Hard coating composition

Abstract

Disclosed is a hard coating composition which has: a (meth)acryloyloxy group-containing compound that has an acrylic equivalent of less than 160 g / eq and the average number of (meth)acryloyloxy groups in one molecule of 7 or more; a polyoxyalkylene group-containing (meth)acrylate that has the average number of (meth)acryloyloxy groups in one molecule of 2 to 6; and inorganic particles that are surface-modified with a silane coupling agent. The content of the (meth)acryloyloxy group-containing compound in 100 mass% of the total solid content of the hard coating composition is 30 mass% or less.

Description

Hard Coat Composition

[0001] The present invention relates to a hard coat composition.

[0002] In order to prevent scratches, cracks, etc. from occurring on the surface of a substrate such as a display or touch panel of an image display device, a hard coat layer for surface protection is formed on the surface of the substrate. Furthermore, in order to improve the functionality and aesthetics of the display, touch panel, etc., the display, touch panel, etc. are made curved or made flexible.

[0003] For example, Patent Document 1 describes a flexible plastic film including a support substrate and an ultraviolet-curable coating layer formed on at least one surface thereof, the ultraviolet-curable coating layer comprising a crosslinked copolymer of a tri- to hexa-functional acrylate binder and a 7- to 20-functional urethane acrylate binder, and inorganic particles having a bimodal particle distribution, including a first group of inorganic particles having a d50 of 20 to 35 nm and a second group of inorganic particles having a d50 of 40 to 130 nm. Patent Document 1 also describes that if the acrylate equivalent of the 7- to 20-functional urethane acrylate binder is too high, the hardness of the coating layer may be insufficient, and that if the acrylate equivalent is low, the hardness may be improved but the flexibility may be reduced, and that the acrylate equivalent may be in the range of about 200 to about 1,500 g / mol.

[0004] Japanese Patent Application Laid-Open No. 2019-51718

[0005] The inventors of the present invention confirmed that the flexible plastic film described in Patent Document 1 could not be used for evaluation of repeated bending properties because the film of the ultraviolet-curable coating layer curled.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hard coat composition that can provide a hard coat layer that has high hardness and is also excellent in flexibility and repeated bending properties.

[0007] The present invention is based on the finding that a hard coat layer having high hardness and excellent flexibility and repeated bending properties can be obtained by using a combination of a (meth)acryloyloxy group-containing compound having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups in one molecule of 7 or more and a polyoxyalkylene group-containing (meth)acrylate having an average number of (meth)acryloyloxy groups in one molecule of 2 to 6, using inorganic particles whose surfaces have been modified with a silane coupling agent as the inorganic particles, and adjusting the content of the (meth)acryloyloxy group-containing compound within a specific range.

[0008] The present invention provides the following: [1] A hard coat composition comprising: a (meth)acryloyloxy group-containing compound having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups per molecule of 7 or more; a polyoxyalkylene group-containing (meth)acrylate having an average number of (meth)acryloyloxy groups per molecule of 2 to 6; and inorganic particles surface-modified with a silane coupling agent, wherein the content of the (meth)acryloyloxy group-containing compound is 30% by mass or less based on 100% by mass of the total solid content of the hard coat composition. [2] The hard coat composition according to [1] above, wherein the content of the polyoxyalkylene group-containing (meth)acrylate is 10 to 60% by mass based on 100% by mass of the total solid content of the hard coat composition. [3] The hard coat composition according to [1] or [2] above, wherein the inorganic particles have an average particle size of 10 nm to 50 nm. [4] The hard coat composition according to any one of [1] to [3] above, wherein the content of the inorganic particles is 10 to 70 mass% in 100 mass% of the total solid content of the hard coat composition. [5] The hard coat composition according to any one of [1] to [4] above, wherein the polyoxyalkylene group-containing (meth)acrylate has an acrylic equivalent of 160 g / eq or more. [6] The hard coat composition according to any one of [1] to [5] above, which is used for producing a flexible plastic film.

[0009] According to the present invention, it is possible to provide a hard coat composition that can give a hard coat layer that has high hardness and is also excellent in flexibility and repeated bending resistance.

