Coating composition

Abstract

The present invention provides a coating composition that has excellent stability over time, and exhibits excellent transparency when formed into a coating film. The present invention is a coating composition that comprises a zirconium element-containing metal oxide (A) and a silane compound (B), the coating composition being characterized in that the zirconium element-containing metal oxide (A) has a zeta potential value of at least 30 mV as measured by the following method. <Method for measuring zeta potential> 10 mass% of a zirconium element-containing metal oxide (A) aqueous dispersion is measured at room temperature (25 °C) by using an electrophoretic laser doppler method.

Description

Coating composition

[0001] The present invention relates to a coating composition, and more particularly to a coating composition useful for lenses such as eyeglasses.

[0002] In recent years, plastic lenses have become the mainstream for eyeglass lenses, with high-refractive-index lenses becoming increasingly popular. This is due to the increasing demand for corrective eyeglasses and the market demand for lighter, thinner (high-refractive-index) lenses, driven by the increasing popularity of digital devices such as PCs and smartphones, which has led to an increase in vision loss. However, if the refractive index of the hard coating applied to high-refractive-index plastic lenses to prevent scratches does not match the refractive index of the lens substrate, light interference can cause rainbow patterns known as interference fringes to appear, detracting from the lens's aesthetic appearance. To address this issue, a technology has been proposed to match the refractive index of the hard coating to that of the lens.

[0003] For example, Patent Document 1 proposes fine particles in which titanium oxide, iron oxide, and silicon oxide are integrally bonded in the form of a complex oxide or solid solution as a composition for improving the refractive index of a hard coat film. Hard coat films using such fine particles have a high refractive index, and by adjusting the blending amount, they can be applied to lenses with various refractive indices. However, eyeglass lenses with an anti-reflection coating applied on top of the hard coat suffer from the drawback of darkening due to ultraviolet light, resulting in reduced optical performance.

[0004] Furthermore, Patent Document 2 proposes composite fine particles made of oxides of titanium, silicon, zirconium and / or aluminum for the same purpose as Patent Document 1. However, when these fine particles are used, the above-mentioned blackening does not occur, but there are problems with weather resistance, such as cracks occurring in the hard coat film due to the photocatalytic activity of titanium oxide on spectacle lenses that are not provided with an anti-reflection film.

[0005] Patent Document 3 proposes composite microparticles of rutile titanium oxide, zirconium oxide, silicon oxide, and tin oxide. When these microparticles are used, the weather resistance described above is improved, but there is a problem that eyeglass lenses laminated with anti-reflection films turn blue due to ultraviolet light. Thus, when microparticles mainly composed of titanium oxide are used as hard coat film components, problems with light resistance and weather resistance are inherent. Therefore, a technology using zirconium oxide microparticles has been proposed (see, for example, Patent Document 4). Systems using zirconium oxide microparticles improve the weather resistance described above, but the transparency of the coating film is insufficient, and there are also problems with the stability over time of the coating liquid.

[0006] Japanese Patent Laid-Open No. 7-76671 Japanese Patent Laid-Open No. 8-48940 Japanese Patent Laid-Open No. 2006-251760 Japanese Patent Laid-Open No. 2009-155541

[0007] As described above, although various coating compositions have been disclosed, there is still room for improvement in terms of stability over time and transparency of the coating film formed.

[0008] The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide a coating composition that has excellent stability over time and exhibits excellent transparency when a coating film is formed.

[0009] The present inventors have conducted extensive research into coating compositions and have found that by combining a zirconium-containing metal oxide having a zeta potential of 30 mV or more as measured by a predetermined method with a silane compound, the composition has excellent stability over time and exhibits excellent transparency when a coating film is formed. This led to the realization that the above-mentioned problems can be solved beautifully, and has led to the present invention.

[0010] That is, the present invention provides a coating composition containing a zirconium-containing metal oxide (A) and a silane compound (B), wherein the zirconium-containing metal oxide (A) has a zeta potential of 30 mV or more as measured by the following method: <Method for measuring zeta potential> A 10 mass% aqueous dispersion of the zirconium-containing metal oxide (A) is measured at room temperature (25°C) by an electrophoretic laser Doppler method.

[0011] The zirconium-containing metal oxide (A) preferably has an average primary particle size of 1 to 20 nm as measured by dynamic light scattering.

[0012] The silane compound (B) is represented by the following general formula (1): １ R ２ ａ Si(OR ３ ) ３－ａ (1) (wherein, R １ represents an alkyl group having 1 to 3 carbon atoms, a phenyl group, a vinyl group, an organic group having an epoxy group, an organic group having a (meth)acrylic group, an organic group having an amino group, or an organic group having a mercapto group. ２ represents an alkyl group having 1 to 2 carbon atoms. ３ are the same or different and represent an alkyl group having 1 to 3 carbon atoms; and a is 0 or 1.

[0013] The content of the zirconium-containing metal oxide (A) is preferably 4 to 25% by mass relative to 100% by mass of the coating composition.

[0014] The content of the silane compound (B) is preferably 30 to 260 mol % relative to 100 mol % of the zirconium-containing metal oxide (A).

