Void-Containing Polyester Shrink Film Density Retention
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Solution Overview
Problem
Polyester shrink labels have high densities that make them difficult to separate from PET bottles in recycling processes, leading to contamination and inefficiencies, as they sink with the PET during recycling, causing issues like color and haze contamination and offgassing of hazardous substances.
Innovation Solution
Development of a void-containing polyester shrink film with a high shrinkage of at least 40% and a density of 1.05 g/cc or less after shrinkage, achieved by incorporating 5 to 35 wt% of a voiding agent such as cellulose acetate or inorganic compounds into the polyester, which maintains low density even after exposure to recycling temperatures, allowing for efficient sink/float separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyester shrink labels are used, then high shrinkage and good aesthetic properties are achieved, but high density causes contamination in recycling processes
Solution Approach 1:
The patent applies parameter changes by modifying the density parameter of the polyester shrink label through void formation. By incorporating voiding agents and creating micropores within the polyester matrix, the density is reduced from typical values (1.30-1.33 g/cc) to below 1.05 g/cc, enabling the label to float during sink/float separation in recycling processes while maintaining shrinkage and aesthetic properties
Solution Approach 2:
The patent employs porous materials by introducing a void-containing structure into the polyester shrink label. Voids or micropores are formed within the polyester matrix through the use of voiding agents, creating a porous structure that reduces density and enables floatation during recycling separation while preserving the label's functional properties
2Reliability
If voiding agents are incorporated to reduce density, then sink/float separation is enabled, but film strength and tear resistance may be compromised
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration and type of voiding agents to achieve the right balance between density reduction and strength maintenance. By controlling void formation parameters and selecting appropriate voiding agent chemistry, the patent achieves sink/float separability while preserving tear resistance and film strength
Solution Approach 2:
The patent employs composite materials by combining polyester with specific voiding agents to create a composite structure. The voiding agents are selected and distributed within the polyester matrix to form a composite material that simultaneously provides low density for separation and maintains mechanical strength through the polyester continuous phase
3Shape
If high shrinkage is achieved, then label conformability is improved, but density retention after shrinkage becomes problematic
Solution Approach 1:
The patent applies parameter changes by modifying the physical and chemical parameters of the polyester formulation to achieve both high shrinkage and density retention. By optimizing polyester composition, molecular weight, and void distribution, the patent enables the label to shrink conformally while maintaining low density through the stable void structure
Solution Approach 2:
The patent applies the inversion principle by addressing density retention not as a problem to be minimized, but as a key feature to be maximized. Instead of trying to maintain high density for strength, the patent inverts the approach by creating a low-density void-containing structure that inherently retains its density through the stable porous architecture, enabling both shrinkage and density stability
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 void-containing polyester shrink film effectively separates from PET bottles during recycling, reducing contamination and maintaining recyclability while maintaining high shrinkage and aesthetic properties like printability and tear resistance.
Implementation Method 1
Voids are obtained by incorporating about 5 to about 50 weight % of small organic or inorganic particles or 'inclusions' (referred in the art as 'voiding' or 'cavitation' agents) into a polyester and orienting the polymer by stretching in at least one direction. During stretching, small cavities or voids are formed around the voiding agent.
Implementation Method 2
the separation of these two materials can be easily accomplished by a sink/float process in which the flaked bottle and the label are suspended in water and separated on the basis of their densities. PET, with a density of around 1.35 g/cc, will sink to the bottom during recycling processing. Polypropylene, however, has a density of about 0.90 g/cc and will float to the top
Implementation Method 3
the film has a shrinkage of at least 40% after 5 seconds in water bath at 95° C.
Data Source
AI summary
Disclosed are void-containing polyester shrink films which show excellent density retention upon exposures to high temperatures. The films have high shrinkage and retain their low density after processing under conditions of temperature and moisture used in typical recycling processes. The films are useful for sleeve label and other shrink film applications, and their lower density allows them to be readily separated from soft drink bottles, food containers and the like during recycling operations. Also disclosed is a process for void-containing polyester shrink films having high shrinkage and low density after exposure to elevated temperatures.