Inorganic pigments. using the Laux process

Transcription

1 Inorganic pigments using the Laux process 2

2 The LANXESS pigments business has been committed for many years to sustainable production processes as one of its core competencies. The Laux process in Krefeld-Uerdingen duction method for iron oxide pigments. The method is exemplary in that it fully exploits the heat produced by the chemical reaction to generate steam and hot wa- The Laux process is the key to the special properties of LANXESS s yellow, black and red shades. Particularly with the reds, a very broad range of hues can be produced, from reds with a yellow to reds with a blue undertone. The red shades with a blue undertone are quite unique compared with other iron oxide reds available on the market because they display only a slight color shift even under intense milling conditions. trobenzene with metallic iron to aniline and iron oxides, was implemented on an industrial scale as far back as 1911 at the Krefeld-Uerdingen site. While the aniline was needed to manufacture dyestuffs, the iron oxide byproduct could not be put to 1914 to use the resulting iron oxide as a colorant, but the quality of the iron oxide was not adequate for pigment applications. It took another eleven years before Dr. Laux, a chemist, succeeded in optimizing the process and obtaining iron 1926, one year after its discovery, iron oxide production was launched in Krefeld. Since then, iron oxide production at the Krefeld plant has undergone remarkable development. After starting out with a capacity of roughly 1,000 metric tons in 1926, production has steadily increased. At present, 280,000 metric tons of iron oxide pigment are produced at the plant, two-thirds of that by the Laux process. In other words, LANXESS operates the world s largest production plant for synthetic iron oxide pigments in Krefeld. 2

3 In the Laux process, nitrobenzene is reacted with cast iron borings. Depending on the reaction conditions and the control chemicals, a suspension of black or yellow iron oxide results, which subsequently is washed, concentrated and dried. Red pigments cannot be obtained directly by these means; they are produced by subsequent calcining of the black paste under oxidative conditions. Nitrobenzene Fe 3 O 4 Black Reaction Cast iron FeO(OH) Yellow Aniline 2 Fe + C 6 H 5 - NO H 2 O 2 FeO(OH) + C 6 H 5 - NH 2 9 Fe + 4 C 6 H 5 - NO H 2 O Reaction 3 Fe 3 O C 6 H 5 - NH 2 Fe 2 O 3 Red Mixture Brown 2 Fe 3 O 4 + 0,5 O 2 3 Fe 2 O 3 Fig. 2: Diagram of the Laux process Fig. 1: Basic patent on the Laux process 3

4 The basic reaction in the Laux process, i.e. the reaction of nitrobenzene with cast iron, is extremely exothermic. After various process and plant optimizations, LANXESS has succeeded in exploiting virtually all the heat of reaction to produce hot water and steam for use in downstream processing steps. This reduces primary energy demand by 28 % and cooling water output by as much as 56 %, making the Laux process one of the most ecologically compatible and resource-conserving processes for the production of iron oxide pigments. One raw material in the Laux process is nitrobenzene, obtained by the nitration of benzene with nitric acid. The second raw material, cast iron borings, is a byproduct from the machining of cast iron parts in various industries, such as automotive manufacturing. 4

5 Pigment properties In the Laux process, all three basic iron oxide colors - red, yellow and black - are available in a relatively broad color spectrum. Due to the scattering power of iron oxides, the particle size has a direct influence on the shade. Red When it comes to red, the smaller the particles, the more pronounced the yellow undertone, while larger particles produce more of a blue undertone. The difference in prevailing particle size spans a rather wide range, from 0.09 μm for Bayferrox 105 M to 0.7 μm for Bayferrox 180 M. One unique advantage of the Laux process is its ability to produce red shades with a blue undertone. Significant differences exist in this area between the Laux process and others, because the other manufacturing processes have difficulty obtaining the required particle sizes. Black In the case of black, the shade of the pigment likewise depends on the size of the primary particles, ranging from the bluish Bayferrox 306 to the high-tinting-strength Bayferrox 330. size. The larger the primary particles, the bluer the undertone of the shade. However, this effect is obtained at the cost of tinting Bayferrox 318 Bayferrox 306 Bayferrox 110 M Bayferrox 140 M Bayferrox 180 M Particle size Increasing Tinting strength Decreasing Shade Brownish Bluish Fig. 3: The Laux process produces red pigments with a bluish undertone that set it apart from other processes. Fig. 4: Particle size affects the shade. 5

