Particles having rutile crystal structure, production method therefor, and production method for particle dispersion liquid, coating liquid, and substrate with film

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

Particles having a rutile crystal structure, method for producing the same, and methods for producing particle dispersions, coating solutions, and film-coated substrates

[0001] The present invention relates to particles having a rutile crystal structure and a method for producing the same.

[0002] High-refractive-index films have been formed on substrates using coating solutions containing oxide particles with high refractive indexes. Such films are used in, for example, eyeglasses, lenses, smartphone touch panels, and the like.

[0003] To form a film with a high refractive index, it is preferable that the refractive index of the particles is high. For example, titanium oxide is known to have a high refractive index. Titanium oxide having a rutile crystal structure in particular has a high refractive index (see, for example, JP 2010-42947 A). Titanium oxide containing tin oxide is likely to have a rutile crystal structure.

[0004] In addition, titanium oxide particles containing inorganic oxides such as silica are known to be easily dispersed (see, for example, WO 2018 / 181241).

[0005] In Patent Documents 1 and 2, rutile composite particles containing titanium oxide and silica are used, which results in a low titanium oxide content in the particles, which in turn results in a low refractive index of the film.

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

[0007] Therefore, the present invention provides particles having a rutile crystal structure, and the crystallite diameter is 7 nm or more. Such particles are easily dispersed in a solvent. Here, the particles are TiO ２ It contains 90% by weight or more of titanium oxide in terms of SnO ２ The particles contain 0.2 to 10% by weight of tin oxide in terms of the weight of the particles. Such particles have a high refractive index.

[0008] It is also preferable that no tin is detected on the particle surface.

[0009] Furthermore, the particle diameter when dispersed in a solvent is preferably 100 nm or less.

[0010] A method for producing particles having a rutile crystal structure includes the steps of preparing a dispersion of a titanium-containing compound, preparing a dispersion of core particles having a rutile crystal structure, preparing a mixture by mixing the dispersion of the titanium-containing compound and the dispersion of the core particles, and heating the mixture to 80° C. or higher to cause crystal growth of the core particles. The core particles contain titanium oxide and tin oxide.

[0011] The present invention relates to particles (hereinafter simply referred to as particles) having a rutile-type crystal structure, and the crystallite diameter is 7 nm or more. ２ 90% by weight or more of titanium oxide and SnO ２ Even if the particles contain 0.2 to 10% by weight of tin oxide, they are easily dispersed in a solvent. In particular, even if the particle concentration is 20% by weight or more, such particles are easily and stably dispersed in water. Therefore, they are easy to handle industrially.

[0012] The larger the crystallite diameter of the particles, the smaller the specific surface area of ​​the particles. Therefore, the particles are more easily dispersed in a solvent. Furthermore, the larger the crystallite diameter of the particles, the lower the specific surface area, and therefore the higher the particle density. Therefore, the refractive index of the particles (hereinafter referred to as the particle refractive index) becomes higher. The refractive index of a film containing such particles (hereinafter referred to as the film refractive index) becomes higher. The crystallite diameter of the particles is preferably 9 nm or more, and more preferably 12 nm or more.

[0013] The higher the titanium oxide content of the particles, the higher the particle refractive index. ２ This content is 90% by weight or more in terms of TiO ２ The tin oxide content is preferably 92% by weight or more, more preferably 95% by weight or more, calculated as SnO. Furthermore, when the particles contain tin oxide, the crystal structure of the particles tends to be rutile. However, from the viewpoint of the refractive index of the particles, it is preferable that the tin oxide content of the particles is low. Therefore, the tin oxide content is SnO. ２ The tin oxide content is 10% by weight or less in terms of SnO ２ More preferably, the amount is 5% by weight or less in terms of converted amount.

[0014] Furthermore, if tin is not detected on the particle surface, i.e., 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 is likely to be high. On the other hand, if tin oxide is contained in the center side of the particle (hereinafter referred to as the core), the particle is likely to have a rutile crystal structure. In other words, when the core contains a sufficient amount of tin oxide to form a rutile crystal structure of the particle, 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 titanium and tin atoms.

[0015] Furthermore, when the ratio of the average minor axis of the particles to the crystallite diameter (average minor axis / crystallite diameter) is close to 1, the crystallite diameter 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 are to disperse in a solvent or binder. Therefore, the haze of the film tends to be lower. Furthermore, the smaller the aspect ratio, the smaller the specific surface area of ​​the particles. Therefore, the aspect ratio is preferably 1.0 to 2.3. In particular, when the crystallite diameter is 7 nm or more and the aspect ratio is 2.3 or less, the particles are more easily dispersed in a solvent. The aspect ratio is preferably 1 to 2.1, more preferably 1 to 1.9, and even more preferably 1 to 1.6. 1 to 1.5 is even more preferable. In particular, when the crystallite diameter is 10 nm or more, the aspect ratio is preferably 1 to 1.9, when the crystallite diameter is 12.5 nm or more, the aspect ratio is preferably 1 to 1.8, and when the crystallite diameter is 17 nm or more, the aspect ratio is preferably 1 to 1.5. The aspect ratio is the ratio of the average minor axis of a particle to the average major axis of the particle.

