Hard coating film and image display device equipped therewith

Abstract

The present invention provides a hard coating film comprising a transparent substrate and a hard coating layer formed on at least one side of the transparent substrate, wherein the hard coating layer is formed from a hard coating composition comprising a light-transmitting resin, a photoinitiator, and a solvent, the light-transmitting resin comprising an ethylene oxide group-containing 3-6 functional (meth)acrylate and a 10-functional or more functional urethane (meth)acrylate, and the 10-functional or more functional urethane (meth)acrylate having a viscosity of 50,000-55,000 cP at 25°C, and an image display device equipped therewith. [Effects] The hard coating film according to the present invention has high hardness and excellent scratch resistance, and can minimize the occurrence of curl due to curing shrinkage.

Description

[Technical Field]

[0001] The present invention relates to a hard coating film and an image display device equipped therewith, and more particularly to a hard coating film that is excellent in hardness and scratch resistance and minimizes the occurrence of curl due to curing shrinkage, and an image display device equipped with the hard coating film. [Background technology]

[0002] Hard coating films are used in image display devices such as liquid crystal displays, electroluminescent (EL) displays, plasma displays (PDs), and field emission displays (FEDs) for purposes such as surface protection.

[0003] In recent years, flexible or foldable display devices, which can maintain their display performance even when bent like paper by using flexible materials such as plastic or UTG (ultra-thin glass) instead of existing inflexible glass substrates, have rapidly emerged as next-generation display devices. Accordingly, research is being conducted on hard coating films that not only have high hardness and good scratch resistance, but also do not exhibit curling at the film edges during the manufacturing process or use, and possess appropriate flexibility so that cracks do not occur when stretched.

[0004] However, ensuring the hardness and scratch resistance of a hard coating film is a trade-off with suppressing curling. When using a compound with polyfunctional groups as a resin to improve the hardness and scratch resistance of the film, it is difficult to prevent curling from occurring in the formed film.

[0005] Korean Patent Publication No. 10-2012-0078457 discloses a hard coating composition comprising a rubber core, an impact reinforcement agent including one or more shell layers, a photopolymerizable compound, and a photopolymerization initiator, and describes that a hard coating film to which the hard coating composition is applied can achieve excellent scratch resistance, adhesion to films, impact resistance, solvent resistance, processability, and flexibility.

[0006] However, the hard coating film has the problem of not being able to secure sufficient hardness and flexibility to be applied to foldable display devices, and also of curling occurring in the formed film. [Overview of the initiative] [Problems that the invention aims to solve]

[0007] One objective of the present invention is to provide a hard coating film that exhibits excellent hardness and scratch resistance, and minimizes curling due to curing shrinkage.

[0008] Another object of the present invention is to provide an image display device equipped with the hard coating film.

[0009] Another object of the present invention is to provide a window for a foldable display device equipped with the hard coating film. [Means for solving the problem]

[0010] On the other hand, the present invention provides a hard coating film comprising a transparent substrate and a hard coating layer formed on at least one side of the transparent substrate, wherein the hard coating layer is formed from a hard coating composition comprising a light-transmitting resin, a photoinitiator, and a solvent, the light-transmitting resin comprising an ethylene oxide group-containing 3-6 functional (meth)acrylate and a 10-functional or more functional urethane (meth)acrylate, and the 10-functional or more functional urethane (meth)acrylate has a viscosity of 50,000 to 55,000 cP at 25°C.

[0011] In one embodiment of the present invention, the ethylene oxide group-containing 3- to 6-functional (meth)acrylate may be present in an amount of 50-70% by weight with respect to 100% by weight of the total translucent resin, and the 10- or more-functional urethane (meth)acrylate may be present in an amount of 30-50% by weight.

[0012] In one embodiment of the present invention, the ethylene oxide group-containing 3- to 6-functional (meth)acrylate may be a compound represented by the following chemical formula 1.

[0013] [ka]

[0014] In the above formula, The sum of a, b, c, and d is 5.

[0015] In the other hand, the present invention provides an image display device equipped with the hard coating film.

[0016] In addition, the present invention provides a window for a foldable display device equipped with the hard coating film. [Effects of the Invention]

[0017] The hard coating film according to the present invention is excellent in hardness and scratch resistance, minimizes curling caused by curing shrinkage, and can be effectively used for a window of a foldable display device. MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, the present invention will be described in more detail.

