JPH1111948A - Stable anatase type titanium dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a titanium dioxide high in whiteness, hardly discoloring even under high temp. treatment, excellent in light resistance and weather resistance and having good chemical stability by forming an anatase type titanium dioxide, containing aluminum or zinc in the crystal and having an alumina coating film on the surface. SOLUTION: The coating weight of alumina is preferably 0.01-2.0 wt.% and the alumina coating film can further be surface treated. One containing 0.02-0.5 wt.% aluminum or 0.05-1.0 zinc in a crystal is properly used. The anatase type titanium dioxide, into the crystal of which aluminum or zinc is introduced, is obtained by adding an aluminum compound and/or a zinc compound in the quantity corresponding to the introducing quantity into a hydrous titanium dioxide obtained by hydrolysis of titanium sulfate and firing. The alumina coating film is obtained by dissolving the aluminum compound in a suspension of titanium dioxide and depositing it on the surface of titanium dioxide by hydrolysis or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an anatase-type titanium dioxide having a bluish tint and a high whiteness, by adding a small amount of aluminum and / or zinc in the crystal to enhance the stability of the crystal and to improve the surface stability. The present invention relates to a titanium dioxide having further improved chemical stability by providing an alumina layer.

[0002]

2. Description of the Related Art Titanium dioxide has two crystal systems, an anatase type which is a low-temperature stable phase and a rutile type which is a high-temperature stable phase. When these are used as pigments, they are properly used so as to make use of their respective characteristics. For example, anatase-type titanium dioxide is characterized by having a bluish color tone as compared with rutile-type titanium dioxide. On the other hand, conventional anatase-type titanium dioxide has a problem that it is easily discolored as compared with rutile-type titanium dioxide and has low light resistance or low weather resistance. That is, in general, titanium dioxide crystals have some or some partial structural defects, and when these structural defects increase, the chemical stability decreases, and when used as a pigment, discoloration occurs due to ultraviolet light, heat, grinding power, etc. Easier to do. Conventional anatase-type titanium dioxide has more crystal defects than rutile-type titanium dioxide, and is easily discolored. Therefore, when used as a coloring agent for plastics, the conventional anatase-type titanium dioxide has a problem that the discoloration becomes remarkable at a processing temperature of 300 ° C. or more, and the color tone of the plastics is impaired.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the conventional anatase type titanium dioxide, and has a high degree of whiteness, is resistant to discoloration even under high-temperature treatment, and has excellent chemical resistance to light and weather. An object of the present invention is to provide anatase-type titanium dioxide having good stability. In the following description, color stability is sometimes referred to as high for the sake of convenience because of its high whiteness, difficulty in discoloring at high temperatures, and good chemical stability with excellent light resistance and weather resistance.

[0004]

The present inventors have proposed an anatase type titanium dioxide in which aluminum or zinc having an ionic radius close to that of tetravalent titanium ions is introduced into a crystal to compensate for crystal defects, thereby improving the color of the titanium dioxide. It has been found that the stability is improved (Japanese Patent Application No. 07-351283,
08-142052). In the present invention, the chemical stability of the anatase type titanium dioxide in which aluminum or zinc is introduced into the crystal is further improved by further providing an alumina coating on the surface.

That is, the present invention relates to (1) anatase type titanium dioxide which contains at least one of aluminum and zinc in a crystal and has an alumina coating on the surface. The titanium dioxide of the present invention suitably has (2) an alumina coating amount of 0.01 to 2.0% by weight, and (3) an alumina coating layer whose surface is further treated. In the titanium dioxide of the present invention, (4) the aluminum content in the crystal is from 0.02 to
0.5% by weight, preferably 0.04 to 0.2% by weight, and (5) the zinc content in the crystal is 0.05 to 1.0% by weight, preferably 0.1 to 0.6%. % By weight is suitable.