[0017] When particles are dispersed in a solvent, the average particle size of the particles (hereinafter referred to as the dispersed particle size) is preferably 100 nm or less. When particles of this size are used to form a film, the film becomes highly transparent. In addition, the particles are less likely to settle. The dispersed particle size is more preferably 80 nm or less. On the other hand, if the dispersed particle size is 20 nm or more, the particles are more easily dispersed in a solvent or binder. In particular, it is preferable that the crystallite size is 7 nm or more and the dispersed particle size is 20 nm or more.

[0018] The refractive index of particles varies depending on factors such as particle composition, density, crystal structure, and crystallite size. This refractive index is preferably 1.95 or more, more preferably 2.05 or more, and even more preferably 2.10 or more. It is difficult to obtain particles with a refractive index of 2.8 or more.

[0019] The particle dispersion will be described below. The particle dispersion contains the above-mentioned 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-mentioned particles to be dispersed in an organic solvent, the particle surfaces must be treated with a surface treatment agent. A portion of this surface treatment agent may not be bonded to the particles and may be dispersed in the organic solvent. Furthermore, 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 contained. Examples of surface treatment agents include silicon compounds, titanium compounds, zirconium compounds, and aluminum compounds. Of these, silicon compounds are easy to handle industrially.

[0020] When an organic solvent dispersion contains a surface treatment agent having an alkoxy group, the alkoxy group undergoes hydrolysis. In the dispersion, the hydrolyzed alkoxy group undergoes a dehydration condensation reaction with the OH groups on the particle surface (hereinafter referred to as chemical bonding). This makes it easier for the particles to disperse in the organic solvent. Furthermore, the organic solvent dispersion contains a catalyst, water, etc., which promotes the hydrolysis reaction of the alkoxy group. This also promotes chemical bonding.

[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 compound represented by the general formula (RO) ｎ M(X) ４－ｎ n is an integer of 1 to 4. M represents any of Si, Ti, and Zr. When M is Si, it is easy to handle industrially. When there is only one M in a molecule, it is easy to control the reaction rate of this molecule, and it is easy to handle industrially. X is a hydrocarbon group. For example, Me, Et, Pr, -(CH ２ ) ３ OC(=O)C(CH ３ ) (=CH ２ ), -(CH ２ ) ３ OC(=O)CH(=CH ２ ), -CH=CH ２ where R is a hydrocarbon group. When M is Si, R is Me or Et, which makes it easy to control the reaction rate of this molecule. Therefore, it is easy to handle industrially.

[0023] The more alkoxy groups a surface treatment agent has, the easier it is to chemically bond to the particle surface. Furthermore, when a surface treatment agent with many alkoxy groups is bonded to the particle surface, the number of alkoxy groups on the particle surface increases. This makes it easier for the particles to disperse in alcohol. It is preferable that the surface treatment agent has 3 to 4 alkoxy groups. When the solvent is alcohol, it is preferable that the surface treatment agent has 4 alkoxy groups. Hereinafter, a surface treatment agent having 4 alkoxy groups will be referred to as a first surface treatment agent.

[0024] 20 to 85 parts by mass (oxide equivalent {SiO if the surface treatment agent is a silicon compound) per 100 parts by mass of particles ２ When the dispersion contains 3 to 30 parts by mass of the first surface treatment agent (calculated as 100 parts by mass), the particles are easily dispersed in alcohol. Note that the larger the crystallite size of the particles, the more the amount of the surface treatment agent can be reduced.

[0025] When particles are treated with a surface treatment agent having a hydrocarbon group (hereinafter referred to as the second surface treatment agent), the particles are easily dispersed in an organic solvent (hereinafter referred to as the hydrophobic solvent) that is more hydrophobic than alcohol. In this case, the second surface treatment agent has three alkoxy groups and one hydrocarbon group, which makes the particles even 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] Hydrophobic solvents include organic solvents having at least one of an ester bond, an ether bond, and a ketone group. Organic solvents having such bonds or functional groups readily dissolve UV-curable binders. Among these organic solvents, polyethylene glycol monomethyl ether acetate (PGMEA) is preferred.

[0027] When the particle surfaces are treated with the first surface treatment agent and the second surface treatment agent, the particles become more easily dispersed in a hydrophobic solvent or an ultraviolet-curable binder.

[0028] Furthermore, when a surface treatment agent having a (meth)acrylate group is bonded to the particles, the particles can be bonded to the UV-curable binder by UV irradiation. As a result, the film becomes denser and the film refractive index increases. Therefore, it is preferable that the hydrocarbon group of the second surface treatment agent has a (meth)acrylate group or that the hydrocarbon group of the second surface treatment agent is a (meth)acrylate group.

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

[0030] When the solvent is water, SiO ２ It is preferable that the particle surface is treated with 2 parts by mass or more of silica in terms of oxide. 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 the particles, and that the isoelectric point of the aqueous dispersion is 3 or less. Even if the amount of the surface treatment agent is small, such particles are easily dispersed in organic solvents (particularly alcohol). The silica content is more preferably 4 parts by mass or more. On the other hand, if the silica content is too high, the particle refractive index becomes low. Therefore, the silica content is preferably 20 parts by mass or less per 100 parts by mass of the particles. When the particle surface is treated with 2 parts by mass or more of silica per 100 parts by mass of the particles, 10 to 30 parts by mass (oxide equivalent {SiO if the surface treatment agent is a silicon compound) per 100 parts by mass of the particles) is used. ２ It is preferable that the particle surfaces are treated with a first surface treatment agent in an amount of 3 to 10 parts by mass (calculated as a carbon black).

