Particles having a rutile-type crystalline structure and a method for producing the same, as well as a dispersion of the particles, a coating solution, and a method for producing a film-coated substrate.

Abstract

The present invention pertains to particles having a rutile crystal structure. The crystallite diameter of the particles is at least 7 nm. The particles include at least 90% by weight of titanium oxide on a TiO2 basis and 0.2%–10% by weight of tin oxide on an SnO2 basis. These particles are readily dispersed in a solvent and have a high refractive index.

Description

[Technical Field]

[0001] This invention relates to particles having a rutile-type crystalline structure and a method for producing the same. [Background technology]

[0002] Conventionally, coating solutions containing oxide particles with a high refractive index have been used to form films with a high refractive index on substrates. Such films are used, for example, in eyeglasses, lenses, and smartphone touch panels.

[0003] To form a film with a high refractive index, it is preferable for the particles to have a high refractive index. For example, titanium dioxide is known to have a high refractive index. In particular, titanium dioxide having a rutile-type crystal structure has a high refractive index (see, for example, Japanese Patent Publication No. 2010-42947). Titanium dioxide containing tin oxide tends to form a rutile-type crystal structure.

[0004] Furthermore, titanium oxide particles containing inorganic oxides such as silica are known to be easily dispersed (see, for example, International Publication No. 2018 / 181241). [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent documents 1 and 2 use rutile-type composite particles containing titanium dioxide and silica, resulting in a low titanium dioxide content in the particles. Consequently, the refractive index of the film becomes low.

[0006] Therefore, the object of the present invention is to provide particles that are easily dispersed in a solvent and have a high refractive index. [Means for solving the problem]

[0007] Therefore, the present invention relates to particles having a rutile-type crystal structure, with a crystallite diameter of 7 nm or more. Such particles are easily dispersed in a solvent. Here, the particles contain 90% by weight or more of titanium oxide (based on TiO2) and 0.2 to 10% by weight of tin oxide (based on SnO2). Such particles have a high refractive index.

[0008] Furthermore, it is preferable that tin is not detected on the particle surface.

[0009] Furthermore, it is preferable that the particle size when the particles are dispersed in the solvent is 100 nm or less.

[0010] Furthermore, the method for producing particles having a rutile-type crystalline structure comprises the steps of: preparing a dispersion of a titanium-containing compound; preparing a dispersion of core particles having a rutile-type crystalline structure; preparing a mixture by mixing the dispersion of the titanium-containing compound and the dispersion of core particles; and growing the core particles by heating the mixture to 80°C or higher. The core particles contain titanium oxide and tin oxide. [Modes for carrying out the invention]

[0011] The present invention relates to particles having a rutile-type crystalline structure (hereinafter simply referred to as "particles"), with a crystallite size of 7 nm or larger. This allows the particles to disperse easily in a solvent, even when containing 90% or more titanium oxide (in TiO2 equivalent) and 0.2 to 10% tin oxide (in SnO2 equivalent). In particular, such particles disperse stably in water even at particle concentrations of 20% or more. Therefore, they are easy to handle industrially.

[0012] The larger the crystallite size of the particles, the smaller the specific surface area of ​​the particles. Therefore, the particles disperse more easily in the solvent. Also, because the specific surface area is lower with larger crystallite sizes, the particle density is higher. Therefore, the refractive index of the particles (hereinafter referred to as particle refractive index) is higher. The refractive index of a film containing such particles (hereinafter referred to as film refractive index) is higher. The crystallite size of the particles is preferably 9 nm or larger, and more preferably 12 nm or larger.

[0013] The higher the titanium oxide content of the particles, the higher the particle refractive index. Therefore, this content should be 90% by weight or more in terms of TiO2. Preferably, this content should be 92% by weight or more in terms of TiO2, and more preferably 95% by weight or more. Also, if the particles contain tin oxide, the crystal structure of the particles tends to become rutile-type. However, from the viewpoint of particle refractive index, it is better for the tin oxide content of the particles to be low. Therefore, this tin oxide content should be 10% by weight or less in terms of SnO2. Preferably, this tin oxide content should be 5% by weight or less in terms of SnO2.

[0014] Furthermore, if tin is not detected on the particle surface, that is, if tin oxide is not present on the particle surface, the proportion of titanium oxide on the particle surface side (hereinafter referred to as the shell) is high. Therefore, the titanium oxide content of the particle as a whole tends to be high. On the other hand, if the center side of the particle (hereinafter referred to as the core) contains tin oxide, the particle tends to form a rutile-type crystal structure. That is, when the core contains a sufficient amount of tin oxide for the particle's crystal structure to become rutile-type, the shell does not need to contain tin oxide. The lower the proportion of tin in the core, the higher the titanium oxide content of the particle can be. Therefore, the proportion of tin in the core is preferably 6.5 atomic% (at%) or less. Here, the proportion of tin in the core is the number of tin atoms relative to the total number of tin atoms of titanium and tin.

[0015] Furthermore, when the ratio of the average minor axis of the particles to the crystallite size (average minor axis / crystallite size) is close to 1, the crystallite size becomes close to the minor axis of the particles. As a result, the particle density increases. Therefore, this ratio is preferably 0.8 to 3.0, more preferably 0.8 to 2.0, and even more preferably 0.8 to 1.5.

[0016] Furthermore, the smaller the average aspect ratio of the particles (hereinafter referred to as the aspect ratio), the easier the particles disperse in the solvent or binder. As a result, the haze of the film tends to be lower. Also, the smaller the aspect ratio, the smaller the specific surface area of ​​the particles. Therefore, an aspect ratio of 1.0 to 2.3 is preferable. In particular, when the crystallite diameter is 7 nm or more and the aspect ratio is 2.3 or less, the particles disperse easily in the solvent. An aspect ratio of 1 to 2.1 is preferable, 1 to 1.9 is more preferable, and 1 to 1.6 is even more preferable. 1 to 1.5 is even more preferable. In particular, when the crystallite diameter is 10 nm or more, an aspect ratio of 1 to 1.9 is preferable, when the crystallite diameter is 12.5 nm or more, an aspect ratio of 1 to 1.8 is preferable, and when the crystallite diameter is 17 nm or more, an aspect ratio of 1 to 1.5 is preferable. The aspect ratio is the ratio of the average value of the short axis to the average value of the long axis of a particle.

