JP7204198B2 - Titanium oxide photochromic material and composite containing molybdenum - Google Patents

Description

The present invention relates to a molybdenum-containing titanium oxide photochromic material, a photochromic sol containing the same, a photochromic composite, a solution for forming a photochromic composite, and a method for producing a photochromic composite.

Organic dyes such as azobenzene and diarylethene are commercially available as photochromic dyes (dyes that change color when stimulated by light). The color change in these dyes is caused by optical geometric isomerization (cis-trans isomerization) and absorption peak shift due to ring-opening/closing reaction. However, these organic photochromic materials are less durable than inorganic photochromic materials, and are difficult to synthesize. On the other hand, as an inorganic photochromic material, the reduction reaction of silver halide to silver atoms has been known for a long time, and this is the same principle as the formation of a blackened image by exposure of a silver halide photographic emulsion. However, in the case of black-and-white photography using this principle, halogen is removed from the reaction system to stabilize the latent image. Also, when silver halide is confined in glass or the like, since the halogen is not removed, the silver atoms are oxidized again to return to the original state, so the dark color when colored does not become completely black. Photochromic glass, which has been put to practical use as sunglasses, utilizes a phenomenon in which silver precipitates and darkens when silver chloride is irradiated with ultraviolet rays.

Furthermore, photochromism of oxide semiconductors such as tungsten oxide and molybdenum oxide is known as an inorganic photochromic material. In tungsten oxide and molybdenum oxide, charge separation occurs due to light absorption, and hexavalent tungsten and molybdenum are reduced to pentavalent by electrons excited in the conduction band. A charge transfer transition occurs and a blue color develops. In the case of tungsten oxide, when light irradiation is continued, the color changes from blue to ultramarine blue to black. When light irradiation is stopped, electrons move to oxygen in the air, and tungsten returns to hexavalent, resulting in fading. do. On the other hand, molybdenum oxide does not readily transfer electrons to oxygen, so its discoloration is extremely slow and its reversibility is extremely low. Inorganic oxides such as tungsten oxide have the advantage that they are thermally and chemically stable and can be easily synthesized by a sol-gel method or the like (Patent Document 1). In contrast, in the case of titanium oxide, which is also an oxide semiconductor, photochromism due to conduction band electrons generated by charge separation usually does not occur. This is because recombination with holes or transfer of excited electrons to oxygen proceeds rapidly. As an example of photochromism with titanium oxide, there is a method of creating a state in which electrons are accumulated in the conduction band by consuming holes in the presence of an organic material, and reducing tetravalent titanium to trivalent to produce a blue color. There is a method of precipitating silver by conduction band electrons in the coexistence of silver ions to develop a color, a method of mixing with tungsten oxide, etc., but photochromism using only titanium oxide nanoparticles has not been reported so far.

As described above, organic photochromic materials have durability problems. On the other hand, in most cases, oxide semiconductors typified by tungsten oxide, which are chemically stable and easy to synthesize, emit blue color. The black color produced by using these materials changes from blue to ultramarine blue to black with irradiation of light, that is, the darkening of the blue color makes it visible as black. Therefore, there has been a demand for a photochromic material that is an inorganic material and turns black without going through blue.

JP 2014-62218 A

An object of the present invention is to solve the above problems and to provide an inorganic photochromic material that develops a black color without passing through blue, and a film or the like using the same.

The present inventors have conventionally conducted research on photochromism using tungsten oxide and the like. On the other hand, we have been researching the synthesis of metal ion-doped visible-light-responsive photocatalysts by doping a small amount of metal ions into titanium oxide nanoparticles. The present inventors have so far synthesized ion-doped titanium oxide photocatalyst powder by doping with more than 10 kinds of metal ions. We discovered that photochromism can be seen in titanium oxide sol, which cannot be seen. Moreover, absorption was observed in all wavelength regions from ultraviolet to infrared when the color was developed, and the conventional blue color was not exhibited. Although the mechanism of the color development phenomenon is still unknown, we were able to obtain an optical functional material that can reversibly change rapidly between colorless transparent and black without passing through blue in the sol state or solid film state. The present invention has been completed in this way.