[0031] The coating liquid will be described below. The coating liquid contains particles, a surface treatment agent, a binder, and an organic solvent. Forming a film using a coating liquid containing the above-mentioned particles increases the film refractive index. A film can be formed using a coating liquid containing a binder. If a portion of the surface treatment agent functions as a binder, the binder need not be included. Examples of binders include monomers and oligomers before polymerization, and polymers obtained after polymerization of these. Of these, monomers or oligomers are preferred. When curing a film, a coating liquid containing a monomer or oligomer is more likely to produce a dense film than a coating liquid containing a polymer. Because the refractive index of the adamantane skeleton is high, using an adamantane derivative as the monomer or oligomer increases the film refractive index. The organic solvent can be selected appropriately depending on the type of binder added when preparing the coating liquid.

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

[0033] If the boiling point of the organic solvent is 80°C or higher, the coating liquid can be dried slowly, resulting in a dense film. The boiling point is more preferably 100°C or higher. On the other hand, if the boiling point is 200°C or lower, the organic solvent is less likely to remain, resulting in the film being more likely to shrink. Therefore, the film becomes harder. The boiling point is more preferably 180°C or lower.

[0034] The particle manufacturing method will be described below. First, a dispersion of a titanium-containing compound and a dispersion of core particles (hereinafter referred to as core particles) having a rutile crystal structure are prepared (preparation step). Then, the dispersion of the titanium-containing compound and the dispersion of the core particles are mixed to prepare a mixed solution (mixing step). The mixed solution is heated to 80°C or higher, causing crystal growth from the core particles (crystal growth step). By causing crystal growth from the core particles, the tin oxide content of the particles decreases. Therefore, the titanium oxide content of the particles becomes relatively high. In addition, the crystallite diameter 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 will be described in detail below.

[0035] <Preparation step> The core particles, which are the starting points for crystal growth, contain tin oxide and have a rutile crystal structure. Even if the titanium-containing compound does not contain tin oxide, by growing crystals from such core particles, the particles will have a rutile crystal structure. Here, since the titanium-containing compound does not contain tin oxide, the refractive index of the particles will be high.

[0036] When the core particles contain tin oxide, the core particles tend to be rutile. The tin oxide content of the core particles may be an amount that allows the core particles to have a rutile crystal structure. If the core particles have a crystal structure other than rutile, the particles will become mixed crystals or have a crystal structure other than rutile. The core particles may have a crystallite size that allows them to be dispersed in a solvent. If the solvent is water, the core particles tend to disperse.

[0037] The titanium-containing compound may contain titanium oxide or hydroxide. A gel is obtained by neutralizing the titanium compound, and then a dispersion of the titanium-containing compound is obtained by peptizing the gel. There are no particular limitations on the titanium compound 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 film refractive index and particle dispersibility. Therefore, it is preferable to wash the gel with water. When the gel is peptized using hydrogen peroxide, the core particles are likely to grow as rutile crystals. Adding hydrogen peroxide to the gel and then heating the gel to 50°C to 100°C facilitates peptization of the gel.

[0038] <Mixing step> In this step, a mixture is prepared by mixing a dispersion of a titanium-containing compound with a dispersion of core particles. When the weight ratio of the titanium-containing compound to the core particles (amount of titanium-containing compound / amount of core particles) is 7 or less, crystals other than rutile are unlikely to be formed. Here, the weights of the solid content and core particles are determined by the amounts of Ti and Sn in the raw materials, respectively, in the ratio of TiO ２ , SnO ２ The weight of the titanium-containing compound is the solid content of the dispersion of the titanium-containing compound.

[0039] <Crystal Growth Step> In this step, the mixed solution is heated to 80°C or higher, causing crystal growth from the core particles. If the mixed solution is below 80°C, the crystal growth rate is slow, resulting in a small crystallite size of the particles. Furthermore, in this case, the reaction is insufficient, resulting in the remaining yellow titanium-containing compound. When the mixed solution is heated to 80°C or higher, it is preferable to subject the mixed solution to hydrothermal synthesis (autoclave treatment). The higher the hydrothermal synthesis temperature, 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, production efficiency is increased. This temperature is more preferably 250°C. Furthermore, the longer the hydrothermal synthesis time, the higher the density of the particles. Therefore, this time is preferably 1 hour or higher, more preferably 5 hours or higher, and even more preferably 10 hours or higher. On the other hand, if this time is 50 hours or lower, production efficiency is increased. This time is more preferably 40 hours or lower, and even more preferably 20 hours or lower.

[0040] Repeating crystal growth multiple times increases the titanium oxide content of the particles. The crystallite size and particle size also increase. The aspect ratio also decreases. The number of crystal growths is preferably 2 to 5. When crystal growth is performed 2 to 3 times, the haze of the particle film is low. In this case, the film refractive index is also high. When crystal growth is performed 4 to 5 times, the particle refractive index is higher than when crystal growth is performed 2 to 3 times. On the other hand, when crystal growth is performed 4 to 5 times, the film haze is higher than when crystal growth is performed 2 to 3 times. From the second crystal growth onwards, the crystal-grown particles are used as core particles to carry out the mixing process and the crystal growth process.

