant to dirt, and even if dirt does adhere, it has excellent abrasion resistance, making it resistant to scratches from repeated wiping or wiping with a hard cotton cloth.

[0006] Patent No. 6607510 Patent No. 7205815 Patent No. 7354087

[0007] Conventional abrasion resistance was evaluated by applying a load to steel wool and rubbing it, as shown in Patent Documents 1 to 3, and assessing the number of scratches that resulted. However, in recent years, not only scratch resistance but also high abrasion resistance against frictional forces has become required. Even materials that show good abrasion resistance against steel wool still do not have sufficient abrasion resistance when a larger load is applied to a surface, such as resistance to eraser abrasion, and there is a need for a higher balance between low reflectivity and abrasion resistance.

[0008] The present invention relates to a composition for forming a low refractive index layer that is excellent in low reflectivity and also excellent in resistance to eraser abrasion, an optical film containing a low refractive index layer obtained from the composition, and an image display device.

[0009] The present invention relates to the following [1] to [3]. [1] A composition for forming a low refractive index layer, comprising a binder resin (A), a photopolymerization initiator (B), inorganic oxide particles having internal voids (C), inorganic oxide particles without internal voids (D), and a surface modifier (E), wherein the binder resin (A) contains 10% by mass or more of a (meth)acryloyl modified compound having at least one of a silsesquioxane structure and a hydroxyl group in its molecule, the content of the photopolymerization initiator (B) is 1 to 9% by mass of the total amount of solid components, the content of inorganic oxide particles having internal voids (C) is 20 to 55% by mass of the total amount of solid components, and the content of inorganic oxide particles without internal voids (D) is 4 to 20% by mass of the total amount of solid components, wherein the composition for forming a low refractive index layer. [2] An optical film comprising, in this order, a hard coat layer and a low refractive index layer formed from the low refractive index layer forming composition described in [1] on at least one surface of a transparent substrate. [3] An image display device comprising the optical film described in [2].

[0010] The low refractive index layer-forming composition of the present invention exhibits the excellent effect of providing a low refractive index layer that achieves both low reflectivity and resistance to eraser abrasion.

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

[0012] The low refractive index layer-forming composition of the present invention, by combining a binder resin (A) having a specific structure with a photopolymerization initiator (B), inorganic oxide particles with internal voids (C), inorganic oxide particles without internal voids (D), and a surface modifier (E), makes it possible to produce an optical film that achieves both low reflectivity and high resistance to eraser abrasion.

[0013] The binder resin (A) used in the present invention is characterized by containing 10% by mass or more of a (meth)acryloyl modified compound having at least one of a silsesquioxane structure and a hydroxyl group in its molecule. By containing such a compound in the binder resin, the shedding of inorganic oxide particles (C) having internal voids from the surface of the low refractive index layer is suppressed. This is presumed to be because, when a silsesquioxane structure is present, its structure increases its affinity for inorganic oxide particles (C) having internal voids, thereby increasing the bonding strength between the two. Furthermore, when a hydroxyl group is present, it is presumed to be easier to form hydrogen bonds with the hydroxyl group on the surface of inorganic oxide particles (C) having internal voids, thereby increasing the bonding strength between the two. Therefore, the binder resin (A) contains at least one of a (meth)acryloyl modified compound (A1) having a silsesquioxane structure in its molecule and a (meth)acryloyl modified compound (A2) having a hydroxyl group in its molecule. In this specification, "(meth)acrylic" refers to acrylic, methacrylic, or both, and "(meth)acryloyl" refers to acryloyl, methacryloyl, or both.

[0014] The silsesquioxane structure is (RSio １．５ The (meth)acryloyl modified compound (A1) has a constituent unit represented by ), and can form polysilsesquioxanes with random structures, ladder structures, cage structures, etc., through siloxane bonds. In (meth)acryloyl modified compounds (A1) having a silsesquioxane structure in the molecule, R is mainly a polymerizable (meth)acryloyl group, but it may also contain hydrogen atoms, hydroxyl groups, or other reactive functional groups as long as the silsesquioxane structure can bond with inorganic oxide particles (C) that have voids inside. In other words, it may be a (meth)acryloyl modified compound that has both a silsesquioxane structure and a hydroxyl group in the molecule.