That is, the present invention is specified by the matters shown below.
(1) A titanium oxide photochromic material containing molybdenum.
(2) The titanium oxide photochromic material according to (1) above, wherein the ratio of the amount of molybdenum to the total amount of titanium and molybdenum is 0.1 to 3.0%.
(3) The titanium oxide photochromic material of (1) or (2), which develops a black color when irradiated with ultraviolet rays.
(4) A photochromic sol containing the titanium oxide photochromic material according to any one of (1) to (3) above.
(5) A photochromic composite containing the titanium oxide photochromic material according to any one of (1) to (3) above and a binder component.
(6) The photochromic composite of (5) above, which contains a water-soluble polymer compound as a binder component.
(7) The photochromic complex of (6) above containing an alcohol.
(8) The photochromic composite according to any one of (5) to (7) above, which is used for grayscale formation.
(9) A solution for forming a photochromic complex containing the titanium oxide photochromic material according to any one of (1) to (3) above and a water-soluble polymer compound.
(10) Prepare a dispersion containing the titanium oxide photochromic material and the water-soluble polymer compound according to any one of (1) to (3) above, apply the dispersion onto a substrate and dry it, or A method for producing a photochromic composite comprising filling a mold with a liquid and drying the liquid.

Since the photochromic material of the present invention is an inorganic material, it is superior in durability to organic materials, and can develop a black color without going through blue. In addition, unlike oxide semiconductors, which emit blue and become darker and appear black, even when light irradiation is weak, they absorb light over a wide wavelength range, so they develop blackish colors. By controlling the time, the color tone can be changed from transparent to gray to black. The photochromic sol, photochromic composite and solution for forming a photochromic composite of the present invention contain the photochromic material of the present invention and similarly exhibit the above effects. Moreover, the method for producing a photochromic composite of the present invention can produce a photochromic composite having the above effects.

FIG. 1 is a graph showing the photochromism of a 2.0 atom % Mo—TiO ₂ sol, and is a graph showing the absorption spectrum of the sol for each UV light irradiation elapsed time. FIG. 2 is a photograph showing the state of color development of the 2.0 atom % Mo—TiO ₂ sol after 98 minutes of irradiation with ultraviolet light. FIG. 3 is a graph showing the photochromism of a 0.6 atom % Mo--TiO ₂ sol, and is a graph showing the absorption spectrum of the sol for each UV light irradiation elapsed time. FIG. 3(a) is an example using a sol 2 days after preparation, and FIG. 3(b) is an example using a sol 30 days after preparation. FIG. 4 is a graph showing the photochromism of a 0.6 atom % Mo--TiO ₂ /EG/MC film, and is a graph showing the absorption spectrum of the sol for each UV light irradiation elapsed time. FIG. 4(a) is an example of using a film of EG/Ti (molar ratio)=12, and FIG. 4(b) is an example of using a film of EG/Ti (molar ratio)=6, FIG. 4(c) is a photograph showing the color development state of the film when the film of EG/Ti (molar ratio)=12 is used. FIG. 5 shows the UV absorbance at 614 nm of 0.6 atom % Mo—TiO ₂ /EG/MC films (EG/Ti (molar ratio)=12 film, EG/Ti (molar ratio)=6 film) It is the graph which showed the change by irradiation time. FIG. 6(a) is a graph showing changes in absorption spectrum of a 0.6 atom % Mo--TiO ₂ /EG/MC film due to photochromism. FIG. 6(b) is a photograph showing the color development state of the film depending on the ultraviolet light irradiation time. From the top, 70 minutes, 60 minutes, 50 minutes, 40 minutes, 30 minutes, 20 minutes, 10 minutes, and before irradiation.