[0019] One embodiment of the present invention is a hard coating film comprising a transparent substrate and a hard coating layer formed on at least one surface of the transparent substrate, wherein the hard coating layer is formed from a hard coating composition containing a light-transmitting resin, a photoinitiator and a solvent, the light-transmitting resin comprises an ethylene oxide group-containing 3 to 6 functional (meth)acrylate and a 10 or more functional urethane (meth)acrylate, and the 10 or more functional urethane (meth)acrylate has a viscosity of 50,000 to 55,000 cP at 25° C.

[0020] The hard coating film according to one embodiment of the present invention is formed from a hard coating composition comprising an ethylene oxide group-containing 3 to 6 functional (meth)acrylate and a 10 or more functional urethane (meth)acrylate having a viscosity of 50,000 to 55,000 cP at 25° C, is excellent in hardness and scratch resistance, and can suppress occurrence of curling due to curing shrinkage.

[0021] In one embodiment of the present invention, any transparent plastic film can be used as the transparent substrate. Examples thereof include films formed from polymers such as triacetyl cellulose, acetyl cellulose butyrate, ethylene-vinyl acetate copolymers, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, polyesters, polystyrene, polyamides, polyetherimides, polyacrylics, polyimides, polyether sulfones, polysulfones, polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyether ketone, polyether ether ketone, polyether sulfone, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polycarbonate. These polymers may be used alone or as a mixture of two or more thereof.

[0022] The thickness of the transparent substrate is not particularly limited, and may be 10 to 1,000 µm, specifically 20 to 150 µm. If the thickness of the transparent substrate is less than 10 µm, the strength of the film decreases, resulting in poor processability; if it exceeds 1,000 µm, problems such as decreased transparency and increased weight of the hard coating film occur.

[0023] In one embodiment of the present invention, the hard coating composition may comprise a light-transmitting resin, a photoinitiator and a solvent.

[0024] From the perspective of improving curling properties, the light-transmitting resin comprises an ethylene oxide group-containing 3- to 6-functional (meth)acrylate, and from the perspective of ensuring hardness and scratch resistance, the light-transmitting resin comprises a 10-functional or higher urethane (meth)acrylate.

[0025] Specific examples of the ethylene oxide group-containing 3-6 functional (meth)acrylates include trimethylolpropane(EO)3-tri(meth)acrylate, trimethylolpropane(EO)6-tri(meth)acrylate, trimethylolpropane(EO)9-tri(meth)acrylate, and trimethylolpropane(EO) 15 Tri(meth)acrylate, trimethylolpropane(EO) 20 Tri(meth)acrylate, glycerin (EO)3, Tri(meth)acrylate, glycerin (EO)6, Tri(meth)acrylate, glycerin (EO)9, Tri(meth)acrylate, pentaerythritol (EO)4, Tetra(meth)acrylate, pentaerythritol (EO)8, Tetra(meth)acrylate, pentaerythritol (EO) 12 Tetra(meth)acrylate, dipentaerythritol(EO)6, hexa(meth)acrylate, dipentaerythritol(EO) 12 Hexa(meth)acrylate, dipentaerythritol (EO) 18 Hexa(meth)acrylate, dipentaerythritol (EO) 24 Examples include hexa(meth)acrylate.

[0026] In one embodiment of the present invention, the ethylene oxide group-containing 3- to 6-functional (meth)acrylate may be a compound represented by the following chemical formula 1.

[0027] [ka]

[0028] In the above formula, The sum of a, b, c, and d is 5.

[0029] The aforementioned 10-function or more urethane (meth)acrylate can be produced by reacting a (meth)acrylate having a hydroxyl group in its molecule with an isocyanate compound in the presence of a catalyst.

[0030] Specific examples of (meth)acrylates having a hydroxyl group in the molecule include 2-hydroxyethyl (meth)acrylate, 2-hydroxyisopropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone ring-opened hydroxyacrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Specific examples of compounds having an isocyanate group include 1,4-diisocyanate butane, 1,6-diisocyanate hexane, 1,8-diisocyanate octane, 1,12-diisocyanate dodecane, 1,5-diisocyanate-2-methylpentane, trimethyl-1,6-diisocyanate hexane, 1,3-bis(isocyanatemethyl)cyclohexane, trans-1,4-cyclohexene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and isophorone diiso Examples include cyanates, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, xylene-1,4-diisocyanate, tetramethylxylene-1,3-diisocyanate, 1-chloromethyl-2,4-diisocyanate, 4,4'-methylenebis(2,6-dimethylphenyl isocyanate), 4,4'-oxybis(phenyl isocyanate), trifunctional isocyanates derived from hexamethylene diisocyanate, and adducts of trimethylolpropane and toluene diisocyanate.