[0015] The coating composition is preferably used for lenses.

[0016] The present invention also relates to a lens coated with the above coating composition.

[0017] The coating composition of the present invention has the above-mentioned constitution, has excellent stability over time, and can exhibit excellent transparency when a coating film is formed, and therefore can be suitably used for lenses of spectacles and the like.

[0018] Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description and can be appropriately modified and applied within the scope of the present invention. Note that a combination of two or more of the individual preferred embodiments of the present invention described below also falls within the scope of the present invention.

[0019] The coating composition of the present invention is characterized by containing a zirconium-containing metal oxide (A) having a zeta potential value of 30 mV or more as measured by the above method. This improves the dispersibility of the zirconium-containing metal oxide (A), making the coating composition stable over time and enabling it to exhibit excellent transparency when coated on a lens or the like. The coating composition of the present invention also has excellent adhesion to lenses, and lenses obtained by coating the composition with the coating composition also have excellent scratch resistance and weather resistance.

[0020] The zeta potential of the zirconium-containing metal oxide (A) may be 30 mV or more, but is preferably 35 mV or more. This allows the effects of the present invention to be more fully exhibited. It is more preferably 40 mV or more, and even more preferably 45 mV or more. The zeta potential of the zirconium-containing metal oxide (A) is preferably 100 mV or less.

[0021] The zirconium-containing metal oxide (A) is not particularly limited as long as it contains zirconium atoms and oxygen atoms, and may contain elements other than zirconium atoms and oxygen atoms. The other elements are not particularly limited, but include at least one stabilizing element selected from aluminum, magnesium, titanium, and rare earth elements. When the zirconium-containing metal oxide (A) contains the other elements, the thermal stability of the metal oxide (A) is further improved. A specific example of the rare earth element is yttrium.

[0022] The content of the other elements in the zirconium-containing metal oxide (A) is not particularly limited, but is preferably 0 to 20 mol %, more preferably 0 to 10 mol %, and even more preferably 0 to 5 mol %, relative to 100 mol % of zirconium element.

[0023] The average primary particle size of the zirconium-containing metal oxide (A) measured by dynamic light scattering is not particularly limited, but is preferably 1 to 20 nm, more preferably 1 to 15 nm, and even more preferably 1 to 10 nm.

[0024] The zirconium-containing metal oxide (A) may be surface-treated with an inorganic or organic compound. Examples of inorganic compounds include silicon oxide and aluminum oxide. Examples of organic compounds include silane coupling agents, titanate coupling agents, and phosphate esters. The silane coupling agent is preferably a compound represented by the general formula (1).

[0025] In the coating composition, the content of the zirconium-containing metal oxide (A) is preferably 4 to 25 mass% relative to 100 mass% of the coating composition. This allows the effects of the present invention to be more fully exhibited. The content of the zirconium-containing metal oxide (A) is more preferably 8 to 20 mass%.

[0026] The method for producing the zirconium-containing metal oxide (A) is not particularly limited, and examples thereof include a method in which an aqueous zirconium salt solution is heated and hydrolyzed (hydrolysis method), a method in which an alkali is added to an aqueous zirconium salt solution to form zirconium hydroxide, which is then peptized (neutralization coprecipitation method), and a method in which an acid and an alkali are added to zirconium hydroxide, followed by hydrothermal treatment (hydrothermal synthesis method).

[0027] A preferred method for producing the zirconium-containing metal oxide (A) includes a neutralization coprecipitation step of adding an alkali to an aqueous solution containing a zirconium salt to form a hydroxide, which is then peptized, and a hydrothermal step of adding an acid to the product obtained in the neutralization coprecipitation step to subject it to hydrothermal treatment.

[0028] The zirconium salt used in the neutralization coprecipitation step is not particularly limited as long as it contains zirconium element, but chlorides, oxychlorides, sulfates, nitrates, etc. are preferred. Chlorides and oxychlorides are more preferred. Zirconium compounds used as raw materials in the production of a slurry containing a zirconium element-containing compound include hydroxides, hydroxide oxides, chlorides, sulfides, sulfates, nitrates, carbonates, hydrogencarbonates, acetates, phosphates, oxalates, butyrates, selenates, iodates, fluorides, oxychlorides, etc. Among these, oxychlorides, chlorides, sulfates, nitrates, acetates, etc., which are water-soluble zirconium compounds suitable for production, are preferred.

[0029] When the zirconium-containing metal oxide (A) contains elements other than zirconium and oxygen, it is preferable to add salts of the other elements in the neutralization coprecipitation step, such as chlorides, oxychlorides, sulfates, nitrates, and acetates.

[0030] The alkali used in the neutralization coprecipitation step is not particularly limited, and examples thereof include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; ammonia; organic amines; etc. Among these, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide are preferred.

[0031] The amount of alkali used in the neutralization coprecipitation step is not particularly limited, but is preferably 10 to 1,000 mol % relative to 100 mol % of the total of zirconium element and the other elements.

