JP5500448B2 - Surface coating method of pigmentary titanium dioxide for forming crystalline alumina hydrate on particle surface - Google Patents

Description

  The present invention relates to a titanium dioxide pigment for pigment that forms a crystalline alumina hydrate on a particle surface by adding an inorganic acid to a dispersion of titanium dioxide and sodium aluminate when coating the surface of titanium dioxide particles. The present invention relates to a surface coating method. Further, the present invention relates to a titanium dioxide surface coating method for pigments in which a dilute silicic acid solution is added to deposit hydrous silica on a crystalline alumina hydrate precipitation layer.

  Titanium dioxide particles have optical activity and cause an oxidation reaction by the ultraviolet rays of sunlight. Therefore, this optical activity is removed to improve the affinity with the resin, dispersibility, gloss of the coating film, and durability. Therefore, many proposals have been made.

[Patent Document 1] discloses that as a surface treatment of titanium dioxide, sodium silicate is added to a titanium dioxide slurry heated to a temperature of 85 ° C. to 100 ° C. in the presence of citric acid, and a hydrous silica layer is formed on the surface of titanium dioxide particles. TiO ₂ pigment manufacturing method is disclosed, in which sodium aluminate is added, pH is adjusted to 5 to 9 with an inorganic acid, and alumina is deposited on the surface of silica-coated particles.

  [Patent Document 2] describes a method in which sodium aluminate is added to a titanium dioxide slurry, heated to a temperature of 50 ° C. to 70 ° C., sulfuric acid is added, and a boehmite alumina layer is formed on the titanium dioxide at a pH of about 1.5. A durable color material for plastic has been proposed in which an amorphous alumina layer is coated on one layer.

[Patent Document 1] describes a method in which sodium silicate is added to a titanium dioxide slurry heated to 85 ° C. to 100 ° C. in the presence of citric acid to deposit a hydrous silica layer on the surface of titanium dioxide particles, and then aluminate. It is a method in which soda is added and adjusted to pH 5 to 9 with an inorganic acid, and alumina is deposited on the surface of the silica-coated particles, but neutralizing sodium aluminate to pH 5 to 9 with an inorganic acid, Amorphous aluminum hydroxide (Al (OH) ₃ ) is generated inside the liquid of the dispersion, and this aggregates and accumulates. Therefore, adhesion to the surface of the titanium dioxide particles is impaired, and it is easy to peel off from the surface of the titanium dioxide particles. The paint film is disadvantageous in that the brightness and glossiness are low and the film resistance is not high.

In [Patent Document 2], sodium aluminate is heated to a temperature of 50 ° C. to 70 ° C., adjusted to pH = 1.5 with sulfuric acid to form a boehmite layer, and then an alumina coating agent is added to adjust the pH to 6-9. As a method for forming second and third boehmite alumina layers, a hard needle crystal of boehmite alumina (Al ₂ O ₃ H ₂ O) is generated at a high temperature of 50 ° C. to 70 ° C. Since the speed is too high, it becomes difficult to coat the titanium dioxide particle surface, and boehmite alumina is produced in the liquid part of the titanium dioxide slurry dispersion, causing poor coating of the titanium dioxide particle surface. Films have the disadvantage of low brightness and loss of gloss.

These proposals are neutralization methods in which an inorganic acid is added to a sodium aluminate solution at a high temperature of 50 to 100 ° C. to adjust the pH to 5 to 9. When sodium aluminate is used as a solution, it is strongly alkaline with a pH of 13 or less, and aluminate ions are dissolved in this strong alkali solution. In the above neutralization method, sodium aluminate becomes amorphous alumina hydrate (aluminum hydroxide Al (OH) ₃ ) by acid neutralization, precipitates in the liquid part of the dispersion, and coats the particle surface. There are still significant challenges that will be difficult.

The present invention relates to crystalline alumina hydrate (Al ₂ O ₃ .3H ₂ O) which is gradually formed by hydrolysis reaction of aluminate ions (H ⁺ AlO ₂ ⁻ ) in a sodium aluminate aqueous solution at a low temperature of 40 ° C. or lower. In the conventional patent technology, there is no description relating to the production of crystalline alumina hydrate produced by the hydrolysis reaction of the present invention.

