CS262121B1 - Process for surface treatment of iron or titanium inorganic pigments - Google Patents

Abstract

The solution relates to the field of surface treatment inorganic pigments. Surface treatment The inorganic pigments are neutralized reactions between alkaline-reacting calcium compound and phosphoric acid to form insoluble phosphates calcium in aqueous inorganic suspension pigment. It is used as a base in powder form calcium oxide, calcium hydrate, calcium carbonate, in an aqueous suspension calcium hydroxide and calcium carbonate. The way neutralization is conducted the nature of the phosphate precipitate is controlled calcium. Subsequent pigment pruning with water, a high specific pigment is obtained resistance which is suitable for pigmentation coatings applied to the substrate elcktrophoretically, and which has increased corrosion resistance.

Description

The invention relates to the field of surface treatment of inorganic pigments. The surface treatment of the inorganic pigments is performed by a neutralization reaction between the alkaline reacting calcium compound and the phosphoric acid to form insoluble calcium phosphates in the aqueous suspension of the inorganic pigment. Calcium oxide, calcium hydrate, calcium carbonate, calcium hydroxide and calcium carbonate in aqueous suspension are used as bases.

By the way in which neutralization is conducted, the nature of the calcium phosphate precipitate is controlled. Subsequent piercing of the pigment with water yields a high resistivity pigment, which is suitable for pigmenting paints applied to the substrate electrophoretically, and which has increased corrosion resistance.

The invention relates to a process for the surface treatment of inorganic pigments with insoluble calcium phosphates.

An important operation in the production of inorganic pigments is the surface treatment, the purpose of which is to improve the processing properties of the pigments both directly in the technology of their production and also when used in various processing industries. In particular, the production technology involves reducing the agglomeration of the pigment particles during the drying operation and, due to the reduced agglomeration, an increase in the grinding efficiency as well as an improvement in the optical parameters of the pigment. Among the processing properties, the surface treatment of inorganic pigments is manifested primarily in their application to paints by improving their dispersibility into binders, by improving the theological properties of paint suspensions and by creating less voluminous and easier to mix them than untreated pigments. In coating films, surface-treated pigments increase light fastness and weather resistance.

Another requirement arising from the development of modern coating processes and the increased demands on the quality of the coating films formed is that of a high resistivity of inorganic pigments. The resistivity affects, for example, the applicability of the pigment in the electrophoretic coating application. The quality of the coating film is also influenced by the water-soluble salt content. At a low content of these salts, ie in a high specific resistance of pigments, the film is not damaged by atmospheric conditions and the corrosion protection of the substrate is more durable.

The inorganic surface treatment of pigments is conveniently accomplished by precipitation of colloidal hydroxides, oxides or hydrated oxides, either one element or in combination with another, on the surface of the pigment particles in an aqueous suspension. Of the most commonly used surface treatment agents, Si, Al, Ti, Zr are soluble. In the actual surface treatment, the use of these substances produces an equivalent amount of water-soluble salts which must be removed from the pigment by washing with water to obtain a high resistivity pigment.

It is an object of the present invention to provide a method of surface treatment of inorganic pigments, wherein the surface treatment components form an insoluble precipitate and water, so that the water-soluble salt content is only given by the product of the solubility of the insoluble precipitate. SUMMARY OF THE INVENTION The present invention is directed to the precipitation of colloidal dicalcium phosphate CaHPO ₄ or tris (pentasodium hydroxide phosphate CasfPOJ 5 OH or a mixture thereof) on pigment particles dispersed in an aqueous suspension. Preferably, CaHPCl 2 is formed, a colloidal nature which in a neutral environment ages to a very fine crystalline precipitate of calcium hydrogen phosphate dihydrate CaHPO 2, 2 H _and O.

When the neutralization of acid occurs preferentially Ca 5 (PO / J ₃ OH as amorphous villi which remain with the aging of the crystalline form. In the pH range of 6-10 produced mixture of both phosphates.

