Dispersion liquid, method for producing same, and cured product thereof

Abstract

Provided is a dispersion liquid containing titanium oxide particles, a silane coupling agent and a monomer having a polymerizable functional group. The titanium oxide particles are particles obtained by surface treating a core of rutile titanium oxide with a hydrous oxide of tin or zirconium. The viscosity of the monomer at 25°C is 100 mPa·s or less. After the dispersion liquid is strongly heated for 2 hours at 925°C, the solid content amount is 15-55 mass%. In the dispersion liquid, the content of the silane coupling agent is 2-15 mass%, the content of the monomer is 30-85 mass%, and the content of organic solvents having no polymerizable functional group is 10 mass% or less. The viscosity of the dispersion liquid at 25°C is 500 mPa·s or less. Due to this configuration, provided is a curable dispersion liquid which contains titanium oxide particles, which has a high refractive index, which exhibits excellent transparency, which has a low content of volatile solvents, which has a low viscosity, and which exhibits excellent viscosity stability.

Description

Dispersion, its manufacturing method and cured product

[0001] The present invention relates to a dispersion containing titanium oxide particles and a method for producing the same, a curable sealing material comprising the dispersion, and a cured product obtained by curing the dispersion.

[0002] Since many electronic devices are susceptible to deterioration due to oxygen and moisture, they are widely protected with encapsulants made of curable resins. Various encapsulants are known for use depending on the application.

[0003] For example, in the case of optical elements, luminescent materials are susceptible to degradation by moisture and oxygen, and therefore, the optical elements must be sealed. When sealing optical elements, it is important from the viewpoint of brightness and clarity that the light emitted from the element can be efficiently extracted to the outside. Therefore, the sealing material is required to be transparent and also to have a high refractive index. A high refractive index can reduce the difference in refractive index between the high-refractive index member constituting the optical element and the sealing material, thereby reducing light loss due to reflection and refraction.

[0004] For these reasons, various encapsulants with high refractive indexes and excellent transparency have been proposed as encapsulants for optical elements. For example, Patent Document 1 describes a resin composition containing a compound having a reactive functional group containing multiple sulfur atoms and an aromatic ring, a compound having a polymerizable double bond and an aromatic ring, and a photocationic polymerization initiator. By curing this composition, a cured product with a high refractive index is obtained, which is said to be useful as an encapsulant for organic EL elements. Patent Document 2 also describes an epoxy polymerizable composition containing an S-containing epoxy compound, a thiol compound having multiple thiol groups in one molecule, and a curing accelerator. The cured product has a high refractive index and is said to be useful as an encapsulant for organic EL elements. Patent Document 2 also describes that the addition of a silane coupling agent to the composition can improve adhesion to a substrate, etc. However, special compounds were required to produce these compositions.

[0005] Furthermore, Patent Document 3 describes a curable composition as an encapsulant for organic EL devices, which contains a compound having a polymerizable double bond bonded to a naphthalene ring and a polymerization initiator, and is said to be solvent-free and low-viscosity, and to produce a cured film with a high refractive index. Patent Document 3 also describes that the refractive index of the resulting cured product can be further increased by further blending the composition described in Patent Document 3 with metal oxide particles having a primary particle diameter of 100 nm or less and a refractive index of 1.6 or more, such as titanium oxide particles. However, it is difficult to disperse titanium oxide particles to the order of several tens of nanometers, and it is not easy to obtain a cured product with excellent transparency while blending titanium oxide particles.

[0006] On the other hand, Patent Document 4 describes a titanium oxide organosol containing rutile-type titanium oxide particles surface-treated with a hydrated oxide such as tin, a silane coupling agent, a basic additive, and a water-insoluble organic solvent. It also describes that a dispersion liquid is prepared by adding a UV-curable resin to the organosol, and then the dispersion liquid is applied to evaporate the water-insoluble organic solvent, followed by ultraviolet irradiation to form a coating film with a high refractive index and high hardness, which is suitable for use in optical elements. However, the dispersion liquid described in Patent Document 4 contains a large amount of a water-insoluble organic solvent. Furthermore, even when the coating film is finished, the solvent remains at a high rate, making it unsuitable for use as an encapsulant for electronic devices.

[0007] WO2017 / 170888A1 WO2013 / 005441A1 JP2020-26515A WO2021 / 193262A1

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a dispersion containing titanium oxide particles, which has a high refractive index, excellent transparency, a low content of volatile solvents, and low viscosity and excellent viscosity stability, and a method for producing the same. It is also an object of the present invention to provide a sealant comprising such a dispersion, and to provide a cured product obtained by curing such a dispersion and uses thereof.

[0009] The above problem is solved by a dispersion liquid containing titanium oxide particles, a silane coupling agent, and a monomer having a polymerizable functional group; the titanium oxide particles are particles obtained by surface-treating a core of rutile-type titanium oxide with a hydrated oxide of tin or zirconium, and the content of titanium oxide in the particles is TiO ２ The content of tin or zirconium hydrate oxide is SnO ２ or ZrO ２ The above-mentioned problems are solved by providing a dispersion in which the content of the silane coupling agent is 2 to 15 mass %, the content of the monomer is 30 to 85 mass %, and the content of the organic solvent having no polymerizable functional group is 10 mass % or less, and the viscosity of the dispersion at 25°C is 500 mPa s or less.

[0010] At this time, the wet specific surface area of ​​the titanium oxide particles measured by pulse NMR is 20 to 150 m ２ / g. It is also preferable that the titanium oxide particles are peptized using a basic additive. It is also preferable that the average particle size of the titanium oxide particles in a liquid having an ignition solid content of 5% by mass obtained by diluting the dispersion with the monomer is 20 to 50 nm. It is also preferable that the haze at an optical path length of 10 mm in a liquid having an ignition solid content of 5% by mass obtained by diluting the dispersion with the monomer is 40% or less.

[0011] A preferred embodiment is a curable encapsulant made from the dispersion. In this case, it is more preferable that the encapsulant is used to encapsulate optical elements. A cured product obtained by curing the dispersion is also a preferred embodiment of the present invention. In this case, it is preferable that the refractive index of the cured product at 20°C and 633 nm is 1.6 or more. It is also preferable that the residual ratio of the organic solvent in the cured product is 0.1 to 10 mass %. Furthermore, an optical element encapsulated with the cured product is also a preferred embodiment.

[0012] The above-mentioned problems can also be solved by providing a method for producing the dispersion, which comprises removing water from the aqueous dispersion of titanium oxide particles and replacing it with the organic solvent, adding the silane coupling agent to the obtained dispersion, and then removing the organic solvent and replacing it with the monomer. In this case, it is preferable to add the silane coupling agent and a basic additive to the dispersion in which the organic solvent has been replaced to peptize the titanium oxide particles, and then removing the organic solvent and replacing it with the monomer.

