DE2009566B1 - Process for the production of titanium dioxide or titanium dioxide aquate coatings - Google Patents

Description

For applying titanium dioxide coatings to various types of Several methods are known for surfaces, e.g. B. hydrolysis of evaporated Titanium tetrachloride films by water vapor (Gmelins liandbuch der Inorganic Chemistry, 8th edition, Vol. 41, Titan, p. 231), hydrolysis of titanic acid ester layers or Solutions of the same in organic solvents (U.S. Patents 2,768,909 and 2943 955) or vapor deposition of metallic titanium and subsequent oxidation (German patent 855 767).

Depending on the disgusted process, the coatings serve to improve the optical properties of the coated objects, e.g. B. to change the Refiexion 'ability or to generate interference colors, - to achieve more durable Coatings (German Auslegeschrift 1 055 193) or for the formation of intermediate layers, in order to be able to apply further coatings more firmly. With the coated bodies whether it is glass, metals or plastics.

In part, these coatings are made in such a way that they are of the coated surfaces can be removed mechanically, in order to be lamellar in this way To obtain titanium dioxide pigments with iridescent properties (USA.-Patents 3 071 482 and 2 941 895 as well as German interpretation document 1 136 042). Also has already been suggested the pigment properties of finely divided mica flakes with those of titanium dioxide and possibly to conspire the pigment on the mica (U.S. Patent 2,278,970). A process, those coated with titanium dioxide Producing mica pigments is described in U.S. Patent 3,087,828 and in the Belgian patent 619 447 described. After this process, finely divided Mica flakes in aqueous suspension by hydrolysis of a dilute sulfuric acid Titanium (IV) oxide sulfate solution coated with titanium dioxide aquate at boiling point. From the chemistry of normal titanium dioxide pigments it is known which influence on the later pigment properties the type of hydrolysis of the sulfuric acids used there Titanium (IV) oxide sulfate solutions (G m e 1 in 1. c., Pp. 97 to 103). A big Number of patents takes these circumstances into account, with all of these methods being used by sulfuric acid titanium (IV) oxide sulfate solutions and to titanium dioxide products to lead.

The previously known processes for the production of titanium dioxide coatings are still relatively expensive, since these processes are used to produce very uniform Coatings could only be realized via the gas phase.

It has now been found that the hydrolysis is more dilute, aqueous acidic Titanium salt solutions result in very even coatings under very specific conditions of titanium dioxide aquats with a definable layer thickness on a wide variety of substrates leads. In addition, the method according to the invention avoids the use of a Gas phase as well as the use of complex mechanical devices. After Invention are neither organic solvents nor aggressive inorganic substances rather, the process is only used in an aqueous, weakly acidic medium carried out, whereby the use of a particularly corrosion-resistant vessel material on the one hand, as well as safety precautions due to flammable organic solvents on the other hand unnecessary.

The invention accordingly relates to a method for production of titanium dioxide or

Titanium dioxide aquate coatings, which consists in being converted to an aqueous Suspension of materials to be coated at temperatures between about 50 and about 1000 C and a pH between 0.5 at the same time an aqueous 0.001 to Smolar solution of a titanium salt with a content of free acid corresponding to a Normality of 0.002 to 3 and an aqueous 0.025 to 10 normal alkali or ammonium hydroxide solution or gaseous ammonia is added, the supply of the base being kept in such a way that that just the one contained in the titanium salt solution and that of the reaction able to neutralize the resulting acid and thus maintain a constant pH value can be. The amount of titanium salt added per minute is of the same order of magnitude from about 0.01 to 20 10-6 mol of titanium salt per square meter of surface to be covered.

It is essential that an excess of the titanium salt is avoided. The method of the present invention defeats excess titanium salt and almost completely prevents free, hydrated titanium dioxide particles, which do not rest on the surface to be coated are present in the suspension are. Rather, the hydrated TiO2 forms homogeneous and amorphous deposits of the same and even layer thickness on the surface to be coated. This The effect is achieved by using only such an amount of titanium salt per unit of time for hydrolysis as required for even coverage with the hydrated TiO2 is required and as absorbed by the available surface area per unit of time can be.

