Coating liquid for forming low refractive index layer, and antireflection film

Abstract

Disclosed is a coating liquid for forming a low refractive index layer, the coating liquid containing: hollow polymer particles (A) that have an average particle diameter of 150 nm or less; and a (meth)acrylate compound (B) that contains no fluorine atoms and has a (meth)acryloyl group equivalent of 115 or more. The (meth)acrylate compound (B) contains a urethane (meth)acrylate (b).

Description

Coating liquid for forming low refractive index layer and anti-reflection film

[0001] An embodiment of the present invention relates to a coating liquid for forming a low refractive index layer and an antireflection film.

[0002] BACKGROUND ART An anti-reflection film or anti-glare film having a low refractive index layer is provided on the image display surface of an image display device such as a liquid crystal display, an organic EL display, or a touch panel in order to suppress reflection of external light.

[0003] An anti-reflection film is a laminate that reduces luminous reflectance by the light interference effect caused by light reflected from the surface of a low refractive index layer and light reflected from the interface between the low refractive index layer and a layer adjacent to the low refractive index layer (e.g., a hard coat layer or a high refractive index layer).

[0004] Anti-reflection films are often laminated on the outermost surface layer of displays, and are required to be scratch-resistant and wear-resistant.

[0005] In recent years, smartphones and tablet devices equipped with foldable displays have been developed. The anti-reflection film laminated on the foldable display is required to have sufficient bending resistance to follow the bending without causing changes in appearance or cracking.

[0006] The antireflection film disclosed in Patent Document 1 contains hollow polymer particles in a low refractive index layer, and it has been revealed that the antireflection film has improved flex resistance compared to conventional low refractive index layers using hollow silica particles. Since organic polymer particles are flexible compared to the rigidity derived from inorganic silica, the antireflection film disclosed above is thought to have high flex resistance in a mandrel test.

[0007] Japanese Patent Application Laid-Open No. 2020-189978

[0008] Foldable displays used in smartphones and the like are required to have bending resistance that allows them to withstand not only one bending but also multiple repeated bending tests. However, the anti-reflection film disclosed in Patent Document 1 has a problem in that the appearance changes or cracks occur during repeated bending tests using a mandrel test.

[0009] The problem to be solved by the present invention is to provide a coating liquid for forming a low refractive index layer for use in an antireflection film, which has excellent durability in a repeated bending test and also excellent durability in a scratch resistance test.

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have arrived at the following invention. That is, the present invention includes the following embodiments. However, the present invention is not limited to the following embodiments and includes various embodiments. <1> A coating liquid for forming a low refractive index layer, comprising hollow polymer particles (A) having an average particle size of 150 nm or less and a (meth)acrylate compound (B) that does not contain fluorine atoms and has a (meth)acryloyl group equivalent of 115 or more, wherein the compound (B) comprises a urethane (meth)acrylate (b).

[0011] <2> The coating liquid for forming a low refractive index layer according to <1>, further comprising a (meth)acrylate compound (C) having a (meth)acryloyl group equivalent of less than 115.

[0012] <3> The coating liquid for forming a low refractive index layer according to <2>, containing 20 to 200 parts by mass of the (meth)acrylate compound (C) relative to 100 parts by mass of the (meth)acrylate compound (B).

[0013] <4> The coating liquid for forming a low refractive index layer according to any one of <1> to <3>, further comprising inorganic oxide fine particles having an average particle diameter of 50 to 90 nm.

[0014] <5> The coating liquid for forming a low refractive index layer according to <4>, wherein the content of the inorganic oxide fine particles is 0.4 to 3 mass % relative to 100 mass % of the nonvolatile content of the coating liquid for forming a low refractive index layer.

[0015] <6> The coating liquid for forming a low refractive index layer according to any one of <1> to <3>, further comprising aluminum oxide fine particles having an average particle diameter of 50 to 90 nm, wherein the content of the aluminum oxide fine particles is 0.4 to 3 mass% relative to 100 mass% of the nonvolatile content of the coating liquid for forming a low refractive index layer.

[0016] <7> An antireflection film comprising a transparent substrate and a low refractive index layer formed on the transparent substrate, the low refractive index layer being a cured film of the coating liquid for forming a low refractive index layer according to any one of <1> to <6>.

[0017] According to the present invention, it is possible to provide a coating liquid for forming a low refractive index layer suitable for use in an antireflection film, which has excellent flex resistance in a repeated bending test and excellent scratch resistance.

[0018] An embodiment of the present invention will be described below. First, the terms used in this specification will be described. In this specification, unless otherwise specified, the terms "(meth)acrylic" and "(meth)acryloyl" mean "acrylic or methacrylic" and "acryloyl or methacryloyl," respectively. Similarly, the terms "(meth)acrylic acid," "(meth)acrylate," and "(meth)acryloyloxy" mean "acrylic acid or methacrylic acid," "acrylate or methacrylate," and "acryloyloxy or methacryloyloxy," respectively. Furthermore, "(meth)acryloyl group equivalent" may be referred to as "equivalent," and "hollow polymer particles (A) having an average particle size of 150 nm or less" may be referred to as "hollow polymer particles (A)." Furthermore, in this specification, "low refractive index layer" refers to a layer having a refractive index of 1.49 or less. Furthermore, the "average particle size" refers to the particle size at which the cumulative value is 50% in the volume-based particle size distribution determined from particle size distribution measurements, and can be determined using a Nanotrac particle size distribution analyzer that utilizes dynamic light scattering.