[0032] The acid used in the hydrothermal step is not particularly limited, but examples thereof include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid; and organic acids such as acetic acid, tartaric acid, glutamic acid, malonic acid, maleic acid, trimellitic anhydride, succinic acid, malic acid, glycolic acid, alanine, fumaric acid, oxalic acid, glutaric acid, and formic acid. Among these, organic acids are preferred, and acetic acid is more preferred. By using acetic acid in the hydrothermal step, it is possible to sufficiently obtain a zirconium-containing metal oxide (A) having a zeta potential of 30 mV or more.

[0033] The amount of acid used in the hydrothermal step is not particularly limited, but is preferably 50 to 1,000 mol % relative to 100 mol % of the total of zirconium and the other elements. This allows for sufficient production of zirconium-containing metal oxide (A) having a zeta potential of 30 mV or more. The amount of acid used is more preferably 100 to 500 mol %.

[0034] The hydrothermal temperature in the hydrothermal step is not particularly limited, but is preferably 170 to 230°C, and more preferably 175 to 220°C.

[0035] The hydrothermal treatment time in the hydrothermal step is not particularly limited, but is preferably 1 to 10 hours, more preferably 1.5 to 6 hours.

[0036] The method for producing the zirconium-containing metal oxide (A) preferably includes a washing step after the neutralization coprecipitation step and / or the hydrothermal step. The washing method in the washing step is not particularly limited, and can be performed by a commonly used method. For example, after the neutralization coprecipitation step, a washing method such as filtration and water washing is preferred. Furthermore, after the hydrothermal step, it is preferred to use an ultrafiltration membrane or the like.

[0037] When the zirconium-containing metal oxide (A) is produced by the above-mentioned production method, it is obtained as an aqueous dispersion, and therefore, when it is used in the coating composition of the present invention, it is preferable to replace it with an organic solvent.

[0038] The organic solvent is not particularly limited as long as it has excellent miscibility with the silane compound (B). Examples include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, butyl acetate, ethyl lactate, and propylene glycol monoethyl ether acetate; polyhydric alcohols and their ethers such as ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether; and cyclic ethers such as dioxane and tetrahydrofuran, all of which have good compatibility with water. These may be used alone or in combination. Aromatic hydrocarbons such as benzene and toluene, which have good compatibility with these organic solvents, may also be used in combination. Among these, lower alcohols having 1 to 3 carbon atoms are preferred. Lower alcohols have high miscibility with water and the silane compound (B), making it easy to replace the water-dispersed zirconium-containing metal oxide (A) with an organically dispersed zirconium-containing metal oxide (A). Furthermore, lower alcohols having 1 to 3 carbon atoms are less likely to cause a burden on the environment than alcohols having a larger number of carbon atoms, and are also preferred in that the solvent can be removed at low temperatures during film formation.

[0039] The coating composition of the present invention contains a silane compound (B). The silane compound (B) is not particularly limited, but is preferably a hydrolyzate of an alkoxysilane compound. More preferably, the silane compound (B) is a compound represented by the following general formula (1): １ R ２ ａ Si(OR ３ ) ３－ａ (1) (wherein, R １ represents an alkyl group having 1 to 3 carbon atoms, a phenyl group, a vinyl group, an organic group having an epoxy group, an organic group having a (meth)acrylic group, an organic group having an amino group, or an organic group having a mercapto group. ２ represents an alkyl group having 1 to 2 carbon atoms. ３are the same or different and represent an alkyl group having 1 to 3 carbon atoms. a is 0 or 1. These silane compounds are compounds that can be hydrolyzed to have a highly reactive silanol group and also have an organic group. This is an element that imparts strong adhesion and scratch resistance to the hard coat film sandwiched between a plastic lens (organic material) and an anti-reflection film (inorganic material), and also has excellent dispersibility with the zirconium oxide fine particles, giving the hard coat film high transparency. Furthermore, when it is desired to further impart scratch resistance to the hard coat film, a compound represented by the following general formula (2): Si(OR ４ ) ４ (2) (wherein, R ４ and X are the same or different and represent an organic group having 1 to 4 carbon atoms. １ ３－ｍ -Si(R ５ ｍ )-Y-Si(R ６ ｍ )-X ２ ３－ｍ (3) (wherein, R ５ and R ６ are the same or different and represent a hydrocarbon group having 1 to 6 carbon atoms. １ and X ２ represents a hydrolyzable group; Y represents an organic group containing a carbonate group or an epoxy group; and m is 0 or 1. Addition of a disilane compound represented by the following formula is also effective.

[0040] Specific examples of the organic group having an epoxy group include glycidoxyalkyl groups having 3 to 10 carbon atoms, such as a 3-glycidoxypropyl group and a 4-glycidoxybutyl group, and epoxyalkyl groups having 3 to 10 carbon atoms, such as a 2-(3,4-epoxycyclohexyl)ethyl group, a 3-(3,4-epoxycyclohexyl)propyl group, a 3,4-epoxybutyl group and a 7,8-epoxyoctyl group.

[0041] In the above general formula (1), a is 0 or 1, and is preferably 0.

[0042] Specific examples of the organic group having a (meth)acrylic group include (meth)acryloxyalkyl groups having 3 to 10 carbon atoms, such as methacryloxypropyl and acryloxypropyl.

