AU675161B2

AU675161B2 - Pure-coloured iron oxide direct red pigments and a process for their production as well as their use

Info

Publication number: AU675161B2
Application number: AU74127/94A
Authority: AU
Inventors: Gunter Buxbaum; Peter Kiemle; Klaus Lerch; Rolf Naumann
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1993-09-23
Filing date: 1994-09-21
Publication date: 1997-01-23
Anticipated expiration: 2014-09-21
Also published as: JPH0797218A; BR9403815A; JP3868511B2; DE59402131D1; AU7412794A; ES2100612T3; CN1109079A; EP0645437A1; CN1083469C; EP0645437B1

Description

Our Ref: 5.21965 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT o r sc a o p Applicant(s): Bayer Aktiengesellschaft D-51368 LEVERKUSEN

GERMANY

Address for Service: Invention Title: DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Pure-coloured iron oxide direct red pigments and a process for their production as well as their use The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 Pure-Coloured Iron Oxide Direct Red Pigments and a Process for their Production as well as their Use The present invention relates to new iron oxide direct red pigments and a process for their production as well as their use.

Iron oxide red pigments are used in the building material, ceramics, plastics and paint industries.

Four processes for the production of red iron oxides are known Patton, Pigment Handbook, Vol. 1, New York 1988, p. 288). One of these is the direct precipitation of red iron oxides. In this case an iron(II) salt solution and an alkali solution are mixed in approximately equivalent amounts and air passed through the suspension of iron(II) hydroxide or carbonate obtained. The iron(III) oxide hydroxide seed suspension is built up to the red 20 pigment by adding iron(II) salt and alkali solution accompanied by heating and oxidation with oxygen-containing gases.

Compared with red pigments containing heavy metals, such as CdSe, iron oxides certainly have ecological advantages, but also the disadvantage of an inadequate colour purity for many applications.

Pure-coloured red pigments having a high red component have recently been increasingly required in the building materials industry in order to obtain aesthetic brick-red shades.

There is therefore a requirement for ecologically completely harmless pure-coloured red pigments.

Le A 29 929-FC I I- II It is the object of the present invention to provide iron oxide red pigments with the properties described.

It has now surprisingly been found that these requirements are met by novel iron oxide direct red pigments in the production of which a simple pigment ripening stage at reaction temperature is coupled to the precipitation usual process. Ripening stages for the changing of pigment properties are certainly already known, but these usually proceed under extreme hydrothermal) conditions. It was all the more surprising that a noteworthy ripening effect can be achieved with such a sparingly soluble and unreactive compound as alpha-Fe 2 03 even under mild reaction conditions. After the ripening stage, pigments are obtained that in the red component of the building material test (heavy spar) surpass all previously known iron oxide pigments.

The present invention therefore provides iron oxide 20 pigments that are characterised in that in the building material test they have a red component of more than 33, preferably more than 34, CIELAB units.

The iron oxide pigments according to the invention are obtainable by coupling to the usual process for the production of a direct red suspension according to the precipitation method a ripening stage in which the pH value of the suspension is adjusted and the mixture thereafter is .oe.ei S agitated at reaction temperature without further gassing.

The present invention therefore also provides a process for the production of iron oxide direct red pigments according to the precipitation process, characterised in that after conclusion of the pigment formation the pH value is adjusted by the addition of alkali solution to 3 to preferably 4 to 4.5, and the suspension is agitated at Le A 29 929-FC

I--L

to 95 preferably 80 to 90 without further gassing for 0.5 to 30 hours, preferably 1 to 10 hours.

In the pH range described, alpha-Fe 2

O

3 is the most stable phase. The ripening stage therefore leads to a dissolution of the extraneous phase (alpha-FeOOH), which can form during the pigment synthesis. The second positive effect of the pigment ripening to be mentioned is the healing-up of the pigment surface. As can be inferred from the electron photomicrographs (Figs. 1 and the rough, irregular surface of the particles is transformed as a result of the ripening process into smooth, clean crystalline surfaces. The effect becomes noticeable by the reduction of the specific surface area (BET, DIN 66 131) (see Table 1) The two effects lead to the described coloristic advantages *I of the pigments according to the invention.

20 For the testing of pigments for applications in the oo building materials field (DIN 53237), heavy spar pellets were prepared. For this purpose 0.5 g pigment with 10 g heavy spar were placed in a shaking jar of volume about 250 ml. After adding 200 steel balls of 5 mm diameter, the jar was shaken for 3 minutes with an automatic table rotary shaker. The mixture was pressed to a cylindrical body.