[0013] The dispersion of the present invention contains titanium oxide particles, has a high refractive index, excellent transparency, a low content of volatile solvents, and has low viscosity and excellent viscosity stability. This dispersion can be easily cured by ultraviolet irradiation or the like and is suitable as a sealant for electronic devices, particularly as a sealant for optical elements. Furthermore, such a dispersion can be obtained by the manufacturing method of the present invention.

[0014] The dispersion of the present invention is a dispersion containing surface-treated titanium oxide particles, a silane coupling agent, and a monomer having a polymerizable functional group. This dispersion will be described below.

[0015] The titanium oxide particles contained in the dispersion of the present invention are particles obtained by surface-treating a rutile-type titanium oxide core with a hydrated oxide of tin or zirconium. The titanium oxide contained in the particles has a rutile crystalline form. This increases the refractive index and reduces photocatalytic activity, making it less likely to adversely affect electronic devices when used as a sealant. The hydrated oxide of tin or zirconium present on the surface of the titanium oxide core has a high affinity with silane coupling agents and basic additives, helping to stably disperse the titanium oxide particles in a dispersion medium. This also prevents the viscosity of the dispersion from increasing over time, resulting in a dispersion with high viscosity stability. Furthermore, since the hydrated oxide of tin or zirconium has a relatively high refractive index, it is possible to prevent a decrease in the refractive index due to surface treatment.

[0016] In the particles, the content of titanium oxide is TiO ２The content of tin or zirconium hydrated oxide is SnO ２ or ZrO ２ The titanium oxide content is 5 to 30% by mass, calculated as a percentage. A titanium oxide content of 70% by mass or more allows for a dispersion with a high refractive index to be obtained. The titanium oxide content is preferably 75% by mass or more, and more preferably 80% by mass or more. In this case, the content of tin or zirconium hydrated oxide is preferably 25% by mass or less, and more preferably 20% by mass or less. Furthermore, a tin or zirconium hydrated oxide content of 5% by mass or more improves the viscosity stability and transparency of the dispersion of the present invention. The tin or zirconium hydrated oxide content is preferably 7% by mass or more, and more preferably 8% by mass or more. In this case, the titanium oxide content is preferably 93% by mass or less, and more preferably 92% by mass or less. Note that the content here is expressed as a percentage when the total mass of all oxides or hydrated oxides of metals or silicon contained in the particles is converted into oxides and taken as 100.

[0017] The titanium oxide particles have a wet specific surface area of ​​20 to 150 m as measured by pulse NMR. ２ / g. If the wet specific surface area is too large, the stability of the viscosity of the dispersion over time may decrease, and the viscosity may increase during storage. The wet specific surface area is more preferably 120 m ２ / g or less. ２ If the average particle size is less than 1 / g, the average particle size becomes large, the haze increases, and sufficient transparency may not be obtained.

[0018] The ignition solid content when the dispersion of the present invention is ignited at 925°C for 2 hours is preferably 15 to 55% by mass. An ignition solid content of 15% by mass or more increases the refractive index of the dispersion. The ignition solid content is more preferably 20% by mass or more, and even more preferably 25% by mass or more. On the other hand, an ignition solid content of 55% by mass or less can reduce the viscosity of the dispersion. The ignition solid content may be 50% by mass or less, 45% by mass or less, 40% by mass or less, or 35% by mass or less. Here, the ignition solid content refers to the ash obtained by completely oxidizing the metal component and silicon component by heating a sample dispersion in air at 925°C for 2 hours.

[0019] The TiO in the ignition solid obtained by igniting the dispersion of the present invention at 925°C for 2 hours ２ The content of TiO is preferably 70 to 95 mass %. ２ When the content of TiO is 70 mass % or more, a dispersion liquid having a high refractive index can be obtained. ２ On the other hand, from the viewpoint of the viscosity stability and transparency of the dispersion, the content of TiO ２ The content is preferably 95% by mass or less.

[0020] The dispersion of the present invention contains a silane coupling agent. By containing the silane coupling agent, the dispersibility of the titanium oxide particles is improved, and a dispersion excellent in transparency and viscosity stability can be obtained. As the silane coupling agent, known ones can be used, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, p-styryltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltrimethoxysilane. Among these, in consideration of affinity and reactivity with the monomer used as the dispersion medium, those having a polymerizable functional group are preferred, and those having a polymerizable double bond such as a (meth)acrylic group or a vinyl group are suitable. Among these, silane coupling agents containing a (meth)acrylic group, which has good polymerizability, are suitable, and examples thereof include 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane.

[0021] The content of the silane coupling agent in the dispersion of the present invention is 2 to 15% by mass. The above-mentioned effects of adding the silane coupling agent can be achieved by having a content of the silane coupling agent of 2% by mass or more. The content of the silane coupling agent is preferably 4% by mass or more, more preferably 5% by mass or more, and even more preferably 6% by mass or more. On the other hand, if the amount of the silane coupling agent is too high, the refractive index decreases. The content of the silane coupling agent is preferably 12% by mass or less, and more preferably 10% by mass or less. The silane coupling agent may be bonded to the surface of the titanium oxide particles, or some of the alkoxy groups contained in the silane coupling agent may be hydrolyzed.

[0022] The dispersion medium in the dispersion of the present invention is a monomer having a polymerizable functional group. By dispersing titanium oxide particles in such a monomer, a polymerization reaction can be promoted, allowing the dispersion to easily harden. The type of monomer used here is not limited as long as it has a polymerizable functional group. Monomers having a polymerizable double bond capable of addition polymerization or a monomer having an epoxy group capable of ring-opening polymerization can be used, but those having a polymerizable double bond such as a (meth)acrylic group or a vinyl group are preferred because they can be easily hardened by ultraviolet light or the like. Among these, monomers containing a (meth)acrylic group, which has good polymerizability, are preferred. Since too many (meth)acrylic groups per monomer molecule increases viscosity, the number is preferably 1 to 3, and more preferably 1 to 2. When multiple monomers are used, the simple average value of their content should fall within the above range.

[0023] Specific examples of monomers containing a (meth)acrylic group include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, n-octyl (meth)acrylate, biphenylmethyl (meth)acrylate, phenoxybenzyl (meth)acrylate, ethoxylated phenyl (meth)acrylate, tripropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, naphthalenemethyl (meth)acrylate, and dimethyl (meth)acrylamide.

