Color concentrate

Acetal resins are typically suppHed in 25-kg multiwall bags and 500-kg Gaylords (rigid containers). Precompounded custom colors are available from manufacturers or the customer may use color concentrates. 

Color. ABS is sold as an unpigmented powder, unpigmented pellets, precolored pellets matched to exacting requirements, and "salt-and-pepper" blends of ABS and color concentrate. Color concentrates can also be used for online coloring during mol ding. 

Modified ethylene—tetrafluoroethylene copolymers are commercially available ia a variety of physical forms (Table 6) and can be fabricated by conventional thermoplastic techniques. Commercial ETFE resias are marketed ia melt-extmded cubes, that ate sold ia 20-kg bags or 150-kg dmms. In the United States, the 1992 price was 27.9—44.2/kg, depending on volume and grade color concentrates are also available. 

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. 

Rubber-mill chips are dissolved similarly to resins, to provide color concentrates. Dough mixer and chip concentrates must be diluted with solvent and other vehicles to make finished inks. Media milling is becoming a method of choice in both flexo and gravure ink manufacturing. Other high speed dispersing units, such as the Morehouse, Cowles, Kady, and others, are also used. 

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). 

Pigments are available ia a number of commercial forms including dry powders (either surface treated or untreated), presscakes, flushed colors (thick pastes), fluidi2ed dispersions (pourable pastes), resia predispersed pigments (powders), and plastic color concentrates or master batches (granules) (see PiGLffiNTDISPERSIONS). 

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. 

Color Concentrates. Color concentrates have become the method of choice to incorporate colorants into resins. Color concentrates have high ratios of colorant to a compatible vehicle. The colorant may be added at 70% colorant to 30% vehicle in a titanium dioxide mixture whereas the ratio may be 15% colorant to 85% vehicle in a carbon black mixture. The amount of colorant that can be added is dependent on the surface area and the oil absorption of the colorant and the wetting abiHty of the vehicle. The normal goal is to get as much colorant in the concentrate as possible to obtain the greatest money value for the product. Furthermore, less added vehicle minimizes the effect on the physical or chemical properties of the resin system. 

To quantify the concentration of a colorant, one must consider that linearity between the colorant concentration and the fluorescence emission intensity exists only at very low concentrations. The reason for deviation from linearity may be reabsorption of the emission light by other fluorophores or formation of dimers. If no extraction and controlled dilution of the fluorescent colorant are performed, the colorant quantification will be only qualitative. 

Five synthetic and five natural colorants were identified and quantified in lyo-philized dairy products and fatty foods using an automatic method based on solid phase extraction using a stationary phase followed by RP-HPLC C,g columns for the sequential retention of colorants and diode array detection. Lyophilization of the samples coupled with the separation procedure provided clean extracts despite the complexity of the food matrices and preserved the sample for at least 2 months without changes in colorant concentrations. The detection limits achieved for the colorants were found in a wide range from 0.03 to 75 pg/g of the lyophilized sample, according to the limits established by the European Union. ... 

Pigment powders continue to be used in thick-walled articles, such as extruded sheets, or hollow objects, or in injection-molded products although color concentrates are beginning to be more important even in these areas. 

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...

Figure 8.18 Cross-sectional views of extrudate samples at a letdown ratio of 100 to 1 of a white pigmented ABS resin with a black color concentrate for a melting-mixing experiment. The samples were produced at screw speeds ranging from 30 to 150 rpm. The large round white regions for the cross sections at screw speeds of 90 rpm and higher are solid particles discharged with the extrudate...

The mixing requirement presented here is extremely difficult and noncommercial due to the very high letdown ratio used and the use of TlOj in the main resin. For experiments where natural ABS resin (no added Ti02) was used at a 100 1 letdown ratio with the black color concentrate, the very small white streaks at screw speeds... 

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