[0017] When particles are dispersed in a solvent, the average particle size (hereinafter referred to as the dispersed particle size) is preferably 100 nm or less. Forming a film using particles of this size results in high transparency of the film. Furthermore, the particles are less likely to settle. A dispersed particle size of 80 nm or less is more preferable. On the other hand, if the dispersed particle size is 20 nm or larger, the particles disperse more easily in the solvent or binder. In particular, a crystallite size of 7 nm or larger and a dispersed particle size of 20 nm or larger are preferred.

[0018] The refractive index of particles varies depending on factors such as particle composition, density, crystal structure, and crystallite size. A refractive index of 1.95 or higher is preferred, 2.05 or higher is more preferred, and 2.10 or higher is even more preferred. Obtaining particles with a refractive index of 2.8 or higher is difficult.

[0019] The dispersion of particles will be described below. The dispersion of particles contains the above-described particles and a solvent. When the solvent is water, 20% by weight or more of the particles can be stably dispersed in water. On the other hand, in order for the above-described particles to be dispersed in an organic solvent, the particle surface must be treated with a surface treatment agent. A part of this surface treatment agent does not have to be bonded to the particles and may be dispersed in the organic solvent. Also, when the solvent is an organic solvent (in the case of an organic solvent dispersion), two or more types of surface treatment agents may be included. Examples of the surface treatment agent include silicon compounds, titanium compounds, zirconium compounds, aluminum compounds, etc. Among these, silicon compounds are easy to handle industrially.

[0020] When the organic solvent dispersion contains a surface treatment agent having an alkoxy group, the alkoxy group is hydrolyzed. In the dispersion, the hydrolyzed alkoxy group and the OH group on the particle surface undergo a dehydration condensation reaction (hereinafter referred to as a chemical bond). Therefore, the particles are more likely to be dispersed in the organic solvent. Furthermore, when the organic solvent dispersion contains a catalyst, water, etc., the hydrolysis reaction of the alkoxy group is promoted. Along with that, the chemical bond is promoted.

[0021] An alkyl group is bonded to the oxygen atom of the alkoxy group. The smaller the molecular weight of this alkyl group, the faster the hydrolysis reaction of the alkoxy group. Therefore, the alkyl group is preferably a methyl group or an ethyl group.

[0022] As the surface treatment agent, a molecule of the general formula (RO) n M(X) 4-n is mentioned. n is an integer from 1 to 4. M represents any one of Si, Ti, and Zr. When M is Si, it is easy to handle industrially. When there is one M in the molecule, it is easy to control the reaction rate, etc. of this molecule, so it is easy to handle industrially. X is a hydrocarbon group. For example, it represents Me, Et, Pr, -(CH2)3OC(=O)C(CH3)(=CH2), -(CH2)3OC(=O)CH(=CH2), -CH=CH2. R is a hydrocarbon group. When M is Si, R being Me or Et makes it easy to control the reaction rate, etc. of this molecule. Therefore, it is easy to handle industrially.

[0023] The more alkoxy groups the surface treatment agent has, the easier it is for the surface treatment agent to chemically bond to the particle surface. Further, when a surface treatment agent having many alkoxy groups binds to the particle surface, the number of alkoxy groups on the particle surface increases. Therefore, the particles become easier to disperse in alcohol. It is preferable for the surface treatment agent to have 3 to 4 alkoxy groups. When the solvent is alcohol, it is preferable for the surface treatment agent to have 4 alkoxy groups. Hereinafter, a surface treatment agent having 4 alkoxy groups is referred to as a first surface treatment agent.

[0024] When the dispersion liquid contains 20 to 85 parts by mass (3 to 30 parts by mass in terms of oxide conversion {SiO2 conversion if the surface treatment agent is a silicon compound}) of the first surface treatment agent with respect to 100 parts by mass of the particles, the particles are easily dispersed in alcohol. Note that the larger the crystallite diameter of the particles, the smaller the amount of the surface treatment agent can be.

[0025] When the particles are treated with a surface treatment agent having a hydrocarbon group (hereinafter referred to as a second surface treatment agent), the particles are easily dispersed in an organic solvent having higher hydrophobicity than alcohol (hereinafter referred to as a hydrophobic solvent). At this time, when the second surface treatment agent has 3 alkoxy groups and 1 hydrocarbon group, the particles are more easily dispersed in the hydrophobic solvent. The second surface treatment agent is different from the first surface treatment agent. The first surface treatment agent does not have a hydrocarbon group. The hydrocarbon group is not an alkyl group bonded to the oxygen atom of the alkoxy group.

[0026] Examples of the hydrophobic solvent include an organic solvent having at least one of an ester bond, an ether bond, and a ketone group. An organic solvent having such a bond or functional group easily dissolves an ultraviolet curable binder. Among such organic solvents, polyethylene glycol monomethyl ether acetate (PGMEA) is preferable.

[0027] When the particle surface is treated with the first surface treatment agent and the second surface treatment agent, the particles are easily dispersed in the hydrophobic solvent and the ultraviolet curable binder.

[0028] Furthermore, if a surface treatment agent having (meth)acrylate groups is bound to the particles, the particles can bond with an UV-curable binder upon UV irradiation. As a result, the film becomes denser and the refractive index of the film increases. For this reason, it is preferable that the hydrocarbon groups of the second surface treatment agent have (meth)acrylate groups, or that the hydrocarbon groups of the second surface treatment agent are (meth)acrylate groups.

[0029] When the solvent is water, the silica treatment of the particle surface creates a denser layer on the particle surface due to the surface treatment agent. Such particles disperse easily in organic solvents (especially alcohols) even with a small amount of surface treatment agent. In other words, with such particles, it is easy to replace the solvent in the dispersion from water to an organic solvent. The isoelectric point of the aqueous dispersion of these particles is 3 or less (however, this is the isoelectric point when the solid content concentration is 0.5 mass%). On the other hand, if the particle surface is not treated with silica, the isoelectric point of the aqueous dispersion of these particles is in the range of 4 to 6. Note that if the particle surface is treated with silica or a surface treatment agent, crystal structures other than the rutile type may be observed.