[0024] Furthermore, the viscosity of the monomer used in the present invention at 25°C is 100 mPa·s or less. By using such a low-viscosity monomer, the viscosity of the resulting dispersion is also low, providing a dispersion with excellent fluidity. The viscosity of the monomer is preferably 50 mPa·s or less, more preferably 30 mPa·s or less. On the other hand, the viscosity of the monomer is usually 1 mPa·s or more. Here, when multiple types of monomers are used, it is sufficient that the viscosity of the mixture thereof falls within the above range.

[0025] The refractive index of the monomer used in the present invention at 20°C and 589 nm is preferably 1.45 or more, more preferably 1.5 or more, and even more preferably 1.55 or more. On the other hand, the refractive index of the monomer is usually 1.7 or less. Here, when multiple types of monomers are used, the refractive index of the mixture thereof should be within the above range. In order to increase the refractive index, it is preferable to use a monomer having an aromatic ring in the molecule.

[0026] The content of the monomer in the dispersion of the present invention is 30 to 85% by mass. By having a monomer content of 30% by mass or more, a dispersion with low viscosity can be obtained. The content of the monomer may be 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more. On the other hand, if the amount of the monomer is too large, the refractive index cannot be increased. The content of the monomer is preferably 80% by mass or less, and more preferably 75% by mass or less.

[0027] The content of the organic solvent not having a polymerizable functional group in the dispersion of the present invention is 10% by mass or less. Therefore, the organic solvent is included in the dispersion of the present invention as an optional component. A solvent that is mutually soluble with the monomer and has a boiling point lower than that of the monomer is preferably used as the organic solvent. Ketones, esters, ethers, alcohols, etc. can be used. Specifically, methyl ethyl ketone, acetone, methyl acetate, ethyl acetate, diethyl ether, tetrahydrofuran, methanol, ethanol, propanol, isopropanol, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, etc. can be used. In consideration of handling safety and the impact on the working environment, the boiling point of the organic solvent is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. On the other hand, in consideration of the efficiency of substitution of the organic solvent with the monomer, the boiling point of the organic solvent is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. The difference in boiling point between the organic solvent and the monomer is preferably 80° C. or more, but even if there is no difference in boiling point, substitution with the monomer is not an issue.

[0028] By keeping the content of such organic solvent at 10% by mass or less, it is possible to suppress the evaporation of the organic solvent into the surrounding environment during application or filling. Furthermore, even if a small amount of organic solvent is incorporated during curing, there is often no problem as long as the organic solvent does not volatilize. The content of the organic solvent is preferably 8% by mass or less, more preferably 6% by mass or less. On the other hand, the lower the content of the organic solvent, the less the organic solvent volatilizes, which is good, but the amount of monomer used for substitution may be too large, or the amount of energy required for substitution may be too large, which is uneconomical and may also result in poor stability of the dispersion over time. The content of the organic solvent in the dispersion of the present invention may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more.

[0029] A method for producing the dispersion of the present invention will be described below. A suitable method for producing the dispersion is to remove water from an aqueous dispersion of titanium oxide particles and replace it with an organic solvent, add a silane coupling agent to the obtained dispersion, then remove the organic solvent and replace it with the monomer.

[0030] First, the step of preparing an aqueous dispersion of titanium oxide particles will be described. The method for preparing the aqueous dispersion is not particularly limited, and known methods can be used. Examples include a method in which a water-soluble tin compound (rutilizing agent) and a water-soluble titanium compound are dissolved in water, hydrolyzed, salts are removed, and then an acid or alkali is added to perform peptization; and a method in which a water-soluble tin compound is dissolved in water and hydrolyzed by heating to precipitate a portion of the water-soluble tin compound, a water-soluble titanium compound is added to perform hydrolysis, salts are removed, and then an acid or alkali is added to perform peptization.

[0031] Examples of water-soluble titanium compounds include titanyl sulfate, titanium tetrachloride, and titanium sulfate, and examples of water-soluble tin compounds (rutile-forming agents) include tin sulfate, tin chloride, and tin nitrate. Examples of acids include hydrochloric acid, nitric acid, and oxalic acid, and examples of alkalis include sodium hydroxide and amines such as tert-butylamine, isopropylamine, diethylamine, and triethanolamine. The amount of tin compound added is determined by the ratio of SnO ２ Converted to titanium oxide (TiO ２ The amount is usually 1 to 25 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass (calculated as a saturation agent).

[0032] Specific examples of the above steps include the following: First, titanyl sulfate and a small amount of tin sulfate are dissolved in water. The tin compound added at this time is a rutile-forming agent that converts the crystal form of the resulting titanium oxide particles to rutile. The resulting aqueous solution is then neutralized with an alkali to precipitate a mixture of hydrated titanium oxide and hydrated tin oxide. The mixture is then filtered and washed with water to obtain a cake, which is then peptized with the addition of hydrochloric acid and stirring to obtain an aqueous dispersion of rutile-type titanium oxide particles.

[0033] Next, the obtained titanium oxide particles are surface-treated. The method for performing the surface treatment is not particularly limited, and known methods can be used. Examples include a method in which a water-soluble compound of tin or zirconium is added to the aqueous dispersion of rutile-type titanium oxide particles obtained as described above, and then the pH is adjusted with an acid or alkali, and a method in which the pH of the aqueous dispersion of rutile-type titanium oxide particles is adjusted with an acid or alkali while adding a water-soluble compound of tin or zirconium. In this way, the core of the rutile-type titanium oxide is covered with a hydrated oxide of tin or zirconium, thereby performing the surface treatment. At this time, if the content of the hydrated oxide of tin or zirconium in the titanium oxide particles is SnO ２ or ZrO ２ The concentration of the rutile-type titanium oxide particles is adjusted to 5 to 30 mass % in terms of the total mass of the rutile-type titanium oxide particles. The precipitate is then filtered and washed as necessary, and water is added again to obtain an aqueous suspension of rutile-type titanium oxide particles surface-treated with a hydrated oxide of tin or zirconium. The aqueous suspension thus obtained is cloudy due to the aggregation of the surface-treated titanium oxide particles.

[0034] Next, the dispersion medium of the aqueous suspension of surface-treated rutile titanium dioxide particles obtained in the above process is replaced with an organic solvent. After adding a water-soluble organic solvent such as an alcohol (e.g., methanol, ethanol, or isopropanol), a ketone (e.g., acetone), or an ether (e.g., tetrahydrofuran) to the aqueous suspension of titanium dioxide particles, the solvent can be replaced with the water-soluble organic solvent by techniques such as ultrafiltration, dialysis, or evaporation. If necessary, the dispersion medium can then be replaced with a water-insoluble organic solvent. Examples of water-insoluble organic solvents include ketones (e.g., methyl ethyl ketone and methyl isobutyl ketone), esters (e.g., methyl acetate and ethyl acetate), and ethers (e.g., diethyl ether). Water-insoluble organic solvents have good affinity with the monomer to be subsequently replaced, facilitating the replacement process with the monomer. Here, water-soluble organic solvents are solvents that can be mixed with water in any ratio, while water-insoluble organic solvents are other organic solvents.