The titanium oxide photochromic material of the present invention is a photochromic material made of titanium oxide containing molybdenum (hereinafter also referred to as "Mo-titanium oxide"). The molybdenum content of titanium oxide is not particularly limited as long as it exhibits photochromism to the extent that it can be used as a photochromic material, but the ratio of the amount of molybdenum to the total amount of titanium and molybdenum is 0.1 to 3. 0%, more preferably 0.1 to 2.0%. The molybdenum-containing titanium oxide in the present invention contains molybdenum in the structure of titanium oxide and contains molybdenum in the crystal structure or amorphous structure of titanium oxide. The titanium oxide photochromic material of the present invention is composed of Mo-titanium oxide particles, and the particle size of the Mo-titanium oxide particles is not particularly limited as long as photochromism can be expressed. For example, it is 10 nm or less. can be preferably used. The Mo-titanium oxide particles are photochromic particles exhibiting photochromism. Also, the particle shape of the titanium oxide photochromic material of the present invention is not particularly limited, but, for example, spherical particles can be used. The titanium oxide photochromic material of the present invention develops a black color without passing through blue when irradiated with ultraviolet rays, and can also develop color with ultraviolet rays in sunlight. The titanium oxide photochromic material of the present invention can also be used by being dispersed in a dispersion medium such as water. The photochromic sol of the present invention is obtained by dispersing the titanium oxide photochromic material of the present invention in a dispersion medium. The dispersion medium is not particularly limited as long as it can disperse the titanium oxide photochromic material of the present invention. However, water is preferred because it has good dispersibility and can be prepared directly from the production process of Mo-titanium oxide particles. The photochromic sol of the present invention turns black without passing through blue when irradiated with ultraviolet rays. However, in the case of the Mo-titanium oxide particles as they are or in the case of a sol in which the Mo-titanium oxide particles are dispersed in water, the Mo-titanium oxide particles oxidize and fade when exposed to air, so oxygen is removed with nitrogen gas or the like. When exposed to UV light, it becomes bright black.

The method for producing the titanium oxide photochromic material of the present invention is not particularly limited as long as it is a method that allows molybdenum to coexist with titanium oxide particles and produces molybdenum-containing titanium oxide particles. method can be mentioned. Acid such as concentrated nitric acid is added to an aqueous solution of molybdic acid salt such as sodium molybdate to adjust the pH, titanium alkoxide such as titanium tetraisopropoxide is added dropwise while stirring with a stirrer, and stirring is continued for a certain period of time. By continuing, a colloidal aqueous solution (sol) can be prepared. Stirring is preferably carried out for about 4 to 6 days. Impurities such as nitrate ions are preferably removed from the obtained sol by a dialysis membrane or the like. Thus, a sol in which Mo-titanium oxide particles are dispersed is obtained. The Mo-titanium oxide particles in the sol may be separated and used, or they may be used as they are in the sol state. Also, the Mo-titanium oxide particles may be used in an amorphous state without being crystallized.

The photochromic composite of the present invention is characterized by containing the titanium oxide photochromic material of the present invention and a binder component. A composite in the present invention means a product containing a titanium oxide photochromic material and a binder component and formed into a certain shape, and the shape is not particularly limited. The composite includes, for example, a film attached to the surface of a substrate, a film that can be used alone, and a molded article molded into various shapes. The binder is not particularly limited as long as it promotes molding of the composite, but water-soluble polymer compounds are preferred. The water-soluble polymer compound in the present invention is not particularly limited, but examples include natural water-soluble polymer compounds, semi-synthetic water-soluble polymer compounds, synthetic water-soluble polymer compounds, and the like. can.