There are therefore no hydrated titanium dioxide particles that are not deposited on the surface to be coated. Unless as to coating surface mica flakes are used, the finished pigment is made up rather, exclusively from small leaflets, which are even and even Layer of hydrated titanium dioxide are coated. This homogeneous layer contains no coarse particles of hydrated TiO2, nor are they coarse Particles deposited on the surface. Such non-homogeneous agglomerates of hydrated TiO2 would degrade the luster of the pigments and the formation of uniform interference colors as well as non-precipitated TiO2. According to the process of the invention, a coated pigment having a Surface that is optimally the flat surface to be coated, for. B. of mica flakes, corresponds.

This effect is best achieved when one involves hydrolysis as completely constant temperature as possible and with approximately constant pH values performs. The pH value is adjusted by adding a base, preferably an alkali metal hydroxide, z. B.

NaOH, maintained.

One of the most characteristic and important features of the present Invention is the feed rate of the titanium salt in moles per minute per square meter of the area to be covered.

According to the invention, the hydrolysis takes place in aqueous solutions Temperatures between 50 and 100 "C, preferably between 70 to 80" C. At this hydrolysis Care must be taken that the amount of titanium salt introduced in the unit of time or the resulting amount of titanium dioxide aquat on the surface to be covered is adequate, d. H. is completely absorbed by this surface and not remains freely suspended in the reaction liquid. Hydrolysis is expedient carried out in such a way that the objects or substances to be covered are suspended in water or be suspended therein. After the suspension to the necessary temperature (about 50 to 100 "C) is heated, a dilute, aqueous, 0.001- to Smolare titanium salt solution, which has a content of free acid corresponding to a Normality of 0.002 to 3, expediently below the liquid surface, fed in. At the same time, the dilute aqueous base is left in the suspension flow in or feed in gaseous ammonia. The base is used to neutralize the contained in the titanium salt solution and continuously arising therefrom through hydrolysis Acid necessary.

Both the titanium salt solution and the base become beneficial supplied via suitable metering devices. As a metering device come in particular the usual metering pumps and liquid rotameters are in question.

If a titanium (III) salt solution is used, an additional one is required Oxidation required. The preferred oxidizing agent is oxygen, especially in Form of air. The oxygen necessary for the oxidation increases with vigorous stirring the interface taken from the air. In the case of awkwardly shaped vessels, it is necessary to bubble a weak air flow through the suspension liquid permit. Water-soluble titanium (III) salts are preferred as titanium (III) salts strong acids, in particular titanium (III) chloride, bromide or sulfate, in question. Suitable titanium (IV) salts are the chlorides and bromides and titanyl sulfates. the Anions of these salts play practically no role in the course of the process.

Alkali hydroxide solutions, in particular, can preferably be used as the aqueous base Caustic soda or potassium hydroxide, or ammonium hydroxide, can be used. Appropriate one uses 0.025 to 10 normal solutions. However, it can also be gaseous ammonia can be used. The amount of base supplied in the unit of time can be narrow Limits can be varied without undesired by-products. At this Variation changes the pH value, which is an important measured variable for control the whole procedure will. It has been shown that pH values in the range of 0.5 to 5.0, in particular between 1.5 and 2.5, especially for producing good coatings are suitable.

If desired, buffer substances can also be used to maintain this pH can be added. All buffer systems can be used that are commonly used for this pH range come into question, z. B. phosphates, acetates, citrates or glycoll buffers.

According to the method of the invention, it is therefore possible to assign the Surfaces to offer only so little titanium salt in the unit of time that the entire Titanium hydroxide or titanium dioxide aquate can deposit on the surfaces and none Freely moving by-products can arise in the suspension liquid.

Maintain the amount of titanium salt used per minute themselves in the order of magnitude from 0.01 to 20-10-5 moles of titanium salt per square meter covering surface. The reaction can vary greatly over time, depending on which titanium salt solution is used and which materials are to be covered. Of course, the quantities used also play a major role.