[0015] The (meth)acryloyl-modified compound (A1) having a silsesquioxane structure in its molecule can be synthesized according to known methods or is a commercially available product and is not particularly limited in its use. Examples of commercially available products include "AC-SQ TA-100", "MAC-SQ TM-100", "AC-SQ SI-20", and "MAC-SQ SI-20" manufactured by Toagosei Co., Ltd.

[0016] The (meth)acryloyl-modified compound (A2) having a hydroxyl group in its molecule is not particularly limited, as long as the hydroxyl group can form a bond with the surface of the inorganic oxide particle (C) having internal voids. It may be a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate, as long as it has a hydroxyl group.

[0017] Examples of monofunctional (meth)acrylate compounds having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-(meth)acryloyloxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, and 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate.

[0018] Examples of polyfunctional (meth)acrylate compounds having hydroxyl groups include tris-2-hydroxyethyl isocyanurate di(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate.

[0019] The (meth)acryloyl-modified compound (A2) having a hydroxyl group in the molecule can be synthesized according to known methods or is a commercially available product and is not particularly limited in its use. Examples of commercially available products include Kyoeisha Chemical's "Light Acrylate® PE-3A", "Epoxy Ester M-600A", "HOA-MS(N)", "Light Acrylate® HOA-HH(N)", "HOA-MPE(N)", and "Light Ester G-201P".

[0020] The (meth)acryloyl group in these compounds may be a functional group containing a polymerizable (meth)acryloyl group, or it may be partially substituted with an alkyl group or ε-caprolactone.

[0021] The above (meth)acryloyl modified compounds may be used individually or in combination of two or more. Multiple (meth)acryloyl modified compounds (A1) having a silsesquioxane structure in the molecule may be used, multiple (meth)acryloyl modified compounds (A2) having a hydroxyl group in the molecule may be used, or both may be used in combination. Furthermore, these may be monomers in the composition, or partially polymerized oligomers.

[0022] In the binder resin (A), the content of the (meth)acryloyl modified compound having at least one of a silsesquioxane structure and a hydroxyl group in its molecule is 10% by mass or more, preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and still more preferably 50% by mass or more, from the viewpoint of suppressing the shedding of inorganic oxide particles (C) having internal voids. The upper limit is not particularly limited and may be 100% by mass. Note that the content referred to here means the total content when a (meth)acryloyl modified compound (A1) having a silsesquioxane structure and a (meth)acryloyl modified compound (A2) having a hydroxyl group are used in combination.

[0023] When using a combination of a (meth)acryloyl modified compound (A1) having a silsesquioxane structure and a (meth)acryloyl modified compound (A2) having a hydroxyl group, the content ratio [(A1) / (A2)] is preferably 80 / 20 to 30 / 70, and more preferably 70 / 30 to 40 / 60, from the viewpoint of more stably retaining inorganic oxide particles (C) having internal voids.

[0024] The binder resin (A) is not particularly limited to any compound other than the (meth)acryloyl-modified compound mentioned above, and known compounds can be used. For example, a resin that polymerizes and hardens upon irradiation with active energy rays such as ultraviolet light or electron beams can be used, and monofunctional, bifunctional, or trifunctional or higher (meth)acrylate monomers can be used. Examples include (meth)acryloyl compounds that do not have a silsesquioxane structure or hydroxyl group in their molecule.

[0025] Examples of monofunctional (meth)acrylate compounds include 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, isobornyl (meth)acrylate, 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 Examples include adamantane derivative mono(meth)acrylates such as phenoxy(meth)acrylate modified from 2-adamantane and adamantanediol, which have a monovalent mono(meth)acrylate.

[0026] Examples of difunctional (meth)acrylate compounds include ethylene glycol di(meth)acrylate, propylene 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, hydroxypivalate neopentyl glycol di(meth)acrylate, and other di(meth)acrylates.

[0027] Examples of trifunctional (meth)acrylate compounds 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 compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate. Examples include polyfunctional (meth)acrylate compounds 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 compounds in which some of these (meth)acrylates are substituted with alkyl groups or ε-caprolactone.

[0028] 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.

[0029] 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, and dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer.

[0030] The content of the (meth)acryloyl compound in the binder resin (A) that does not have a silsesquioxane structure and a hydroxyl group in its molecule is not particularly limited and can be appropriately adjusted depending on the content of the (meth)acryloyl modified compound that has at least one of a silsesquioxane structure and a hydroxyl group in its molecule. As an example, the ratio of the content of the (meth)acryloyl compound that does not have a silsesquioxane structure and a hydroxyl group in its molecule to the total content of the (meth)acryloyl modified compound (A1) that has a silsesquioxane structure and the (meth)acryloyl modified compound (A2) that has a hydroxyl group is 10 / 90 to 90 / 10.

