DE2207912A1 - PROCESS FOR MANUFACTURING A AFTER-TREATED TITANIUM DIOXIDE PIGMENT - Google Patents

Description

KROHOS TITAN-GMBH Leverkusen, February 8, 1972

Leverkusen Dr.v.B / Br

Process for the production of a post-treated
Titanium dioxide pigments

The invention relates to a method of making one with an aluminum compound and optionally others Post-treated titanium dioxide pigment.

A titanium dioxide pignient is known after its manufacture to improve the optical and pigraenttechnischen Properties in aqueous slurry with one water-soluble aluminum salt and optionally one or to add several other water-soluble metal salts and / or optionally a water-soluble silicon compound and then by changing the pH in the suspension to the pigment non-colored and poorly soluble To precipitate oxide hydrates and / or other non-colored and sparingly soluble metal compounds. After that the pigment separated from the suspension, washed, dried and ground. Here, a water-soluble aluminum salt can be used Aluminate, for example an alkali metal urainate, can be used. About the alkaline-reacting slurry after the addition of aluminate a strong acid, e.g. B. sulfuric acid or hydrochloric acid, or a strongly acidic salt added, so as to lower the pH and precipitate aluminum oxide hydrate (see FR-PS 829- ^ 30).

This method has several disadvantages. A strong change occurs locally at the point where the acid is added the pH value; Alurainium oxide hydrate precipitates, which partially dissolves again when the suspension is stirred, but small amounts remain undissolved, with these proportions around

TG 73 - 2 -

30SS34 / 1008

the greater are the more you focus on the neutral point in the Suspension is approaching. Especially in the early stages of precipitation, if only small amounts of hydrate oxide remain undissolved, most of them are not on the surface of the Titanium dioxide pigment particles, but separate from them free in suspension. There they act as crystallization nuclei for further precipitating oxide hydrate. A consequence of the known procedure is therefore that in the aftertreatment only part of the alumina hydrate is on the Surface of the titanium dioxide pigment particles is located, while the rest is freely present next to the pigment particles in the suspension is. The titanium dioxide pigment particles are only imperfectly encased in this way. This gives pigments that are unsatisfactory have optical properties and are also not sufficiently stable against the effects of light and / or weathering.

Another disadvantage of the known method is that due to the strong local changes in the pH value the addition of the acid or the acid salt and / or due to the high local electrolyte concentration in the suspension arises in the aftertreatment, the state of dispersion of the pigment is adversely affected. Pigment flocculates prematurely off, and these pigment flakes can no longer be adequately coated with oxide hydrate.

It has also been suggested in U.S. Patent 3.5U5.99U, to change the pH of the titanium dioxide suspension mixed with aftertreatment substances in that in the suspension a weak acid is formed in situ. For this purpose, urea is added to the suspension. the The suspension is then slowly heated to a temperature of 60-100 ° C and kept at this temperature so that the Urea decomposes with the formation of carbon dioxide and ammonia, with the suspension in the case of an alkaline reaction the latter escapes.

BATHROOM ORIGINAL TG 73 - 3 -

309834/1008

Although this method has the disadvantages of the aforementioned Procedures are avoided, it also has factual parts. The substance added to form the acid is relatively expensive. Further costs arise from the fact that the suspension is kept at elevated temperatures for a long time must become. Furthermore, the process is not readily suitable when dealing with strongly alkaline suspensions starts with pH values above 10, as is often the case with the use of aluminates in post-treatment, because then very large amounts of urea have to be used and the decomposition time is disproportionately long. It also leads the resulting ammonia causes considerable nuisance if you do not work with closed containers.

There has now been an improved method of making one with an aluminum compound and optionally others Substances of aftertreated titanium dioxide pigraents found, whereby a titanium dioxide pigment prepared in any way in an aqueous slurry with a water-soluble aluminate and optionally one or more other water-soluble ones Metal salts and / or optionally a water-soluble one or water-dispersible silicon compound is added in any order and by changing the The pH of the suspension is non-colored and poorly soluble Oxide hydrates and / or other non-colored and poorly soluble Metal compounds are precipitated, after which the titanium dioxide pigment is separated from the suspension, washed, is dried and ground. The method is characterized in that the suspension after adding all the liquid treatment substances has a pH value above 9 and still contains dissolved aluminate; after the addition of the post-treatment substances, possibly also at the same time as the addition of post-treatment substances, carbon dioxide or a gas containing carbon dioxide is introduced into the Suspension introduced until the pH has dropped to at least 8.5.