[0019] In addition, in this specification, the "(meth)acryloyl group equivalent" is calculated by dividing the molecular weight (Mw) of the (meth)acrylate compound by the number (f) of (meth)acryloyl groups in the same molecule. The average (meth)acryloyl group equivalent of a mixture of multiple (meth)acrylate compounds is calculated by the following formula (1). Formula (1): Average (meth)acryloyl group equivalent = {Mw （１） / f （１）} x Q （１） + {Mw （２） / f （２）} x Q （２） +...+{Mw （ｎ） / f （ｎ）} x Q （ｎ） In formula (1), n ​​represents a number that distinguishes the various (meth)acrylate compounds in the mixture, and Mw （ｎ） is the molecular weight of each component n, f （ｎ） is the number of acryloyl groups in each component n, Q （ｎ） represents the mass % of each component n in the total mass of the (meth)acrylate compound. The repeated bending resistance test is performed using a repeated bending tester (a planar body no-load U-shaped extension tester manufactured by Yuasa System Co., Ltd.). The bending resistance measured by the cylindrical mandrel method is determined in accordance with JIS K5600-5-1. Details are described in the Examples section. Unless otherwise noted, the various components described in this specification may be used independently, either alone or in combination of two or more.

[0020] <1> Coating liquid for forming a low refractive index layer One embodiment of the present invention relates to a coating liquid for forming a low refractive index layer. The coating liquid for forming a low refractive index layer contains hollow polymer particles (A) having an average particle size of 150 nm or less and a (meth)acrylate compound (B) that does not contain fluorine atoms and has a (meth)acryloyl group equivalent of 115 or more, the (meth)acrylate compound (B) containing a urethane (meth)acrylate (b). The coating liquid for forming a low refractive index layer preferably further contains a (meth)acrylate compound (C) having a (meth)acryloyl group equivalent of less than 115.

[0021] <Hollow Polymer Particles (A)> Hollow polymer particles are particles having internal voids and an outer shell made of an organic polymer layer. Examples of polymers constituting hollow polymer particles include crosslinked acrylic polymers, crosslinked styrene polymers, and vinyl polymers. Crosslinked acrylic polymers are preferred from the viewpoint of easily achieving a low refractive index. Commercially available products include Techpolymer XX-5964Z (average particle size 80 nm, Sekisui Plastics Co., Ltd.).

[0022] In this embodiment, the hollow polymer particles (A) may have an average particle diameter of 150 nm or less. Generally, the film thickness of a low refractive index layer in an antireflection film is approximately 50 to 150 nm due to its properties as a light interference layer. Therefore, if the average particle diameter of the hollow polymer particles contained in the layer exceeds 150 nm for a low refractive index layer with a film thickness of 150 nm, the unevenness formed on the layer surface becomes large, resulting in increased haze due to light scattering. From the viewpoint of reducing haze, the average particle diameter of the hollow polymer particles (A) is more preferably 100 nm or less, and even more preferably 80 nm or less. While the lower limit of the average particle diameter is not particularly limited, it is preferably 50 nm or more to achieve a low refractive index. In one embodiment, the average particle diameter of the hollow polymer particles (A) is preferably 50 to 150 nm.

[0023] The average particle size of the hollow polymer particles can be determined using a Nanotrac particle size distribution analyzer that utilizes dynamic light scattering. Examples of Nanotrac particle size distribution analyzers include the "Nanotrac UPA" manufactured by Nikkiso Co., Ltd. Specifically, the dilution liquid can be added so that the loading index value in the analysis software "Microtrac" becomes 1.0, and then the measurement can be performed. It is preferable to use the same dispersion solvent as the main component of the dispersion solvent for the hollow polymer particles as the dilution liquid. Examples include methyl isobutyl ketone, methyl ethyl ketone, and propylene glycol monomethyl ether.

[0024] In order to reduce the refractive index, the content of hollow polymer particles (A) is preferably 10 to 80% by mass relative to 100% by mass of the nonvolatile content of the low refractive index layer-forming coating liquid. This content is more preferably 15 to 70% by mass, and even more preferably 19 to 47% by mass. Here, the mass of the nonvolatile content of the low refractive index layer-forming coating liquid is the mass of the components remaining after the low refractive index layer-forming coating liquid is dried by heating at 120°C for 20 minutes. The same applies hereinafter unless otherwise specified.

[0025] <(Meth)acrylate Compound (B)> The (meth)acrylate compound (B) does not contain a fluorine atom and has a (meth)acryloyl group equivalent of 115 or more. In this embodiment, the (meth)acrylate compound (B) includes a urethane (meth)acrylate (b). The urethane (meth)acrylate (b) is a reaction product of a polyol (meth)acrylate and a diisocyanate. Examples of the urethane (meth)acrylate (b) include, but are not limited to, a reaction product (equivalent weight 137) of pentaerythritol tri(meth)acrylate and isophorone diisocyanate, a reaction product (equivalent weight 127) of pentaerythritol tri(meth)acrylate and hexamethylene diisocyanate, and a reaction product (equivalent weight 127) of dipentaerythritol penta(meth)acrylate and isophorone diisocyanate.

[0026] The (meth)acrylate compound (B) may contain a (meth)acrylate compound (b') other than (b) that does not contain a fluorine atom and has a (meth)acryloyl group equivalent of 115 or more. The (meth)acrylate compound (b') other than (b) that does not contain a fluorine atom and has a (meth)acryloyl group equivalent of 115 or more may be, for example, a polyol poly(meth)acrylate compound, but is not limited thereto. Specific examples of polyol poly(meth)acrylate compounds include trimethylolpropane EO-modified triacrylate (equivalent weight 143) and trimethylolpropane PO-modified triacrylate (equivalent weight 157).

