JP7637536B2 - Dispersion of surface-treated metal oxide particles and method for producing same - Google Patents

Description

The present invention relates to a dispersion of metal oxide particles that have been surface-treated with an organosilicon compound having a functional group, and a method for producing the same.

Conventionally, in order to improve the pencil hardness (hardness) and scratch resistance (strength) of the surfaces of substrates such as glass, plastic sheets, and plastic lenses, and display devices, it is known to form a transparent coating having a hard coat function on the surface of the substrate. Specifically, a transparent organic resin film or inorganic film is formed on the surface of glass, plastic, display device substrate, etc. At this time, it is known that the adhesion to the substrate, strength, etc. are improved by blending particles such as silica in the coating. In addition, it is known that the refractive index difference between the coating and the substrate is reduced by blending high refractive index particles such as titanium oxide and zirconium oxide in the coating, thereby suppressing interference fringes, and that antistatic performance is imparted by blending conductive particles such as antimony pentoxide, tin-doped indium oxide, and antimony-doped tin oxide in the coating. When such metal oxide particles are used, it is known that the surface is treated with an organosilicon compound to improve the dispersibility in the matrix component (see, for example, Patent Document 1).

Metal oxide particles that have been surface-treated with an organosilicon compound have a layer in which the OH groups on the particle surface are chemically bonded to the organosilicon compound, and a layer in which the two are physically adsorbed. The presence of this chemically bonded layer has the effect of suppressing the aggregation of particles in the resin, and the presence of the physically adsorbed layer is known to improve compatibility with the resin (see, for example, Patent Documents 2 and 3).

WO2011/059081 JP 2005-298740 A JP 2015-189637 A

A substrate with a coating using metal oxide particles surface-treated with an organosilicon compound is required to have high hardness and strength. When an organosilicon compound is physically adsorbed on the metal oxide particles, the compatibility of the particles with the resin is improved, and the hardness and strength are expected to be improved. However, a substrate with a coating using such surface-treated metal oxide particles is insufficient in terms of improvement in hardness and strength. This is thought to be because the presence of at least one of the organosilicon compound physically adsorbed on the metal oxide particles and the unreacted organosilicon compound inhibits the metal oxide particles and the resin from chemically bonding to each other to form a three-dimensional crosslink, resulting in insufficient denseness as a coating. Therefore, metal oxide particles with a more precise surface treatment are required. In addition, the particles are required to have high dispersibility in the dispersion medium or resin. Furthermore, the substrate with a coating using these particles is required to have sufficient hardness and strength by suppressing particle aggregation.

To solve these problems, the following dispersion of surface-treated metal oxide particles was discovered. This dispersion contains surface-treated metal oxide particles that contain 3 to 60 parts by mass of an organosilicon compound having a functional group as solid content per 100 parts by mass of metal oxide particles. The organosilicon compound in the liquid excluding the surface-treated metal oxide particles from the dispersion is 0.20 parts by mass or less as solid content per metal oxide particle.

The average primary particle diameter (D) of these surface-treated metal oxide particles, as determined by image analysis, is 5 to 120 nm. The ratio (L/D) of this to the average particle diameter (L) as determined by dynamic light scattering is 1.0 to 1.5.

These surface-treated metal oxide particles have high dispersibility. They also have many polymerization points with the matrix-forming components, and the amount of "unreacted and physically adsorbed organosilicon compounds" that inhibit polymerization with the matrix-forming components is small. A coating solution containing such particles can be used to obtain a coated substrate with high hardness and strength.

To obtain these surface-treated metal oxide particles, we discovered the following manufacturing method.

First, a dispersion liquid containing metal oxide particles is prepared, and an organosilicon compound represented by the following formula (1) is added to the dispersion liquid to surface-treat the metal oxide particles (first step). Next, the organosilicon compound is removed from the dispersion liquid of the metal oxide particles after the surface treatment (second step).

R _n -SiX _4-n ...Formula (1)
(In the formula, R represents an unsubstituted or substituted hydrocarbon group having 1 to 10 carbon atoms, and may be the same or different. Examples of the substituent include an alkyl group, a vinyl group, an epoxy group, an alkoxy group, a (meth)acryloxy group, a mercapto group, a glycidoxy group, a halogen atom, an amino group, a phenyl group, and a phenylamino group. X represents an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom, and n represents an integer of 0 to 4.)

The properties of the surface-treated metal oxide particles in the dispersion obtained in the second step are similar to those of the dispersion of surface-treated metal oxide particles described above.

The dispersion of surface-treated metal oxide particles of the present invention provides a coating solution that has excellent adhesion to the substrate and can produce a coating film with high hardness and strength.

[Dispersion of surface-treated metal oxide particles]
The dispersion (hereinafter, sometimes simply referred to as "dispersion") of surface-treated metal oxide particles (hereinafter, sometimes simply referred to as "particles") according to the present invention will be described below.

The particles in the dispersion contain 3 to 60 parts by mass of an organosilicon compound having a functional group as solid content per 100 parts by mass of metal oxide particles. In addition, the amount of the organosilicon compound in the liquid excluding the particles from the dispersion is 0.20 parts by mass or less as solid content per 100 parts by mass of metal oxide particles.

The average primary particle size (D) of these particles as determined by image analysis is 5 to 120 nm. The ratio (L/D) of this to the average particle size (L) of the particles as determined by dynamic light scattering is 1.0 to 1.5.

The particles contain a functional group derived from a surface treatment agent (an organosilicon compound represented by formula (1)). The functional group is preferably at least one selected from a vinyl group, an epoxy group, an alkoxy group, a (meth)acryloxy group, a mercapto group, a glycidoxy group, a halogen group, an amino group, a phenyl group, and a phenylamino group. Among these, the vinyl group, the epoxy group, the alkoxy group, the (meth)acryloxy group, the amino group, and the mercapto group are more preferred in that they have high polymerization ability.

The solid content of the organosilicon compound relative to the metal oxide particles can be calculated by thermogravimetry. By heating at 500°C, the metal oxide particles and the silicon content derived from the organosilicon compound remain. Therefore, only the surface-treated metal oxide particles are taken out by centrifugation and heated at 500°C, and the mass loss before and after the heating is measured, and the silicon content derived from the organosilicon compound is calculated from the difference with the amount of the metal oxide particles. Next, this is converted into the amount of solid content (R _n -SiO _(4-n)/2 ) derived from the organosilicon compound from the structure of the organosilicon compound used for the surface treatment, so that the solid content of the organosilicon compound can be calculated.

When the particles contain 3 to 60 parts by mass of an organosilicon compound as solid content per 100 parts by mass of metal oxide particles, the particles can exist in the dispersion liquid without agglomerating or settling. In addition, they have good dispersibility in the coating liquid and in the film, and using these particles makes it possible to obtain a coating with high hardness and strength.