Examples of natural water-soluble polymer compounds include gum arabic, tragacanth gum, galactan, guar gum, carob gum, karaya gum, carrageenan, pectin, agar, quince seed (quince), algecolloid (cassou extract), starch, plants such as glycyrrhizic acid. microbiological polymers such as xanthan gum, dextran, succinoglucan and pullulan; and animal polymers such as collagen, casein, albumin and gelatin. Examples of semi-synthetic water-soluble polymer compounds include starch-based polymer compounds such as carboxymethyl starch and methylhydroxypropyl starch; alkylcelluloses such as methylcellulose and ethylcellulose; hydroxyalkylcelluloses such as hydroxyethylcellulose and hydroxypropylcellulose; Hydroxyalkylalkylcellulose such as hydroxypropyl cellulose; cellulose-based polymer compounds such as nitrocellulose, sodium cellulose sulfate, sodium carboxymethylcellulose (CMC), crystalline cellulose, oxidized cellulose nanofiber TEMPO, cellulose powder; sodium alginate, propylene glycol alginate and other alginic acid-based polymers. Examples of synthetic water-soluble polymer compounds include vinyl polymer compounds such as polyvinyl alcohol, polyvinyl methyl ether polymer, polyvinylpyrrolidone, and carboxyvinyl polymer; polyethylene glycol 20,000, polyethylene glycol 6,000, polyethylene glycol; Polyoxyethylene polymer compounds such as 4,000; copolymer polymer compounds such as polyoxyethylene polyoxypropylene copolymer and PEG/PPG methyl ether; sodium polyacrylate, polyethyl acrylate, polyacrylamide and the like; An acrylic polymer compound can be mentioned. These can be used singly or in combination of two or more. Among these, alkyl cellulose is preferred, and methyl cellulose is particularly preferred. The weight-average molecular weight (Mw) of these water-soluble polymer compounds is not particularly limited as long as the composite of the present invention can be produced. 1,000 to 500,000.

The complex of the present invention may contain a water-soluble compound having a hydroxy group (excluding those compounded as the above water-soluble polymer compound). The water-soluble compound having a hydroxy group in the present invention is a relatively low-molecular-weight compound other than the above water-soluble polymer compound. color fast. Also, the flexibility of the composite is improved and the transparency is improved. The water-soluble compound having a hydroxy group is an organic compound that has one or more hydroxy groups, is water-soluble, and preferably does not evaporate when the film is dried at room temperature to about 40°C. However, inorganic compounds may also be used. For example, organic compounds include hydrocarbons having a hydroxy group that may have an oxygen atom as a linking group, organic acids, and the like, and inorganic compounds include phosphoric acid, boric acid, and the like. acids. Among them, alcohols and organic acids are preferred.

The "hydrocarbon" of "hydrocarbon having a hydroxy group" includes aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons and the like. Examples of aliphatic hydrocarbons include alkanes such as ethyl, propane, butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, heptadecane, and octadecane; ethylene, propylene, butene, pentene, hexene, and octene; alkenes such as , nonene, decene, butadiene and isoprene; and alkynes such as ethyne, propyne, butyne and pentyne. Examples of alicyclic hydrocarbons include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclobutene, cyclopentene, cyclohexene, cycloheptene, and cyclooctene.

Alcohols are exemplified below as water-soluble compounds having a hydroxy group. Alcohols in the present invention include water-soluble polyhydric alcohols having 2 or more carbon atoms, preferably 2 to 30 carbon atoms. Any monohydric alcohol may be used as long as it is water-soluble and does not evaporate at room temperature to about 40°C. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, butanediol, glycerin, neopentylene glycol, trimethylolpropane, pentaerythritol, hexanetriol, di(trimethylolpropane), dipentaerythritol, trihydroxystearyl alcohol, Aliphatic alcohols such as 3-buten-1-ol; cyclic alcohols such as cyclopentanetriol, cyclohexanetriol and cyclohexanehexaol. These may be used singly or in combination of two or more, and preferably have a boiling point of 100° C. or higher. More preferably, it contains a dihydric or trihydric alcohol, and more preferably ethylene glycol and glycerin.

Examples of aromatic hydrocarbons include benzene and naphthalene, and examples of water-soluble aromatic hydrocarbons having a hydroxyl group include phenol, catechol, and pyrogallol. A hydrocarbon having an oxygen atom as a linking group means a compound having one or two or more oxygen atoms in the above hydrocarbon molecule. Examples of hydrocarbons having a hydroxy group and having an oxygen atom as a linking group include sugars such as glucose and maltose.

