MXPA98009599A - Yellow pigments of iron oxide, non-flexible, with high density of co - Google Patents

Abstract

Yellow pigments of iron oxide were obtained in the modification of a-FeOOH with a silky index of less than 5, in which: a) nuggets of a-FeOOH are produced by precipitation from a solution containing Fe (II) in the presence of aluminum salts soluble in an amount of 3 to 9% by weight calculated as Al2O3, with respect to precipitated a-FeOOH, and subsequent oxidation to a-FeOOH, and (b) the development of pigment is performed by the precipitation of additional iron with simultaneous oxidation, where the nugget-time yield is less than 0.3 h-1 and the pH value is less than 3.9 during the entire period of pigment development, and (c) the pigment development is completed a reproduction factor between 3 and

Description

YELLOW PIGMENTS OF IRON OXIDE, NON-SILKY WITH HIGH COLOR DENSITY The present patent application relates to yellow pigments of iron oxide in the modification of α-FeOOH with a low s-level index having a high yellow index b *, a process for its preparation and its use. The yellow pigments of iron oxide in the modification of α-FeOOH can be prepared by precipitation processes from solutions of salts of Fe (II) followed by oxidation with air or other oxidizing agents or by the so-called process of .Penniman -Zoph in the presence of metallic iron and simultaneous oxidation with air or by the oxidation of metallic iron oxide with other oxidation agents, in particular with aromatic nitro compounds. The yellow iron oxides prepared in this way are mainly used as pigments in lacquers and paints, building materials or for coloring plastic materials. The coloring properties of the yellow pigments of iron oxide are REF .: 28921 determined substantially by the particle size, particle shape, particle size distribution and the state of agglomeration. The α-FeOOH particles that have been prepared by the processes mentioned above generally crystallize in a well-defined needle shape. The dispersion and absorption coefficients perpendicular and parallel to the axis of the needle differ considerably. If the needles are first arranged perpendicular and then parallel to the direction of observation, considerable differences in color are visible to the observer. This effect is called the silky effect because they change is observed in the silk tissues. With reference to the pigments of iron oxide, the silky effect is a particular annoyance in the case of lacquers that are applied in one direction (the beloved 11 image framing effect) and as a result of the alignment of the pigments during the extrusion and calendering of plastics and plastic sheets. The 'DE-C 33 26 632 patent describes processes for preparing yellow pigments of iron oxide with a low silky effect. The described pigments are prepared in such a way that the production of nuggets takes place in the presence of compounds of the elements B, Al, Ga, Si, Ge, Sn or Pb, in particular in the presence of silicates or aluminates, in amounts from 0.05 to 10% by weight, calculated as the 3 or 4 valent oxides and with respect to the a-FeOOH precipitated during the production of pips, and a yellow pigment of iron oxide can be developed on the yellow nugget prepared in this manner from a conventional way With regard to the pigment development process in DE-C 33 26 632 reference is made to the prior art. The patent examples show that the precipitation is formed at a constant pH of 4.0 ± 0.1 and that the development takes place relatively quickly so that the reproduction factors from 7 to 14 are achieved after 12 to 25 hours. The pigments are characterized in that they have a very low silky effect and in a lacquer color test based on Alkydal F48R (alkyd resin lacquer in oil vehicle, Bayer AG) at a pigment / volume concentration of 10%, the limits for L * they are between 52 and 63, for a * they are between 8 and 14 and for b * they are between 40 and 48, in the CIELAB color coordinates. The elimination of the silky effect is achieved since the highly dendritic needles are produced, which develop together to give spherical aggregates (similar to small "hedgehogs"). These approximately isometric aggregates can not be aligned any longer in specific, preferred directions. The disadvantage of the pigments prepared according to DE-C 33 26 632 is that they are sensitive to grinding and on the other hand they do not completely achieve peak values for the yellow index b * which is obtained by iron oxide pigments, light yellows , with a silky effect. Thus, the object was to prepare yellow pigments of iron oxide, not silky that are relatively insensitive to grinding and have a high yellow index b *. Surprisingly, the desired pigment can be prepared from the same nuggets described in DE-C 33 26 632 which accumulate in the process of the development of pigment to primary particles completely free of dendrite. These primary primary particles agglomerate into packages, where several particles are side by side. The primary particles have by themselves only one very tendency to be formed into needles. Technically, the modified primary particles and the agglomerated structure are achieved by accumulating the pigment at pH values less than 3.9, preferably less than 3.8, and at the same time by accumulating the pigments very slowly. The invention provides a process for preparing yellow pigments of iron oxide from a modification of α-FeOOH in which a-FeOOH nuggets are produced by precipitation from a solution containing Fe (II) using an alkaline precipitation agent in the presence of soluble aluminum salts in an amount of 3 to 9% by weight calculated as A1203, with respect to a a-FeOOH precipitate, and the subsequent oxidation to give a-FeOOH, and b) the pigment is produced by precipitating additional iron with simultaneous oxidation, where the yield of nugget / time is less than 0.3 h "1, preferably less than 0.2 h "1, and the pH during the entire period of pigment development is less than 3.9, preferably less than 3.8, and c) the pigment development is terminated at a reproduction factor between 3 and 20.