Here, if the amount of the organosilicon compound is less than 3 parts by mass, sufficient dispersibility and stability cannot be obtained, and when the particles are used in a coating, there is a risk that a coating with sufficient hardness and strength cannot be obtained. Conversely, if the amount exceeds 60 parts by mass, there is no further improvement in dispersibility or stability, and there is no improvement in the hardness and strength of the coating. The amount of this organosilicon compound is preferably 3 to 45 parts by mass, and more preferably 3 to 30 parts by mass.

The amount of organosilicon compounds in the dispersion liquid after removing the particles can be calculated from GC-MS measurements. The particles settle during centrifugation, while unreacted organosilicon compounds that have not reacted with the metal oxide particles are extracted into the supernatant. By performing GC-MS measurements on this supernatant, the amount of organosilicon compounds in the dispersion liquid after removing the particles can be calculated.

The amount of organosilicon compound in the liquid excluding the particles from the dispersion is 0.20 parts by mass or less as solid content relative to 100 parts by mass of metal oxide particles, which indicates that there is little unreacted organosilicon compound and physically adsorbed organosilicon compound. Here, if the amount of such organosilicon compound is more than 0.20 parts by mass, when this particle is used for a coating, there is a risk that a coating having sufficient hardness and strength will not be obtained. This is because the presence of unreacted organosilicon compound or physically adsorbed organosilicon compound reduces the degree of polymerization of the matrix forming component during coating formation, and a dense film cannot be obtained. The amount of this organosilicon compound is preferably 0.10 parts by mass or less, more preferably 0.08 parts by mass or less, even more preferably 0.05 parts by mass or less, and particularly preferably substantially 0 parts by mass. Here, "substantially 0 parts by mass" means that the organosilicon compound is below the detection limit of the measuring instrument.

As such, one of the features of the particles of the present invention is that they have a necessary amount of "organosilicon compounds having functional groups" that are chemically bonded to the OH groups on the surface of the metal oxide particles, and the content of "unreacted and physically adsorbed organosilicon compounds" is suppressed, i.e., they have undergone "precise surface treatment."

The average primary particle diameter (D) determined by particle image analysis is 5 to 120 nm. When the average primary particle diameter (D) is within this range, the particles can exist in the dispersion liquid without agglomerating or settling. They also have good dispersibility in the coating liquid and in the film, and a film with high transparency, hardness, and strength can be obtained.

Here, it is difficult to obtain particles with an average primary particle diameter (D) of less than 5 nm. Conversely, if it exceeds 120 nm, a transparent coating may not be obtained. This average (D) is preferably 5 to 100 nm, more preferably 7 to 80 nm, and even more preferably 7 to 50 nm.

The ratio (L/D) of the average particle size (L) measured by dynamic light scattering to the average primary particle size (D) of the particles is 1.0 to 1.5. A ratio (L/D) in this range indicates that the proportion of aggregated particles is low and the particles are in a monodispersed state. Therefore, the particles are highly dispersible in the dispersion medium or matrix-forming components. In addition, when used as a coated substrate, high hardness, strength, and transparency are obtained.

Here, if the ratio (L/D) exceeds 1.5, there is a risk that sufficient hardness, strength, and transparency of the coating will not be obtained.

The ratio (L/D) is preferably 1.0 to 1.4, and more preferably 1.0 to 1.3.

The metal oxide particles preferably contain at least one element selected from Si, Al, Sn, Sb, Ti, Zr, Zn, W, Fe, In, and Ba. These oxides may be used alone, in the form of a mixture, or in the form of a composite oxide. However, the content of these elements in the metal oxide particles is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 100% by mass.

Pulsed NMR is a measurement method in which magnetization in a thermal equilibrium state in a static magnetic field is excited by irradiating it with pulsed radio waves of several tens of MHz, and the phenomenon in which the excited magnetization returns to its original thermal equilibrium state over time is observed. Here, the response to changes in the magnetic field is different between liquid molecules in contact with or adsorbed to the particle surface and liquid molecules in a free state that are not in contact with the particle surface.

In general, the movement of liquid molecules adsorbed to particle surfaces is restricted, while liquid molecules not adsorbed to particle surfaces can move freely. As a result, the relaxation time of liquid molecules adsorbed to particle surfaces is shorter than the relaxation time of other liquid molecules. The relaxation time observed in a liquid with dispersed particles is the average value of two relaxation times reflecting the liquid volume concentration on the particle surfaces and the liquid volume concentration in the free state.

In a dispersion of metal oxide particles that have been surface-treated with an organosilicon compound, in addition to the organosilicon compounds that are chemically bonded to the metal oxide particles, there may be unreacted organosilicon compounds that are not chemically bonded to the metal oxide particles, and organosilicon compounds that are only physically adsorbed. These organosilicon compounds have a very small molecular weight compared to the metal oxide particles, and therefore have a very large specific surface area. In addition, the movement of liquid molecules adsorbed to these unreacted and only physically adsorbed organosilicon compounds relative to the particles in the dispersion is restricted, so when unreacted and only physically adsorbed organosilicon compounds are present in the dispersion, the measured relaxation time will be short, i.e., the specific surface area calculated from the relaxation time will be a large value.

The specific surface area (A1) of particles in a dispersion liquid determined by pulse NMR measurement indicates the specific surface area of the particles in the part wetted with the dispersion medium. Metal oxide particles surface-treated with an organosilicon compound have fewer OH groups on the particle surface due to the reaction between the organosilicon compound and the OH groups on the particle surface, so the specific surface area of the particles in the part wetted with the hydrophilic dispersion medium is small. In contrast, unreacted organosilicon compounds and metal oxide particles with only physically adsorbed organosilicon compounds still have OH groups, so when these are present in the dispersion liquid, the specific surface area of the part wetted with the hydrophilic dispersion medium is large. For this reason, the value of this specific surface area (A1) also changes depending on the degree of surface treatment (chemical bonding) of the organosilicon compound on the metal oxide particles and the amount of unreacted organosilicon compounds and only physically adsorbed organosilicon compounds in the dispersion liquid. The value of the specific surface area (A1) also changes depending on the type of dispersion medium used during measurement.