[0030] When the solvent is water, it is preferable that the particle surface is treated with 2 parts by mass or more of silica (in terms of SiO2) per 100 parts by mass of particles. That is, it is preferable that the silica content of the particles is 2 parts by mass or more per 100 parts by mass of particles, and that the isoelectric point of the aqueous dispersion is 3 or less. Even with a small amount of surface treatment agent, such particles disperse easily in organic solvents (especially alcohols). A silica content of 4 parts by mass or more is more preferable. On the other hand, if the silica content is too high, the refractive index of the particles will decrease. Therefore, a silica content of 20 parts by mass or less per 100 parts by mass of particles is preferable. When the particle surface is treated with 2 parts by mass or more of silica per 100 parts by mass of particles, it is preferable that the particle surface is treated with 10 to 30 parts by mass (3 to 10 parts by mass in terms of oxide {in terms of SiO2 if the surface treatment agent is a silicon compound}) of a first surface treatment agent per 100 parts by mass of particles.

[0031] The coating solution is described below. The coating solution contains particles, a surface treatment agent, a binder, and an organic solvent. By forming a film with the coating solution containing the aforementioned particles, the refractive index of the film is increased. A film can be formed by using a coating solution containing a binder. If a portion of the surface treatment agent functions as a binder, the binder does not need to be included. Examples of binders include monomers before polymerization, oligomers, and polymers after polymerization. Of these, monomers or oligomers are preferred. When curing the film, a coating solution containing monomers or oligomers tends to produce a denser film than a coating solution containing polymers. Because the refractive index of the adamantane skeleton is high, using an adamantane derivative as a monomer or oligomer increases the refractive index of the film. The organic solvent can be appropriately selected depending on the type of binder added when preparing the coating solution.

[0032] The higher the solid content concentration of the coating solution, the easier it is to form a thick film. Furthermore, the coating solution is easier to handle industrially. Therefore, a concentration of 10% by weight or more is preferred, and 20% by weight or more is more preferred. On the other hand, if the concentration is 50% by weight or less, the viscosity of the coating solution tends to be low. A concentration of 30% by weight or less is preferred.

[0033] If the boiling point of the organic solvent is 80°C or higher, the coating solution can dry slowly, resulting in a denser film. A boiling point of 100°C or higher is more preferable. On the other hand, if the boiling point is 200°C or lower, less organic solvent remains, making the film more prone to shrinkage. As a result, the film becomes harder. A boiling point of 180°C or lower is more preferable.

[0034] The method for manufacturing the particles is described below. First, a dispersion of a titanium-containing compound and a dispersion of core particles having a rutile-type crystal structure (hereinafter referred to as core particles) are prepared <preparation step>. Then, the dispersion of the titanium-containing compound and the dispersion of core particles are mixed to prepare a mixture <mixing step>. The mixture is heated to 80°C or higher to induce crystal growth from the core particles <crystal growth step>. By growing crystals from the core particles, the tin oxide content of the particles is reduced. As a result, the titanium oxide content of the particles becomes relatively higher. Also, the crystallite size increases. After the crystal growth step, the core particles become the core of the particles, and the titanium-containing compound becomes the shell of the particles. Each step is described in detail below.

[0035] <Preparation process> The core particles that serve as the starting point for crystal growth contain tin oxide and have a rutile-type crystal structure. Even if the titanium-containing compound does not contain tin oxide, growing such core particles will result in particles with a rutile-type crystal structure. Here, the absence of tin oxide in the titanium-containing compound increases the refractive index of the particles.

[0036] If the core particles contain tin oxide, they tend to form a rutile crystal structure. The tin oxide content of the core particles should be such that the crystal structure of the core particles becomes rutile. If the crystal structure of the core particles is anything other than rutile, the particles will become mixed crystals or have a crystal structure other than rutile. The crystallite size of the core particles should be such that they can be dispersed in the solvent. If the solvent is water, the core particles disperse easily.

[0037] The titanium-containing compound may contain titanium oxides or hydroxides. After obtaining a gel by neutralizing the titanium compound, a dispersion of the titanium-containing compound is obtained by disintegrating this gel. The titanium compound is not particularly limited as long as it is water-soluble. Specific examples of titanium compounds include titanium tetrachloride, titanium trichloride, titanium sulfate, titanyl sulfate, and titanium hydride. The resulting gel contains titanium hydroxide. Salts in the gel reduce the refractive index of the film and the dispersibility of the particles. Therefore, it is preferable to wash the gel with water. When the gel is disintegrated using hydrogen peroxide, the core particles tend to crystallize in a rutile-type state. After adding hydrogen peroxide to the gel, the gel disintegrates more easily when heated to 50°C to 100°C.

[0038] <Mixing process> In this process, a mixture is prepared by mixing a dispersion of titanium-containing compound with a dispersion of core particles. By keeping the weight ratio of the titanium-containing compound to the core particles (amount of titanium-containing compound / amount of core particles) at 7 or less, it becomes difficult for crystals other than rutile to form. Here, the weight of the solids and the weight of the core particles are the weights of Ti and Sn in the raw materials converted to TiO2 and SnO2, respectively. The titanium-containing compound is the solid content of the dispersion of the titanium-containing compound.

[0039] <Crystal growth process> In this process, crystal growth is initiated from the core particles by raising the temperature of the mixture to 80°C or higher. If the temperature of the mixture is below 80°C, the rate of crystal growth is slow, resulting in smaller crystallite sizes. In this case, the reaction is insufficient, and yellow titanium-containing compounds remain. When raising the temperature of the mixture to 80°C or higher, it is preferable to perform hydrothermal synthesis (autoclave treatment) of the mixture. The higher the temperature of hydrothermal synthesis, the larger the crystallite size. Therefore, this temperature is preferably 100°C or higher, and more preferably 130°C or higher. On the other hand, if this temperature is 300°C or lower, the production efficiency is higher. This temperature is more preferably 250°C. Also, the longer the hydrothermal synthesis time, the denser the particles become. Therefore, this time is preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more. On the other hand, if this time is 50 hours or less, the production efficiency is higher. This time is more preferably 40 hours or less, and even more preferably 20 hours or less.