6 Yellow With yellow, the range of shades achieved in pigments manufactured by the Laux process is narrower. By selecting the right raw materials, the Laux process also can produce yellow pigments that nearly rival precipitated pigments. Bayferrox 3420 is the micronized version of Bayferrox 420 and frequently selected as an alternative to precipitated yellow in paint and coating applications. The yellow grade, Bayferrox 415, is mainly used to color building materials on account of its darker, bluer shade. Iron oxide pigments are lightfast thanks to their chemical and physical properties. In practical pigment applications, however, the interface between pigment and binder is a critical factor, this being particularly evident in coloring laminates yellow. A distinct difference in color shift can be observed when using a yellow iron oxide pigment produced by the precipitation process (Bayferrox 920), one by the Laux process (Bayferrox 420) and a post-treated yellow pigment (Colortherm Yellow 10). UV radiation at the interface of the pigment/binder matrix presumably leads to partial reduction of the resin, expressed by a green shift. This may be attributable to catalytic effects. In the Lightfastness of Bayferrox 920, 420 and Colortherm 10 (Blue Wool Scale, level 8) Bayferrox 920 Std 03 Bayferrox 420 Std 99 Colortherm Yellow 10 Test conditions: Xenotest 150 S/ca. 160 h until wool sample 8 fades Fig. 5: Differences in lightfastness E*ab case of Colortherm Yellow 10, the inorganic post-treatment ening catalytic degradation and greatly reducing color shift. 6

7 Laminates increasingly are used in outdoor applications, a trend that tightens quality requirements on the lightfastness of the decorative papers. In terms of temperature stability, Laux pigments again offer distinct advantages over precipitated iron oxide pigments. Although red as hematite (Fe 2 O 3 ) is heat-stable thanks to its chemical structure, the various iron oxide reds nevertheless display remarkable differences attributable to the production process. The red iron oxide pigments produced by the Laux process are heated to as high as 800 C during calcining and therefore characterized by high temperature stability. Thermal stability is of particular importance in coloring plastics, because the elevat- less color change versus red precipitated pigments. (to DIN-EN Method B) Colortherm Red 110M Precipitated Red Limit to DIN-EN Part C 220 C 240 C 260 C 280 C 300 C 320 C Fig. 6: Thermal stability of various red pigments 7

8 In contrast to Laux red pigments, precipitated red iron oxide pigments often have some water bound in the crystal lattice, which evaporates at high temperatures. This results in a decrease in weight and a change in shade. Similarly, Laux yellow pigments are more stable than precipitated products because of the manufacturing process. The post-treated Laux products Colortherm Yellow 10 and Colortherm Yellow 20 are particularly stable. 100 C 500 C (to DIN-EN Method B) Calcined red: Decrease in weight: 0.11 % = 0.1 Decrease in weight: 0.31 % = Bayferrox 420 Colortherm Yellow 20 Bayferrox 920 Max. level according to the European standard Calcined red, yellowish: Decrease in weight: 0.15 % = 0.1 Decrease in weight: 0.45 % = Precipitated red: Decrease in weight: 0.33 % = 0.2 Decrease in weight: 1.85 % = Precipitated red, yellowish: Decrease in weight: 0.51 % = 0.1 Gewichtsverlust: 2.57 % = Fig. 7: Moisture content and color change as a function of temperature Fig. 8: Thermal stability of various yellow pigments 8

9 Sintering occurs during the calcining step of the Laux process, with the primary particles forming larger agglomerates. These are hard and must be broken up by intensive milling to ensure good dispersibility in the end application. As a result, Laux reds are much more stable than precipitated red pigments when exposed to any additional milling or other high shear forces in a customer application. For instance, the shade of Laux red pigments changes much less during bead milling than that of precipitated red pigments. The bluer the undertone of the red pigment, the more pronounced the difference between these two production processes. The very strong shear forces prevailing in concrete applications bring out the advantages of Laux pigments. Even Bayferrox 130 shows better color consistency in the application than a precipitated red iron oxide pigment. The darker the shade, the more pronounced the difference. Because of the needle structure of yellow iron oxide pigments, their viscosity behavior is a very critical parameter. In general, the more pronounced the needle structure, the more problematic the viscosity behavior. Pigment comparison: (Olbrich shaker: Binder: Alkydal F48, PVC 10%) Calcined red Precipitated red 10 Dissolver 5 Shaking 15 Shaking 30 Shaking 60 Shaking Dispersing time to strong shear forces Bayferrox 420 Bayferrox 415 Fig. 10: Prismatic particle structures are characterized by low viscosity 9

