Buyer's Guide to Pigments
Pigments find enormous types of application in broad range of industries and encompasses a huge variety of Colorants.
High performance inorganic pigments offer comparatively weak color strength, but can give excellent opacity and durability. To give another example, high cost organic pigments though offer excellent color strength but comes with the limitation of poor opacity. Thus Formulators are left with very difficult choices to make.Buying Tips
Here are few tips that are valuable in pigment selection:
Important Selection criteria in Pigment applications
- Selection of Pigment generally is balancing of many types of variables, therefore changes made in the existing commercial formulations should be done judiciously considered and only after color rematching. For example a manufacturer who randomly switches colorant suppliers or reduces expenditure by adopting less costly colorants is under the risk of problems during processing and end-use.
- Consideration should be given towards particle size of the Pigment as it affects light scattering, which in turn can affect shading. To cite an example, finer particles has a tendency to shift a red pigment's shade towards blue, while coarser particles tends to move it towards yellower shades.
- In the case of application in plastics, adding pigments and dyes asks for matching the right mix of colorants to the shade and intensity of the required colors.
- Organic pigments generally can withstand temperatures 400°F and 475°F, while inorganic pigments has been seen to withstand 550°F or even more. In case of some complex inorganic pigments, there is a greater heat stability than some polymers. In case of inorganic pigments like yellow iron oxide, a surface treatment is required to increase their heat stability above 400°F. So, it is imperative that a careful selection of inorganic and organic pigments must be done from the standpoint of temperature so as to maximize color and performance.
- It has been seen that in some cases, organic pigments has a tendency to cause part warpage. This generally occurs when pigments interfere with the polymer crystallization. Now the point here is that warpage issues arises more with some kind of pigments than with others. Examples are that of green or blue phthalocyanine pigments. Resins like high-density polyethylene, are more prone to warpage due to their rapid crystallization.
- The pigment that is chosen must show compatibility with the base resin so as to prevent a color shift over time.
Different applications require different sets of properties. The table given below follows some popular applications along with selection criteria for pigments:
|Application ||Selection Criteria |
|Metallic/Effect Shade ||Transparency- The most significant criteria for the colored pigment in the case of a metallic/effect shade. |
|Coil Coating ||Important criteria for selection are:- |
- Complete hiding
- Heat resistance
- Good durability
- Chemical resistance
|Powder Coating ||Powder coating can involve complex procedures. Pigment selection among others include: |
- Heat stability
- Resistance to wear and tear