In this way, in the previous process step, a-FeOOH nuggets are prepared by initially introducing a Fe (II) salt solution, preferably a FeS04 solution, and an aluminum salt solution, preferably a sulphate solution. aluminum, this mixture is heated to the pip production temperature, desired, can vary between room temperature and 80 ° C, then part of the iron ions is precipitated using an alkaline precipitation agent, with stirring, where the oxides of the alkali metal and alkaline earth metal, the hydroxides or carbonates and ammonia can be mentioned as precipitating agents, and then the precipitated product is oxidized to a-FeOOH using air or other oxidation agents. The concentration of A1203 is between 3 and 9% by weight with respect to the a-FeOOH produced. In the second process step, these nuggets are developed via a precipitation and oxidation process to give pigments by adding additional iron (II) salt solution, and converting the iron (II) to a-FeOOH by controlled addition of the precipitation and simultaneous oxidation. In order to be able to obtain pigments according to the invention, it must be ensured that the pH value during the complete step of the pigment production is less than 3.9, preferably less than 3.8 and at the same time as the development of the pigment be done very slowly. The concentration-independent amount, the so-called nugget / time yield has to be proven useful to characterize the rate of development of the pigment. This is defined as: Amount of pigment produced Nugget yield / time = Amount of nugget used x pigment development period RF-1 Pigment development period The so-called reproduction factor (RF) and the ratio in the total amount of pigment (= amount of pip + amount of pigment produced) to the amount of pip. In order to prepare pigments according to the invention, a nugget / time yield of less than 0.3 h "1, preferably less than 0.1 IX1 is required, the pipit / time yield can be controlled by the pH value and the aeration rate The seeds accumulate at reproduction factors between 3 and 20, depending on whether the pigment is intended to be used with a pure tone or for clarification Highly accumulated pigments with a reproduction factor between 8 and 20 They are characterized by a CIELAB b * index, particularly high when used as a pure tone.These types of yellow pigments of iron oxide have color indices in the CIELAB color coordinates, in a pure tone with a concentration of pigment / volume of 10% in a test lacquer, from a * between 8 and 14, b * between 48.5 and 52 and L * between 54 and 62 .. The less highly accumulated pigments with a reproduction factor between 3 and 8 characterized by an index b * of CIELAB particularly high for clarification. These types of yellow iron oxide pigments have color indices in the color coordinates of CIELAB for clarification with a pigment of titanium oxide in the ratio 1: 5, at a pigment / volume concentration of 10% in the lacquer test, from a * between 3 and 7 and b * between 38 and 41. The electron microscopic photographs show that the primary particles, in contrast to the processes known to date, have only a weakly expressed needle shape, are completely free of nitrites and agglomerate into packages where the primary particles are side by side. The yellow index b * of the pigments changes only very slightly during grinding. The pigments according to the invention are all characterized by a low silky index of less than 5, particularly less than 3, and particularly less than 1. In addition, the pigments according to the invention are characterized by a low requirement of binder during the preparation of the lacquers. This can be characterized by oil absorption rates of less than 40 g / 100 g. Due to their properties, the pigments according to the invention are particularly suitable for preparing lacquers and paints and for coloring plastic materials. The use of the pigments according to the invention to color lacquers, paints and plastic materials is therefore an object of the invention. The parts and percentages cited in the following examples refer to the weight unless otherwise indicated. 1. silky index The so-called silky index is defined as a norm, an independent quantity, to measure the silky effect. The silky index is measured and calculated using the following methods: 1. 1 Preparation in an alkyd resin paste to measure the silky index The pigment is prepared using an automatic milling knife in a non-drying test binder. The test binder (paste) consists of two components: Component 1 Component 1 is an alkyd resin binder based on linseed oil and phthalic anhydride. It corresponds to the specifications that are mentioned in the standards DIN EN ISO 787-24: 1995, ISO 787-25: 1993 and DIN 55 583 (1983) as specifications for a test binder for colored pigments. The product Sacolyd L 640R, (Krems Chemie, formerly Alkydal L 64R, Bayer AG) is used.