JP 2005-507968 Gazette U.S. Pat. No. 5,700,328 ATLAS OF ELECTROCHEMICAL EQUILIBRIA IN AQUEOUS SOLUTION BY MALE POURBAIX (1966) Electrochemistry Vol. 28 (p302-312, 358-364, 1935)

Problems to be solved by the invention

  According to the present invention, when alumina hydrate is formed on the surface of titanium dioxide particles, sodium aluminate can be added without forming alumina hydrate in the liquid part of the dispersion of sodium aluminate and titanium dioxide particles. It is to propose a surface coating method for titanium dioxide for pigments, in which a crystalline alumina hydrate is deposited uniformly and densely on the particle surface by adjusting the decomposition rate.

Means for solving the problem

  In the present invention, in order to precipitate a uniform and dense crystalline alumina hydrate on the surface of titanium dioxide particles, by adjusting the hydrolysis rate of sodium aluminate in a dispersion of titanium dioxide and sodium aluminate, It is noticed that the production rate of the produced alumina hydrate can be controlled, and crystalline alumina hydrate is produced in the liquid part of the dispersion by adding inorganic acid and gradually adjusting the pH. However, it was found that all precipitates were formed on the surface of the titanium dioxide particles.

The basics of the present invention will be described.
The present invention provides titanium dioxide to which titanyl ions are added in order to activate the surface activity of the raw material titanium dioxide particles in order to precipitate crystalline alumina hydrate uniformly and densely on the surface of titanium dioxide particles. The dispersion of the slurry and sodium aluminate is neutralized with 2N—H ₂ SO ₄ as an inorganic acid to free alkali components of sodium aluminate, initially pH 13 or higher to about pH 11.5. By adjusting the hydrolysis rate of aluminate (H ⁺ AlO ₂ ⁻ ) while neutralizing the alkali component generated by decomposition and adjusting the pH to 11.5 to 10.75, the crystalline alumina of the hydrolysis product The hydrate is a crystalline alumina hydrate that gradually precipitates toward the surface of the titanium dioxide particles and does not occur in the liquid part of the dispersion. After precipitated form Hydra distearate write _{(Al 2 O 3 · 3H 2} O), was added to neutralize adjusted solution of dilute sodium silicate solution, in which the basic techniques of depositing the hydrous silica.

The crystalline alumina hydrate of the present invention was confirmed by analysis by X-ray diffraction and differential thermal balance analysis (see [FIG. 2] and [FIG. 3]). Crystal determination by an X-ray diffraction apparatus is difficult to determine if the content of the target substance in the sample is 5% or less. When coated with 5% or less with respect to the titanium dioxide TiO _2, determined by X-ray diffraction it becomes impossible. Determination of most surface-treated titanium dioxide-containing alumina components by X-ray diffraction is difficult.
The determination by differential thermal balance analysis is based on the dehydration data of amorphous alumina hydrate and crystalline alumina hydrate based on the dehydration amount of a minute amount of water and the endothermic energy generated during dehydration. It was confirmed that it was possible to determine the crystal system of the alumina coating inside.