On the other hand, the specific surface area (A2) calculated from the average primary particle diameter (F) of the metal oxide particles is roughly equal to the specific surface area by the BET method. Therefore, the ratio (A1/A2) of the specific surface area (A1) of the "surface-treated metal oxide particles" to the specific surface area (A2) of the "non-surface-treated metal oxide particles" is an index of the degree of hydrophobicity of the particle surface and the amount of unreacted organosilicon compounds and organosilicon compounds that are merely physically adsorbed in the dispersion. Here, the ratio (A1/A2) of the specific surface area (A1) obtained from the pulse NMR measurement of the methanol dispersion of the surface-treated metal oxide particles to the specific surface area (A2) calculated from the average primary particle diameter (F) of the metal oxide particles is preferably 0.80 or less. The ratio (A1/A2) being in this range indicates that the particle surface is sufficiently hydrophobic and that the amount of unreacted organosilicon compounds and organosilicon compounds that are merely physically adsorbed in the dispersion is small. The use of such particles results in good dispersibility in the coating solution and film, resulting in a film with high transparency, hardness, and strength.

Here, if the ratio (A1/A2) exceeds 0.80, there is a risk that the hydrophobization of the particle surface is insufficient, or that a large amount of unreacted organosilicon compound and organosilicon compound that is merely physically adsorbed is present in the dispersion liquid. There is no particular lower limit for the ratio (A1/A2), but taking into account the particle size, it is, for example, 0.30. The ratio (A1/A2) is more preferably 0.70 or less, and even more preferably 0.65 or less.

The specific surface area (A1) of the particles is calculated by the following formula (3) using the volume concentration (Ψp) of the metal oxide particles calculated by the following formula (2):

Ψp=(Sc/Sd)/[(1-Sc)/Td]...Formula (2)
(In the formula, Sc represents the solid concentration (mass %) of the metal oxide particles in the dispersion, Sd represents the density (g/cm ³ ) of the components of the metal oxide particles, and Td represents the density (g/cm ³ ) of the dispersion medium at 25° C.)

Here, the solid content concentration is the concentration of the target substance (here, metal oxide particles) converted into the solid content in the dispersion liquid (same below). For example, Sd is 2.2 when the constituent component of the metal oxide particles is silica, 3.9 when it is alumina, 6.9 when it is tin oxide, 5.2 when it is antimony oxide, 3.9 when it is titania (anatase), 4.3 when it is titania (rutile), 6.0 when it is zirconia, 5.6 when it is zinc oxide, 7.2 when it is tungsten oxide, 5.2 when it is iron (III) oxide, 7.2 when it is indium oxide, and 5.7 when it is barium oxide. If the metal oxide particles are composite oxide particles, particles containing mixed oxides, or mixtures of oxide particles, Sd can be calculated according to the ratio of the oxides. For example, Td is 0.79 when the dispersion medium is methanol. If another type of dispersion medium or a mixture of dispersion mediums is used, the density corresponding to it is used.

A1={[(Ra/Rb)-1]×Rb}/(Ka×Ψp) ...Formula (3)
(In the formula, A1 is the specific surface area ( ^m2 /g) of the particles, Ra is the inverse of the pulse NMR relaxation time in the measurement of the dispersion liquid, Rb is the inverse of the pulse NMR relaxation time in the measurement of the dispersion medium, and Ka is a coefficient depending on the dispersion medium and metal oxide particles used.)

The coefficient Ka is calculated assuming that the specific surface area (A2) obtained from the average primary particle diameter (F) of the metal oxide particles is the same as the specific surface area (A3) obtained by pulsed NMR measurement of the metal oxide particle dispersion.

The specific surface area (A2) of the metal oxide particles can be calculated using the average primary particle diameter (F) of the metal oxide particles according to the following formula (4).

A2=6000/Sd/F...Formula (4)
(In the formula, Sd represents the density (g/cm ³ ) of the metal oxide particles.)

The specific surface area (A3) of the metal oxide particles is calculated using the volume concentration (Ψp) of the metal oxide particles calculated using formula (2) according to formula (5).

A3={[(Rc/Rd)-1]×Rd}/(Ka×Ψp) ...Formula (5)
(In the formula, A3 is the specific surface area ( ^m2 /g) of the metal oxide particles, Rc is the reciprocal of the pulse NMR relaxation time in the measurement of the metal oxide particle dispersion, Rd is the reciprocal of the pulse NMR relaxation time in the measurement of the dispersion medium, and Ka is a coefficient depending on the dispersion medium and metal oxide particles used.)

Here, the coefficient Ka is set so that the specific surface area (A2) and the specific surface area (A3) have the same value. Therefore, from the formulas (4) and (5),
Ka={[(Rc/Rd)-1]×Rd}/(Ψp×A2) ...Formula (6)
It can be calculated as:

There are no particular limitations on the dispersion medium and concentration of the dispersion liquid, so long as the particles are stably dispersed in the liquid without aggregation or precipitation.

Examples of dispersion media include alcohols, esters, glycols, ethers, ketones, etc. These may be used alone or in combination of two or more.

The concentration of the dispersion liquid is preferably 0.1 to 50% by mass in terms of solid concentration as metal oxide. Here, if the concentration is less than 0.1% by mass, the processing time required for manufacturing the coating liquid may be long. Conversely, if the concentration exceeds 50% by mass, the stability of the dispersion liquid may decrease. The concentration of the dispersion liquid is more preferably 5 to 45% by mass, and even more preferably 10 to 40% by mass.

The content of each of the elements belonging to the alkali metals and alkaline earth metals, which are impurities of the particles, when expressed as oxide, is preferably 500 ppm or less relative to the particles. This reduces particle adhesion, resulting in high stability of the dispersion and coating liquid. In addition, the particles are uniformly dispersed in the coating liquid and coating, resulting in a coating with high hardness and strength.

If the content of each exceeds 500 ppm, the proportion of particles adhering to each other increases, and there is a risk that sufficient stability of the dispersion or coating liquid may not be obtained, or sufficient hardness and strength of the coating may not be obtained. The content is more preferably 100 ppm or less. Note that alkali metals refer to Li, Na, K, Rb, Cs, and Fr, and alkaline earth metals refer to Be, Mg, Ca, Sr, Ba, and Ra.

The shape of the particles is not particularly limited. Examples include spherical, ellipsoidal (rugby ball), cocoon, confetti, chain, and dice shapes. Among these, spherical particles are preferred because they have high dispersibility and can be uniformly dispersed in the coating.

[Method for producing a dispersion of surface-treated metal oxide particles]
The method for producing a dispersion of surface-treated metal oxide particles according to the present invention includes a first step of surface-treating metal oxide particles with an organosilicon compound represented by formula (1) and a second step of removing the organosilicon compound from the dispersion of surface-treated metal oxide particles obtained in the first step, thereby obtaining a dispersion of surface-treated metal oxide particles with high dispersibility.

The surface-treated metal oxide particles produced in this way have reduced aggregation and have sufficient hardness and strength when used in a coating. Each process is described below.

