JP4382607B2 - Titanium oxide particles - Google Patents

Description

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

  Titanium oxide has a high refractive index and white concealment, and also has UV absorption capability, so it can be used in paints, cosmetics, visible light transmitting UV light cut films for automobiles and window glass, and in-air purification equipment using photocatalytic properties. It is used in various fields such as a semiconductor electrode of a dye-sensitized solar cell using photoconductivity, a white reflector used for a backlight of liquid crystal, and the like.

  Among these uses, the particle size of titanium oxide is visible light (wavelength: 380 to 700 nm) in coatings where concealment is important and for scattering particles in semiconductor electrodes of dye-sensitized solar cells that require appropriate light scattering properties. About half of the near infrared (700 to 1100 nm) is preferable. This is because, as explained in Mie's light scattering theory, a particle size of about half the wavelength has a strong scattering ability. Therefore, in order to scatter visible light and near-infrared light with monodispersed titanium oxide particles, a particle size of about 150 nm to 600 nm is required.

However, a technique for producing titanium oxide particles having the above-mentioned particle size range has not been sufficiently established, and establishment of highly scattering titanium oxide particles that eliminate the dependency on the particle size has been desired.
JP-A-63-229139

  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.

In order to achieve the above object, the present invention provides:
While having a plurality of extending portions extending radially, the extending portion has a ridge at a substantially central portion in the length direction, and has a star shape as a whole ,
The plurality of extending portions are composed of six extending portions, and the six extending portions extend radially at substantially equal intervals from each other .

  The inventors of the present invention have intensively studied to achieve the above object. As a result, by preparing a reaction solution composed of the above-described raw materials and reacting these raw materials with heating, the raw material has a plurality of radially extending portions, and the extending portions are ridges at substantially the center in the length direction. As a result, titanium oxide particles having a star shape as a whole were successfully produced. The titanium oxide particles have a high scattering effect without depending largely on the particle diameter or the like depending on the star shape. Accordingly, the light scattering ability from visible light to near infrared light is excellent.

  The titanium oxide particles can have a configuration in which six extending portions extend radially by controlling various production conditions in a production method described in detail below. In this case, the light scattering ability can be further improved. Moreover, the primary particle diameter can be made into the range of 100 nm-1000 nm, and it comes to have a high light-scattering ability in the range from visible light to a near infrared depending on the external appearance shape and a particle size range.

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

  The details of the present invention and other features and advantages will be described in detail below based on the best mode.

  In preparing the titanium oxide particles of the present invention, first, a hydrolysis product of titanium alkoxide or a hydrolysis product of titanium metal salt and an organic alkali 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. Examples of the titanium metal salt include titanium tetrachloride and titanium sulfate.

  These hydrolysis products are hydrous titanium oxide cake-like substances called metatitanic acid or orthotitanium, and the cake contains alcohols, hydrochloric acid, and sulfuric acid produced during the hydrolysis process. Since these substances become inhibitory substances during crystal growth, it is preferable to use pure water and wash using a method such as decantation, Nutsche method, or ultrafiltration method.

  Examples of the organic alkalis include amines, polymer 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, tetrapropyl. Examples include ammonium chloride, tetrabutylammonium chloride, octylamine, laurylamine, stearylamine and the like. Examples of the polymer amine and salts thereof include polymer amines composed of the amines and salts thereof. The organic alkalis function 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, more preferably 9.5 to 10.5. This makes it possible to easily obtain titanium oxide particles in which six extending portions, which are preferred embodiments of the titanium oxide particles of the present invention, extend radially at substantially equal intervals. Moreover, the primary particle diameter can be made into the range of 100 nm-1000 nm, and the titanium oxide particle which has a high light-scattering ability in the range from visible light to a near infrared depending on the external appearance shape and a particle size range. Be able to get. 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, 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 titanium oxide particles to be formed, it is necessary to set the titanium atom concentration appropriately according to the desired particle size of the titanium oxide particles. , 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 within the preferable ranges as described above, the reaction solution generally becomes a slurry.

