Polyethylene terephthalate coloring method
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Solution Overview
Problem
The production of colored polyethylene terephthalate (PET) for products like carpet often results in unnecessary waste due to inefficiencies in coloring systems, particularly when switching between colors.
Innovation Solution
A method involving a static mixing assembly with at least twenty static mixers and a liquid metering system to thoroughly mix liquid colorants with PET polymer melt, allowing for seamless color changes with minimal waste by injecting and mixing colorants downstream from the extruder, reducing residual colorant issues and waste production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If liquid colorant is added to polymer melt for coloring, then the polymer can be produced in different colors, but waste increases during color changeovers
Solution Approach 1:
The mixing process is divided into multiple discrete mixing zones (at least twenty static mixers arranged in series), allowing the colorant to be progressively distributed through the polymer melt. This segmentation enables more efficient color transitions by creating distinct mixing stages that can be optimized for minimal waste during color changes.
Solution Approach 2:
The system prepares for color changes by maintaining a reservoir of polymer melt without colorant (or with minimal colorant) in the mixing assembly before a color change is initiated. This preliminary preparation allows for faster color transitions and reduces the amount of wasted material during changeovers.
2Manufacturing precision
If multiple mixing units are used to achieve uniform coloration, then mixing efficiency improves, but device complexity increases
Solution Approach 1:
The system replaces dynamic mixing mechanisms (moving parts, rotating elements) with static mixing elements that rely on the flow of material through carefully designed geometries. This substitution maintains effective mixing while eliminating the complexity of moving parts, bearings, and drive mechanisms associated with dynamic mixers.
Solution Approach 2:
The static mixing elements are designed to automatically distribute and mix the colorant through their inherent geometry as the polymer melt flows through them. The mixing action is self-generated by the flow pattern itself, eliminating the need for external power sources or control mechanisms for each mixing zone.
3Productivity
If colorant is injected upstream in the extruder, then mixing occurs early in the process, but residual colorant causes waste during color changes
Solution Approach 1:
The colorant injection point is extracted from the upstream extruder zone and relocated to a downstream position where the polymer melt has already been formed. This extraction allows the colorant to be added closer to the final product formation, reducing the length of pipeline and processing equipment that must be flushed during color changes, thereby minimizing waste.
Solution Approach 2:
The colorant is injected at a specific localized position downstream from the extruder rather than being distributed throughout the entire extrusion process. This localized injection point allows for more precise control over colorant distribution and enables quicker color changes by limiting the volume of material that contains residual colorant from previous runs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces waste during color changes, enabling the production of bulked continuous carpet filament with consistent colors while minimizing the amount of unsuitable filament produced, resulting in cost savings and improved efficiency.
Implementation Method 1
passing the polymer melt and the first liquid colorant through the static mixing assembly to substantially thoroughly mix the polymer melt with the first liquid colorant
Data Source
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AI summary
A method of manufacturing a plurality of colors of bulked continuous carpet filament from a single multi-screw extruder which, in various embodiments, comprises: (A) passing PET through an extruder that melts the PET and purifies the resulting PET polymer melt; (B) adding a liquid colorant to the polymer melt using a liquid metering system; (C) using one or more static mixers (e.g., up to forty static mixers) to substantially uniformly mix (e.g., homogeneously mix) the polymer melt and the liquid colorant; and (D) feed the uniformly mixed and colored polymer melt into a spinning machine that turns the polymer into filament for use in manufacturing carpet, rugs, and other products.