[0040] Repeating crystal growth multiple times increases the titanium dioxide content of the particles. It also increases the crystallite size and particle size, and lowers the aspect ratio. Two to five crystal growth cycles are preferable. When crystal growth is performed 2 to 3 times, the haze of the particle film is low, and the refractive index is high. When crystal growth is performed 4 to 5 times, the refractive index of the particles is higher than when it is performed 2 to 3 times. Conversely, when crystal growth is performed 4 to 5 times, the haze of the film is higher than when it is performed 2 to 3 times. In the second and subsequent crystal growth cycles, the crystal-grown particles are used as core particles during the mixing and crystal growth processes.

[0041] It is preferable to treat the particle surface with silica before treating it with a surface treatment agent. Specifically, silica is added to an aqueous dispersion of crystal-grown particles, and then this aqueous dispersion is subjected to hydrothermal synthesis. This results in the formation of a dense silica layer on the particle surface. The specific surface area of ​​the silica is 100 to 600 m². 2 When the concentration is 200 / g, fine and coarse particles are less likely to be generated. The specific surface area of ​​silica is 200-550 m². 2 / g is more preferable, 300-550m 2A value of / g is even more preferable. When performing hydrothermal synthesis, the lower the solid content concentration of the aqueous dispersion, the more densely the silica layer is formed on the particle surface. Therefore, when performing hydrothermal synthesis, the solid content concentration is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1.5% by weight or less. When performing hydrothermal synthesis, the higher the temperature of the hydrothermal synthesis, the more densely the silica layer is formed on the particle surface. Therefore, this temperature is preferably 100°C or higher, and even more preferably 150°C or higher. On the other hand, if this temperature is 200°C or lower, the production efficiency increases. This temperature is more preferably 180°C or lower. Also, the longer the hydrothermal synthesis time, the more densely the silica is treated on the particle surface. Therefore, this time is preferably 1 hour or more, and more preferably 15 hours or more. On the other hand, if this time is 40 hours or less, the production efficiency is high. This time is more preferably 20 hours or less.

[0042] The following describes a method for producing a dispersion of particles in an organic solvent. A surface treatment agent is added to an aqueous dispersion of crystal-grown particles, thereby treating the particle surface with the surface treatment agent. Subsequently, the solvent in the dispersion is replaced from water to an organic solvent. The surface treatment agent preferably has an alkoxy group. Since a surface treatment agent having an alkoxy group can chemically bond to the particle surface, the particles become more easily dispersed in the organic solvent.

[0043] After adding the surface treatment agent, holding the dispersion at 40°C or higher for at least one hour allows the surface treatment agent to rapidly treat the particles. A holding time of 20 hours or less is preferable.

[0044] By treating the particle surface in the aqueous dispersion with the first surface treatment agent, the particles become less likely to aggregate in the alcohol. After this treatment, an alcohol dispersion can be prepared by replacing the solvent with alcohol. By adding the second surface treatment agent to this alcohol dispersion, the particle surface can be treated with the second surface treatment agent. Subsequently, the solvent (alcohol) in the alcohol dispersion is replaced with a hydrophobic solvent. Replacing the solvent in this way makes the particles less likely to aggregate. If the amount of the second surface treatment agent added is 10 parts by mass or more per 100 parts by mass of particles, the particles disperse easily in the hydrophobic solvent. This amount is more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. On the other hand, in order to increase the particle concentration in the film, this amount is preferably 50 parts by mass or less per 100 parts by mass of particles, and more preferably 40 parts by mass or less. Furthermore, when treating the particle surface with the second surface treatment agent, adding water or a catalyst promotes the hydrolysis reaction of the second surface treatment agent.

[0045] A coating solution is obtained by adding a binder to a dispersion of particles in an organic solvent. If a portion of the surface treatment agent functions as a binder, the organic solvent dispersion may be used as the coating solution.

[0046] A film is formed on the substrate using the above-described coating solution to produce a film-coated substrate. Specifically, the coating solution is applied to the substrate, and then the coating solution is dried to form a film. Coating methods include spin coating, bar coating, gravure coating, and slit coating. Drying refers to the removal of the solvent by evaporation. If the drying temperature is 60°C or higher, the drying time is shortened. Also, less solvent remains in the film. Therefore, a dense film can be obtained. On the other hand, if this temperature is 120°C or lower, the substrate is less likely to deform. This temperature is more preferably 100°C or lower, and even more preferably 80°C or lower. Furthermore, in order to increase production efficiency, it is preferable to cure the film after drying the coating solution.

[0047] [Example 1] The particle preparation method will be described in detail below. The particle preparation conditions are shown in Table 1.

[0048] [Particle preparation] <Preparation process> First, dispersions of titanium-containing compounds and core particles were prepared as follows: 523 g of an aqueous titanium tetrachloride solution with a concentration of 7.66% by mass (based on TiO2) was mixed with 523 g of aqueous ammonia with a concentration of 7.66% by mass. This prepared a white slurry (gel) with a pH of 9.2. This slurry was filtered. By washing the gel with pure water, 400.5 g of a cake with a solid content of 10% by mass was obtained. The cake was diluted with pure water to 1.5% by mass to obtain another slurry. 457.7 g of aqueous hydrogen peroxide with a concentration of 35% by mass was added to this slurry. This dispersion was heated at 80°C for 1 hour. By adding 877 g of pure water to this dispersion, a dispersion of the titanium-containing compound (with a titanium oxide concentration of 1.0% by weight (based on TiO2)) was obtained. The pH of this dispersion was 7.8, and the laser particle size was 37 nm. The laser particle size was measured by electrophoretic light scattering using an ELSZ-2000S manufactured by Otsuka Electronics Co., Ltd. after diluting the dispersion to 0.01% by weight with water. In the following examples and comparative examples, the laser particle size was measured at this concentration.

[0049] A cation exchange resin (manufactured by Mitsubishi Chemical Corporation) was added to 4005 g of a titanium-containing compound dispersion. 495 g of a potassium stanate aqueous solution diluted to 1% by weight with pure water was added to this dispersion. The ion exchange resin was separated from this dispersion. 4500 g of a core particle dispersion was obtained by hydrothermal synthesis of this dispersion at 165°C for 18 hours in an autoclave.

[0050] <Mixing process> Next, a mixture was prepared by mixing 4500 g of a titanium-containing compound dispersion with 4500 g of a core particle dispersion. The laser particle size of the mixture was 37 nm.