[0010] The definitions and meanings of terms and notations used in this specification are as follows. "(Meth)acrylate" is a general term for acrylate and methacrylate. Similarly, "(meth)acryloyloxy" is a general term for acryloyloxy and methacryloyloxy, and "(meth)acrylic" is a general term for acrylic and methacrylic. Numerical ranges expressed using "to" mean that the numbers before and after "to" are the lower and upper limits. The weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights determined by gel permeation chromatography (GPC) based on a calibration curve created using a standard polystyrene sample. Specifically, they are determined by the method described in the Examples. The solid content refers to components excluding the solvent. Components other than the solvent are included in the solid content even if they are not solid (such as liquid components). The acrylic equivalent is determined as follows. [Weight average molecular weight of (meth)acryloyloxy group-containing compound]÷[number of (meth)acryloyloxy groups] or [Weight average molecular weight of polyoxyalkylene group-containing (meth)acrylate]÷[number of (meth)acryloyloxy groups] The number of (meth)acryloyloxy groups is H １ A (meth)acryloyloxy group-containing compound having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups per molecule of 7 or more is sometimes referred to as component (A), a polyoxyalkylene group-containing (meth)acrylate having an average number of (meth)acryloyloxy groups per molecule of 2 to 6 is sometimes referred to as component (B), and inorganic particles surface-modified with a silane coupling agent are sometimes referred to as component (C).

[0011] [Hard Coat Composition] The hard coat composition according to this embodiment is a hard coat composition containing a (meth)acryloyloxy group-containing compound having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups in one molecule of 7 or more, a polyoxyalkylene group-containing (meth)acrylate having an average number of (meth)acryloyloxy groups in one molecule of 2 to 6, and inorganic particles surface-modified with a silane coupling agent, wherein the content of the (meth)acryloyloxy group-containing compound in the hard coat composition is 30 mass% or less in 100 mass% of the total amount of solids.

[0012] The hard coat composition according to this embodiment can provide a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance. While the details of the reason for this are unclear, it is presumed to be as follows. Because the hard coat composition according to this embodiment contains a (meth)acryloyloxy group-containing compound having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups per molecule of 7 or more, a hard coat layer with high hardness can be obtained. Furthermore, because the content of component (A) is 30% by mass or less relative to 100% by mass of the total solids content of the hard coat composition, the flexibility of the hard coat layer is not impaired. Furthermore, because the hard coat composition according to this embodiment contains a polyoxyalkylene group-containing (meth)acrylate having an average number of (meth)acryloyloxy groups per molecule of 2 to 6, it is presumed that a hard coat layer with better flexibility and repeated bending resistance can be obtained compared to polyalcohol polyfunctional (meth)acrylates that do not contain polyoxyalkylene groups.

[0013] <(Meth)acryloyloxy Group-Containing Compound Having an Acrylic Equivalent of Less than 160 g / eq and an Average Number of (Meth)acryloyloxy Groups Per Molecule of 7 or More> The hard coat composition according to this embodiment contains a (meth)acryloyloxy group-containing compound (component (A)) having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups per molecule of 7 or more. Because the acrylic equivalent is less than 160 g / eq, a hard coat layer with high hardness can be obtained. The acrylic equivalent is preferably 20 g / eq or more. When the acrylic equivalent is 20 g / eq or more, a hard coat layer with high hardness and excellent flexibility and repeated bending properties can be easily obtained. From these viewpoints, the acrylic equivalent is preferably 20 g / eq or more and less than 160 g / eq, more preferably 30 to 150 g / eq, even more preferably 40 to 140 g / eq, even more preferably 40 to 120 g / eq, and particularly preferably 40 to 70 g / eq.

[0014] The average number of (meth)acryloyloxy groups in one molecule of the component (A) is 7 or more. When the number is 7 or more, a hard coat layer having high hardness and excellent flexibility and repeated bending resistance can be obtained. From this viewpoint, the average number of (meth)acryloyloxy groups in one molecule of the component (A) is preferably 7 to 200, and more preferably 10 to 150.

[0015] Component (A) is preferably a compound having a multi-branched structure and having a (meth)acryloyloxy group at the end of each branched chain, and may be at least one of a hyperbranched polymer and a dendrimer, or may be a dendrimer. Dendrimers are polymers that are branched with high regularity, while hyperbranched polymers are polymers that are branched with low regularity, and they have lower viscosity and better solvent solubility than linear polymers. Examples of dendrimers include those represented by the following structural formulas (1) to (8), but are not limited thereto. Any compound having a dendrimer structure and having a (meth)acryloyloxy group at the end of each branched chain may be used.