[0027] The (meth)acryloyl group equivalent of the (meth)acrylate compound (B) is 115 or more, and the upper limit is not particularly limited. From the viewpoint of scratch resistance, the (meth)acryloyl group equivalent is preferably 250 or less, more preferably 200 or less, and even more preferably 150 or less. In one embodiment, the (meth)acryloyl group equivalent of the (meth)acrylate compound (B) may be 115 to 250.

[0028] <(Meth)acrylate Compound (C)> The (meth)acrylate compound (C) is not limited as long as the (meth)acryloyl group equivalent is less than 115. In one embodiment, the (meth)acryloyl group equivalent is preferably 113 or less, and more preferably 105 or less. In one embodiment, the (meth)acryloyl group equivalent is preferably 85 or more, and more preferably 88 or more.

[0029] The (meth)acrylate compound (C) may include, for example, one or more compounds selected from the group consisting of polyol poly(meth)acrylate compounds, monofunctional (meth)acrylate compounds, and difunctional (meth)acrylate compounds.

[0030] The polyol poly(meth)acrylate compound refers to a compound in which a hydroxyl group in a polyol is esterified with (meth)acrylic acid. Examples of the polyol poly(meth)acrylate compound include trimethylolpropane triacrylate (99 equivalents), trimethylolpropane trimethacrylate (113 equivalents), glycerin triacrylate (85 equivalents), glycerin trimethacrylate (99 equivalents), pentaerythritol triacrylate (99 equivalents), pentaerythritol trimethacrylate (113 equivalents), pentaerythritol tetraacrylate (88 equivalents), pentaerythritol tetramethacrylate (102 equivalents), dipentaerythritol pentaacrylate (105 equivalents), dipentaerythritol hexaacrylate (96 equivalents), and dipentaerythritol hexamethacrylate (110 equivalents).

[0031] Examples of monofunctional (meth)acrylate compounds include methyl acrylate (equivalent weight: 86) and methyl methacrylate (equivalent weight: 100). Examples of bifunctional (meth)acrylate compounds include 1,6-hexanediol diacrylate (equivalent weight: 113) and ethylene glycol dimethacrylate (equivalent weight: 99).

[0032] From the viewpoint of achieving both flex resistance and abrasion resistance, the content of the (meth)acrylate compound (C) is preferably 20 to 200 parts by mass, more preferably 20 to 120 parts by mass, and even more preferably 20 to 50 parts by mass, relative to 100 parts by mass of the (meth)acrylate compound (B).

[0033] From the viewpoint of achieving both scratch resistance, flex resistance, and a low refractive index, the total content of the (meth)acrylate compound (B) and the (meth)acrylate compound (C) is preferably 10 to 90% by mass relative to 100% by mass of the non-volatile content of the coating liquid for forming a low refractive index layer. This total content is more preferably 20 to 70% by mass. In one embodiment, the coating liquid for forming a low refractive index layer preferably contains, as components other than the hollow polymer particles (A), a urethane (meth)acrylate (b1) that does not contain fluorine atoms and has a (meth)acryloyl group equivalent of 115 to 150, and a (meth)acrylate (C) that has a (meth)acryloyl group equivalent of 85 to 113. The (meth)acrylate (C) more preferably contains a polyol poly(meth)acrylate. In another embodiment, the coating liquid preferably further contains a polyester acrylate (b1') having a (meth)acryloyl group equivalent of 115 to 150. The total content of these (b1), (C) and optional (b1') is preferably within the same range as above.

[0034] <Optional Components> The coating liquid for forming a low refractive index layer of this embodiment may further contain various additives. Examples of additives include photopolymerization initiators, inorganic oxide fine particles, thermosetting resins, polymerization inhibitors, leveling agents, slip agents, scratch-resistant inorganic fillers, antifoaming agents, surfactants, antibacterial agents, antiblocking agents, plasticizers, ultraviolet absorbers, infrared absorbers, antioxidants, silane coupling agents, conductive agents, and inorganic fillers. In one embodiment, in order to improve the scratch resistance of the low refractive index layer, the coating liquid for forming a low refractive index layer preferably contains inorganic oxide fine particles. In addition, in one embodiment, in order to improve the smoothness of the low refractive index layer, the coating liquid for forming a low refractive index layer preferably contains a leveling agent.

[0035] (Inorganic Oxide Fine Particles) From the viewpoint of improving the scratch resistance of the low refractive index layer, the average particle diameter of the inorganic oxide fine particles is preferably 50 to 90 nm, more preferably 65 to 90 nm. The average particle diameter of the inorganic oxide fine particles can be determined using a Microtrack particle size distribution analyzer or the like that utilizes dynamic light scattering. Examples of Microtrack particle size distribution analyzers include the "Nanotrack UPA" manufactured by Nikkiso Co., Ltd. Specifically, an inorganic oxide fine particle dispersion in which inorganic oxide fine particles are dispersed in a solvent is added to a dilution liquid so that the loading index value becomes 1.0, and the measurement can be performed. It is preferable to use the same dispersion solvent as the main component of the dispersion solvent for the inorganic oxide fine particles as the dilution liquid. Specific examples of dispersion solvents include methyl isobutyl ketone, methyl ethyl ketone, and propylene glycol monomethyl ether.

[0036] The inorganic oxide particles are not particularly limited, but aluminum oxide (Al ２ O ３ ) fine particles, or silica (SiO ２ From the viewpoint of transparency and scratch resistance, aluminum oxide fine particles are preferred. From the viewpoint of easily improving scratch resistance, the crystal structure of the aluminum oxide fine particles is preferably θ-type and / or α-type.

