CZ115999A3 - Process for preparing color pigments containing titanium dioxide - Google Patents

Abstract

The invention concerns a method for preparing coloured pigments with titanium dioxide base comprising the calcination of octahedrite dioxide until complete transformation of the octahedrite titanium dioxide into rutile titanium dioxide, in which is used an octahedrite titanium dioxide having a rutile phase temperature of at least 1000 DEG C and a proportion of sulphate, expressed in SO3, of at most 1 wt. %.

Description

Technical field

The present invention relates to a process for preparing titanium dioxide colored pigments. The invention also relates to color pigments obtained by this process.

BACKGROUND OF THE INVENTION

Color pigments based on rutile, i.e. composed predominantly of titanium dioxide in the form of rutile, are generally used as coloring agents for plastic materials, paints and varnishes, as well as in the cosmetic and pharmaceutical fields.

Pigments of this kind known in the art are generally prepared by (i) mixing titanium dioxide in the form of anatase with one or more pigmentary additives, (ii) grinding and then (iii) calcining.

These color pigments must meet certain criteria and in particular have good stability to thermal and light effects as well as to decomposition by acidic or basic chemical agents. DE 36 04 317 discloses color pigments having improved thermal stability, as disclosed in DE 36 04 317. Containing a ternary system consisting of titanium, antimony and chromium, which additionally contains 0.1 to 2 % wt. magnesium.

In fact, it is essential that pigments' colors are not degraded, for example, during their incorporation into plastic materials or paints, or when they are subjected to particularly harsh climatic conditions. In the same spirit, EP 318 783 recommends the addition of lithium in a ratio of 0.01 to 0.25% by weight. to reduce the tendency to decolorize pigments based on rutile chromium and antimony compounds dipped.

In any case, the pigments in rutile form which have been used hitherto are not satisfactory in terms of color intensity and saturation.

These disadvantages are overcome by the solution of the present invention.

SUMMARY OF THE INVENTION

The present invention relates to a solution to the problem of color enhancement according to the present improved process for preparing titanium dioxide color pigments. The color pigments obtained according to the present invention offer a variety of colors better suited than those currently available on the market.

SUMMARY OF THE INVENTION The present invention provides a process for preparing colored titanium dioxide pigments, comprising calcining anatase titanium dioxide to complete transformation of anatase titanium dioxide into rutile titanium dioxide, wherein anatase titanium dioxide having a rutile conversion temperature of at least 1000 ° C is used, preferably at least 1060 ° C and with a sulfate content, expressed as SO ₃ , of at most 1% by weight, preferably less than 0.8%.

An essential feature of the present invention is that the titanium dioxide used must contain an amount of sulfate, expressed as SO ₃ , of at most 1% by weight, preferably less than 0.8%. In fact, when starting from anatase titanium dioxide containing too much sulfate, the color of the resulting pigment is not intense enough. Thus, the smallest possible amount of sulfate is particularly preferred.

One skilled in the art will determine the amount of sulfate by any analytical method known in the art, for example, by X-ray fluorescence.

This sulfate content of anatase titanium dioxide can be controlled during the production of anatase titanium dioxide.

The starting anatase titanium oxides useful in the process of the invention are prepared by methods known in the art. These methods are described in the works of Ullman Band (vol. 18, p. 574) and Kirk Othmer (vol. 23, p. 146). According to a preferred method, anatase titanium dioxide is obtained in three stages: 1) hydrolysis of the titanyl sulfate solution, 2) filtration of the hydrolyzate and 3) washing of the filtrate with water.

In particular, the titanium dioxide sulfate content can be checked during step 3, i.e. the washing of the filtrate.

• 4 4 4 4 4

4444 · ··

4 4 4 4 · · 44 ·· ··

Another essential feature of the present invention is that the titanium dioxide used must have a rutilization temperature of at least 1000 ° C, preferably at least 1060 ° C.

Generally, control of the titanium dioxide rutilization temperature is performed during the titanium dioxide synthesis. The degree of purity of titanium dioxide in the form of anatase may also be a control element of this temperature, since the more the amount of titanium dioxide in the anatase approaches 100%, the higher the rutilization temperature will be.