[0016]

[0017] (In the formula R １ each independently represents a hydrogen atom or a methyl group, R ２ each independently represents a hydrocarbon group having 1 to 4 carbon atoms.

[0018] As the dendrimer-type component (A), commercially available products such as "SIRIUS501" [weight average molecular weight (Mw) of approximately 13,000 to 14,000, average number of (meth)acryloyloxy groups per molecule of 110], "SP-1106" manufactured by MIWON Corporation [weight average molecular weight (Mw) of approximately 1,000 to 1,100, average number of (meth)acryloyloxy groups per molecule of 18], and "CN2301" and "CN2302" manufactured by SARTOMER Corporation [average number of (meth)acryloyloxy groups per molecule of 16] and "CN2304" [average number of (meth)acryloyloxy groups per molecule of 18] may be used. These may be used alone or in combination of two or more types. Furthermore, from the viewpoint of obtaining a hard coat layer that has high hardness and excellent flexibility and repeated bending resistance, the weight average molecular weight (Mw) of the component (A) is preferably 1,000 to 30,000.

[0019] The molecular weight distribution of the component (A) is preferably 1 to 15, more preferably 1 to 10, even more preferably 1 to 5, and still more preferably 1 to 3, from the viewpoint of obtaining a hard coat layer that has high hardness and excellent flexibility and repeated bending properties.

[0020] The content of component (A) in 100% by mass of the total solid content of the hard coat composition is 30% by mass or less. When the content is 30% by mass or less, a hard coat layer having high hardness and excellent flexibility and repeated bending properties can be obtained. From this viewpoint, the content of component (A) in 100% by mass of the total solid content of the hard coat composition is preferably 2 to 30% by mass, more preferably 5 to 25% by mass, even more preferably 10 to 25% by mass, and even more preferably 15 to 20% by mass.

[0021] The content of component (A) in 100% by mass of the hard coat composition is preferably 25% by mass or less from the viewpoint of obtaining a hard coat layer that is also excellent in flexibility and repeated bending properties. Furthermore, the content of component (A) in 100% by mass of the hard coat composition is preferably 1% by mass or more from the viewpoint of obtaining a hard coat layer that is high in hardness. From these viewpoints, the content of component (A) in 100% by mass of the hard coat composition is preferably 1 to 25% by mass, more preferably 1 to 20% by mass, even more preferably 2 to 15% by mass, still more preferably 5 to 15% by mass, and particularly preferably 8 to 14% by mass.

[0022] From the viewpoint of obtaining a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance, the content of the component (A) in 100% by mass of the total amount of the component (A) and the component (B) is preferably 5 to 45% by mass, more preferably 5 to 40% by mass, even more preferably 10 to 40% by mass, still more preferably 20 to 40% by mass, and particularly preferably 25 to 35% by mass.

[0023] <Polyoxyalkylene Group-Containing (Meth)acrylate Having an Average Number of (Meth)acryloyloxy Groups in One Molecule of 2 to 6> The hard coat composition according to this embodiment contains a polyoxyalkylene group-containing (meth)acrylate (component (B)) having an average number of (meth)acryloyloxy groups in one molecule of 2 to 6. Component (B) may be an ester obtained by reacting a hydroxyl group of an adduct obtained by adding an alkylene oxide to a polyhydric alcohol with a carboxyl group of (meth)acrylic acid.

[0024] From the viewpoint of obtaining a hard coat layer having high hardness and excellent flexibility and repeated bending properties, the average number of oxyalkylene groups in one molecule of component (B) is preferably 6 to 40, more preferably 10 to 30, even more preferably 14 to 26, and still more preferably 16 to 24. From the viewpoint of obtaining a hard coat layer having high hardness and excellent flexibility and repeated bending properties, the oxyalkylene group is preferably at least one of an oxyethylene group and an oxypropylene group, more preferably an oxyethylene group or both an oxyethylene group and an oxypropylene group, and even more preferably an oxyethylene group.