[0037] From the viewpoint of achieving both scratch resistance, a low refractive index, and transparency, the content of inorganic oxide fine particles is preferably 0.3 to 5 mass %, and more preferably 0.4 to 3 mass %, relative to 100 mass % of the nonvolatile content of the coating liquid for forming a low refractive index layer. In one embodiment, the coating liquid for forming a low refractive index layer preferably contains aluminum oxide fine particles having an average particle size of 50 to 90 nm within the above content range.

[0038] (Leveling Agent) The leveling agent is not particularly limited as long as it has the effect of reducing surface tension. Examples include acrylic leveling agents, fluorine-based leveling agents, and silicone-based leveling agents. From the viewpoint of improving scratch resistance, fluorine-based leveling agents are preferred. The content of the leveling agent is preferably 0.1 to 10% by mass, and more preferably 1 to 6% by mass, relative to 100% by mass of the nonvolatile content of the coating liquid for forming the low refractive index layer.

[0039] <2> Antireflection Film One embodiment of the present invention relates to an antireflection film having a transparent substrate and a low refractive index layer formed on the transparent substrate. The antireflection film has a low refractive index layer formed on the transparent substrate using the coating liquid for forming a low refractive index layer of the above embodiment. By forming a low refractive index layer using the coating liquid for forming a low refractive index layer in this manner, an antireflection film with excellent scratch resistance and bending resistance can be realized. The antireflection film may further have a hard coat layer or another cured film layer such as an optical adjustment layer. However, it is preferable that the outermost layer of the antireflection film be a low refractive index layer. In one embodiment, the luminous reflectance of the antireflection film is preferably 1.5% or less, more preferably 1% or less, and even more preferably 0.5% or less.

[0040] In a bending resistance test, the anti-reflection film preferably has bending resistance such that, when the anti-reflection film is bent 180° with a curvature radius of 1 mm and the low refractive index layer of the anti-reflection film facing outward, no cracks occur even after 10,000 folds. Anti-reflection films having the above bending resistance are suitable for use in foldable displays. The repeated bending test may be performed using an anti-reflection film having a 100 nm low refractive index layer on a 50 μm thick polyethylene terephthalate (PET) film. Detailed test methods are described in the Examples section.

[0041] In one embodiment, when the coating liquid for forming a low refractive index layer contains a (meth)acrylate compound (C) in addition to the hollow polymer particles (A) and the (meth)acrylate compound (B), the desired flex resistance tends to be easily obtained. For example, when the content of the (meth)acrylate compound (C) is 20 to 200 parts by mass per 100 parts by mass of the (meth)acrylate compound (B), an antireflection film can be easily realized that does not crack even after 10,000 folds in a repeated bending test, when the film is bent 180° with a curvature radius of 1 mm so that the low refractive index layer is on the outside.

[0042] When the content of the (meth)acrylate compound (C) is adjusted to 20 parts by mass or more per 100 parts by mass of the (meth)acrylate compound (B), the flex resistance tends to be easily improved. Furthermore, when the content is adjusted to 200 parts by mass or less, the rigidity of the low refractive index layer is improved, thereby preventing the flex resistance from decreasing. An anti-reflection film formed using the coating liquid for forming a low refractive index layer having the above composition can be suitably used for foldable displays.

[0043] [Low Refractive Index Layer] The low refractive index layer is a layer having a refractive index lower than that of an adjacent layer. The low refractive index layer may be formed, for example, in a structure of transparent substrate (support) / low refractive index layer for use as an anti-reflection film. In another embodiment, it may be formed in a structure of ultra-thin glass (support) / hard coat layer (intermediate layer) / low refractive index layer. In either structure, the low refractive index layer-forming coating liquid of one embodiment of the present invention can be suitably used to form the low refractive index layer. The low refractive index layer can be obtained, for example, by applying the low refractive index layer-forming coating liquid to a transparent substrate or the like, drying it, and then curing it.

[0044] In one embodiment, the refractive index of the low refractive index layer may be 1.49 or less. To reduce luminous reflectance, the refractive index is preferably 1.45 or less. Here, the refractive index is a value measured using a commercially available refractive index measuring device, for example, at a wavelength of 594 nm. To reduce luminous reflectance, the thickness of the low refractive index layer is preferably 80 to 150 nm, and more preferably 100 to 140 nm.

[0045] [Transparent substrate] The transparent substrate is not particularly limited as long as it is a substrate having optical transparency, and examples thereof include glass, synthetic resin moldings, films, etc. The thickness of the substrate is not particularly limited, but is usually about 50 to 200 μm. From the viewpoint of flex resistance, the type of transparent substrate is preferably a synthetic resin molding or a film.

[0046] Examples of synthetic resin moldings include moldings of synthetic resins such as polymethyl methacrylate resin, copolymer resins containing methyl methacrylate as the main component, polystyrene resin, styrene-methyl methacrylate copolymer resin, styrene-acrylonitrile copolymer resin, polycarbonate resin, cellulose acetate butyrate resin, polyallyl diglycol carbonate resin, polyvinyl chloride resin, and polyester resin.

[0047] Examples of films include polyester films, polyethylene films, polypropylene films, cellophane films, diacetyl cellulose films, triacetyl cellulose (TAC) films, acetyl cellulose butyrate films, polyvinyl chloride films, polyvinylidene chloride films, polyvinyl alcohol films, ethylene vinyl alcohol films, polyolefin films, polystyrene films, polycarbonate films, polymethylpentel films, polysulfone films, polyether ether ketone films, polyether sulfone films, polyether imide films, polyimide films, fluororesin films, nylon films, and acrylic films.