[First step]
The metal oxide particles prepared as the starting material in this step are preferably oxides containing at least one element selected from Si, Al, Sn, Sb, Ti, Zr, Zn, W, Fe, In, and Ba. These oxides may be used alone, in mixtures, or in composite oxides. However, the content in the particles is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 100% by mass.

In the surface treatment, first, a dispersion liquid of metal oxide particles is prepared. As the dispersion medium, water or alcohols such as methanol and ethanol are preferably used. A predetermined amount of an organosilicon compound represented by formula (1) is added to the dispersion liquid to hydrolyze the organosilicon compound. Water can be added to the hydrolysis as necessary. The ratio (Mw/Mo) of the number of moles of water (Mw) to the number of moles of the organosilicon compound (Mo) to be added is preferably 1 or more. Here, if the ratio (Mw/Mo) is less than 1, the hydrolysis is insufficient, and the hardness, strength, transparency, haze, etc. of the coating may be insufficient. Although there is no particular upper limit for the ratio (Mw/Mo), if the ratio (Mw/Mo) exceeds 200, the hydrolysis reaction becomes intense, and the organosilicon compounds polymerize with each other, and there is a risk that the organosilicon compound treatment on the metal oxide surface cannot be performed efficiently, so the upper limit is, for example, 200. This ratio (Mw/Mo) is more preferably 1 to 100.

In addition, in this hydrolysis, an acid or an alkali can be used as a hydrolysis catalyst as necessary. Among them, ammonia is preferable. When ammonia is used, it is easy to remove even if it remains in the dispersion, and the stability of the dispersion is easily maintained. The ratio (M _N /Mo) of the mole number of ammonia (M _N ) to the mole number of the organosilicon compound (Mo) to be added is preferably in the range of 0.005 to 5. Here, when the ratio (M _N /Mo) is less than 0.005, the hydrolysis becomes insufficient, and the hardness, strength, transparency, haze, etc. of the coating may become insufficient. When this ratio (M _N /Mo) exceeds 5, the hydrolysis reaction becomes intense, and the organosilicon compounds polymerize with each other, and the organosilicon compound treatment on the metal oxide surface may not be performed efficiently.

The surface treatment is preferably carried out in a homogeneous system, and in order to promote chemical bonding between the metal oxide particles and the organosilicon compound, it is preferable to heat the dispersion medium at a temperature below the boiling point (e.g., room temperature to 120°C) for 0.5 to 48 hours.

When the metal oxide particles have their surfaces chemically bonded to the organosilicon compound by this surface treatment, they have high adhesion to the substrate and high hardness and strength when used on a coated substrate.

Examples of organosilicon compounds include those shown in Table 1. These organosilicon compounds may be present in the particles alone or in combination. In surface treatment, these organosilicon compounds can be used alone or in mixtures, and it is also possible to treat the particles in stages using the same type, a mixture of multiple types, or multiple types separately.

[Second step]
In the first step, the organosilicon compounds surface-treated include those chemically bonded to the metal oxide particles, as well as unreacted organosilicon compounds and those that are merely physically adsorbed. The second step is aimed at removing "unreacted and physically adsorbed organosilicon compounds" from the metal oxide particles. Methods for removing these organosilicon compounds from the surface-treated metal oxide particles include, for example, ultrafiltration membrane method, centrifugation method, distillation method, etc. Among these, the ultrafiltration membrane method is preferred because of its high removal efficiency. In addition, ultrasonic treatment may be combined with the purpose of separating the organosilicon compounds that are merely physically adsorbed from the metal oxide particles.

In order to efficiently perform this "removal of organosilicon compounds", it is preferable that the concentration of metal oxide in the dispersion of the metal oxide particles surface-treated in the first step is 10 to 60 mass% as solids. Here, if the concentration is less than 10 mass%, the amount of cleaning liquid used in the second step is large relative to the obtained surface-treated metal oxide particles, resulting in poor productivity. Conversely, if it exceeds 60 mass%, there is a risk of thickening or gelation during the second step. In addition, the amount of cleaning liquid used for "removal of organosilicon compounds" is preferably three times or more the amount of the dispersion of the metal oxide particles surface-treated in the first step, although it depends on the amount of surface treatment in the first step and the concentration of the dispersion. Here, if the amount of cleaning liquid is less than three times, there is a risk of "removal of organosilicon compounds" being insufficient. There is no particular upper limit on the amount of this cleaning liquid, but even if 10 times or more of the cleaning liquid is used, the "removal of organosilicon compounds" is not significantly improved, so for example, it is 10 times. It is preferable to use the same type of cleaning liquid as the dispersion medium used in the first step.

Here, since at least a portion of the organosilicon compound added in the first step is removed by the removal in the second step, the amount of organosilicon compound added in the first step does not remain on the particles as it is. Therefore, it is necessary that the organosilicon compound having a functional group finally contained in the particles is 3 to 60 parts by mass as solid content per 100 parts by mass of metal oxide particles, and that the amount of organosilicon compound in the liquid excluding the particles from the dispersion is 0.20 parts by mass or less as solid content per 100 parts by mass of metal oxide particles. This allows for a "precise surface treatment" to be realized in which the necessary amount of "organosilicon compound having a functional group" that is chemically bonded to the OH groups on the metal oxide particle surface is present, and the content of "unreacted and physically adsorbed organosilicon compound" that may cause a decrease in performance is suppressed.

The particles obtained have an average primary particle diameter (D) of 5 to 120 nm as determined by image analysis. The ratio (L/D) of this to the average particle diameter (L) of the particles as determined by dynamic light scattering is 1.0 to 1.5.

The preferred ranges for these physical properties are the same as those for the surface-treated metal oxide particles described above.

By the way, although this may be due to the difference in the amount of surface treatment, it may be difficult to satisfy the two ranges of "the amount of organosilicon compound having functional groups contained in the particles" and "the amount of organosilicon compound in the liquid excluding the particles" in a single operation from the first step to the second step. This depends on the reaction efficiency between the OH groups on the metal oxide particle surface and the organosilicon compound, but in order to advance the chemical bond with the OH groups on the metal oxide particle surface and efficiently obtain the desired particles, it is preferable to repeat the first step to the second step and then the first step to the second step multiple times. Furthermore, it is possible to achieve "precise surface treatment" more efficiently by reducing the amount of surface treatment per time compared to the final target amount and repeating the steps.

[Coating liquid for film formation]
The particles of the present invention can be applied to a coating liquid for forming a coating film. This coating liquid contains particles, a matrix forming component, and an organic dispersion medium. In addition to these, the coating liquid may contain additives such as a polymerization initiator, a leveling agent, and a surfactant.

The concentration of particles in the coating solution is preferably 20 to 70% by mass in terms of solids, based on the total amount of solids, such as the particles and matrix-forming components, contained therein.

