Shrinkable Polyolefin Face Film for PET Label Recycling
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Solution Overview
Problem
Existing labels on polymer containers, such as PET bottles, are difficult to remove during conventional washing processes, leading to interference in recycling and increased costs due to remnants of adhesive and ink, which affect the clarity and processability of recycled PET.
Innovation Solution
Development of a label laminate structure comprising a face film with a multilayer structure, including a first and second skin layer and a core layer, made from specific polyolefin materials, which is shrinkable and designed to detach under elevated washing temperatures, ensuring easy removal and efficient recycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional labels are used on PET bottles, then the labels provide decoration and identification, but the labels are difficult to remove during washing processes and interfere with recycling
Solution Approach 1:
The label is designed as a multilayer structure with distinct functional layers: a release liner layer, an adhesive layer, and a face stock layer. This segmentation allows each layer to perform its specific function - the adhesive provides initial bonding, the face stock provides decoration and identification, and the release liner facilitates controlled removal during washing while leaving minimal remnants on the PET bottle.
Solution Approach 2:
The adhesive layer is formulated with specific rheological parameters including a storage modulus of 10-1000 Pa at 20°C and a storage modulus of 10-1000 Pa at 60°C, with a specific loss tangent value. These parameter changes with temperature allow the adhesive to maintain strong bonding at room temperature but become more compliant and easier to remove during hot washing, thus resolving the contradiction between strong adhesion and easy removal.
2Strength
If the label adhesive is made stronger to ensure proper attachment, then the label stays firmly on the bottle, but the label becomes more difficult to remove during washing
Solution Approach 1:
The adhesive composition is designed with temperature-dependent rheological properties. At room temperature (20°C), the adhesive exhibits high storage modulus (10-1000 Pa) for strong bonding. At washing temperature (60°C), the storage modulus remains in the same range but the loss tangent changes, making the adhesive more compliant and easier to remove. This parameter change with temperature resolves the contradiction between strong attachment and easy removal.
Solution Approach 2:
The label is designed as a disposable element that serves its purpose during product use and then is intentionally removed during recycling. The adhesive is formulated to provide sufficient bonding strength during the product's lifecycle but to allow complete or near-complete removal during hot washing, sacrificing permanent adhesion for recyclability.
3Reliability
If the label face stock is made more durable to withstand handling and washing, then the label maintains its appearance, but the label resists removal and contaminates the recycling process
Solution Approach 1:
The label structure separates the face stock (providing decoration and identification) from the adhesive layer. The face stock is designed to maintain its appearance and integrity during handling and initial washing, while the adhesive layer controls the detachment process. This segmentation allows the face stock to be durable for its primary function while enabling controlled removal to prevent recycling contamination.
Solution Approach 2:
The adhesive layer's rheological parameters are specifically designed to change with temperature and mechanical stress during washing. The storage modulus and loss tangent values are optimized so that the adhesive maintains bonding during normal conditions but becomes more compliant under hot washing conditions, allowing the face stock to be removed without leaving harmful remnants that would interfere with PET recycling.
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 label laminate effectively separates from the container during washing, facilitating efficient recycling by preventing contamination and maintaining the clarity and processability of recycled PET.
Implementation Method 1
the oriented face film provides shrinkage capability for the film... the label comprising the oriented face film is able to detach itself form the surface attached in a subsequent washing procedure
Implementation Method 2
the oriented face film provides shrinkage capability for the film... generating forces providing e.g. lifting the regions of the label away from the bottle
Data Source
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AI summary
The invention relates to a face film for a wash-off label and a wash-off label comprising said face film. According to an embodiment the face film is at least uniaxially oriented and comprises at least one of the polyolefins: cyclic olefin copolymer, propylene terpolymer, propylene random copolymer, propylene homopolymer, heterophasic polypropylene and linear low density polyethylene. The face film has density between 0.85 and 0.94 g/cm3 at room temperature (23±2 ºC). Further the invention relates to a labelled item comprising the wash-off label.