[0043] Specific examples of the organic group having an amino group include aminoalkyl groups having 1 to 10 carbon atoms, such as aminomethyl, aminoethyl, and aminopropyl groups, and aminoaryl groups having 6 to 10 carbon atoms, such as N-phenylaminopropyl.

[0044] Specific examples of the organic group having a mercapto group include mercaptoalkyl groups having 1 to 10 carbon atoms, such as mercaptopropyl.

[0045] The above R １ is preferably an organic group having an epoxy group.

[0046] Specific examples of the compound represented by the general formula (1) include methyltrimethoxysilane, ethyltriethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

[0047] Preferred compounds represented by the general formula (1) are γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, with γ-glycidoxypropyltrimethoxysilane being more preferred. These silane compounds are preferably used after prior hydrolysis or partial hydrolysis. Hydrolysis can be carried out by mixing the silane compound with water in the presence of an acid catalyst. Other methods include mixing the silane compound with an organic solvent such as alcohol to achieve uniform hydrolysis, or by mixing the silane compound with the zirconium oxide fine particles and then hydrolyzing. Acid catalysts used for hydrolysis include dilute hydrochloric acid, dilute sulfuric acid, phosphoric acid, acetic acid, and formic acid. Dilute hydrochloric acid, acetic acid, and formic acid are particularly preferred. As the organic solvent, alcohols such as methanol, ethanol, isopropanol, and butanol, as well as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether can be used, and among these, methanol, ethanol, isopropanol, and propylene glycol monomethyl ether are preferred.

[0048] The content of the silane compound represented by the general formula (1) in the coating composition is preferably 25 to 75 wt %, more preferably 30 to 70 wt %, in terms of the solid content in the resulting hard coat film. When the content of the silane compound in the hard coat film is 25 wt % or more, it is possible to sufficiently prevent a decrease in adhesion to the plastic substrate or primer film, firmly fix the zirconium oxide particles and other components in the hard coat film, and sufficiently prevent scratches caused by the application of strong rubbing stress to eyeglass lenses. When the content of the silane compound in the hard coat film is 75 wt % or less, it is possible to further improve the refractive index of the hard coat film.

[0049] Furthermore, when it is desired to impart scratch resistance to the hard coat film, as described above, the addition of (di)silane compounds represented by the general formulas (2) and (3) is also effective. Specific examples of silane compounds represented by general formula (2) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Disilane compounds represented by general formula (3) can be synthesized by conventional methods, for example, by subjecting diallyl carbonate to an addition reaction with trichlorosilane or the like, followed by alkoxylation. Alternatively, they can be obtained by subjecting a compound containing substituents that can be added to both ends and an epoxidizable functional group therein to an addition reaction with trichlorosilane or the like, followed by alkoxylation. These (di)silane compounds are used in combination with the silane compound represented by general formula (1), and are therefore appropriately selected according to their properties. These silane compounds may be used alone or in combination of two or more.

[0050] The total amount of the (di)silane compounds represented by the general formulas (2) and (3) is preferably in the range of 0.05 to 0.3 parts, and more preferably 0.1 to 0.25 parts, per part of the silane compound represented by the general formula (1). If the amount of the (di)silane compounds represented by the general formulas (2) and (3) is 0.05 parts or more, the scratch resistance of the hard coat film is further improved, and if it is 0.3 parts or less, the water resistance of the hard coat film is reduced and cracks occurring during curing of the hard coat film can be more sufficiently suppressed.

[0051] In the coating composition, the content of the silane compound (B) is preferably 30 to 260 mol% relative to 100 mol% of the zirconium-containing metal oxide (A). This allows the effects of the present invention to be more fully exhibited. The content of the silane compound (B) is more preferably 50 to 215 mol%, even more preferably 70 to 150 mol%, and particularly preferably 80 to 110 mol%. Even when the silane compound represented by the general formula (1) and the (di)silane compounds represented by the general formulas (2) and (3) are used in combination, the preferred range of the total amount of these silane compounds is as described above. By using such a blend, a hard coat film having a refractive index in the range of 1.56 to 1.67 can be produced.

[0052] The coating composition may contain other components in addition to the zirconium-containing metal oxide (A) and the silane compound (B). The content of these other components is not particularly limited, but examples include solvents, curing agents or curing catalysts, surfactants, ultraviolet absorbers, and antioxidants. Other thermosetting resins, such as melamine resins, urea resins, epoxy resins, and phenolic resins, can also be used in combination to improve adhesion and dyeability. The content is preferably 0 to 30% by mass relative to 100% by mass of the coating composition. It is more preferably 0 to 20% by mass, even more preferably 0 to 10% by mass, and particularly preferably 0 to 5% by mass.

[0053] The other components are not particularly limited, but examples thereof include solvents, curing catalysts, surfactants, dispersants, ultraviolet absorbers, antioxidants, disperse dyes, and the like.

[0054] Examples of the solvent include water and the above-mentioned organic solvents.

[0055] The curing catalyst is not particularly limited, but examples thereof include amines, amino acids, metal acetylacetonates, organic acid metal salts, perchloric acids, salts of perchloric acids, acids, inorganic acids, organic acids, and metal chlorides. Aluminum chelates, tin chelates, and iron chelates are preferred.

