JP2002129107A - Thermosetting water-based coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide thermosetting water-based coating compositions which excel in the dispersibility of pigments and form coating films with good gloss and, in addition, have improved storage stability. SOLUTION: The thermosetting water-based coating compositions comprise (a) a resin having a hydroxyl group and a carboxyl group, (b) a crosslinking agent, (c) a neutralizing agent, and (d) a titanium dioxide pigment whose surface has been coated with 1.0-5.0 wt.% hydrated oxide of silicon in terms of SiO2 and 1.0-4.0 wt.% hydrated oxide of aluminum in terms of Al2O3 in the order named.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous coating composition which is excellent in pigment dispersion stability, forms a coating film having good gloss, and has improved storage stability.

[0002]

2. Description of the Related Art Thermosetting organic solvent-based paints are often used as intermediate paints and top coats for automobiles. However, from the viewpoint of resource saving and global environmental protection,
There is a strong demand for the development of water-based thermosetting paints that use little or no organic solvents.

[0003] As a thermosetting aqueous coating material, there has been known a coating composition obtained by mixing and dispersing a resin containing a hydroxyl group and a carboxyl group, a crosslinking agent and a neutralizing agent in water. It contains a titanium dioxide pigment and the like.

[0004] However, in water-based paints, there is a drawback that a coating film formed due to insufficient dispersion stability of the titanium dioxide pigment is inferior in glossiness to a coating film formed from an organic solvent-based coating material. In addition, such a water-based paint also has a disadvantage that the titanium dioxide pigment particles aggregate and settle during storage.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned various drawbacks of a thermosetting water-based coating composition containing a titanium dioxide pigment. The present inventors have conducted intensive studies and as a result, this time, by using a titanium dioxide pigment whose surface is coated with a silicon hydrated oxide and an aluminum hydrated oxide as a titanium dioxide pigment, the above object was achieved. Find out what can be achieved,
The present invention has been completed.

Thus, according to the present invention, a thermosetting water-based paint containing a resin (a) containing a hydroxyl group and a carboxyl group, a crosslinking agent (b), a neutralizing agent (c) and a titanium dioxide pigment (d). In the composition, a titanium dioxide pigment (d)
Is 1.0 in terms of SiO _{2 based} on the weight of titanium dioxide.
-5.0% by weight of hydrated oxide of silicon and 1.0-4.0% by weight of aluminum hydrated oxide in terms of Al ₂ O ₃ There is provided a thermosetting aqueous coating composition (hereinafter, referred to as "the present composition"), which is a titanium pigment.

Hereinafter, the present composition will be described more specifically.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION (a) Hydroxyl group and carboxyl group
A resin containing, on average, two or more hydroxyl groups and carboxyl groups in one molecule, and specifically, a resin for coating known per se having both these functional groups, For example, acrylic resin, vinyl resin, polyester resin, alkyd resin, urethane resin and the like can be mentioned. These resins (a) are generally 10 to 200,
Especially the hydroxyl value in the range of 20 to 150, generally 10 to 2
Acid number in the range from 15 to 90, and
It preferably has a number average molecular weight in the range of 00 to 1,000,000, especially 2000 to 20,000. (B) Cross-linking agent: a compound capable of reacting with the hydroxyl group of the resin (a) to cross-link and cure the resin, for example, an amino resin and a blocked polyisocyanate compound.

As the amino resin, for example, melamine,
Methylolated amino resins obtained by reacting an aldehyde with an amino component such as urea and benzoguanamine are exemplified. Further, those obtained by etherifying the methylolated amino resin with an appropriate alcohol can also be used. Examples of the alcohol that can be used for the etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, and i-propyl alcohol. And monohydric alcohols having 1 to 10 carbon atoms, such as n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