Here, if the particle concentration is less than 20% by mass, the hardness of the coating may be insufficient. Conversely, if it is more than 70% by mass, cracks may occur in the coating, adhesion to the substrate may be insufficient, and hardness, strength, transparency, haze, etc. may deteriorate. The particle concentration is more preferably 30 to 65% by mass, and even more preferably 40 to 60% by mass.

As the matrix-forming component, an organic resin-based matrix-forming component is suitable. Examples include components that form a matrix such as ultraviolet-curable resins, thermosetting resins, and thermoplastic resins.

Examples of UV-curable resins include (meth)acrylic resins, gamma-glycyloxy resins, urethane resins, vinyl resins, etc.

Thermosetting resins include urethane resin, melamine resin, silicon resin, butyral resin, reactive silicone resin, phenolic resin, epoxy resin, unsaturated polyester resin, and thermosetting acrylic resin.

Thermoplastic resins include polyester resin, polycarbonate resin, polyamide resin, polyphenylene oxide resin, thermoplastic acrylic resin, polyvinyl chloride resin, fluororesin, vinyl acetate resin, silicone rubber, etc.

These resins may be copolymers or modified products of two or more kinds, or may be used in combination. These resins may also be emulsion resins, water-soluble resins, or hydrophilic resins.

The components that form these resins are preferably monomers or oligomers, due to their particle dispersibility and ease of coating.

The concentration of the matrix-forming components in the coating solution is preferably 30 to 80% by mass in terms of solid content relative to the total amount of solid content, such as the particles and matrix-forming components, contained therein.

Here, if the concentration of the matrix-forming component is less than 30% by mass, it is difficult to form a coating. Even if a coating is obtained, there is a risk that the coating may crack, that adhesion to the substrate may be insufficient, and that hardness, strength, transparency, haze, etc. may deteriorate. Conversely, if it is more than 80% by mass, the amount of particles is small, and the hardness of the coating may be insufficient. The concentration of this matrix-forming component is more preferably 35 to 70% by mass, and even more preferably 40 to 60% by mass.

As the organic dispersion medium, one that can disperse particles uniformly and dissolve or disperse additives such as matrix-forming components and polymerization initiators is used. Among them, hydrophilic dispersion media and polar dispersion media are preferred. As shown in Table 2, examples of hydrophilic dispersion media include alcohols, esters, glycols, and ethers. Examples of polar dispersion media include esters and ketones. These may be used alone or in a mixture of two or more.

Any additive that can be used conventionally for film formation can be used. For example, polymerization initiators, leveling agents, etc. are used to promote polymerization of the matrix-forming components and improve film-forming properties.

Examples of polymerization initiators include those shown in Table 3.

Examples of leveling agents include acrylic leveling agents, silicone leveling agents, and acrylic silicone leveling agents. Among these leveling agents, those having a fluorine group are preferably used from the viewpoint of improving strength.

For the sake of convenience, the concentrations of these additives in the coating solution that are contained as solids when the coating is formed are counted as matrix-forming components, and after coating, they are counted as the matrix.

The solids concentration of the coating solution (the ratio of the total solids of the particles and the matrix-forming components to the coating solution) is preferably 1 to 60% by mass.

Here, if the solids concentration of the coating solution is less than 1% by mass, the coating may be difficult to apply due to low concentration stability, and a uniform coating may not be obtained. In addition, haze or poor appearance may result, which may reduce productivity and manufacturing reliability. Conversely, if the solids concentration is more than 60% by mass, the stability of the coating solution may be poor. In addition, the viscosity of the coating solution may increase, which may reduce coatability. Furthermore, the haze of the coating may increase, resulting in insufficient strength. The solids concentration of the coating solution is more preferably 5 to 50% by mass.

[Coated substrate]
The coating film is formed on a substrate using the above-mentioned coating liquid. From the viewpoint of visibility, the resulting coating film is preferably transparent.

Specifically, the coating liquid is applied onto the substrate, then drying and ultraviolet irradiation are performed to form a coating on the substrate. There are no particular limitations on the method of applying the coating liquid, as long as it can form a coating on the substrate. For example, well-known methods such as spraying, spinner, roll coating, bar coating, slit coater printing, gravure printing, and microgravure printing can be used. Drying is performed, for example, by heating to about 50 to 150°C to evaporate and remove the dispersion medium. After that, ultraviolet irradiation is performed to promote polymerization of the resin component and harden the coating. The coating is mainly formed of a matrix (resin) component and particles.

In the case of a coating, the ratio of the solid content of the particles and matrix-forming components in the coating liquid is the same as the ratio of the particle components and matrix in the coating. As mentioned above, any additives in the coating liquid that remain as solids are counted as matrix.

The thickness of the coating can be selected appropriately depending on the application. For example, for a hard coat film, a thickness of 0.5 to 20 μm is preferable.

Here, if the film thickness is less than 0.5 μm, the hardness and strength of the coating may be insufficient. Conversely, if the film thickness is greater than 20 μm, the film shrinks significantly, causing noticeable curling and insufficient adhesion to the substrate. Furthermore, if the shrinkage is very large, cracks may occur. This film thickness is more preferably 1 to 15 μm, and even more preferably 4 to 12 μm.

The light transmittance of the coated substrate is preferably 85.0% or more.

Here, if the light transmittance is less than 85.0%, the clarity of the image on a display device or the like may be insufficient. This light transmittance is more preferably 90.0% or more.

The haze of the coated substrate is preferably 1.0% or less, and more preferably 0.5% or less.

The strength (scratch resistance) of the coating is evaluated by rubbing it with #0000 steel wool at a load of 1 kg/ ^cm2 . It is preferable that no streaky scratches are observed on the surface of the coating after at least 40 rubbings. More preferably, the scratch resistance is such that no scratches are observed after 60 rubbings, and even more preferably, no scratches are observed after 100 rubbings.

The coating's pencil hardness should preferably be 3H or higher.

Here, if the hardness is less than 3H, the hardness is insufficient for a hard coat film. The pencil hardness is more preferably 4H or more, and even more preferably 5H or more.

Any known substrate can be used. For example, transparent resin substrates such as polycarbonate, acrylic resin, polyethylene terephthalate, triacetyl cellulose (TAC), polymethyl methacrylate resin, and cycloolefin polymer are preferred. These substrates have excellent adhesion to the coating formed by the above-mentioned coating liquid, and a substrate with a coating excellent in hardness, strength, etc. can be obtained. For this reason, it is suitable for use with thin substrates. There is no particular restriction on the thickness of the substrate, but it is preferably 20 to 100 μm, and more preferably 30 to 80 μm.