[0025] In component (B), the average number of (meth)acryloyloxy groups per molecule is 2 to 6. This allows for the production of a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance. From this perspective, the average number of (meth)acryloyloxy groups per molecule is preferably 2 to 5, more preferably 2 to 4, even more preferably 3 to 4, and even more preferably 3. From the perspective of producing a hard coat layer that is also excellent in flexibility and repeated bending resistance, the acrylic equivalent of component (B) is preferably 160 g / eq or more. Furthermore, from the perspective of producing a hard coat layer that is excellent in flexibility, the acrylic equivalent of component (B) is preferably 600 g / eq or less. Therefore, from the viewpoint of obtaining a hard coat layer that is excellent in flexibility and repeated bending properties, the acrylic equivalent of the component (B) is preferably 160 to 600 g / eq, more preferably 200 to 600 g / eq, even more preferably 300 to 500 g / eq, still more preferably 350 to 500 g / eq, and particularly preferably 400 to 500 g / eq.

[0026] The weight average molecular weight (Mw) of the component (B) is preferably 500 to 10,000, more preferably 1,000 to 2,000, from the viewpoint of obtaining a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance.

[0027] A specific example of the compound of component (B) is ethoxylated trimethylolpropane triacrylate, and a commercially available product thereof is AT-20E (ethoxylated trimethylolpropane triacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.).

[0028]

[0083] From the viewpoint of obtaining a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance, the content of component (B) in 100% by mass of the total solid content of the hard coat composition is preferably 10 to 60% by mass, more preferably 20 to 60% by mass, even more preferably 30 to 60% by mass, still more preferably 30 to 50% by mass, and particularly preferably 30 to 45% by mass.

[0029]

[0083] From the viewpoint of obtaining a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance, the content of the component (B) in 100% by mass of the hard coat composition is preferably 10 to 40% by mass, more preferably 15 to 40% by mass, even more preferably 20 to 40% by mass, still more preferably 20 to 35% by mass, and particularly preferably 25 to 30% by mass.

[0030] From the viewpoint of obtaining a hard coat layer that is high in hardness and also excellent in flexibility and repeated bending resistance, the content of the component (B) in 100% by mass of the total amount of the component (A) and the component (B) is preferably 55 to 95% by mass, more preferably 60 to 95% by mass, even more preferably 60 to 90% by mass, still more preferably 60 to 80% by mass, and particularly preferably 65 to 75% by mass.

[0031] <Inorganic particles> Examples of inorganic particles include silica particles, alumina particles, titania particles, and zinc oxide particles. The inorganic particles may be used alone or in combination of two or more types. Furthermore, from the viewpoint of obtaining a cured coating film with high hardness due to good dispersibility in the cured coating film, inorganic particles having an average particle size of two or more types may be used in combination.

[0032] The average particle size of the inorganic particles is preferably 10 to 100 nm, more preferably 10 to 80 nm, and even more preferably 10 to 50 nm. Here, the average particle size of the inorganic particles is determined by the specific surface area (m ２ / g).

[0033] The inorganic particles are preferably surface-modified with a silane coupling agent in order to improve compatibility (wettability) with the (A) and (B) components and obtain a hard coat layer with high hardness and excellent repeated bending resistance. Examples of silane coupling agents include (meth)acryloyl group-containing silane compounds, vinyl group-containing silane compounds, epoxy group-containing silane compounds, and mercapto group-containing silane compounds. The silane coupling agents may be used alone or in combination of two or more. Among these, in terms of affinity with the (A) and (B) components, (meth)acryloyl group-containing silane compounds ((meth)acrylate silane coupling agents) are preferred. In terms of uniform dispersibility in the hard coat composition, the inorganic particles may be pre-dispersed in an organic solvent (medium), for example, an organosol.

[0034] Commercially available inorganic particles include MEK-AC-2140Z (manufactured by Nissan Chemical Industries, Ltd., silica particles surface-modified with a methacrylate silane coupling agent, average particle size: 12 nm), MEK-AC-4130Y (manufactured by Nissan Chemical Industries, Ltd., silica particles surface-modified with a methacrylate silane coupling agent, average particle size: 45 nm), IDISIL VPS NJ20 MEK (manufactured by Evonik Japan, silica particles surface-modified with a tetraalkoxysilane coupling agent, average particle size: 15 nm), and NANOBYK-3605 (manufactured by BYK Japan, silica particles surface-modified with an acrylic, average particle size: 20 nm).