[0056] The surfactant may be anionic, cationic, nonionic or amphoteric, but nonionic surfactants are preferred.

[0057] In addition, in the present invention, for the purpose of improving the light resistance of the hard coat film, it is possible to add a benzophenone-based ultraviolet absorber, a benzotriazole-based ultraviolet absorber, a hindered amine-based light stabilizer, etc. Furthermore, for the purpose of improving the dyeability of the coating film, it is also possible to add a multifunctional epoxy resin, a polyvinyl butyral resin, etc.

[0058] The coating method for forming the hard coat film is not particularly limited, and known methods such as dipping, spin coating, flow coating, and spraying can be used. The hard coat layer applied to the surface of the eyeglass lens using such a method is then cured by thermal energy (heat conduction, convection, radiation). For example, when curing is performed in a thermal environment of hot air convection, the curing conditions are preferably an ambient temperature of 80°C to 130°C for 1 to 5 hours.

[0059] As materials for the eyeglass lenses, aliphatic allyl carbonate-based, polyamide-based, polyurea-based, methacrylate-based, aromatic allyl carbonate-based, polycarbonate-based, polyurethane-based, polythiourethane-based, and episulfide-based resins are commercially available, and these can be suitably used.

[0060] The coating composition of the present invention can be suitably used for coating optical plastics such as lenses. The present invention also relates to a method for coating optical plastics such as lenses with the coating composition. The present invention also relates to a method for coating optical plastics such as lenses with the coating composition. The present invention also relates to a lens coated with the coating composition.

[0061] The lens is not particularly limited as long as it is coated with the coating composition, but it is preferable that a primer film is provided on the lens substrate and a hard coat film containing the coating composition is provided on the outer layer thereof. It is also preferable that the lens is further laminated with an antireflection film.

[0062] The refractive index of the lens is preferably 1.55 to 1.70, and more preferably 1.56 to 1.67.

[0063] The lens preferably has a haze of 0.5% or less, more preferably 0.3% or less, as measured by a haze meter.

[0064] The lens is not particularly limited, but is preferably used for eyeglasses. The embodiment in which the lens is an eyeglass lens is one of the preferred embodiments of the present invention.

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0066] <Evaluation of Physical Properties> The physical properties of the obtained zirconium-containing metal oxide (A) and coating composition were evaluated by the following procedures. (1) The average primary particle diameter D50 of the zirconium-containing metal oxide particles was measured by dynamic light scattering (UPA-UT manufactured by Nikkiso Co., Ltd.). The average primary particle diameter was also measured by a TEM (transmission electron microscope) under the following conditions. Measuring device: Field emission transmission electron microscope JEM-2100F manufactured by JEOL Ltd. Acceleration voltage: 200 kV Magnification: 250,000 times or 500,000 times

[0067] (2) Zeta Potential of Zirconium-Containing Metal Oxide Particles The zeta potential was measured by an electrophoretic laser Doppler method using an SZ-100 (manufactured by Horiba, Ltd.) A portion of the aqueous dispersion obtained in each of the Examples and Comparative Examples was collected and diluted with ion-exchanged water to prepare 20 g of a 10 mass % aqueous dispersion of zirconium-containing metal oxide (A), which was used as a measurement sample.

[0068] (3) Total Light Transmittance and Haze of Lens After Hard Coating Treatment The total light transmittance and haze of the obtained lens were measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0069] (4) Adhesion test of lens after hard coat film treatment The obtained lens surface was cut at 1 mm intervals using a knife to form 100 1 mm squares, and after strongly pressing a cellophane adhesive tape against the surface, the lens was suddenly pulled in a 90° direction relative to the in-plane direction of the plastic lens base, and this operation was repeated 10 times in total, and the number of unpeeled squares was counted and evaluated according to the following criteria: ◯: The number of unpeeled squares was 95 or more; ×: The number of unpeeled squares was less than 95.

[0070] (5) Scratch Resistance Test of Lens After Hard Coat Film Treatment The surface of the obtained lens was rubbed with steel wool #0000 under a load of 600 g for 30 strokes / 100 seconds over a distance of 3 cm, and the degree of scratches was visually evaluated according to the following criteria: ◯: Almost no scratches Δ: Slight scratches ×: Significant scratches

[0071] (6) Weather resistance test of lens after hard coat film treatment The obtained lens was subjected to an exposure test using a xenon weather meter (manufactured by Suga Test Instruments Co., Ltd.), after which cracks were checked and a test similar to the above-mentioned adhesion test was carried out, and the lens was evaluated according to the following criteria. The exposure time was 40 hours. (Appearance) ◯: No change in appearance ×: Cracks occurred (Adhesion) ◯: Number of unpeeled squares was 95 or more ×: Number of unpeeled squares was less than 95

