JPH0551210A - Production of photochromic fine titanium dioxide powder - Google Patents

Abstract

PURPOSE:To industrially advantageously produce photochromic fine powder having high lightness before discoloration, excellent color rendering properties under irradiation with light and very excellent dispersibility in a medium system. CONSTITUTION:Fine powder of anatase type titanium dioxide is dry-mixed with fine iron oxide powder of granule shape and this mixture is heated in a temp. range in which photochromism is exhibited below a temp. at which anatase type titanium dioxide is transformed into rutile type titanium dioxide. Photochromic fine titanium dioxide powder is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a photochromic titanium dioxide fine powder suitable for a photochromic color rendering material.

[0002]

TECHNICAL BACKGROUND AND PROBLEMS OF THE INVENTION A phenomenon in which a substance changes its color when exposed to light such as ultraviolet rays and returns to its original state when the light irradiation is stopped, that is, a reversible change occurs in the absorption spectrum upon light irradiation. The phenomenon is called photochromism, and it is a dimming element in cosmetics, paints, etc. that uses this phenomenon.
Various applications are expected as functional materials such as sensor elements, display elements, and light shielding elements, and various organic or inorganic compounds are used as photochromic materials. In general, organic photochromic compounds represented by, for example, spiropyran-based and spirooxazine-based compounds have high absorbance of a colored body,
In addition, since the difference in absorption wavelength between the colored body and the decolored body is large and the absorption wavelength of the colored body can be relatively easily changed by a substituent, a bright color rendering property is expected, and it has recently attracted attention as a functional material. Is being done. However, the organic photochromic compound is apt to be deteriorated by light, and as a result, deterioration of color rendering performance due to repeated use and deterioration of continuous stability of color rendering performance are unavoidable, and improvement thereof is desired.

However, the present inventors have long been doped with an element forming a photochromic center,
For example, we focused on the fact that perovskite-type oxides such as strontium titanate and photochromic inorganic compounds such as titanium dioxide have excellent photodegradability, and in particular, developed a photochromic titanium dioxide with excellent whiteness and safety. We are proceeding with various studies. In order to form a photochromic center in titanium dioxide, it is generally known to dope transition metal ions such as iron, molybdenum and nickel, but when trying to enhance the color rendering effect, the amount of added metal ions such as iron ions should be controlled. It is necessary to increase the amount, and as a result, the coloring due to the added metal ions becomes large, and further, during the heat treatment process of doping the added metal ions, coarse particles are likely to be formed due to the sintering of the particles of titanium dioxide particles and between the particles. , The dispersibility in various photochromic composition systems using the same is markedly impaired, and the desired color rendering effect cannot be obtained. The present inventors, as a result of further various studies in order to solve the above problems, after the iron oxide fine powder of a specific particle shape is mixed with titanium dioxide in a dry system, the photochromic property is developed, and Surprisingly, by heating below the rutile transition temperature, iron ions are likely to be uniformly doped. Therefore, a photochromic center with a relatively small amount of iron source and a heat treatment at a relatively low temperature is sufficient. The present invention has been completed with the knowledge that a photochromic titanium dioxide fine powder having good dispersibility can be formed without substantially causing coarsening due to sintering or particle growth. Is

[0004]

The present invention relates to a method for producing the photochromic titanium dioxide fine powder shown below. (1) Dry-mixing anatase-type titanium dioxide fine powder and granular iron oxide fine powder, and then expressing the mixture at a temperature below the temperature at which anatase-type titanium dioxide is transformed into rutile-type titanium dioxide and which exhibits photochromic properties. A method for producing a fine powder of photochromic titanium dioxide, which is heat-treated with. (2) The granular iron oxide fine powder has an average particle size of 0.05 to 0.5 obtained by heat-treating granular magnetite.
The method for producing the photochromic titanium dioxide fine powder according to item (1), which is 0.5 μm α-Fe ₂ O ₃ fine powder, and (3) the granular iron oxide fine powder contains acicular iron-containing hydrous oxide. Average particle size obtained by heat treatment is 0.05 to 0.5 μm
The method for producing a photochromic titanium dioxide fine powder according to the above item (1), which is the α-Fe ₂ O ₃ fine powder having a granular shape.