[0041] It is preferable to treat the particle surface with silica before treating the particle surface 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 a dense silica layer being formed on the particle surface. When the specific surface area of ​​the silica is 100 to 600 m, ２ When the specific surface area of ​​silica is 200 to 550 m / g, fine particles and coarse particles are unlikely to be generated. ２ / g is more preferable, and 300 to 550m ２ / g is more preferable. During hydrothermal synthesis, the lower the solids concentration of the aqueous dispersion, the denser the silica layer is formed on the particle surface. Therefore, during hydrothermal synthesis, the solids concentration is preferably 5 wt% or less, more preferably 3 wt% or less, and even more preferably 1.5 wt% or less. During hydrothermal synthesis, the higher the temperature of hydrothermal synthesis, the denser the silica layer is formed on the particle surface. Therefore, this temperature is preferably 100°C or more, and more preferably 150°C or more. On the other hand, if this temperature is 200°C or less, production efficiency is high. This temperature is more preferably 180°C or less. Furthermore, the longer the hydrothermal synthesis time, the denser 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, production efficiency is high. This time is more preferably 20 hours or less.

[0042] A method for producing an organic solvent dispersion of particles will be described below. A surface treatment agent is added to an aqueous dispersion of crystal-grown particles, thereby treating the particle surfaces with the surface treatment agent. The solvent of the dispersion is then replaced from water to an organic solvent. The surface treatment agent preferably has an alkoxy group. A surface treatment agent having an alkoxy group can chemically bond to the particle surface, making the particles more easily dispersible in an organic solvent.

[0043] After adding the surface treatment agent, the dispersion is kept at 40° C. or higher for 1 hour or more, so that the surface treatment agent is quickly applied to the particles. The keeping time is preferably 20 hours or less.

[0044] By treating the particle surfaces in an aqueous dispersion with a first surface treatment agent, the particles become less likely to aggregate in alcohol. After this treatment, an alcohol dispersion can be prepared by replacing the solvent with alcohol. By adding a second surface treatment agent to this alcohol dispersion, the particle surfaces can be treated with the second surface treatment agent. Then, the solvent (alcohol) of the alcohol dispersion is replaced with a hydrophobic solvent. By replacing the solvent in this process, the particles become less likely to aggregate. When the amount of the second surface treatment agent added per 100 parts by mass of particles is 10 parts by mass or more, the particles become more easily dispersed 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, to increase the particle concentration in the film, this amount is preferably 50 parts by mass or less, and more preferably 40 parts by mass or less, per 100 parts by mass of particles. Furthermore, when treating the particle surfaces with the second surface treatment agent, adding water or a catalyst promotes the hydrolysis reaction of the second surface treatment agent.

[0045] A coating liquid can be obtained by adding a binder to an organic solvent dispersion of particles. When a part of the surface treatment agent functions as a binder, the organic solvent dispersion can be used as the coating liquid.

[0046] A film is formed on a substrate using the above-mentioned coating liquid to produce a film-coated substrate. Specifically, the coating liquid is applied to the substrate, and then dried to form a film. Examples of coating methods include spin coating, bar coating, gravure coating, and slit coating. Drying refers to the removal of the solvent by volatilization. If the drying temperature is 60°C or higher, the drying time is shortened. Furthermore, the solvent is less likely to remain in the film. Therefore, a dense film is 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, to improve production efficiency, it is preferable to harden the film after drying the coating liquid.

[0047] Example 1 A method for preparing particles will now be described in detail. The conditions for preparing the particles are shown in Table 1.

[0048] [Preparation of Particles] <Preparation Step> First, a dispersion of a titanium-containing compound and a dispersion of core particles were prepared as follows. ２523 g of a 7.66% by mass titanium tetrachloride aqueous solution and 523 g of a 7.66% by mass ammonia water were mixed. This produced a white slurry (gel) with a pH of 9.2. This slurry was filtered. The gel was washed with pure water to obtain 400.5 g of a cake with a solids concentration of 10% by mass. The cake was diluted with pure water to 1.5% by mass to obtain a slurry again. 457.7 g of a 35% by mass hydrogen peroxide solution was added to this slurry. This dispersion was heated at 80°C for 1 hour. 877 g of pure water was added to this dispersion to obtain a dispersion of a titanium-containing compound (TiO ２ A titanium oxide concentration of 1.0% by weight was obtained in terms of the concentration of the dispersion. The pH of this dispersion was 7.8, and the laser particle diameter was 37 nm. The laser particle diameter was measured by diluting this dispersion with water to 0.01% by weight and using an electrophoretic light scattering method with an ELSZ-2000S manufactured by Otsuka Electronics Co., Ltd. In the following examples and comparative examples, the laser particle diameter was measured at this concentration.

[0049] A cation exchange resin (manufactured by Mitsubishi Chemical Corporation) was added to 4,005 g of a dispersion of a titanium-containing compound. 495 g of a 1 wt % aqueous solution of potassium stannate diluted with pure water was added to the dispersion. The ion exchange resin was separated from the dispersion. The dispersion was subjected to hydrothermal synthesis in an autoclave at 165°C for 18 hours to obtain 4,500 g of a dispersion of core particles.

