Effect pigment
Effect pigments are pigments that give the system in which they are embedded additional properties such as angle-dependent changes in color or gloss ( flop effect) or texture. Since almost all effect pigments have an influence on the luster of the system, the term luster pigment is also common, with luster pigments being strictly speaking defined for predominantly platelet-shaped effect pigments.
history
While metallic effect pigments , initially made of gold and later made of brass , were already known in the fourth to third centuries BC, the development of pearlescent pigments did not begin until the middle of the 17th century. It was only possible to synthesize these with the clarification of the mode of action around 1920. In 1963 and 1964 the first patents for the production of interference pigments were filed. In the years from 1990 onwards, several new classes of interference pigments were developed very rapidly, based on liquid crystal polymers (LCD pigments), synthetic mica, aluminum oxide and silicon dioxide and borosilicate.
Classification
Classification according to composition
Effect pigments are divided into metallic effect pigments and special effect pigments. While the former group is relatively sharply delineated, the boundaries within the special effect pigments are less pronounced.
Metallic effect pigments are luster pigments made of metal , the platelets of which orient themselves parallel in use and show a metal-like effect produced by the reflection of light on the metal platelets. Important metallic effect pigments are aluminum , brass and copper flakes .
Since pearlescent pigments and interference pigments cannot be sharply delimited, especially with newer pigment classes, this group is summarized under the term special effect pigments. Pearlescent pigments are effect pigments that consist of transparent platelets with a high refractive index . They create a pearl-like effect through multiple reflections . Interference pigments are effect pigments whose coloring effect is based entirely or primarily on interference . Interference pigments can be based on transparent or non- transparent platelets. The most widespread use in industry are metal oxide-coated mica pigments, which, depending on the type and thickness of the coating, can belong to the pearlescent pigments or to the interference pigments. Commercially available pearlescent pigments are fish silver , basic lead carbonate , bismuth oxychloride and platelet-shaped iron oxide red . The most important interference pigments are platelet-shaped titanium dioxide , platelet-shaped organic pigments, metal oxide mica pigments, aluminum oxide flakes, borosilicate flakes, silicon dioxide flakes, metal oxide-coated metal flakes, multilayer pigments (Fabry-Perot structure), liquid-crystal effect pigments and structured pigments.
Classification according to appearance
The application-related classification relates to the appearance of the pigments. These are color impression and transparency used. Opaque effect pigments can be black, silver, colored or goniochromatic (angle-dependent color impression). There are no black pigments in the case of semi-transparent and transparent effect pigments.
| Color impression | Opaque pigments | Semi-transparent pigments | Transparent pigments |
|---|---|---|---|
| black |
Graphite molybdenum sulfide mica / Fe 3 O 4 |
- | - |
| silver | Metallic effect pigments | Mica / FeTiO 3 | Mica / TiO 2 BiOCl |
| Colorful | Single coated aluminum plates | Mica / Fe 2 O 3 Al 2 O 3 / Fe 2 O 3 flaky Fe 2 O 3 Mica / TiO 2 |
Mica / TiO 2 |
| Angle-dependent color | Multi-coated aluminum plates | Mica / TiO 2 / org. Pigment mica / Fe 2 O 3 Fe 2 O 3 / SiO 2 / Fe 2 O 3 SiO 2 / Fe 2 O 3 cut polyester film |
Liquid crystal pigments SiO 2 / TiO 2 |
properties
In contrast to classic pigments, effect pigments are platelet-shaped. The effect is not based on scattering and absorption, as is usual with those, but on directed reflection and interference. While the effect of metallic effect pigments is based exclusively on directed reflection, the modes of action in the area of pearlescent and interference pigments are different. Interference pigments are distinguished by the fact that their effect is predominantly or entirely based on interference.
What all effect pigments have in common is that the visual impression is angle-dependent. The coloristic assessment must therefore be carried out from several viewing angles. In the case of visual comparison, this is carried out in a simple manner by tilting the samples to be compared. Conventional colorimeters are not sufficient for colorimetric assessment, as they can only measure at one angle. Color measuring devices for assessing effect pigments are able to determine the color from up to 10 angles.
The diameter of the platelets is around 5 to 100 µm, depending on the type. The thickness of the individual platelets is less than 1 µm. The platelets can consist of one or more layers. The carrier material is crystalline (for example mica) or amorphous (glass or silicon dioxide flakes). In order to achieve a good effect, the particles must have the smoothest possible surface and align themselves in the respective application.
literature
- G. Pfaff: Special effect pigments . 2nd Edition. Vincentz Network, Hannover 2007, ISBN 978-3-86630-895-4 .
- Egbert Buhr, Alfred Schirmacher, Andreas Höpe: Effect Pigments: A Challenge for Optical Metrology , PTB Communications 125 (2015), Issue 4
Web links
Individual evidence
- ↑ a b c d G. Pfaff: Special effect pigments . 2nd Edition. Vincentz Network, Hannover 2007, ISBN 978-3-86630-895-4 , p. 16 ff .
- ↑ H. Kittel, J. Spille: Textbook of paints and coatings . 2nd Edition. Volume V: Pigments, Fillers and Colorimetry. Hirzel, Stuttgart 2003, ISBN 3-7776-1015-1 , p. 130 ff .
- ↑ G. Pfaff: Special effect pigments . 2nd Edition. Vincentz Network, Hannover 2007, ISBN 978-3-86630-895-4 , p. 15 .
- ^ H. Römpp: Römpp Lexikon Lacke und Druckfarben . Thieme, Stuttgart 1998, ISBN 3-13-776001-1 .
- ^ Raimund Schmid: Identification of effect pigment for color matching . BASF Aktiengesellschaft, Ludwigshafen (English).