The blocked polyisocyanate compound is a compound in which the isocyanate group of the polyisocyanate compound is blocked with a blocking agent. The polyisocyanate compound is a compound having two or more isocyanate groups in one molecule, for example, aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as hydrogenated xylylene diisocyanate and isophorone diisocyanate And tolylene diisocyanate, 4,4'-
Aromatic diisocyanates such as diphenylmethane diisocyanate; adducts of these organic polyisocyanate compounds with polyhydric alcohols, low molecular weight polyester resins, water, etc .; cyclized polymers of polyisocyanate compounds; isocyanate biuret bodies, etc. Can be On the other hand, examples of the blocking agent include phenol-based, lactam-based, active methylene-based, alcohol-based, mercaptan-based, acid amide-based, imide-based, amine-based, imidazole-based, urea-based, carbamate-based, imine-based, oxime-based Systems, sulfite systems and the like can be used. The isocyanate groups blocked by these blocking agents are stable at room temperature, but when heated above the dissociation temperature, the blocking agents dissociate, the isocyanate groups are regenerated, and react with the hydroxyl groups of the resin (a). .

[0011] These crosslinking agents (b) are generally
It preferably has a number average molecular weight in the range of 10,000, especially 200-5000.

The mixing ratio of the resin (a) and the crosslinking agent (b) described above is generally from 50 to 90%, especially from 65 to 90%, based on the total solid weight of these two components.
~ 80%, and the crosslinker (b) is generally 50-10%,
In particular, it is suitable to be within the range of 35 to 20%. (C) neutralizing agent: for neutralizing the carboxyl group of the resin (a), for example, ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, Dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, ethylenediamine,
Morpholine, N-alkylmorpholine, pyridine, monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine,
Examples thereof include amines such as triethanolamine, diethylethanolamine, and triethanolamine. These can be used alone or in combination of two or more. The amount of these neutralizing agents to be used is usually 0.1 to 2.0 equivalents, particularly preferably 0.1 equivalent to the carboxyl group in the resin (a).
A range of 3 to 1.2 equivalents is suitable. (D) with titanium dioxide by weight, 1 in terms of SiO _2.
0-5.0% by weight of hydrated oxide of silicon and Al ₂ O ₃
Hydration oxidation of aluminum in an amount of 1.0 to 4.0% by weight
Titanium dioxide face coated with objects
Materials : As the titanium dioxide pigment before being coated with both hydrated oxides of silicon and aluminum, those produced by a method known per se can be used. For example, a titanium dioxide solution can be hydrolyzed by hydrolysis. Examples thereof include those obtained by a so-called sulfuric acid method of calcining the obtained hydrous titanium oxide; and those obtained by a so-called chlorine method of vapor-phase oxidation of titanium tetrachloride. These are in the form of granules or powders, and the particle size is usually preferably included in the range of 0.1 to 1.0 μm. The crystal form may be either rutile type or anatase type. The rutile type is preferable in consideration of the optical scattering ability (underlayer concealing property) and weather resistance in the coating film formed by the object.

In preparing the coated titanium dioxide pigment (d), first, the surface of the titanium dioxide pigment is coated with a hydrated oxide of silicon. The coating method is preferably a wet method for uniform coating. Specifically, for example, titanium dioxide particles are dispersed in a solvent such as water to form a slurry, a silicon source is added to the slurry, and an acid,
It is carried out by neutralizing with a neutralizing agent such as an alkali to precipitate a hydrated oxide of silicon on the surface of the titanium dioxide pigment. As a silicon source that can be used for coating, an aqueous silicate solution is preferable, and for example, an aqueous sodium silicate solution, an aqueous potassium silicate solution, and the like can be suitably used.

The coating amount of the hydrated oxide of silicon is in the range of 1.0 to 5.0% by weight, particularly 1.5 to 4.0% by weight in terms of SiO ₂ , based on the weight of titanium dioxide. Preferably, there is. If the coating amount of the hydrated oxide of silicon is less than 1.0% by weight, it becomes difficult to obtain sufficient storage stability, and the titanium dioxide particles tend to aggregate and settle during storage.
If the coating amount is more than 5.0% by weight, the initial dispersibility in the present composition is poor, and the finish (gloss and smoothness) of the coating film may be reduced.

Titanium dioxide coated with a hydrated oxide of silicon
At high temperatures (eg, 50 ° C. to 90 ° C.)
Perform a so-called high-density treatment of neutralizing with an alkaline solution.
It is preferable that the coating amount of the silicon hydrated oxide is
SiO based on titanium oxide weight _TwoConverted to 3.0% by weight
In systems with less, instead of high-density processing,
Can also be managed.