Hereinafter, the present invention will be described in detail with reference to examples. (I) The cause of discoloration of aluminum / zinc-doped titanium dioxide is that free electrons generated by crystal defects are taken into tetravalent titanium ions and trivalent titanium
(Purple) is considered to be the main reason for the crystal structure. Therefore, the chemical stability can be increased by doping the titanium crystal with a divalent or trivalent metal ion to form holes and trap free electrons. This doped ion has a tetravalent titanium ion and an ion radius (Ti ⁴⁺ :
It is required that the ion is an ion which is close to 0.75Å) and is not colored as much as possible so as not to impair the white color of titanium dioxide. The titanium dioxide of the present invention contains aluminum (Al ³⁺ : ion radius 0.68 °) or zinc (Zn
²⁺ : Anatase-type titanium dioxide whose chemical stability is enhanced by introducing at least one of them into the crystal using an ionic radius of 0.88 °).

The amount of aluminum or zinc introduced into the crystal is suitably 0.02 to 0.5% by weight, preferably 0.04 to 0.2% by weight, as aluminum ions.
The appropriate amount of zinc ion is 0.05 to 1.0% by weight, preferably 0.1 to 0.6% by weight. When aluminum and zinc are used in combination, the total amount of these ions is 0.02.
A suitable range is from 1.0 to 1.0% by weight, preferably from 0.04 to 0.6% by weight and an aluminum content of 0.5% by weight or less.

If the amount of aluminum or zinc introduced is less than the above range, the effect of improving the chemical stability of titanium dioxide is insufficient. On the other hand, when the amount is larger than the above range, free aluminum and zinc which do not enter the crystal are mixed with the titanium dioxide particles in the form of oxide, and thus the pigment performance such as hiding power and whiteness is undesirably deteriorated. The upper limit of the doping amount of aluminum is about half of that of zinc, but in the case of aluminum, if the addition amount is too large, the particles are likely to solidify and the dispersibility as a pigment is impaired. . Zinc is less prone to this tendency.

[0009] Aluminum and zinc are attached to the particle surface in addition to those incorporated in the crystal, but the aluminum content and zinc content of the present invention are introduced into the titanium dioxide crystal. The amount does not include the amount attached to the particle surface. Some anatase-type titanium dioxides produced industrially contain about 0.01% aluminum, including those derived from the raw ore and those mixed in the middle of the production process. However, with this amount, the effect of increasing the chemical stability (color stability) cannot be obtained.

Next, the anatase type titanium dioxide of the present invention preferably has an average primary particle diameter of 0.01 to 1.0 μm. If the average particle size of the primary particles is less than 0.01 μm, the surface area increases and becomes chemically unstable. On the other hand, if the particle diameter exceeds 1.0 μm, the basic physical properties as a pigment cannot be maintained, so that it is not appropriate.

The anatase type titanium dioxide in which aluminum or zinc is introduced into the crystal is calcined by adding an aluminum compound and / or a zinc compound according to the amount of dope (doped amount) to hydrous titanium dioxide obtained by hydrolysis of titanium sulfate. Can be obtained. Specifically, an aqueous solution of titanium sulfate obtained by dissolving ores such as ilmenite and titanium slag with sulfuric acid is hydrolyzed to produce a slurry of hydrous titanium dioxide, which is washed, dried, and dried.
By baking at 0 to 1100 ° C., an anatase type titanium dioxide powder can be obtained. To introduce aluminum and zinc into the crystal, the hydrated titanium dioxide is washed, the concentration of titanium dioxide in the suspension is adjusted, and then an aluminum compound or zinc compound in an amount corresponding to the introduced amount is added. After drying, baking is performed.

The aluminum compound and the zinc compound may be added in a wet manner using a water-soluble compound, or may be added in a dry manner using a powdery one. In any of the wet and dry production methods, the total amount of aluminum or zinc contained in the aluminum compound or zinc compound added to titanium dioxide is not taken into the crystal, and the addition method, mixing method, firing conditions, etc. Therefore, it is preferable to determine the addition amount according to these conditions. In addition, in addition to aluminum and zinc, small amounts of potassium and phosphorus compounds can be added before firing in order to adjust the particle size and hardness and further suppress the generation of rutile crystals.