[0048] [Method for Producing an Antireflective Film] The method for producing an antireflective film is not particularly limited. For example, an antireflective film can be obtained by forming a low refractive index layer on a substrate using a coating liquid for forming a low refractive index layer. In one embodiment, the method for producing an antireflective film includes applying a coating liquid for forming a low refractive index layer on a substrate to form a coating film, and curing the coating film to form a cured film. Prior to curing, the coating film may be heated to dry it. Curing of the coating film can be carried out by irradiating it with active energy rays such as ultraviolet light according to a well-known method. When the antireflective film includes a hard coat layer, for example, the hard coat layer is formed on the substrate, and then a low refractive index layer is laminated on the hard coat layer to obtain an antireflective film. In addition, the antireflective film may further include another functional layer, such as an optical adjustment layer, between the substrate and the hard coat layer or between the hard coat layer and the low refractive index layer. Such a method for producing an antireflective film may further include forming a cured film on the substrate using a solution for forming a functional layer other than the low refractive index layer.

[0049] The present invention will be explained in more detail below with reference to examples and comparative examples, but the following examples do not limit the technical scope of the present invention in any way. The blending amounts in the tables are in mass % and, except for the solvent, are values ​​calculated as nonvolatile content. Blank spaces in the tables indicate that no blending was performed. The average particle size of the hollow particles and the film thickness of the low refractive index layer were measured by the following methods.

[0050] <Average particle size of hollow polymer particles> Measurement was performed using a Nanotrac particle size distribution measuring device utilizing dynamic light scattering, "Nanotrac UPA-EX150 (measurement light source: 780 nm wavelength semiconductor laser)" manufactured by Nikkiso Co., Ltd. Using "Microtrac" software, hollow polymer particles were added to a dilution solution so that the loading index value was 1.0, and measurement was performed. The dilution solution used was the same as the dispersion solvent that was the main component, depending on the dispersion solvent for the hollow polymer particles.

[0051] <Film Thickness of Low Refractive Index Layer> The film thickness of the low refractive index layer was measured using an optical non-contact film thickness meter (FILMETRICS, Inc., F20 film thickness measuring device).

[0052] <Synthesis of Urethane Acrylate> (Synthesis Example 1) Urethane Acrylate Compound (P1) Into a four-necked flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel, 597 parts by mass of Pentaerythritol Triacrylate (manufactured by Thermo Fisher Scientific Co., Ltd., pentaerythritol triacrylate (PET3A), purity 97% or more, molecular weight 298) and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst) were placed, and the liquid temperature was raised to 50 ° C. Thereafter, 224 parts by mass of Desmodur I (manufactured by Sumika Covestro Co., Ltd., isophorone diisocyanate (IPDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the temperature was raised to 80 ° C. and the reaction was allowed to proceed for 3 hours. After confirming that the peak of the isocyanate group had disappeared by FT-IR, the temperature was lowered to room temperature, and thus a urethane acrylate compound solution P1 containing 100 mass % of urethane acrylate (b1) (acryloyl group equivalent weight: 137) having a molecular weight of 821 and six acryloyl groups was obtained.

[0053] Synthesis Example 2 Urethane Acrylate Mixture (P2) Into a four-neck flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel, 533 parts by mass of pentaerythritol triacrylate (pentaerythritol triacrylate (PET3A), purity 97% or higher, molecular weight 298, manufactured by Thermo Fisher Scientific Co., Ltd.), 237 parts by mass of Aronix M306 (manufactured by Toagosei Co., Ltd., a mixture of 67.5% by mass of pentaerythritol triacrylate (PET3A(c3)) having a molecular weight of 298 and 32.5% by mass of pentaerythritol tetraacrylate (PET4A(c4)) having a molecular weight of 352), and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst) were placed, and the liquid temperature was raised to 50°C. Thereafter, 224 parts by mass of Desmodur I (manufactured by Sumika Covestro Co., Ltd., isophorone diisocyanate (IPDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the temperature was raised to 80°C and the reaction was allowed to proceed for 3 hours. After confirming that the isocyanate group peak had disappeared by FT-IR, the temperature was lowered to room temperature. In this way, a urethane acrylate mixture solution P2 was obtained, containing, in the non-volatile matter, 82.6% by mass of urethane acrylate (b1) (acryloyl group equivalent 137) having a molecular weight of 821 and 6 acryloyl groups, 9.7% by mass of pentaerythritol triacrylate (c3) (PET3A, acryloyl group equivalent 99), and 7.7% by mass of pentaerythritol tetraacrylate (c4) (PET4A, acryloyl group equivalent 88).

[0054] (Synthesis Example 3) Urethane acrylate mixture (P3) A four-neck flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel was charged with 950 parts by mass of Aronix M306 (manufactured by Toagosei Co., Ltd., a mixture of 67.5% by mass of pentaerythritol triacrylate (PET3A (c3)) having a molecular weight of 298 and 32.5% by mass of pentaerythritol tetraacrylate (PET4A (c4)) having a molecular weight of 352), and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst), and the liquid temperature was raised to 50°C. Thereafter, 168 parts by mass of Desmodur 50M-HDI (manufactured by Sumika Covestro Co., Ltd., hexamethylene diisocyanate (HDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the mixture was heated to 80°C and allowed to react for 3 hours. After confirming that the peaks of the isocyanate groups had disappeared by FT-IR, the temperature was lowered to room temperature. In this way, a urethane acrylate mixture solution P3 was obtained, which contained, in the non-volatile matter, 68.4 mass% of a urethane acrylate (b2) (acryloyl group equivalent: 127) having a molecular weight of 765 and six acryloyl groups, 4.0 mass% of a pentaerythritol triacrylate (c3) (PET3A, acryloyl group equivalent: 99), and 27.6 mass% of a pentaerythritol tetraacrylate (c4) (PET4A, acryloyl group equivalent: 88).