For example, you can get an occupancy after about 1 to 4 hours (e.g. with barium sulfate), while with other materials to be coated considerably longer times up to several days - required.

Naturally, the process of the invention results in titanium dioxide aquate coatings. These coatings can be removed by simply allowing them to stand in the air or by drying be completely or partially dewatered in conventional drying devices. The higher the temperatures chosen during the drying, for example when the coated Materials glows, the less water there is in the applied layers and all the more the anatase lines can be seen in the X-ray diagram. Will be at higher Annealed temperatures are shown in the X-ray diagram next to the lines of the base body to recognize those of rutile.

The method according to the invention only works if the specified values are adhered to Conditions for uniform coatings. One avoids that as by-products Freely moving particles of titanium dioxide quatene found in the suspension liquids will. Such freely moving particles in the suspension can subsequently reach the surface to be covered and thus disturb the homogeneity of the coatings. As a result, the adhesive strength and the optical properties of the applied material suffer Layers.

A wide variety of materials can be used in the process of the invention in the most varied of forms with titanium dioxide or titanium dioxide aquate coatings be provided. The prerequisite, however, is that the substances to be covered in the weak acidic suspension medium at temperatures from about 50 to about 100 "C sparingly soluble are or do not decompose. As soon as the Substances to be coated ions or molecules to a greater extent in the reaction medium are handed over, the occupancy that can then still be achieved is either incomplete or not practically feasible. For example, the following substances can be occupied become: minerals, e.g. B. mica or graphite, glass, plastics, metals or other artificial or natural inorganic or organic products, such as B. barium sulfate, or phosphors, such as calcium tungstate, activated with manganese Zinc silicates, cadmium silicates or cadmium borates, or with manganese, antimony respectively.

Cerium activated calcium halophosphates.

It is also possible to use titanium dioxide to cover larger contiguous areas to be documented in the specified manner. It is useful to have the body in question to hang in a suspension of a finely divided, possibly other material, which is then also coated with titanium dioxide, so that the available Total surface area is large enough to allow free titanium dioxide aquat germs to stay for longer to prevent in the suspension liquid. For example, if you have larger sheets of glass wants to cover with titanium dioxide according to the invention, it is recommended that these glass plates into a suspension to hang from mica flakes or glass beads, as this makes it possible to provide a sufficiently large surface that prevents that freely movable titanium dioxide aqua occur in the reaction medium.

According to the method of the invention, titanium dioxide or titanium dioxide aquat are used Coated products obtained, which are characterized by a particularly uniform coating. The coated materials therefore all consist of such uniform ones Advantages derived from titanium dioxide or titanium dioxide aquate coatings, such as good reflectivity, Clarity, transparency, protection against corrosion and pure interference colors. Until now Such coated materials could not in terms of color quality and color brilliance obtained for the first time by the Ver; drive the present invention possible became.

Especially mica coated with titanium dioxide produces pearlescent pigments any color. The interference colors obtained are only from the Dependent on the thickness of the applied film. It is desirable to be photosensitive Pigments obtained by the method of the invention by calcination To stabilize temperatures between 700 and 1000 "C, preferably between 900 and 1000" C.

It is also possible to apply a metal oxide layer on top of the titanium dioxide layer to apply or to mix with this. In this way special Color effects can be achieved, especially with those metal oxides that are colored by themselves are, such as iron, nickel, cobalt or chromium oxide. These additional oxides can contribute their own color as well as interference colors and thus color effects of particular beauty.

Example 1 10g of wet ground mica of the commercial type ORS with a according to the BET method Journal American Chemical Society, Vol. 60 (1938), p. 309, and Journal American Chemical Society, Brd. 62 (1940), p. 1723) of 2.3 m2 / g are suspended in 1 l of water. The suspension has a pH of 6.8. It is heated to 740 ° C. while stirring.

During the occupancy, a weak flow of air is directed with a Glass frit through the suspension.