[0035] The content of the inorganic particles in 100% by mass of the total solid content of the hard coat composition is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and even more preferably 20 to 50% by mass. The content of the inorganic particles in 100% by mass of the hard coat composition is preferably 10 to 40% by mass, more preferably 15 to 40% by mass, and even more preferably 15 to 35% by mass.

[0036] <Polymerization Initiator> The hard coat composition according to this embodiment may contain a polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator, and may be a photopolymerization initiator or a thermal polymerization initiator, and any known initiator can be used. From the viewpoint of ease of control of the polymerization reaction, the photopolymerization initiator is preferably one that can be used by irradiation with ultraviolet light having a wavelength of 380 nm or less, and the thermal polymerization initiator is preferably one that can be used by heating within a range of 50 to 120°C.

[0037] Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, diethoxyacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropanone, 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropanone, 4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, and benzoin phenyl ether. ter, benzyl dimethyl ketal, benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone-4-methoxybenzophenone, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, methylphenyl glyoxylate, benzil, and camphorquinone. The photopolymerization initiator may be used alone or in combination of two or more.

[0038] Examples of the thermal polymerization initiator include azo compounds; and organic peroxides such as hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides. Specific examples include azobisisobutyronitrile, benzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoyl)peroxyhexane, tert-butylperoxybenzoate, te Examples of the thermal polymerization initiator include rt-butyl peroxide, cumene hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-dibutylperoxyhexane, 2,4-dichlorobenzoyl peroxide, 1,4-di(2-t-butylperoxyisopropyl)benzene, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, methyl ethyl ketone peroxide, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate. One type of thermal polymerization initiator may be used alone, or two or more types may be used in combination.

[0039] From the viewpoint of an appropriate polymerization rate, the content of the polymerization initiator in the hard coat composition is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 10 parts by mass, and even more preferably 0.1 to 7 parts by mass, relative to 100 parts by mass of the total of the components (A) and (B).

[0040] When a hard coat composition is irradiated with light to obtain a cured product, the light source can be appropriately selected depending on the light absorption ability of the photopolymerization initiator to be blended. For example, ultraviolet light-emitting diodes (LEDs), low-pressure mercury lamps, high-pressure mercury lamps, mercury-xenon lamps, metal halide lamps, tungsten lamps, arc lamps, excimer lamps, excimer lasers, semiconductor lasers, YAG lasers, laser systems combining lasers with nonlinear optical crystals, and high-frequency induced ultraviolet generators can be used as light sources. The cumulative light amount is, for example, 0.01 to 50 J / cm. ２ To that extent.

[0041] <Organic Solvent> The hard coat composition according to this embodiment may contain an organic solvent. The organic solvent also functions as a dispersion medium for the components contained in the hard coat composition, and is used to ensure that each component is uniformly dissolved or dispersed and to provide appropriate fluidity and coatability. Examples of organic solvents include alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; alkoxy alcohols such as 2-methoxyethanol, 2-ethoxyethanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and cyclohexanone; glycol monoethers such as propylene glycol monopropyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, and diethylene glycol-2-ethylhexyl ether; and aromatic solvents such as benzene, toluene, and xylene. The organic solvents may be used alone or in combination of two or more.

[0042] The content of the organic solvent in the hard coat composition is within a range in which the effects of the present invention are not hindered, and from the viewpoint of appropriate fluidity, coatability, etc. of the hard coat composition, it is preferably 50 parts by mass or less, more preferably 10 to 50 parts by mass, and even more preferably 10 to 40 parts by mass.

[0043] <Other Components> The hard coat composition may or may not contain other components in addition to the above-mentioned components depending on the ease of handling and its application.The other components include, for example, other monomer components and resin components other than the above-mentioned component (A) and component (B), catalysts, colorants such as pigments and dyes, silane coupling agents, tackifier resins, antioxidants, light stabilizers, metal deactivators, rust inhibitors, antiaging agents, moisture absorbents, hydrolysis inhibitors, antifoaming agents, and fillers.These other components in the hard coat composition can be blended in a content range that does not impair the effects of the present invention.