TG 73 - k-

309834/1008

Good titanium dioxide pigments are obtained if the post-treatment substance is only a water-soluble aluminate, for example an alkali aluminate is used. Above all, these pigments have better optical properties. If a water-soluble titanium salt and / or a water-soluble or water-dispersible one is used in addition to the aluminate Silicon compound, then the weather resistance improved by paints that contain these pigments. The use of others for follow-up treatments is also more common Metal salts are possible.

For special purposes it may be advantageous if at the same time as or after the addition Addition of the aluminate and optionally the other metal salt or salts and / or optionally the silicon compound an organic substance is added and applied to the titanium dioxide pigment. For example, silicon can also be used here as an organic silicon compound, e.g. as an alkylchlorosilane or as a silicic acid ester.

The process can be carried out batchwise. In this case, the aluminate and any further aftertreatment substances are added to the titanium dioxide pigment suspension into a kettle equipped with a stirrer and then conducts carbon dioxide or a gas containing carbon dioxide on until the desired pH is reached; then the suspension is withdrawn from the boiler and worked up in a manner known per se.

However, the process can also be carried out continuously. Here, in an advantageous embodiment at least some of the aftertreatment substances are added to the titanium dioxide pigment suspension in a first vessel and then the suspension in a continuous

^{TG T3} BATH ORIGINAL " ⁵

3 C i 8 3 A '1 0 0 8

Stream successively transferred into one or more precipitation vessels, wherein carbon dioxide or a carbon dioxide-containing gas is introduced into at least one precipitation vessel. Behind A collecting vessel can also be connected to the precipitation vessels, which can also be used as a settling vessel for the ready-made pigment can serve.

By introducing the carbon dioxide or the carbon dioxide-containing Gases occur in the suspension, in contrast to the previously known addition of strong acids or strongly acidic reacting salts, no sudden sharp changes in pH; rather, the carbon dioxide is distributed within of the entire suspension and leads to slow precipitation of the aftertreatment substances, with the precipitated Essentially, the products only settle on the titanium dioxide pigment grain. This is enveloped evenly. Only ■ venn If a large amount of post-treatment substance is used, there are also proportions of the precipitated particles in addition to the pigment particles Products. The dispersion state of the pigment in the suspension is not disturbed, so that the pigment during the is well dispersed in the suspension throughout the duration of the aftertreatment.

The carbon dioxide is quickly absorbed in the suspension. As a result, the method according to the invention is very time-saving and in the continuous mode of operation, the dimensions of the vessels can be kept small even with a high throughput will. The carbon dioxide can easily be dosed, »and it is easily possible to keep track of the changes in the pH in monitor the suspension. The method can be determined by the number and location of the individual carbon dioxide feeds and by the Amount of carbon dioxide supplied in each case can be easily adapted to the respective needs.

TG 73 - 6 -

3 t 9 8 3 i »/ ■; 0 0 8

When the carbon dioxide or the carbon dioxide-containing gas is introduced, an additional stirring effect occurs. It is it is often advantageous to feed this gas through a ventilation stirrer.

In the method according to the invention, the non-colored and sparingly soluble oxide hydrates or the other non-colored and sparingly soluble metal compounds even at low temperatures in a relatively short time Time completely failed. An advantageous embodiment of the method according to the invention is that the Addition of the aftertreatment substances and the precipitation of the non-colored and sparingly soluble oxide hydrates and / or the other non-colored and sparingly soluble metal compounds is carried out at temperatures up to 60 ° C. Temperatures above 60 ° C are generally not appropriate, because at normal pressure pH values of 0.0 are usually not reached or only very slowly. Turns if overpressure is applied, lower pH values can indeed be achieved at temperatures above 60 ° C., however the use of positive pressure is disadvantageous. The post-treatment can often be carried out at room temperature. The suspension can after the end of the supply of carbon dioxide be kept at a higher temperature for some time,. but this measure usually offers no advantages.