[0031] The content of the binder resin (A) is not particularly limited, but from the viewpoint of improving the adhesion between the (meth)acryloyl modified compound and the inorganic oxide particles (C) having internal voids, it is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 46% by mass or more, even more preferably 50% by mass or more, and even more preferably 53% by mass or more of the total amount of solid components. Examples of upper limits include 75% by mass or less and 70% by mass or less. In this specification, the total amount of solid components refers to the total content of all components of the composition other than the solvent.

[0032] The photopolymerization initiator (B) can be any substance that triggers a polymerization reaction upon irradiation with ultraviolet light or electron beams, and examples include 2,2-ethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, Michler ketone, acetophenone, and 2-chlorothioxanthone. These may be used individually or in combination of two or more.

[0033] The content of the photopolymerization initiator (B) is 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, of the total amount of solid components, from the viewpoint of polymerization reaction. Furthermore, from the viewpoint of stably retaining the inorganic oxide particles (C) having internal voids inside the low refractive index layer, it is 9% by mass or less, preferably 8% by mass or less, and more preferably 7% by mass or less. If the content of the photopolymerization initiator (B) is too low, the curing of the binder resin (A) will be insufficient, making it difficult to achieve eraser abrasion resistance. Conversely, if it is too high, an excessive amount of photopolymerization initiator will remain in the coating film, and the total amount of binder resin will also decrease, making it difficult to achieve eraser abrasion resistance.

[0034] Inorganic oxide particles (C) with internal voids have fine voids inside, which have the effect of lowering the refractive index and reflectivity of the coating film. Examples include hollow silica, hollow alumina, zeolite, talc, kaolin, and diatomaceous earth. These may be used individually or in combination of two or more. Furthermore, these particles may be surface-treated with known surface treatment agents.

[0035] The average particle size of the inorganic oxide particles (C) having internal voids is preferably 40 nm or more, more preferably 50 nm or more, even more preferably 60 nm or more, and preferably 120 nm or less, more preferably 110 nm or less, and even more preferably 100 nm or less, from the viewpoint of refractive index reduction ability of the low refractive index layer and film thickness. In this specification, the average particle size of the inorganic oxide particles is the volume median particle size (D) at which the cumulative volume frequency calculated by volume fraction accounts for 50% when calculated from the smallest particle size. ５０ ) means.

[0036] The content of inorganic oxide particles (C) having internal voids is 20% by mass or more, preferably 22% by mass or more, more preferably 23% by mass or more, and even more preferably 27% by mass or more, of the total amount of solid components, from the viewpoint of improving low reflectivity. Furthermore, from the viewpoint of improving eraser abrasion resistance, it is 55% by mass or less, preferably 54% by mass or less, more preferably 53% by mass or less, even more preferably 50% by mass or less, and even more preferably 44% by mass or less. As the content of inorganic oxide particles (C) having internal voids increases, the number of voids in the coating film also increases, making it more difficult to achieve eraser abrasion resistance.

[0037] Inorganic oxide particles (D) that do not have internal voids possess the refractive index inherent to the constituent inorganic compound. Compared to inorganic oxide particles (C) that have internal voids, they exhibit better eraser abrasion resistance, but they do not have the effect of lowering the refractive index of the coating film. Examples include solid silica and solid alumina. Furthermore, inorganic oxide particles (D) that do not have internal voids have higher hardness than inorganic oxide particles (C) that have internal voids, so improved eraser abrasion resistance can be expected; for example, solid alumina particles are preferred. These may be used individually or in combination of two or more types. These particles may also be surface-treated with known surface treatment agents.

[0038] The average particle size of the inorganic oxide particles (D) that do not have internal voids is preferably 30 nm or more, more preferably 40 nm or more, and preferably 100 nm or less, more preferably 95 nm or less, from the viewpoint of eraser abrasion resistance.

[0039] The content of inorganic oxide particles (D) that do not have internal voids is 4% by mass or more, preferably 5% by mass or more, more preferably 6% by mass or more, and even more preferably 7% by mass or more, of the total amount of solid components, from the viewpoint of improving eraser abrasion resistance. Furthermore, from the viewpoint of improving low reflectivity and not reducing transparency, it is 20% by mass or less, preferably 19% by mass or less, and more preferably 18% by mass or less.