[0051] <Crystal growth process> Core particles were grown by hydrothermal synthesis of this mixture in an autoclave. The hydrothermal synthesis conditions were 165°C for 18 hours. The laser particle size of the dispersion after the first crystal growth was 37 nm.

[0052] In this example, core particles were grown twice. In the second crystal growth, the particles were grown in the same manner as in the first crystal growth, except that the dispersion from the first crystal growth was used as the dispersion for the core particles. The laser particle diameter of the dispersion from the second crystal growth was 43 nm. The laser particle diameter (dispersed particle diameter) of the particle dispersions in other examples and comparative examples is also shown in Table 3. By concentrating this dispersion using an ultrafiltration membrane apparatus, 2250 g of an aqueous dispersion of particles (solid content concentration of 4% by mass) was obtained.

[0053] [Preparation of organic solvent dispersion of particles] The preparation of the organic solvent dispersion of particles will be described in detail below. The conditions for preparing the dispersion are shown in Table 2.

[0054] First, an alcohol dispersion of particles was prepared as follows: 2250 g of an aqueous dispersion of particles was mixed with 2250 g of methanol and 56.3 g of orthosilicate ethyl (containing 28.8% by mass of silicon in terms of SiO2) as a primary surface treatment agent. This dispersion was heated and stirred at 50°C for 18 hours to obtain an aqueous / methanol dispersion of particles. After the dispersion was cooled to room temperature, the solvent in the dispersion was replaced with methanol using an ultrafiltration membrane. This dispersion was concentrated to obtain 531 g of an alcohol dispersion of particles (solid content concentration of 20% by mass). The water content in this dispersion was 0.3% by mass.

[0055] 10.6 g of 5% by mass aqueous ammonia was added to 531 g of an alcohol dispersion of particles. Furthermore, 31.9 g of 3-methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd., containing 24.2% by mass silicon in terms of SiO2) was added as a second surface treatment agent. This dispersion was heated and stirred at 50°C for 18 hours. This dispersion was cooled to room temperature. Using a rotary evaporator, the solvent of this dispersion was replaced with propylene glycol monomethyl ether acetate (PGMEA), which is more hydrophobic than alcohol. This yielded 570 g of an organic solvent dispersion of particles (solid content concentration 20% by mass).

[0056] [Preparation of the coating solution] The preparation method for the coating solution is described below. The preparation conditions for the coating solutions of other examples and comparative examples are also shown in Table 2. 100.0 g of an organic solvent dispersion of particles, 6.0 g of DiaPurest® ADDA (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a binder, and 0.4 g of Omnirad TPO-H as a photopolymerization initiator were added and mixed.

[0057] The physical properties of the particles were measured using the following method. The results for other examples and comparative examples are also shown in Table 3.

[0058] (1) Particle composition The aqueous dispersion of particles was diluted to a solid content of 1%. 100g of this aqueous dispersion was dried at 100°C for 10 minutes to obtain a particle powder. The powder was heated with a burner to ash the organic matter. The powder was dissolved by adding sodium peroxide and sodium hydroxide. Further dissolution of the powder was achieved by adding sulfuric acid and hydrochloric acid. The Sn, Ti, and Si content of this solution was measured using ICP-OES (SPS5520 from SII or ICPS-8100 from Shimadzu Corporation). These content percentages were converted to the SnO2, TiO2, and SiO2 content of the particles, respectively.

[0059] (2) Crystal structure and crystallite size The aqueous dispersion of particles was diluted to a solid content concentration of 1%. 200 g of this aqueous dispersion was dried at 110°C for 20 hours (only in Example 7 at 60°C for 48 hours) to prepare a sample for measurement. X-ray structural analysis of the sample was performed using RIGAK's RINT(registered trademark) 1400. The diffraction peak pattern was analyzed using PDXL to confirm that the particle's crystal structure was rutile. The crystallite size of the particle was calculated from the full width at half maximum of the diffraction peak using Scherrer's equation (D=K×λ / (β×cosθ)). The Miller index (110) of the rutile type was selected as the diffraction peak. D is the crystallite size (nm), K is the Scherrer constant, λ is the X-ray wavelength (nm), β is the diffraction line width broadening (rad), and θ is the Bragg angle (rad).

[0060] (3) Mean value of the minor axis and aspect ratio A water dispersion of particles was diluted to a solid content concentration of 0.002%. One drop of the diluted dispersion was placed onto a collodion membrane. This was dried at 50°C for 10 minutes. Photographs of these particles were taken using a Hitachi High-Technologies S-5500 scanning electron microscope (SEM). 100 particles were randomly selected from the images taken with the SEM, and their short and long axes were measured. The average values ​​of the short and long axes were calculated. The ratio of the average short to the average long axis (average short axis / average long axis) was defined as the aspect ratio.

[0061] (4) Whether or not tin is detected on the particle surface The absence of tin oxide on the particle surface and the presence of tin oxide in the core can be measured using X-ray photoelectron spectroscopy (XPS). However, since measurement is difficult with particles alone, a film is prepared as a measurement sample as follows. First, a dispersion (coating solution) was prepared by adding 1.1 g of diphenyl (2,4,6-trimethylbenzoyl)-phenylphosphine oxide (manufactured by IGMresins B.V.: Omnirad® TPO-H) as a photopolymerization initiator to 300 g of organic solvent dispersion of particles. This dispersion solution was coated onto a silicon wafer substrate and dried at 80°C for 2 minutes. A high-pressure mercury lamp (manufactured by GS Yuasa: EYEUVMETER) was used to measure 3000 mJ / cm². 2 XPS measurement samples (films) were prepared by irradiating the dried coating solution with ultraviolet light under the specified conditions. XPS measurements were performed as follows, and it was confirmed that no tin oxide was detected on the particle surface.

[0062] Because a surface treatment agent is present on the outermost surface of the film, titanium may not be detected. Therefore, the proportion of tin on the particle surface is measured by etching to a depth where titanium can be detected. For example, in this embodiment, etching is performed to a depth of 1.2 nm, where titanium is detected. At this depth, Ar etching is performed for 20 seconds, i.e., Ar etching is performed at 0.06 nm / second. Titanium is detected when the proportion of titanium reaches 1.0 at% or more. This proportion is the number of titanium atoms relative to the total number of atoms of carbon, oxygen, titanium, and tin. The detection limit for general XPS is 0.1 at%; therefore, if it is lower than this, tin is not present on the particle surface. For this reason, when the proportion of tin at the depth where titanium is detected is less than 0.1 at% (i.e., no tin is detected), it is considered that tin oxide is not present on the particle surface. In this embodiment, since this proportion was less than 0.1 at%, tin was not detected from the particle surface. If tin is present in the core, further etching will allow tin to be detected (the proportion of tin will reach 0.1 at% or more).