The use of low temperatures makes handling considerably easier and reduces the risk of corrosion, so that for the vessels and lines materials can be used that are not suitable at higher temperatures. In addition, energy is saved when working at low temperatures.

TG 73 -T-

30983W 1 008

Compared to the method proposed in US Pat. No. 3 x 5 ^ 5 x 99 ^ shows the present method in addition to the fact that the pH lowering is much faster and at Lower temperatures takes place, the advantage that the Starting suspension can easily be strongly alkaline and the carbon dioxide is very inexpensive.

The titanium dioxide pigment can be produced in any number of ways and have a rutile structure or anatase structure. So it can e.g. according to the so-called Gulfatproß or from Titanium tetrachloride, for example by vapor phase oxidation, can be produced.

A particularly advantageous embodiment of the method is that the carbon dioxide-containing gas in the Chlorination of titanium compounds, preferably titanium-containing ores or slags, resulting exhaust gas is used. This Large quantities of gas are produced as a by-product in the manufacture of titanium tetrachloride. Therefore this embodiment is Particularly recommended if that corresponds to the invention Process to be subjected to titanium dioxide pigment Titanium tetrachloride was generated; in this case the carbon dioxide-containing gas is practically free in a large excess available.

The method according to the invention can be either a non-aftertreated as well as an already post-treated titanium dioxide pigment. According to the invention Post-treatment, the pigment can be subjected to one or more further post-treatments of a different or the same type will.

BATH ORIGINAL

TG 73 - 8 -

3 r 9 8 3 kl " Q0 8

In detail, the method can be carried out as follows will:

The titanium dioxide pigment is, optionally with additive a dispersing aid and / or alkali, in water slurried and possibly known per se Way wet-ground and / or wet-classified. To the thus prepared slurry is aluminate, for example one aqueous solution of sodium aluminate was added. The suspension thereafter has a pH value above 9- After the addition of aluminate, carbon dioxide is introduced until the desired A lower pH value is reached, the suspension being stirred during the addition of aluminate and carbon dioxide will. The addition of carbon dioxide can also take place during the addition of aluminate. In many cases it is enough to go through the addition of carbon dioxide to lower the pH value to 8.5-8.0, however, it may be desirable under certain circumstances to add carbon dioxide continue until pH 7.0-6.5. The suspension can be processed immediately, but also before can be left for further processing. The treated pigment is removed from the suspension in a manner known per se separated, washed, dried and ground. It is also possible to remove the aftertreated pigment before separating it to be treated in the same or similar way as the first time or after separation and, if necessary, washing, Slurry drying and grinding again and in the same or in a similar way to retreating the first time.

If other secondary treatment substances are used in addition to the aluminate, they can be used in any order be added before, during or after the addition of aluminate. It has often proven useful to add them before the aluminate. You can also, for example Alkali silicate, during the manufacture of the titanium dioxide

TG 73 - 9 -

309834/1008

Pigment suspension are added, using it as a dispersing aid can serve.

Before the addition of the aluminate, the pigment suspension have any pH. It is only essential that it has a pH of has at least 9. Therefore, a titanium dioxide pigment produced by vapor phase oxidation of titanium tetrachloride needs not deacidified before the after-treatment.

If the suspension is acidic before the addition of aluminate and alkali metal silicate is added to this acidic suspension, then it must Under certain circumstances, care must be taken that the addition of aluminate is not too long in coming, otherwise Silica flocculates and so poorer results are obtained in the aftertreatment. Even with the addition of others After-treatment substances make sure that flocculation does not occur prematurely.

If the process takes place continuously, then the silicon compounds, the titanium salt and possibly also at least part of the aluminate is added to the vessel verden, in which the titanium dioxide pigment suspension is produced, or in a downstream vessel, however is arranged in front of the precipitation vessels. However, the aluminate can also at least partially in one or more of the precipitation vessels be admitted. The carbon dioxide is either stored in a single precipitation vessel or in several cascading vessels Precipitation vessels initiated, in the latter case the carbon dioxide feed separated by the individual feeds can be regulated.