(II) Alumina Coating As described above, the titanium dioxide of the present invention contains aluminum or zinc in the crystal and further has an alumina coating on the surface. The alumina coating preferably covers the entire surface of the titanium dioxide particles uniformly, and the coating amount is 0.0 in the coated titanium dioxide.
1 to 2.0% by weight is suitable, and 0.05 to 0.5% by weight.
Is preferred.

The method for forming the alumina coating is not limited. As an example, an alumina film on the surface of titanium dioxide particles can be formed by dissolving an aluminum compound in a suspension of titanium dioxide particles, depositing the aluminum compound on the surface of the titanium dioxide particles by hydrolysis, dehydrating, and drying at a high temperature. it can. As the aluminum compound, an aluminate such as sodium aluminate or an aluminum salt such as aluminum sulfate can be used. Specifically, for example, sodium aluminate in an amount corresponding to the coating amount is added to a suspension of titanium dioxide, sulfuric acid is further added and stirred and mixed, and sodium aluminate is neutralized to convert aluminum hydroxide into dioxide. Deposit on the titanium particle surface. Alternatively, when aluminum sulfate is used instead of sodium aluminate,
Aluminum hydroxide is deposited on the surface of the titanium dioxide particles by neutralizing the aluminum sulfate with sodium hydroxide. This is dehydrated and dried at 50 ° C. or higher to obtain titanium dioxide particles having an alumina coating.

The above-mentioned alumina coating may be obtained by further surface treatment. The alumina coatings of the present invention include those that have been surface treated. Examples of the surface treatment include a reaction with active sites such as surface hydroxyl groups using a silane coupling agent, trimethylolpropane, or the like, and a surface immobilization treatment by adsorption.

For example, titanium dioxide is mixed with a silane compound such as dimethylsilane, methyltrimethoxysilane, acrylic silane or aminosilane, a siloxane, a paraffinic compound such as trimethylolpropane, or an amine such as triethanolamine to form a mixture. Is fixed. These surface treatment agents may be used in an amount of about 0.1 to 1.0% by weight based on titanium dioxide.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples and comparative examples of the present invention are shown below. In addition, the amount of aluminum, the amount of zinc, and the particle diameter contained in titanium dioxide were measured by the following methods. (A) Amount of aluminum and zinc : (1) 1 g of titanium dioxide particles were mixed with 100 g of 5% hydrochloric acid and extracted by heating. The aluminum concentration and zinc concentration in the extract were determined by ICP or the like, and the aluminum amount on the particle surface was determined. ,
The amount of zinc was determined. (2) To a mixture of 5 g of ammonium sulfate and 10 ml of 98% concentrated sulfuric acid,
A titanium dioxide sample (0.7 g) was added, and the mixture was heated and stirred to dissolve the titanium dioxide. After cooling to room temperature, the volume was adjusted to 100 ml, and the aluminum and zinc concentrations were determined by the ICP method. I asked. The amount inside the crystal was determined by subtracting the amount adhering to the particle surface in the above (1) from this amount. (B) Particle size : The size of primary particles of titanium dioxide was measured using a transmission electron microscope, and the average particle size was determined by weight average.