[0063] An ESCALAB220Xi X-ray photoelectron spectroscopy analyzer manufactured by Thermo Fisher Scientific was used. Spectrum measurement conditions were as follows: X-Ray: 190W, Pass Energy: Wide 100eV, Narrow 20eV, Analysis size: 250 × 1000 μm, Charge Neutralizer: On. An Ar Gass Cluster Ion was used as the ion gun, and measurements were performed with an acceleration voltage of 3kV and an etching rate of 3.5 nm / min (silicon oxide film). The binding energy of 1s(CH) was calibrated at 284.8eV. The peak energy intensity of C1s was observed at 284–286eV. O1s was observed at 532–534eV, Ti2p at 454–467eV, and Sn3d5 at 483–490eV.

[0064] (5) Particle refractive index Np' The particle refractive index Np' was determined using the following method. The refractive index Np' was similarly determined in the following examples and comparative examples.

[0065] First, three levels of coating solutions (a) to (c) were prepared, and then these solutions were applied to a silicon wafer (Matsuzaki Seisakusho Co., Ltd.: 6-inch dummy wafer (P-type), thickness: 625 μm) by spin coating. The coating solution was dried at 80°C for 2 minutes. An eye UV meter was used to measure 3000 mJ / cm². 2 Film-coated substrates (silicon wafers) were fabricated by irradiating a dried coating solution with ultraviolet light under the specified conditions. The refractive index Nav' of these film-coated substrates (silicon wafers) was measured using a spectroscopic ellipsometry (SE-2000, manufactured by Nippon Semilab Co., Ltd.).

[0066] Three levels of coating solutions (a) to (c) were prepared as follows. (a) Preparation of coating solution by weight ratio [particles:ADDA=6:4] 60.0 g of an organic solvent dispersion of particles with a solid content of 20% by mass was mixed with 8.0 g of ADDA and 0.5 g of Omnirad TPO-H. Coating solution (a) was prepared by adding 60.0 g of PGMEA to this mixture. (b) Preparation of coating solution by weight ratio [particles:ADDA=7:3] 70.0 g of an organic solvent dispersion of particles with a solid content of 20% by mass was mixed with 6.0 g of ADDA and 0.4 g of Omnirad TPO-H. Coating solution (b) was prepared by adding 70.0 g of PGMEA to this mixture. (c) Preparation of coating solution by weight ratio [particles:ADDA=8:2] 80.0 g of an organic solvent dispersion of particles with a solid content concentration of 20% by mass was mixed with 4.0 g of ADDA and 0.3 g of Omnirad TPO-H. Coating solution (c) was prepared by adding 80.0 g of PGMEA to this mixture.

[0067] Next, the film refractive index Nav (calculated value) is calculated using Equation 1 (conversion formula between volume fraction and weight fraction) and Equation 2 (Maxwell-Garnett equation). Equation 1

[0068] TIFF0007909514000001.tif49143

[0069] In Equation 1, f(m) is the volume fraction of particles with respect to the total solid content. m is the weight fraction of particles with respect to the total solid content, dm is the specific gravity of the binder (here, the specific gravity of ADDA is taken as 1.1 g / ml), and dp is the specific gravity of the particles. Here, the specific gravity dp is the sum of the products of the content rates and specific gravities of the respective components contained in the particles. The specific gravities dp of the components TiO2, SiO2, and SnO2 contained in these particles were 4.3 (3.8 g / ml for Comparative Example 4 only because it is anatase type), 2.2, and 7.0 g / ml, respectively. The content rate of each component is the value obtained by dividing the content rate (% by mass) obtained from the composition of the particles by 100. Equation 2

[0070] TIFF0007909514000002.tif58149

[0071] In Equation 2, Nav is the film refractive index, Nm is the refractive index of the binder (here, the refractive index of ADDA is taken as 1.7), and Np is the particle refractive index.

[0072] The weight fraction m of the particles, the specific gravity dm of the binder, and the specific gravity dp of the particles in the coating liquids (a) to (c) were substituted into Equation 1. Since the weight fraction m has three levels in (a) to (c), it means that f(m) for three levels was obtained. Values in increments of 0.01 in the range of 1.70 to 2.70 were substituted into the particle refractive index Np of Equation 2, and the film refractive index Nav was calculated. For the three levels of f(m), these film refractive indices Nav were calculated respectively. The deviation σ (Nav - Nav’) between these film refractive indices Nav (calculated values) and the film refractive index Nav’ (measured) was obtained. From these deviations, the squared deviation σ 2 and the sum of squared deviations Σσ 2 were calculated respectively. Among these, the particle refractive index Np for which the sum of squared deviations Σσ 2 becomes the minimum value was taken as the particle refractive index Np’. That is, the particle refractive index Np’ was determined by the least squares method. The particle refractive index Np’ determined by this method includes factors such as the affinity of the particles for the binder in the film, the particle diameter, the particle shape, and the properties of the particle surface (the amount of surface treatment agent and the composition / structure of the particle surface, etc.).

[0073] [Preparation of Substrate with Coating Film] As described below, films were formed on a glass substrate and a silicon wafer using a coating solution, and film-coated substrates (glass substrate) and film-coated substrates (silicon wafer) were fabricated. The total light transmittance and haze of the film-coated substrate (glass substrate) were measured using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.). In addition, the refractive index and film thickness of the film-coated substrate (silicon wafer) were evaluated using a spectroscopic ellipsometry (SE-2000, manufactured by Nippon Semilab Co., Ltd.). The measurement and evaluation results of other examples and comparative examples are also shown in Table 3.

[0074] (Preparation of film-coated substrates (glass substrates)) The coating solution was applied to a glass substrate (Hamashinsha: FL glass, thickness: 3 mm, refractive index: 1.51) by spin coating. After drying at 80°C for 2 minutes, a pressure of 3000 mJ / cm² was measured using a high-pressure mercury lamp (GS Yuasa: EYEUVMETER). 2 A film-coated substrate (glass substrate) was fabricated by irradiating the film with ultraviolet light under the specified conditions. The uncoated glass substrate had a total light transmittance of 99.0% and a haze of 0.1%.

