Coloration batch ratio

An important aspect of forensic fiber examinations involves the comparison of dyestuffs used to impart color on or in textile fibers. Information obtained from dyes used to color fibers can provide supporting evidence in forensic casework when comparing two fibers obtained from different locations. To determine that two fibers are of the same or in, it is necessary that they be shown to have the same dye components and that the ratio in which these components are present should be identical. Comparisons of absolute dye concentrations (i.e. nano-grams dye per mm fiber) may not be necessary - or even advisable. Dye intensity may not be distributed uniformly along different fibers from the same coloring batch, or even along the length of a particular fiber. Thus, a forensic evaluation should comprise a qualitative evaluation of dye content and a quantitative determination of the relative amounts in which those dyes are present. 

In the manufacture of color master batches, the current industry practice is to perform eritieal color measurements off-line. Typically, a sample of the pelletized color concentrate is diluted with natural resin at a standard ratio and milled, extruded or injection molded into a physieal form suitable for visual and instrumental evaluation. These methods are slow and labor intensive. Furthermore, they do not lend themselves well to statistical process eontrol strategies because of the time lag between production and testing. Since relatively few samples can be examined, laboratory measurements may not give a true indication of the consistency of the concentrate product over the entire manufacturing process. 

The molding material used was a natural DOW Magnum 344 resin. Colorant was a Toreador Red supplied by PMS Consolidated. Red colorant was chosen in part because it is widely used in industry and is notoriously difficult to color match. The colorant was blended with the resin at a 25 1 ratio and was batch blended to assure uniform consistency. Drying was performed according to the manufacturefs recommendation of 82"C and a moisture content of 0.04%. 

While some parts, as a cost-saving measure, could be molded with less color than others, the mixing of several batches with different let-down ratios is generally considered impractical. 

Indigo-5,5 -disulfonate (or trisulfonate) reacts with ozone as described in the CL section. The blue color of IDS disappears on reaction with ozone and the decrease in absorbance at 610 mn is measured. As the molar absorptivity ( 2x 10" moll cm ) depends on the brand and batch of commercially available IDS probably due to impurity, the apparent reaction stoichiometry of IDS to ozone is not exactly unity. However, the stoichiometric ratio is reproducible when the same IDS reagent is used throughout. Nitrogen dioxide interferes positively by 6% of the mass of NO2, but SO2, NO, HF, H2S, H2O2, and peroxyacetyl nitrate do not interfere. Sampling time... 

The color concentrates (masterbatches) used for ABS are of the universal or of the ABS-based types. A typical let down ratio (concentration) for the universal type is 1 to 2% whereas a ratio of between 3 to 7% is used for the ABS based master-batch. Before using a universal masterbatch it is important to ascertain it s compatibility with ABS. Pastel shades can now be readily achieved due to the availability of polymers with a lighter (i.e. whiter) base color. Back pressure is often used with masterbatches so as to assist in the dispersion of the pigment within the polymer melt. 

Stein et al. used fatty acid esters and vaporized SO3 diluted with air [41,45]. The apparatus was a cascade-type reactor with five vessels. In each vessel a batch sulfonation took place at different temperatures starting with 50°C and ending with 85°C. The amount of SO3 added to each vessel could be controlled individually so that a lighter colored product is obtained. The final molar ratio of SO3 to fatty acid ester was 1 3, and the SO3 was diluted to 5 vol % in air. 

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