Skin coloured extrusions using a cavity transfer mixer
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June 1992 Additives for Polvmers Skin coloured extrusions Skin coloured extrusion using only one extruder is possible by using a cavity transfer mixer using liquid colour injection into a Cavity Transfer Mixer fitted with a rotor bypass. At an early stage in the development of the Cavity Transfer Mixer (or CTM) it was real&d that the unusually efficient mixing made possible many innovative extrusion processes. Increased profits from the elimination of precompounding is still the main incentive, and one of the many effective systems has been that of direct injection of liquid additives into a CTM located between barrel and die. For in- line extrusion, a very simple system has been devised at Rapra which combines the CTM with a feedblock arrangement to produce a skin containing colour by liquid addition. Molten polymer flows from the extruder into the CTM entry which has a blister restriction to the mixing zone. This mixer consists of a fixed stator containing hemispherical cavities and a rotor which has similar but overlapping cavities turning with the screw. A small proportion of the molten polymer passes through the mixing zone and the rest flows through a central passage within the rotor via slots at the entry. Liquid colour is injected into the mixing zone and homogeneously distributively mixed throughout the melt. The coloured melt is then reunited with the natural polymer which has passed through the central passage, but due to viscous laminar flow it remains on the surface throughout its passage through the die. By fitting a tube die to the exit, a pipe is formed with coloured polymer confined to the skin. Many other die forms can be used. The two main benefits are reduced pigmentation costs and quicker colour changes. It has been demonstrated that the combination of separately injecting red, yellow and blue with individual pump stroke adjustment can produce the complete colour spectrum. Although not recommended as a precise colour matching technique, quick colour changeovers are possible for identification colours . The confinement of expensive additives to the surface need not be restricted to colours. Stabilizers for improved weathering, antistatic agents, cross-linking agents, foaming agents etc. can also be added, with melting by preheating where necessary. Incorporation of liquid additives into the outside surface of blown film is possible providing a spider die of the type typically used for PVC medical film is employed. O1992 Elsevier Science Publishers Ltd.
Transcript of Skin coloured extrusions using a cavity transfer mixer
June 1992 Additives for Polvmers
Skin coloured extrusions Skin coloured extrusion using only one extruder is possible by using a cavity transfer mixer using
liquid colour injection into a Cavity Transfer Mixer fitted with a rotor bypass. At an early stage in the development of the Cavity Transfer Mixer (or CTM) it was real&d that the unusually efficient mixing made possible many innovative extrusion processes. Increased profits from the elimination of precompounding is still the main incentive, and one of the many effective systems has been that of direct injection of liquid additives into a CTM located between barrel and die. For in- line extrusion, a very simple system has been devised at Rapra which combines the CTM with a feedblock arrangement to produce a skin containing colour by liquid addition. Molten polymer flows from the extruder into the CTM entry which has a blister restriction to the mixing zone. This mixer consists of a fixed stator containing hemispherical cavities and a rotor which has similar but overlapping cavities turning with the screw. A small proportion of the molten polymer passes through the mixing zone and the rest flows through a central passage within the rotor via slots at the entry.
Liquid colour is injected into the mixing zone and homogeneously distributively mixed throughout the melt. The coloured melt is then reunited with the natural polymer which has passed through the central passage, but due to viscous laminar flow it remains on the surface throughout its passage through the die. By fitting a tube die to the exit, a pipe is formed with coloured polymer confined to the skin. Many other die forms can be used.
The two main benefits are reduced pigmentation costs and quicker colour changes. It has been demonstrated that the combination of separately injecting red, yellow and blue with individual pump stroke adjustment can produce the complete colour spectrum. Although not recommended as a precise colour matching technique, quick colour changeovers are possible for identification colours .
The confinement of expensive additives to the surface need not be restricted to colours. Stabilizers for improved weathering, antistatic agents, cross-linking agents, foaming agents etc. can also be added, with melting by preheating where necessary. Incorporation of liquid additives into the outside surface of blown film is possible providing a spider die of the type typically used for PVC medical film is employed.
O1992 Elsevier Science Publishers Ltd.
Additives for Polymers June 1992
New anti-corrosion pigment
Multilayer weathering of PVC
END USE TRADE NAME(S)
CHEMICAL TYPE COMPANY
For further details of this application of CTM, contact: Dr. Martin Gale at Rapra Technology Ltd, Shawbury, Shrewsbury, Shropshire, SY4 4NR, (UK). Tel: +44-939- 250383. Fax: +44-939-251118.
This article briefly refers to tests carried out on a new phosphate-based anti-corrosion pigment, with extended solubility, trade-named Wacot ZBP-M, from: Waardals AS, P. 0. Box 1229, 5001 Bergen, (Norway).
Preliminary work in designing and testing Wacor as an anti- corrosive pigment indicates that there is a positive effect observed when using corrosion inhibitors characterized by their water solubility and other physical factors. The results of these tests show these pigments to be comparable. Further work in the future will relate to the exact mechanism behind these pigments in paints with varying properties.
Poly. Paint Col. L&l, 1992, 182, (Mar 18) 154, 156-7
The natural weathering of rigid PVC is a surface phenomenon made up of two stages: dehydrochlorination and oxidation. The practical properties of a profile (colouration and mechanical resistance) change in a cyclic way. The tensile impact test, a test of impact resistance which reacts very sensitively on microcrack formulation, shows these changes. Kinetics of chemical reactions are controlled by the climatic conditions of the exposure site. Changes of colour and mechanical strength of the PVC materials are different according to the climate where the profiles are tested. Some of the phenomena can be observed only after a short exposure time in very sunny and hot climates.
Kunststoffe, 1991, 81, (Dee), 1113-1117
MATERIALS
BLOWING AGENT MASTERBATCHES MAXITHERM HP 78980 MAXITHERM HP 79720 Unspecified KD Thermoplastics Ltd, 119 Guildford Street, Chertsey, Surrey, KT16 9AL, (UK).
“1992 Elsevier Science Publishers Ltd.
