Color concentrate processing

Coloring and Decorating. Commercial pigments that are thermally stable at the resin processing temperature maybe used. Pigments maybe dry-blended with the resin, or ETFE pellets may be blended with color concentrates, which are available ia pellet form. 

Thermoplastics. The highest consumption of color concentrates is in thermoplastic resins, such as low and high density polyethylene, polypropylene, PVC, and polystyrene. Processing techniques for thermoplastics are usually based on dry color dispersion in a compatible resin (36). 

With few exceptions, thermoplastics are marketed in the form of pellets. They are shipped in containers of various sizes, from 25-kg bags to railroad hopper cars. Resins are conveyed to silos for storage and from there to the processing equipment. Colored resins are available, but frequentiy it is more convenient and economical to buy uncolored resins and blend them with color concentrates. Using concentrates avoids handling dusty pigments and ensures uniform color distribution. 

Figure 8.15 Schematic of the melting and mixing process that occurs during the plastication of natural ABS (white) resin with a red color concentrate resin using a conventional, single-flighted screw...

Freeze concentration involves the concentration of an aqueous solution by partial freezing and subsequent separation of the resulting ice crystals. It is considered to be one of the most advantageous concentration processes because of the many positive characteristics related with its application. Concentration processes such as evaporation or distillation usually result in removal of volatiles responsible for arom in addition the heat addition in these processes causes a breakdown in the chemical structure that affects flavor characteristics and nutritive properties. In contrast freeze concentration is capable of concentrating various comestible liquids without appreciable change in flavor, aroma, color or nutritive value (1.2.3) The concentrate contains almost all the original amounts of solutes present in the liquid food. 

A typical masterbatch for extrusion, injection, or blow molding would consist of an appropriate carrier resin for the polymer being processed, a fluorescent pigment, and a wax additive. The following example illustrates a 25% color concentrate formula for injection molding which should be let down at 4% to yield a final color loading of 1% ... 

A second method for introducing color is known in the plastics industry as salt and pepper. This process requires that a supplier blend the base polymer and color concentrate together before shipping the mixture to the fabricator. Care must be taken to prevent any segregation of the two phases, but this is a very effective route for some applications. 

Pumping of liquid colors was inefficient until the development of the microprocessor. Some liquid color was simply measured into batches with dippers. If a pump was used to deliver liquid color to an extruder, synchronizing the pump with the process was nearly impossible. If the speed of the extruder varied, color concentration in the product varied. When the extruder stopped, the liquid color could overflow and make a horrible mess. 

Liquid colors are compatible with a wide variety of polymers, including PVC, polyethylene vinyl acetate (EVA), nylons, PET, polycarbonate, alloys, high-temperature polymers, and the full range of polyolefins and styrenics. Many liquid colors are suitable to color food-contact polymers and comply with all government regulations worldwide for shipping, use, and disposal. Lead times for liquid color are typically less than those for pellet or other melted color concentrates, since the processing is quick and efficient. 

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