The adhesion between the coating and the substrate is determined by scratching the surface of the coated substrate with a knife into a grid pattern, adhering cellophane tape to the scratched pattern, and then peeling off the cellophane tape. The more grid patterns that remain, the more likely the coating will not peel off and the stronger the adhesion to the substrate, which is preferable.

It is also possible to use a coated substrate in which another coating is formed on such a substrate. Examples of other coatings include conventionally known anti-reflection films, primer films, high refractive index films, conductive films, etc.

The following describes an embodiment of the present invention.

[Example 1]
Preparation of Dispersion of Metal Oxide Particles
2000 g of an aqueous dispersion of silica particles (KGC Catalysts and Chemicals, Cataloid SI-30, solid content concentration 30% by mass) was subjected to ion exchange for 3 hours using 300 g of a cation exchange resin (Diaion SK-1BH, Mitsubishi Chemical Corporation), and then ion exchange for 3 hours using 200 g of an anion exchange resin (Diaion SA-20A, Mitsubishi Chemical Corporation). Thereafter, ion exchange was performed for 3 hours at 80° C. using 100 g of a cation exchange resin to prepare an aqueous dispersion of silica particles. Next, the dispersion medium was replaced with methanol by ultrafiltration, and the mixture was concentrated to prepare a methanol dispersion of silica particles having a solid content concentration of 30% by mass.

<Surface treatment of metal oxide particles with organosilicon compound (first step)>
To 2000 g of this methanol dispersion of silica particles, 4.4 g of 28% by mass ammonia water and 39.8 g of pure water were added, and the mixture was stirred at room temperature for 0.5 hours.

Next, 90 g (15 parts by mass of R _n -SiX _4-n per 100 parts by mass of silica particles) of γ-methacryloxypropyltrimethoxysilane (KBM-503 manufactured by Shin-Etsu Chemical Co., Ltd.) was added as an organosilicon compound, and the mixture was stirred at 50° C. for 19 hours to obtain a dispersion of surface-treated silica particles.

<Removal of organosilicon compounds (second step)>
This dispersion of surface-treated silica particles was cooled to room temperature, and 10 kg of methanol (equivalent to 5 times the amount of the methanol dispersion of silica particles) was used to remove "unreacted and physically adsorbed organosilicon compounds" by ultrafiltration membrane method, thereby producing a methanol dispersion of surface-treated silica particles of the present invention having a solid content concentration of 30 mass% as metal oxide particles.

The dispersion of surface-treated metal oxide particles was measured using the following method.

The characteristics of each manufacturing process of the particles, and the properties of the particles and dispersion liquid are shown in Table 4 (the same applies to the following examples and comparative examples).

(1) Organosilicon Compound Having a Functional Group The presence or absence of a functional group contained in the particles and the type of the functional group were determined by the following method.

First, the dispersion was dried in an evaporator and then dried at 150 ° C. The powder was measured by a diffuse reflectance method using a Fourier transform infrared spectrometer (FT-IR) (FT / IR-6100 manufactured by JASCO Corporation) in a wave number region of 700 cm ^-1 to 4000 cm ^-1 , a TGS detector, a resolution of 4.0 cm ^-1 , and an accumulation count of 50 times, and the peak was detected. The functional group was identified by referring to the organic compound spectrum database SDBS (https://sdbs.db.aist.go.jp (National Institute of Advanced Industrial Science and Technology, 2021.01)).

(2) Solid content of organosilicon compound having functional group
The dispersion was centrifuged for 30 minutes using a small ultracentrifuge (CS150GXL manufactured by Hitachi Koki Co., Ltd.) at a temperature of 10°C and a rotation speed of 1,370,000 rpm (1,000,000 G). The precipitate of the treatment solution was collected and dried by vacuum drying, and then the mass loss before and after heating at 500°C was measured using a thermogravimetric differential thermal analyzer (TG/DTA EXSTAR6000 MSD manufactured by Hitachi High-Tech Science Co., Ltd.), and the silicon content derived from the organosilicon compound was calculated from the difference with the amount of metal oxide particles. Next, this was converted from the structure of the organosilicon compound used in the surface treatment into the amount of solids derived from the organosilicon compound (R _n -SiO _(4-n)/2 ), and the solids content of the organosilicon compound having a functional group was calculated.

(3) Amount of organosilicon compound in the liquid after removing particles from the dispersion The dispersion was centrifuged in the same manner as described above using a small ultracentrifuge (CS150GXL manufactured by Hitachi Koki Co., Ltd.) The supernatant of the treated liquid was collected, and the amount of organosilicon compound in the liquid after removing particles was measured using a thermal extraction gas chromatograph (Agilent5977BGC/MSD manufactured by Agilent Technologies, Inc.).

(4) Average primary particle size of particles (D) and average primary particle size of metal oxide particles (F)
The particle dispersion was diluted to 0.01% by mass and then dried on a collodion film of a copper cell for an electron microscope. This was then photographed at a predetermined magnification using a field emission scanning electron microscope (S-5500, manufactured by Hitachi High-Technologies Corporation). The particle areas of 300 randomly selected particles in the obtained photographic projection (SEM image) were calculated by image processing, and the equivalent circle diameter was calculated from the area. The average value of the equivalent circle diameters was taken as the average primary particle diameter (D) of the particles.

The silica particle dispersion was also subjected to image analysis in the same manner to determine the average primary particle size (F) of the silica particles.

(5) Average particle size (L) measured by dynamic light scattering method
The dispersion was adjusted to an appropriate concentration using ethanol, and the particle size was measured using a dynamic light scattering particle size measurement device (FPAR-1000, manufactured by Otsuka Electronics Co., Ltd.) to obtain the average particle size (L). The appropriate concentration means a concentration at which the amount of scattered light is 15,000 to 30,000 CPS. The measurement was performed under the following conditions: a solvent refractive index of 1.3614 and a temperature of 20°C.

(6) Content of Metal Elements, Alkali Metals, and Alkaline Earth Metals The contents of metal elements (Si, Al, Sn, Sb, Ti, Zr, Zn, W, Fe, In, Ba), alkali metals, and alkaline earth metals in the particles and metal oxide particles were measured by dissolving the particles in hydrofluoric acid, heating to remove the hydrofluoric acid, adding pure water as necessary, and measuring the resulting solution using an ICP inductively coupled plasma optical emission spectrometer (ICP-8500, manufactured by Shimadzu Corporation).

(7) Specific surface area (A1) by pulsed NMR
Using a pulse NMR (Acorn Area manufactured by Xigo nanotools), the relaxation times of the dispersion and the dispersion medium were measured, and the specific surface area (A1) was calculated from the above formula (2). The measurement conditions were a magnetic field of 0.3 T, a measurement frequency of 13 MHz, a measurement nucleus of ¹ H NMR, a measurement method of CPMG pulse sequence method, a sample amount of 1 ml, a Ka value of 0.000039, and a temperature of 25 ° C. Here, the Ka value was calculated from the above formulas (4) to (6) by performing pulse NMR measurement on a methanol dispersion and a methanol dispersion medium of metal oxide particles (here, silica particles) with a solid content concentration of 30 mass% and 25 ° C.