A 0.0324 molar titanium (III) chloride solution, which is 0.118 N hydrochloric acid, with a feed rate of 225 ml / hour. under fed into the liquid surface. After the pH of the suspension has increased to 2.3 has fallen (5 minutes), a 0.22 normal is passed through a second metering pump Pour aqueous sodium hydroxide solution into the suspension. The progressive occupancy of the The mica surface with the titanium dioxide aquat is due to the Newtonian interference colors that occur to recognize.

The weak iridescence of the mica flakes at the beginning of the experiment in the suspension becomes increasingly stronger. Starting with a light gray-blue, the known color levels are run through.

The procedure described is repeated several times, the experiment being terminated with the colors white, yellow, red, blue and green. The final pH is between 1.9 and 1.7. The ratio of the number of moles of titanium dioxide used / m2 / minute is in the present case. 5,310-6. After the desired color has been achieved, the suspension is filtered off, washed free of chloride with hot water and dried at 200 ° C. Half of the substance obtained in this way is calcined at 500 ° C. Drying and calcining do not result in any change in the interference colors. The X-ray diagram of both products shows In addition to the lines of mica, those of anatase. In the test vessel, a very even coating can be seen on the walls and on the bottom by means of the uniform interference color that occurs. The quantities of solutions required to achieve the respective color as well as the duration of the coating and the titanium dioxide - The content of the end products can be found in the following table: Consumption 0.0324-0 22 nor OIo TiO2 Duration of molar painter im TiCI, - wall end product color Solution NaO ml ml 200 ° cl 500 ° c 3 hours 40 minutes 825 805 17.8 18.4 white 5h 25 min. 1218 1198 24.6 25.7 yellow 6 hours 15 minutes 1405 1385 27.7 28.4 red 8 hours 10 minutes 1837 1817 34.3 34.9 blue 9h 15 min. 2080 2060 36.8 38.2 green Example 2 Fine glass beads, about 70μ in diameter, as used to cover projection walls, are suspended in water (1 kg glass beads / 21 water). The pH of such a suspension is alkaline; it is acidified to about 2.5 by adding dilute aqueous hydrochloric acid. After heating to about 80 "C, the pH rises again.

-This hydrochloric acid addition is continued until a stopped pH value of 2.5 remains unchanged for several hours. Then the Glass beads washed and dried. 550 g of the thus treated glass beads will be suspended in 1 l of water. This suspension is fed with stirring and heating to 74 "C 680 ml of a 0.0324 molar titanium (III) chloride solution containing 0.118 N hydrochloric acid is, with a feed rate of 120 ml / hour. and 670 ml of a 0.22 N sodium hydroxide solution and a feed rate of 120ml / hour. over the course of 5 hours and 40 minutes a. The ratio of TiO2 / m2 / minute is 5.2 10-6. After filtration, the pearls are with an even layer of titanium dioxide that can be seen under the microscope overdrawn.

The reflectivity of the coated glass beads is greatly increased.

Example 3 Graphite, as is commercially available for use in heating baths is, is wet-ground in a ball mill with water and passed through a sieve of 75 p Mesh size sieved, filtered and dried. 10 g of the graphite treated in this way are suspended in 11 water and heated to 74 ° C with stirring. In this suspension allowed to flow at a rate of 225 ml / hour. a dilute titanium (III) chloride solution Flow in according to example 1 and 2 through a metering device. After 20 ml of this solution are fed in, a 0.22 ml sodium hydroxide solution is added via a second metering device added at the same feed rate.

There will be a weak air flow during the experiment in the suspension initiated. After consumption of 1818 ml of titanium (III) chloride solution and 1800 ml of sodium hydroxide solution is the end of the experiment. The pH is at the end of the Reaction 2.1. The graphite is filtered off and washed free of chloride with hot water and dried at 2000 C. It shows a bronze color; the titanium dioxide content is 29.60 /, TiO2. The suspension liquid is clear; no titanium can be detected in it.