The present invention has the following configuration.
(1) When an inorganic acid is added to a dispersion of titanium dioxide slurry containing titanyl ions and sodium aluminate to perform surface coating treatment on titanium dioxide particles, the inorganic acid is added while maintaining the temperature at 40 ° C. or lower. Without neutralizing aluminate ions, after neutralizing only free alkali ions, the hydrolysis rate of aluminate (H ⁺ AlO ₂ ⁻ ) is increased while neutralizing alkali ions generated by hydrolysis of sodium aluminate. Crystalline alumina hydrate is deposited on the surface of titanium dioxide particles by adjusting, and then a dilute sodium silicate neutralization adjustment solution is added to deposit hydrous silica. It is a titanium dioxide surface coating method for pigments which is deposited on the surface.
(2) The titanyl ion is titanyl dichloride (TiOCl ₂ ) or titanyl sulfate (TiO (SO ₄ ) ₂ ), and activates the surface activity on the surface of the titanium dioxide particles. It is a surface coating method for titanium dioxide for pigments, in which the crystalline alumina hydrate described in (1) above, to which .about.0.02% by weight is added, is deposited on the particle surface.
(3) Adjustment of the hydrolysis rate of aluminate (H ⁺ AlO ₂ ⁻ ) adjusts the addition of an inorganic acid to meet the precipitation of crystalline alumina hydrate while maintaining the slurry pH 11.5 to 10.75. This is a surface coating method for titanium dioxide for pigments, wherein the crystalline alumina hydrate described in (1) and (2) above is deposited on the particle surface.
(4) Crystalline alumina hydrate is hydratedilite (Al ₂ O ₃ .3H ₂ O), dehydrated at a drying temperature of 295 ° C. (± 3 ° C.), and boehmite (Al ₂ O ₃ .H ₂ O) The surface coating method of titanium dioxide for pigments, wherein the crystalline alumina hydrate described in the above (1), (2) and (3) is deposited on the particle surface.
(5) A neutralization adjustment solution is added so that the diluted sodium silicate solution has a concentration of SiO ₂ 20 g / l or less and a pH of 6.8 with an inorganic acid, and (1) (2) (3) (4) It is a surface coating method for titanium dioxide for pigments, in which hydrous silica is deposited on the crystalline alumina hydrate layer to be described, and the crystalline alumina hydrate is deposited on the particle surface. The water-containing silica on the outer layer is for improving the lipophilicity, and the compatibility is high even if it is a very small amount in order to improve the compatibility between the resin and the particle surface during coating.

Hydrolysis reaction of sodium aluminate solution

  About the hydrolysis reaction of the sodium aluminate of this invention, the production | generation process of the crystalline alumina hydrate by 40 degreeC or less of the sodium aluminate aqueous solution which does not contain a titanium dioxide particle is demonstrated below based on a basic experiment.

The sodium aluminate used in the present invention is NaAlO ₂ flakes of Kanto Chemical Co., Ltd. Deer grade Na ₂ O 19.2%, Al ₂ O ₃ 20.0%, and free (excess) Na ₂ O 10%. Contains.

In the present invention, the above-mentioned sodium aluminate 30 g / l single aqueous solution (corresponding to 3% of titanium dioxide 300 g / l dispersion TiO ₂ ) was prepared as a basic test. In the aqueous solution of sodium aluminate, the alkaline component (NaOH) of dissociated sodium aluminate (NaAlO ₂ ) and aluminate ions (H ⁺ AlO ₂ ⁻ ) coexisted with alkaline and free alkali components (Na ₂ O) of pH 13 or more. Yes. (See Non-Patent Document 1)

さらに、
（２）イオン状アルミン酸ソーダ（Ｎａ^＋（ＡｌＯ_２）⁻）は解離する。式（２）に示す。

（３）続いてアルミン酸イオン（Ｈ^＋（ＡｌＯ_２）⁻）は、解離したＮａＯＨを中和除去すると、周辺の水（Ｈ_２Ｏ）と直ちに加水分解を起こしアルミナ水和物を生成する。式（３）に示す。

(1) Sodium aluminate in which NaAlO ₂ is dissolved and ionized together with a free alkali component (Na ₂ O) is represented by the formula (1).

further,
(2) Ionic sodium aluminate (Na ⁺ (AlO ₂ ) ⁻ ) dissociates. It shows in Formula (2).

(3) Subsequently, when the aluminate ions (H ⁺ (AlO ₂ ) ⁻ ) neutralize and remove the dissociated NaOH, it immediately hydrolyzes with surrounding water (H ₂ O) to produce alumina hydrate. It shows in Formula (3).

In other words, the production of crystalline alumina hydrate by the hydrolysis reaction that neutralizes and removes the alkali component from the inorganic acid in the aqueous sodium aluminate solution causes the above reactions (1), (2), and (3) to proceed simultaneously. Since the 2N—H ₂ SO ₄ solution is gradually added dropwise as an inorganic acid while adjusting the pH to 11.5 to 10.75, there is no precipitation surface like titanium dioxide particles, so that a very fine acicular crystal To produce crystalline alumina hydrate.
The Al ₂ O ₃ .3H ₂ O production hydrolysis curve of the sodium aluminate aqueous solution is shown in FIG.

FIG. 1 is a neutralization line showing a first neutralization zone showing free NaOH and dissociative NaOH in sodium aluminate, neutralization pH 13 to 11.5.
The second neutralization zone pH 11.5 to 10.75 is due to neutralization of alkaline NaOH generated by dissociation of ionized Na ⁺ AlO ₂ ⁻ and simultaneously hydrolysis of H ⁺ (AlO ₂ ) ^−. It is the 2nd neutralization zone part of the hydrolysis zone which adjusts the production | generation rate of crystalline alumina hydrate. It can be seen that the hydrolysis pH of 10.75 consumed 96.3% of the total neutralizer amount.

As a result of differential thermal balance analysis, the crystalline alumina hydrate hydrate dilite Al ₂ O ₃ .3H ₂ O of the present invention shows that the endothermic energy shows the highest value of 16.5 μV / 100 g at a heating temperature of 295 ° C. confirmed. For differential thermal balance analysis, a Yamato-differential heat and thermogravimetric simultaneous measurement device (TG / DTA6200 type) was used. As shown in FIG.
Hydrargillite _{Al 2 O} 3 · 3H 2 _O is not dehydrating almost the heated 100 ° C. to 250 DEG ° C., at 295 ° _C., 2 water molecules in the _{Al 2 O 3 · 3H 2 O} (2H 2 O ) was _dehydrated, it was confirmed that became _{Al 2 O 3 · H 2 O} .
Al ₂ O ₃ · 3H ₂ O and Al ₂ O ₃ · H ₂ O are X-ray diffraction and Al ₂ O ₃ · 3H ₂ O is hydratedite and Al ₂ O ₃ · H ₂ O is boehmite. confirmed. (See Non-Patent Document 2)

The dehydration line of amorphous alumina hydrate Al (OH) ₃ produced by the neutralization method of the conventional method starts at a heating temperature of 150 ° C. and reaches a maximum value at 200 ° C., and then reaches 300 ° C. and 400 ° C. Followed. It is known that amorphous hydrate does not have a specific dehydration temperature.

Regarding the determination of the crystal system of the hydratedilite Al ₂ O ₃ .3H ₂ O of the crystalline alumina hydrate of the present invention, the analysis confirmation means using the differential thermal balance analysis and the X-ray diffraction in combination is employed. It is the first technique by those.

The fact that the present invention employs the differential thermal balance analysis method for discriminating the crystal system of crystalline alumina hydrate is that, if the content of alumina Al ₂ O _{3 in} titanium dioxide TiO ₂ is 5% or less, the crystal by X-ray diffraction is used. Since it is difficult to identify the shape, as a result of pursuing the difference in generation temperature of dehydration endothermic energy of crystallization water of crystalline alumina hydrate by differential thermobalance, as shown in the examples described later, titanium dioxide It was confirmed that even when the Al ₂ O ₃ content in the medium was 2% or less, the crystal form could be discriminated.

In addition, it is known that the crystal system can be identified by measuring the dehydration rate of crystal water and the change in dehydration temperature of crystalline alumina hydrate by differential thermal balance analysis. (See Non-Patent Document 2)
FIG. 3 shows the measurement results of the dehydration rate and dehydration temperature of the hydrated dilite Al ₂ O ₃ .3H ₂ O of the crystalline alumina hydrate of the present invention.
Amorphous alumina hydrate is also described.

[FIG. 3] From FIG. 3, crystalline alumina hydrate Hydraldilite Al ₂ O ₃ .3H ₂ O has a dehydration rate of 7.5% at a heating temperature of 150 ° C. to 250 ° C., but a dehydration rate of 22% at 295 ° C. becomes .5%, 2 molecules of crystal water 3 molecule water _{(3H 2 O) (2H 2} O) was confirmed determined that dehydrated. The amorphous alumina hydrate Al (OH) ₃ has a dehydration rate of 31% at a heating temperature of 150 ° C. to 200 ° C., becomes anhydrous alumina Al ₂ O ₃ , and 90% of the trimolecular water (3H ₂ O) is dehydrated. And completely dehydrated at 400 ° C. to form anhydrous alumina Al ₂ O ₃ .

Deposition of hydrous silica with neutralization conditioning solution of dilute sodium silicate solution

The solidification stability of the dilute sodium silicate solution of the present invention and the deposition of hydrous silica will be described. The sodium silicate solution used in the present invention is a Kanto Chemical Co., Ltd. deer grade 1 (Na ₂ O 17-19%, SiO ₂ 35-38%, free NaO 10.0% contained) diluted with purified water SiO ₂ 100 g / l Sodium silicate solution was used.

In the present invention, a sodium silicate solution of SiO ₂ 20 g / l or less obtained by diluting a sodium silicate solution with purified water is referred to as a diluted sodium silicate solution.

The sodium silicate solution SiO ₂ 30 g / l concentration produced colloidal silica during neutralization at pH 9.5 to 8.8 when neutralized with an inorganic acid, and solidification occurred in a short time. As a result of quantitative analysis, it was found that an alkali component was included.

The inventors have conducted extensive studies to eliminate the occurrence of solidification due to the formation of colloidal silica during the neutralization, and as a result, when diluted with dilute sodium silicate SiO ₂ 20% or less, inorganic acid, up to pH 6.80. It has been found that the neutralization adjustment solution can maintain a stable state even after elapse of 7 hours or more without generating a colloidal precipitate.

The neutralized adjustment solution of dilute sodium silicate solution SiO ₂ 20 g / l is obtained by gradually adding crystalline alumina hydrate into a slurry that precipitates and forms crystalline alumina hydrate on the surface of titanium dioxide particles. It was found that hydrous silica was formed and deposited on the precipitation forming layer, and the present invention was completed.

In addition, the present inventors have obtained the following knowledge about a neutralization adjustment solution of a mixed solution of sodium aluminate aqueous solution and dilute sodium silicate solution. It shows to Formula (4)-(8).

  That is, the mixed solution of sodium aluminate aqueous solution and dilute sodium silicate solution is an alkali component of the product alumina-silica hydrate by preferentially neutralizing and adjusting the dissociated alkali component generated by hydrolysis. It was confirmed by quantitative analysis and a differential heat and thermogravimetric simultaneous measurement device that a certain sodium content was extremely small and the product alumina-silica hydrate was crystalline alumina hydrate.

Effect of the invention

In the titanium dioxide for pigments formed by depositing the crystalline alumina hydrate of the present invention on the particle surface, the hydrated dilite Al ₂ O ₃ .3H ₂ O of crystalline alumina hydrate is uniformly and densely deposited on the titanium dioxide particles. A small amount of water-containing silica is deposited on the formed layer, surface-treated, and then dried by heating to convert the coating layer to boehmite (Al ₂ O ₃ .H ₂ O). Since the acid (SiO ₂ ) is deposited, the surface coating does not peel off when it is made into a paint, it is well-familiar with the resin, is highly dispersible, has high gloss, and has a long-term weather resistance. It is characterized by maintaining its properties and is highly effective as a basic pigment for the automobile industry.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below.
In the present invention, the temperature of a dispersion obtained by mixing sodium aluminate with titanium dioxide slurry containing titanyl ions is maintained at 40 ° C. or less, and neutralization of free alkali components contained in sodium aluminate is carried out with an inorganic acid at a pH of 13 to 11. Leave for 10-15 minutes, adjusting to .5. Subsequently, hydrolysis of sodium aluminate is gradually performed while adjusting the pH to 11.5 to 10.75.
In the hydrolysis of sodium aluminate, since the hydrolysis rate of sodium aluminate is slow, an inorganic acid is dropped so as to match this rate, and the dissociated NaOH is neutralized gradually, so that sodium aluminate NaAlO ₂ is added. Hydral dilite Al ₂ O ₃ .3H ₂ O is produced as crystalline alumina hydrate without direct neutralization.

The titanium dioxide of the present invention may be chlorine method TiO ₂ or sulfuric acid method TiO ₂ .
The present invention may be potassium aluminate in addition to sodium aluminate.
Also, the use of an inorganic acid can be a hydrochloric acid solution.

Hereinafter, the present invention will be described in detail with reference to examples.
Titanyl chloride chlorine process titanium dioxide 300g / l _(TiOCl 2) 0.05g and slurry was added (raw material TiO _2: 0.01%), sodium aluminate _{(Na 2 O19.2%, Al 2} O 3 20. %) 47 g (equivalent to 3.0% of TiO ₂ vs. Al ₂ O ₃ ) was dissolved with stirring to obtain 1 l of a dispersion. The pH of the dispersion is 12.8. After stirring this dispersion for 45 minutes, 21 ml of 6N—H ₂ SO ₄ solution is gradually added dropwise while maintaining the temperature at 35 ° C., and the pH of 11.75 is maintained for 10 minutes. Subsequently, 24 ml of 6N—H ₂ SO ₄ solution was dropped at a rate of 0.6 ml / min, and sodium aluminate was hydrolyzed while adjusting the pH to 11.5 to 10.75, and then 6N—H ₂ SO ₄ solution. 3 ml was added dropwise to adjust the pH to 8.8, and an alumina hydrate coating slurry was obtained. To this alumina coating treatment slurry, 150 cc of dilute sodium silicate (SiO ₂ 20 g / l) neutralization adjustment solution is gradually added to deposit hydrous silica, readjusted to pH 7.8, and hydrated on the titanium dioxide particle surface. A slurry obtained by subjecting the product to precipitation formation was obtained. The slurry was subjected to solid-liquid separation by filtration in the usual manner, followed by washing filtration, drying, and high-temperature airflow pulverization to obtain alumina hydrate surface-treated titanium dioxide.
As a result of analyzing the endothermic energy and dehydration amount (rate) due to dehydration of the water content using differential thermal balance analysis to identify the shape of the alumina hydrate deposited on the surface of the resulting titanium dioxide particles, the crystallinity The hydrated dilite Al ₂ O ₃ .3H ₂ O of alumina hydrate was confirmed.

In addition, as a result of chemical analysis of alumina hydrate surface-treated titanium dioxide, Al ₂ O ₃ 2.88% and SiO ₂ 1.00% were obtained. Similarly, in the X-ray diffraction, the crystal system could not be discriminated because the content of the alumina hydrate in the object was less than the identification range of the X-ray diffractometer (5% or less).

According to Example 1, a slurry during pH adjustment corresponding to the hydrolysis rate of sodium aluminate was sampled at 35 ° C. in titanium dioxide slurry, and aluminate ion concentration analysis and particle surface observation were performed with an electron microscope apparatus.
As a comparative test, when the slurry temperature was 60 ° C., a scanning electron microscope observation of the same particle surface as described above was performed.
As a result, in Example 1,. When the slurry temperature is 35 ° C., the particle surface of the scanning electron micrograph is flat and uniform, and no contamination (generator in liquid) is observed in the entire visual field (see [FIG. 4]). When the slurry temperature is 60 ° C., the particle surface is rough and adhesion of fine particles generated outside the surface is observed (see [FIG. 5]). When the slurry temperature is 60 ° C. or higher, the hydrolysis rate of sodium aluminate is too high, so the hydrolysis product is generated quickly and cannot be deposited on the particle surface. It can be said that this is the result of the generation.

As the sodium silicate solution of this example, a 10% sodium silicate solution of Kanto Chemical Co., Ltd. deer first grade reagent (SiO ₂ 35%, Na ₂ O 18%) was used, and a diluted solution of 20 g / l or less as SiO ₂ Neutralization was carried out. As a result, the SiO ₂ 20 g / l sodium silicate solution does not aggregate for more than 7 hours at a neutralization pH of 7.6, whereas the SiO ₂ 30 g / l sodium silicate solution has a neutralization pH of 9.0. It solidified. As a result of quantitative analysis after washing and drying the coagulated product, it was confirmed that it contained Na ₂ O in addition to SiO ₂ .