[0040] The content ratio of inorganic oxide particles having internal voids (C) to inorganic oxide particles without internal voids (D) (inorganic oxide particles having internal voids (C) / inorganic oxide particles without internal voids (D)) is preferably 90 / 10 to 51 / 49, more preferably 88 / 12 to 53 / 47, and even more preferably 83 / 17 to 57 / 43, from the viewpoint of improving eraser abrasion resistance while exhibiting low reflectivity.

[0041] The surface modifier (E) is not particularly limited as long as it has the effect of reducing the surface tension of the low refractive index layer, and examples include leveling agents, defoaming agents, interfacial tension modifiers, and surface tension modifiers. Examples include acrylic, vinyl, silicone, and fluorine-based surface modifiers.

[0042] The content of the surface conditioner (E) is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more, from the viewpoint of improving water repellency, based on the total solid content. Also, from the viewpoint of maintaining good abrasion resistance against erasable rubber, it is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 7% by mass or less, and still more preferably 6% by mass or less.

[0043] The composition for forming a low refractive index layer of the present invention contains a solvent for mixing the above-described components. Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone; alcohol solvents such as ethanol, methanol, isopropyl alcohol (IPA), and isobutanol; ether solvents such as ethylene glycol dimethyl ether and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, propylene glycol monomethyl ether acetate, and 2-ethoxyethyl acetate; and aromatic hydrocarbon solvents such as toluene. These may be used alone or in combination of two or more.

[0044] Further, the composition for forming a low refractive index layer of the present invention may contain additives such as dyes, oil repellents, water repellents, fingerprint adhesion preventives, antistatic agents, ultraviolet absorbers, infrared absorbers, antioxidants, light stabilizers, photosensitizers, conductive materials, refractive index adjusters, adhesion improvers, polymerization inhibitors, etc., in addition to the above-described components. The content of these can be appropriately adjusted according to known techniques.

[0045] The low refractive index layer of the present invention can be produced by applying the composition for forming a low refractive index layer of the present invention onto a substrate (such as a transparent substrate) using a known coating method (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.), followed by drying and photocuring.

[0046] The refractive index of the low refractive index layer is preferably 1.25 to 1.45, more preferably 1.28 to 1.42.

[0047] The thickness of the low refractive index layer is not particularly limited and may be, for example, 50 to 200 nm or 50 to 150 nm.

[0048] The present invention also provides an optical film comprising a hard coat layer on at least one surface of a transparent substrate, and a low refractive index layer of the present invention on the hard coat layer, in this order.

[0049] The transparent substrate may be a resin substrate or an inorganic compound substrate. Examples of materials for forming the resin substrate include triacetylcellulose substrates, polyethylene naphthalate substrates, polyethylene terephthalate substrates, cycloolefin polymer substrates, polycarbonate substrates, acrylic substrates, polyimide substrates, and polyamide substrates. Examples of materials for forming the inorganic compound substrate include silicon dioxide, silicon oxynitride, and silicon nitride. These materials may be used individually or in combination of two or more. The transparent substrate may be manufactured using the above materials according to known methods, or a commercially available product may be used. Surface modification treatment may be applied to improve 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.

[0050] The thickness of the transparent substrate is not particularly limited and may be, for example, 10 to 200 μm.

[0051] The hard coat layer is not particularly limited, and known materials can be used. It may be prepared according to known methods using materials containing monofunctional, bifunctional, or trifunctional or more (meth)acrylates, urethane (meth)acrylates, etc. For example, it can be formed by applying a hard coat layer-forming composition containing the said material to the surface of a transparent substrate and curing the coating film.

[0052] The thickness of the hard coat layer is not particularly limited and may be, for example, 2 to 15 μm.

[0053] The method for forming the low refractive index layer of the present invention on a hard coat layer is not particularly limited as long as the low refractive index layer forming composition of the present invention is used. For example, after forming a hard coat layer on a transparent substrate, the low refractive index layer forming composition of the present invention can be deposited by a known coating method.