Organic acids are exemplified below as water-soluble compounds having a hydroxy group. Examples of organic acids in the present invention include carboxylic acids or sulfonic acids having 1 or more carbon atoms, preferably 1 to 10 carbon atoms. Carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid Acids, malic acid, tartaric acid, citric acid and the like can be mentioned. Sulfonic acids include methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, camphorsulfonic acid and the like.

The ratio of the titanium oxide photochromic material and the water-soluble polymer compound in the composite of the present invention is not particularly limited as long as the composite of the present invention can be formed, but from the viewpoint of improving strength and photoresponsiveness. Therefore, the water-soluble polymer compound is preferably 30 to 150 parts by mass, more preferably 60 to 120 parts by mass, with respect to 100 parts by mass of the titanium oxide photochromic material. If the amount of the water-soluble polymer compound added is more than the above range, the strength of the composite of the present invention increases, but the viscosity increases and air is included, resulting in strong white turbidity of the composite. On the other hand, when the amount of water-soluble polymer compound added is less than the above range, the strength of the composite becomes weak. Further, when a water-soluble compound having a hydroxy group is blended, the water-soluble compound having a hydroxy group is added to 100 parts by mass of the titanium oxide photochromic material from the viewpoint of making the composite easier to handle and further improving photochromism. , 20 to 200 parts by mass. If the added amount of the water-soluble compound having a hydroxy group is more than the above range, the resulting composite will contain a large amount of water, making the film and molded product difficult to handle. On the other hand, if the amount added is less than the above range, the effect of improving the photochromism of the composite and the effect of improving flexibility and transparency cannot be sufficiently obtained.

When the water-soluble compound having a hydroxy group is an alcohol, the alcohol/Mo-titanium oxide (molar ratio) is, for example, ethylene glycol/Mo-titanium oxide from the viewpoint of further improving the photoresponsivity of the composite. In the case of , the ethylene glycol/titanium (molar ratio) is preferably 2.0 or more, more preferably 3.0 or more, and even more preferably 5.0 or more. Moreover, ethylene glycol/titanium (molar ratio) is preferably 18.0 or less, preferably 15.0 or less, and more preferably 13.0 or less.

(Method for producing photochromic composite)
The method for producing the photochromic composite of the present invention is not particularly limited. It can be produced by applying it to a mold and drying it, or by filling it in a mold by pouring it, etc., and drying it. In the former case, a film that can be used alone can be produced by forming a film in close contact with the substrate, or by peeling off a film formed on the substrate. In the latter case, moldings in the form of molds can be produced. The drying temperature can be appropriately selected according to the type of binder to be used and the required crystalline state (crystalline or amorphous) of Mo-titanium oxide. The photochromic composite forming solution of the present invention is characterized by containing the titanium oxide photochromic material of the present invention and a water-soluble polymer compound. The solvent for the photochromic composite forming solution of the present invention is not particularly limited as long as it disperses the titanium oxide photochromic material and dissolves the water-soluble polymer compound, but water is preferable. The photochromic composite forming solution of the present invention preferably contains Mo-titanium oxide particles and a water-soluble polymer compound, and is a dispersion in which the Mo-titanium oxide particles are dispersed.

(Preparation of solution for forming photochromic complex)
The method for producing a solution for forming a photochromic composite containing the titanium oxide photochromic material of the present invention and a water-soluble polymer compound is not particularly limited. can be prepared by mixing In mixing these, heating, stirring, ultrasonic treatment, etc. are performed as necessary. In preparing the photochromic composite-forming solution of the present invention, it is preferable to use a Mo-titanium oxide colloidal aqueous solution in order to uniformly disperse the Mo-titanium oxide particles in the composite-forming solution. As the Mo-titanium oxide colloid aqueous solution, the Mo-titanium oxide sol prepared in paragraph 0012 above can be used. The concentration of Mo-titanium oxide in the sol is not particularly limited, but for example, a sol of about 0.01 to 0.60 mol/L can be used, preferably 0.01 to 0.30 mol/L. More preferably, a sol of about 0.01 to 0.20 mol/L can be used. The concentration of Mo-titanium oxide sol can be determined by inductively coupled plasma emission spectrometry or the like. The Mo-titanium oxide sol thus prepared is mixed with a water-soluble polymer compound. The concentration of the water-soluble polymer compound in the complex-forming solution of the present invention is not particularly limited as long as the complex can be formed, but can be, for example, about 0.1 to 10% by mass. Furthermore, a water-soluble compound having a hydroxy group is mixed as necessary. The concentration of the water-soluble compound having a hydroxy group in the complex-forming solution is not particularly limited as long as the complex can be formed, but can be, for example, about 0.1 to 10% by mass. The compounding ratio of each component in the complex-forming solution is the same as the compounding ratio of each component in the complex.