[0050] <Mixing Step> Next, 4500 g of the dispersion of the titanium-containing compound and 4500 g of the dispersion of the core particles were mixed to prepare a mixture. The laser particle diameter of the mixture was 37 nm.

[0051] <Crystal Growth Step> This mixture was subjected to hydrothermal synthesis in an autoclave to grow core particles. The hydrothermal synthesis conditions were 165°C and 18 hours. The laser particle diameter of the dispersion after the first crystal growth was 37 nm.

[0052] In this example, core particles were subjected to crystal growth twice. In the second crystal growth, the particles were subjected to crystal growth in the same manner as in the first crystal growth, except that the dispersion after the first crystal growth was used as the dispersion of core particles. The laser particle diameter of the dispersion after the second crystal growth was 43 nm. The laser particle diameters (dispersed particle diameters) of particle dispersions in other examples and comparative examples are also shown in Table 3. This dispersion was concentrated using an ultrafiltration membrane device to obtain 2,250 g of an aqueous dispersion of particles (solid concentration of 4% by mass).

[0053] [Preparation of Particle Dispersion in Organic Solvent] The preparation of the particle dispersion in organic solvent will be specifically described below. Table 2 shows the conditions for preparing the dispersion.

[0054] First, an alcohol dispersion of particles was prepared as follows: 2250 g of the aqueous dispersion of particles was mixed with 2250 g of methanol and ethyl orthosilicate (SiO ) as a first surface treatment agent. ２ 56.3 g of 28.8% by mass of silicon (calculated as silicon dioxide) was added. This dispersion was heated and stirred at 50°C for 18 hours to obtain a water / methanol dispersion of particles. After the dispersion was cooled to room temperature, the solvent of the dispersion was replaced with methanol using an ultrafiltration membrane. This dispersion was concentrated to obtain 531 g of an alcohol dispersion of particles (solids concentration: 20% by mass). The water content of this dispersion was 0.3% by mass.

[0055] 10.6 g of 5% by mass aqueous ammonia was added to 531 g of the alcohol dispersion of the particles. Furthermore, 3-methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd., SiO ２ To the mixture was added 31.9 g of an organic solvent (containing 24.2% by mass of silicon, calculated as silicon dioxide). The dispersion was heated and stirred at 50°C for 18 hours. The dispersion was cooled to room temperature. The solvent in the dispersion was replaced with propylene glycol monomethyl ether acetate (PGMEA), which is more hydrophobic than alcohol, using a rotary evaporator. This yielded 570 g of an organic solvent dispersion of particles (solids concentration 20% by mass).

[0056] [Preparation of Coating Solution] A method for preparing a coating solution will be 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 (registered trademark) ADDA (manufactured by Mitsubishi Gas Chemical Company, Inc.) 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 by the following methods. The results of other examples and comparative examples are also shown in Table 3.

[0058] (1) Particle Composition The aqueous dispersion of particles was diluted to a solids concentration of 1%. 100 g of this aqueous dispersion was dried at 100°C for 10 minutes to obtain a particle powder. The powder was heated over a burner to incinerate the organic matter. Sodium peroxide and sodium hydroxide were added to the powder to melt it. Furthermore, sulfuric acid and hydrochloric acid were added to the powder to dissolve it. The Sn, Ti, and Si contents of this solution were measured using an ICP-OES (SPS5520 manufactured by SII or ICPS-8100 manufactured by Shimadzu Corporation). These contents were then used to measure the Sn, Ti, and Si contents of the particles, respectively. ２ , TiO ２ , and SiO ２ The results were converted into percentage content.

[0059] (2) Crystal Structure and Crystallite Size The aqueous dispersion of particles was diluted to a solids concentration of 1%. 200 g of this aqueous dispersion was dried at 110°C for 20 hours (60°C for 48 hours in Example 7 only) to prepare a sample for measurement. X-ray structural analysis of the sample was performed using a Rigaku RINT (registered trademark) 1400. The diffraction peak pattern was analyzed using PDXL to confirm that the crystalline structure of the particles was rutile. The crystallite size of the particles was calculated from the half-width of the diffraction peak using Scherrer's formula (D = K × λ / (β × cos θ)). 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 (rad), and θ is the Bragg angle (rad).

[0060] (3) Average Minor Diameter and Aspect Ratio An aqueous dispersion of particles was diluted to a solids concentration of 0.002%. One drop of the diluted dispersion was placed on a collodion film. This was dried at 50°C for 10 minutes. A photograph of the particles was taken using a scanning electron microscope S-5500 (SEM) manufactured by Hitachi High-Technologies Corporation. One hundred particles projected on the photograph taken using the SEM were randomly selected, and their minor and major diameters were measured. The average of these minor diameters and the average of the major diameters were calculated. The ratio of the average minor diameter to the average major diameter (average minor diameter / average major diameter) was taken as the aspect ratio.