After the surface of the titanium dioxide pigment is coated with the hydrated oxide of silicon, the surface of the particle is coated with the hydrated oxide of aluminum to obtain the coated titanium dioxide pigment (d).

The aluminum hydrated oxide coating comprises:
The coating can be performed in the same manner as the above-mentioned coating of the hydrated oxide of silicon, and it is particularly preferable to perform coating by a wet method. Specifically, for example, titanium dioxide pigment particles coated with a hydrated oxide of silicon are dispersed in a solvent such as water, an aluminum source is added to the slurry, and an acid, a neutralizing agent such as an alkali is added. Neutralize and precipitate aluminum hydrated oxide on the surface of the pigment particles. As the aluminum source that can be used for coating, a water-soluble aluminum salt is suitable, and for example, sodium aluminate, aluminum sulfate, aluminum chloride, and the like can be suitably used.

The coating amount of the aluminum hydrated oxide is 1.0 to 4.0 in terms of Al ₂ O _{3 based} on the weight of titanium dioxide.
It is preferably in the range of 0% by weight, in particular 1.5 to 3.0% by weight. Aluminum hydrated oxide coverage of 1.
If the amount is less than 0% by weight, the finished appearance (eg, gloss, smoothness, etc.) and weather resistance of the coating film may be reduced. If the amount is more than 4.0% by weight, the storage stability of the present composition is not sufficient. , The titanium dioxide pigment may settle out.

As a coating method, titanium dioxide particles coated with a hydrated oxide of silicon are dispersed in a solvent such as water, and an aluminum source and an acid or alkali for neutralizing the aluminum source are dispersed in the slurry. While simultaneously adding a neutralizing agent and maintaining a constant pH (for example, 4.0 to 10.0),
The so-called simultaneous neutralization method of depositing a hydrated oxide of aluminum on the surface of titanium dioxide particles coated with a hydrated oxide of silicon is preferred.

As the coated titanium dioxide pigment (d), the surface of the titanium dioxide particles is coated with both the hydrated oxide of silicon and the hydrated oxide of aluminum as described above, and then the outermost layer surface is coated with a small amount. It is preferable to use those coated with a hydrated oxide of silicon and adjusted for charge, pH conditions and the like. Thereby, depending on the amount and ratio of the hydroxyl group and carboxyl group of the resin (a) in the present composition, the amount of the crosslinking agent (b) and the amount of neutralization by the neutralizing agent (c), etc. The effect of eliminating the adverse effect on the storage stability of the product is obtained.

The method of coating a small amount of hydrated oxide of silicon on the outermost layer surface is, for example, as described above except that titanium dioxide particles coated with both components of hydrated oxide of silicon and hydrated oxide of aluminum are used. and can be carried out in the same manner, the coating amount is in titanium dioxide by weight, SiO ₂
It is preferably in the range of 0.2 to 1.0% by weight, especially 0.5 to 0.9% by weight. The coating amount is 0.2
If the amount is less than 10% by weight, the amount of change in the charge on the surface of the titanium dioxide particles is small, and the effect of improving the storage stability may be small. Although effective, the gloss of the coating film may be reduced.

The titanium dioxide pigment whose surface is coated as described above has an adverse effect on the dispersion stability of the titanium dioxide pigment by shifting the pH in an aqueous medium to the alkaline side of 8.0 to 10.0. Can remove impurities such as sulfate ions, which are considered to exert the following effects. As a result, the finished appearance (for example, gloss, smoothness, etc.) of a coating film formed using the present composition and the present composition Storage stability can be improved.

The titanium dioxide particles whose surface is coated with the hydrated oxide of silicon and the hydrated oxide of aluminum are washed so that the electrolyte component is 200 μS / cm or less, and then dried. It is preferable to volatilize the water by a method such as the above, and pulverize by a pulverizer or the like. As the crusher, it is preferable to use a strong crusher such as a fluid energy mill.