[0072] Example 1 (I) Preparation of an aqueous dispersion of zirconium-containing metal oxide particles with a zeta potential of 30 mV or more. 90 L of a mixed aqueous solution of 0.6 mol / L zirconium oxychloride and 0.03 mol / L yttrium chloride and 68 L of a 1.9 mol / L sodium hydroxide solution were prepared. The mixed aqueous solution of zirconium oxychloride and yttrium chloride and the sodium hydroxide solution were simultaneously poured into a precipitation reactor containing 82 L of pure water. The zirconium oxychloride and yttrium chloride were co-precipitated by simultaneous neutralization to obtain a first aqueous slurry of coprecipitated particles of zirconium oxide and yttrium. This first aqueous slurry was filtered, washed, and repulped in pure water to a solids content of 11 wt % calculated as zirconium oxide and yttrium oxide, yielding 60 L of a second aqueous slurry. The electrical conductivity of this second aqueous slurry was 70 μS / cm. 4.2 kg of acetic acid (1.3 molar parts per 1 molar part of the total amount of zirconium and yttrium in the slurry) was added to the second aqueous slurry, and the mixture was hydrothermally treated at 190°C for 3 hours to obtain a transparent aqueous dispersion. This transparent dispersion was washed and concentrated using an ultrafiltration membrane to obtain an aqueous dispersion of zirconium-containing metal oxide particles having a content of 30 wt% of zirconium-containing metal oxide particles, which are a solid solution containing 4.8 mol% yttrium. The aqueous dispersion of zirconium-containing metal oxide particles thus obtained had a total light transmittance of 90% and a viscosity at 25°C of 6 mPa·s. Water was removed from the aqueous dispersion of zirconium-containing metal oxide particles, and the resulting zirconium-containing metal oxide particles were dried. When the obtained zirconium-containing metal oxide particle powder was observed using a TEM (transmission electron microscope), the average primary particle diameter of the zirconium-containing metal oxide particles was 3 nm. On the other hand, the dispersed particle diameter D50 of the zirconium-containing metal oxide particles in the aqueous dispersion of the zirconium-containing metal oxide particles was 3 nm. Therefore, it was found that there was almost no aggregation of the zirconium-containing metal oxide particles in the obtained aqueous dispersion of the zirconium-containing metal oxide particles. Furthermore, when the zeta potential of the obtained aqueous dispersion of the zirconium-containing metal oxide particles was measured, it was confirmed to be 60 mV.

[0073] (II) Preparation of a methanol dispersion of zirconium-containing metal oxide particles having a zeta potential of 30 mV or more: 10 kg of the aqueous dispersion of zirconium-containing metal oxide particles obtained in (I) above was concentrated using an ultrafiltration membrane, and an equal amount of methanol to the amount of filtrate was added to the concentrated dispersion. The concentration of the dispersion and dilution with methanol were performed continuously and simultaneously in parallel, thereby maintaining the content of zirconium-containing metal oxide particles in the dispersion at 30 wt %. The dispersion medium of the dispersion was replaced from water to methanol, resulting in a methanol dispersion of zirconium-containing metal oxide particles with a content of 30 wt %. The amount of methanol used for dilution was 90 L. The methanol dispersion of zirconium-containing metal oxide particles obtained in this manner had a total light transmittance of 90% and a viscosity of 2 mPa·s at 25°C.

[0074] (III) Preparation of a hard coating solution containing zirconium-containing metal oxide particles with a zeta potential of 30 mV or more. 69.7 g of γ-glycidoxypropyltrimethoxysilane was hydrolyzed by adding 52.3 g of methyl alcohol and 16.0 g of dilute hydrochloric acid (0.1 N) dropwise to 69.7 g of γ-glycidoxypropyltrimethoxysilane for 48 hours. 45.3 g of propylene glycol monomethyl ether and 115.1 g of the zirconia methanol dispersion (zirconium oxide concentration 30 wt%, average particle size 3 nm) prepared in (II) were added to 1.40 g of tris(2,4-pentadionato)aluminum(III) as a curing catalyst and 0.11 g of Futergent 222F (manufactured by Neos Co., Ltd.) as a surfactant, and the mixture was stirred for 24 hours to prepare a hard coating composition paint (hard coating solution) with a refractive index of 1.60. The ratio of the zirconium-containing metal oxide in the hard coating liquid was 11.5 mass %, and the ratio of the hydrolyzate of γ-glycidoxypropyltrimethoxysilane to the zirconium-containing metal oxide was 106 mol %.

[0075] (IV) Lens Coating The hard coating solution prepared in (III) was dropped onto the lens substrate, and the lens was tilted in all directions to distribute the coating solution evenly over the lens surface. The lens coated with the hard coating solution was then cured in a dryer in an atmosphere of 120°C for 3 hours to obtain a lens with a hard coating film.