[0061] (4) Presence or Absence of Detection of Tin on Particle Surface Whether tin oxide is detected on the particle surface or whether the core contains tin oxide can be measured using X-ray photoelectron spectroscopy (XPS). However, since measurement is difficult using particles alone, a film was prepared as a measurement sample as follows. First, a dispersion (coating liquid) was prepared by adding 1.1 g of diphenyl(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Omnirad (registered trademark) TPO-H manufactured by IGM Resins B.V.) as a photopolymerization initiator to 300 g of an organic solvent dispersion of particles. This dispersion was applied to a silicon wafer substrate, and the coating liquid was dried at 80°C for 2 minutes. A high-pressure mercury lamp (EYEUVMETER manufactured by GS Yuasa Corporation) was used to measure tin oxide at 3000 mJ / cm. ２ A sample (film) for XPS measurement was prepared by irradiating the dried coating liquid with ultraviolet light under the conditions described below. Measurement by XPS was performed as follows, and it was confirmed that no tin oxide was detected on the particle surface.

[0062] Titanium may not be detected on the outermost surface of the film due to the presence of a surface treatment agent. Therefore, the proportion of tin on the particle surface is measured by etching to a depth at which titanium is detectable. For example, in this example, etching was performed to a depth of 1.2 nm, at which titanium is detectable. For this depth, Ar etching was performed for 20 seconds. That is, Ar etching was performed at 0.06 nm / sec. Titanium is detected when the proportion of titanium is 1.0 at% or greater. This proportion is the number of titanium atoms relative to the total number of carbon, oxygen, titanium, and tin atoms. Since the detection limit of XPS is generally 0.1 at%, if it is lower than this, tin is not present on the particle surface. Therefore, if the proportion of tin at the depth at which titanium is detected is less than 0.1 at% (i.e., tin is not detected), it is determined that tin oxide is not present on the particle surface. In this example, since this proportion was less than 0.1 at%, tin was not detected on the particle surface. If tin is present in the core, the tin will be detected by continuing the etching (when the tin content reaches 0.1 at % or more).

[0063] The X-ray photoelectron spectrometer used was an ESCALAB220Xi manufactured by Thermo Fisher Scientific. The spectral measurement conditions were: X-ray: 190 W, Pass Energy: Wide 100 eV, Narrow 20 eV, Analysis Diameter: 250 x 1000 μm, Charge Neutralizer: On. Measurements were performed using an Ar Gas Cluster Ion gun at an acceleration voltage of 3 kV and an etching rate of 3.5 nm / min (silicon oxide film). Calibration of the C1s (C-H) bond energy was performed at 284.8 eV. The energy intensity of the C1s peak was observed at 284-286 eV. O1s is 532-534 eV, Ti2p is 454-467 eV, Sn3d ５ is observed at 483-490 eV.

[0064] (5) Particle Refractive Index Np' The particle refractive index Np' was determined by the following method: In the following examples and comparative examples, the refractive index Np' was determined in the same manner.

[0065] First, three levels of coating solutions (a) to (c) were prepared, and then these coating solutions were applied by spin coating onto a silicon wafer (manufactured by Matsuzaki Seisakusho Co., Ltd.: 6-inch dummy wafer (P-type), thickness: 625 μm). The coating solution was dried at 80°C for 2 minutes. An EYEUVMETER was used to measure 3000 mJ / cm. ２ The dried coating liquid was irradiated with ultraviolet light under the conditions of 1. The refractive index Nav' of these film-coated substrates (silicon wafers) was measured using a spectroscopic ellipsometer (SE-2000 manufactured by Nippon Semilab Co., Ltd.).

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

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

[0068]

[0069] In Equation 1, f(m) is the volume fraction of particles relative to the total solid content. m is the weight fraction of particles relative to the total solid content, dm is the specific gravity of the binder (here, 1.1 g / ml, the specific gravity of ADDA), and dp is the specific gravity of the particles. Here, the specific gravity dp is the sum of the products of the content and specific gravity of each component contained in the particles. The component TiO contained in these particles ２ , SiO ２ , SnO ２ The specific gravities dp of the powders were 4.3 (only Comparative Example 4 was anatase type, so it was set to 3.8 g / ml), 2.2, and 7.0 g / ml, respectively. The content of each component was calculated by dividing the content (mass%) obtained in (1) Particle composition by 100. Formula 2

[0070]

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

[0072] The particle weight fraction m, binder specific gravity dm, and particle specific gravity dp in coating liquids (a) to (c) were substituted into formula 1. Since there are three levels of weight fraction m (a) to (c), three levels of f(m) were determined. Values ​​in increments of 0.01 in the range of 1.70 to 2.70 were substituted into the particle refractive index Np in formula 2 to calculate the film refractive index Nav. These film refractive indices Nav were calculated for each of the three levels of f(m). The deviation σ (Nav - Nav') between these film refractive indices Nav (calculated value) and film refractive index Nav' (measured value) was determined. From these deviations, the squared deviation σ ２ and the sum of squared deviations Σσ ２ The sum of squared deviations, Σσ ２ The particle refractive index Np' was determined 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 the surface treatment agent, the composition and structure of the particle surface, etc.).

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

[0074] (Preparation of Film-Coated Substrate (Glass Substrate)) The coating solution was applied to a glass substrate (FL glass manufactured by Hamashin Co., Ltd., thickness: 3 mm, refractive index: 1.51) by spin coating. After drying at 80°C for 2 minutes, a high-pressure mercury lamp (EYEUVMETER manufactured by GS Yuasa Corporation) was used to apply a 3000 mJ / cm ２ The film was irradiated with ultraviolet light under the conditions of 100° C. to 120° C., thereby preparing a film-coated substrate (glass substrate). The uncoated glass substrate had a total light transmittance of 99.0% and a haze of 0.1%.