[0054] The optical film of the present invention may include other layers besides the aforementioned layers, such as an adhesive layer, a coloring layer, a high refractive index layer, a medium refractive index layer, an antistatic layer, an electromagnetic wave shielding layer, an infrared absorption layer, an ultraviolet absorption layer, and a color correction layer. For example, other layers may be included between the hard coat layer and the low refractive index layer of the present invention, or between the transparent substrate and the hard coat layer.

[0055] The thickness of the optical film of the present invention is not particularly limited and may be, for example, 10 to 220 μm.

[0056] The reflectance (SCI reflectance: Y value) of the optical film of the present invention using the SCI (Special Component Include) method is preferably less than 2.0%, more preferably 1.8% or less, even more preferably 1.5% or less, and even more preferably 1.0% or less. If the SCI reflectance is less than 2.0%, it indicates that reflection at the outermost surface is suppressed and that low reflectivity is good. For example, it may be 1.8% or less, 1.7% or less, 1.6% or less, or 1.5% or less, and if it is less than 1.5%, low reflectivity is even better. In this specification, the SCI reflectance is measured using a spectrophotometer (CM-26dG, manufactured by Konica Minolta) after applying a matte black treatment to the back surface of the optical film (the surface on which the hard coat layer and low refractive index layer are not formed).

[0057] The optical film of the present invention exhibits a water contact angle of preferably 90° or higher, more preferably 95° or higher, after a test in which the film surface (the surface on the low refractive index layer side) is slid 2000 times with an eraser under a load of 1 kg (1 kg / 6 mmΦ). A water contact angle of 90° or higher after the sliding test indicates good eraser abrasion resistance, and a higher value indicates better performance. In the present invention, the quality of abrasion resistance is judged by the pure water contact angle after rubbing the coating surface with an eraser for abrasion testing a certain number of times. A higher value means that the water repellency is less likely to be impaired, thus indicating superior abrasion resistance. The water contact angle of the optical film of the present invention before the above test is 109 to 115°. In this specification, the sliding test is performed using an abrasion friction tester (TYPE-30S, manufactured by Shinto Kagaku), and the water contact angle of the film surface is measured using a contact angle meter (LSE-ME4, manufactured by Nick).

[0058] The optical film of the present invention has a total haze (according to JIS K 7136) of preferably 1.0% or less, more preferably 0.7% or less, and even more preferably 0.5% or less. When the total haze is 1.0% or less, diffuse reflection is suppressed, transparency is ensured, and visibility is good.

[0059] The reflectance (SCE reflectance: Y value) of the optical film of the present invention using the SCE (Special Component Exclude) method is preferably 0.20% or less, more preferably 0.18% or less, even more preferably 0.16% or less, and even more preferably 0.12% or less. If the SCE reflectance is 0.20% or less, diffusion at the outermost surface is sufficiently suppressed, and whitening of the appearance due to diffused light can be suppressed. In this specification, the SCE reflectance is measured in the same manner as the SCI reflectance.

[0060] The present invention also provides an image display device comprising the optical film of the present invention. Examples of image display devices include televisions, monitors, mobile phones, portable game consoles, personal information terminals, personal computers, e-books, video cameras, digital still cameras, head-mounted displays, navigation systems, sound playback devices (car audio systems, digital audio players, etc.), photocopiers, facsimile machines, printers, multifunction printers, vending machines, automated teller machines (ATMs), personal authentication devices, optical communication devices, IC cards, and the like. The display device may also be foldable, for example, a smartphone, tablet, portable game console, or other personal information terminal. The display device may also be rollable, for example, a rollable television.

[0061] 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.

[0062] Examples 1-32 and Comparative Examples 1-15 <Transparent Substrate> A triacetylcellulose film with a thickness of 60 μm, a polyethylene terephthalate film with a thickness of 50 μm, or a polyimide film with a thickness of 50 μm was used.

[0063] <Hard Coat Layer> A composition for forming a hard coat layer was prepared by diluting 50 parts by mass of pentaerythritol triacrylate, 50 parts by mass of dipentaerythritol hexaacrylate, 1.5 parts by mass of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, and 0.1 parts by mass of acrylic polymer (DIC, PC4300) in a solvent prepared by mixing methyl ethyl ketone and propylene glycol monomethyl ether in a 70 / 30 (mass ratio), and stirring.

[0064] The obtained hard coat layer forming composition was applied to a transparent substrate using a wire bar coater to form a coating film. After drying at 65°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 A 5 μm thick hard coat layer was fabricated on a transparent substrate by irradiating it with ultraviolet light.