Phosphoric acid is used as the acid for the precipitation reaction, and calcium oxide, lime hydrate, calcium carbonate, calcium hydroxide and calcium carbonate in aqueous suspension are used as bases. These calcium components are used very pure in a fine dispersion form and, if they contain particles larger than 0.045 mm, it is advisable to remove larger particles by dry or wet separation by known methods.

The advantage of the coating process according to the invention is that the pH to which the coating is applied can vary the ratio between CaHPO ₄ and Car, (POJ, OH), thereby affecting the particle size of the precipitated phosphates as well as the pH value of the aqueous extract of the treated pigment. Another advantage of this process is that the water formed during the precipitation reaction does not increase the salinity of the reaction suspensions above the solubility product of the resulting precipitates, which results in a saving of washing water during further pigment processing and lowering of soluble salts in wastewater discharged into recipients.

The method of surface treatment of the inorganic pigments according to the invention and the effect thus obtained will be documented by several examples of its implementation, which, however, do not mean a limitation of the subject matter of the invention.

In the embodiments of the surface treatment method and subject matter of the invention, the stated conductivity and resistivity values are based on a temperature of 20 ° C.

Example 1

A 2 L beaker equipped with a glass paddle stirrer, a laboratory thermometer, a pH electrode was charged with 1.5 L of a 190 g pigment / L washed red iron suspension.

While stirring at 23.0 ° C, the pH of the suspension was adjusted to 7 by the addition of NaOH, and 1.82 grams of SiO ₂ in aqueous sodium glass solution was added. Next, 1.03 grams of Al 2 O 1 in aluminum sulfate solution was added to the stirred suspension and stirred for a further 30 minutes. After this time, a pH of 3.75 was read, stirring was turned off and the suspension was left to sediment. The clear solution over the 0.595 L sediment was separated and showed a water-soluble salt content of 3.62 g / l and a specific conductivity of 2.837 gS. . cm ¹ . The 0.966 L treated ferric red sediment was washed in 10 L process water, the pigment after sedimentation was filtered off, dried at 105 degrees Celsius and ground. The ground pigment νι / preached a specific resistance of 8.990 Ω. cm, SiO ₂ content 0.53 wt%, Al ₂ O content _{, t} 0.36 wt%

Example 1 a d 2

In a beaker of 2 L content was submitted

1.5 I washed red ferric suspension at a concentration of 190 g pigment / l. To the slurry at 25.4 ° C, 1.67 g of H 2 PO 4 / J in aqueous solution was added with stirring, and the suspension was neutralized with Ca (OH) ₃ as an aqueous suspension. The pH of the suspension reached 9.06 during neutralization; a total of 2.10 g of Ca (OH) ₂ was added. After addition of the base, the suspension was stirred for 30 minutes and then set aside for sedimentation. The volume of the clear solution above. the pigment sediment amounted to 0.486 l and contained 0.962 g / l of water-soluble salts at a specific conductivity of 1. . 146 gS. cm ^-1 . The 1.104 L pigment sediment was suspended in 5 L process water, sedimented, the deposited pigment filtered off, dried at 105 ° C and ground. The ground pigment showed a resistivity of 10,770 Ω. cm at a total CaO + P ₃ O ₅ content of 0.97 wt.

Example 1 a d 3

In a beaker of 2 L content was submitted

1.5 1 washed yellow ferric suspension at a concentration of 150 g pigment / l.

To the suspension at 35.2 ° C 0.59 g of CaCO ₂ was added with stirring, and H-PO 2 ·, in aqueous solution was added until pH 6.10. During the next 30 minutes, pH was maintained by addition of H _<PCB "whose total addition amounted to 0.5 g. The suspension was then sedimented, the clear solution above the sediment volume of about 0.526 l showed a content of water soluble salts

1.1.5 g / l and specific conductivity 1.181 uS. cm ¹ . The pigment sediment was suspended in 5 L process water, sedimented, the deposited pigment filtered off, dried at 105 ° C and ground. The ground pigment showed summary CaO content of _{P 1} or 0.28 wt%. and a resistivity of 10.160 Ω. cm.