The CIELAB data (DIN 6174) were determined in a use- 3 specific binder. For this purpose heavy spar mixtures were prepared according to a standard laid down by the building material industry (DIN 53 237, Secton 0.5 g of pigment and 10 g of heavy spar (Blanc Fixe G, Commercial Product of Solvay AG, synthetic heavy spar of a specific particle size) were placed in a shaking jar of a capacity of about 250 ml. After addirig 200 steel balls of a diameter of 5 mm the mixture was shaken for 3 minutes in an automatic table rotary shaker.

Le A 29 929-FC "s L The mixture of heavy spar and pigment was pressed to form cyclindrical bodies in a hydraulic press (die diameter: mm, pressure: 30 bar, pressing time: 5 In order to obtain a matt surface of the cylinder, as commonly required for building materials, a commercially available contact paper was placed between the press die and the heavy spar mixture. After pressing, the contact paper was removed and the surface obtained measured coloristically.

The standard colour values were determined with a commercially available colour-i asuring device.

A colour-measuring device of a measuring geometry of d/8 0 (diffuse illumination at 80 to the perpendicular) was used.

The standard colour values for the 2° normal observer and the standard illuminant C (approximately equal to daylight) *were measured. As described in DIN 6174 the brightness the red component and the yellow component were calculated from the standard colour values.

So Table 1 and Fig. 3 contain the colorimetric data of some pigments according to the invention and the comparative values of some commercial products produced by the known processes. In the test for the building materials field, the pigments according to the invention have higher red components than all previously known iron oxide red pigments Bayferrox 510, a commercial product of Bayer AG, producible according to US-A 3 946 103 and Pfizer Croma Red Ro 3097, a commercial product of the firm of Pfizer USA, producible according to US-A 2 785 991).

As a result of the ripening process according to the invention, the red component a* is raised by 1.4 to 3.4 units. In this way brilliant brick-red shades are obtained in building material applications, compared with which the shades obtained by use of conventional iron oxides have a relatively dirty brown effect.

Le A 29 929-FC By reason of the uniform, isometric particle shape, resulting from the ripening process, of the pigments according to the invention, several process advantages arise during the pigment workup. The brine can be separated not only by filtration and washing, as is usual, but also by sedimentation.

The red paste can be processed to slurries or dried and ground to a powdery pigment.

Alternatively, a spray drying to granular pigment is also possible.

During the drying, a filter discharge with an unusually high solids content of 60 to 75 wt.% can be processed. In the conventional drying or granulation of red pigments, solids contents of ca. 50 are common. During the drying of the pigments according to the invention, therefore, considerably less water must be vaporized than was usual 20 previously, which leads to a considerable saving of energy and cost.

A preferred embodiment of the process according to the invention consists therefore in the drying of iron oxide red pastes that have a solids content of more than 60 on charging to the drying unit.

The invention also provides the use of the pigments produced according to the invention for colouration in the building material, ceramics, plastics and paint fields, both as powdery or granular pigments and in the form of pastes or slurries.

Fig. 1 shows an electron photomicrograph of a direct red pigment produced by the preci:,itation process without ripening. Fig. 2 shows an electron photomicrograph of a direct red pigment produced by the process according to the Le A 29 929-FC invention by precipitation and subsequent ripening. Fig. 3 shows the CIELAB data of some iron oxide red pigments in the building material test (a plot in the plane) The invention is described in the following by means of examples, which are not to be regarded as restricting it.

o r r r o e r Le A 29 929-FC Example 1 64 m 3 of gamma-Fe 2 0 3 seed suspension with an Fe 2 0 3 concentration of 17.3 g/l are introduced into a 100 m 3 reactor. 5000 kg of FeSO 4 (a solution with 200 g/l FeSO 4 are pumped in and the whole charge heated to 85 oC.

Thereafter NaOH solution (300 g/l) is pumped in at a rate of 90 kg/h and the charge gassed with 300 m 3 /h of air. The pigment synthesis is arrested after 9 hours and a sample taken. Thereafter the pH value is adjusted to 4.2 by the addition of NaOH and the suspension agitated for 3 hours without further gassing.

Intermediate and final samples are worked up separately and tested. To this end the samples are filtered, washed free of salt and dried at 85 OC and the pigment obtained is ground.

Example 2 20 64.3 m 3 of gamma-Fe 2 0 3 seed suspension with an Fe 2 03 concentration of 19.4 g/1 are introduced into a 100 m 3 reactor. 5000 kg of FeSO 4 (a solution with 200 g/l FeSO 4 are pumped in and the whole charge heated to 85 OC.