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

  In addition, it is preferable to perform the said heat processing in the temperature range of 120 to 350 degreeC, Furthermore, it is 200 to 350 degreeC, Furthermore, it is preferable to carry out in the temperature range of 230 to 350 degreeC. The heat treatment time is preferably 2 hours or longer, and more preferably 12 hours to 36 hours. In this 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. Furthermore, in the heat treatment, it is preferable to forcibly stir the reaction solution using a stirrer or a stirring blade from the viewpoint of homogenization of crystallinity.

  In addition, a preliminary heat treatment can be performed before the heat treatment. In addition to the above-mentioned star-shaped titanium oxide particles of the present invention, granular titanium oxide particles may be formed only by the heat treatment described above, and the production yield of the target star-shaped titanium oxide particles is reduced. There is a case. 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 is reduced, and the production yield of the star-shaped titanium oxide particles can be improved. become.

  In addition, it is preferable to perform the said preheating process in the temperature range of 70 degreeC-150 degreeC, Furthermore, 80 degreeC-120 degreeC Furthermore, it is preferable in the temperature range of 100 degreeC-120 degreeC. The preheating time is preferably 1 hour or longer, and more preferably in the range of 2 hours to 4 hours. Further in this case, it is preferable to forcibly stir the reaction solution using a stirrer or a stirring blade from the viewpoint of homogenization of crystallinity.

  Through the manufacturing steps as described above, the star-shaped titanium oxide particles of the present invention can be obtained. Further, in the above-described production process, by taking a preferred embodiment in terms of the pH of the reaction solution, etc., it is possible to obtain star-shaped titanium oxide particles having six extending portions radially extending, which is a preferred embodiment of the present invention. Can do.

  Each of the extending portions of the star-shaped titanium oxide particles is composed of anatase single phase, and as a result, twins are formed as a whole. Titanium oxide has a crystalline phase such as a brookite phase, anatase phase and rutile phase, but since the anatase phase is a metastable phase, when heat treatment is performed to form titanium oxide particles of a certain size, The anatase phase transitions to the rutile phase, which is a stable phase. As a result, regardless of the shape of the titanium oxide particles, when obtaining titanium oxide particles having a primary particle size of 100 nm or more, the titanium oxide particles contain a rutile phase. Therefore, since 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 a single anatase phase, titanium oxide particles composed of a crystal phase other than the rutile phase can be obtained. It is also important from a viewpoint. Moreover, each extension part turns into a single crystal by adjustment of conditions.

  The titanium oxide particles can be used by adding a water-soluble resin or an additive to the liquid phase in which the titanium oxide particles remain. Moreover, it can also be dried and powdered by methods such as spray drying, freeze drying, Nutsche, hot air drying, evaporator, vacuum drying, thermal jet drying, and centrifugal separation. Further, it can be directly used as a non-aqueous dispersion or suspension from the liquid phase state by a flushing method or solvent replacement. In this case, residual alcohols and amines at the time of particle synthesis can be obtained by decantation, Nutsche washing, ultrafiltration, microfiltration, centrifugation, etc. in the state of the dispersion or the suspension. Impurities derived from additives can also be removed.

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

  The titanium oxide particles of the present invention are excellent in light scattering properties, reflectivity, photocatalytic properties, ultraviolet shielding properties, and the like, and can form a film with particularly excellent whiteness by being dispersed in a solvent to form a paint. it can.

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

  As the solvent, water or an organic solvent can be used, and there is no particular limitation. Examples of the organic solvent include methanol, ethanol, propanol, butanol, diacetone alcohol, isopropyl alcohol, furfuryl alcohol, alcohols such as ethylene glycol and hexylene glycol, esters such as acetic acid methyl ester and ethyl acetate, 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 and other ketones, toluene , Ethyl acetate, butyl acetate, cyclohexane, xylene, cellosolve Tate, and the like. These may be used alone or in combination of two or more.

