Method for stabilizing a dye in a colored plastic article and method for decoloring the colored article
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Plastic articles colored with high molecular weight dyes are difficult to recycle due to their inability to be removed, leading to undesirable color tones and environmental concerns, while low molecular weight dyes migrate easily, compromising food and medicinal packaging safety.
Innovation Solution
Exposing the colored surface of plastic articles to ionizing radiation creates a migration barrier close to the surface, allowing for the use of low molecular weight dyes that are stable and easily recyclable, with a method involving electron beams and specific radiation doses to enhance color stability and facilitate recycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high molecular weight dyes are used to prevent migration, then color stability is improved, but recyclability deteriorates
Solution Approach 1:
The patent divides the plastic article into two distinct zones: a colored surface layer containing the dye and a bulk interior layer that remains uncolored. This segmentation allows the dye to be confined to the surface where it provides color stability, while the bulk material remains free of dye contamination, enabling efficient recycling. The surface layer can be separated and recovered, leaving the bulk plastic suitable for reuse.
Solution Approach 2:
The patent applies different properties to different parts of the plastic article. The surface layer is colored with low molecular weight dyes for aesthetic purposes, while the bulk interior maintains its original properties without dye contamination. This local differentiation allows the surface to provide color stability where needed, while the bulk material retains recyclability.
2Ease of manufacture
If low molecular weight dyes are used to improve recyclability, then ease of recycling is improved, but dye migration deteriorates
Solution Approach 1:
The patent applies a surface treatment or coating to the plastic article before recycling processing. This preliminary action creates a barrier that prevents low molecular weight dyes from migrating during subsequent recycling operations, allowing the use of easily recyclable low molecular weight dyes while maintaining color stability.
Solution Approach 2:
The patent introduces an intermediary substance or treatment at the surface that acts as a barrier between the low molecular weight dye and the recycling environment. This intermediary prevents dye migration during recycling while allowing the dye to provide color stability during normal use.
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
The method stabilizes color and enables efficient recycling of plastic articles by creating a thin migration barrier that prevents dye migration, allowing for the recovery of over 85% of the plastic and dye, while maintaining high color stability and environmental safety.
Implementation Method 1
Exposing the colored surface of plastic articles to ionizing radiation creates a migration barrier close to the surface
Implementation Method 2
with a method involving electron beams and specific radiation doses to enhance color stability
Data Source
AI summary
The present invention is directed to a method for stabilizing a dye in a colored plastic article, wherein the method comprises the steps: a) providing the colored plastic article by i) exposing a surface of an uncolored plastic article to a coloring bath comprising the dye or ii) by using a color masterbatch or liquid color comprising the dye in a plastic forming process, wherein the colored plastic article comprises a plastic basis material, and the dye, - wherein the plastic basis material is based on a polar polymer or on a polymer blend, wherein the polymer blend comprises at least 0.25 wt.-% of the polar polymer, wherein the polar polymer has a molecular weight Mw ≥ 1000 g/mol and has at least 5 wt.-% of heteroatoms based on the molecular weight of the polar polymer, and wherein heteroatoms are any atoms except C and H atoms; or - wherein the plastic basis material is based on a further polymer blend, wherein the further polymer blend comprises at least 99.75 wt.-% of a non-polar polymer and a carrier; wherein the non-polar polymer has a molecular weight Mw ≥ 1000 g/mol and has less than 5 wt.-% of heteroatoms based on the molecular weight of the non-polar polymer; wherein the carrier is a polar compound or a blend comprising at least 10 wt.-% of a polar-compound, and wherein the polar-compound has a molecular weight Mw < 1000 g/mol and has at least 5 wt.-% of heteroatoms based on the molecular weight of the polar compound; - wherein the dye has a molecular weight Mw in the range of about ≥ 250 g/mol to about ≤ 750 g/mol; b) exposing a colored surface of the colored plastic article to ionizing radiation, such that a depth-dose distribution in the colored surface comprises a maximum radiation dose at a depth of > 0 µm to ≤ 10 µm of the colored surface.