In the present invention, as the anatase type titanium dioxide fine powder, those produced by various methods can be used. For example, titanium sulfate solution or titanium tetrachloride solution is hydrolyzed by heating or with an alkali. After neutralization or the like to generate hydrous titanium dioxide, it is fired and pulverized to obtain titanium dioxide fine powder mainly composed of anatase type crystals. This has an average particle size of 0.05-
It is about 1 μm, preferably about 0.1 to 0.5 μm, and it is desirable that the particle size distribution is uniform. Further, the granular iron oxide means iron oxide generally referred to as a granular shape having an axial ratio (longest particle diameter / shortest particle diameter) of 1.5 or less, and an average particle diameter (average longest particle diameter) of 0. 05-
A material having a thickness of 0.5 μm is desirable for uniformly doping titanium dioxide. As these iron oxides, those produced by various methods can be used.
(1) Neutralizing and oxidizing a ferrous salt solution with an alkali to produce magnetite (Fe ₃ O ₄ ) in the form of particles, which is dried and made into a fine powder, (2) The granular Fe _{3 of the} above (1) O ₄ is fired in a non-reducing atmosphere to form granular hematite (α-
Fe ₂ O ₃ ) finely divided powder, (3) a ferrous salt solution is neutralized with an alkali and oxidized to form acicular hydrous iron oxide (eg, α-FeOOH, γ-FeOOH). Of α-Fe in a granular form by firing the product in a non-reducing atmosphere
₂ O ₃ fine powder, (4) ferric salt solution is neutralized with alkali generally at a temperature of 100 ° C. or higher, and aged to produce α-Fe ₂ O ₃ in a granular form. However, a fine powder after drying can be used. As described above, the granular iron oxide is made into a fine powder having a uniform particle size distribution, and therefore, before being mixed with the titanium dioxide fine powder, for example, a compaction type crusher such as a crusher, an edge runner mill, or a ring roller mill. If a small amount of iron ions are efficiently doped on the surface of the titanium dioxide particles, the photochromic titanium dioxide having high brightness and high color rendering can be more advantageously obtained.

In the present invention, dry mixing of the anatase type titanium dioxide fine powder and the granular iron oxide fine powder as an iron ion source is carried out by using various dry type pulverizers and mixers. obtain. The mixing ratio of the granular iron oxide fine powder is 0.1 to 5%, preferably 0.5 to 2%, based on the weight of the anatase type titanium dioxide fine powder. If the mixing ratio of the iron oxide is less than the above range, the desired photochromic properties are not provided, and if it is more than the above range, coloring due to iron ions becomes large, or the particles become coarse due to sintering between particles or between particles. Particle formation is likely to occur. Incidentally, as shown in Comparative Examples below, in the case of performing wet mixing instead of dry mixing, fine powder of the desired photochromic titanium dioxide is easily obtained in which particle sintering or the like easily occurs in the subsequent heat treatment process. hard.

In the present invention, the heat treatment temperature of the mixture is required to be in a temperature range below the temperature at which the photochromic property is exhibited and the anatase type crystal is substantially transformed into the rutile type crystal. 1 from the transition temperature
It is desirable to set the temperature to 0 to 120 ° C., more preferably 30 to 100 ° C. lower. The heat treatment temperature varies depending on the type and amount of the granular iron oxide fine powder, the type of heat treatment apparatus, the size, etc., and cannot be generally stated, but is usually 67.
It is 0 to 780 ° C, preferably about 690 to 760 ° C. If the heating temperature is lower than the above range, the desired photochromic property cannot be imparted without the progress of iron ion doping, while if the heating temperature is too high, intra-particle and inter-particle sintering will be induced and dispersed. As a result, the desired photochromic properties cannot be obtained while the properties are significantly impaired. The desired photochromic property means that the color rendering index represented by ΔL is 4.5 or more.

The photochromic titanium dioxide obtained in the present invention is extremely suitable as a functional material for various color rendering element, for example, it is coated on the surface of the base of the color rendering element to form a film, Alternatively, it can be used by filling it into a substrate.

[0009]

【Example】

Example 1 Ferrous sulfate (FeS) was added to 2000 ml of water kept at 60 ° C.
O ₄ · _7H 2 O) 180g was charged with dissolved. 132 ml of 400 g / l sodium hydroxide solution in this aqueous solution
Was gradually added and stirring and mixing were continued for 60 minutes. Then 1 liter
After blowing air for 3 hours at a speed of 1 / min, the precipitated product was filtered, washed with water, and dried to give granular F having an average particle size of 0.15 μm.
e ₃ O ₄ (by electron microscope observation: the same hereinafter) was obtained.
The granular Fe ₃ O ₄ was heated in the atmosphere at 500 ° C. for 2 hours to obtain granular α-Fe ₂ O ₃ having an average particle diameter of 0.20 μm, and then pulverized with a crusher. Α-F thus obtained
1 g of e ₂ O ₃ fine powder and 100 g of anatase-type titanium dioxide fine powder having a specific surface area of 10.2 m ² / g and an average particle diameter of 0.22 μm produced by a sulfuric acid method were put in a grinder and mixed well. Next, this mixture was heat-treated in the air at 750 ° C. for 4 hours to obtain a photochromic titanium dioxide of the present invention (Sample A).