[0044] The total content of the (A), (B), and (C) components in 100% by mass of the hard coat composition according to this embodiment is preferably 40 to 100% by mass, more preferably 40 to 90% by mass, and even more preferably 55 to 80% by mass. When the hard coat composition according to this embodiment contains an organic solvent, the total content of the (A), (B), (C) components, and the organic solvent in 100% by mass of the hard coat composition is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass.

[0045] The total content of the (A), (B) and (C) components in the hard coat composition according to this embodiment, relative to the total solid content (100% by mass), is preferably 40 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass.

[0046] [Uses] The hard coat composition according to this embodiment is suitable for use as a coating agent for various substrates, particularly as a surface protective coating agent for preventing scratches, cracks, etc. on displays and touch panels of image display devices, etc. In particular, a cured product of the hard coat composition has high hardness and excellent flexibility and repeated bending properties, and is therefore suitable for a hard coat layer for surface protection of flexible plastic films used in flexible displays, foldable devices, etc.

[0047] [Hard Coat Layer] The hard coat layer according to this embodiment is a cured product of the hard coat composition according to this embodiment described above. By applying the hard coat composition according to this embodiment to a film substrate and curing it, a film having a hard coat layer formed thereon can be obtained. The hard coat layer according to this embodiment has high hardness, is less likely to cause warping of the film, and has excellent repeated bending resistance. In a film having a film substrate and a hard coat layer formed on the film substrate, it is preferable that the hard coat layer is the outermost layer, and that the surface of both sides of the hard coat layer opposite the film substrate is exposed. The hard coat layer may be provided directly on the film substrate, or another layer such as a primer layer may be provided between the hard coat layer and the film substrate.

[0048] The hard coat composition (coating agent) can be applied by any known method, such as bar coating, knife coating, roll coating, blade coating, die coating, microgravure coating, comma coating, slot die coating, lip coating, or cast coating.

[0049] The thickness of the hard coat layer is preferably 3 μm or more, more preferably 3 to 20 μm, and even more preferably 3 to 15 μm, from the viewpoint of achieving high hardness, resistance to warping of the film, and excellent resistance to repeated bending.

[0050] According to the hard coat layer of this embodiment, these properties are exhibited in the above-mentioned applications, and therefore, coated products having the hard coat layer, particularly products such as flexible displays and foldable devices having a surface on which the hard coat layer is formed, can be suitably provided.

[0051] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible within the scope of the gist of the present invention. In the following, Examples 1 to 5 are examples, and Examples 6 to 14 are comparative examples.

[0052] [Raw materials used, etc.] The raw materials used in the examples are shown in Tables 1 and 2 below.

[0053]

[0054]

[0055] [Examples 1 to 14] The raw materials shown in Table 3 were blended in the blending ratios shown in Table 3 and mixed for 1 hour with a magnetic stirrer to produce hard coat compositions according to Examples 1 to 14. In Table 3, the contents of component (A), component (A'), component (B), component (B'), component (C), and component (C') are the contents converted to solid content. In Table 3, the content of solvent is the total amount including the solvent contained in component (A), component (A'), component (B), component (B'), component (C), and component (C').

[0056] [Preparation of Flexible Plastic Film] Each of the hard coat compositions prepared in Examples 1 to 14 was applied to the film substrate shown in Table 2 using a bar coating film applicator, and dried at 100°C for 3 minutes. Then, the film was dried on a UV conveyor (integrated ultraviolet irradiation dose 1000 mJ / cm ２ The hard coat composition on the film substrate was cured by the above-mentioned method to prepare a flexible plastic film having a film substrate and a hard coat layer on the film substrate. The thickness of the hard coat layer was 10 μm.

[0057] The hard coat layer and flexible plastic film thus produced were evaluated for the following items. Table 3 shows the evaluation results.