[0065] <Low Refractive Index Layer> The compositional raw materials shown in Tables 1 to 4 were added to a mixed solvent of propylene glycol monomethyl ether acetate / methyl isobutyl ketone / isopropyl alcohol (mass ratio 15 / 80 / 5) and mixed to prepare a composition for forming a low refractive index layer. The composition was applied to the hard coat layer using a wire bar coater to form a coating film (applied so that the layer thickness after curing was 100 nm), dried at 60°C for 60 seconds, and then exposed to ultraviolet light at 500 mJ / cm² in a conveyor-type ultraviolet curing device under a nitrogen atmosphere. ２ A low refractive index layer was fabricated by ultraviolet irradiation, and an optical film was obtained.

[0066] The raw materials shown in Tables 1-4 are as follows: <Low refractive index layer> Binder resin (A1): Acryloyl compound having a silsesquioxane structure in its molecule, AC-SQ TA-100 (manufactured by Toagosei) Binder resin (A2): Acryloyl compound having a hydroxyl group in the molecule, Light Acrylate® PE-3A (manufactured by Kyoeisha Chemical Co., Ltd.), pentaerythritol triacrylate Binder resin (X): Acryloyl compound not having a silsesquioxane structure or hydroxyl group in the molecule, Light Acrylate® TMP-A (manufactured by Kyoeisha Chemical Co., Ltd.), trimethylolpropane triacrylate Binder resin (Y): Acryloyl compound not having a silsesquioxane structure or hydroxyl group in the molecule, Light Acrylate® PE-4A (manufactured by Kyoeisha Chemical Co., Ltd.), pentaerythritol tetraacrylate Photopolymerization initiator (B): Inorganic oxide particles with voids inside 1-hydroxycyclohexyl phenyl ketone (C): Hollow silica particles with an average particle size of 75 nm Inorganic oxide particles without voids inside (D): Alumina particles with an average particle size of 70-85 nm Surface modifier (E): Optool DAC-100 (manufactured by Daikin Industries, Ltd.) <Transparent substrate> T: Triacetylcellulose film with a thickness of 60 μm P: Polyethylene terephthalate film with a thickness of 50 μm I: Polyimide film with a thickness of 50 μm

[0067] The obtained optical films were evaluated as follows. The results are shown in Tables 1 to 4.

[0068] Test Example 1 [SCI Reflectance] For the optical film, after applying a matte black treatment to the back surface (the side where the hard coat layer and low refractive index layer are not formed), the reflectance (Y value) was measured in SCI mode using a spectrophotometer (CM-26dG, manufactured by Konica Minolta), and the low reflectivity was evaluated according to the following evaluation criteria.

[0069] [Evaluation Criteria for Low Reflectivity] ◎: Y value less than 1.5% ○: Y value 1.5% or more but less than 2.0% △: Y value 2.0% or more but less than 2.5% ×: Y value 2.5% or more

[0070] Test Example 2 [Eraser Abrasion Resistance] After thoroughly removing static electricity from the surface of the low refractive index layer of the optical film, an abrasion test was performed using an abrasion friction tester (TYPE-30S, manufactured by Shinto Kagaku) ​​under the following conditions. The contact angle of 1 μL of pure water on the test surface was measured using a contact angle meter (LSE-ME4, manufactured by Nick), and the eraser abrasion resistance was evaluated according to the following evaluation criteria. In this test, measurements were taken at three random locations on the surface of the low refractive index layer, and the average value was calculated. (Test conditions) Rubbing material: Eraser (cylindrical shape with a diameter of 6 mm, made by Hwarang) Stroke: 10 mm Rubbing speed: 50 cpm Load: 1000 g Number of rubs: 2000 times [Evaluation criteria for eraser abrasion resistance] ◎: Water contact angle after test is 95° or higher ○: Water contact angle after test is 90° or higher but less than 95° △: Water contact angle after test is 80° or higher but less than 90° ×: Water contact angle after test is less than 80°

[0071] Test Example 3 [Water Repellency] The initial water contact angle (initial water contact angle) of the low refractive index layer surface of the optical film was measured in the same manner as in Test Example 2. In this test, the water contact angle was measured at three random locations on the low refractive index layer surface, and the average value was calculated. An initial water contact angle of 109° or higher is preferable as it indicates good water repellency.