Example 1 A hydrous titanium dioxide slurry was obtained by hydrolyzing titanium sulfate based on a general method for producing titanium dioxide by a sulfuric acid method. The slurry was filtered and washed to obtain an aqueous suspension having a titanium dioxide concentration of 33%.
O ₂ in terms of 33 kg) of potassium carbonate with respect to 130 g, as diammonium phosphate 70g and terms of aluminum 33
g (0.10% Al addition) of aluminum sulfate was added. After drying this mixed slurry, it was baked in a continuous tunnel furnace for 8 hours. The heating rate is 500 ° C after 2 hours of furnace input and 74 after 4 hours.
0 ° C., 960 ° C. after 6-8 hours. After firing, this was pulverized to obtain a titanium dioxide powder having an average primary particle diameter of 0.20 μm. This powder was confirmed to be anatase type titanium dioxide by X-ray diffraction. When the aluminum content of this titanium dioxide powder was measured, the aluminum content of the entire grain was 0.12%, the aluminum content of the grain surface was 0.01%, and the aluminum content in the crystal was 0.11%. Met. Next, this anatase type titanium dioxide was pulverized with a hammer mill, and
0kg in water and 20 liter slurry (TiO ₂ concentration 500g / l)
And Subsequently, the slurry was put into a wet mill (Dynomill), and after a lapse of 5 minutes, transferred to an enamel container, and water was added to make a total volume of 50 liters (TiO ₂ concentration: 200 g / l). The slurry was heated to 60 ° C., and alumina (Al
₂ O ₃ ) Sodium aluminate solution 2 with reduced concentration of 100 g / l
After adding 00 ml (0.2% of Al ₂ O ₃ added), the mixture was stirred for 1 hour.
Further, the pH of the slurry was adjusted to 7.0 in 30 minutes by gradually adding 10% strength diluted sulfuric acid, and stirring was continued for 1 hour. Thereafter, the slurry was cooled to 40 ° C., filtered, dehydrated, washed with water, and dried with hot air. The obtained dried product is pulverized with a hammer mill, and further pulverized with a steam micronizer,
A titanium dioxide powder having an alumina coating on the surface was obtained.

Example 2 The procedure of Example 1 was repeated, except that 1000 ml of an aluminum sulfate solution (1.0% of Al ₂ O _{3 was} added) was used instead of the sodium aluminate solution. An anatase type titanium dioxide powder having an alumina coating was obtained.

Example 3 The amount of the sodium aluminate solution was increased from 200 ml to 50
A titanium dioxide powder having aluminum in the crystal and having an alumina coating on the surface was obtained in the same manner as in Example 1 except that the amount was changed to 0 ml (Al ₂ O ₃ addition rate: 0.5%). Subsequently, 1 kg of this titanium dioxide powder was placed in a Henschel mixer, and methyltrimethoxysilane (Toshiba Silicone Co .: T
SL8113) (20% added to TiO ₂ ) and stirred for 1 hour. Further, the pH of the slurry was adjusted to 7.0 in 30 minutes by gradually adding 10% strength diluted sulfuric acid, and stirring was continued for 1 hour. Thereafter, the slurry was cooled to 40 ° C., washed with water after dehydration by filtration, dried with hot air and pulverized,
An anatase-type titanium dioxide powder having the surface of the alumina coating surface-treated with a silane coupling agent was obtained.

Example 4 A 1000% aluminum sulfate solution (Al ₂ O ₃ addition rate: 1.0%) was used in place of the sodium aluminate solution, and a 10% aqueous solution of trimethylolpropane was added to titanium dioxide in place of methyltrimethoxysilane. Anatase-type titanium dioxide having aluminum in the crystal and alumina coating on the surface, and the surface of the alumina coating was surface-treated with trimethylol, in the same manner as in Example 3 except that the amount used was 0.5%. A powder was obtained.

Example 5 In Example 1, zinc chloride was used in place of aluminum sulfate so that the zinc content in the crystal was 0.13% by weight, and the alumina coating amount was 1.0% by weight. In the same manner as in Example 1 except that sodium aluminate was added, anatase type titanium dioxide powder containing zinc in the crystal and having an alumina coating on the surface was obtained. Example 6 In Example 3, zinc chloride was used in place of aluminum sulfate so that the zinc content in the crystal was 0.13% by weight, and alumina acid was used so that the alumina coating amount was 0.5% by weight. Add sodium and further substitute for methyltrimethoxysilane with acrylic silane (Toshiba Silicone Co., Ltd .: TSL837
In the same manner as in Example 3 except that (0) was used, anatase-type titanium dioxide powder containing zinc in the crystal and having an alumina coating on the surface and having the alumina coating surface-treated was obtained.