[0075] (Preparation of Film-Coated Substrate (Silicon Wafer)) The coating liquid was applied to a silicon wafer (manufactured by Matsuzaki Seisakusho Co., Ltd.: 6-inch dummy wafer (P-type), thickness: 625 μm) by spin coating. After drying at 80° C. for 2 minutes, the coating liquid was measured at 3000 mJ / cm 2 using an EYEUVMETER. ２ The film was irradiated with ultraviolet light under the conditions of (a) to (c) to prepare a film-coated substrate (silicon wafer).

[0076] Example 2 The dispersion after the first crystal growth in Example 1 was concentrated using an ultrafiltration membrane device to obtain 2250 g of an aqueous dispersion of particles (solid content concentration: 4% by mass). An alcohol dispersion of particles (solid content concentration: 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 75 g of ethyl acetate were added to 2250 g of the aqueous dispersion of particles in the preparation of an organic solvent dispersion of particles. 11.2 g of 5 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 the addition of KBM-503, an organic solvent dispersion of particles (solid content concentration: 20% by mass) was obtained in the same manner as in Example 1. A coating liquid was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used in the preparation of the coating liquid.

[0077] Example 3 Crystal growth was performed in the same manner as in Example 1, except that the number of crystal growth rounds in the crystal growth step was five. In the (n+1)th crystal growth round, the dispersion after the nth crystal growth round was used as the dispersion of core particles. Except for this, crystal growth was performed in the same manner as in the first round (where n is 1 to 4). The dispersion after the fifth crystal growth round was concentrated using an ultrafiltration membrane device to obtain 2250 g of an aqueous dispersion of particles (solid content concentration: 4% by mass). An alcohol dispersion of particles (solid content concentration: 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 37.5 g of ethyl acetate were added to 2250 g of the aqueous dispersion of particles in the preparation of the organic solvent 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: 20% by mass) was obtained in the same manner as in Example 1. A coating liquid was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used in the preparation of the coating liquid.

[0078] [Example 4] Core particles were crystal-grown in the same manner as in Example 1, except that in the mixing step, the amount of the titanium-containing compound dispersion was changed to 7716 g and the amount of the core particle dispersion was changed to 1286 g. The number of crystal growth cycles was one. This dispersion was concentrated using an ultrafiltration membrane device, yielding 2250 g of an aqueous dispersion of particles (solid content concentration: 4% by mass). A coating liquid was prepared in the same manner as in Example 1, except that this aqueous dispersion was used in preparing the organic solvent dispersion of the particles.

[0079] [Example 5] In preparing an organic solvent dispersion of particles, the amount of ethyl orthosilicate 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. Except for this, a coating solution was prepared in the same manner as in Example 1.

[0080] [Example 6] The aqueous dispersion of the particles of Example 1 was diluted to a solid content of 1% by mass. 9000 g of this aqueous dispersion was mixed with silica sol (manufactured by JGC Catalysts and Chemicals Co., Ltd.: Cataloid (registered trademark) SN-350, silica specific surface area 375 m ２ 36 g of 15% by weight of 5000 sucrose (containing 15% by weight of silica) was added to the dispersion. This dispersion was subjected to hydrothermal synthesis at 165°C for 18 hours using an autoclave. The dispersion was cooled to room temperature. This dispersion was concentrated using an ultrafiltration membrane device to obtain 2385 g of an aqueous dispersion of particles (solid content concentration: 4% by mass). That is, the particles were surface-treated with silica. An alcohol dispersion of particles (solid content concentration: 20% by mass) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 19.9 g of ethyl acetate were added to 2250 g of the aqueous dispersion of particles in the preparation of the organic solvent 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 the addition of KBM-503, an organic solvent dispersion of particles (solid content concentration: 20% by mass) was obtained in the same manner as in Example 1. A 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. In addition, the XPS measurement sample was prepared using particles before the silica surface treatment. That is, the same XPS measurement sample as in Example 1 was used.

[0081] The isoelectric point of the aqueous dispersion of particles obtained in this example was measured as follows. Using a zeta potential measuring device ("ZETASIZER Nano-ZS" manufactured by Malvern), the zeta potential was measured at each pH while adjusting the pH at intervals of pH 1 or less. When two points on either side of the zeta potential of ±0 mV were connected with a straight line, the pH at which the zeta potential on the line was ±0 mV was defined as the isoelectric point. In this case, the particle concentration to be measured was 0.25% by mass, and pure water was used for dilution. An automatic titrator ("MPT-2" manufactured by Malvern) was used for pH adjustment. A 0.1 M aqueous sodium hydroxide solution was used to increase the pH, and 0.1 M hydrochloric acid was used to decrease the pH. The isoelectric point was 2.3.

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

[0083] Comparative Example 1 The dispersion of core particles of Example 1 was concentrated using an ultrafiltration membrane device to obtain 1125 g of an aqueous dispersion of particles (solid content concentration: 4% by mass). ２ When this aqueous dispersion was heated at 50° C., the viscosity of the dispersion increased and the dispersion became cloudy.