The pigmentary titanium dioxide obtained by coating the crystalline alumina hydrate obtained in Example 1 on titanium dioxide particles was blended with 40% PWC using a melamine alkyd resin as a substrate, and dispersed using an ultrahigh-speed rotating ball mill to form a paint. .
The paint was diluted, applied to a paint film test panel with a spray gun, and baked at 130 ° C. for 30 minutes to form a paint film.
As a result of the coating film test, the gloss value representing the glossiness is as high as 60 ° -60 ° 86.2%, 20 ° -20 ° 80.0%, and the product of Company A 60 ° -60 ° 85%, 20 ° -20 ° exceeded 58.5%.
In addition, the gloss value was high even after 3 years of natural exposure test of the coating film test panel, and chalking did not occur.

Industrial applicability

  As is apparent from the above description of the examples, the surface coating method of titanium dioxide for pigments for forming the crystalline alumina hydrate of the present invention on the particle surface is characterized in that the crystalline alumina hydrate is uniform on the titanium dioxide particles. Since it is densely deposited, when it is kneaded with a synthetic resin to form a paint, it becomes a paint product without the surface coating being peeled off from the titanium dioxide. Since the paint film is characterized by maintaining a high gloss value and long-term weather resistance, it is expected to be applied particularly to automobile paints for luxury cars.

Sodium aluminate _{30g / l (Al 2 O 3} 18.6%, Na 2 O11.4%) solution in _{2N-H 2 SO 4 Al 2} O 3 · 3H 2 O produced when the solution was added dropwise, hydrolysis curve FIG. By differential thermal balance analysis apparatus, when heating the Al 2 _{O 3} · _3H 2 _O crystalline alumina hydrate shows the measurement data detected endothermic energy due to decomposition dehydration. It is an endothermic energy curve figure by a differential thermal balance analysis method. By differential thermal balance analysis, is a diagram showing the dewatering rate in the dehydration by heating the Al 2 _{O 3} · _3H 2 _O crystalline alumina hydrate. It is a scanning electron micrograph (replica method) of the layer surface in which crystalline alumina hydrate was deposited on the surface of titanium dioxide particles at a temperature of 40 ° C. or lower. It is the scanning electron micrograph (replica method) of the titanium dioxide particle surface in the case of 60 degreeC temperature, and an external product.

Claims (5)

When the crystalline alumina hydrate is deposited uniformly and densely on the surface of titanium dioxide particles, the dispersion of titanium dioxide slurry containing titanyl ions and sodium aluminate is kept at a temperature of 40 ° C. or less, while aluminate The free alkali component contained in the soda was neutralized to a pH of 13 to 11.5 with an inorganic acid, allowed to stand for 10 to 15 minutes, and then further neutralized to a pH of 11.5 to 10.75, so that the sodium aluminate was hydrolyzed. By gradually decomposing, crystalline alumina hydrate precipitates on the surface of the titanium dioxide particles, and dilute sodium silicate solution is added to deposit hydrous silica to form crystalline alumina hydrate on the crystalline alumina hydrate. Titanium dioxide surface coating method for pigments to form precipitates Since titanyl dichloride (TiOCl ₂ ) or titanyl sulfate (TiO (SO ₄ ) ₂ ) as a titanyl ion activates the surface activity on the surface of the raw material titanium dioxide particles, it is 0.01% by weight to 0% with respect to titanium dioxide. A method for coating a titanium dioxide surface for pigments, wherein 0.03% by weight is added, and the crystalline alumina hydrate according to claim 1 is deposited on the particle surface.   By maintaining the pH of the titanium dioxide slurry at 11.5 to 10.75, adjusting the hydrolysis rate of sodium aluminate, and controlling the production rate of the crystalline alumina hydrate to be produced, The titanium dioxide coating method for pigments, wherein the crystalline alumina hydrate described in 1 is deposited on the surface of titanium dioxide particles The crystalline alumina hydrate is hydratedilite (Al ₂ O ₃ .3H ₂ O) and dehydrated at 290 ° C. (± 3 ° C.) to become boehmite (Ai ₂ O ₃ .H ₂ O). A surface coating method for titanium dioxide for pigments, wherein the crystalline alumina hydrate according to claims 1 to 3 is deposited on the particle surface. The method for coating the surface of titanium dioxide for pigments, wherein the dilute sodium silicate solution to be added is a SiO ₂ solution of 20 g / l or less, wherein the crystalline alumina hydrate is deposited on the particle surface.

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