[0075] (Fabrication of film-coated substrates (silicon wafers)) The coating solution was applied to a silicon wafer (Matsuzaki Seisakusho Co., Ltd.: 6-inch dummy wafer (P-type), thickness: 625 μm) by spin coating. After drying at 80°C for 2 minutes, a 3000 mJ / cm² reading was measured using an EYEUVMETER. 2 A film-coated substrate (silicon wafer) was fabricated by irradiating the film with ultraviolet light under the specified conditions.

[0076] [Example 2] By concentrating the dispersion after the first crystal growth in Example 1 using an ultrafiltration membrane apparatus, 2250 g of an aqueous dispersion of particles (solid content concentration of 4% by mass) was obtained. In the preparation of the organic solvent dispersion of particles, an alcohol dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 75 g of orthopropyl ethyl acid were added to the 2250 g aqueous dispersion of particles. 11.2 g of 5% by mass aqueous ammonia was added to this alcohol dispersion. Furthermore, 33.5 g of KBM-503 was added to this alcohol dispersion as a second surface treatment agent. After adding KBM-503, an organic solvent dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1. In the preparation of the coating solution, the coating solution was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used.

[0077] [Example 3] In the crystal growth process, crystal growth was carried out in the same manner as in Example 1, except that the number of crystal growth cycles was increased to 5. In the (n+1)th crystal growth cycle, the dispersion after the nth crystal growth cycle was used as the core particle dispersion. Otherwise, crystal growth was carried out in the same manner as in the first cycle (where n is 1 to 4). By concentrating the dispersion after the 5th crystal growth cycle using an ultrafiltration membrane apparatus, 2250 g of an aqueous dispersion of particles (solid content concentration of 4% by mass) was obtained. In the preparation of the organic solvent dispersion of particles, an alcohol dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 37.5 g of orthopropyl ethyl acid were added to the 2250 g aqueous dispersion of particles. 10.1 g of 5% by mass aqueous ammonia was added to this alcohol dispersion. Furthermore, 30.2 g of KBM-503 was added to this alcohol dispersion as a second surface treatment agent. After adding KBM-503, an organic solvent dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1. The coating solution was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used in the preparation of the coating solution.

[0078] [Example 4] In the mixing process, the amount of the titanium-containing compound dispersion was changed to 7716 g and the amount of the core particle dispersion to 1286 g, but the core particles were grown in the same manner as in Example 1. The crystal growth cycle was performed once. By concentrating this dispersion using an ultrafiltration membrane apparatus, 2250 g of an aqueous dispersion of particles (solid content concentration of 4% by mass) was obtained. In the preparation of the organic solvent dispersion of particles, the coating solution was prepared in the same manner as in Example 1, except that this aqueous dispersion was used.

[0079] [Example 5] In preparing the organic solvent dispersion of particles, the amount of ethyl orasilicate added was 43.8 g, the amount of aqueous ammonia added was 10.3 g, and the amount of KBM-503 added was 30.8 g. Otherwise, the coating solution was prepared in the same manner as in Example 1.

[0080] [Example 6] The aqueous dispersion of particles from Example 1 was diluted to a solid content concentration of 1% by mass. 9000 g of this aqueous dispersion was mixed with silica sol (manufactured by JGC Catalysts & Chemicals: Cataloid® SN-350, with a specific surface area of ​​silica of 375 m²). 2 36 g of silica (containing 15% by weight) was added. This dispersion was hydrothermally synthesized at 165°C for 18 hours using an autoclave. This dispersion was cooled to room temperature. By concentrating this dispersion using an ultrafiltration membrane apparatus, 2385 g of an aqueous dispersion of particles (solid content concentration of 4% by mass) was obtained. In other words, the particles were surface-treated with silica. In the preparation of the organic solvent dispersion of particles, an alcohol dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 19.9 g of orthopropyl ethyl acid were added to 2250 g of this aqueous dispersion of particles. 10.1 g of 5% by mass aqueous ammonia was added to this alcohol dispersion. Furthermore, 30.1 g of KBM-503 was added to this alcohol dispersion as a second surface treatment agent. After adding KBM-503, an organic solvent dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1. In the preparation of the coating solution, the coating solution was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used. Furthermore, the XPS measurement samples were prepared using silica particles before surface treatment. In other words, the same XPS measurement samples as in Example 1 were used.

[0081] The isoelectric point of the aqueous dispersion of particles obtained in this example was measured as follows. Zeta potential measurements were taken at each pH while adjusting the pH at intervals of less than 1 using a zeta potential analyzer (Malvern, "ZETASIZER Nano-ZS"). The isoelectric point was defined as the pH at which the zeta potential was ±0 mV when two points on either side of the zeta potential ±0 mV were connected by a straight line. The concentration of the particles to be measured was 0.25% by mass, and pure water was used for dilution. An automatic titrator (Malvern, "MPT-2") was used for pH adjustment. A 0.1 M sodium hydroxide aqueous solution was used to raise the pH, and a 0.1 M hydrochloric acid was used to lower the pH. The isoelectric point was 2.3.

[0082] [Example 7] In the crystal growth process, instead of hydrothermal synthesis, core particles were grown by heating and stirring with reflux at 90°C for 40 hours. Otherwise, the coating solution was prepared in the same manner as in Example 1.

[0083] [Comparative Example 1] The dispersion of core particles from Example 1 was concentrated using an ultrafiltration membrane apparatus to obtain 1125 g of an aqueous dispersion of particles (solid content concentration of 4% by mass). 1125 g of methanol and 28.2 g of orthosilicate ethyl (manufactured by Tama Chemical Co., Ltd., containing 28.8% by mass of silicon in terms of SiO2) were added to this aqueous dispersion. When this aqueous dispersion was heated to 50°C, the viscosity of the dispersion increased and the dispersion became cloudy.

[0084] [Comparative Example 2] The mixture from Example 1 was stirred at 60°C for 40 hours to obtain an aqueous dispersion of particles. This aqueous dispersion was pale yellow. The particles in the aqueous dispersion were mixed crystals of rutile and anatase.

