Choosing a Pigment

Before choosing a pigment and formulating paint, one question must be answered will an active or a passive role be required of the pigment The role of the pigment — active or passive — must be decided at the start for the fairly straightforward 

Once the role of the pigment has been decided, choice of pigment depends on such factors as  

For corrosion-protective purposes, the most important components of a coating are the binder and the anticorrosion pigment. Additives are necessary for the manufacture, application, and cure of a coating however, with the exception of corrosion inhibitors, they play a relatively minor role in corrosion protection. 

This section presents a brief overview of some of the additives found in modem anticorrosion coatings. The field of coating composition is too complex to be covered in any depth in the following sections and, in any case, numerous texts devoted to the science — or art — of coating formulation already exist. 

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To choose a pigment to carry out a given selection of these seven functions, we must know about the following properties of the... 

Choose a plant or animal and research it in order to write, in detail, the steps for extracting pigment from the chosen plant or animate.g., describe the chemical process for extracting the red pigment from a rose). 

Although porphyrins are quite colorful, they are not particularly good choices for photosynthetic pigments. Nature would prefer, given enough time, to choose a species which absorbed more highly in the visible, rather than in the near UV. 

Absorb radiation efficiently. Avoid contaminants, pigments, additives, or resinous materials which compete for the available radiation. Choose a photoinitiator which has the optimum balance of extinction coefficients for the given application. In pigmented systems, choose photoinitiators which absorb strongly at wavelengths where the pigment absorbs weakly. In many cases, a blend of two photoinitiators will make better use of the available radiation, as will be discussed later. 

Choose a known material and discuss how the properties and the fabrication methods should be altered to make it suitable for a novel application. A functional example would be fluorescent pigments—actuators and a structural example porcelain—ship hulls. 

Color Matching. Many pigmented coatings are color matched. The customer chooses a color for a product and a coating formulator is given a sample to match the color. Before starting the initial laboratory color match, the color matcher needs certain information ... 

In many operations, for example the coating of paper on the machine at high speeds, the elimination of water becomes a bottleneck. In choosing a binder for clay and pigment, there is an increasing tendency to abandon starch solutions in favor of combinations of casein or soy protein with synthetic latexes. 

There are various types of wood stains and criteria used to choose the right type for a job. Although there are several distinct groups or types of stains, it is safe to categorize wood stains into two groups dye stains and pigmented stains. 

Choosing the most stable TiO modification. It has been shown that chalking is the result of two main processes UV degradation and the photocatalytic oxidation cycle. What can be done to stabilize Ti02 pigments in such a way that they cause as little chalking as possible A few possibilities have already been mentioned ... 

Monascus colorants have been consumed for hundreds of years and are believed to be safe for human consumption. Tests with a series of microorganisms have demonstrated no mutagenicity. No toxicity was observed in rodents or in fertile chicken eggs. The yellow pigments have an LD50 for mice of 132mg/20g. No ADI is available.11 There has been some concern that some of the strains produced antibiotics which is obviously undesirable for a food colorant, but it is possible to choose strains of Monascus which do not produce antibiotics. 

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