Comparative Example 1 Aluminum in the crystal and alumina coating on the surface were prepared in the same manner as in Example 1 except that aluminum sulfate was not added to the hydrated titanium dioxide slurry and the alumina coating step after firing the slurry was omitted. An anatase-type titanium dioxide powder was obtained. Comparative Example 2 The same procedure as in Example 1 was carried out except that aluminum sulfate was not added to the hydrous titanium dioxide slurry and aminosilane (TSL8331 manufactured by Toshiba Silicone Co., Ltd.) was used as a silane coupling agent, and no aluminum was contained in the crystal. Thus, an anatase type titanium dioxide powder having an alumina coating on the surface was obtained. Comparative Example 3 An anatase-type titanium dioxide powder containing aluminum in the crystal but having no alumina coating on the surface was obtained in the same manner as in Example 1 except that the alumina coating step after firing the hydrous titanium dioxide slurry was omitted. .

Evaluation Test of Whiteness 5 g of the titanium dioxide powder of the above Examples and Comparative Samples was added to 45 g of polyethylene resin (Mirason 402 manufactured by Mitsui Petrochemical Co., Ltd.), kneaded at 150 ° C. using a two-roll mill, and 1 mm
It was formed into a thick sheet. Measure the whiteness of this sheet with a color difference meter
(Suga Test Machine Co., Ltd. color computer SM-5 type) was used for measurement. The results are shown in Table 1.

Evaluation Test of Light Stability The polyethylene sheet used for the measurement of the whiteness was molded into a predetermined size (70 mm × 150 mm × 1 mm), and subjected to a 50 cycle test using a Du-cycle tester (Ska Test Machine Co., Ltd.). The change in color before and after the time light irradiation was measured. The test was performed in a cycle of 1 hour of light irradiation and 12 minutes of no irradiation. When no irradiation was performed, pure water was sprayed on the back surface of the sample. The results are shown in Table 1.

Evaluation Test of Thermal Stability The polyethylene sheets containing titanium dioxide of the above Examples and Comparative Samples were heated at 310 ° C. for 20 minutes using a small muffle furnace. The sheet was measured using the above color difference meter. The color difference from the sheet before heating was calculated using the Hunter color difference formula specified in JIS-Z-8370. The results are shown in Table 1.

[0027]

[Table 1]

As shown in the results of Table 1, Comparative Example 1, which did not contain aluminum in the crystal and had no alumina coating on the surface, had a low whiteness and a color difference ΔE in the light stability and thermal stability tests. All of them are large and have poor color stability. In Comparative Example 2 having an alumina coating on the surface but no aluminum in the crystal, the light stability was slightly improved, but the thermal stability was the lowest. Further, in Comparative Example 3, which contains aluminum in the crystal but has no alumina coating on the surface, the heat stability is slightly improved, but the light stability is significantly inferior. On the other hand, Example 1 using the titanium dioxide powder of the present invention
Nos. 6 to 6 have high whiteness and a small color difference ΔE in the light stability and heat stability tests. As described above, the anatase type titanium dioxide of the present invention has excellent color stability due to the synergistic effect with the doping of aluminum or zinc in the crystal and the alumina coating on the surface.

[0029]

The anatase type titanium dioxide of the present invention has higher whiteness than conventional products and has the most suitable properties as a pigment which is hardly discolored. In particular, at the time of kneading with plastics, there is little discoloration even under a high-temperature treatment at around 300 ° C., and it is suitable as a material for a plastic molded body to be subjected to a high-temperature treatment.

Claims (5)

[Claims] 1. An anatase type titanium dioxide which contains at least one of aluminum and zinc in a crystal and has an alumina coating on the surface. 2. The titanium dioxide according to claim 1, wherein the coating amount of alumina is 0.01 to 2.0% by weight. 3. The titanium dioxide according to claim 1, wherein the alumina coating layer is further surface-treated. 4. The aluminum content in the crystal is 0.02.
The titanium dioxide according to claim 1, 2 or 3, wherein the amount is from 0.5 to 0.5% by weight, preferably from 0.04 to 0.2% by weight. 5. The method according to claim 1, wherein the zinc content in the crystal is 0.05 to 1.0% by weight, preferably 0.1 to 0.6% by weight.
4. The titanium dioxide according to 2 or 3.