MATERIALS | COLOURS AND MASTERBATCH
Liquid colours There are numerous ways of obtaining metallic effects in parts through the use of additives. Special-effect liquid colours from Riverdale Global enable manufacturers of packaging and consumer products to enhance shelf appeal and add value while using lower let-downs of colourant than with pellet masterbatch, the company claims. Specialty colours include pearlescents, metallics, and colours that can be used at loadings of only 0.1% to tint clear resins. Riverdale says the in- creased colouring efficiency of liquid colour is attributable to a higher pigment loading per pound of colourant and enhanced dispersion as a result of the liquid carrier. Last October, at the K2019 exhibition in
Germany, Riverdale unveiled a patent-pending colour metering control system for injection moulding, which it says ensures colour uniformity and saves costs by dosing colourant during the injection phase, when conventional colour and additive metering systems are inactive. “During the injection moulding cycle, about 75%
of virgin resin enters the screw during the screw recovery phase and 25% during injection,” the company says. “Because conventional metering systems add colour only during recovery, insuffi- cient mixing can occur, which is particularly problematic when shot size approaches screw capacity or when the end product is translucent. In the new 100% Injection Coloring system, a special controller receives signals from the processing machine for both phases, ensuring that colour is added throughout the cycle. Metering takes place at a faster rate during injection because of the rapid screw movement during that phase.” Riverdale says that with 100% Injection Coloring technology, there is no need for an upstream pre-mixer, or over-colour- ing to compensate for insufficient mixing. A controller outfitted with 100% Injection Coloring technol- ogy is available to liquid colour users at no cost from Riverdale Global, which supplies meter- ing equipment as part of its
Plaques from Riverdale. Metallics above and pearlescents on the right
service to customers. “100% Injection Coloring technology saves colour costs and ensures product uniformity in many moulding applications and is particularly valuable when shot size is close to barrel capacity,” says Paul Maguire, President of Riverdale Global. “With conventional colour metering systems, there simply is not enough mixing time in the barrel to colour the 25% of barrel content to which colourant has not been added. Over-colouring can usually fix the problem, but not always, and especially not with translucent parts. For these you need to use either a larger machine or an upstream pre-mixer.”
PET colouring
Bidding against not only conventional pelletised colourants but liquid colourants as well is Chroma Color Corporation in the US. It says its G-series patented pelletised colorant technology is, for example, ideal for eliminating instability of some colorants, and inefficient let-down rates. Chroma Color serves diverse markets that include packaging, wire and cable, building/ construction, consumer, medical, healthcare, lawn/ garden, durables, sanitation, recreation and leisure, and transportation.
Discussing colouring applications in PET
processing, the company claims that using conven- tional PET resin-based pellet concentrates can be disadvantageous, primarily because of the low pigment/dye loadings compared to liquid colour. “In addition, PET carrier systems often require the color concentrate to be dried prior to moulding,” it says. The company’s UltraPET is said to overcome these challenges with a proprietary carrier system that has high compatibility with PET polymers. UltraPET is based on Chroma Color’s G3 technology, which the company says processes at a much lower tempera- ture than conventional PET pellet concentrates, significantly reduc- ing thermal heat stress on the colourant. In addition, the concentrates have “exceptionally high” loadings of pigments and dyes, it says. The low let-down rates eliminate the need for
drying and recrystallisation that is common with conventional PET pellet concentrates. UltraPET is available in mini-beads that provide a high surface-to-volume ratio, promoting a high incorporation rate. “This feature is especially useful for tints as the rheology and larger surface area of the mini-beads promote a faster incorporation rate,” says the supplier. A
36 INJECTION WORLD | July/August 2020
www.injectionworld.com
IMAGE: RIVERDALE
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