(8) Specific surface area (A2)
The specific surface area (A2) was calculated using the average primary particle size (F) of the metal oxide particles according to the following formula (4).

A2=6000/Sd/F...Formula (4)
(In the formula, Sd represents the density (g/cm ³ ) of the metal oxide particles.)

<Production of Coating Solution for Film Formation>
The dispersion medium of the methanol dispersion of the produced surface-treated silica particles was replaced with methyl isobutyl ketone (MIBK) using centrifugation and ultrasonic dispersion methods to prepare an MIBK dispersion of surface-treated silica particles with a solid content concentration of 40 mass%.

6.00 g of the MIBK dispersion of these particles, 1.60 g of a multifunctional acrylate resin (Light Acrylate DPE-6A, manufactured by Kyoeisha Chemical Co., Ltd.), 0.10 g of a photopolymerization initiator (Omnirad 184, manufactured by IGM Resins B.V.), 0.10 g of an acrylic silicone leveling agent (Disparlon NSH-8430HF, manufactured by Kusumoto Chemical Co., Ltd., solids concentration 10% by mass), 1.20 g of MIBK, and 1.00 g of acetone were thoroughly mixed to produce a coating solution for forming a coating with a solids concentration of 40% by mass.

<Production of coated substrate>
This coating solution was applied to a TAC film (FT-PB40UL-M, 40 μm thick, manufactured by Fujifilm Corporation) using a bar coater method (#16), dried at 80° C. for 120 seconds, and then cured by irradiating with 300 mJ/ ^cm2 of ultraviolet light in a _N2 atmosphere to produce a coated substrate.

The coated substrate was measured for the following items. The results are shown in Table 5 (the same applies to the following Examples and Comparative Examples).

(9) Film Thickness The film thickness was determined as the average value of measurements taken at any five points on the film using a digital gauge (gauge stand ST-0230 and digital gauge counter DG-5100, manufactured by Ono Sokki Co., Ltd.).

(10) Haze and Total Light Transmittance The haze and total light transmittance of the coated substrate were measured using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

(11) Measurement of Scratch Resistance Using #0000 steel wool, the coating was rubbed a specified number of times under a load of 1 kg/ ^cm2 . After each number of rubs, the surface of the coating was visually observed. The results were classified into the following categories to evaluate the strength.
Evaluation criteria:
60 or more times: ◎
Between 40 and 60 times: ○
20 or more but less than 40 times: △
20 times or less: ×

(12) Pencil hardness The pencil hardness was measured using a pencil hardness tester in accordance with JIS K 5400. That is, a pencil was set at a 45 degree angle to the coating surface, and a specific load was applied and pulled at a constant speed to observe whether there was any damage. The hardness was evaluated by classifying it as follows.
Evaluation criteria:
4H or more: ◎
3H: ○
2H: △
H or less: ×

(13) Overall Evaluation of Strength and Hardness The scratch resistance and pencil hardness were evaluated and scored as follows.
◎: 4 points ○: 3 points △: 2 points ×: 1 point

Using these scores, a total score was calculated using the following formula, and an overall judgment was made by classifying the scores into four levels.

Total score calculation formula: (pencil hardness score) x (scratch resistance score)

The overall evaluation was as follows: "◎" or "○" was considered a pass.
12 or more and 16 or less: ◎
9 or more but less than 12 times: ○
6 or more but less than 9: △
Less than 6: ×

(14) Adhesion The surface of the coated substrate was scratched with a knife in 11 parallel lines spaced 1 mm apart to form 100 squares, to which cellophane tape was attached. The cellophane tape was then peeled off and the number of squares that remained without the coating was counted. The adhesion was evaluated by classifying the results as follows:
Evaluation criteria:
Number of remaining squares: 100
Number of remaining squares: 99 or less: ×

[Example 2]
In Example 1, after the second step, the first step and the second step were carried out again in this order to produce a methanol dispersion of surface-treated silica particles (the first step and the second step were repeated twice).

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 3]
A methanol dispersion of surface-treated silica particles was prepared in the same manner as in Example 2, except that 30 g of γ-methacryloxypropyltrimethoxysilane (5 parts by mass as R _n -SiX _4-n per 100 parts by mass of silica particles) was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 4]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 1, except that 300 g of γ-methacryloxypropyltrimethoxysilane (50 parts by mass of R _n -SiX _4-n per 100 parts by mass of silica particles) was used and the first and second steps were repeated 10 times in sequence.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 5]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 6 kg of methanol was used in the second step.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 6]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 4.8 kg of methanol was used in the second step.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 7]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 1,500 g of an aqueous dispersion of silica particles (Cataloid SI-80P manufactured by JGC Catalysts and Chemicals, Ltd., solid content concentration 40% by mass) was diluted with 500 g of water and used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 8]
The dispersion medium of 3,750 g of an aqueous dispersion of silica-alumina particles (JGC Catalysts and Chemicals Co., Ltd., Cataloid SN-350, solid content concentration 16% by mass) was replaced with methanol by ultrafiltration, and then the mixture was concentrated to prepare a methanol dispersion of silica-alumina particles with a solid content concentration of 30% by mass. A methanol dispersion of surface-treated silica-alumina particles was produced in the same manner as in Example 2, except that this dispersion was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 9]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 3,000 g of an aqueous dispersion of silica particles (Cataloid SI-550, manufactured by JGC Catalysts and Chemicals, Ltd., solid content concentration 20% by mass) was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 10]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 3,333 g of an aqueous dispersion of silica particles (Spherica Slurry SS-120, manufactured by JGC Catalysts and Chemicals, Ltd., solid content concentration 18% by mass) was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 11]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 1,500 g of an aqueous dispersion of silica particles (Cataloid SI-80P, manufactured by JGC Catalysts and Chemicals Co., Ltd.) was diluted with 500 g of water, and 18 g of γ-methacryloxypropyltrimethoxysilane (3 parts by mass as R _n -SiX _4-n per 100 parts by mass of silica particles) was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 12]
A dispersion medium of 3000 g of an aqueous dispersion of silica-alumina particles (Cataloid SN, manufactured by JGC Catalysts and Chemicals, Ltd., solid content concentration 20% by mass) was replaced with methanol by ultrafiltration, and then concentrated to prepare a methanol dispersion of silica-alumina particles with a solid content concentration of 30% by mass. A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that this dispersion was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 13]
4500g of titanium tetrachloride aqueous solution containing 2% by mass of titanium tetrachloride in terms of _TiO2 and 1760g of ammonia water with a concentration of 15% by mass were mixed to prepare a white slurry. The slurry was filtered and then washed with pure water to obtain 1800g of a cake with a solid content concentration of 5% by mass. 2056g of 35% by mass of hydrogen peroxide solution and 5144g of pure water were added to this, and heated at 80°C for 1 hour to obtain 9000g of a titanic acid peroxide aqueous solution containing 1% by mass of titanic acid in terms of _TiO2 .