  As the binder, either an organic binder or an inorganic binder may be used. Examples of organic binders include acrylic resins, alkyd resins, urethane resins, polyester resins, fluorine resins, silicone resins, polyamideimides, epoxy resins, amino resins, butyral resins, urea-melamine resins, phenol resins, Vinyl chloride resin, vinyl acetate resin, polyacetal resin, polycarbonate resin, styrene resin, polyvinyl acetal resin, polyvinyl butyral resin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol, silicon modified polyvinyl alcohol, polyacrylamide, cluster dextrin, chitosan, Cellulose resins such as alginate, carboxymethylcellulose and hydroxyethylcellulose, styrene-acrylic copolymer, styrene-butadiene copolymer Body, ethylene - vinyl acetate copolymer, and polypropylene.

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

  Examples of the dispersant include, for the purpose of improving dispersibility, coupling agents such as silanes, titanates, and zircoaluminates, metal chelates, organometallic compounds such as metal alkoxides, polyoxyethylene alkyl phosphate esters, A surfactant such as a polyester acid salt or a commercially available resin-type dispersant may be added. Further, the surface may be coated with a silicone resin or the like.

Other inorganic particles such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), magnesia (MgO), zinc oxide (ZnO), aluminum hydroxide, barium sulfide, magnesium silicate if necessary. Organic particles such as resin beads such as acrylic, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, and polyamide, or a flame retardant, colorant, conductive agent, and the like may be included.

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

  Although the compounding quantity of the said titanium oxide in the coating material of this invention is not specifically limited, 0.1 to 80 weight% is preferable, Furthermore, 10 to 40 weight% is preferable. Moreover, as a dispersing agent, 0.5 to 2% is mix | blended as a standard. The binder component is preferably 10 to 80% by weight, more preferably 10 to 40% by weight.

  The coating using the titanium oxide particles of the present invention is coated on a substrate, and if necessary, dried and heated to form a film excellent in light scattering, whiteness, reflectivity, photocatalytic properties, ultraviolet shielding properties, etc. can do.

  It does not restrict | limit especially as a base material, It can apply to organic substance base materials, such as inorganic base materials, such as glass, ceramics, and a metal, a plastic film, 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, polycarbonate, polystyrene, polyolefin, cellulose acetate, and vinyl chloride.

As a coating method, a normal coating method such as spin coating, spray coating, or screen printing can be used.
The heating temperature after coating can be appropriately selected depending on the substrate and the binder.

(Resin composition)
The titanium oxide particles of the present invention are excellent in light scattering properties, reflectivity, photocatalytic properties, and ultraviolet shielding properties by being directly contained and dispersed in the resin by kneading or the like, and in particular, a resin composition excellent in whiteness. 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, carboxymethylcellulose and hydroxyethylcellulose Cellulose resins such as styrene-acrylic copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer Body, polypropylene, ABS resin, polyethylene, polyvinylidene chloride, polystyrene, nylon, EVA resins, polyamide resins, melamine resins, urea resins, silicone resins, fluorine resins.

Other inorganic particles such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), magnesia (MgO), zinc oxide (ZnO), aluminum hydroxide, barium sulfide, magnesium silicate if necessary. Organic particles such as resin beads such as acrylic, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, and polyamide, or a flame retardant, colorant, conductive agent, and the like may be included.

  As a mixing and 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. In the dispersion step, for the purpose of improving dispersibility, coupling agents such as silane, titanate and zircoaluminate and metal chelate, organometallic compounds such as metal alkoxide, polyoxyethylene alkyl phosphate ester, A surfactant such as a polyester acid salt or a commercially available resin-type dispersant 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 reflective plate can be formed.

  White reflection films, white reflection plates, 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 for backlights, light guide plates, light diffusions, and reflectors in liquid crystal display devices.

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

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

  In any case, in the case of anatase-type titanium oxide, titanium oxide has the property of absorbing ultraviolet rays and decomposing organic matter. Therefore, if necessary, the decomposition force can be reduced by coating the particle surface with other elements. Examples of the other elements include Zr, Si, Ta, Y, Sr, and Al. 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 water vapor atmosphere to adsorb hydroxyl groups on the particle surface. . Then, after removing excess moisture on the particle surface by performing vacuum treatment, by dispersing in the metal alkoxide solution of the other element, the other element is chemically bonded to the surface, and then dried. Stabilize.