[0035] By adding a silane coupling agent to the suspension thus obtained in which titanium oxide particles are dispersed in an organic solvent and mixing the mixture, the titanium oxide particles are peptized, thereby obtaining a dispersion in which the titanium oxide particles are finely dispersed in the organic solvent. In this case, peptization can be more effectively achieved by further adding an amine or a dispersant having an amine value as a basic additive. Examples of amines that can be used as the basic additive include alkylamines such as tert-butylamine, isopropylamine, diisopropylamine, diethylamine, propylamine, n-butylamine, and isobutylamine; alkanolamines such as triethanolamine, diethanolamine, N-methylethanolamine, and 2-amino-2-methyl-1-propanol; and heterocyclic amines such as pyridine. Examples of dispersants having an amine value that can be used as the basic additive include dispersants such as DISPERBYK-108, DISPERBYK-109, and DISPERBYK-180 (manufactured by BYK Japan KK). The amount of the basic additive added can be determined by the amount of titanium oxide (TiO ２ The amount of the basic additive is preferably 1 to 20 parts by mass per 100 parts by mass (based on the total mass of the dispersion liquid), but if the boiling point of the basic additive is low, most of it will be removed from the dispersion liquid in the subsequent substitution operation. When used as an encapsulant for electronic devices, it may be preferable for the basic additive not to remain in the dispersion liquid, and in such cases, it is preferable to use a basic additive with a low boiling point. The preferred boiling point is the same as the boiling point of the organic solvent not having a polymerizable functional group. Note that, for the purpose of further improving the dispersion stability of the titanium oxide particles in the dispersion liquid, a dispersant that does not fall under the category of a basic additive (i.e., a dispersant without an amine value) may be added.

[0036] The dispersion medium of the dispersion obtained through the above steps is replaced with a monomer having a polymerizable functional group. The method of replacement is not particularly limited, and techniques such as ultrafiltration, dialysis, and evaporation can be used. Among these, evaporation is preferred because it is simple and low-cost. The dispersion of the present invention is obtained by evaporating while appropriately adding monomer and concentrating until the appropriate concentration is reached. Alternatively, the dispersion medium may be concentrated to 3 to 10% by mass, solidified, and then the monomer may be added for replacement. In this case, it is preferable to crush the mixture using a bead mill or the like after replacement.

[0037] The dispersion of the present invention has good transparency. Specifically, when the dispersion is diluted with the monomer and the ignition solid content is 5% by mass, the haze at an optical path length of 10 mm is preferably 40% or less. The haze is more preferably 35% or less, and even more preferably 30% or less.

[0038] Furthermore, the average particle size of the titanium oxide particles in a liquid having an ignition solid content of 5 mass % obtained by diluting the dispersion of the present invention with the monomer used as the dispersion medium is preferably 20 to 50 nm. By having an average particle size of 50 nm or less, a dispersion with excellent transparency can be obtained. The average particle size is more preferably 45 nm or less.

[0039] The viscosity of the dispersion of the present invention at 25°C is 500 mPa·s or less. The low viscosity of the dispersion makes it easy to apply when used as a sealant. For example, it can be applied only to the necessary areas using an inkjet printer or the like, and it can easily conform to uneven surfaces. Furthermore, when filling between an electronic device and a cover member, it can easily and uniformly fill a narrow gap. The viscosity of the dispersion is preferably 300 mPa·s or less, more preferably 200 mPa·s or less, and even more preferably 100 mPa·s or less.

[0040] The method for curing the dispersion of the present invention is not particularly limited. Curing may be achieved by heating, or by irradiating with ultraviolet light or electron beams. Preferably, a polymerization initiator is mixed into the dispersion before curing, followed by heating or ultraviolet irradiation. Examples of polymerization initiators include radical polymerization initiators, ionic polymerization initiators, and photopolymerization initiators. When used as an encapsulant for electronic devices, it is best to avoid heating, so a photopolymerization initiator is preferably used. Specific examples include 1-hydroxycyclohexyl phenyl ketone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 3-hydroxybenzophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, monoacylphosphine oxide, 4,4'-bis(dimethylamino)benzophenone, and 2,4-diethylthioxanthone. These polymerization initiators can be used alone or in combination.

[0041] When the dispersion of the present invention is filled into a narrow space and cured, the residual organic solvent ratio (mass %) of the cured product is the same as the organic solvent content (mass %) of the dispersion, and therefore the preferred range of the residual organic solvent ratio of the cured product in such a case is the same as the preferred range of the organic solvent content of the dispersion of the present invention.

[0042] The refractive index of the dispersion of the present invention at 20°C and 633 nm is preferably 1.55 or more. This makes it possible to obtain a cured product with a high refractive index. The refractive index of the dispersion is more preferably 1.6 or more, and even more preferably 1.65 or more. Furthermore, the refractive index of the cured product obtained by curing the dispersion of the present invention at 20°C and 633 nm is preferably 1.6 or more. The refractive index is more preferably 1.65 or more, and even more preferably 1.7 or more. By obtaining a cured product with a high refractive index, when the cured product is used as an encapsulant for an electronic device, the difference in refractive index between the encapsulant and a high-refractive-index component constituting the device can be reduced, thereby reducing light loss due to reflection and refraction.

[0043] A suitable application of the dispersion of the present invention is as an encapsulant. To protect electronic devices from oxygen and moisture, the encapsulant of the present invention is applied or filled, and then cured to protect the electronic devices. In particular, the dispersion of the present invention, which has a high refractive index and high transparency, is suitable for use in applications in which light passes through the encapsulant, such as optical elements such as organic EL elements, liquid crystal elements, and LED elements.

[0044] Among these, the sealing material is particularly useful as a sealing material used to seal organic EL elements. Organic EL elements are susceptible to deterioration due to oxygen and moisture, so it is important to protect them with a sealing material. The sealing material of the present invention has a low viscosity, so when applying the sealing material to an organic EL element, it can be applied only to the necessary areas using an inkjet printer or the like, and it can easily conform to uneven surfaces. Furthermore, when filling the gap between an organic EL element and a cover member with a sealing material, the sealing material of the present invention has a low viscosity, so it can easily and uniformly fill a narrow gap.

[0045] The present invention will be explained in more detail below with reference to examples.