Next, 9,000 g of this titanic acid peroxide aqueous solution was added to an aqueous dispersion of 92 g of an aqueous dispersion of silica alumina particles (Cataloid SN-350, manufactured by JGC Catalysts and Chemicals Co., Ltd.) diluted with 5,890 g of pure water. This aqueous dispersion was then heated at 165°C for 18 hours in an autoclave. Next, the resulting aqueous dispersion was cooled to room temperature and concentrated using an ultrafiltration membrane device. Next, ion exchange was performed using a cation exchange resin to obtain 10,472 g of an aqueous dispersion of titania silica particles with a solid content concentration of 1% by mass.

To this aqueous dispersion, 79.9 g of tetraethoxysilane (manufactured by Tama Chemicals Co., Ltd.) (22 parts by mass as R _n -SiX _4-n per 100 parts by mass of titania silica particles) having a SiO ₂ content of 28.8% by mass as an organosilicon compound and 10,472 g of methanol were added, and the mixture was stirred for 19 hours at 50° C. After cooling the dispersion to room temperature, the dispersion medium was replaced with methanol by ultrafiltration and the mixture was concentrated to prepare a methanol dispersion of titania silica particles having a solid content concentration of 30% by mass as metal oxide particles.

To 425.8 g of this methanol dispersion of titania silica particles, 2.3 g of 28% ammonia water and 10.5 g of pure water were added and stirred at room temperature for 0.5 hours. Next, 63.9 g of γ-methacryloxypropyltrimethoxysilane (50 parts by mass of R _n -SiX _4-n per 100 parts by mass of titania silica particles) was added as an organosilicon compound and stirred at 50° C. for 19 hours to obtain a dispersion of surface-treated titania silica particles.

This dispersion of surface-treated titania silica particles was cooled to room temperature, and 2.1 kg of methanol (equivalent to 5 times the amount of the methanol dispersion of titania silica particles) was used to remove "unreacted and physically adsorbed organosilicon compounds" by ultrafiltration membrane method.

Next, the surface was again treated with gamma-methacryloxypropyltrimethoxysilane as described above, and the "unreacted and physically adsorbed organosilicon compounds" were removed by ultrafiltration membrane method to produce a methanol dispersion of the surface-treated titania silica particles of the present invention having a solids concentration of 30 mass% as metal oxide particles.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Example 14]
A methanol dispersion of surface-treated silica particles was prepared in the same manner as in Example 2, except that γ-methacryloxyoctyltrimethoxysilane (KBM-5803, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the organosilicon compound.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Comparative Example 1]
A methanol dispersion of surface-treated silica particles was prepared in the same manner as in Example 1, except that 6 g of γ-methacryloxypropyltrimethoxysilane (1 part by mass as R _n -SiX _4-n per 100 parts by mass of silica particles) was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Comparative Example 2]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 1, except that the second step was not carried out and a molecular sieve (3A 1/16, manufactured by Kanto Chemical Co., Ltd.) was used to remove moisture and ammonia from the dispersion of surface-treated silica particles obtained in the first step to adjust the solid content concentration as metal oxide particles to 30 mass %.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Comparative Example 3]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 1, except that 2 kg of methanol (corresponding to one time the amount of the methanol dispersion of silica particles) was used in the second step.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

[Comparative Example 4]
A methanol dispersion of surface-treated silica particles was produced in the same manner as in Example 2, except that 3,750 g of an aqueous dispersion of silica particles (Spherica Slurry 160, manufactured by JGC Catalysts and Chemicals, Ltd., solid content concentration 16% by mass) was used.

Next, a coating solution and a coated substrate were produced in the same manner as in Example 1, except that this dispersion was used, and the properties were evaluated.

Claims (4)

A dispersion liquid of surface-treated metal oxide particles containing 3 to 60 parts by mass of an organosilicon compound having a functional group as a solid content per 100 parts by mass of metal oxide particles,
the organosilicon compound in the liquid remaining after removing the surface-treated metal oxide particles from the dispersion is 0.20 parts by mass or less in terms of solid content relative to the metal oxide particles;
the surface-treated metal oxide particles have an average primary particle size (D) of 5 to 120 nm as determined by image analysis, and the ratio (L/D) of the average particle size (L) of the surface-treated metal oxide particles as determined by dynamic light scattering to the average primary particle size (D) is 1.0 to 1.5;
a ratio (A1/A2) of a specific surface area (A1) of the surface-treated metal oxide particles determined by pulse NMR measurement of a methanol dispersion of the surface-treated metal oxide particles to a specific surface area (A2) of the metal oxide particles determined from an average primary particle diameter (F) of the metal oxide particles by image analysis is 0.30 to 0.80 . The dispersion according to claim 1, characterized in that the metal oxide particles contain at least one element selected from Si, Al, Sn, Sb, Ti, Zr, Zn, W, Fe, In, and Ba. A first step of surface-treating the metal oxide particles by adding an organosilicon compound represented by the following formula (1) to a dispersion liquid containing the metal oxide particles;
a second step of removing the organosilicon compound from the dispersion of surface-treated metal oxide particles obtained in the first step , the dispersion having a solid content concentration as metal oxide of 10 to 60 mass % , using a cleaning liquid amount per one time that is at least three times the amount of the dispersion ,
the surface-treated metal oxide particles in the dispersion obtained in the second step contain, as a solid content, 3 to 60 parts by mass of an organosilicon compound having a functional group per 100 parts by mass of the metal oxide particles;
the organosilicon compound in the liquid remaining after removing the surface-treated metal oxide particles from the dispersion is 0.20 parts by mass or less in terms of solid content relative to the metal oxide particles;
a ratio (L/D) of an average particle size (L) of the surface-treated metal oxide particles measured by a dynamic light scattering method to the average primary particle size (D) of the surface-treated metal oxide particles measured by an image analysis method is 1.0 to 1.5.
R _n -SiX _4-n (1)
(In the formula, R is an unsubstituted or substituted hydrocarbon group having 1 to 10 carbon atoms, X is an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom, and n is an integer of 0 to 4.) 4. The method for producing a dispersion liquid of surface-treated metal oxide particles according to claim 3 , wherein the first step and the second step are repeated in sequence after the second step.