In particular, the anatase content can be adjusted in step (1) by introducing the seed crystal into the hydrolysis medium. This helps to regulate the nature of the forming hydrolyzate: depending on the nature of the titanium dioxide seed crystal, the resulting hydrolyzate, consisting predominantly of anatase titanium dioxide, will contain a more or less significant portion of the rutile titanium dioxide, with the aim of limiting this portion.

Anatase titanium oxides having the features required to be used in accordance with the present invention are commercially available, for example, from Rhône Poulenc. The titanium dioxide sold by Rhône Poulec under the designation G5 is a powder, and Rhône-Poulenc also makes available a titanium dioxide salt under the designation S5-300.

The rutilization temperature, which is not always indicated by the manufacturer, is readily determinable by one skilled in the art according to the following procedure.

1 1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

The rutilization temperature is generally defined as the temperature at which 50 wt. the amount of anatase phase of anatase titanium dioxide is changed by calcination into the rutile phase. According to the present invention, the rutilization temperature is determined diffractometrically by high-temperature X-rays.

In order to eliminate the influence of secondary parameters (such as precise conditions under which the temperature rises), this determination is carried out under precisely defined operating conditions: the titanium dioxide sample in the pineapple form is placed on a flat platinum support and kept in a closed atmosphere for calcination. (without air purging), for example in an enclosed space. The temperature in this space is raised

at a rate of 5 ° C per minute up to 1250 ° C. Between temperatures 650 ° C and 1250 ° C j sou implemented diffractometric measurement. In regular intervals

(for example, every 50 ° C) a diffractogram is performed, the data acquisition time being fixed at 10 seconds in an angular sector of 10 ° to 60 °, which is recorded in steps of 0.032 °.

Preliminary experiments were carried out as described above with reference samples, represented by titanium dioxide containing 100% rutile phase and titanium dioxide containing 100% atanasic phase, respectively.

Lines corresponding to atanasic titanium dioxide and rutile titanium dioxide, respectively, are located on the obtained reference diffraction patterns.

• <9 ·· ·

Subsequently, experiments are carried out under the same conditions on the titanium dioxide samples to be analyzed.

The proportion of the rutile phase formed at each of the temperatures measured is then calculated by comparing the area of the most intense line of the diffractogram for both phases with the areas of the diffractograms obtained from the reference samples.

The temperature at which the same percentage of rutile phase and anatase phase is observed is considered to be the rutilization temperature.

According to the present invention, the rutilization temperature must be at least 1000 ° C, preferably at least 1060 ° C. A temperature below 1000 ° C is insufficient in terms of color intensification and color saturation.

In a preferred embodiment, the method of the invention comprises the following stages:

a) mixing the atanasic titanium dioxide with at least one pigmentary additive;

(b) grinding the resulting mixture; and

c) calcination under an oxidizing atmosphere.

The mixture of the pineapple titanium dioxide with the pigment additive or pigment additives may be dry or starting from an aqueous suspension.

In order to facilitate the mixing operation, atanasic titanium dioxide having a specific BET surface area of at least 250 g / m ² is preferably selected.

A BET specific surface is understood to be a BET specific surface area, i.e., based on nitrogen adsorption according to ASTM 03663-78, based on the BRUNAUEREMMETT-TELLER method as described in "The Journal of the American Society, 60, 309" (1938). If the titanium dioxide is in the form of an aqueous suspension (for example, a sol), a preliminary spraying of the aqueous suspension is performed before measuring its specific surface area.

When operation (a) is carried out dry, the atanasic titanium dioxide is in the form of a powder consisting of particle agglomerates, the mean size of which is between 1 and 2 μτη and the mean particle size is between 40 and 60 nm.

Such a powder can be obtained in a manner known per se by carrying out the following steps:

- hydrolysis of the titanyl sulphate solution,

- filtration of the hydrolyzate,

- washing the filtrate with water,

reconstituting the filtrate in water, and

spraying the resulting suspension.

In another embodiment of the invention, the stirring according to a) may be carried out in a solution formed from the titanium dioxide particles in the atanasic form in suspension in an aqueous medium, the mean particle size being in the range of 40 to 60 nm. In this case, the water is removed from the aqueous suspension prior to grinding and calcination. This second embodiment is particularly advantageous in that it leads to the formation of pigments which have an even more permanent coloration as compared to the first embodiment in which the dry mixing operation is carried out using the powder of the corresponding atanasic titanium dioxide.