10 Compared to the distinct needle shape of Bayferrox 420, the primary particles in Bayferrox 415 are more prismatic. Pigment preparations of Bayferrox 415 therefore have a significantly lower viscosity than those of Bayferrox 420, a property that becomes most evident in pigment suspensions for the building industry. Bayferrox 415 permits a significantly higher solids content. For concrete manufacturers, it is important to minimize the influence of a color pigment on the consistency of the concrete as much as possible, because more water otherwise may have to be added to achieve the same workability. More water, however, translates into lower concrete strength. Yellow Laux pigments therefore have less of an influence on concrete consistency than yellow pigments produced by other methods. Viscosity in universal paste after production Bayferrox 420 Std. 99 Bayferrox 415 Std. 83 Viscosity [P a*s] Shear rate [1/s] Fig. 11: Viscosity in universal paste after production 10

11 105 M A red shade with a yellow undertone for the paint and coatings industry Bayferrox 110 (M) 120 N(M) 120 (M) 130 (M) 130 B(M) 140 (M) 160 (M) 180 N(M) 180 (M) The shade exhibits an increasingly blue undertone as the number increases A red shade with a blue undertone for the paint and coatings industry Bayferrox 420 Standard yellow pigment 415 Low-viscosity yellow pigment primarily for the building materials industry 3420 Micronized variant of Bayferrox Black shade with a blue undertone Bayferrox M Iron oxide black for the paint and coatings industry 320 Black pigment for the building materials industry 330 Very high-tinting-strength black pigment for the building materials industry 340 Black pigment for the building materials industry Colortherm Yellow 20 Yellow 10 Heat-stabilized yellow pigment for the paint and coatings industry Black 318 Heat-stabilized black pigment with high tinting strength for all common plastics applications 11

12 Health and Safety Information: Appropriate literature has been assembled which provides information concerning the health and safety precautions that must be observed when handling the LANXESS products mentioned in this publication. For materials mentioned which are not LANXESS products, appropriate industrial hygiene and other safety precautions recommended by their manufacturers should be followed. Before working with any of these products, you must read and become familiar with the available information on their hazards, proper use and handling. This cannot be overemphasized. Information is available in several forms, e.g., material safety data sheets, product informa-tion and product labels. Consult your LANXESS representative in Germany or contact the Regulatory Affairs and Product Safety Department of LANXESS Germany or for business in the USA the LANXESS Product Safety and Regulatory Affairs Department in Pittsburgh, Pennsylvania. Regulatory Compliance Information: Some of the end uses of the products described in this publication must comply with applicable regulations, such as the FDA, BfR, NSF, USDA, and CPSC. If you have any questions on the regulatory status of these products, please consult your LANXESS representative in Germany or contact the Regulatory Affairs and Product Safety Department of LANXESS Germany or for business in the USA your LANXESS Corporation representative, the LANXESS Regulatory Affairs Manager in Pittsburgh, Pennsylvania. Bayferrox is a registered trademark of Bayer AG, Leverkusen, Germany. Colortherm is a registered trademark of the LANXESS Group, Leverkusen, Germany. The manner in which you use and the purpose to which you put and utilize our products, technical assistance and information (whether verbal, written or by way of production evaluations), including any suggested formulations and recommendations are beyond our control. Therefore, it is imperative that you test our products, technical assistance and information to determine to your own satisfaction whether they are suitable for your intended must at least include testing to determine suitability from a technical as well as health, safety, and environmental standpoint. Such testing has not necessarily been done by us. Unless we otherwise agree in writing, all products are sold strictly pursuant to the terms of our General Conditions of Sale and Delivery. All information and technical assis-tance is given without guarantee and is subject to change without notice. It is expressly understood and agreed that you assume and hereby expressly release us from all liability, in tort, contract or otherwise, incurred in connection with the use of our products, technical assistance, and information. Any statement or recommendation not contained in this brochure is unauthorized and shall not bind us. Nothing herein shall be construed as a recommendation to use as patents covering any material or its use. No license is implied or in fact granted under the claims of industrial property rights such as patents. Edition 11/2011 LANXESS Deutschland GmbH Business Unit Inorganic Pigments Krefeld GERMANY Tel.: Fax: