Titanium oxide particle and production method thereof

The present invention relates to titanium oxide particles and a method for producing titanium oxide particles.

Titanium oxide has a high refractive index, white hiding property, and ultraviolet absorption ability, so it is a visible light transmitting ultraviolet light cut film for paints, cosmetics, automobiles and window glasses, and an air purification device using photocatalytic properties. , It is used in various fields such as semiconductor electrodes of dye-sensitized solar cells utilizing photoconductivity, white reflectors used for liquid crystal backlights, and the like.

Of these applications, the particle size of titanium oxide is visible light (wavelength 380 to 700 nm) for scattered particle applications in semiconductor electrodes of dye-sensitized solar cells that require appropriate light scattering properties and paints where concealment is important. And about half of the near infrared (700 to 1100 nm) is preferable. This is because the particle size, which is about half the wavelength, has a strong scattering ability as explained by Mie's light scattering theory. Therefore, in order to scatter visible light and light in the near-infrared region with titanium oxide particles in a monodisperse state, a particle size of about 150 nm to 600 nm is required.

However, the technique for producing the titanium oxide particles in the above-mentioned particle size range has not been sufficiently established, and it has been desired to establish highly scatterable titanium oxide particles excluding the dependence on the particle size.<patcit num="1"><text>Japanese Patent Application Laid-Open No. 63-229139</text></patcit>

<p> An object of the present invention is to provide novel titanium oxide particles having excellent light scattering ability from visible light to near infrared light.</p>

<p> In order to achieve the above object, the present invention has a plurality of radially extending extending portions, and the extending portions have a ridge at a substantially central portion in the length direction and exhibit a star shape as a whole. It relates to a characteristic titanium oxide particle.</p><p> Further, the present invention comprises a step of mixing a hydrolysis product of titanium alkoxide or a hydrolysis product of a titanium metal salt and organic alkalis in a predetermined solvent to prepare a reaction solution, and the reaction solution in a closed container. In addition to having a plurality of radially extending extending portions, the extending portion has a ridge at a substantially central portion in the length direction to produce titanium oxide particles having a star shape as a whole. The present invention relates to a method for producing titanium oxide particles.</p><p> The present inventors have conducted diligent studies to achieve the above object. As a result, by preparing a reaction solution composed of the above-mentioned raw materials and heating and reacting these raw materials, a plurality of radially extending extending portions are provided, and the extending portions have a ridge at a substantially central portion in the length direction. As a result, we succeeded in producing titanium oxide particles that have a star shape as a whole. The titanium oxide particles have a high scattering effect depending on the star shape and the particle size and the like. Therefore, it is excellent in light scattering ability of visible light to near infrared light.</p><p> The titanium oxide particles can be configured such that six extending portions are radially extended by variously controlling the production conditions in the production method described in detail below. In this case, the light scattering ability can be further improved. Further, the primary particle size can be set in the range of 100 nm to 1000 nm, and depending on the appearance shape and the particle size range, it has a high light scattering ability in the range from visible light to near infrared light.</p>

<p> As described above, according to the present invention, it is possible to provide novel titanium oxide particles having excellent light scattering ability, particularly excellent light scattering ability from visible light to near infrared light.</p>

Hereinafter, the details of the present invention, as well as other features and advantages, will be described in detail based on the best mode.

In producing the titanium oxide particles of the present invention, first, a hydrolysis product of titanium alkoxide or a hydrolysis product of a titanium metal salt and organic alkalis are mixed in a predetermined solvent to prepare a reaction solution.

Examples of the titanium alkoxide include tetraethoxytitanium, tetraisopropoxytitanium, tetranormalpropoxytitanium, and tetranormalbutoxytitanium. From the viewpoint of controllability of hydrolysis rate and availability, tetraisopropoxytitanium and tetranormalbutoxytitanium can be preferably used, and tetraisopropoxytitanium is particularly preferable. Moreover, as the titanium metal salt, titanium tetrachloride and titanium sulfate can be exemplified.

These hydrolysis products are cake-like substances of hydroxide-containing titanium called metatitanium acid and orthotitanium, and the inside of the cake contains alcohols, hydrochloric acid, and sulfuric acid produced in the process of hydrolysis. Since these substances become inhibitors during crystal growth, it is preferable to wash them with pure water using a method such as decantation, a nutche method, or an ultrafiltration method.

Further, examples of the organic alkalis include amines, high molecular weight amines and salts thereof, and ammonia. Examples of the amines include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium chloride, tetraethylammonium chloride, and tetrapropyl. Examples thereof include ammonium chloride, tetrabutylammonium chloride, octylamine, laurylamine, stearylamine and the like. Further, as the polymer amine and a salt thereof, a polymer amine composed of the amines and a salt thereof can be exemplified. The organic alkalis act as a pH adjuster for the reaction solution.

Further, the solvent is not particularly limited, but water is preferable.

The pH in the reaction solution is preferably 9 to 11, and more preferably 9.5 to 10.5. This makes it possible to easily obtain titanium oxide particles in which six extending portions, which are a preferred embodiment of the titanium oxide particles of the present invention, extend radially at substantially equal intervals from each other. Further, the primary particle size can be set in the range of 100 nm to 1000 nm, and titanium oxide particles having a high light scattering ability in the visible light to near infrared range can be produced depending on the appearance shape and the particle size range. You will be able to get it. The pH in the reaction solution is adjusted by controlling the concentration of the organic alkalis.

The titanium atom concentration in the reaction solution is preferably in the range of 0.05 mol / L to 10 mol / L, and particularly preferably in the range of 0.1 mol / L to 2.5 mol / L. Since the titanium atom concentration directly affects the particle size of the formed titanium oxide particles, it is necessary to appropriately set it according to the desired particle size of the titanium oxide particles. However, by setting the titanium atom concentration as described above, , Titanium oxide particles having a primary particle size in the range of 100 nm to 1000 nm can be easily produced. The titanium atom concentration can be controlled by appropriately adjusting the concentration of the hydrolysis product of titanium alkoxide or the hydrolysis product of titanium metal salt in the reaction solution.

Further, by setting the pH and titanium atom concentration of the reaction solution to the preferable ranges as described above, the reaction solution is generally in the form of a slurry.

Then, in the present invention, the reaction solution is heated in a closed container such as stainless steel. In this case, the hydrolysis product of titanium alkoxide or the hydrolysis product of titanium metal salt in the reaction solution is decomposed under high temperature and pressure, and the crystal growth of the obtained titanium source proceeds, which is the target. Star-shaped titanium oxide particles can be obtained.

The heat treatment is preferably performed in a temperature range of 120 ° C to 350 ° C, further preferably 200 ° C to 350 ° C, and further preferably in a temperature range of 230 ° C to 350 ° C. The heat treatment time is preferably 2 hours or more, and more preferably 12 hours to 36 hours. Further, in such a heat treatment, the heating rate from room temperature to the above temperature range is not particularly limited, but is preferably 100 ° C./hour or less. Further, in the heat treatment, from the viewpoint of homogenizing the crystallinity, it is preferable to forcibly stir the reaction solution using a stirrer, a stirring blade or the like.

Further, a preliminary heat treatment can be performed before the heat treatment. In addition to the star-shaped titanium oxide particles of the present invention, granular titanium oxide particles may be formed only by the above-mentioned heat treatment, and the yield of producing the target star-shaped titanium oxide particles is lowered. May be done. On the other hand, by performing the preliminary heat treatment in addition to the heat treatment, the formation ratio of the granular titanium oxide particles can be reduced, and the production yield of the star-shaped titanium oxide particles can be improved. become.

The preheat treatment is preferably performed in a temperature range of 70 ° C to 150 ° C, further preferably 80 ° C to 120 ° C, and further preferably 100 ° C to 120 ° C. The preheating time is preferably 1 hour or more, and more preferably 2 hours to 4 hours. Further, also in this case, from the viewpoint of homogenizing the crystallinity, it is preferable to forcibly stir the reaction solution using a stirrer, a stirring blade or the like.

By going through the above-mentioned production steps, the star-shaped titanium oxide particles of the present invention can be obtained. Further, in the above-mentioned production step, by adopting a preferred embodiment for the pH of the reaction solution and the like, a star-shaped titanium oxide particle having six extending portions radially extending, which is a preferred embodiment of the present invention, can be obtained. Can be done.

In the star-shaped titanium oxide particles, each extending portion is composed of anatase single phase, and as a result, twin crystals are exhibited as a whole. Titanium oxide has a crystal phase such as a brookite phase, an anatase phase and a rutile phase, but since the anatase phase is a semi-stable phase, when heat treatment is performed to form titanium oxide particles having a certain size, the above-mentioned The anatase phase shifts to the stable phase, the rutile phase. As a result, when trying to obtain titanium oxide particles having a primary particle size of 100 nm or more regardless of the shape of the titanium oxide particles, the titanium oxide particles contain a rutile phase. Therefore, the present invention can provide titanium oxide particles having a primary particle size in the range of 100 nm to 1000 nm and composed of anatase single phase, so that titanium oxide particles composed of a crystal phase other than the rutile phase can be obtained. It is also important from the point of view. Further, by adjusting the conditions, each extending portion becomes a single crystal.

The titanium oxide particles can also be used by adding a water-soluble resin or an additive to the liquid phase in which the titanium oxide particles remain. It can also be dried and pulverized by methods such as spray drying, freeze drying, nutche, hot air drying, evaporator, vacuum drying, therma jet drying, and centrifugation. Further, it can be directly used as a non-aqueous dispersion or suspension from the state of the liquid phase by a flushing method or solvent substitution. In this case, residual alcohols, amines, etc. during particle synthesis may be used in the state of the dispersion or suspension by decantation, nutche washing, ultrafiltration, microfiltration, centrifugation, or the like. It is also possible to remove impurities derived from additives.

(Paint) The titanium oxide particles of the present invention produced as described above and having the above-mentioned characteristics are particularly light scattered from visible light to near-infrared light due to their appearance shape and particle size. Excellent in ability. Therefore, it can be suitably used as a paint.

By dispersing the titanium oxide particles of the present invention in a solvent to form a coating material, it is possible to form a film having excellent light scattering property, reflectivity, photocatalytic property, ultraviolet shielding property, etc., and particularly excellent whiteness. it can.

The coating material containing titanium oxide particles of the present invention may contain a solvent,, if necessary, a binder component, a dispersant, a surface treatment agent, other inorganic particles, organic particles, and the like.

The solvent may be water or an organic solvent, and is not particularly limited. Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, butanol, diacetone alcohol, isopropyl alcohol, furfuryl alcohol, ethylene glycol and hexylene glycol, esters such as acetate methyl ester and acetate ethyl ester, and diethyl. Ethers, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and other ethers, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, acetoacetate ester and other ketones, toluene , Ethyl acetate, butyl acetate, cyclohexane, xylene, cellosolve acetate and the like. These can be used alone or in admixture of two or more.

The binder may be either an organic binder or an inorganic binder. Examples of the organic binder include acrylic resin, alkyd resin, urethane resin, polyester resin, fluororesin, silicone resin, polyamideimide, epoxy resin, amino resin, butyral resin, urea-melamine resin, and phenol resin. Vinyl chloride resin, vinyl acetate resin, polyacetal resin, polycarbonate resin, styrol resin, polyvinyl acetal resin, polyvinyl butyral resin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, polyacrylamide, cluster dextrin, chitosan, Examples thereof include cellulose-based resins such as alginate, carboxymethyl cellulose and hydroxyethyl cellulose, styrene-acrylic copolymers, styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, polypropylene and the like.

Examples of the inorganic binder include metal alkoxides such as Si, Al, and Zr, hydrolysates of these metal alkoxides, and metal oxide sol such as silica sol and alumina sol.

Examples of the dispersant include coupling agents such as silane-based, titanate-based and zircoaluminate-based, metal chelated products, organometallic compounds such as metal alkoxide, and polyoxyethylene alkyl phosphates for the purpose of improving dispersibility. A surfactant such as polyesterate, a commercially available resin-type dispersant, or the like may be added. Further, the surface may be coated with a silicone resin or the like.

If necessary, silica (SiO)₂), Alumina (Al₂O₃), Zirconia (ZrO)₂), Magnesia (MgO), zinc oxide (ZnO), aluminum hydroxide, barium sulfide, magnesium silicate and other inorganic particles, acrylic, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and other resin beads, etc. The organic particles of the above, flame retardant, colorant, conductive agent and the like may be contained.

The coating material using the titanium oxide particles of the present invention is obtained by mixing and dispersing each of the above components in the solvent. As a mixing / dispersing method, a usual method such as a ball mill or a high-speed bead mill can be used.

The blending amount of the titanium oxide in the coating material of the present invention is not particularly limited, but is preferably 0.1 to 80% by weight, more preferably 10 to 40% by weight. The dispersant is blended in an amount of 0.5 to 2% as a guide. The binder component is preferably 10 to 80% by weight, more preferably 10 to 40% by weight.

The paint using the titanium oxide particles of the present invention is applied onto a base material, and if necessary, dried and heated to form a film having excellent light scattering properties, whiteness, reflectivity, photocatalytic properties, ultraviolet shielding properties, and the like. can do.

The base material is not particularly limited, and can be applied to an inorganic base material such as glass, ceramics and metal, and an organic base material such as a plastic film and a plastic plate. The material of the plastic film and the plastic plate is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acrylic resins, polycarbonates, polystyrenes, polyolefins, cellulose acetates, vinyl chlorides and the like.

As the coating method, a usual coating method such as spin coating, spray coating, or screen printing can be used. As the heating temperature after coating, a temperature suitable for the base material and the binder can be appropriately selected.

(Resin Composition) The titanium oxide particles of the present invention are excellent in light scattering property, reflectivity, photocatalytic property, ultraviolet ray shielding property, and particularly excellent in whiteness by being directly contained and dispersed in the resin by kneading or the like. The resin composition can be formed.

Examples of the resin include acrylic resin, alkyd resin, urethane resin, polyester resin, fluorine resin, silicone resin, polyamideimide, epoxy resin, amino resin, butyral resin, urea-melamine resin, phenol resin, vinyl chloride resin. , Vinyl acetate resin, polyacetal resin, polycarbonate resin, styrene resin, polyvinyl acetal resin, polyvinyl butyral resin, polyvinyl alcohol, modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, polyacrylamide, cluster dextrin, chitosan, alginate, carboxymethyl cellulose and hydroxyethyl cellulose. Cellular resin such as, styrene-acrylic copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polypropylene, ABS resin, polyethylene, vinylidene chloride, polystyrene, nylon, EVA resin, polyamide resin, melamine resin , Uria resin, silicone resin, polystyrene resin and the like.

If necessary, silica (SiO)₂), Alumina (Al₂O₃), Zirconia (ZrO)₂), Magnesia (MgO), zinc oxide (ZnO), aluminum hydroxide, barium sulfide, magnesium silicate and other inorganic particles, acrylic, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and other resin beads, etc. The organic particles of the above, flame retardant, colorant, conductive agent and the like may be contained.

As a mixing / dispersing method, a paint shaker, a roll mill, a sand mill, a ball mill, an attritor, a jet mill, a homogenizer or the like can be used. Further, in the dispersion step, for the purpose of improving dispersibility, coupling agents such as silane-based, titanate-based and zircoaluminate-based, metal chelated products, organometallic compounds such as metal alkoxide, polyoxyethylene alkyl phosphates, etc. A surfactant such as polyesterate, a commercially available resin-type dispersant, or the like may be added. Further, the surface may be coated with a silicone resin or the like.

(Plastic film, plastic plate) Using the titanium oxide particles of the present invention, a plastic film such as a white reflective film and a light scattering film, and a plastic plate such as a light scattering plate and a white reflecting plate can be formed.

White reflectors, white reflectors, light scattering films, and light scattering plates are widely used in various fields, and high-performance characteristics are required. In particular, in the liquid crystal field, it is used in various applications such as a backlight, a light guide plate, a light diffusing plate, and a reflector in a liquid crystal display device.

The titanium oxide particles of the present invention can be obtained, for example, by applying the above-mentioned paint on a plastic film or a plastic plate to form a film, or after preparing the above-mentioned resin composition, the above-mentioned resin composition is formed into a film or formed. It can be obtained by processing it into a plate shape.

When a plastic film or a plastic plate is formed by applying the paint, the base material is not particularly limited, but a polyester resin such as polyethylene terephthalate or polyethylene naphthalate is preferable. In this case, the particle size of the titanium oxide particles of the present invention is preferably 100 nm to 500 nm.

Further, in any of the above cases, in the case of anatase-type titanium oxide, titanium oxide has a property of absorbing ultraviolet rays and decomposing organic substances. Therefore, if necessary, the decomposing power can be reduced by coating the particle surface with another element. Examples of the other element include Zr, Si, Ta, Y, Sr, Al and the like. As a coating method, for example, titanium oxide particles are dispersed in hydrochloric acid or nitric acid aqueous solution and heated, or as a simple treatment, the powder is treated in a saturated steam atmosphere to adsorb hydroxyl groups on the particle surface. .. Then, after removing excess water on the surface of the particles by performing vacuum treatment, the other element is chemically bonded to the surface by dispersing in a metal alkoxide solution of the other element, and then dried. Stabilize.

On the other hand, when a plastic film or a plastic plate is formed by processing the resin composition, for example, it is carried out according to the following steps. First, the titanium oxide particles of the present invention and the polyester resin to which various additives are added are melted at 260 to 350 ° C, discharged from the mouthpiece, and cooled into a film on a cooling drum at 5 to 50 ° C. , Mold. When stretching uniaxially or biaxially, the stretching temperature is preferably 70 to 150 ° C and the stretching ratio is 2.5 to 5 times as the conditions for longitudinal stretching, and when stretching over biaxially, the stretching temperature is 70 as the condition for transverse stretching. It is preferably ~ 150 ° C and a draw ratio of 2.5 to 5 times, and heat fixing is preferably performed at 100 to 250 ° C.

At this time, the content of the titanium oxide particles in the resin composition is preferably 0.1 wt% to 50 wt%, more preferably 3 wt% to 30 wt%. If the content of the titanium oxide particles is less than 1 wt%, the whiteness of the obtained film or plate may not be sufficient. On the other hand, if the content of the titanium oxide particles exceeds 50% by weight wt%, molding becomes difficult when the film or plate is formed, or the titanium oxide particles are likely to fall off from the surface.

If necessary, the titanium oxide particles of the present invention are surface-treated with TEOS (tetraethoxysilane) or the like before being mixed in the resin.

(Other Application Examples) As described above, the titanium oxide particles of the present invention are particularly excellent in light scattering ability from visible light to near infrared light due to their appearance shape and particle size. Therefore, in addition to the above-mentioned paints, it is also useful for UV protection inks and photographic photoconductors. When the titanium oxide particles of the present invention are used for these purposes, various solvents, binders, various additives and fillers can be mixed with the titanium oxide particles.

For example, when used as an ultraviolet protection ink, it is used in the form of a liquid or paste dispersed in a solvent such as water, alcohols, carbitols, and glycols. At this time, in order to improve the smoothness and adhesion strength of the coating film, it is possible to add a dispersant, a synthetic resin binder such as polyvinyl alcohol, polyacetal, acrylic resin, polyester resin, epoxy resin, or phenol resin, or an inorganic binder such as silica. preferable. A metal stearate salt or a metal naphthenic acid salt can also be added to control the drying of the coating film.

(Preparation and Evaluation of Star-shaped Titanium Oxide Particles) [Example 1]

250 mL of pure water cooled to 10 ° C was placed in a glass container having a capacity of 1 L, and 71 g of titanium tetraisopropoxide manufactured by High Purity Chemical Co., Ltd. was added dropwise using a dropping funnel while stirring at 300 rpm with a stirring blade. After stirring for 1 hour, the titanium tetraisopropoxide was hydrolyzed to a white aqueous suspension. This white aqueous suspension was suction-filtered with Nutche and filter paper No. 2 manufactured by Toyo Filter Paper Co., Ltd., and then washed with 500 mL of pure water to obtain a white cake-like substance. This white cake-like substance and 1.4 g of a 26% aqueous solution of tetramethylammonium hydroxide manufactured by Tokyo Kasei Co., Ltd. were added to pure water to bring the total amount to 200 g. The obtained reaction solution was in the form of a slurry and had a pH of 10.23. The titanium atom concentration in the reaction solution was 1.25 mol / L.