Example 2 In Example 1, granular Fe ₃ O ₄ was heat-treated in air at 600 ° C. for 2 hours to obtain granular α-having an average particle size of 0.22 μm.
A photochromic titanium dioxide (Sample B) of the present invention was obtained by the same process as in Example 1 except that Fe ₂ O ₃ was used.

Example 3 The same treatment as in Example 1 was carried out except that in Example 1, the mixture was heat-treated at 700 ° C. for 4 hours in air.
A photochromic titanium dioxide (Sample C) of the present invention was obtained.

Example 4 Granular Fe ₃ O ₄ was obtained by the method described in Example 1, and 1 g of fine powder obtained by pulverizing the granular Fe ₃ O ₄ with a crusher was used as anatase titanium dioxide having an average particle diameter of 0.22 μm. Fine powder 10
Mixed with 0 g. Next, this mixture was heat-treated in the atmosphere at 750 ° C. for 4 hours to obtain a photochromic titanium dioxide of the present invention (Sample D).

Comparative Example 1 A comparative sample (Sample E) was prepared in the same manner as in Example 1 except that the heating temperature of the mixture was 650 ° C.

Comparative Example 2 A comparative sample (Sample F) was prepared in the same manner as in Example 1 except that the heating temperature of the mixture was 850 ° C.

Comparative Example 3 In Example 1, 1 g of granular α-Fe ₂ O ₃ and 100 g of anatase type titanium dioxide were suspended in water to form a slurry, which was thoroughly wet-mixed with a homomixer, Other than using the dried and crushed mixture,
The sample was treated in the same manner as in Example 1 to obtain a comparative sample (Sample G).

Comparative Example 4 Ferrous sulfate (FeS) was added to 2000 ml of water kept at 60 ° C.
O ₄ · _7H 2 O) 60g ferric sulfate _(Fe 2 (S
O ₄₎ was dissolved ₃ · 8.6H ₂ O) was charged 120 g. 110 ml of 400 g / l sodium hydroxide solution was gradually added to this aqueous solution, and the mixture was stirred and mixed for 60 minutes, and then the precipitated product was filtered, washed with water and dried to obtain an average particle diameter of 0.01 μm.
m granular Fe ₃ O ₄ was obtained. This granular Fe ₃ O ₄ was heat-treated in air at 450 ° C. for 2 hours to obtain an average particle diameter of 0.02 μm.
After being made into granular α-Fe ₂ O _{3 of} m, it was pulverized by a crusher.
1 g of the α-Fe ₂ O ₃ fine powder thus obtained,
100 g of anatase type titanium dioxide fine powder having a specific surface area of 10.2 m ² / g and an average particle diameter of 0.22 μm, which was produced by the sulfuric acid method, was put into a crusher and mixed well. Then, this mixture was heat-treated in the air at 750 ° C. for 4 hours to obtain a comparative sample (Sample H).

Example 5 Ferrous sulfate (FeS) was added to 2000 ml of water kept at 50 ° C.
O ₄ . 7H ₂ O) (556 g) was added and dissolved. 112 ml of 400 g / l sodium hydroxide solution in this aqueous solution
Was gradually added and stirring and mixing were continued for 60 minutes. Then 1 liter
After blowing air for 5 hours at a speed of / min, the precipitated product was filtered, washed with water and dried to have an average major axis diameter of 0.5 μm and an axial ratio of 10
To obtain needle-shaped α-FeOOH. This needle-shaped α-FeOOH
Is heat-treated at 800 ° C. for 2 hours in the air to have an average particle size of 0.
It was made into 15 μm granular α-Fe ₂ O ₃ and then pulverized with a crusher. Α-Fe ₂ O ₃ fine powder 1 thus obtained
g and a specific surface area of 10.2 m ² / produced by the sulfuric acid method
100 g of anatase type titanium dioxide fine powder having an average particle diameter of 0.22 μm was put in a crusher and mixed well. Then, this mixture was heat-treated in the atmosphere at 750 ° C. for 4 hours to obtain a photochromic titanium dioxide (Sample I) of the present invention.

Example 6 In Example 5, needle-like α-FeOOH was added to 750 in air.
The photochromic titanium dioxide of the present invention (sample) was treated in the same manner as in Example 5 except that it was heated at 0 ° C. for 2 hours to obtain almost granular α-Fe ₂ O ₃ having an average particle diameter of 0.15 μm. J) was obtained.

Example 7 In Example 5, 1.75 g of α-Fe ₂ O ₃ fine powder was used.
Other than the above, the same treatment as in Example 5 was carried out to obtain a photochromic titanium dioxide (Sample K) of the present invention.