Thereafter NaOH solution (300 g/l) is pumped in at a rate 25 of 90 kg/h and the charge gassed with 300 m 3 /h of air. The g 0e pigment synthesis is arrested after 7.75 hours and a sample taken. Thereafter the pH value is adjusted to 4.5 by the addition of NaOH and the suspension agitated for 5 hours at 85 OC without further gassing.

Le A 29 929-FC Examl2e 3 63.1 m 3 of gamma-Fe 2 0 3 seed suspension with an Fe20 3 concentration of 14.3 g/l are introduced into a 100 m 3 reactor. 5000 kg of FeS04 (a solution with 200 g/l FeSO 4 are pumped in and the whole charge heated to 85 OC.

Thereafter NaOH solution (300 g/1) is pumped in at a rate of 90 kg/h and the charge gassed with 300 m3/h of air. The pigment synthesis is arrested after 15 hours and a sample taken. Thereafter the pH value is adjusted to 4.1 by the addition of NaOH and the suspension agitated for 5.5 hours at 85 OC without further gassing.

*ee Le A 29 929-FC _s ~e o r o o r o Table 1 Colorimetric Data of Iron Oxide Pigments Testing in heavy spar (building material application) Pigment Red Component Yellow BET surface Comments Component area [m 2 /g] Bayferrox 110 30.6 26.9 calcined black iron oxide Bayferrox 510 31.2 32.2 direct red according to US-A 3 946 103 Pfizer Croma Red 28.8 22.8 direct red according to RO 3097 US-A 2 785 991 Silo 212 32.4 30.2 direct red Example 1 without ripening 33 33 17.2 with ripening 34.4 35.4 14.6 Example 2 without ripening 31.1 28 25.1 with ripening 34.1 28.2 10.4 Example 3 without ripening 30.2 37.2 15.3 with ripening 33.6 38.1 12.9 I

Claims

1. Iron oxide pigments, wherein the red component a* in the building material test is more than 33 CIELAB units.

2. Iron oxide pigment, wherein the red component a* in the building material test is more than 34 CIELAB units.

3. Process for the production of pure-colored iron oxide pigments according to claim 1, wherein a ripening stage comprising agitation without further gassing is added to the known precipitation process and wherein before the ripening the pH value is adjusted to 3.0 to 5.5 and wherein the temperature of the suspension during the ripening is to 95 0 C.

4. Process according to clahnim 3, wherein the pigment suspension is agitated for 0.5 to hours.

5. Process for the production of pure-colored iron oxide pigments wherein the red component a* in the building material test is more than 33 CIELAB units, said process comprising: a) adding an alkali solution to an iron (II) salt solution to form a suspension; b) passing air through the suspension; heating the suspension; d) adding an alkali solution to the heated suspension; e) passing air through the heated suspension; f) terminating the flow of air through the heated suspension; g) adjusting the pH of the suspension to 3.0 to h) agitating the heated suspension; i) removing liquid from the suspension to form an iron oxide paste; and j) feeding the paste to a drying unit, further wherein the iron oxide paste, on D ~feeding to the drying unit, has a solids content of at least 60 wt. I II--- I Vll (1'9M6I\SII 1 I .CIM i/I /b

11- 6. A method of using the iron oxide pigments according to claim 1, wherein the pigment is formed into a paste or slurry before being added to a material for coloration. 7. A method of using the iron oxide pigments according to claim 1, wherein the pigment is formed into a granular material before being added to a material for coloration. 8. Process for the production of pure-colored iron oxide pigments according to claim 2, wherein a ripening stage comprising agitation without further gassing is added to the known precipitation process and wherein before the ripening the pH value is adjusted to 3.0 to 5.5 and wherein the temperature of the suspension during the ripening is to 95 0 C. 9. Process according to claim 3, wherein before the ripening the pH value is adjusted to i 4.0 to o Process according to claim 3, wherein the temperature of the suspension during the ripening is 80 to 90 0 C. 11. Process according to claim 3, wherein the pigment su.pension is agitated for 1 to hours.

12. Iron oxide pigments wherein the red component a* in the building material test is more than 33 CIELAB units and processes for the production of the same, substantially as hereinbefore described with reference to the examples. DATED this 5th day of November 1996 BAYER AKTIENGESELLSCHAFT By Its Patent Attorney DAVIES COLLISON CAVE Pure-Coloured Iron Oxide Direct Red Pigments and a Process for their Production as well as their Use Abs tract The present invention relates to new iron oxide direct red pigments and a process for their production as well as their use. o a a o o s o a r rr e a a a a a a a Le A 29 929-FC