Example 4

In a beaker of 2 L content was submitted

1.5 1 washed black ferric slurry * concentration of 380 g pigment / l. To the suspension at 16.8 ° C was added 12.14 grams of H ₃ PO ₄ in aqueous solution with stirring and the suspension was neutralized to pH 8.0 Ca (OH) ₂ as an aqueous suspension. After neutralization, stirring was continued for 30 minutes while maintaining the pH of the slurry at 8.0 with additional Ca (OH) _{2 additions} . The total addition of Ca (OH) ₂ was 12.85 g.

The slurry was then sedimented, a clear solution over a 0.55 L sediment, a specific conductivity of 920 / zS.cm ¹ and a water soluble salt content of 0.75 g / L was separated and the pigment sediment was homogeneously washed in 5 L process water. suspension.

This suspension was sedimented, the deposited pigment filtered off, dried at 105 degrees Celsius and ground. The ground pigment contained in total 3.20 wt. CaO + + P2O5 and showed a resistivity of 14.080 Ω. . cm.

Example 5

To a 2 L beaker was charged 1.5 liters of a suspension prepared by flushing the ground anatase modification TiO ₂ calcine in process water clarified to a concentration of 300 g of calcine / l.

To the slurry at 19.2 ° C was added 5.03 g of Ca (OHj ₂₎ as an aqueous suspension with stirring. With continuous stirring, the pH of the slurry was adjusted to 8.25 by addition of H ₃ PO / i in aqueous solution and for 30 minutes, this pH was maintained by the corrective addition of H ₃ PO ₄ and a total of 4.43 g H ₃ PO ₄ was added.

The suspension was then rinsed in process water demineralized to a volume of 10 liters and filtered. The filtrate showed a water-soluble salt content of 1.5 g / l and a specific conductivity of 1.280 gS.cm ¹ . The filter cake was dried at 105 ° C, milled and analyzed for CaO and P2O5 content. The total CaO + + Ρ ₂ Ο ₅ content was 1.51% by weight. It also showed a resistivity of 12,060 Ω. cm.

Example 6

Into a 2 L beaker was charged 1.5 liters of a suspension prepared by flushing the ground TiO ₂ calcine of rutile modification in process water clarified to a concentration of 450 g of calcine / l.

To a suspension with a temperature of 22.6 ° C was added with stirring 10.17 g _H PO ^ _and in aqueous solution, whereupon the suspension is neutralized by addition of Ca (OH) ₃ as an aqueous suspension to pH 9.5. Stirring was continued for 30 minutes during which time the pH of 9.5 was maintained by further periodic additions of Ca (OH) ₃ , the total amount of Ca (OH) ₃ added being 12.91 g.

The suspension was then rinsed in techno10 L and filtered. The filtrate showed a water soluble salt content of 1.62 g / l and a specific vo262121 specificity of 1.390 / zS.cm ^-1 . The filter cake was dried at 105 ° C, ground and analyzed with the following values:

Claims (1)

Subject A method of surface treatment of ferric or titanium inorganic pigments which imparts enhanced corrosion resistance and high resistivity to pigments, characterized in that it is added to an aqueous suspension containing 100 to 500 g / l of ferric or titanium pigment with stirring at 10 to 40 ^° C either 0.04 to 2.0% by weight, based on pigment, of CaO in the form of alkaline reacting calcium compounds and neutralization with phosphoric acid to a final pH in the range of 6 to por 10.080 Ω. cm, total CaO + + P ₂ O ₅ content 2.52 wt. OF THE INVENTION 10, or 0.05 to 2.6% by weight, based on the phosphoric acid pigment, and the alkaline reacting calcium compounds are neutralized again to a final pH in the range of 6 to 10, using calcium oxide as the alkaline reacting calcium compounds, calcium hydrate, calcium carbonate or calcium hydroxide, either in powder form or as an aqueous suspension and phosphoric acid as 5 to 85 why. wt. aqueous solution.