[0084] Comparative Example 2 The mixture of 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] TiO ２2,250 g of a 2 wt% titanium tetrachloride aqueous solution and 880 g of a 15 wt% ammonia water were mixed. This resulted in a white slurry (gel) with a pH of 8.6. This slurry was filtered, and the gel was washed with pure water. This resulted in 900 g of a cake with a solids concentration of 5 wt%. To 900 g of the cake, 514 g of 35 wt% hydrogen peroxide solution and 2,100 g of pure water were added. This was heated at 80°C for 1 hour. Further, 986 g of pure water was added to this. To 4,500 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, resulting in 5,232.6 g of a dispersion of core particles. To 4,500 g of this dispersion, 4,500 g of the dispersion of the titanium-containing compound of Example 1 was added. This dispersion was subjected to hydrothermal synthesis for 18 hours at 165° C. using an autoclave. The dispersion after hydrothermal synthesis had a laser particle size of 400 nm and was cloudy.

[0086] Comparative Example 4 The dispersion of core particles obtained in Comparative Example 3 was concentrated using an ultrafiltration membrane device to obtain an aqueous dispersion of particles (solids concentration: 10% by weight). A cation exchange resin was added to this aqueous dispersion to perform dealkalization. The ion exchange resin was separated from the aqueous dispersion. An alcohol dispersion of particles (solids concentration: 20% by weight) was obtained in the same manner as in Example 1, except that 2250 g of methanol and 65.5 g of ethyl acetate were added to 2250 g of this aqueous dispersion in the preparation of an organic solvent dispersion of particles. 12.4 g of 5% by weight 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 the addition of KBM-503, an organic solvent dispersion of particles (solids concentration: 20% by weight) was obtained in the same manner as in Example 1. A coating liquid was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used in the preparation of the coating liquid.

[0087] [Comparative Example 5] TiO ２2,000 g of a 7.5 wt% titanium tetrachloride aqueous solution and 2,000 g of a 7.5 wt% aqueous ammonia solution were mixed. This resulted in a white slurry (gel) with a pH of 9.2. This slurry was filtered and the gel was washed with pure water. This resulted in 1,500 g of a cake with a 10 wt% solids content. This 1,500 g cake was diluted to 1.5 wt% with pure water. 1,714 g of a 35 wt% aqueous hydrogen peroxide solution was added to this. This was heated at 80°C for 1 hour. 3,286 g of pure water was added to this to obtain a dispersion of a titanium-containing compound. The pH of this aqueous solution was 7.8. A cation exchange resin was added to 15,000 g of this dispersion to perform dealkalization. 1,901 g of a 1 wt% aqueous potassium stannate solution was added to the dispersion. The ion exchange resin was separated from the dispersion. To this dispersion, 634 g of Cataloid SN-350 and 3,591 g of pure water were added. This dispersion was subjected to hydrothermal synthesis at 165°C for 18 hours using an autoclave. This dispersion was concentrated using an ultrafiltration membrane device. A cation exchange resin was added to 2,641 g of this dispersion to perform dealkalization. An aqueous dispersion of particles was prepared by separating the ion exchange resin from the dispersion. The laser particle diameter of this aqueous dispersion was 15 nm. An alcohol dispersion of particles (solids concentration 20% by mass) was obtained in the same manner as in Example 1, except that in the preparation of an organic solvent dispersion of particles, 2,250 g of methanol and 165.1 g of ethyl acetate were added to 2,250 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, an organic solvent dispersion of particles (solid content concentration: 20% by mass) was obtained in the same manner as in Example 1. A coating liquid was prepared in the same manner as in Example 1, except that this organic solvent dispersion was used in the preparation of the coating liquid.

[0088]

[0089]

[0090]

Claims

1. Particles having a rutile type crystal structure, the particles comprise a core comprising tin and titanium and a shell comprising titanium; The crystallite size is 7 nm or more, The particles contain titanium oxide in an amount of 90% by weight or more calculated as TiO 2 , The particles contain tin oxide in an amount of 0.2 to 10% by weight calculated as SnO 2 , The tin content of the core is 0.1 to 6.5 at %, Particles wherein the shell has a tin content of less than 0.1 at %.

2. A particle dispersion comprising the particles according to claim 1 and a solvent, A dispersion having an average particle size of 100 nm or less.

3. the solvent is water, The particles contain SiO ２ Contains 2 parts by mass or more of silica, 3. The dispersion according to claim 2, wherein the dispersion has an isoelectric point of 3 or less.

4. preparing a dispersion of a titanium-containing compound; preparing a dispersion of core particles having a rutile crystal structure; a mixing step of mixing the dispersion of the titanium-containing compound and the dispersion of the core particles to prepare a mixed liquid; and a crystal growth step of heating the mixture to 80° C. or higher and growing crystals from the core particles to prepare particles. the core particle comprises titanium oxide and tin oxide, A method for producing particles, comprising mixing the dispersion of the titanium-containing compound and the dispersion of the core particles in the mixing step so that the particles contain 95% by weight or more of titanium oxide calculated as TiO 2 and 0.2 to 5% by weight of tin oxide calculated as SnO 2 .

5. adding silica to the dispersion after the crystal growth step; and subjecting the dispersion liquid to hydrothermal synthesis after the silica has been added.

6. A coating liquid comprising the particles according to claim 1.

7. A method for producing a film-coated substrate, comprising forming a film on a substrate by using the coating liquid according to claim 6.