Next, the reaction solution was placed in a closed container and preheated at 120 ° C. for 4 hours with stirring, and then heat-treated at 270 ° C. for 12 hours to prepare an aqueous suspension containing titanium oxide particles. Obtained. The aqueous suspension was filtered and washed, and the obtained washing cake was dried at 120 ° C. for 24 hours to obtain powdered titanium oxide particles.

[Comparative example 1]

Titanium oxide particles were prepared by performing preliminary heat treatment and heat treatment in the same manner as in Examples except that the reaction solution was prepared without adding tetramethylammonium hydroxide. The pH of the reaction solution in this comparative example was 8.2. The titanium atom concentration in the reaction solution was 1.25 mol / L.

[Comparative example 2]

Titanium oxide particles were prepared by performing preliminary heat treatment and heat treatment in the same manner as in Examples except that 5 g of nitric acid 1.42 manufactured by Wako Pure Chemical Industries, Ltd. was added in place of tetramethylammonium hydroxide. The pH of the reaction solution in this comparative example was 2.0. The titanium atom concentration in the reaction solution was 1.25 mol / L.

[Test Example 1]

In order to analyze the titanium oxide particles produced in the above Examples and Comparative Examples 1 and 2, the particle shape was measured with an electron microscope, and the crystal phase was identified by powder X-ray diffraction. The evaluation results are shown in Table 1. In the examples, it was found that twin titanium oxide particles having a star shape, a primary particle size of 200 nm to 350 nm, and each extending portion exhibiting an anatas single phase were obtained. Further, in Comparative Example 1, it was found that granular titanium oxide particles composed of anatas single phase having a primary particle size of about several tens of nm were obtained. Further, in Comparative Example 2, it was found that titanium oxide particles in which an anatas phase and a rutile phase having a primary particle size of several tens of nm were mixed were obtained.

<tables num="1"><img file="JP2005298316A_D0001.tif" /></tables>

The SEM photograph of the titanium oxide particles obtained in this example is shown in FIG. 1, and the TEM photograph is shown in FIG. Moreover, the graph of the X-ray diffraction pattern of the titanium oxide particle in this Example is shown in FIG.

[Test Example 2]

With the titanium oxide particles of the above Examples and Comparative Examples 1 and the granular titanium oxide particles composed of anatase single phase having a primary particle size of 20 nm and an average aggregation particle size of 300 nm (manufactured by Wako Pure Chemical Industries, Ltd .: Comparative Example 3). The light scattering property was investigated. First, a vehicle was prepared by dissolving 5 g of ethyl cellulose 45 (manufactured by Kanto Chemical Co., Inc.) in 70 g of α-terpineol (manufactured by Kanto Chemical Co., Inc.) with a homogenizer. Next, 25 g of the titanium oxide particles obtained in Examples and Comparative Example 1 and 25 g of the titanium oxide particles of Wako Pure Chemical Industries, Ltd. were added to the vehicle while stirring with a homogenizer. Next, the titanium oxide paste thus obtained was kneaded with a three-roll mill to obtain a printing paste.

The print paste was then screen-printed on 1.1 mm thick Pyrex® glass using a 350 mesh stainless steel screen and then fired for 30 minutes in an electric furnace held at 500 ° C. As a result, the printed paste portion on the Pyrex (registered trademark) glass became a white translucent to opaque porous titanium oxide film having a film thickness of 2 μm. Next, the light reflectance of each wavelength of the porous titanium oxide film was measured by an ultraviolet-visible near-infrared spectrometer attached to an integrating sphere. The results are shown in Table 2.

<tables num="2"><img file="JP2005298316A_D0002.tif" /></tables>

As is clear from Table 2, it was found that the star-shaped titanium oxide particles obtained in the examples exhibited a high reflectance of 40% or more at all wavelengths. Further, although the titanium oxide particles in Comparative Example 3 are granular, it can be seen that they have a reflectance of 20% or more at all wavelengths because their average aggregated particle size is about 300 nm. Further, comparing Examples and Comparative Example 3, although the particle size of the titanium oxide particles is almost the same, the titanium oxide particles in the examples exhibit a high reflectance by exhibiting a star-shaped appearance. You can see that. On the other hand, it was found that the titanium oxide particles of Comparative Example 2 having a primary particle size of several tens of nm and exhibiting a granular appearance had a low reflectance of about 10% at each wavelength.