TG 73 - 10 -

30983AM008

Among the aluminates, alkali aluminates are particularly suitable, sodium aluminate is often preferred for reasons of cost.

Alkali silicate can be used as the silicon compound. But it is also possible to use silicon tetrachloride, an alkylchlorosilane, a silicic acid ester or other water-soluble or water-dispersible silicon compounds to use.

Titanium tetrachloride, for example, can be used as the titanium compound.

The aftertreatment substances can be used in customary amounts. It is particularly advantageous if the aluminate in amounts of O, 5 ~ 5 wt. ^ Calculated as Aigoo and is based on the pigment used, applied, wherein the range is more preferably 3 wt.%.

If a titanium salt and / or a silicon compound is used, the titanium salt is preferably used in amounts up to 2% by weight , calculated as T1O2, and / or the silicon compound in amounts up to 2% by weight , calculated as S1O2, both amounts based on pigment used, applied.

The following examples are intended to explain the process in more detail.

TG 73 - 11 -

3 I ¹ 9 8 3 A / 1 0 0 8

example 1

A rutile pigment produced according to the sulfate process was made into a paste in water with the addition of sodium hydroxide solution and sodium hexametaphosphate, which had a TiO2 content of 250 g per liter and a pH of 9> 0. An aqueous lithium aluminate solution of 50 g / l KaAlOo was added to this suspension in an amount corresponding to T »5 g Al2O0 per liter of suspension. The pH of the suspension rose to 12 hours .

In 2 l of this suspension, which was at room temperature, carbon dioxide was passed in with stirring at a flow rate of Uo l / h. During the introduction of carbon dioxide, the pH of the suspension was measured repeatedly. After 10 minutes it was 10.6, after 25 minutes 9.2, and after 35 minutes it had _{dropped to T 5} 5.

Then readily standing, the suspension was filtered and the titanium dioxide Pigxnent washed, milled at 110 ⁰ C and dried in an air jet mill. It had good optical properties.

Example 2

In a stirred vessel equipped with a gassing stirrer, 32 liters of an acidic suspension containing a titanium dioxide pigment obtained by vapor phase oxidation of titanium tetrachloride in an amount of H50 g of T1O2 per liter were mixed with 2.88 λ of a sodium silicate solution at room temperature with stirring whose SiO2 content was 100 g / l. After the addition of the sodium silicate, the suspension had a pH of 10.6.

TG 73 - 12 -

3,99834,008

With further stirring, 20 l of an sodium aluminate solution were then added over a period of 10 minutes, the concentration of which was adjusted so that after the addition the aluminate content of the suspension was 2%, calculated as Al2O3 and based on TiOp. Towards the end of the addition, the pH had risen to 12.6.

Then a carbon dioxide-air mixture with a content of 50 % by volume of C0 _{o was} introduced into the suspension via the gassing stirrer. Over the course of 30 minutes, the pH of the suspension fell to 7.8. The aftertreated titanium dioxide pigment could easily be filtered and washed and was ^{dried at 110 °} C. and ground in a steam jet mill.

The pigment had very good optical properties and a high resistance to graying when used in PVC.

Electron micrographs showed that the aftertreatment substances were quantitatively deposited on the pigment.

Example 3

This example describes the continuous aftertreatment of a rutile pigment produced by the sulfate process.

In a storage vessel, 6 kg of the pigment, as described in Example 1, were suspended in 15 l of water. To the An aqueous titanium tetrachloride solution was added to the suspension at room temperature with stirring. The amount of this Solution was 60 g, calculated as T1O2. After the addition of titanium tetrachloride the pH of the suspension was 1.0 U.

TG T3 - 13 -

3C9834 / 1008

Thereafter, an aqueous sodium aluminate solution was added with further stirring in an amount of 3 / », calculated as Al2O3 and based on the pigment used, added and the suspension is diluted with water up to a content of 300 g / l T1O2.

With the aid of a metering pump, this suspension was continuously passed through a stirrer equipped with aeration three-stage stirred tank cascade pumped at a flow rate of 12 l / h. The useful volume of each cascade level was 665 ml.

