Shrink Wrap Label Coating for Caustic-Wash Seam Separation
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Solution Overview
Problem
Current plastic container recycling processes are hindered by the inability to efficiently separate shrink wrap labels, particularly those made from PET-G, due to their high density, which prevents effective separation in sink/floatation tanks, leading to reduced recycling yields and increased costs.
Innovation Solution
Development of a coating composition for shrink wrap labels that includes a first resin with a glass transition temperature (Tg) above 25°C, preferably above 50°C, and a second resin that is hydrolysable in a hot caustic bath, allowing for strong bonding during recycling processes and easy separation of the label from the container.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shrink wrap labels are made from PET-G with high density, then label strength and shrink properties are improved, but separation in sink/floatation tanks becomes difficult
Solution Approach 1:
The label structure is segmented into two functional parts: an inner layer made of low-density material (polyolefin, COC, or alpha-polyolefin) that provides buoyancy for easy separation, and an outer PET-G layer that provides strength, shrink properties, and printability. This segmentation allows each layer to fulfill its specific function without compromise.
Solution Approach 2:
The invention uses a composite label structure combining dissimilar materials with different densities and properties. The inner low-density layer and outer PET-G layer are bonded together to create a composite material that exhibits both the buoyancy needed for separation and the mechanical properties needed for label performance.
2Ease of manufacture
If low density films are used for shrink wrap labels, then separation in sink/floatation tanks is improved, but shrink properties and printability deteriorate
Solution Approach 1:
The label is divided into functional segments where the inner layer handles buoyancy and the outer layer handles shrink and print requirements, allowing each material to be optimized for its specific function.
Solution Approach 2:
By combining low-density polyolefin/COC/alpha-polyolefin with PET-G in a composite structure, the invention achieves both low overall density for separation and high PET-G content for shrink and print performance.
3Quantity of substance
If printing is done in the margins of shrink wrap structure, then label information completeness is improved, but seam bonding strength deteriorates
Solution Approach 1:
The coating is applied locally only to the seam regions where bonding is required, leaving the printed areas untouched. This local application ensures that printing can extend to the edges of the label without compromising seam strength, as the coating is present only where structural bonding is needed.
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 robust bonding at the seam while facilitating efficient de-seaming during recycling, maintaining label integrity and transparency, and reducing the need for additional seaming solvents, thus enhancing recycling efficiency and reducing material waste.
Implementation Method 1
The coating enables removal of the sleeve label during recycling... promote good bonding at the seam
Implementation Method 2
a second resin hydrolysable in a hot caustic bath... allowing for strong bonding during recycling processes and easy separation of the label from the container
Data Source
AI summary
The present invention discloses a method of enabling the easy separation of labels, including wrap around labels and sleeve labels, particularly shrink sleeve labels, from containers during recycling through the use of a specially formulated coating to be applied in the seam area. The coatings ensure proper bonding, and shrink properties, of the labels, and have been designed to help de-bonding of the seam in a hot caustic wash step, or a solvent wash step. The method does not rely on floatation separation and therefore may be applied to any container / label material combination regardless of their specific gravity differences.