In all cases, the smaller particle sizes facilitate the mixing operation.

An aqueous slurry containing atanasic titanium dioxide can be obtained by performing the following steps:

- hydrolysis of the titanyl sulphate solution,

- filtration of the hydrolyzate,

- washing the filtrate in water,

re-forming the filtrate dispersion in an acidified medium, for example in a solution of nitric acid or hydrochloric acid. Sulfuric acid is not used in this step in order not to increase the sulfate content.

As pigment additives, substances which are commonly used for these purposes are used. They are, for example, selected from the group consisting of compounds of transition elements Sb, Cr, Ni, Co, Zn, Cu, Mn and W and are either in the form of an oxide of said element (especially Sb ₂ O ₅ , Cr ₂ O ₃ , NiO, CuO, MnO and WO ₃ ) or in the form of compounds oxidizable in an oxidizing atmosphere that is used in the calcination step.

Preferably, for carrying out the process of the present invention, a mixture of titanium dioxide and chromium and antimony compounds is selected in which the molar ratio of antimony and chromium is close to 1, for example a ratio ranging from 0.8 to 1.2.

• ·

By way of example, calcination may be carried out in an oxygen atmosphere or in air, the calcination temperature preferably being in the range of 800 ° C to 1400 ° C.

Mineral additives (commonly referred to as "mineralizers") such as sodium fluoride, sodium chloride, potassium chloride, calcium fluoride or calcium chloride may be added to the mixture prior to grinding and calcining the titanium dioxide containing composition. It is also contemplated to add lithium compounds such as those described in EP 318 783 (carbonate, fluoride, chloride, oxide, hydroxide, sulfate, nitrate, phosphate, antimony or lithium titanate) or magnesium compounds as described in DE 36 04 317 (carbonate or magnesium oxide).

The invention also relates to color pigments obtained by the process of the present invention as described above. These pigments are useful in the production of plastics, paints and varnishes, but also in cosmetics and pharmaceuticals.

Finally, the invention also relates to the use of atanasic titanium dioxide having a rutilization temperature of at least 1000 ° C, preferably at least 1060 ° C, and a sulfate content, expressed as SO ₃ , of at most 1% by weight, preferably less than 0.8% by weight. , for the preparation of color pigments containing titanium dioxide.

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BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail by means of specific examples, the results of which are shown in the accompanying drawings, in which Fig. 1 shows the changes in the percentage of rutile and anatase phase in a sample having a specific BET surface area of 300 m ^z / g. less than 0.8 wt. and a rutilization temperature of 1080 ° C;

Figure 2 shows changes in the percentage of rutile and anatase phase in a comparative sample having a BET surface area greater than 250 m ² / g and a sulfate content, expressed as SO ₃ , of 5% by weight. and a rutilization temperature of 850 ° C;

DETAILED DESCRIPTION OF THE INVENTION

The following examples are provided to facilitate understanding of the invention without limiting it in any way.

Example 1

Determination of rutilization temperature of atanasic titanium dioxide

The samples used in the examples had the following properties:

- Sample 1: G5 powder, sold by Rhone-Poulenc.

This titanium dioxide has a specific BET surface area of 300 m ² / g and a sulfate content, expressed as SO 3, of less than 0.8% by weight; the powder is in the form of particle agglomerates, the mean size of the agglomerates being close to 1.5 µm.

- sample 2: The powder to be compared, which has a BET surface area greater than 250 m ² / g and a sulphate content, expressed as SO 3, equal to 5% by wt .; the powder is in the form of particle agglomerates, the mean size of the agglomerates being close to 1.5 µm.

The rutilization temperatures of these samples were measured as follows.

The sample powders were first studied by high temperature X-ray diffraction. Powders containing 100% anatase form and 100% rutile form, respectively, were used as reference samples for locating lines corresponding to the rutile and anatase phases. Each of these reference powders to be measured was placed on a flat platinum carrier which was placed in an enclosed space. The temperature in this space was gradually increased with a heating rate of 5 ° C / min. Diffractograms were performed at the following temperatures:

650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200 and 1250 ° C under the following conditions:

• ·

- diffraction time: 10 seconds,

- angular sector 10 ° to 60 ° in 0.032 ° increments.