Component 2 Component 2 is a rheological additive that is added to make the paste thixotropic. A castor oil, hydrogenated, modified, powder, -LUVOTHIX HT (Lehmann &Voss &Co) at a concentration of 5.0% is used. The Luvothix HT dissolves in the Sacolyd L 640 at 75 to 95 ° C. The extendable, cooled material is passed once through a triple roller mill. The pasta is then ready for use.

An automatic muller is used to prepare the pigment paste, as described in DIN EN SO 8780-5 (1995). An ENGELSMANN JELR 25/53 mallet with an effective plate diameter of 24 cm is used. The rotation speed of the plate is approximately 75 min. "When dispersing a load weight of 2.5 kg at the load joint, the force between the plates is adjusted to approximately 0.5 kN. 5.00 g of the paste in three stages of 25 revolutions each according to the method described in DIN EN ISO 8780-5 (1995) section 8.1 Then, the pigment mixture of the pastes is painted on a paste film support which corresponds to the pulp film support in DIN 55983 (December 1983) The blade associated with the pulp support is dragged over the depression in the support filled with the pigment and paste mixture so that a surface is produced The blade moves in an orientation at a speed of about 3 to 7 cm / s.Any needle-shaped particle present in the paste is then aligned in the direction of extension.The sample is measured within a few minutes 1. 2 Instrument to measure the sedóse index The 8 / d measurement geometry used to measure the silky effect is described in ISO 7724 / 2-1984 (E) point 4.1.1, in DIN 5033 part 7 (1983) point 3.2.4 and in DIN 53 236 (January 1983 ) point 7.1.1. A PERKIN ERLMER LAMBDA 19R spectrophotometer with a 15 cm diameter LABSPHERER integration sphere is used. A commercially available polarization filter of suitable size is placed outside the integration sphere, in the illumination beam for the sample orifice, in a defined position for measurement, so that the direction of the electric field Vector E of the beam of transmitted light is known in the sample hole. The filter has a degree of polarization > 99% The reference beam remains unchanged without a filter. The reference hole in the integration sphere is covered by a standard opal glass, blar. a, diffuse dispersion. A brightness trap is not used.

A standard opal, white, additional glass (working standard) is mounted in the sample hole and the instrument is calibrated. The work standard complies with the specifications described in ISO 7724 / 2-1984 (E) section 8.3. The reflectance data for the working standard against a perfect reflection diffuser are stored in the computer so that all color measurements are given with respect to the perfect reflection diffuser after calibration with the white work standard. The dark current at the zero point is measured with a black cavity light trap, stored in the computer and taken into account by the measurement program during calibration. 1. 3 Measurement and calculation of the silky index The measurement takes place immediately after the preparation of the test specimen. The temperature of the spectrophotometer and the sample is approximately 25 ° C ± 5 ° C. The sample is measured in two positions at right angles to each other with reference to the polarization filter: Measurement Yl: The pigment particles are directed with their longer axes largely parallel to the electric field vector of the illumination beam. The direction of spreading in the pulp film support is parallel to the electric field vector.