[0058] [Evaluation] (Weight-average molecular weight and number-average molecular weight) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of components (A), (A'), (B), and (B') in Table 1 were measured by gel permeation chromatography (GPC) under the following measurement conditions. <Measurement conditions> - Instrument used: "HLC-8320GPC" manufactured by Tosoh Corporation - Column used: The following two columns were connected in series: "TSKgel (registered trademark) Super HZ2500" manufactured by Tosoh Corporation, two columns; and "TSKgel (registered trademark) Super HZ4000" manufactured by Tosoh Corporation, two columns. - Column temperature: 40°C - Detector: Refractive index (RI) detector - Eluent: Tetrahydrofuran - Flow rate: 0.8 mL / min - Sample concentration: 0.5% by mass - Sample injection amount: 100 μL - Standard sample: Polystyrene

[0059] (Thickness) The thickness of the hard coat layer was measured with a dial thickness gauge ("PEACOCK G-6C", manufactured by Ozaki Manufacturing Co., Ltd.). Specifically, the thickness (50 μm) of the polyimide film was measured in advance. In addition, a hard coat layer was formed on the polyimide film to prepare a flexible plastic film, and then the thickness of the flexible plastic film was measured. The value obtained by subtracting the thickness (50 μm) of the polyimide film from the thickness of the flexible plastic film was taken as the thickness of the hard coat layer.

[0060] (State of flexible plastic film) The state (shape) of the flexible plastic film was evaluated by visual observation. The evaluation criteria for the results shown in Table 3 are as follows: A: A flat state (0 mm≦(average lift height)<1 mm) was maintained. B: A nearly flat state (1 mm≦(average lift height)<5 mm) was maintained. C: Warpage (curl) occurred.

[0061] (Pencil hardness) According to JIS K 5600-5-4:1999, a pencil was pressed against the hard coat layer with a load of 750 g at an angle of 45°, and the pencil was moved back and forth 5 cm three times, and then the coating surface was inspected with the naked eye to determine the hardness. A pencil hardness of 4H or higher can be said to be sufficiently high.

[0062] (Scratch test) Steel wool (#0000) was pressed against the hard coat layer by hand and rubbed back and forth 10 times, and then the state of scratches formed was visually inspected and evaluated. The evaluation criteria for the results shown in Table 3 are as follows: A: No scratches formed. B: Scratches were observed in some areas. C: Scratches formed over the entire area rubbed with the steel wool.

[0063] (Repeated Bending Test) A 140 mm x 40 mm sample cut from a flexible plastic film (a polyimide film having a hard coat layer formed thereon) was fixed at both longitudinal ends to the clamps of a sheet-shaped no-load U-shaped stretch tester ("DLDMLH-FS," manufactured by Yuasa System Co., Ltd.) with double-sided tape. The test involved bending and stretching the sample 100,000 times at a speed of 50 times / min, so that the sample was bent into a U-shape (bending radius: 1.5 mm) with the hard coat layer side facing inward (hard coat layer inside). The same repeated bending and stretching test was also conducted for a sample with the hard coat layer side facing outward in the U-shape (hard coat layer outside). The condition of the hard coat layer of the sample after the test was visually inspected and evaluated. The evaluation criteria for the results shown in Table 3 are as follows: A: No change; B: Scratches occurred; C: The coating peeled off.

[0064]

[0065] As can be seen from Table 3, it was confirmed that the flexible plastic films having a hard coating layer formed by applying and curing the hard coating composition of the present invention (Examples 1 to 5) maintained a flat state without curling, had high hardness, were resistant to scratches, and had excellent resistance to repeated bending.

Claims

1. A hard coat composition comprising: a (meth)acryloyloxy group-containing compound having an acrylic equivalent of less than 160 g / eq and an average number of (meth)acryloyloxy groups in one molecule of 7 or more; a polyoxyalkylene group-containing (meth)acrylate having an average number of (meth)acryloyloxy groups in one molecule of 2 to 6; and inorganic particles surface-modified with a silane coupling agent, wherein the content of the (meth)acryloyloxy group-containing compound in the total amount of solids in the hard coat composition (100% by mass) is 30% by mass or less.

2. The hard coat composition according to claim 1, wherein the content of the polyoxyalkylene group-containing (meth)acrylate is 10 to 60 mass % in 100 mass % of the total amount of solids in the hard coat composition.

3. The hard coat composition according to claim 1 or 2, wherein the inorganic particles have an average particle size of 10 nm to 50 nm.

4. The hard coat composition according to claim 1 or 2, wherein the content of said inorganic particles is 10 to 70 mass % in 100 mass % of the total amount of solids in said hard coat composition.

5. The hard coat composition according to claim 1 or 2, wherein the polyoxyalkylene group-containing (meth)acrylate has an acrylic equivalent of 160 g / eq or more.

6. The hard coat composition of claim 1 or 2, used in the manufacture of flexible plastic films.

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