[0072] Test Example 4 [Haze] For the optical film, the total haze was measured using a turbidimeter (NDH2000, manufactured by Nippon Denshoku Industries) in accordance with JIS K7105, without applying a matte black treatment to the back surface (the side where the hard coat layer and low refractive index layer are not formed). A total haze of 1.0% or less is preferable as it indicates good transparency.

[0073] Test Example 5 [SCE Reflectance] For the optical film, a sample was prepared in the same manner as in Test Example 1, and the reflectance (Y value) was measured in SCE mode using a spectrophotometer (CM-26dG, manufactured by Konica Minolta). An SCE reflectance of 0.20% or less is preferable because it shows excellent suppression of diffuse reflection.

[0074]

[0075]

[0076]

[0077]

[0078] From the above results, it can be seen that Examples 1 to 32 exhibit low reflectivity while also having excellent resistance to eraser abrasion, compared to Comparative Examples 1 to 15. In the present invention, abrasion resistance is evaluated by applying a larger load, so it is suggested that using the low refractive index layer-forming composition of the present invention results in higher abrasion resistance and, consequently, superior durability, even with a thin coating film.

[0079] Comparative Examples 1 and 2, compared to Examples 1 to 10, show that despite having the same content ratios of components (A) to (E), the lower content ratio of the (meth)acryloyl-modified compound having a specific structure in the binder resin (A) makes it easier for hollow silica particles to detach from the surface of the low refractive index layer, resulting in a significant decrease in eraser abrasion resistance. On the other hand, the same effect is observed whether the structure is a silsesquioxane structure or a hydroxyl group (Examples 1 to 5), and it is also observed that when a certain amount of the (meth)acryloyl-modified compound having a specific structure is included, the detachment of hollow silica particles is suppressed even when it is present in coexistence with resins that do not have such a structure (Examples 6 to 10). Furthermore, this effect is similarly exhibited even when the type of transparent substrate changes (Examples 11 and 12).

[0080] Furthermore, even when the content of component (D) increased to 8% by mass or 9% by mass compared to Table 1, if the content of the (meth)acryloyl modified compound having a specific structure in the binder resin (A) was low, the shedding of hollow silica particles from the surface of the low refractive index layer could not be suppressed (Comparative Examples 3-6). On the other hand, even when the content of component (D) increased to 8% by mass or 9% by mass, if the content of the (meth)acryloyl modified compound having a specific structure in the binder resin (A) was 10% by mass or more, diffuse reflection was suppressed while low reflectivity was maintained, and good eraser abrasion resistance was observed (Examples 13-20).

[0081] However, when the content of component (D) is less than 4% by mass, it is found that although transparency is excellent, the effect of eraser abrasion resistance is not exhibited (Comparative Examples 7-9). Furthermore, when it is too high, exceeding 20% ​​by mass, even if a certain amount of (meth)acryloyl modified compound having a specific structure is included, the content of binder resin (A) becomes low to begin with, so the effect of eraser abrasion resistance is not achieved, and the effects of diffuse reflection suppression and low reflectivity are also weakened (Comparative Examples 10-11).

[0082] Regarding component (B), it was found that if the content was within the range of 1 to 9% by mass, a cured product exhibiting low reflectivity and excellent resistance to eraser abrasion could be obtained (Examples 25 and 26). On the other hand, if the content was less than 1% by mass, curing did not proceed sufficiently, and if it exceeded 9% by mass, an excessive amount of photopolymerization initiator remained in the coating film. In both cases, even if a certain amount of hollow silica particles or alumina particles were included, the resistance to eraser abrasion was poor (Comparative Examples 12 and 13).

[0083] Regarding component (C), when the content is low, it is sufficiently retained by the (meth)acryloyl modified compound having a specific structure, resulting in excellent resistance to eraser abrasion. However, at around 15% by mass, low reflectivity could not be obtained (Comparative Example 14). Conversely, when the content is high, excellent low reflectivity is achieved, but when it is contained at 60% by mass, it tends to detach from the surface of the low refractive index layer, resulting in poor resistance to eraser abrasion (Comparative Example 15).

[0084] It can be seen that even if the content of component (E) changes, when components (A) to (D) are included in a specific composition, both low reflectivity and resistance to eraser abrasion can be achieved (Examples 28 to 32).

[0085] The low refractive index layer-forming composition of the present invention can be used to form a low refractive index layer in an optical film used in an image display device, and is particularly suitable for use as a protective film for a foldable display device.