Comparative Example 5 A comparative sample (Sample L) was prepared in the same manner as in Example 5, except that the heating temperature of the mixture was 650 ° C.

Comparative Example 6 A comparative sample (Sample M) was prepared in the same manner as in Example 5, except that the heating temperature of the mixture was 800 ° C.

Comparative Example 7 A comparative sample (Sample N) was prepared in the same manner as in Example 5, except that the heating temperature of the mixture was 850 ° C.

Comparative Example 8 In Example 5, needle-shaped α-FeOOH was added to the air at 700
Example 5 except that heat treatment was performed at 0 ° C. for 2 hours to obtain α-Fe ₂ O ₃ having an average major axis diameter of 0.5 μm and a substantially needle shape.
A comparative sample (Sample O) was obtained by the same treatment as described above.

Comparative Example 9 Acicular α-FeOOH was obtained by the method described in Example 5, and 1 g of fine powder obtained by crushing the acicular α-FeOOH with a crusher was used as anatase titanium dioxide having an average particle diameter of 0.22 μm. Mixed with 100 g of fine powder. This mixture is then placed in the atmosphere 7
A comparative sample (Sample P) was obtained by heat treatment at 50 ° C. for 4 hours.

Comparative Example 10 Acicular α-FeOOH was obtained by the method described in Example 5, and 1 g of fine powder obtained by pulverizing the acicular α-FeOOH with a crusher was anatase type titanium dioxide having an average particle diameter of 0.22 μm. Mixed with 100 g of fine powder. This mixture is then placed in the atmosphere 8
A comparative sample (Sample Q) was obtained by heat treatment at 00 ° C. for 4 hours.

COMPARATIVE EXAMPLE 11 In Example 5, needle-shaped α-FeOOH was added to the atmosphere at 950
Heat treatment for 2 hours at 0 ° C to obtain granular α- with an average particle diameter of 1 μm.
A comparative sample (Sample R) was obtained by treating in the same manner as in Example 5 except that Fe ₂ O ₃ was used.

The specific surface areas (BET method) of the samples A to R of the examples and comparative examples were measured, and X-ray diffraction was performed to determine the diffraction intensity of the (101) plane of the anatase type crystal as 100, and the rutile type crystal was obtained. The degree of rutile formation was displayed from the ratio with the diffraction intensity of the (110) plane.

For each of the above samples, 4 g of the sample, 7.1 ml of urethane resin (solid content 30%) and 6.4 ml of methyl ethyl ketone / toluene mixed solvent (1/1) were shaken for 1 hour on a paint shaker, and the obtained coating liquid was obtained. Was coated on a polyethylene terephthalate film (75 μm) with a doctor blade (125 μm) and dried at room temperature for 24 hours to prepare a coated plate. Regarding the obtained coated plate of each sample, the light source HOYA UV Light Source was used.
(HLS-200u), UV light was applied to the surface of the coating film at an intensity of 30 mW / cm ² , and the L value (brightness) before and after the irradiation was measured (color difference meter: manufactured by Nippon Denshoku), and the difference (ΔL Value) was calculated (the larger the value, the better the photochromic property).
Further, the glossiness (60 ° -60 °) of the coated plate was visually observed, and it was indicated by A: no coarse particles, B: almost no coarse particles, C: some coarse particles, and D: many coarse particles. The results are shown in Tables 1 and 2.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

INDUSTRIAL APPLICABILITY The present invention provides a photochromic fine powder having high brightness before discoloration, excellent color rendering properties by light irradiation, and extremely excellent dispersibility in a medium system.
It can be economically produced by a relatively simple means, and is of great significance in expanding the application of photochromic color rendering material.

Claims (3)

[Claims] 1. Anatase-type titanium dioxide fine powder and iron oxide fine powder in the form of particles are dry-mixed, and then the mixture is exposed to photochromic properties and at a temperature at which the anatase-type titanium dioxide is converted to rutile-type titanium dioxide. A method for producing a photochromic titanium dioxide fine powder, which is heat-treated at a temperature of less than 1. 2. An iron oxide fine powder having a granular shape has an average particle diameter of 0.0 obtained by heat-treating granular magnetite.
A fine powder of α-Fe ₂ O ₃ having a particle size of 5 to 0.5 μm.
A method for producing the fine powder of photochromic titanium dioxide described. 3. An iron oxide fine powder in the form of particles having an average particle diameter of 0.05 to 0.
Claim 1 photochromic titanium dioxide fine powder production method of wherein the α-Fe ₂ O ₃ fine powders of granulated shape of 5 [mu] m.