[0031] The 10-function or more urethane (meth)acrylate may have a viscosity of 50,000 to 55,000 cP at 25°C. If the viscosity is less than 50,000 cP, the crosslinking density will be high, leading to problems such as severe curling of the hard coating film. If it exceeds 55,000 cP, the crosslinking density will be low, which may reduce the hardness of the film.

[0032] In a hard coating composition according to one embodiment of the present invention, the ethylene oxide group-containing 3- to 6-functional (meth)acrylate is included in an amount of 50-70% by weight and the 10- or more-functional urethane (meth)acrylate may be included in an amount of 30-50% by weight per 100% by weight of the total translucent resin. When the respective contents fall within the above ranges, excellent hardness and scratch resistance can be observed, and curling due to shrinkage during curing can be suppressed.

[0033] The translucent resin may be included in the hard coating composition in an amount of 70 to 95% by weight, preferably 85 to 95% by weight, more preferably 90 to 95% by weight, and even more preferably 92 to 95% by weight, based on 100% by weight of the total solids content. If the translucent resin content is less than 70% by weight, it is difficult to achieve sufficient hardness improvement, and if it exceeds 95% by weight, there is a problem of severe curling.

[0034] In one embodiment of the present invention, the photoinitiator is included for photocuring induction of the hard coating composition and may include, for example, a photoradical initiator that can form radicals upon light irradiation.

[0035] The aforementioned photoinitiator may be used without particular limitations, as long as it is used in the art. For example, one or more selected from the group consisting of hydroxyketones, aminoketones, hydrogen abstraction type photoinitiators, and combinations thereof may be used.

[0036] Examples of the aforementioned photoinitiators include type I initiators that generate radicals by decomposing molecules due to differences in chemical structure or molecular bond energy, and type II initiators that induce hydrogen abstraction in coexistence with tertiary amines.

[0037] For example, the type I initiator may include acetophenones such as 4-phenoxydichloroacetophenone, 4-t-butyldichloroacetophenone, 4-t-butyltrichloroacetophenone, diethoxyacetophenone, 2-hydroxy-2-methyl-l-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone, and 1-hydroxycyclohexylphenyl ketone; benzoin compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, and benzyldimethyl ketal; phosphine oxides; and titanocene compounds.

[0038] The aforementioned type II initiator may include benzophenones such as benzophenone, benzoylbenzoic acid, benzoylbenzoate methyl ether, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, and 3,3'-methyl-4-methoxybenzophenone; and thioxanthones such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, and isopropylthioxanthone.

[0039] The photoinitiators described above may be used individually or in combination of two or more. Furthermore, the Type I and Type II initiators may be used individually or in combination.

[0040] In one embodiment of the present invention, the photoinitiator may be present in an amount of 3 to 10% by weight, preferably 5 to 10% by weight, and more preferably 5 to 8% by weight, based on 100% by weight of the total solids content in the hard coating composition. If the photoinitiator content is less than 3% by weight, the curing rate of the composition will be slow, resulting in uncured material and a decrease in mechanical properties. If it exceeds 10% by weight, overcuring may occur, causing cracks in the coating film.

[0041] In one embodiment of the present invention, the solvent may be used without particular limitation as long as it is capable of dissolving or dispersing the above-described composition and is known in the art. Usable solvents include alcohol-based solvents (methanol, ethanol, isopropanol, butanol, methyl cellosolve, ethyl cellosolve, etc.), ketone-based solvents (methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, cyclohexanone, etc.), and acetate-based solvents (ethyl acetate, propyl acetate, n-butyl acetate, t-butyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, propylene The solvents may include (such as propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, methoxybutyl acetate, methoxypentyl acetate), hexane-based solvents (such as hexane, heptane, octane), benzene-based solvents (such as benzene, toluene, xylene), ether-based solvents (such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, etc.). The solvents exemplified above may be used individually or in combination of two or more.

[0042] The solvent may be present in an amount of 10 to 95% by weight, preferably 20 to 80% by weight, relative to 100% by weight of the hard coating composition. If the solvent content is below the range, the viscosity will be high, resulting in poor workability and insufficient sweeping of the substrate. Conversely, if it exceeds the range, the drying process will take a long time, making it economically unviable, and the sweeping of the substrate film may become severe, causing haze. For this reason, the solvent should be used appropriately within the range.

[0043] The hard coating composition may further contain a leveling agent to impart smoothness and coating properties to the coating film during the coating process.