[0046] Example 1 (Step A: Preparation of aqueous dispersion of titanium oxide particles) Titanyl sulfate dihydrate (TioSO ４ ・2H ２ 303 g of TM crystal (TiO) manufactured by Teika Corporation ２ 100 g of tin sulfate (SnSO ４ ) 4.3g (SnO ２ 3.0 g as TiO ２ A solution of 3 parts by mass of titanium oxide per 100 parts by mass of titanium dioxide was dissolved in 1692.7 g of water. The pH of the resulting aqueous solution was then adjusted to 7.0 using a 10% by mass aqueous solution of sodium hydroxide, resulting in the precipitation of a mixture of hydrated titanium oxide and hydrated tin oxide. The mixture was then filtered and washed with water to obtain a cake with a solids content of 11.0% by mass. 278 g of concentrated hydrochloric acid (100 g as HCl) and 785.6 g of water were gradually added to 936.4 g of this cake, and the cake was peptized with stirring to obtain 2000 g of an aqueous dispersion of rutile-type titanium oxide particles (TiO ２ A concentration of 5% by weight was obtained.

[0047] (Step B: Surface Treatment of Titanium Oxide Particles) Tin sulfate (SnSO 4 ) was added to 2000 g of the aqueous dispersion of rutile-type titanium oxide particles obtained in step A. ４ ) 14.3g (SnO ２ 10.0 g as TiO ２ The resulting aqueous dispersion was then adjusted to pH 6.0 using a 10% by mass aqueous solution of sodium hydroxide, and a surface treatment was performed by precipitating tin hydrate oxide on the surfaces of the titanium oxide particle cores. Next, the precipitate was filtered and washed, and water was added to adjust the concentration, and 100 parts by mass (TiO ２ 10 parts by mass (SnO ２ 1000 g of an aqueous suspension of rutile-type titanium dioxide particles surface-treated with hydrated tin oxide (TiO ２ A concentration of 10% by weight was obtained.

[0048] (Step C: Substitution of Dispersion Medium from Water to Organic Solvent) 1000 g of isopropanol and 1000 g of methyl ethyl ketone were added to 1000 g of the aqueous suspension of surface-treated titanium oxide particles obtained in step B. Then, ultrafiltration was carried out while further adding methyl ethyl ketone, and the dispersion medium was replaced with methyl ethyl ketone, until a total amount of 1000 g (TiO ２ A methyl ethyl ketone suspension with a concentration of 10% by mass was obtained. Next, 25 g of 3-acryloxypropyltrimethoxysilane (TiO ２ 25 parts by mass per 100 parts by mass), and 5 g of tert-butylamine (TiO ２ To the aqueous solution (5 parts by mass per 100 parts by mass of titanium dioxide), 1030 g of a methyl ethyl ketone dispersion of surface-treated rutile-type titanium dioxide particles was obtained.

[0049] (Step D: Substitution of Dispersion Medium from Organic Solvent to Monomer) 500 g of benzyl acrylate (refractive index at 20°C and 589 nm: 1.52; viscosity at 25°C: 3 mPa s) was added as a monomer having a polymerizable functional group to 1,030 g of the methyl ethyl ketone dispersion obtained in step C. The mixture was concentrated in an evaporator while further adding benzyl acrylate, thereby substituting the methyl ethyl ketone with benzyl acrylate. After concentrating to 313 g, the mixture was subjected to a dispersion treatment in a bead mill, yielding a dispersion of surface-treated rutile-type titanium oxide particles.

[0050] (Evaluation of Dispersion) The content of methyl ethyl ketone in the dispersion thus obtained was 4.6% by mass. Here, the solvent (methyl ethyl ketone) content in the dispersion was obtained by creating a calibration curve for methyl ethyl ketone using a gas chromatograph "GASCHROMATOGRAPH GC-14B" manufactured by Shimadzu Corporation, and then quantifying the content (% by mass) of methyl ethyl ketone in the dispersion.

[0051] When the dispersion was ignited at 925°C, the ignition solid content was 31.4 mass%. ２ The content of TiO was 26.3% by mass. The ignition solid content was calculated by placing a certain amount (W) of about 1 g of the dispersion in a crucible, heating it at 925°C for 2 hours, and measuring the mass (h) of the solid content, using the following formula: Ignition solid content (mass%) = (h / W) x 100. ２ The content of TiO in the dispersion was determined by analyzing the solid content using a fluorescent X-ray analyzer "SUPER MINI" manufactured by Rigaku Corporation. ２ The content (mass %) was determined.

[0052] From the above analysis results, it was found that TiO ２ 26.3 mass% (82.3 g), SnO ２The mixture contained 3.4 mass% (10.7 g) of the silane coupling agent 3-acryloxypropyltrimethoxysilane, 8.0 mass% (25 g) of the silane coupling agent 3-acryloxypropyltrimethoxysilane, and 4.6 mass% (14.4 g) of the organic solvent methyl ethyl ketone. From this, it can be calculated that the remaining 58 mass% (181 g) is the monomer benzyl acrylate. Here, TiO ２ SnO per 100 parts by mass ２ It was estimated that the silane coupling agent contained 13 parts by mass. It was assumed that the silane coupling agent did not volatilize and did not undergo hydrolysis. It was also estimated that isopropanol had been replaced by methyl ethyl ketone and did not remain, and that tert-butylamine (boiling point 45.5°C) had volatilized and did not remain.

[0053] The viscosity of the dispersion immediately after production was 12 mPa s. After a 2-week aging test at 40°C, the viscosity was 14 mPa s, indicating a viscosity increase of 17%. Here, the viscosity of the dispersion was measured using an E-type viscometer at 25°C and a rotation speed of 60 rpm (mPa s). The viscosity of the dispersion after aging was measured in the same manner at 25°C after leaving it to stand in a thermostatic bath at 40°C for 2 weeks.

[0054] The haze value of the dispersion obtained by diluting with a monomer so that the ignition solid content was 5% by mass was 28% at an optical path length of 10 mm. The haze value was measured as follows. The dispersion was diluted with the same monomer used to prepare the dispersion so that the ignition solid content was 5% by mass. This diluted solution was placed in a quartz cell with an optical path length of 10 mm, and the haze value (%) of the dispersion was measured using a haze meter "NDH 4000" manufactured by Nippon Denshoku Industries Co., Ltd.

[0055] The average particle size of the liquid obtained by diluting with a monomer so that the ignition solid content was 5% by mass was 36 nm. The average particle size was measured as follows. The dispersion was diluted with the same monomer used to prepare the dispersion so that the ignition solid content was 5% by mass. The particle size distribution of this diluted liquid was measured using a Zeta-Potential & Particle Size Analyzer ELSZ-1000 manufactured by Otsuka Electronics Co., Ltd., and D50 (median diameter) was taken as the average particle size (nm).