[0076] Example 2 (I) Preparation of an Aqueous Dispersion of Zirconium-Containing Metal Oxide Particles with a Zeta Potential of 30 mV or More 0.76 L of a 0.6 mol / L aqueous zirconium chloride solution and 0.53 L of a 1.7 mol / L aqueous sodium hydroxide solution were prepared. The zirconium oxychloride aqueous solution and the sodium hydroxide aqueous solution were simultaneously poured into a precipitation reactor containing 0.74 L of pure water to neutralize the zirconium oxychloride, yielding a slurry of zirconium-containing metal oxide particles. The resulting slurry was filtered, washed, and repulped in pure water to give a zirconium oxide content of 5.6 wt %. The electrical conductivity of this slurry was 258 μS / cm. 82.2 g of acetic acid (3 molar parts per 1 molar part of zirconium in the slurry) was added to the slurry, which was then hydrothermally treated at 200°C for 3 hours to obtain a translucent dispersion. This translucent dispersion was washed using an ultrafiltration membrane to obtain a zirconium-containing metal oxide dispersion C having a zirconium oxide content of 30% by weight. The aqueous dispersion of zirconium-containing metal oxide particles thus obtained had a total light transmittance of 75% and a viscosity of 4 mPa·s at 25°C. Furthermore, water was removed from the aqueous dispersion of zirconium-containing metal oxide particles obtained, and the resulting zirconium-containing metal oxide particles were dried. When the obtained zirconium-containing metal oxide particle powder was observed using a transmission electron microscope (TEM), the average primary particle diameter of the zirconium-containing metal oxide particles was 8 nm. Meanwhile, the dispersed particle diameter D50 of the zirconium-containing metal oxide particles in the aqueous dispersion of zirconium-containing metal oxide particles was 8 nm. Therefore, it was found that there was almost no aggregation of the zirconium-containing metal oxide particles in the aqueous dispersion of zirconium-containing metal oxide particles obtained. Furthermore, the zeta potential of the aqueous dispersion of zirconium-containing metal oxide particles obtained was measured and confirmed to be 45 mV.

[0077] (II) Preparation of a methanol dispersion of zirconium-containing metal oxide particles having a zeta potential of 30 mV or more A methanol dispersion of zirconium-containing metal oxide particles having a zeta potential of 30 mV or more was prepared in the same manner as in (II) of Example 1, except that the aqueous dispersion of zirconium-containing metal oxide particles obtained in (I) of Example 2 was used.

[0078] (III) Preparation of hard coating liquid containing zirconium-containing metal oxide particles having a zeta potential of 30 mV or more Using the methanol dispersion prepared in (II) of Example 2, a hard coating liquid containing zirconium-containing metal oxide particles having a zeta potential of 30 mV or more was prepared in the same manner as in (III) of Example 1.

[0079] (IV) Lens Coating Using the hard coating solution prepared in (III) above, a lens having a hard coating film was obtained in the same manner as in (IV) of Example 1.

[0080] Comparative Example 1 (I) Preparation of an aqueous dispersion of zirconium-containing metal oxide particles with a zeta potential of less than 30 mV 0.76 L of a mixed aqueous solution of 0.6 mol / L zirconium oxychloride and 0.03 mol / L yttrium chloride and 0.53 L of a 1.9 mol / L sodium hydroxide solution were prepared. The mixed aqueous solution of zirconium oxychloride and yttrium chloride and the sodium hydroxide solution were simultaneously poured into a precipitation reactor containing 0.74 L of pure water, and the zirconium oxychloride and yttrium chloride were co-precipitated by simultaneous neutralization to obtain a slurry of coprecipitate particles of zirconium oxide and yttrium. The obtained slurry was filtered, washed, and repulped in pure water so that the solids content of the slurry was 5.6 wt % in terms of zirconium oxide and yttrium oxide, yielding 1 L of slurry. The electrical conductivity of this slurry was 235 μS / cm. 140.8 g of sodium citrate dihydrate (1 molar amount per 1 molar amount of the total amount of zirconium and yttrium in the slurry) was added to the slurry, and the mixture was hydrothermally treated at 200°C for 3 hours to obtain a translucent dispersion. This translucent dispersion was washed and concentrated using an ultrafiltration membrane to obtain an aqueous dispersion of zirconium-containing metal oxide particles, which are a solid solution containing yttrium, with a zirconium-containing metal oxide content of 30 wt%. The aqueous dispersion of zirconium-containing metal oxide particles thus obtained had a total light transmittance of 80% and a viscosity at 25°C of 4 mPa·s. Water was removed from the aqueous dispersion of zirconium-containing metal oxide particles, and the resulting zirconium-containing metal oxide particles were dried. When the obtained zirconium-containing metal oxide particle powder was observed using a TEM (transmission electron microscope), the average primary particle diameter of the zirconium-containing metal oxide particles was 6 nm. On the other hand, the dispersed particle diameter D50 of the zirconium-containing metal oxide particles in the aqueous dispersion of zirconium-containing metal oxide particles was 6 nm. Therefore, it was found that there was almost no aggregation of the zirconium-containing metal oxide particles in the obtained aqueous dispersion of zirconium-containing metal oxide particles. Furthermore, when the zeta potential of the obtained aqueous dispersion of zirconium-containing metal oxide particles was measured, it was confirmed to be -41 mV.

[0081] (II) Preparation of a methanol dispersion of zirconium-containing metal oxide particles having a zeta potential of less than 30 mV A methanol dispersion of zirconium-containing metal oxide particles having a zeta potential of less than 30 mV was prepared in the same manner as in (II) of Example 1, except that the aqueous dispersion of zirconium-containing metal oxide particles obtained in (I) of Comparative Example 1 was used.