(Application of star-shaped titanium oxide particles to paint) [Example 2]

20% by weight of the anatase-type star-shaped titanium oxide particles (approximately hexagonal) of the present invention having a primary particle diameter of 200 nm to 300 nm in a mixed solution of isopropyl alcohol, t-butanol, and acetone, and Triton-X, a polyoxyethylene dispersant. 5% by weight and 25% by weight of acrylic resin were mixed, 1 mm diameter glass beads were added in the same amount as the volume of the mixed solution, and dispersion was performed at 2500 rpm for 3 hours using a high-speed bead mill to obtain a paint. Using this paint, an acrylic substrate preheated to 50 ° C was applied by a spin coating method and dried at 70 ° C to obtain an acrylic plate with a white film having a thickness of 3 μm.

[Comparative example 4]

An acrylic plate with a film was prepared in the same manner as in Example 2 except that commercially available anatase particles manufactured by Wako with an average primary particle diameter of 200 nm were used instead of the anatase-type star-shaped titanium oxide particles of the present invention. Got

(Evaluation of whiteness) The whiteness of the acrylic plate with a film obtained as described above was measured using a color difference meter (GC-5000, manufactured by Nippon Denshoku Co., Ltd.). The results are shown in Table 3.

<tables num="3"><img file="JP2005298316A_D0003.tif" /></tables>

As is clear from Table 3, it can be seen that the film made of the coating material containing the star-shaped titanium oxide particles of the present invention is particularly excellent in whiteness as compared with the conventional film containing titanium oxide particles.

(Application of star-shaped titanium oxide particles to a plastic film) [Example 3]

25 wt% of the anatase-type star-shaped titanium oxide particles (approximately hexagonal) of the present invention having a primary particle diameter of 100 to 500 nm whose surface is coated with silicon alkoxide is mixed with a polyester resin, melted at 260 to 350 ° C, and then melted from the base. The polyester resin containing the titanium oxide particles was formed into a film by discharging, applying the mixture on a cooling drum at 25 ° C., and then cooling the mixture. Next, the film-shaped polyester resin was subjected to a biaxial stretching step to obtain a white film having a film thickness of 150 μm. In the biaxial stretching step, the stretching temperature was 100 ° C, the stretching ratio was 3 times, and the heat fixation was 200 ° C.

Next, the whiteness of the obtained film was measured using a color difference meter (GC-5000, manufactured by Nippon Denshoku Co., Ltd.), and the reflectance was measured using an ultraviolet-visible near-infrared spectrophotometer (UV-3100, manufactured by Shimadzu Corporation). The evaluation was made using the average value of 300 nm to 700 nm. The results are shown in Table 4.

[Comparative example 5]

A white film was prepared in the same manner as in Example 3 except that rectangular anatase particles manufactured by Wako with an average primary particle diameter of 200 nm were used instead of the anatase-type star-shaped titanium oxide particles of the present invention, and whiteness and reflection were produced. The rate was evaluated. The results are shown in Table 4.

<tables num="4"><img file="JP2005298316A_D0004.tif" /></tables>

As is clear from Table 4, the white film containing the star-shaped titanium oxide particles of the present invention has a higher degree of whiteness than the conventional white film containing titanium oxide particles, and is due to its star-shaped shape. It can be seen that it exhibits high reflectance.

Although the present invention has been described in detail based on the embodiments of the invention by giving specific examples, the present invention is not limited to the above contents, and any modification or modification as long as it does not deviate from the scope of the present invention. It can be changed.

<figref num="1">It is an SEM photograph which shows an example of the titanium oxide particle of this invention.</figref><figref num="2">It is a TEM photograph which shows an example of the titanium oxide particle of this invention.</figref><figref num="3">It is an X-ray diffraction profile of an example of the titanium oxide particle of this invention.</figref>