Measurement Y2: The particles and pigments are aligned with their longer axes greatly perpendicular to the electric field vector in the illumination beam. The spreading direction in the pulp film holder and the electric field vector are perpendicular to each other A device for rotating the sample around 90 ° is useful, but is not absolutely necessary if the appropriate markings are applied in the sample orifice. The trichromatic value Y is calculated from the reflectance spectra measured according to the calculation instructions in ASTM E 308 - 1985, point 7. The weighting fractions 1931 for Standard Illu inant C and 2 ° Standard Observer are used in the Table 5.6. The wavelength range is between 400 nm and 700 nm. The wavelength range is 20 nm. The specular component is included in the calculations. The silky index SI is then calculated as follows from the trichromatic value Y: SI = (1 - Yl / Y2-) x 10 The results are rounded to the nearest whole number. 2. Color coordinates CIELAB 2.1 Preparation in an alkyd resin lacquer to measure the mass tone (full tone).

The pigment is dispersed in an air drying lacquer system using a lathe. The lacquer system consists of the following components: 95. 26% ALKYDAL F 48R (binder, Bayer AG, alkyd resin, air drying, oil vehicle, based on fatty acids from drying plant in white alcohol / xylene mixture 38: 7 with a nonvolatile fraction of approximately 55 5 %, content of acetyl / triglyceride in the nonvolatile fraction approximately 48%, phthalic anhydride in the non-volatile fraction to approximately 26%) 0.78% "2-butanone oxime, 55% concentration in 10 white alcohol (preventive agent of the skin) 1.30 Octa Soligen calciumR (wetting agent, calcium salt of fatty acids of 6 to 19 carbon atoms, branched, in one mixture of hydrocarbons (contains 4% Ca), Borchers AG) 0.22% Octa Soligen cobalt 6R (drying agent, cobalt salt (2+) of fatty acids of 6 to 19 carbon atoms, branched, in 20 a mixture of hydrocarbons (contains 6% cobalt), Borchers AG) 0.87% Octa Soligen zirconium 6R (drying agent, zirconium salt of fatty acids of 6 to 19 carbon atoms, branched, in a mixture of hydrocarbons (contains 6% of Zr), Borchers AG) 1.57% n-butyl glycolate (= butyl hydroxyacetic acid ester) (squeezing agent) The components are mixed with a high speed agitator to give the final lacquer. A wheel as described in DIN EN ISO 8780-5 (April • 10 of 1995) is used. An ENGELSMANN JEL 25 / 53R mallet with an effective plate diameter of 24 cm is used. The rotation speed of the lower plate is approximately 75 min-1. By dispersing a load weight of 2.5 kg at the load junction, the force between the plates is adjusted to approximately 0.5 kN. Disperse 0.80 g of the pigment and 2.00 g of • the lacquer in a step at 100 revolutions with a load weight of 2.5 kg according to the process described in DIN EN ISO 8780-5 (April 1995) section 8.1. 20 The wheel opens and the lacquer is quickly placed on the bottom plate away from the midpoint. Then, an additional 2.00 g of lacquer is added and the plates are joined together: After two stages at 50 rotations without a load weight, the preparation.

The pigmented lacquer is painted with a film applicator (empty space of at least 150 μm, at most 250 μm) on a non-absorbable white paper. The lacquered frame is then dried for at least 12 hours at room temperature. Prior to the invention of color, the picture is dried at about 65 ° C (± 5 ° C) for 1 hour and then cooled. 2. 2 Preparation in an alkyd resin lacquer to measure the reduction.