[0082] (III) Preparation of hard coating liquid containing zirconium-containing metal oxide particles having a zeta potential of less than 30 mV Using the methanol dispersion prepared in (II) of Comparative Example 1, a hard coating liquid containing zirconium-containing metal oxide particles having a zeta potential of less than 30 mV was prepared in the same manner as in (III) of Example 1.

[0083] (IV) Lens Coating Using the hard coating solution prepared in (III) of Comparative Example 1, a lens having a hard coating film was obtained in the same manner as in (IV) of Example 1.

[0084] Comparative Example 2: A hard coating solution having a refractive index of 1.60 was prepared using a zirconia aqueous dispersion (manufactured by Daiichi Kigenso Co., Ltd., zirconium oxide concentration 20 wt%) with a particle size of 10 nm, with reference to Japanese Patent No. 5196993. Using the obtained hard coating solution, a lens having a hard coating film was obtained in the same manner as in Example 1 (IV). The zeta potential of the zirconia aqueous dispersion was measured and found to be -61 mV.

[0085] Comparative Example 3 (I) Preparation of an aqueous dispersion of zirconium-containing metal oxide particles having a positive zeta potential of less than 30 mV 170.5 g of caustic potassium with a concentration of 0.5 wt % was added to 339.7 g of the aqueous dispersion of zirconium-containing metal oxide particles obtained in (I) of Example 1, and the pH was adjusted to 5.3. The zeta potential of the obtained aqueous dispersion of zirconium-containing metal oxide particles was measured and found to be 28 mV.

[0086] (II) Preparation of a methanol dispersion of zirconium-containing metal oxide particles having a positive zeta potential of less than 30 mV A methanol dispersion of zirconium-containing metal oxide particles having a positive zeta potential of less than 30 mV was prepared in the same manner as in (II) of Example 1, except that the aqueous dispersion of zirconium-containing metal oxide particles obtained in (I) of Comparative Example 3 was changed.

[0087] (III) Preparation of a hard coating liquid containing zirconium-containing metal oxide particles having a positive zeta potential of less than 30 mV Using the methanol dispersion prepared in (II) above, a hard coating liquid containing zirconium-containing metal oxide particles having a positive zeta potential of less than 30 mV was prepared in the same manner as in (III) of Example 1.

[0088] (IV) Lens Coating Using the hard coating solution prepared in (III) above, a lens having a hard coating film was obtained in the same manner as in (IV) of Example 1.

[0089] The results of measurements of the physical properties of the zirconia sol, hard coating solution, and lenses having hard coating films obtained in Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 1.

[0090]

[0091] The results in Table 1 demonstrate that lenses having low-haze hard coating films can be obtained by using zirconium-containing metal oxides with a zeta potential (surface charge) of 30 mV or more. Furthermore, Comparative Example 3, which has a zeta potential of less than 30 mV, exhibits similar physical properties to those of Examples 1 and 2 immediately after preparation, but exhibits poor stability over time. It was also confirmed that the use of zirconium-containing metal oxides with a zeta potential of 30 mV or more improves the stability over time in terms of transparency and viscosity. Furthermore, the coating compositions of Examples 1 and 2 also exhibit excellent adhesion to lenses, and the lenses obtained by coating them with these compositions also exhibit excellent scratch resistance and weather resistance.

Claims

1. A coating composition containing a zirconium element-containing metal oxide (A) and a silane compound (B), wherein the zirconium element-containing metal oxide (A) has a zeta potential value of 30 mV or more as measured by the following method, the coating composition being characterized thereby. <Method for measuring zeta potential> A 10% by mass aqueous dispersion of the zirconium element-containing metal oxide (A) is measured at room temperature (25°C) by the electrophoretic laser Doppler method.

2. The coating composition according to claim 1, wherein the zirconium element-containing metal oxide (A) has an average primary particle diameter of 1 to 20 nm as measured by the dynamic light scattering method.

3. The silane compound (B) has the following general formula (1): R １ R ２ ａ Si(OR ３ ) ３－ａ (1) (In the formula, R １ represents an alkyl group having 1 to 3 carbon atoms, a phenyl group, a vinyl group, an organic group having an epoxy group, an organic group having a (meth)acrylic group, an organic group having an amino group, or an organic group having a mercapto group. R ２ represents an alkyl group having 1 to 2 carbon atoms. R ３ are the same or different and each represents an alkyl group having 1 to 3 carbon atoms. a is 0 or 1.) The coating composition according to claim 1 or 2, which is a hydrolyzate of the compound represented by the formula.

4. The coating composition according to claim 1 or 2, wherein the content ratio of the zirconium element-containing metal oxide (A) is 4 to 25% by mass based on 100% by mass of the coating composition.

5. The coating composition according to claim 1 or 2, wherein the content ratio of the silane compound (B) is 30 to 260 mol% based on 100 mol% of the zirconium element-containing metal oxide (A).

6. The coating composition according to claim 1 or 2, wherein the coating composition is used for lens applications.

7. A lens coated with the coating composition according to claim 1 or 2.