Further, titanium dioxide particles whose surface is coated with a hydrated oxide of silicon and a hydrated oxide of aluminum,
Furthermore, it is also possible to perform a surface treatment with a polyol or amine such as trimethylolethane, trimethylolpropane, dimethylethanolamine, and triethanolamine. The amount of surface treatment by these can be arbitrarily selected, but is preferably as small as possible without impairing the coating properties such as hydrophilicity.

In the present composition, the blending ratio of the coated titanium dioxide pigment (d) thus obtained can be arbitrarily changed according to the purpose of use of the present composition, etc., and generally, the resin (a) and the resin (a) are crosslinked. 1 to 300 parts by weight, especially 30 to 150 parts by weight, per 100 parts by weight in total with the agent (b) is suitable. This composition: This composition is converted into SiO _{2 based} on the weight of the above-mentioned resin (a) containing a hydroxyl group and a carboxyl group, a crosslinking agent (b), a neutralizing agent (c) and titanium dioxide. 1.0-5.0% by weight of hydrated oxide of silicon and Al ₂
A hydrated oxide of aluminum of 1.0 to 4.0% by weight in terms of O ₃ is prepared by mixing and dispersing a titanium dioxide pigment (d), the surface of which is coated in the order described, in water. be able to. In the present composition, if necessary,
Further, solid color pigments, metallic pigments, light interference pigments, fine metal powders, extender pigments, hydrophilic organic solvents, anti-settling agents, ultraviolet absorbers, coating surface preparation agents and the like can be added.

The composition can be applied directly to a metal or plastic substrate (for example, an automobile body), or to an undercoat and, if necessary, an intermediate coat, for example, Air spray, airless spray,
It can be painted by electrostatic painting or the like. The thickness can be appropriately changed depending on the purpose.
μm, especially in the range from 15 to 35 μm, is suitable. The coating is usually from about 120 to about 170 ° C, preferably from about 130 ° C.
Crosslinking and curing can be performed by heating at a temperature of about 150 ° C. for about 10 to 40 minutes.

Regarding the cured coating film formed by the present composition, the coating film containing only the component (d) as a pigment is white, and the present composition may further contain other solid color pigments, metallic pigments, light interference By blending a pigment, it is possible to form a solid color coating other than white, a metallic coating, and a light interference coating.

[0028]

The present composition contains a specific surface-treated titanium dioxide pigment, so that the coated titanium dioxide pigment is excellent in dispersibility and hardly aggregates or precipitates during storage. Moreover, it has the effect of improving the finished appearance of the formed coating film, for example, gloss and smoothness.

[0029]

The present invention will be described below more specifically with reference to examples and comparative examples. All parts and percentages are based on weight, and the thickness of the coating film is for a cured coating film. Example 1 Titanium dioxide pigment (b-1) coated with 20 parts (solid content) of a hydroxyl group-containing water-soluble resin (a-1) (note 1) and a hydrated oxide of silicon and a hydrated oxide of aluminum (Note 2)
After mixing with 70 parts of deionized water, the mixture is dispersed by a sand mill, and then 50 parts of a hydroxyl group-containing water-soluble resin (a-1) (solid content) and a crosslinking agent (c-1) (Note 3) 30 (Solid content), and after stirring, deionized water was further added to adjust the viscosity to 40 seconds / Ford cup # 4/20 ° C. to obtain a thermosetting aqueous coating composition (A).

(Note 1) Hydroxyl group-containing water-soluble paint (a-
1): A saturated polyester resin containing a hydroxyl group and a carboxyl group having a hydroxyl value of 80 and an acid value of 30, whose carboxyl group is neutralized by one equivalent of dimethylethanolamine and having a number average molecular weight of 3000.