The pigment and the clarifying pigment are dispersed using a pin in an air dried lacquer system. As the clarifier, a commercially available Bayertitan R-KB-2R titanium dioxide pigment (Bayer AG) is used. This pigment corresponds to type R 2 in ISO 591-1977. The lacquer system corresponds to that described under point 2.1. The components of the lacquer system are mixed in a high-speed agitator to give the final lacquer. The pigmented lacquer is prepared and the lacquered painting is produced in the same way as described under 2.1, where 0.1500 g of the pigment to be tested is 0.7500 g of the titanium dioxide pigment Bayertitan R-KB-2R and 2 x 2.00 g of lacquer they weigh themselves 2. 3 Spectrophotometer A spectrophotometer with an integration sphere and with the measurement geometry d / 8 without a brightness trap is used. This geometry of the invention is described in ISO 7724/2 1984 (E) point 4.1.1., In DIN 5033 part 7 (July 1983) point 3.2.4 and in rIN 53236 (January 1983) point 7.1.1. A Dataflash 2000R instrument from Datacolor International Co is used. The spectrophotometer is calibrated with a working standard, ceramic, white, as described in ISO 7724 / 2-1984 (E) point 8.3. The reflectance data for the working standard are compared against a perfect reflection diffuser in the color measurement instrument so that after calibration with the white work standard all color measurements are given with reference to the reflection diffuser perfect The zero point calibration is carried out using a black cavity light trap from the manufacturer of the spectrophotometers. 2. 4 Color measurement A brightness trap is not used. The temperature of the spectrophotometer and the specimen is approximately 25 ° C ± 5 ° C. The lacquered frame prepared in accordance with 2.1 or 2.2 is mounted in the sample hole of the spectrophotometer so that the sample hole covers a central location in the painted layer. The sample must be flat without any separation between the painting and the sample office. The measuring opening must be completely covered by the lacquer layer. Then the measurement takes place. 2. 5 Calculation of the coordinates of CIÉ The coordinates L *, a * and b * of CIÉ, 1976, are calculated from the reflectance spectrum measured according to the calculation instructions in ASTM E 308-1985, point 7. The weighting functions for standard illuminant C and 1931 2nd standard observer in ASTM E 308-1985, table 5.6 are used. The wavelength integrator is between 400 nm and 700 nm. The wavelength range is 20 nm. The specular component is included in these calculations.

E j emplos The invention is described in the following by way of example, without being considered as a restriction.

Use 1 8 1 of a technical grade iron sulphate solution with a concentration of 170 g / 1 is placed in a glass container. To this is added 321 g of a solution of A12 (S04) 3 containing 7.54% by weight calculated as A1203. The solution is heated to 40 ° C while passing through nitrogen gas. The pH is adjusted to 3.5 by adding NaOH. Then, with further aeration with nitrogen and stirring, 1056 ml of caustic soda solution with a concentration of 344 g of NaOH / 1 are added over the course of 20 minutes. When the precipitation has finished, the mixture is aerated with air at 150 1 / h, with agitation, at 40 ° C. When the pH has dropped to 3.6, the formation of pips is completed. In order to produce the pigment, 4196 ml of the suspension of pips and cores mentioned above are heated to 75 ° C, 1235 ml of iron sulphate solution with a concentration of FeS04 DE 231.4 g / 1 and 569 ml of water, with stirring, in a beaker. glass. Then, the development of the pigment begins by simultaneously controlling the addition from the caustic soda solution and the aeration with air, so that the pH stays between 3.5 and 3.7. Each time the concentration of iron sulphate falls below a value of 5 h / 1, an additional batch of iron sulphate solution is added, so that the concentration after it is exceeded is again increased to 30 g / l. . After an oxidation time of 204 h, a sample is taken, filtered, washed, dried, deagglomerated, grinding in a micro-dismembrator (Braun AG) for 8 seconds and analyzed. The reproduction factor is 17.1. The nugget / time yield calculated from 0.08 is h "1. The data in the color evaluation are given in Table 1. In addition to the absolute color indices, the difference color indices are also given in comparison to the type Bayferrox 920R (Bayer AG) The aluminum content of the pigment is 0.14%.

Example 2 The same as in Example 1, but using pure iron sulfate solution. After an oxidation time of 164 h, a sample is taken, filtered, washed, dried and deagglomerated. The reproduction factor is 15.8. The nugget / time yield "calculated from 0.09 h" 1. The data for the color evaluation are given in Table 1.

Example 3 Same as in Example 2, but the sample is taken after the oxidation time of 184 h. The reproduction factor is 17.7. The calculated nugget / time yield is 0.09 h "1. In a transmission electron microscope photograph, only short needle particles that agglomerate to packages of several major particles can be detected. 100 mm of 60 seconds, respectively, 120 seconds in a micro-dismemberment (Braun Co) during the incorporation in a lacquer to test sensitivity to grinding.The data for the color evaluation are given in Table 1. The color indexes of difference compared to Bayferrox 920 are also cited along with absolute color indices.The aluminum content of the pigment is 0.15%.