Example 4 12.8 g of polyamide powder with an average particle size of about 10 Cu are suspended in 500 ml of water with vigorous stirring and up Heated to 74 ° C. This suspension (pH 3.7) is allowed to flow in at one rate of 60 ml / hour a dilute titanium (III) chloride solution - according to Examples 1 to 3 - flow through a dosing device, which is a feed rate of corresponds to about 5. 10-6 mol / min. / m2. After 10 minutes the pH has reached 2.4 set. A 0.22 N sodium hydroxide solution is now added to a second metering device with the same Feed rate added. After consumption of 420 ml of titanium (III) chloride solution and 410 ml of sodium hydroxide solution (7 hours) the experiment is ended. The final pH is 2.4. The polyamide powder is filtered off, washed free of chloride with warm water and dried at 800 C. It has a pale yellowish color and contains 7.9% titanium dioxide. No titanium can be detected in the clear suspension liquid. Under the microscope are the treated material in contrast to the untreated no agglomerates to be seen. The pourability was due to the titanium dioxide coating significantly increased.

Example 5 10 g of wet-milled mica of the commercial type ORS with a Surface area of about 3 m2 / g is suspended in 1 liter of water. The suspension has a pH of 6.8. It is heated to 74 ° C. with stirring.

During the occupancy, a weak flow of air is directed with a Glass frit through the suspension.

A 0.0167 molar titanium (III) sulfate solution is made using a metering pump in a 0.85 N sulfuric acid with a feed rate of 225 ml / hour. under supplied to the liquid surface. After the pH of the suspension has increased to 2.2 until 2 has fallen (5 minutes), a 0.96 Pour n-sodium hydroxide solution into the suspension.

The progressive coating of the mica surface with the titanium dioxide aquate can be recognized by the Newtonian interference colors that occur. The one at the beginning The weak iridescence of the mica flakes in the suspension intensified increasingly.

The final pH is between 1.9 and 1.7. The ratio of the number of moles of titanium dioxide / m2 / minute is 4 10-6. After the desired color has been achieved, the suspension is filtered off, washed free of chloride with hot water and dried at 200 "C. Half of the substance obtained in this way is calcined at 500" C. Drying and annealing do not result in any change in the interference colors. The X-ray diagram of both products shows, in addition to the lines of mica, those of anatase. Consumption 0.0167 moles. Ole TiO2 im Time Ti2 (So4) 3- 0.96 n- final product color Solution NaOH ml ml 200 "C j 5000 C 5h00min. | 1125 | 1107 | 22.7 | 23 white

Example 6 To a solution of 2.6 g of sodium chloride, 3.3 g of potassium chloride and 10.5 g of barium chloride dihydrate in 5.9 l of water are taken at room temperature Stirring 1.2 l of 1N sulfuric acid slowly added. During the addition of the sulfuric acid the barium sulfate separates out as a slightly iridescent precipitate. One lets the precipitation settle and decanted three times with 2 liters of deionized water each time. the The yield is 10 g of barium sulfate. Under the microscope, the crystals show star-shaped Adhesions that reveal irregular colors of thin leaflets in incident light. The crystal size in the platelet plane is 50 to 70 p; the crystal thickness is about 1 çu.

6 g of such a barium sulfate are suspended in 1 liter of water and the suspension is heated to 74 "C.

A 0.0324 molar is left under the surface of the liquid with stirring Titanium (III) chloride solution, which is 0.118 N hydrochloric acid, is poured in. The feed rate is 22.5 ml per hour. After 15 minutes the suspension has reached a pH of 2.2.

A 0.22N sodium hydroxide solution is now allowed to flow in at the same rate flow into the suspension.

After a test duration of 1 hour, the feed rate of both Solutions increased to 45 ml per hour. After another hour at a time the same is reduced to 90 ml per hour or

120 ml per hour increased for both solutions.

During the experiment, evaporated water is replaced from time to time, so that the suspension volume is kept at 1 liter. After a total of 4 hours is the attempt ended. The final pH is 1.8 to 2. In the suspension liquid no dissolved titanium (III) salt or colloidal titanium dioxide aquate can be detected. The iridescence of the barium sulfate crystals has intensified. The color is white. The crystals are filtered, washed free of chloride with hot water and with 200 "C. The titanium dioxide content is 10.7 ovo.