  On the other hand, when forming a plastic film or a plastic board by processing a resin composition, it carries out according to the following processes, for example. First, the polyester resin to which the titanium oxide particles of the present invention and various additives are added is melted at 260 to 350 ° C., discharged from a base, and cooled and formed into a film on a cooling drum at 5 to 50 ° C. To do. In the case of 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 longitudinal stretching conditions. 70 to 150 ° C and a draw ratio of 2.5 to 5 times are preferable, and heat setting 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%, and more preferably 3 wt% to 30 wt%. When 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, when the content of the titanium oxide particles exceeds 50 wt%, when forming a film or a plate, it becomes difficult to mold, or the titanium oxide particles easily fall off from the surface.

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

(Other application examples)
The titanium oxide particles of the present invention are particularly excellent in light scattering ability from visible light to near-infrared light, as described above, due to their external shape and particle size. Therefore, in addition to the above-mentioned paints, it is useful for ultraviolet protection inks and photographic photoreceptors. When the titanium oxide particles of the present invention are used for these applications, 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, glycols. In this case, a dispersant, a synthetic resin binder such as polyvinyl alcohol, polyacetal, acrylic resin, polyester resin, epoxy resin, phenol resin, or inorganic binder such as silica may be added to improve the smoothness and adhesion strength of the coating film. preferable. In order to control the drying of the coating film, a metal stearate or a metal naphthenate can be added.

(Production and evaluation of star-shaped titanium oxide particles)
[Example 1]
250 mL of pure water cooled to 10 ° C. was put into a glass container having a capacity of 1 L, and 71 g of titanium tetraisopropoxide manufactured by Kojundo 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 into a white aqueous suspension. This white aqueous suspension was subjected to suction filtration with Nutsche and filter paper No. 2 manufactured by Toyo Roshi Kaisha, and subsequently washed with 500 mL of pure water to obtain a white cake-like substance. The white cake-like material and 1.4 g of a 26% aqueous solution of tetramethylammonium hydroxide manufactured by Tokyo Chemical Industry Co., Ltd. were added to pure water so that the total amount became 200 g. The resulting reaction solution was in the form of a slurry and the pH was 10.23. The titanium atom concentration in the reaction solution was 1.25 mol / L.

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

[Comparative Example 1]
Except that a reaction solution was prepared without adding tetramethylammonium hydroxide, a preheating treatment and a heating treatment were carried out in the same manner as in Examples to produce titanium oxide particles. 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]
Preliminary heat treatment and heat treatment were carried out in the same manner as in Example except that 5 g of nitric acid 1.42 manufactured by Wako Pure Chemical Industries, Ltd. was added instead of tetramethylammonium hydroxide to produce titanium oxide particles. 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 diameter of 200 nm to 350 nm, and each extending portion exhibiting an anatase single phase were obtained. Moreover, in the comparative example 1, it turned out that the granular titanium oxide particle which consists of an anatase single phase with a primary particle size of about several tens of nm is obtained. Furthermore, in Comparative Example 2, it was found that titanium oxide particles having an anatase phase and a rutile phase with a primary particle size of several tens of nanometers were obtained.

  In addition, while showing the SEM photograph of the titanium oxide particle obtained in the present Example in FIG. 1, the TEM photograph is shown in FIG. Moreover, the graph of the X-ray-diffraction pattern of the titanium oxide particle in a present Example is shown in FIG. 3, respectively.

[Test Example 2]
The titanium oxide particles of the above Examples and Comparative Examples 1 and the granular titanium oxide particles (manufactured by Wako Pure Chemical Industries, Ltd .: Comparative Example 3) composed of an anatase single phase having an average aggregate particle size of 300 nm and an aggregate having a primary particle size of 20 nm. The light scattering property was examined. First, 5 g of ethyl cellulose 45 (manufactured by Kanto Chemical Co., Inc.) was dissolved in 70 g of α-terpineol (manufactured by Kanto Chemical Co., Ltd.) with a homogenizer to prepare a vehicle. Next, 25 g of the titanium oxide particles obtained in Examples and Comparative Example 1 and 25 g of titanium oxide particles obtained from 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.