E j us 4 8 1 of an iron sulphate solution, according to the technique with a concentration of 170 g / 1 are placed in a glass container. 321 g of a solution of A12 (S0) 3, containing 7.54% by weight calculated as Al203, are added. The solution is heated to 40 ° C, while the nitrogen is passed through it. The pH is adjusted to 3.5 by adding NaOH. Then 1124 ml of caustic soda solution with a concentration of 323 g of NaOH / 1 are added over the course of 20 minutes with additional nitrogen aeration and stirring. After stirring the precipitation, the mixture is aerated with 150 1 / h of air at 40 ° C with further stirring. When the pH has fallen to 3.5, the production of pip is finished. To accumulate the pigment, they are heated to 75 ° C, with stirring in a glass vessel, 4358 ml of a seed suspension of nuclei mentioned above, 1301 ml of iron sulphate solution, with a FeS04 content of 210 g / 1, and 341 ml of water. The production of pigment begins with the simultaneous control of the addition of caustic soda solution and aeration with air, so that the pH is kept between 3.2 and 3.8. each time the iron sulphate content falls to a value below 10 g / 1, a batch of 2857 ml of iron sulphate solution is added. After an oxidation time of 45 h a sample is removed, filtered, washed, dried, deagglomerated by milling for 8 seconds in a micro-dismemberment (Braun Co.) And analyzed. The reproduction factor is 6.2, the nucleus yield / calculated time is 0.12 -i The sample was tested for clarification. The color evaluation data are given in Table 1.

Comparison Example 1 (according to DE-C 33 26 632, Example 4) 250 ml of aluminum sulphate solution containing 117 g of Al2 (S04) 3 • 18H20 is added to 15309 ml of an iron sulphate solution with a FeS0 content of 200 g / 1. The solution is heated to 55 ° C. Then, 2506 ml of NaOH solution with an NaOH content of 323 g / 1 are added over the course of 20 minutes, c: stirring and aeration with nitrogen and then the mixture is aerated with 400 1 / h. Pipit production is completed when the pH value reaches 2.8. Heat 2777 ml of aforementioned seed suspension of 7129 ml of water at 80 ° C. With simultaneous aeration using 1000 1 / h of air and controlled addition of the pH of caustic soda solution with the concentration of 190 g / 1 of NaOH, 10.75 1 of FeS0 solution with a concentration of 200 g / 1 of FeS04 are added drop dropwise over the course of 12 h, so that the pH remains constant 4.0 ± 0.1. The pigment produced is filtered, washed, dried and deagglomerated. The reproduction factor is 11.1. The calculated nugget / time yield of 0.84 h "1. The color evaluation data is given in Table 1. The difference color values compared to Bayferrox 920 are also cited together with the absolute color values.