[0056] The wet specific surface area of ​​the particles in the monomer dispersion is 45 m ２ The wet specific surface area was measured using an NMR wet specific surface area measuring device "Acorn Area" manufactured by Xigo Nanotools, Inc., USA, to determine the wet specific surface area (m ２ / g) was measured.

[0057] (Formation of a coating film) To the thus obtained dispersion of titanium oxide particles, 0.3 g of 1-hydroxycyclohexylphenyl ketone and 0.3 g of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide were added as polymerization initiators, and the mixture was stirred for 1 hour. The thus obtained dispersion was spin-coated onto a microslide glass plate (70 × 55 × 1.3 mm) manufactured by Matsunami Glass Industrial Co., Ltd., under conditions of a temperature of 25°C, a humidity of 50%, 1000 rpm, and a rotation time of 3 seconds. Thereafter, the mixture was left to stand at 25°C for 30 minutes, and then subjected to spin coating at 580 mJ / cm. ２ The coating was cured by irradiating it with ultraviolet light of 1000 kJ / cm to form a coating film with a thickness of 1 μm.

[0058] (Evaluation of Coating Film) The refractive index of the coating film before curing was 1.69, and the refractive index of the coating film after curing was 1.71. Here, the refractive index of the coating film was determined by measuring the refractive index of a coating film sample formed on a glass plate at 20°C and 633 nm using an ellipsometer "DVA-FL3G" manufactured by Mizojiri Optical Laboratory Co., Ltd. The haze of the cured coating film was 0.10%. The haze value (%) of these coating films was measured by measuring a coating film with a film thickness of approximately 1 μm on a glass plate using a haze meter "NDH 4000" manufactured by Nippon Denshoku Industries Co., Ltd. The residual solvent ratio of the cured coating film was 0.5% by mass. Here, the residual solvent ratio of the cured coating film was determined by peeling the cured coating film from the glass plate and heating it at a rate of 5°C / min using a thermogravimetric / differential thermal analyzer "TG-DTA7300" manufactured by Hitachi High-Tech Science Corporation. The residual solvent ratio (mass%) was determined from the weight loss rate at 100°C. The above results are summarized in Tables 1 to 3 together with the results of other examples and comparative examples.

[0059] Example 2 A dispersion in which surface-treated rutile-type titanium oxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that in step D, phenoxyethyl acrylate was used as the monomer and the concentration was carried out to 341 g, and then a coating film was formed.

[0060] Example 3 In step B, the amount of tin sulfate added was 7.1 g (SnO ２ 5.0 g as TiO ２ A dispersion in which the surface-treated rutile-type titanium dioxide particles were dispersed in the monomer was obtained in the same manner as in Example 1, except that the amount of the monomer was changed to 5 parts by mass per 100 parts by mass of the monomer, and that in step D, n-octyl acrylate was used as the monomer and the concentration was carried out to 327 g, and a coating film was then formed.

[0061] Example 4 In step C, 3-methacryloxypropylmethoxysilane was used as the silane coupling agent, and the amount of the silane coupling agent added was set to TiO ２ A dispersion in which the surface-treated rutile-type titanium oxide particles were dispersed in the monomer was obtained in the same manner as in Example 1, except that the amount was changed to 30 parts by mass per 100 parts by mass, and that in step D, biphenyl methyl acrylate was used as the monomer and the concentration was carried out to 481 g, and a coating film was then formed.

[0062] Example 5 A dispersion in which surface-treated rutile-type titanium dioxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that in step C, 3-methacryloxypropylmethoxysilane was used as the silane coupling agent, and in step D, phenoxybenzyl acrylate was used as the monomer, and the concentration was carried out to 397 g, and then a coating film was formed.

[0063] Example 6 In step C, 3-methacryloxypropylethoxysilane was used as the silane coupling agent, and the amount of the silane coupling agent added was set to TiO ２ A dispersion in which the surface-treated rutile-type titanium oxide particles were dispersed in the monomer was obtained in the same manner as in Example 1, except that the amount was changed to 20 parts by mass per 100 parts by mass, and that in step D, ethoxylated phenyl acrylate was used as the monomer and the concentration was carried out to 390 g, and a coating film was then formed.

[0064] Example 7 A dispersion in which surface-treated rutile-type titanium dioxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that in step C, 3-methacryloxypropylethoxysilane was used as the silane coupling agent, and in step D, ethoxylated phenyl acrylate was used as the monomer, and the concentration was carried out to 394 g, and then a coating film was formed.

[0065] Example 8 In step B, the amount of tin sulfate added was 42.9 g (SnO ２ 30 g as TiO ２ A dispersion in which the surface-treated rutile-type titanium dioxide particles were dispersed in the monomer was obtained in the same manner as in Example 1, except that the amount of the monomer was changed to 30 parts by mass per 100 parts by mass of the polymer, and that in step D, tripropylene glycol diacrylate was used as the monomer and the concentration was carried out to 465 g, and a coating film was then formed.

[0066] Example 9 A dispersion in which surface-treated rutile-type titanium oxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that in step D, trimethylolpropane triacrylate was used as the monomer and the concentration was carried out to 597 g, and then a coating film was formed.

[0067] Example 10 A dispersion in which surface-treated rutile-type titanium dioxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that trifluoropropyltrimethoxysilane was used as the silane coupling agent in step C, naphthalene methyl acrylate was used as the monomer in step D, and the concentration was carried out to 480 g, and then a coating film was formed.

[0068] Example 11 A dispersion of surface-treated rutile-type titanium oxide particles dispersed in a monomer was obtained in the same manner as in Example 1, except that in step C, trifluoropropyltrimethoxysilane was used as the silane coupling agent, and in step D, the concentration was carried out to 343 g, and then a coating film was formed.

[0069] Example 12 In step B, 2000 g of the aqueous dispersion of titanium oxide particles obtained in step A was mixed with 13.1 g of zirconium oxychloride octahydrate (ZrO ２ 5g as TiO ２5 parts by mass per 100 parts by mass of the solution was added, and the pH was adjusted to 6.0 using a 10% by mass aqueous solution of sodium hydroxide. ２ 10.0 g as TiO ２ 10 parts by mass of 100 parts by mass of titanium oxide core was added, and the pH was adjusted to 6.0 using a 10% by mass aqueous solution of sodium hydroxide. In this way, hydrated oxides of zirconium and tin were precipitated on the surface of the titanium oxide particle core, thereby performing surface treatment. Next, the precipitate was filtered and washed, and water was added to adjust the concentration, and 100 parts by mass (TiO ２ 5 parts by mass (ZrO ２ 10 parts by mass (SnO ２ 1000 g of an aqueous suspension of titanium oxide particles surface-treated with hydrated tin oxide (TiO ２ A concentration of 10% by mass was obtained. In step D, naphthalene methyl acrylate was used as the monomer, and the concentration was increased to 498 g. Except for these points, the same procedures as in Example 1 were carried out to obtain a dispersion in which the surface-treated rutile-type titanium oxide particles were dispersed in the monomer, and then a coating film was formed.

