Concentrate letdown ratio

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... 

A black-colored concentrate was added at a letdown ratio of 220 1 to a white-tinted ABS resin. Labels indicate the axial distances in screw diameters from the start of the screw... 

Figure 8.30 Cross-sectional views [53] of the extrudate samples using a conventional screw with segmented tip for the testing of different types of dynamic mixers a) conventional screw with no mixer, b) Twente Mixing Ring, and c) Barr Fluxion ring mixer. The extruder was operated at a screw speed of 80 rpm and a letdown ratio of 220 1 of a white pigmented ABS resin to a black color concentrate...

Figure 14.10 Cross-sectional views for a Maddock solidification experiment for the ET screw at a letdown ratio of 220 1 white-pigmented ABS resin to a black color concentrate [29]. The A and B channels are labeled along with the axial positions in diameters. The views were for a screw speed of 66 rpm and a rate of 70 kg/h using a 63.5 mm diameter extruder...

Theoretically, the higher the concentration of colorant in a concentrate the lower the dosage or higher letdown ratio needed to obtain properly colored parts. With... 

Wax concentrates may be in the form of prills, bars, flakes, or granules. Prills are very small spherical pellets, usually made from a pigment blend and wax. They may be blended, like dry colors, or dispensed by a metering device at the throat of the extruder. If they are blended, it is best to use a powder resin, such as polyvinyl chloride (PVC), so they do not sift to the bottom of the container. The other physical forms are applied in different ways some are designed to be metered in at the hopper, the rest to be blended in before reaching the hopper. The carrier may lubricate, so letdown ratios are limited. 

Newest "super-concentrates" provide highest level of melt distribution, greatest letdown ratio, supplier press release. Teknor Apex Company 2008. 

Figure 5.38 Cross-sectional views of extrudate samples at a letdown ratio of 100 1 of a white pigmented ABS resin with a black color concentrate for an ET screw.

The color lab is usually divided into two parts color development and quality control. The color development group works closely with the sales and marketing departments. Anything, from a competitive color concentrate to bottles, films, or injection-molded parts, can be submitted to the lab for color-matching. Pantone books or chips and other color standards are also used to specify or select targets. Specifications regarding resin, letdown ratios, weatherfastness, and price are typically submitted with the target. 

Concentrates require a letdown before molding. On the dry side, a t5q)ical letdown ratio is 25 1, or 25 parts of polymer mixed with 1 part of color concentrate. Viscosities or melt index of the pol5miers should be as alike as possible for the best mixing and color incorporation. The letdown ratio can be adjusted to achieve better economics or dispersion. 

Higher the loadings lower are the conversion charges for the concentrate, and the better the economics. Lower the letdown ratio less colored pellets required, resulting in a lower probability of good mixing and color consistency. 

In plastics, relative viscosity can be defined as the ratio of the viscosity of a concentrate to that of the neat carrier polymer at the same temperature. In this use, relative viscosity predicts relative jetness—defined in the same manner—more accurately than the carbon black loading in a concentrate. A mismatch between masterbatch and letdown viscosities causes incomplete mixing and is the reason that relative jetness can decrease with an increase in relative viscosity [5]. 

All HIDM and twin screw color concentrate samples were letdown into blown film for evaluation of color, strength and dispersion quality. Standard 1.5 mil (37 pm) films were prepared by blending concentrate samples with 1.0 MI LLDPE resin at a letdown of 5.0 weight percent and extruding through a 37.5 mm laboratory film line at a blowup ratio of 2.4 1 and lay flat width of 20 cm. Standard operating procedures were observed throughout. 

Each fiber producer has developed its own method for modifying the fiber-making process to prepare colored fibers from polymer and concentrate. The color concentrates may be ground to powder and fed in a proper ratio with polymer powder. Alternately, the producer can dilute the colored concentrate pellets in a proper ratio with natural pellets to produce a letdown prior to extrusion. Some systems have been designed to inject melted color concentrates directly into the melt stream during fiber preparation. Such a method proves difficult because for some colors four or more pigments must be added accurately with a concentration ratio difference of 1000 1 or more. The rest of the fiber process is quite conventional, as described elsewhere in this chapter. The extruded colored melt must be quenched, drawn, crimped, and cut to make ST or processed to make filaments with or without texturing. 

Color Concentrate (Masterbatch). Expert compounders disperse colorants at 20 to 60 percent concentration in a carrier polymer, using high shear to break down agglomerates and produce uniform dispersion of maximum coloring efficiency. This color concentrate is used by processors, simply blending it with virgin (natural color) resin ( letdown with natural ). Typical ratios of concentrate/natural are 1/20 to 1/100. This technique is low in cosL does not create inventory problems, and is most commonly used with commodity resins. 

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