(Preparation of photochromic complex)
A photochromic complex can be produced by a conventionally known method using the complex-forming solution prepared above. For example, when producing a photochromic film, a solution for forming a composite film is formed on a glass or Teflon (registered trademark) substrate by a conventionally known method such as coating or printing, and then dried to gel. It can be produced by The drying conditions may be a temperature at which the alcohol does not evaporate, and may be dried under normal pressure at a temperature in the range of room temperature to 40° C., or may be dried by heating if an alcohol that is difficult to evaporate is used. The base material used for producing the film is not particularly limited, and conventionally known base materials including inorganic base materials such as glass and metal, and organic base materials such as resins can be used. The photochromic composite film of the present invention has a sufficient thickness for durability. Other layers, such as adhesive layers, can be provided. When other layers are provided, the layers may be provided on top and/or the bottom of the composite membrane of the invention, provided that the compositions of the other layers are applied at the same time as the components of the composite membrane of the invention. A film may be formed. In addition, a film that can be used alone can be produced by forming a film on a substrate with good peelability and peeling it off. In the case of producing a photochromic molded article, a molded article having a predetermined shape can be produced by pouring the composite-forming solution prepared above into a mold and drying it. The base material used for the formwork, the drying temperature, and the like are the same as in the case of producing the membrane. The photochromic composite of the present invention, for example, a photochromic film, a photochromic film, a photochromic molded article, etc., has excellent photochromism due to ultraviolet rays, and can be used as an ultraviolet indicator that indicates the amount of ultraviolet rays exposed. In addition, when the photochromic film of the present invention is formed on an object to be counterfeited, it can be used for counterfeiting prevention because it develops color with ultraviolet rays in sunlight, so that the authenticity of the object can be determined. Here, the film includes films formed in various patterns, and can be printed using a solution for forming a photochromic composite, or the composite can be embedded in fibers or the like. The photochromic composite of the present invention can be used for display elements, erasable rewritable paper, etc. in addition to the above ultraviolet sensor and counterfeit prevention, and has the advantage of providing a clear contrast between dark and light irradiation. It can be used in various fields where a black pigment is required without being limited to its intended use, and can be used, for example, in light-shielding films, plasma displays, displays such as liquid crystal monitors, and the like. In the display field, it can be used, for example, for forming a light-shielding layer for achieving high contrast. In addition, by controlling the light irradiation intensity and light irradiation time, it is possible to create a smooth grayscale color from transparent to black. It can be used for photochromic composites used for

EXAMPLES The present invention will be described in more detail below in Examples, but the technical scope of the present invention is not limited to these. In the examples, the measurement of Mo—TiO ₂ in the sol was performed using an inductively coupled plasma atomic emission spectrometer (Agilent Technologies 5110 ICP-OES), and the absorption spectrum was measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation). manufactured by UV-1800). The particle size was measured using a transmission electron microscope (JEM-2100, manufactured by JEOL Ltd.).