[0070] Example 13 In step B, sodium silicate No. 3 (SiO ２ Concentration: 29% by mass) 17.2g (SiO ２ 5g as TiO ２ 5 parts by mass per 100 parts by mass), and then 14.3 g of tin sulfate (SnO ２ 10.0 g as TiO ２ After adding 10 parts by mass of 100 parts by mass of titanium oxide cores, the pH was adjusted to 6.0 using a 10% by mass aqueous solution of sodium hydroxide. In this way, hydrated oxides of silicon and tin were precipitated on the surfaces of the titanium oxide particle cores, thereby performing surface treatment. Next, the precipitates were filtered and washed, and water was added to adjust the concentration. 100 parts by mass (TiO ２ 5 parts by mass (SiO ２ hydrated oxide of silicon (SnO ２ 1000 g of an aqueous suspension of titanium oxide particles surface-treated with hydrated tin oxide (TiO２ A concentration of 10% by mass was obtained. In step D, the concentration was further increased to 355 g. Except for these points, the same procedures as in Example 1 were carried out to obtain a dispersion in which the surface-treated rutile-type titanium oxide particles were dispersed in a monomer, and then a coating film was formed.

[0071] Example 14 In step C, tert-butylamine was added as a basic additive, and then 5 g of a dispersant (manufactured by BYK Japan, "DISPERBYK-111": TiO ２ A dispersion of surface-treated rutile-type titanium oxide particles dispersed in a monomer was obtained in the same manner as in Example 1, except that a 5% by weight (5 parts by weight per 100 parts by weight) of trimethylolpropane triacrylate was added in step D, and that trimethylolpropane triacrylate was used as the monomer and the concentration was carried out to 498 g, and then a coating film was formed. DISPERBYK-111 is a dispersant that does not have an amine value (i.e., the amine value is zero).

[0072] Example 15 A dispersion in which surface-treated rutile-type titanium oxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that in step D, dimethylacrylamide was used as the monomer and the concentration was carried out to 313 g, and then a coating film was formed.

[0073] Example 16 In step C, 3-methacryloxypropyltrimethoxysilane was used as a silane coupling agent, and after the silane coupling agent and a basic additive were added, a dispersant (5 g of "DISPERBYK-111" manufactured by BYK Japan Co., Ltd.: TiO ２ A dispersion in which the surface-treated rutile-type titanium oxide particles were dispersed in the monomer was obtained in the same manner as in Example 1, except that a 500 parts by mass (5 parts by mass per 100 parts by mass of the monomer) was added, and in step D, the concentration was carried out to 258 g, and then a coating film was formed.

[0074] Example 17 In step C, 3-methacryloxypropyltrimethoxysilane was used as a silane coupling agent, and after the silane coupling agent and a basic additive were added, a dispersant (5 g of "DISPERBYK-111" manufactured by BYK Japan Co., Ltd.: TiO ２A dispersion in which the surface-treated rutile-type titanium oxide particles were dispersed in the monomer was obtained in the same manner as in Example 1, except that a 500 parts by mass (5 parts by mass per 100 parts by mass of the monomer) was added, and that in step D, the concentration was carried out to 229 g, and then a coating film was formed.

[0075] Example 18 A dispersion in which surface-treated rutile-type titanium dioxide particles were dispersed in a monomer was obtained in the same manner as in Example 1, except that in step C, 3-methacryloxypropyltrimethoxysilane was used as the silane coupling agent, and in step D, dimethylacrylamide was used as the monomer and the concentration was carried out to 206 g, and then a coating film was formed.

[0076] Comparative Example 1 A dispersion of surface-treated rutile-type titanium dioxide particles dispersed in a monomer was obtained and evaluated in the same manner as in Example 1, except that in step D, dipentaerythritol hexaacrylate was used as the monomer and the concentration was carried out to 597 g. The viscosity of the resulting dispersion immediately after production was 9,500 mPa s, and the viscosity after an aging test exceeded 10,000 mPa s. As a result, it was not possible to measure the wet specific surface area or form a coating film.

[0077] Comparative Example 2 A dispersion of surface-treated rutile-type titanium dioxide particles dispersed in a monomer was obtained, and then a coating film was formed in the same manner as in Example 1, except that tin sulfate was not added in step B, and trimethylolpropane triacrylate was used as the monomer and concentrated to 547 g in step D. The obtained dispersion had a high wet specific surface area and a high rate of increase in viscosity after a time-dependent test.

[0078] Comparative Example 3 A dispersion of surface-treated rutile-type titanium oxide particles dispersed in a monomer was obtained in the same manner as in Example 1, except that trimethylolpropane triacrylate was used as the monomer and the concentration was carried out to 1,194 g in step D. The resulting dispersion had a low refractive index due to its low ignition solids content.

[0079] Comparative Example 4 In step B, the amount of tin sulfate added was 185.3 g (SnO ２ 130g as TiO ２A coating film was formed after obtaining a dispersion in which surface-treated rutile-type titanium oxide particles were dispersed in a monomer in the same manner as in Example 1, except that the amount of the monomer was changed to 130 parts by mass relative to 100 parts by mass, n-octyl acrylate was used as the monomer, and concentration was carried out to 958 g. The obtained dispersion had a high wet specific surface area and a high rate of increase in viscosity after an aging test. In addition, the refractive index was low due to the large amount of surface treatment.

[0080] Comparative Example 5 In step B, sodium silicate No. 3 (SiO ２ (concentration: 29% by mass) 413.8g (SiO ２ 120g as TiO ２ 120 parts by weight per 100 parts by weight of the mixture) was added, and then 14.3 g of tin sulfate (SnO ２ 10.0 g as TiO ２ After adding 10 parts by mass of 100 parts by mass of titanium oxide cores, the pH was adjusted to 6.0 using a 10% by mass aqueous solution of sodium hydroxide. In this way, hydrated oxides of silicon and tin were precipitated on the surfaces of the titanium oxide particle cores, thereby performing surface treatment. Next, the precipitates were filtered and washed, and water was added to adjust the concentration. 100 parts by mass (TiO ２ 120 parts by mass (SiO ２ hydrated oxide of silicon (SnO ２ 1000 g of an aqueous suspension of titanium oxide particles surface-treated with hydrated tin oxide (TiO ２ A concentration of 10% by mass was obtained. In step D, tripropylene glycol diacrylate was used as the monomer, and concentration was carried out to 958 g. Except for these points, the same procedure as in Example 1 was repeated to obtain a dispersion in which surface-treated rutile-type titanium oxide particles were dispersed in a monomer, and then a coating film was formed. The obtained dispersion had a high wet specific surface area and a high rate of increase in viscosity after an aging test. In addition, the refractive index was low due to the large amount of surface treatment.

