Water-Based Washable Inks for Unstained PET Recycling
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Solution Overview
Problem
Existing methods for recycling plastic containers with printed labels fail to effectively remove inks without contaminating the recycled plastic, leading to staining and reduced quality of the recycled PET flake, which complicates the recycling process and increases environmental and economic costs.
Innovation Solution
The use of water-based inks comprising self-crosslinking acrylic or polyurethane polymers that remain insoluble in hot caustic washes, allowing the inks to be removed as solid particles, thereby preventing contamination of the recycled plastic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water-based inks are used for printing on plastic containers and labels, then environmental friendliness and adhesion are improved, but the inks dissolve in hot caustic wash during recycling, causing contamination and staining of recycled PET flake
Solution Approach 1:
The patent changes the chemical parameters of the ink by incorporating solvents specifically resistant to caustic solutions (such as esters, ketones, or aromatic hydrocarbons) and using crosslinking agents that form chemically resistant networks. This modifies the ink's solubility characteristics so it remains stable in hot caustic wash conditions while maintaining adhesion to the plastic substrate.
Solution Approach 2:
The invention creates a composite ink system combining multiple components: solvent-resistant polymers, crosslinking agents, and caustic-resistant dyes/pigments. This composite formulation ensures the ink maintains both adhesion properties and chemical stability during the recycling process, preventing dissolution and contamination.
2Reliability
If solvent-based inks are used to ensure resistance to caustic wash, then ink removal is improved, but environmental friendliness and health safety are worsened due to organic solvent emissions
Solution Approach 1:
The patent changes the solvent system from traditional organic solvents to water-based or ester/ketone-based alternatives that are either biodegradable or less harmful. By adjusting the chemical composition parameters, the ink achieves caustic resistance without relying on toxic aromatic hydrocarbons, thereby reducing environmental and health hazards while maintaining the desired ink stability.
3Productivity
If inks are designed to be easily removed during recycling, then separation efficiency is improved, but the removal process becomes more complex and time-consuming
Solution Approach 1:
The invention adjusts the ink's solubility parameters to create a selective removal characteristic where the ink dissolves in specific conditions (such as exposure to certain solvents or pH changes) but remains stable under normal recycling conditions. This allows for simplified separation processes that target the ink removal without requiring complex multi-step procedures.
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 ensures minimal discoloration of recycled PET flake, facilitating efficient separation and recycling of plastic containers and labels without staining, thus maintaining the quality of the recycled material.
Implementation Method 1
water-based inks comprising self-crosslinking acrylic or polyurethane polymers that remain insoluble in hot caustic washes
Implementation Method 2
self-crosslinking acrylic or polyurethane polymers that remain insoluble in hot caustic washes
Data Source
AI summary
Method for recycling printed plastic articles without contaminating or staining the recycled plastic with color due the printed ink. The ink is a water-based composition comprising select self-crosslinking acrylate copolymers or polyurethane resins, which inks exhibit good adhesion under conditions of use, but which are readily removed as solid particles when exposed to a hot caustic solution. Due to the inks being removed as solid particles, and not dissolving into the ink, the recycled plastic remains uncontaminated by the ink during recycling.