Example 7 In a 5-liter beaker, 30 g of mica are mixed with a specific surface of 3.37 m2 / g (determined according to BET) with stirring in 1 l of desalinated Suspended water and heated to 75 ° C. With the help of a metering device is First, a 0.132 molar titanium (IV) chloride solution containing 0.948 N hydrochloric acid, drop by drop is introduced at a feed rate of 120 ml per hour. As soon the pH of the suspension has fallen to about 2, with a second dosing device a 1.475 N sodium hydroxide solution was introduced at the same feed rate; this corresponds to a precipitation amount of 2.61 10-6 mol TiO2 / m2 / minute. The known Color levels are run through. After the desired shade is achieved, will the pigment is filtered off, washed neutral with demineralized water, dried at 120 "C and annealed at 950" C.

Example 8 15 kg of mica of the muscovite type, particle size about 10 to 30, are suspended in so much deionized water in a 400-1 vessel that a 5 to 100% solution is formed, which is obtained by adding 250% hydrochloric acid (0.95 N) solution of titanium tetrachloride is brought to a pH of 2.2. the Solution is stirred and heated to a temperature of 70 to 75 "C and during kept at this temperature throughout the coating process.

The 250 /, ige acidic titanium tetrachloride solution is at a rate from 0.8 to 11 per hour and per kilogram of mica supplied to the suspension.

The pH value is kept constant by adding 350/0 strength aqueous NaOH held. The coating is finished when 1.00 kg of titanium tetrachloride per kilogram Mica is used up.

The pigment obtained is washed with deionized water and dried and annealed for 30 minutes at 950 ° C. The pigment is silver in transmitted light.

Example 9 The procedure is analogous to Example 8, with the exception that the following amounts of TiCl4 are used per kilogram of mica in order to obtain other color pigments: Color kg TiCl, lkg mica Gold 1.85 Red 2.07 Blue 2.52 Green 3.30 Claims: 1. A process for the production of uniform titanium dioxide or titanium dioxide aquat coatings, characterized in that an aqueous suspension of materials to be coated is obtained at temperatures between about 50 and about 100 "C and a pH between 0.5 and 5 , 0 allows an aqueous, 0.001 to 5 molar solution of a titanium salt with a content of free acid corresponding to a normality of 0.002 to 3 and an aqueous, 0.025 to 10 normal alkali or ammonium hydroxide solution to run in or the corresponding amount of gaseous ammonia, The supply of the base is controlled so that the acid contained in the titanium salt solution and the acid formed during the reaction are neutralized while maintaining an almost constant pH, and that the amount of titanium salt added per minute is of the order of magnitude of about 0.01 to 20 10 mol per square meter of surface to be covered.

2. The method according to claim 1, characterized in that the Reaction at a temperature between 70 and 80 "C, a pH value of 1.5 to 5.0 and a feed rate of the titanium salt of less than 5 10 -5 moles per minute and square meter of surface to be covered, preferably between 0.1 and 2. 10-5 moles.

3. The method according to claim 1 or 2, characterized in that mica flakes are used as the material to be coated.

4. The method according to claims 1 to 3, characterized in that that titanium tetrachloride is used as the titanium salt.

5. The method according to claims 1 to 3, characterized in that that a titanium (III) salt is used as the titanium salt and the process under action is carried out by atmospheric oxygen.

6. The method according to claims 1 to 5, characterized in that that the pH before hydrolysis to a value between 0.5 and 5.0 by adding an acidic titanium salt solution is set.

7. Process for the production of pigments based on with Titanium dioxide-coated mica flakes, characterized in that the titanium dioxide on the mica flakes by hydrolysis of a titanium salt according to claims 1 until 6 is noticed.

8. The method according to claims 1 to 7; characterized, that it is used for the production of pearlescent pigments.

Claims (1)

9. The method according to claims 1 to 8, characterized in that that it is used for the production of colored pearlescent pigments.