Carbon dioxide was introduced in all three stages via the aeration stirrer. In the individual stages, the pH measured by means of measuring electrodes and by regulating the COg flow rate kept constant. After the third cascade stage, the suspension had a pH of 7 »2. The pigment was processed further as in Example 2 and had very good optical properties.

example k

As in Example 2, it was prepared from a suspension of a titanium dioxide pigment obtained by vapor phase oxidation of titanium tetrachloride assumed, in an amount that corresponds to 6 kg T1O2. This suspension was as in example '/ 3 mixed with a titanium tetrachloride solution. Then, 1.8 liters of a sodium silicate solution was added to the suspension with stirring with a content of 100 g S1O2 per liter added, whereupon the suspension was diluted with water to a TiO2 concentration of 300 g / l. With the addition of sodium silicate the pH rose only slightly.

TG 73 - 11+ -

309834/1008

The suspension was then pumped continuously into the stirred tank cascade mentioned in Example 3. A sodium aluminum oxide solution was continuously pumped into the first stirred vessel at such a rate that the ratio of TiO ₂ pigment: Al ₂ O was 100: 3 and a TiOo concentration of 250 g per liter of suspension was established in the cascade. The addition of carbon dioxide and further processing of the pigment took place as in Example 3-

A pigment with very good optical properties and good weather resistance was obtained.

TG 73 - 15 -

309834/1008

Claims (9)

Claims 1. Method of making one with an aluminum compound and optionally other substances aftertreated titanium dioxide pigment, with any Titanium dioxide pigment prepared in an aqueous slurry with a water-soluble aluminum oxide and optionally one or more other water-soluble metal salts and / or optionally one water-soluble or water-dispersible silicon compound is added in any order and by changing the pH value of the suspension non-colored and sparingly soluble oxide hydrates and / or other non-colored and sparingly soluble :. Borrowed metal compounds are precipitated, after which the Titanium dioxide pigment is separated from the suspension, washed, dried and ground, characterized in that that the suspension has a pH of above 9 after all the aftertreatment substances have been added and still contains dissolved aluminate and, if appropriate, also after the addition of the aftertreatment substances already simultaneously with the addition of post-treatment substances, carbon dioxide or a carbon dioxide-containing one Gas is introduced into the suspension until the pH has dropped to at least 8.5. 2. The method according to claim 1, characterized in that only a water-soluble aluminate is used as the aftertreatment substance. TG 73 - 16 - 30983 ^ / 1008 3. The method according to claim 1, characterized in that as aftertreatment substances in addition to the aluminate a water-soluble titanium salt and / or a water-soluble or water-dispersible silicon compound be used. U. Process according to claims 1 to 3, characterized in that simultaneously with the addition or subsequently the addition of the aluminate and optionally the other metal salt (s) and / or optionally an organic substance is added to the silicon compound and applied to the titanium dioxide pigment. 5. The method according to claims 1 to H, characterized in that at least some of the aftertreatment substances in a first vessel for the titanium dioxide pigment suspension added and the suspension then in a continuous stream successively in one or several precipitation vessels are transferred, with carbon dioxide or a carbon dioxide-containing one in at least one precipitation vessel Gas is introduced. 6. The method according to claims 1 to 5 »characterized in that the addition of the aftertreatment substances and the precipitation of the non-colored and poorly soluble Oxide hydrates and / or the other non-colored and sparingly soluble metal compounds at temperatures up to at 60 ° C is made. 7. Process according to claims 1 to 6, characterized in that the exhaust gas produced in the chlorination of titanium compounds, preferably titanium-containing ores or slags, is used as the carbon dioxide-containing gas. TG 73 - 17 - 30383 ^ / 1008 8. The method according to claims 1 to 7 »characterized in that the aluminate in amounts of 0.5-5 wt. $, calculated as AI2O3 and based on the pigment used, is applied. 9. Process according to claims 1 and 3 to 8, characterized in that the titanium salt is used in amounts up to 2 wt. ^ Calculated as T1G2 and / or the silicon compound in quantities up to 2 Gev./a, calculated as SiC> 2, both quantities based on the titanium dioxide pigment used, can be used. TG 73 30983 ^ / 1008