[0086] 1. Transparent substrate 2. Hard coat layer 3. Low refractive index layer 10. Optical film

Claims

1. A composition for forming a low refractive index layer, comprising a binder resin (A), a photopolymerization initiator (B), inorganic oxide particles having internal voids (C), inorganic oxide particles without internal voids (D), and a surface modifier (E), wherein the binder resin (A) contains 10% by mass or more of a (meth)acryloyl modified compound having at least one of a silsesquioxane structure and a hydroxyl group in its molecule, the content of the photopolymerization initiator (B) is 1 to 9% by mass of the total amount of solid components, the content of the inorganic oxide particles having internal voids (C) is 20 to 55% by mass of the total amount of solid components, and the content of the inorganic oxide particles without internal voids (D) is 4 to 20% by mass of the total amount of solid components.

2. The low refractive index layer forming composition according to claim 1, wherein the binder resin (A) contains at least one of a (meth)acryloyl modified compound (A1) having a silsesquioxane structure in its molecule and a (meth)acryloyl modified compound (A2) having a hydroxyl group in its molecule.

3. The low refractive index layer forming composition according to claim 2, wherein the content ratio [(A1) / (A2)] of a (meth)acryloyl modified compound (A1) having a silsesquioxane structure in the molecule and a (meth)acryloyl modified compound (A2) having a hydroxyl group in the molecule is 80 / 20 to 30 / 70.

4. The low refractive index layer forming composition according to claim 1, wherein the content of the binder resin (A) is 25 to 75% by mass of the total amount of solid components.

5. The low refractive index layer forming composition according to claim 1, wherein the inorganic oxide particles (C) having internal voids are hollow silica particles with an average particle size of 40 to 120 nm.

6. The low refractive index layer forming composition according to claim 1, wherein the inorganic oxide particles (D) that do not have internal voids are solid alumina particles with an average particle size of 30 to 100 nm.

7. The low refractive index layer forming composition according to claim 1, wherein the content ratio of inorganic oxide particles (C) having internal voids to inorganic oxide particles (D) not having internal voids [(C) / (D)] is 90 / 10 to 51 / 49.

8. The low refractive index layer forming composition according to claim 1, wherein the surface modifier (E) is an acrylic, vinyl, silicone, or fluorine-based surface modifier.

9. The low refractive index layer forming composition according to claim 1, wherein the content of the surface modifier (E) is 10% by mass or less.

10. The low refractive index layer forming composition according to claim 2, wherein the binder resin (A) further contains a (meth)acryloyl compound that does not have a silsesquioxane structure and a hydroxyl group in its molecule, and the ratio of the content of the compound to the total content of a (meth)acryloyl modified compound (A1) having a silsesquioxane structure in its molecule and a (meth)acryloyl modified compound (A2) having a hydroxyl group in its molecule is 10 / 90 to 90 / 10.

11. The low refractive index layer-forming composition according to claim 10, wherein the (meth)acryloyl compound that does not have a silsesquioxane structure and a hydroxyl group in the molecule is trimethylolpropane triacrylate or pentaerythritol tetraacrylate.

12. An optical film comprising, in this order, a hard coat layer and a low refractive index layer formed from a low refractive index layer forming composition according to any one of claims 1 to 11, on at least one surface of a transparent substrate.

13. The optical film according to claim 12, wherein the thickness of the low refractive index layer is 50 to 200 nm.

14. The optical film according to claim 12, wherein the transparent substrate is a triacetylcellulose-based substrate, a polyethylene naphthalate-based substrate, a polyethylene terephthalate-based substrate, a cycloolefin polymer-based substrate, a polycarbonate-based substrate, an acrylic-based substrate, a polyimide-based substrate, or a polyamide-based substrate.

15. The optical film according to claim 12, wherein the reflectance measured by the SCI method is less than 2.0%.

16. The optical film according to claim 12, wherein the water contact angle after a test in which an eraser is slid 2000 times on the surface of the low refractive index layer with a load of 1 kg (1 kg / 6 mmΦ) is 90° or more.

17. The optical film according to claim 12, wherein the haze value measured in accordance with JIS K 7136 is 1.0% or less.

18. The optical film according to claim 12, wherein the reflectance measured by the SCE method is 0.20% or less.

19. An image display device comprising the optical film according to claim 12.

Images