[Example 1]
(Preparation of 2.0 atom% Mo-TiO ₂ sol)
0.2401 g of Na ₂ MoO ₄ .2H ₂ O was dissolved in 180 mL of ultrapure water (manufactured by Millipore, manufactured by ultrapure water production apparatus Integral 10) in a flat-bottomed flask, and 1.3 mL of concentrated nitric acid was added. While stirring with a stirrer, 15 mL of titanium tetraisopropoxide (TTIP) was added dropwise. A colloidal aqueous solution (sol) was prepared by stirring for 6 days in a dark place. This was placed in a washed dialysis membrane (molecular weight cut off: 3500), immersed in 2750 mL of ultrapure water, and dialyzed for 8 hours while stirring with a stirrer. The water used for dialysis was replaced with new ultrapure water every hour. The concentrations of TiO ₂ and Mo ions contained in the sol after dialysis for 8 hours were measured with an inductively coupled plasma atomic emission spectrometer and found to be 0.21 mol/L and 0.0042 mol/L, respectively. This is hereinafter referred to as 2.0 atom % Mo--TiO ₂ sol. Here, atom % means the ratio of the amount of Mo to the total amount of Ti and Mo. The particle diameter of the 2.0 atom % Mo--TiO ₂ particles in the sol was 10 nm or less when observed with a transmission electron microscope.

(Evaluation of photochromism)
The obtained 2.0 atom% Mo-TiO ₂ sol was placed in a quartz cell, nitrogen gas was passed through it for 30 minutes to remove oxygen, and then an ultra- ^high pressure mercury lamp (λmax = 365 nm), and the absorption spectrum was measured every 1 minute for the first 10 minutes and every 8 minutes after 10 minutes. A reference cell contained ultrapure water. FIG. 1 shows the absorption spectrum change at each time. The spectrum with the lowest absorbance is the one measured immediately before light irradiation. The absorbance increased over a wide range from the ultraviolet to the infrared by irradiation with ultraviolet light, and an absorption peak was observed near 540 nm. The absorbance increased with the lapse of UV light irradiation time. FIG. 2 is a photograph of a sol colored in jet black after 98 minutes of light irradiation. The colored sol returned to the original transparent sol by opening the lid and exposing it to the air.

[Example 2]
(Preparation of 0.6 atom% Mo-TiO ₂ sol)
A sol was prepared as in Example 1 using 0.0591 g of Na ₂ MoO _{4.2H 2} O. TiO ₂ and Mo ion concentrations contained in the sol after dialysis for 8 hours were measured by inductively coupled plasma emission spectroscopy to be 0.20 mol/L and 0.0012 mol/L, respectively. This is hereinafter referred to as 0.6 atom % Mo--TiO ₂ sol. The particle diameter of the 0.6 atom % Mo--TiO ₂ particles in the sol was 10 nm or less when observed with a transmission electron microscope.
(Evaluation of photochromism)
The obtained 0.6 atom% Mo-TiO ₂ sol was placed in a quartz cell 2 days after preparation, irradiated with ultraviolet light in the same manner as in Example 1, and the absorption spectrum was measured every 20 seconds. The results are shown in FIG. (a) shows. An absorption peak was observed near 540 nm, and the absorbance near 540 nm increased with the lapse of ultraviolet light irradiation time. FIG. 3(b) shows the results of the same experiment 30 days after preparation. Similar results were obtained two days after preparation, and it was found that the sol did not deteriorate. Both returned to the original transparent sol by exposing to the air.

[Example 3]
(Preparation of film)
20 mL of the 0.6 atom% Mo-TiO ₂ sol prepared in Example 2 was placed in four beakers, and 1.3, 2.0, 2.7 and 3.4 mL of ethylene glycol (EG) (molar ratio: EG/Ti = 6, 9, 12, 15) and 0.3 g of methyl cellulose (MC) were added, and the methyl cellulose was dispersed using a glass rod in a water bath of about 55°C, followed by ultrasonic treatment for 5 minutes. Then, the mixture was stirred in an ice bath with a stirrer, and the resulting solution was cast on a hydrophobized petri dish and dried at 40° C. for one day to obtain a film. The results are summarized in Table 1. Although a transparent film was obtained as shown in Table 1, in the case of this film formation condition, when the molar ratio (EG/Ti) was 15, a water-containing film containing a large amount of water was obtained.