Comparison example 2 (according to DE-C 33 26 632, Example 7) 400 ml of aluminum sulphate solution containing 351 g of Al2 (S04) 3 • 18H20 is added to 15309 ml of an iron sulphate solution of a FeS0 900 g / l concentration. The solution is heated to 55 ° C. Then, with stirring and nitrogen aeration, 2506 ml of NaOH solution with a concentration of NaOH with a NaOH concentration of 323 g / 1 are added over the course of 20 minutes and then the mixture is aerated with 400 1 / h of air. The production of pips is finished when pH reaches 2.8. 2978 ml of seed suspension mentioned above and 7022 ml of water are heated to 80 ° C with nitrogen aeration. With simultaneous aeration using 1000 1 / h of air and controlled addition in pH of caustic soda solution with a concentration of 190 g / 1 of NaOH, 7 1 of FeS04 solution with a concentration of 200 g / 1 of FeS04 are added drop drop over the course of 13 hours so that the pH remains constant at 4.0 ± 0.1. The pigment produced is filtered, washed, dried and deagglomerated. The reproduction factor is 7.2. The core / calculated yield is 0.48 h "1. The mixture is ground in a micro-dismemberment (Braun Co.), Using 10 mm agate spheres, for 60 seconds to 120 seconds in order to test the sensitivity to the milling during incorporation into a lacquer The color evaluation data are given in Table 1. The difference color indices compared to Bayferrox 920 are given in addition to the absolute color indices. • 30 Table 1: Sample color evaluations of examples ß Example Index grind Pure tone or L * da * against db * against silky clarification Bayferrox Bayferrox 920 920 8 sec 0.8 Pure tone 12 49.3 59 1.2 2.9 8 sec 0.6 Pure tone 12 48.8 58.2 1.2 2.4 8 sec 0.8 Pure tone 12.1 48.8 58.1 1.3 2.4 60 sec 1.9 Pure tone 11.3 48.8 59.4 0.3 2.6 1. '"sec 2.5 Pure tone 11 48.6 59.8 2.4 8 sec 1.5 Clarification 4.1 39 82.1 -0.3 4.7 8 sec 3.5 Pure tone 11 43.7 58.3 0.1 -2.6 8 sec 1.4 Pure tone 12.7 45.1 56 0.9 • 1.3 60 sec 1.6 Pure tone 12.3 44.6 56.2 1.5 -1 120 seg Pure tone 12.2 44.1 56.2 1.4 -2.3 Comment in example 3 respectively 6: The pigment that was prepared in example 3 (6) was milled as the lacquer during different times (8 sec., 120 respectively 160 sec.). These different lacquer preparations had different colors and color values that are shown in the Table. He demonstrates that the pigment of Example 3 is completely less sensitive to milling than Comparative Example 6 according to b *.

It is noted that with regard to this date, the best method known to the applicant to carry out the present invention is that which is clear from the present description of the invention.

Having described the invention as above, the contents of the following are claimed as property:

Claims (20)

1. A process for preparing yellow pigments of iron oxide in the modification of α-FeOOH, characterized in that it comprises: a) producing nuggets of a-FeOOH by precipitation from a solution containing Fe (II) using an alkaline precipitation agent in the presence of soluble aluminum salts in an amount of 3 to 9% by weight calculated as A1203, with respect to precipitated α-FeOOH, with subsequent oxidation to give α-FeOOH; and b) produce pigment by precipitating additional iron with simultaneous oxidation, where the yield of pip-time is less than 0.3 h "1 and the pH during the entire period of pigment development is less than 3.9, and c) finish the pigment development to a reproduction factor between 3 and 20.

2. A process according to claim 1, characterized in that the production of pigment is terminated at a reproduction factor between 8 and 20.

3. A process according to claim 1, characterized in that the production of pigment is terminated at a reproduction factor between 3 and 8.

4. Yellow pigments of iron oxide in the modification of α-FeOOH, characterized in that they have a silky index, SI, of less than 5, whose color indices in the CIELAB color coordinates in pure tone and with a concentration and pigment / volume of 10% in the test lacquer are a * between 8 and 14, b * between 48.5 and 52 L * between 54 and 62.

5. The yellow pigments of iron oxide according to claim 4, characterized in that the silky index, SI, is less than 3.

6. The yellow pigments of iron oxide according to claim 4, characterized in that the silky index, SI, is less than 1.

7. Yellow pigments of iron oxide in the modification of α-FeOOH, characterized in that they have a silky index, SI, of less than 5, whose color indexes in the CIELAB color coordinates during clarification with a titanium dioxide pigment to a ratio of 1: 5 and with a concentration of pigment / volume of 10% in the test lacquer are from a * between 3y7yb * between 38 and 41.

8. The yellow pigments of iron oxide. according to claim 7, characterized in that the silk index, SI, is less than 3.

9. The yellow iron oxide pigments according to claim 7, characterized in that the silky index, SI, is less than 1.

10. The yellow pigments of iron oxide, characterized in that they are produced by the process of claim 1.

11. The yellow pigments of iron oxide, characterized in that they are produced by the process of claim 2.

12 The yellow pigments of iron oxide, characterized in that they are produced by the process of claim 3.

13. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 4.

14. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of the claim.

15. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 6.

16. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 7.

17. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 8.

18. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 9.

19. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 10.

20. A lacquer, paint or plastic material, characterized in that it is colored with the yellow pigments of iron oxide of claim 11.