Pigments selection

With the notable exception of high acid value acrylics, where basic pigments should be avoided, in order to prevent viscosity instability or premature gelation, pigmentation does not pose special problems in formulating paints based on thermosetting acrylic resins. 

For white paints, rutile grades of titanium dioxide are incorporated at pigment/binder ratios from 0.6/1 for automotive finishes, where very high gloss levels and DOFs (Distinctiveness of Image) are required, to 1.3/1 for metal decorating enamels where opacity is of prime concern. 

High quality inorganic tmd organic coloured pigments are widely used in formulating thermosetting acrylic paints. They should be selected on the basis of fastness to organic solvents, such as aromatic hydrocarbons, esters or ketones, and heat resistance. 

As will be seen later, one of the most important applications for thermosetting acrylics is in automotive finishing, where colour fastness and durability are extremely important. 

Rutile grades of titanium dioxide are used exclusively. Some are treated to enhance both pigment wetting characteristics and exterior durability properties. Foimulators should follow the titanium dioxide manufacturers recommendations for the selection of suitable grades. 

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Pigments and Extenders. Pigments are selected for use in house paints based on thek appearance and performance quaUties. Appearance includes color and opacifying abiUty. Performance quaUties include ultraviolet light resistance, fade resistance, exterior weatherabiUty, chemical resistance, as well as particle size and shape. Toxicity profiles and safety and health related properties are also important criteria in pigment selection. 

The conditions to be met in decorative printing are particularly demanding. Decorative papers for gravure and flexographic printing are used to produce laminated plastic sheets. Pigment selection is a matter not only of the type of resin (melamine or polyester), but also a function of the processing method. 

In recent decades, considerable efforts have been made to restrict or completely eliminate solvent emission during oven drying. Intensive research has focused on developing paint systems which contain very little solvent or none at all [5]. A variety of approaches are possible systems that have found their way to practical use tend to present a special challenge in terms of pigment selection ... 

The respective processing temperatures, which determine the criteria for pigment selection, are as follows ... 

A number of publications describe continuous techniques used to manufacture azo colorants, especially azo pigments (selection see [6]). 

There is better pigment selection due to more points of reference. 

Black pigment selection for outdoor use has to consider weathering performance. Different infrared reflecting blacks have been evaluated in relation to heat build-up properties and actual weathering characteristics. The influence of free iron has also been examined (344). 

Many pigments are now available commercially for use with PVC. Pigment selection should be based on the pigments ability to withstand process conditions, its effect on stabilizer and lubricant, and its effect on end-use properties, such as electrical insulation. 

To sum up, the paint formulator s method of pigment selection is as follows ... 

To produce the broad variety of finished products fiom PVC formulations nearly always requires the incorporation of colorants. Most often, pigments (insoluble particulates) are employed in PVC rather than dyes, although the latter are employed in a few speeial cases. Pigments selected for use in PVC must be acid-degradation resistant, and can be added to the formulation as dry powders, dry dispersions, or concentrates in either liquid or solid carriers. The seleetion of the physical form of the colorant often depends on the formulation (e.g. rigid versus flexible), the compounding process, and the requirements of the appUcation. 

From experience and by application of the principles of subtractive mixing, the pigments likely to give the colour are chosen. The procedure is described under Pigment selection (above). 

For this reason, my conclusion at the 1998 High Performance Pigment Conference was that the definition of an HPP should be The right pigment selection for a specific use with well-defined quality criteria at optimized pigment cost. Today, however, I am more and more convinced that classification into specialties and commodities would better describe how pigment products are positioned in the market. 

Since that time, realizing that the above definition was proposed from a strictly technical basis, Fritz Brenzikofer of Clariant, has offered the following definition from a business perspective A high performance pigment is the right pigment selected for a specific use, with well defined quality criteria, at an optimized pigment cost . 

Add resistance is required for parchment and vulcanized fiber base paper, writing, and printing paper. Organic and inorganic pigments, selected representatives of all colorant groups, are suitable for this purpose. 

Pigment selection is not justified only through esthetic reasons, but also through their influence on the lifetime of finishing articles. 

Compatibility. Problems of incompatibility may occur if wrong pigment selection is made. These problems fall into one of three categories chalking, migration or rub fastness. 

Amino plastics Good light stability but only moderate heat stability (170°C) is required. Cadmiums Phthalocyanine Blue Ultramarine Blue Selected monoazo pigments Selected D is-azo pigments ... 

Chemical reactivity can also be an important consideration in pigment selection. For example, some pigments can react with air pollutants causing discoloration. 

Care is required with pigment selection due to the possibility of interaction of certain pigments with reactive groups in the resin. A variety of adverse reactions have been... 

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