Fig. 4(a) shows the super high pressure of the 0.6 atom% Mo-TiO ₂ /EG/MC film produced with the molar ratio (EG/Ti) = 12 and Fig. 4(b) with the molar ratio (EG/Ti) = 6. The change in absorption spectrum under irradiation with a mercury lamp (intensity 18.3 mW/cm ² , λmax=365 nm) is shown. Unlike the sol, the film developed a black color even in air. Measurement was performed every 5 minutes of light irradiation. FIG. 4(c) also shows a photograph of the blackened film after 70 minutes. FIG. 5 shows the change in absorbance over time at 614 nm near the absorption peak. It can be seen that the molar ratio (EG/Ti) of 12 results in slightly faster color development, but there is no significant difference. Both films faded after one day in the dark.

[Example 4]
(Preparation of film)
Similar to Example 2, 20 mL of 0.5 atom% Mo-TiO ₂ sol prepared by dialysis for 3 days (the concentration of 0.5 atom% Mo-TiO ₂ in the sol was 0.20 mol/L, EG (2.7 mL) was added so that the molar ratio (EG/Ti) was 12, and the amount of MC to be added was 0.3 g to prepare a film. In the dialysis, water was exchanged once a day, and the petri dish used for drying had an inner diameter of 93 mm.

[Example 5]
(0.6 atom% Mo-TiO ₂ -EG-MC film photochromism)
In the same manner as in Example 3, 2.7 mL of ethylene glycol (EG/Ti=12) and 0.3 g of methyl cellulose were added to 20 mL of 0.6 atom % Mo--TiO ₂ sol to prepare a film. This was cut to about 1×3 cm ² , attached to the side surface of a quartz cell, and irradiated with ultraviolet light in air using an ultra-high pressure mercury lamp (irradiation light intensity: 18.3 mW/cm ² ). An absorption spectrum was measured every 10 minutes. An empty quartz cell was used as a reference cell. The results are shown in FIG. FIG. 6(a) is a graph showing changes in the absorption spectrum of the produced film due to photochromism. FIG. 6(b) is a photograph in which the film was placed on the characters and the irradiation time was changed. After 20 minutes, after 10 minutes and before irradiation. As can be seen in FIGS. 6A and 6B, immediately after the light irradiation, the film was discolored blackish, and then changed from gray to black, which does not transmit light at all. After the experiment, the film was left in the dark for one day and the color faded.

The titanium oxide photochromic material of the present invention is an optical functional material that can reversibly change between colorless transparency and black by ultraviolet rays. Therefore, it can be used for applications such as ultraviolet sensors, display elements, erasable rewritable paper, and forgery prevention using coloring. In particular, the titanium oxide photochromic material of the present invention is black in color compared to the blue color produced by an oxide semiconductor such as tungsten oxide. It can be used not only in various fields where black pigments are required, but also in applications such as light-shielding films, plasma displays, and displays such as liquid crystal monitors. In the display field, for example, it can be used for forming a light shielding layer for achieving high contrast. In addition, the titanium oxide photochromic material of the present invention can develop a smooth grayscale color from transparent to black by controlling the light irradiation intensity and light irradiation time. It can also be used for applications in the field where it is used. The titanium oxide photochromic material of the present invention can be used as a sol, a solution for forming a composite, a composite such as a membrane, a film, a molded article, etc., depending on the form of use. Morphology can be used.

Claims (2)

A method for producing a molybdenum-containing titanium oxide photochromic material or a photochromic sol containing the titanium oxide photochromic material, comprising the following steps (i) to (iii).
(i) Step of adding acid to the aqueous solution of molybdic acid salt to adjust the pH (ii) Step of adding titanium alkoxide to the aqueous solution prepared in (i) (iii) Adding titanium alkoxide in (ii) preparing an aqueous colloidal solution by stirring the aqueous solution during and after the addition; The production method according to claim 1 , further comprising the following step (iv).
(iv) Step of removing impurities in the colloidal aqueous solution prepared in (iii) with a dialysis membrane

Images