(Note 2) Titanium dioxide pigment coated with hydrated oxide of silicon and hydrated oxide of aluminum (b-
1): An aqueous slurry (TiO ₂ concentration 300 g / l) containing rutile titanium dioxide particles (average particle diameter 0.25 μm) produced by a sulfuric acid method was heated to 60 ° C.
After adjusting this to pH 9.0 with aqueous sodium hydroxide solution,
An aqueous solution of sodium silicate is converted to SiO _{2 based on the} weight of titanium dioxide.
4.0% was calculated. Subsequently, the slurry pH was lowered to 7.5 over 120 minutes with sulfuric acid, and the slurry was aged for 10 minutes. After completion of the ripening, 2.0% of an aqueous sodium aluminate solution was added in terms of Al ₂ O _{3 based} on the weight of titanium dioxide, and the pH of the slurry was adjusted to 6.5 with sulfuric acid, followed by aging for 30 minutes. After completion of aging, the mixture was sufficiently filtered and washed with water, and dried at 110 ° C. for 12 hours. The obtained dried product was finally pulverized by a fluid energy mill.

(Note 3) Crosslinking agent (c-1): Methyl etherified melamine resin, manufactured by Mitsui Cytec Co., Ltd., trade name, “Cymel 325” Example 2 Hydroxyl group-containing water-soluble resin (a-1) (Note 1) Titanium dioxide pigment (b-2) coated with 20 parts (solid content) and hydrated oxide of silicon and hydrated oxide of aluminum (Note 4)
After mixing 70 parts with deionized water, the mixture was dispersed by a sand mill, and then 50 parts of a hydroxyl group-containing water-soluble resin (a-1) (solid content) and 30 parts of a crosslinking agent (c-1) (Note 3) were added. (Solid content), stirred and then added with deionized water to obtain a viscosity of 4
The temperature was adjusted to 0 sec / Ford cup # 4/20 ° C. to obtain a thermosetting aqueous coating composition (B).

(Note 4) Titanium dioxide pigment coated with hydrated oxide of silicon and hydrated oxide of aluminum (b-
2): In (Note 2) of Example 1, after adding an aqueous solution of sodium aluminate and adjusting the pH to 6.5 with sulfuric acid,
Further, the sodium silicate aqueous solution is converted to S based on the weight of titanium dioxide.
The same operation as (Note 2) was performed, except that 0.6% in terms of iO ₂ was added, and then the slurry pH was adjusted to 6.5 with sulfuric acid. Example 3 Titanium dioxide pigment (b-3) coated with 20 parts (solid content) of a hydroxyl group-containing water-soluble resin (a-1) (Note 1) and a hydrated oxide of silicon and a hydrated oxide of aluminum (Note 5)
After mixing with 70 parts of deionized water, the mixture is dispersed by a sand mill, and then 50 parts of a hydroxyl group-containing water-soluble resin (a-1) (solid content) and a crosslinking agent (c-1) (Note 3) 30 Parts (solids) were mixed and stirred, and then deionized water was added thereto to obtain a viscosity of 4%.
The temperature was adjusted to 0 sec / Ford cup # 4/20 ° C. to obtain a thermosetting aqueous coating composition (C).

(Note 5) Titanium dioxide pigment coated with hydrated oxide of silicon and hydrated oxide of aluminum (b-
3): The same operation as (Note 2) was performed except that, in (Note 2) of Example 1, after adding the aqueous sodium aluminate solution, the slurry pH was adjusted to 8.0 with sulfuric acid. Example 4 Titanium dioxide pigment (b-4) coated with 20 parts (solid content) of a hydroxyl group-containing water-soluble resin (a-1) (note 1) and a hydrated oxide of silicon and a hydrated oxide of aluminum (Note 6)
After mixing with 70 parts of deionized water, the mixture is dispersed by a sand mill, and then 50 parts of a hydroxyl group-containing water-soluble resin (a-1) (solid content) and a crosslinking agent (c-1) (Note 3) 30 Parts (solids) were mixed and stirred, and then deionized water was added thereto to obtain a viscosity of 4%.
The temperature was adjusted to 0 sec / Ford cup # 4/20 ° C. to obtain a thermosetting aqueous coating composition (D).