[0055] (Synthesis Example 4) Urethane acrylate mixture (P4) A four-necked flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel was charged with 2,500 parts by mass of Aronix M403 (manufactured by Toagosei Co., Ltd., a mixture of 55% by mass of dipentaerythritol pentaacrylate (DPPA (c1)) having a molecular weight of 524 and 45% by mass of dipentaerythritol hexaacrylate (DPHA (c2)) having a molecular weight of 579), and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst), and the liquid temperature was raised to 50 ° C. Thereafter, 224 parts by mass of Desmodur I (manufactured by Sumika Covestro Co., Ltd., isophorone diisocyanate (IPDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the mixture was heated to 80 ° C. and allowed to react for 3 hours. After confirming that the peaks of the isocyanate groups had disappeared by FT-IR, the temperature was lowered to room temperature. In this way, a urethane acrylate mixture solution P4 was obtained, which contained, in the nonvolatile matter, 46.7% by mass of urethane acrylate (b3) (acryloyl group equivalent 127) having a molecular weight of 1273 and 10 acryloyl groups, 12.0% by mass of dipentaerythritol pentaacrylate (c1) (DPPA, acryloyl group equivalent 105), and 41.3% by mass of dipentaerythritol hexaacrylate (DPHA, acryloyl group equivalent 96).

[0056] (Synthesis Example 5) Urethane acrylate mixture (P5) A four-necked flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel was charged with 2150 parts by mass of Aronix M306 (manufactured by Toagosei Co., Ltd., a mixture of 67.5% by mass of pentaerythritol triacrylate (PET3A (c3)) having a molecular weight of 298 and 32.5% by mass of pentaerythritol tetraacrylate (PET4A (c4)) having a molecular weight of 352), and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst), and the liquid temperature was raised to 50 ° C. Thereafter, 224 parts by mass of Desmodur I (manufactured by Sumika Covestro Co., Ltd., isophorone diisocyanate (IPDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the mixture was heated to 80 ° C. and allowed to react for 3 hours. After confirming that the peaks of the isocyanate groups had disappeared by FT-IR, the temperature was lowered to room temperature. In this way, a urethane acrylate mixture solution P5 was obtained, which contained, in the non-volatile matter, 34.6 mass% of a urethane acrylate (b1) (acryloyl group equivalent: 137) having a molecular weight of 821 and six acryloyl groups, 36.0 mass% of a pentaerythritol triacrylate (c3) (PET3A, acryloyl group equivalent: 99), and 29.4 mass% of a pentaerythritol tetraacrylate (c4) (PET4A, acryloyl group equivalent: 88).

[0057] (Synthesis Example 6) Urethane acrylate mixture (P6) A four-necked flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel was charged with 3100 parts by mass of Aronix M306 (manufactured by Toagosei Co., Ltd., a mixture of 67.5% by mass of pentaerythritol triacrylate (PET3A (c3)) having a molecular weight of 298 and 32.5% by mass of pentaerythritol tetraacrylate (PET4A (c4)) having a molecular weight of 352), and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst), and the liquid temperature was raised to 50 ° C. Thereafter, 224 parts by mass of Desmodur I (manufactured by Sumika Covestro Co., Ltd., isophorone diisocyanate (IPDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the mixture was heated to 80 ° C. and allowed to react for 3 hours. After confirming that the peaks of the isocyanate groups had disappeared by FT-IR, the temperature was lowered to room temperature. In this way, a urethane acrylate mixture solution P6 was obtained, which contained, in the non-volatile matter, 24.7 mass% of a urethane acrylate (b1) (acryloyl group equivalent: 137) having a molecular weight of 821 and six acryloyl groups, 45.0 mass% of a pentaerythritol triacrylate (c3) (PET3A, acryloyl group equivalent: 99), and 30.3 mass% of a pentaerythritol tetraacrylate (c4) (PET4A, acryloyl group equivalent: 88).

[0058] Synthesis Example 7 Urethane Acrylate Mixture (P7) Into a four-neck flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel, 478 parts by mass of pentaerythritol triacrylate (pentaerythritol triacrylate (PET3A), purity 97% or higher, molecular weight 298, manufactured by Thermo Fisher Scientific Co., Ltd.), 212 parts by mass of Aronix M306 (manufactured by Toagosei Co., Ltd., a mixture of 67.5% by mass of pentaerythritol triacrylate (PET3A(c3)) having a molecular weight of 298 and 32.5% by mass of pentaerythritol tetraacrylate (PET4A(c4)) having a molecular weight of 352), and 0.1 parts by mass of Neostan U-810 (manufactured by Nitto Kasei Co., Ltd., tin catalyst) were placed, and the liquid temperature was raised to 50°C. Thereafter, 224 parts by mass of Desmodur I (manufactured by Sumika Covestro Co., Ltd., isophorone diisocyanate (IPDI)) was added dropwise from the dropping funnel over 30 minutes. After the temperature rise subsided, the temperature was raised to 80°C and the reaction was allowed to proceed for 3 hours. After confirming that the isocyanate group peak had disappeared on FT-IR, the temperature was lowered to room temperature. In this way, a urethane acrylate mixture solution P7 was obtained, containing, in the non-volatile matter, 89.8% by mass of urethane acrylate (b1) (acryloyl group equivalent 137) having a molecular weight of 821 and six acryloyl groups, 2.7% by mass of pentaerythritol triacrylate (c3) (PET3A, acryloyl group equivalent 99), and 7.5% by mass of pentaerythritol tetraacrylate (c4) (PET4A, acryloyl equivalent 88).

