Shrink Wrap Label Coating for Caustic De-seaming
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Solution Overview
Problem
Current methods for recycling plastic containers with shrink wrap labels face challenges in easily separating the labels from the containers, leading to reduced recycling efficiency and increased costs due to the use of less desirable substrates or complex floatable film structures, and existing coatings do not provide both strong bonding and easy de-seaming.
Innovation Solution
A novel coating composition comprising at least one first polyester resin, a second polyester resin, and a third resin with specific Tg and acid value properties, applied to the labels to promote strong bonding at the seam while allowing easy removal during recycling, which includes hydrogenated rosin and is hydrolysable but not solutionable in hot caustic baths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shrink wrap labels are used on plastic containers, then the labels provide good appearance and protection, but the labels are difficult to separate from containers during recycling
Solution Approach 1:
The label structure is segmented into two distinct functional layers: a permanent bonding layer that provides strong adhesion to the container, and a temporary seaming layer that bonds the label to itself at the seam but can be easily removed during recycling. This segmentation allows each layer to perform its specific function optimally without compromising the other.
Solution Approach 2:
The temporary seaming layer acts as an intermediary between the permanent bonding layer and the container. It provides the necessary seam strength during use but is designed to be removable, facilitating label separation during recycling without damaging the permanent bonding layer or container.
2Strength
If traditional seaming methods are used, then the label seam provides strong bonding, but additional solvents are required that complicate the recycling process
Solution Approach 1:
The temporary seaming layer is designed as a disposable, short-lived bonding agent that performs its function during label application and removal, then is easily eliminated during recycling. It sacrifices long-term permanence to enable simple recycling, acting as a temporary but effective bonding solution.
Solution Approach 2:
The coating composition undergoes parameter changes based on environmental conditions: it provides strong bonding at application temperatures, maintains seam integrity during storage and use, but becomes removable under recycling conditions (hot caustic baths). The chemical and physical parameters of the coating are designed to change in response to different processing conditions.
3Ease of operation
If low density floatable film structures are used, then label separation is facilitated, but the substrates have reduced shrink properties and printability
Solution Approach 1:
Different regions of the label have different functional properties: the permanent bonding layer and temporary seaming layer provide shrink and print qualities where needed, while the effervescent layer provides separation capability in specific areas. Each layer is optimized for its specific function rather than requiring the entire substrate to have all properties.
Solution Approach 2:
The label coating is a composite material system combining multiple functional components: bonding resins, temporary seaming agents, and effervescent separation agents. This composite structure allows the label to exhibit multiple properties simultaneously - strong bonding, shrinkability, printability, and easy separation - that would be difficult to achieve with a single material.
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 coating enables efficient de-seaming of labels from containers in hot caustic baths, maintaining bond strength during the recycling process and reducing recycling costs by eliminating the need for additional seaming solvents and simplifying the recycling process.
Implementation Method 1
The coating composition is at least partially hydrolysable but not solutionable in a hot caustic bath
Data Source
AI summary
The present disclosure relates to a coating composition used to form a bond in the seam area of a label substrate material that wraps around an article and is shrunk in conformance to the size and shape of the article. The coating composition is comprised of at least first and second resins, and in some instances, third resins as described herein. The coating composition provides good bond strength in the seam area of the label, and the coating composition and/or each of the resins thereof may be at least partially hydrolysable but not solutionable in a hot caustic bath, enabling separation of the label from the article during recycling. Further disclosed is a method providing for the separation of labels from the articles, and further disclosed are labeled articles employing the coating compositions.