Lines corresponding to the rutile phase and anatase phase were located.

The same measurements were made with samples 1 and 2 above. The obtained diffractograms made it possible to determine the percentage of rutile and anatase phase by comparing the areas of the most intense lines of both phases in the diffractograms with the areas obtained in the diffractograms of the reference samples.

graphically depicted as curves, rutile percentage changes and temperature. These curves, 2, allow easy graphics

The results were representative of the anatase phases shown in Figure 1 and the determination of the rutilization temperature.

Figure 1 corresponds to sample 1 having a rutilization temperature of 1080 ° C.

Figure 2 corresponds to sample 2 having a rutilization temperature of 850 ° C.

Only powder of sample 1 is useful in the process of the present invention since its rutilization temperature exceeds 1000 ° C.

• · · ·

Example 2

Preparation of a color pigment containing atanasic titanium dioxide with a rutilization temperature of 1080 ° C.

Atanasic titanium dioxide powder, sample 1 (see Example 1), is mixed with chromium trioxide (Cr ₂ O 3) and antimony trioxide (Sb ₂ O ₅ ). This mixture is formed in the form of lozenges.

The lozenges are then calcined for 12 hours at 920 ° C in an oxygen atmosphere. Thereafter, the lozenges are ground before being re-calcined, first for 12 hours at 980 ° C in an oxygen atmosphere and then for 4 hours at 970 ° C in air. The resulting powder is ground.

Hereby way se prepare two color samples pigment orange color: sample 3, which has summary formula (TiO, 9Cro, O5Sbo, O5) θ2 sample 4, which has summary formula (TiO, 99CrQ, o05Sbo, o05) o ₂ Chemical formula resulting the compound is obtained using

correspondingly selected starting amounts of chromium trioxide, antimony trioxide and titanium dioxide.

The two pigments thus obtained are tested for their color saturation.

Coloration is measured using the chromatic coordinates L, a and b * of the CIE 1976 system (L *, a * and b *), as defined by the Commission Internationale d'Eclairage and as listed in the French Standards Recueil des Normes Frangaises • 0

0 0 · (AFNOR), Couleur Colorimétrique (colorimetric color), No. X08-12 (1983). Staining was determined using a colorimeter

DATACOLOR supplied by SCIENTIFIC PACIFIC.

L * determines the color reflectance and gives information about the color brightness.

a * and b * determine the color trend:

a positive value of a * represents red, a negative value of a * represents green, a positive value of b * represents yellow, and a negative value of b * represents blue.

Roughly speaking, L * represents the change from white to black (brightness), a * represents the change from green to red, and b * represents the change from blue to yellow.

Measurements performed with samples 3 and 4 gave the results shown in Table 1 below:

Table 1

Pigment

Sample 3 Sample 4

L ’

67,5 a

tT

Example 3 (comparative)

Preparation of color pigments containing atanasic titanium dioxide with a rutilization temperature of 850 ° C.

Two color pigments (samples 5 and 6) with the summary formulas (Tio, ₉ Cro, o5Sbo, o5) 0 ₂ and (Tio.ggCro.oosSbo.oos) O2 were prepared from the atanasic titanium dioxide of sample 2 as described in Of Example 1, following the procedure described in Example 2.

The chromaticity values measured for the sample are given in Table 2 below.

Table 2

Pigment L ’ and' b ’ Sample 5 66 20 May 57 Sample 6 85.8 3.2 28.2

It can be stated that a comparison of pigments of the same chemical composition (Samples 3 and 5 on the one hand and Samples 4 and 6 on the other) shows that the pigments of the present invention show higher values of a * and b * and hence better expressed orange.

Example 4

Preparation of color pigments containing atanasic titanium dioxide with a rutilization temperature of 1080 ° C.