[0059] <Production of Multifunctional Polyester Acrylate> (Production of Multifunctional Polyester Acrylate Mixture Solution (PE)) A four-necked flask equipped with a stirrer, a reflux condenser, a dry air inlet tube, and a thermometer was charged with 80.0 parts of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 250.0 parts of pentaerythritol triacrylate having a hydroxyl value of 122 mg KOH / g (Pentaerythritol triacrylate, manufactured by Nippon Kayaku Co., Ltd., trade name: KAYARAD PET-30, containing pentaerythritol tetraacrylate as a by-product), 0.24 parts of methylhydroquinone, and 217.8 parts of cyclohexanone, and the temperature was raised to 60°C. Next, 1.65 parts of 1,8-diazabicyclo[5.4.0]-7-undecene was added as a catalyst, and the mixture was stirred at 90°C for 8 hours. Next, 78.3 parts of methacrylic glycidyl ether and 54.0 parts of cyclohexanone were added, followed by 2.65 parts of dimethylbenzylamine as a catalyst. The mixture was stirred at 100°C for 6 hours, and the acid value of the reaction mixture was measured periodically while the reaction continued. When the acid value reached 5.0 mgKOH / g or less, the mixture was cooled to room temperature to terminate the reaction. The resulting resin varnish was pale yellow and transparent, and a multifunctional polyester acrylate mixture solution (PE) was obtained, which was a mixture of polyester acrylate (b4) and pentaerythritol tetraacrylate (nonvolatile mass ratio: polyester acrylate:pentaerythritol tetraacrylate = 76:24) with a nonvolatile content of 60%. The polyester acrylate (b'1) had 8 functional groups and a weight-average molecular weight of 3,500.

[0060]

[0061] <Preparation of Aluminum Oxide Microparticle Dispersion> 35 parts of aluminum oxide (θ-type crystals, primary particle diameter 10 nm), 14 parts of a polyfunctional polyester acrylate mixture solution PE (non-volatile content), 25.5 parts of methyl ethyl ketone as an organic solvent, and 25.5 parts of methoxybutanol were mixed and stirred with a disperser. Then, a dispersion treatment was carried out with a sand mill to obtain a uniform aluminum oxide microparticle dispersion containing θ-type crystalline aluminum oxide microparticles. The aluminum oxide microparticles had an average particle diameter of 80 nm.

[0062] The materials used in the production of the Examples and Comparative Examples are as follows: <Hollow particles> Hollow polymer particles (a1): Techpolymer XX-5964Z (hollow polymer particles, crosslinked acrylic resin, average particle size 80 nm, non-volatile content 10%, manufactured by Sekisui Plastics Co., Ltd.) Hollow polymer particles (a2): Techpolymer XX-6289Z (hollow polymer particles, crosslinked acrylic resin, average particle size 65 nm, non-volatile content 10%, manufactured by Sekisui Plastics Co., Ltd.) Hollow particles: Sururia 2320 (hollow silica particles, average particle size 50 nm, non-volatile content 20.5%, manufactured by JGC Catalysts and Chemicals Co., Ltd.)

[0063] <(Meth)acrylate Compound (B)> Propylene oxide-modified pentaerythritol tetraacrylate (b'2); ATM-4P (acryloyl equivalent: 146, manufactured by Shin-Nakamura Chemical Co., Ltd.)

[0064] <Silica fine particles> Reactive silica fine particles: MIBK-SD (average particle size 10 nm, non-volatile content 30%, manufactured by Nissan Chemical Industries, Ltd.)

[0065] <Leveling Agent> Leveling agent: Megafac RS-90 (fluorine-containing UV-reactive oligomer, non-volatile content 10%, manufactured by DIC Corporation)

[0066] <Photopolymerization initiator> OMNIRAD907 (manufactured by IGM RESINS Co., Ltd.)

[0067] Example 1 Preparation of Coating Liquid for Forming Low Refractive Index Layer To a flask equipped with a stirrer, the urethane acrylate compound solution P1 obtained in Synthesis Example 1 was added so that the urethane acrylate (b1) as the (meth)acrylate compound (B) was 100 parts. Furthermore, 100 parts (based on 100% nonvolatile content) of hollow polymer particles (a1) as the hollow polymer particles (A), 5 parts of OMNIRAD907 as a photopolymerization initiator, and 10 parts (based on 100% nonvolatile content) of a fluorinated (meth)acrylate (Megafac RS-90 (manufactured by DIC Corporation)) as a leveling agent were added, and these components were thoroughly mixed. Furthermore, propylene glycol monomethyl ether was added as an organic solvent, and the nonvolatile content of all components was adjusted to 4%, thereby obtaining a coating liquid for forming a low refractive index layer.

[0068] <Production of Antireflection Film> The coating liquid for forming a low refractive index layer was applied onto a 50 μm thick polyethylene terephthalate (PET) film ("Lumirror UH-13" manufactured by Toray Industries, Inc.) using a bar coater so that the film thickness after drying would be 100 nm. Thereafter, the coating liquid was applied with a high-pressure mercury lamp at 400 mJ / cm in a nitrogen atmosphere such that the oxygen concentration was 500 ppm or less. ２ The coating was irradiated with ultraviolet light of 1000 kJ / cm to form a low refractive index layer (a cured film of the dried coating film), thereby obtaining an anti-reflection film.