[0085] [Comparative Example 3] 2250 g of a 2 wt% titanium tetrachloride aqueous solution (in TiO2 equivalent) and 880 g of 15 wt% aqueous ammonia were mixed. This prepared a white slurry (gel) with a pH of 8.6. After filtering the slurry, the gel was washed with pure water. This yielded 900 g of cake with a solid content of 5 wt%. To the 900 g of cake, 514 g of 35 wt% hydrogen peroxide solution and 2100 g of pure water were added. This was heated at 80°C for 1 hour. Further, 986 g of pure water was added. To 4500 g of this dispersion, 48.8 g of cataloid SN-350 and 683.8 g of pure water were added. This dispersion was hydrothermally synthesized in an autoclave at 165°C for 18 hours to obtain 5232.6 g of core particle dispersion. To 4500 g of this dispersion, 4500 g of the titanium-containing compound dispersion from Example 1 was added. This dispersion was hydrothermally synthesized at 165°C for 18 hours using an autoclave. The laser particle size of the dispersion after hydrothermal synthesis was 400 nm, and it was cloudy.

[0086] [Comparative Example 4] A dispersion of core particles obtained in Comparative Example 3 was concentrated using an ultrafiltration membrane apparatus to obtain an aqueous dispersion of particles (solid content concentration of 10% by weight). Dealkalization was performed by adding a cation exchange resin to this aqueous dispersion. The ion exchange resin was separated from the aqueous dispersion. An alcohol dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 65.5 g of orthopropyl ethyl acid were added to 2250 g of this aqueous dispersion. 12.4 g of 5% by mass aqueous ammonia was added to this alcohol dispersion. Furthermore, 77.3 g of KBM-503 was added to this alcohol dispersion as a second surface treatment agent. After adding KBM-503, an organic solvent dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1. In the preparation of the coating solution, the coating solution was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used.

[0087] [Comparative Example 5] 2000 g of a 7.5 wt% titanium tetrachloride aqueous solution (based on TiO2 equivalent) and 2000 g of a 7.5 wt% aqueous ammonia were mixed. This prepared a white slurry (gel) with a pH of 9.2. After filtering the slurry, the gel was washed with pure water. This yielded 1500 g of cake with a solid content of 10 wt%. This 1500 g of cake was diluted to 1.5 wt% with pure water. 1714 g of 35 wt% hydrogen peroxide solution was added to this. This was heated at 80°C for 1 hour. By adding 3286 g of pure water to this, a dispersion of the titanium-containing compound was obtained. The pH of this aqueous solution was 7.8. Dealkalization treatment was performed on 15000 g of this dispersion by adding a cation exchange resin. 1901 g of a 1 wt% potassium stinate aqueous solution was added to the dispersion. The ion exchange resin was separated from the dispersion. 634 g of Cataloid SN-350 and 3591 g of pure water were added to this dispersion. This dispersion was hydrothermally synthesized at 165°C for 18 hours using an autoclave. This dispersion was concentrated using an ultrafiltration membrane apparatus. Dealkalization was performed by adding a cation exchange resin to 2641 g of this dispersion. By separating the ion exchange resin from the dispersion, an aqueous dispersion of particles was prepared. The laser particle size of this aqueous dispersion was 15 nm. In the preparation of the organic solvent dispersion of particles, an alcohol dispersion of particles (solid content concentration of 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 165.1 g of orthopropyl ethyl acid were added to 2250 g of this aqueous dispersion. 31.2 g of 5% by mass aqueous ammonia was added to this alcohol dispersion. Furthermore, 93.9 g of KBM-503 was added to this alcohol dispersion as a second surface treatment agent. After adding KBM-503, a dispersion of particles in an organic solvent (solid content concentration 20% by mass) was obtained in the same manner as in Example 1. The coating solution was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used.

[0088] [Table 1]

[0089] [Table 2]

[0090] Table 3

Claims

1. Particles having a rutile-type crystal structure, The aforementioned particles include a core containing tin and titanium, and a shell containing titanium. The crystallite size is 7 nm or larger. The aforementioned particles contain titanium dioxide TiO ２ It contains more than 94% by weight, The aforementioned particles contain tin oxide (SnO ２ It is contained in an amount of 0.2 to 6% by weight, The tin content of the core is 0.1 to 6.5 at%, Particles in which the tin content of the shell surface is less than 0.1 at% in XPS measurement.

2. A dispersion of particles comprising particles having a rutile-type crystalline structure and a solvent, The aforementioned particles include a core containing tin and titanium, and a shell containing titanium. The crystallite size of the aforementioned particles is 7 nm or larger. The aforementioned particles contain titanium dioxide at a concentration of 90% by weight or more in terms of TiO2. The aforementioned particles contain tin oxide in an amount of 0.2 to 10% by weight, calculated as SnO₂. The tin content of the core is 0.1 to 6.5 at%, In the XPS measurement, the tin content of the shell surface is less than 0.1 at%, A dispersion with an average particle size of 100 nm or less.

3. The solvent is water, The particles are composed of SiO2 in proportion to 100 parts by mass of the particles. ２ Contains 2 parts by mass or more of silica, The dispersion according to claim 2, characterized in that the isoelectric point of the dispersion is 3 or less.

4. A step of preparing a dispersion of titanium-containing compounds, A step of preparing a dispersion of core particles having a rutile-type crystalline structure, A mixing step of preparing a mixed solution by mixing the titanium-containing compound dispersion and the core particle dispersion, The system includes a crystal growth step in which the mixture is heated to 80°C or higher and crystals are grown from the core particles to prepare the particles. The core particles contain titanium oxide and tin oxide. The aforementioned particles are TiO ２ It contains 95% or more titanium dioxide by weight and SnO ２ A method for producing particles, characterized in that, in the mixing step, the dispersion of the titanium-containing compound and the dispersion of the core particles are mixed so that the resulting mixture contains 0.2 to 5% by weight of tin oxide.

5. A step of adding silica to the dispersion after the crystal growth step, The method for producing particles according to claim 4, characterized by comprising, in order, a step of hydrothermally synthesizing the dispersion after adding the silica.

6. A coating liquid characterized by containing the particles described in claim 1.

7. A method for producing a film-coated substrate, characterized by forming a film on the substrate using the coating solution described in claim 6.

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