(Note 6) Titanium dioxide pigment coated with hydrated oxide of silicon and hydrated oxide of aluminum (b-
4): In Example 1 (Note 2), an aqueous sodium aluminate solution was added, the pH was adjusted to 6.5 with sulfuric acid, and then the aqueous sodium silicate solution was further converted to SiO 2 based on the weight of titanium oxide.
The same operation as (Note 2) was performed except that 0.6% was added in terms of ₂ and the slurry pH was subsequently adjusted to 8.0 with caustic soda. Comparative Example 1 Hydroxyl group-containing water-soluble resin (a-1) (Note 1) 20 parts (solid content), and titanium dioxide pigment (b-5) (Note 7) coated with only aluminum hydrated oxide 70 parts 70 parts Is mixed with deionized water, and then dispersed by a sand mill. Then, 50 parts of a hydroxyl group-containing water-soluble resin (a-1) (solid content) and 30 parts of a crosslinking agent (c-1) (Note 3) (solid content) Minutes), and after stirring, add deionized water and add viscosity of 40 seconds / Ford cup
# 4/20 ° C thermosetting aqueous coating composition (E)
I got

(Note 7) (b-5): Titanium dioxide pigment coated only with aluminum hydroxide as an inorganic treatment; trade name, "JR-602", manufactured by Teica Corporation. Performance Test Results The storage stability of the coating compositions obtained in Examples and Comparative Examples and the gloss of the formed coating film were examined. Table 1 shows the results.

The storage stability of the thermosetting aqueous coating composition adjusted to a viscosity of 40 seconds / Ford cup # 4/20 ° C. was measured immediately after preparation (about 1 hour at 20 ° C.) and at 30 ° C.
After 10 days of closed storage at room temperature, the paint state (mainly regarding the occurrence of layer separation) and the viscosity were examined.

The gloss was measured immediately after preparation and at 30 ° C.
The paint after closed storage for 10 days was coated on a tin plate with a smooth surface to a thickness of 40 μm, and the coating was cured by heating at 140 ° C. for 30 minutes. It is.

[0039]

[Table 1]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 7/12 C09D 7/12 // C09D 161/20 161/20 175/04 175/04 175/04 (72) Invention Tsuyoshi Hara 4-7-1-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Prefecture, Kansai Paint Co., Ltd. Toshiyuki 4-17-1, Higashi-Yawata, Hiratsuka-shi, Kanagawa F Kansai Paint Co., Ltd. F-term (reference) 4G047 CA02 CB09 CC01 CD03 CD07 4J037 AA22 CA05 CA12 CA20 CA25 CB04 CB16 DD27 EE03 EE28 EE43 FF15 FF23 FF28 4J031 CG121CG DA162 DA172 DD001 DD121 DG111 DG191 DG301 GA03 GA06 HA156 HA216 HA306 HA446 JB02 JB09 JB29 JB39 KA02 KA03 KA08 KA15 KA20 MA14 NA01 NA26 NA27 PA19

Claims (4)

[Claims] 1. A thermosetting aqueous coating composition containing a resin (a) containing a hydroxyl group and a carboxyl group, a crosslinking agent (b), a neutralizing agent (c), and a titanium dioxide pigment (d). pigment (d) is titanium dioxide weight, in terms of hydrated oxide of 1.0 to 5.0 weight percent silicon in terms of SiO ₂ and Al ₂ O ₃ 1.0 to 4.0 weight%
A thermosetting aqueous coating composition, which is a titanium dioxide pigment whose surface is coated in the order described with a hydrated oxide of aluminum. 2. The titanium dioxide pigment (d) is 0.2 to 1.0 in terms of SiO _{2 based} on the weight of titanium dioxide.
The thermosetting aqueous coating composition according to claim 1, which is a titanium dioxide pigment coated with a hydrated oxide of silicon by weight. 3. The thermosetting aqueous solution according to claim 1, wherein the titanium dioxide pigment (d) is a titanium dioxide pigment further treated with an aqueous alkali solution so that the pH of the final product is 8.0 to 10.0. Paint composition. 4. The titanium dioxide pigment (d) is 0.2 to 1.0 in terms of SiO _{2 based} on the weight of titanium dioxide.
2. A thermosetting aqueous solution according to claim 1, which is a titanium dioxide pigment coated with a hydrated oxide of silicon by weight and then treated with an aqueous alkaline solution so that the pH of the final product is 8.0 to 10.0. Paint composition.