[0069] [Examples 2 to 11, Comparative Examples 1 to 5] Each low refractive index layer-forming coating liquid having a nonvolatile content concentration of 4% was obtained in the same manner as in Example 1, except that the compositions and blending amounts (in terms of nonvolatile content) were set as shown in Table 2. Subsequently, antireflection films were obtained in the same manner as in Example 1, except that the low refractive index layer-forming coating liquids having the respective compositions were used.

[0070] [Evaluation Items and Evaluation Methods] The antireflection films (low refractive index layers) obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 2 and 3.

[0071] <Measurement of Refractive Index> The refractive index of the low refractive index layer at a wavelength of 594 nm was measured at 25° C. using a Prism Coupler Model 2010 manufactured by Metricon Corporation.

[0072] <HZ: Measurement of Haze Value> The haze value (HZ) of the surface of the low refractive index layer of the prepared anti-reflection film was measured using a "Haze Meter SH7000" manufactured by Nippon Denshoku Industries Co., Ltd. Note that B and A represent practically acceptable levels. [Evaluation Criteria] A: 1.5% or less (good) B: more than 1.5% and 2.0% or less (acceptable for practical use) C: more than 2.0% (unacceptable for practical use)

[0073] <Flexibility (Mandrel Bending)> Flexibility was measured by a cylindrical mandrel method in accordance with JIS 5600-5-1 using a coating film flexibility tester (Tester Sangyo, PI-801). The anti-reflection film was wrapped around a mandrel with the low refractive index layer facing outward, and the film was visually inspected for cracks. A cylindrical mandrel with a diameter of 2 mm (radius of curvature 1 mm) was used. [Evaluation Criteria] P (Pass): No cracks occurred (suitable for practical use) F (Fail): Cracks occurred (unsuitable for practical use)

[0074] <Repeated Bending Test> The test was carried out using a bending resistance tester (a planar body no-load U-shaped stretch tester manufactured by Yuasa System Co., Ltd.), and the low refractive index layer was set on the bottom side of the device. Bending was carried out at a speed of 30 times / min with a diameter of 2 mm (radius of curvature 1 mm). The film was evaluated according to the following criteria depending on the number of times it was bent until cracks appeared in the film. ＋ , A and A ＋ A is at a level where there is no practical problem. ＋ A: No cracks occurred up to 50,000 times (very good) A: Cracks occurred between 30,000 times and 50,000 times (better) B: No cracks occurred up to 50,000 times (very good) ＋ A: Cracks occurred after 10,000 or more cycles but less than 30,000 cycles (good) B: Cracks occurred after 5,000 or more cycles but less than 10,000 cycles (suitable for practical use) C: Cracks occurred after less than 5,000 cycles (not suitable for practical use)

[0075] <SW Resistance; Scratch Resistance> The scratch resistance of the prepared anti-reflection films was evaluated using a Gakushin-type abrasion fastness tester manufactured by Tester Sangyo Co., Ltd. A friction element (surface area 1 cm2) with a load of 200 g was attached. ２ Steel wool #0000 was attached to the anti-reflection film, and the anti-reflection film was rubbed five times over the surface (1 cm x 15 cm) of the low refractive index layer. Thereafter, the haze value of the anti-reflection film was measured and evaluated according to the following criteria. ＋ A is at a level where there is no practical problem. ＋A: ΔHz is 1% or less (very good) A: ΔHz is more than 1% and less than 2% (good) B: ΔHz is more than 2% and less than 3% (acceptable for practical use) C: ΔHz is more than 3% (unacceptable for practical use) Here, "ΔHz = haze value after scratch test - haze value before scratch test".

[0076] <Measurement of luminous reflectance> Measurement was carried out in accordance with JIS Z8722 using a "spectrophotometer U4100" manufactured by Hitachi High-Tech Science Corporation and a "5-degree regular reflection accessory." The surface of the film opposite to the anti-reflection layer was sanded with sandpaper, and then black ink was applied and dried to minimize the influence of light reflection from the back surface. Note that B, A, and A ＋ A is at a level where there is no practical problem. ＋ A: 0.5% or less (very good) A: More than 0.5% and less than 1.0% (good) B: More than 1.0% and less than 1.5% (suitable for practical use) C: More than 1.5% (unsuitable for practical use)

[0077]

Claims

1. A coating liquid for forming a low refractive index layer, comprising: hollow polymer particles (A) having an average particle size of 150 nm or less; and a (meth)acrylate compound (B) that does not contain fluorine atoms and has a (meth)acryloyl group equivalent of 115 or more, wherein the (meth)acrylate compound (B) comprises a urethane (meth)acrylate (b).

2. The coating liquid for forming a low refractive index layer according to claim 1, further comprising a (meth)acrylate compound (C) having a (meth)acryloyl group equivalent of less than 115.

3. The coating liquid for forming a low refractive index layer according to claim 2, which contains 20 to 200 parts by mass of the (meth)acrylate compound (C) per 100 parts by mass of the (meth)acrylate compound (B).

4. The coating liquid for forming a low refractive index layer according to claim 1, further comprising inorganic oxide fine particles having an average particle size of 50 to 90 nm.

5. The coating liquid for forming a low refractive index layer according to claim 4, wherein the content of the inorganic oxide fine particles is 0.4 to 3 mass % relative to 100 mass % of the nonvolatile content of the coating liquid for forming a low refractive index layer.

6. The coating liquid for forming a low refractive index layer according to claim 5, wherein the inorganic oxide fine particles are aluminum oxide fine particles.

7. An anti-reflection film comprising a transparent substrate and a low refractive index layer formed on the transparent substrate, the low refractive index layer being a cured film of the coating liquid for forming a low refractive index layer according to any one of claims 1 to 6.

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