[0044] The leveling agent may be a commercially available silicone-based leveling agent, a fluorine-based leveling agent, or an acrylic polymer-based leveling agent, for example, BYK-307, BYK-323, BYK-331, BYK-333, BYK-337, BYK-346, BYK-361N, BYK-373, BYK-375, BYK-377, BYK-378, BYK-3550, BYK-UV3500, BYK-UV3530, BYK-UV3575, BYK-UV3576 from BYK Chemie, and TEGO Glide 410, TEGO Glide 411, TEGO Glide 415, TEGO Glide 420, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Glide from Degussa. You may use 455, TEGO Rad 2100, TEGO Rad 2200N, TEGO Rad 2250, TEGO Rad 2300, TEGO Rad 2500, FC-4430 and FC-4432 from 3M, or KY-1203 from Shin-Etsu Chemical Co., Ltd.

[0045] The leveling agent may be included in the hard coating composition in an amount of 0.01 to 10% by weight relative to 100% by weight of the total solids. If the content of the leveling agent is below the range, it becomes difficult to obtain sufficient smoothness of the optical film, and if it exceeds the range, the hardness and scratch characteristics of the optical film may decrease.

[0046] In addition to the components described above, the hard coating composition may further contain components commonly used in the art, such as ultraviolet stabilizers, heat stabilizers, antioxidants, lubricants, and antifouling agents.

[0047] The aforementioned ultraviolet stabilizers are additives added to protect the coating film by blocking or absorbing ultraviolet light, as prolonged exposure to ultraviolet light causes decomposition, discoloration, and brittleness of the surface of the hardened coating film. These ultraviolet stabilizers can be classified into absorbers, quenchers, and hindered amine light stabilizers (HALS) according to their mechanism of action. They can also be classified into phenyl salicylate (absorber), benzophenone (absorber), benzotriazole (absorber), nickel derivatives (quencher), and radical scavengers according to their chemical structure. The ultraviolet stabilizers are not particularly limited as long as they do not significantly alter the initial hue of the coating film.

[0048] Furthermore, the heat stabilizers may be commercially applicable products, including polyphenol-based primary heat stabilizers, phosphide-based secondary heat stabilizers, and lactone-based heat stabilizers, each used individually or in combination.

[0049] The UV stabilizer and heat stabilizer may be used in appropriate amounts, adjusted so as not to affect UV curability.

[0050] The hard coating layer can be formed by applying the hard coating composition onto a substrate, drying it, and then UV curing it.

[0051] The hard coating composition can be applied to a substrate layer by a coating process using known methods such as die coating, air knife, reverse roll, spray, blade, casting, gravure, microgravure, and spin coating.

[0052] After applying the hard coating composition to the substrate layer, the volatile matter is evaporated and dried at a temperature of 30 to 150°C for 10 seconds to 1 hour, more specifically, for 30 seconds to 30 minutes, and then cured by irradiation with UV light. The amount of UV light irradiated is specifically about 0.01 to 10 J / cm². 2 It can be as follows, or more specifically, 0.1~2 J / cm 2 That's fine.

[0053] In this case, the thickness of the formed hard coating layer may be specifically 1 to 30 μm, and more specifically 3 to 20 μm. When the thickness of the hard coating layer falls within this range, excellent hardness, flexibility, and curl characteristics can be obtained.

[0054] One embodiment of the present invention relates to an image display device equipped with the hard coating film described above. As an example, the hard coating film of the present invention may be used as a window for an image display device, particularly a foldable display device. The hard coating film of the present invention may also be used by attaching it to a polarizing plate, a touch sensor, or the like.

[0055] The hard coating film according to one embodiment of the present invention may be used in reflective, transmissive, or semi-transmissive LCDs, or in LCDs with various driving methods such as TN, STN, OCB, HAN, VA, and IPS types. Furthermore, the hard coating film according to one embodiment of the present invention may be used in various image display devices such as plasma displays, field emission displays, organic EL displays, inorganic EL displays, and electronic paper.

[0056] The present invention will be described in more detail below with reference to examples, comparative examples, and experimental examples. It should be noted that these examples, comparative examples, and experimental examples are merely for illustrative purposes, and it will be obvious to those skilled in the art that the scope of the present invention is not limited thereto.

[0057] [Manufacturing Examples 1-10: Manufacturing of Hard Coating Compositions] Each component having the composition shown in Table 1 below was blended using a stirrer, and filtered using a filter made of PP material to produce a hard coating composition (unit: % by weight).