[0081] Comparative Example 6 In step C, 1000 g of isopropanol and 1000 g of methyl ethyl ketone were added to 1000 g of the aqueous suspension of surface-treated titanium oxide particles obtained in step B. Then, ultrafiltration was carried out while further adding methyl ethyl ketone, and the dispersion medium was replaced with methyl ethyl ketone, until a total amount of 1000 g (TiO ２ A methyl ethyl ketone suspension with a concentration of 10% by mass was obtained. In step C, neither a silane coupling agent nor a basic additive was added. In step D, 500 g of n-octyl acrylate was added as a monomer, and 70 g of "DISPERBYK-111" (manufactured by BYK Japan) (TiO ２ A 70 parts by mass aqueous solution of rutile-type titanium dioxide (70 parts by mass per 100 parts by mass aqueous solution) was added. Further, n-octyl acrylate was added while the mixture was concentrated in an evaporator, thereby replacing the rutile-type titanium dioxide with n-octyl acrylate. The resulting slurry was subjected to a dispersion treatment in a bead mill, yielding 915 g of a dispersion in which the surface-treated rutile-type titanium dioxide particles were dispersed in the monomer. Except for these points, the dispersion was obtained in the same manner as in Example 1, and then a coating film was formed. The obtained dispersion had a high wet specific surface area and a high rate of increase in viscosity after an aging test. Furthermore, the haze of the dispersion and coating film was high.

[0082] Comparative Example 7 300 g of titanium oxide powder "MICRO TITANIUM DIOXIDE MT-05" manufactured by Teika Corporation and 90 g of dispersant "DISPERBYK-111" manufactured by BYK Japan (30 parts by mass per 100 parts by mass of "MT-05") were added to 610 g of biphenyl methyl acrylate to form a slurry. Here, the titanium oxide powder "MT-05" is titanium oxide particles surface-treated with hydrated oxides of silicon and aluminum. The slurry was dispersed in a bead mill to obtain 1000 g of a dispersion in which rutile-type titanium oxide particles were dispersed in a monomer, and then a coating film was formed. The average particle size of the titanium oxide in the obtained dispersion was large, and the haze of the coating film was very large.

[0083] Comparative Example 8 In step C, 1000 g of isopropanol and 1000 g of methyl ethyl ketone were added to 1000 g of the aqueous suspension of surface-treated titanium oxide particles obtained in step B. Then, ultrafiltration was carried out while further adding methyl ethyl ketone, and the dispersion medium was replaced with methyl ethyl ketone, and a total amount of 200 g (TiO ２ A methyl ethyl ketone suspension with a concentration of 50% by mass was obtained. Next, 25 g of 3-acryloxypropyltrimethoxysilane (TiO ２ 25 parts by mass per 100 parts by mass), and 5 g of tert-butylamine (TiO ２ A methyl ethyl ketone dispersion (5 parts by mass per 100 parts by mass of the monomer) was added to obtain 230 g of a methyl ethyl ketone dispersion of surface-treated titanium oxide particles. 100 g of benzyl acrylate was added to the dispersion to obtain a dispersion in which surface-treated rutile-type titanium oxide particles were dispersed in the monomer. Except for these points, the same procedure as in Example 1 was repeated to obtain a dispersion, and a coating film was then formed. The resulting dispersion had a high solvent content, and the coating film also had a high solvent residual rate.

[0084]

[0085]

[0086]

Claims

1. A dispersion liquid containing titanium oxide particles, a silane coupling agent, and a monomer having a polymerizable functional group; The titanium oxide particles are particles having a rutile-type titanium oxide core surface-treated with a hydrated oxide of tin or zirconium, and the titanium oxide content in the particles is TiO ２ The content of tin or zirconium hydrate oxide is SnO ２ Or ZrO ２ This is calculated as 5 to 30 mass %, The viscosity of the monomer at 25° C. is 100 mPa·s or less, The dispersion has an ignition solid content of 15 to 55% by mass when ignited at 925° C. for 2 hours, In the dispersion, the content of the silane coupling agent is 2 to 15 mass %, the content of the monomer is 30 to 85 mass %, and the content of the organic solvent having no polymerizable functional group is 10 mass % or less; and The dispersion has a viscosity of 500 mPa·s or less at 25° C.

2. 2. The dispersion according to claim 1, wherein the ignition solids content is 15 to 45% by weight, and the content of the monomer in the dispersion is 50 to 85% by weight.

3. The titanium oxide particles have a wet specific surface area of ​​20 to 150 m as measured by pulse NMR. ２ 3. The dispersion according to claim 1, wherein the molecular weight of the dispersion is 1 / g.

4. 3. The dispersion according to claim 1, wherein the titanium oxide particles are peptized using a basic additive.

5. 3. The dispersion according to claim 1, wherein the titanium oxide particles have an average particle size of 20 to 50 nm in a liquid having an ignition solid content of 5 mass % obtained by diluting the dispersion with the monomer.

6. 3. The dispersion according to claim 1, wherein a liquid having an ignition solid content of 5% by mass obtained by diluting the dispersion with the monomer has a haze of 40% or less at an optical path length of 10 mm.

7. A curable sealing material comprising the dispersion according to claim 1 or 2.

8. The encapsulant according to claim 7 , which is used for encapsulating an optical element.

9. A cured product obtained by curing the dispersion according to claim 1 or 2.

10. The cured product according to claim 9, which has a refractive index of 1.6 or more at 20°C and 633 nm.

11. The cured product according to claim 9, wherein the residual ratio of the organic solvent is 0.1 to 10 mass %.

12. An optical element encapsulated with the cured product according to claim 9 .

13. 3. The method for producing a dispersion according to claim 1, further comprising removing water from the aqueous dispersion of the titanium oxide particles and replacing it with the organic solvent, adding the silane coupling agent to the obtained dispersion, and then removing the organic solvent and replacing it with the monomer.

14. The method for producing a dispersion liquid according to claim 13, wherein the silane coupling agent and the basic additive are added to the dispersion liquid in which the organic solvent has been substituted to deflocculate the titanium oxide particles, and then the organic solvent is removed to substitute the monomer.