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

  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. Moreover, although the titanium oxide particle in the comparative example 3 is granular, since the average aggregate particle diameter is about 300 nm, it turns out that it has a reflectance of 20% or more at all wavelengths. Further, when the Example and Comparative Example 3 are compared, the titanium oxide particles in the Examples exhibit a high reflectivity by exhibiting a star-shaped appearance even though the particle diameters of the titanium oxide particles are substantially the same. I understand that. On the other hand, it was found that the titanium oxide particles of Comparative Example 2 having a primary particle diameter of several tens of nanometers and having a granular appearance have a low reflectance of around 10% at each wavelength.

(Application of star-type titanium oxide particles to paint)
[Example 2]
20% by weight of anatase-type star-shaped titanium oxide particles (substantially hexagonal) of the present invention having a primary particle size of 200 nm to 300 nm in a mixed solution of isopropyl alcohol, t-butanol and acetone, and a polyoxyethylene-based dispersion material Triton-X. 5% by weight and 25% by weight of acrylic resin were mixed, 1 mm diameter glass beads were added as much 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, it was applied to an acrylic substrate that had been heated to 50 ° C. in advance using 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]
Instead of the anatase-type star-shaped titanium oxide particles of the present invention, a paint was prepared in the same manner as in Example 2 except that commercial anatase particles manufactured by Wako with an average primary particle size of 200 nm were used, and an acrylic plate with a film was prepared. Got.

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

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

(Application of star-shaped titanium oxide particles to plastic films)
[Example 3]
25 wt% of anatase-type star-shaped titanium oxide particles (substantially hexagonal) of the present invention having a primary particle size of 100 to 500 nm coated on the surface with silicon alkoxide are mixed in a polyester resin, melted at 260 to 350 ° C., and discharged from a die. And it apply | coated on the cooling drum of 25 degreeC, and the said polyester-type resin containing the said titanium oxide particle was formed in the film form by cooling after that. Subsequently, the film-like polyester resin was subjected to a biaxial stretching process to obtain a white film having a thickness of 150 μm. In the biaxial stretching step, the stretching temperature was 100 ° C., the stretching ratio was 3 times, and the heat setting was 200 ° C.

  Subsequently, 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 average value of 300 nm to 700 nm was evaluated. 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 having an average primary particle diameter of 200 nm were used instead of the anatase-type titanium oxide particles of the present invention. Rate was evaluated. The results are shown in Table 4.

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

  As described above, the present invention has been described in detail based on the embodiments of the present invention with specific examples. However, the present invention is not limited to the above contents, and all modifications and changes can be made without departing from the scope of the present invention. It can be changed.

It is a SEM photograph which shows an example of the titanium oxide particle of this invention. It is a TEM photograph which shows an example of the titanium oxide particle of this invention. It is an X-ray diffraction profile of an example of the titanium oxide particle of this invention.

Claims (8)

While having a plurality of extending portions extending radially, the extending portion has a ridge at a substantially central portion in the length direction, and has a star shape as a whole ,
The plurality of extending portions are composed of six extending portions, and the six extending portions extend radially at substantially equal intervals .   The titanium oxide particles according to claim 1, wherein the primary particle size is 100 nm or more and 1000 nm or less. The titanium oxide particles according to claim 1 , wherein each of the plurality of extending portions is a single crystal, and the titanium oxide particles exhibit twins as a whole. The titanium oxide particles according to any one of claims 1 to 3 , wherein the extending part is an anatase single phase. A paint comprising the titanium oxide particles according to claim 1 . A resin composition comprising the titanium oxide particles according to claim 1 . A plastic film comprising the titanium oxide particles according to any one of claims 1 to 4 . A plastic plate comprising the titanium oxide particles according to any one of claims 1 to 4 .

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