Pineapple titanium dioxide was used as a sol. This oxide is available from Rhône-Poulenc under the designation S5-300. Said titanium dioxide is characterized by a specific surface area of BET of 300 m ² / g, a sulfate content, expressed as SO ₃ , of less than 0.8% by weight. and a rutilization temperature of 1080 ° C. The solid extract contained in sol S5-300 is 20 wt.

Color titanium dioxide pigments were prepared by (i) mixing S5-300 sol with chromium nitrate and antimony nitrate (ii) spraying the resulting aqueous mixture and (iii) calcining / crushing, wherein the step (iii) of calcination / crushing is performed in the same manner as in Example 2.

In this way, two samples of an orange color pigment are obtained:

sample 7 having the empirical formula (T _{o, the} 9Cr, o5Sbo, O5) O2 sample 8 having the empirical formula (Tio, _the 99Cr, oo5Sb _o oo5) ₂ O

The chemical formula of the resulting compound is achieved using appropriately selected starting amounts of chromium trioxide, antimony trioxide, and S5-300 sol. Measurements performed with samples 7 and 8 gave the results shown in Table 3 below:

Table 3

Pigment L ’ * and b ^ - Sample 7 68 24 61.5 Sample 8 85 8 41.2

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I · · · · · 4

Comparing the a * and b * values of samples 3 and 7 on the one hand and samples 4 and 8 on the other, gives a better expressed coloration of the pigments of samples 7 and 8.

In this way, it was verified that the pigments prepared from the titanium dioxide sol of the present invention lead to intensification of the color shade.

Represented by:

Dr. Pavel Zelený

JUDr. Pavel Zeleny advokat

120 00 Prague 2, Halkova 2

7 ^ /

Claims (12)

PATENT CLAIMS A process for the preparation of colored titanium dioxide pigments, comprising calcining anatase titanium dioxide until the complete transformation of anatase titanium dioxide to rutile titanium dioxide, characterized in that anatase titanium dioxide having a rutilization temperature of at least 1000 ° C, preferably at least 1000 ° C, is used. at least 1060 ° C and with a sulphate content, expressed as SO 3, of at most 1% by weight, preferably less than 0.8%. Method according to claim 1, characterized in that it comprises the steps of: a) mixing said anatase titanium dioxide with at least one pigmentary additive, (b) grinding the resulting mixture; and c) calcination in an oxidizing atmosphere. Method according to either claim 1 or claim 2, characterized in that the BET surface area of the anatase titanium dioxide is at least 250 m ² / g. The process according to any of claims 2 or 3, characterized in that step a) of the mixing is carried out dry, starting from anatase titanium dioxide powder. • · Method according to claim 4, characterized in that the powder form consists of agglomerates of titanium dioxide particles, the mean size of these agglomerates is 1 to 2 µm and the mean particle size is 40 to 60 nm. Method according to either claim 2 or 3, characterized in that step a) of mixing is carried out starting from an aqueous anatase titanium dioxide suspension, the water being removed from the suspension before the mixture is ground. The method of claim 6, wherein the aqueous suspension comprises anatase titanium dioxide particles in suspension having a mean dimension between 40 and 60 nm. The process according to any of claims 2 to 7, wherein the pigment additive is selected from the group consisting of compounds of transition elements Sb, Cr, Ni, Co, Zn, Cu, Mn and W, either in the form of oxides or in the form of oxides. in the form of compounds _f oxidizable in an oxidizing atmosphere. 9. The process of claim 8, wherein in step a) said anatase titanium dioxide is mixed with antimony and chromium compounds in an antimony to asthole molar ratio of between 0.8 and 1.2; in particular, the ratio is 1. 4 4 4 4 444444 4 4 · 444 4 Process according to any one of claims 2 to 9, characterized in that the calcination is carried out at a temperature between 800 to 1400 ° C. er / dty 11th Colored pigments based on titanium dioxide ^of obtained by the process of any of claims 1 to 10 Use of anatase titanium dioxide having a rutilization temperature of at least 1000 ° C, preferably at least 1060 ° C, and a sulphate content, expressed as SO 3, of at most 1% by weight, preferably less _; %, for the preparation of color pigments based on titanium dioxide. Represented by: Dr. Pavel Zelený AVfSV / ' ^{ř ř ř ř f} · · ^{f f f f f f} 1/1