[0058]

Table 1

[0059] A-1: Ethylene oxide group-containing tetrafunctional acrylate (Miramer M4004, manufactured by Miwon) A-2: 10-functional urethane acrylate (KELLOMER LP-9205, manufactured by KELLON, viscosity at 25°C: 55,000 cP) A-3: 10-functional urethane acrylate (ACYMOL I-8906S, manufactured by EXINNO, viscosity at 25°C: 50,000 cP) A-4: 10-functional urethane acrylate (KELLOMER LP-9200, manufactured by KELLON, viscosity at 25°C: 58,000 cP) B: 1-hydroxycyclohexyl phenyl ketone C: Silicone-based leveling agent (BYK-307, manufactured by BYK) D: Methyl ethyl ketone.

[0060] [Examples and Comparative Examples: Production of Hard Coating Films] The hard coating composition produced in the above Preparation Example was coated on a polyethylene terephthalate film (PET, 65 µm) such that the thickness after curing was 20 µm, dried, and then subjected to an integrated UV light intensity of 600 mJ / cm 2 was irradiated to produce a hard coating film.

[0061] Experimental Example 1: Physical properties of the hard coating films produced in the above Examples and Comparative Examples were measured as described below, and the results are shown in Table 2 below.

[0062] (1) Curl characteristics The hard-coated films produced in the examples and comparative examples were cut into 10cm x 10cm squares. When placed on a flat floor with the coated surface facing upwards, the height at which the film lifted at the cut area was measured. If the film was rolled up, its diameter was measured and indicated by φ.

[0063] (2) Scratch resistance After securing the hard coating film to the glass with tape so that the coating side faces upwards, 250 g / cm³ of steel wool (#0000) is used. 2 The film was rubbed back and forth 10 times under a load, and the presence or absence of scratches on the surface was visually checked. Scratch resistance was then evaluated according to the evaluation criteria below. <Evaluation Criteria> ○: No scratch occurred ×: Scratches may occur.

[0064] (3) Pencil hardness After securing the hard coating film to the glass with tape so that the coated side faced upwards, the pencil hardness was measured under a 1kg load. Five tests were conducted using pencils of the same hardness at a length of 1cm, and the hardness that passed four or more tests was expressed as the pencil hardness.

[0065] [Table 2]

[0066] From Table 2 above, it was confirmed that the hard coating films of Examples 1 to 4, formed from hard coating compositions containing ethylene oxide group-containing 3-6 functional (meth)acrylate and 10- or more functional urethane (meth)acrylate with a viscosity of 50,000-55,000 cP at 25°C, exhibit excellent hardness, scratch resistance, and curl characteristics.

[0067] In contrast, the hard coating films of Comparative Examples 1 to 6, which used hard coating compositions that did not contain ethylene oxide group-containing 3-6 functional (meth)acrylate or 10-functional or higher urethane (meth)acrylate, or did not contain the ethylene oxide group-containing 3-6 functional (meth)acrylate and 10-functional or higher urethane (meth)acrylate in amounts of 50-70% and 30-50% by weight, respectively, or contained 10-functional or higher urethane (meth)acrylate with a viscosity outside the range of 50,000-55,000 cP, were found to have poor curl characteristics, poor scratch resistance, or low pencil hardness.

[0068] Although specific parts of the present invention have been described in detail above, it is clear to any person with ordinary skill in the art to which the present invention belongs that such specific technologies are merely preferred embodiments and do not limit the scope of the present invention. A person with ordinary skill in the art to which the present invention belongs will be able to make various applications and modifications within the scope of the present invention based on the above content.

[0069] Therefore, the substantial scope of the present invention can be defined by the claims and their equivalents.

Claims

1. A hard coating film comprising a transparent substrate and a hard coating layer formed on at least one side of the transparent substrate, The hard coating layer is formed from a hard coating composition comprising a light-transmitting resin, a photoinitiator, and a solvent. The light-transmitting resin comprises ethylene oxide group-containing 3- to 6-functional (meth)acrylates and 10-functional or more urethane (meth)acrylates. The aforementioned 10-function or more urethane (meth)acrylate is a hard coating film having a viscosity of 50,000 to 55,000 cP at 25°C.

2. The hard coating film according to claim 1, wherein the ethylene oxide group-containing 3- to 6-functional (meth)acrylate is contained in an amount of 50-70% by weight, and the 10- or more-functional urethane (meth)acrylate is contained in an amount of 30-50% by weight, based on 100% by weight of the total translucent resin.

3. The hard coating film according to claim 1, wherein the ethylene oxide group-containing 3- to 6-functional (meth)acrylate is a compound represented by the following chemical formula 1; 【Chemistry 1】 In the above formula, The sum of a, b, c, and d is 5.

4. An image display device comprising a hard coating film according to any one of claims 1 to 3.

5. A window for a foldable display device, comprising a hard-coated film as described in any one of claims 1 to 3.

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