PET Coloring via Downstream Melt Splitting and Static Mixing
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Solution Overview
Problem
The production of colored polyethylene terephthalate (PET) for carpet and other products often results in unnecessary waste due to the inefficiencies in changing colors during the extrusion process, particularly when using traditional methods where colorants are added upstream of the extruder.
Innovation Solution
A method involving a multi-screw extruder to melt and purify PET, followed by splitting the polymer melt into multiple streams, adding colorants downstream using secondary extruders, and thoroughly mixing with static mixers to produce multiple colors of bulked continuous carpet filament, reducing waste by minimizing residual colorant issues during color changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If colorants are added upstream of the extruder in traditional methods, then the extrusion process can be simplified, but significant waste is generated during color changes due to residual colorant issues
Solution Approach 1:
The patent divides the extrusion process into separate functional sections: a purification section and a coloring section. The polymer melt is split into multiple streams after purification, with each stream going to a separate coloring zone where different colorants can be added independently. This segmentation allows color changes without purging the entire extruder, significantly reducing waste while maintaining process control.
Solution Approach 2:
The patent extracts the coloring function from the main extrusion process by adding colorants downstream in separate coloring zones rather than mixing them upstream with the polymer. This extraction allows the extruder to be optimized for purification while color addition becomes a separate, controllable step that minimizes cross-contamination and waste during color changes.
2Productivity
If multiple colors are produced using a single extruder with upstream colorant addition, then equipment cost is reduced, but productivity decreases due to lengthy purging operations during color changes
Solution Approach 1:
The extruder is segmented into multiple functional zones along the barrel length, with each zone handling a specific task (purification, melting, coloring). Multiple polymer streams are created and directed to different coloring zones, enabling simultaneous production of multiple colors without requiring multiple complete extruders, thus maintaining productivity while controlling equipment complexity.
Solution Approach 2:
A single multi-screw extruder is designed to perform multiple functions: purification of recycled polymer, melting, splitting into multiple streams, and independent coloring of each stream. This multi-functional design allows one piece of equipment to produce multiple colors efficiently without the need for separate extruders for each color, maintaining ease of manufacture while improving productivity.
3Manufacturing precision
If traditional upstream colorant addition is used, then the process is simpler to operate, but manufacturing precision of color consistency is compromised due to residual colorant contamination
Solution Approach 1:
The coloring operation is extracted from the upstream polymer melting zone and moved to downstream coloring zones where purified polymer streams are separately colored. This extraction ensures that colorants do not contaminate the purification process and that each color stream remains pure and consistent, achieving high manufacturing precision while maintaining reasonable operational simplicity through automated colorant addition.
Solution Approach 2:
The patent introduces static mixers as intermediary devices between the colorant addition point and the final product formation. These mixers ensure thorough and uniform distribution of colorants in each polymer stream, achieving consistent coloration without requiring complex operational procedures. The static mixers act as intermediaries that guarantee color precision while keeping the system easy to operate.
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, allowing for efficient production of multiple colors with minimal residual colorant interference, resulting in cost savings and improved process efficiency.
Implementation Method 1
using the multi-screw extruder to at least partially melt the PET into a polymer melt
Implementation Method 2
at least partially purify the polymer melt
Implementation Method 3
using the one or more respective static mixers to substantially thoroughly mix each of the plurality of individual polymer streams with the respective colorant
Data Source
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) splitting the extruded polymer melt into a plurality of melt streams and adding a colorant to each of the plurality of melt streams; (C) using one or more static mixers (e.g., thirty six static mixers) to substantially uniformly mix (e.g., homogeneously mix) each of the plurality of melt streams with its respective added colorant; and (D) feed each of the uniformly mixed and colored plurality of melt streams into a respective spinning machines that turns the polymer into filament for use in manufacturing carpet, rugs, and other products.