Heat-shrinkable Polyester Film Suppressing Recycling Blocking
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Solution Overview
Problem
Conventional heat-shrinkable polyester films used for recycling PET bottles suffer from a blocking phenomenon where flakes adhere, causing clogging and hindering the production of well-shaped recycled pellets, due to their thermal characteristics and adhesion issues, and existing solutions fail to effectively and quantitatively suppress this issue while maintaining fittability.
Innovation Solution
A heat-shrinkable polyester film derived from a combination of amorphous and crystalline polyester resins with specific thermal and crystallization characteristics, including a predetermined mixing ratio, exothermic peak time, and thermal shrinkage ratio, which suppresses the blocking phenomenon and maintains excellent fittability during recycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If PETG film is used as heat-shrinkable film material, then the film can be readily separated from PET bottles during recycling, but the film causes blocking phenomenon where flakes adhere together due to its amorphous structure and lack of melting point
Solution Approach 1:
The patent uses a composite material system consisting of amorphous polyester resin (PETG) blended with 5-50 wt% of low-melting-point crystalline polyester resin. This composite structure combines the ease of separation from PET bottles provided by PETG with the blocking-prevention capabilities of the crystalline component, which melts at 80-120°C to prevent flake adhesion during recycling.
Solution Approach 2:
The patent modifies the thermal parameters of the heat-shrinkable film by controlling the melting point of the crystalline polyester component to be 80-120°C, which is lower than the melting temperature of PET bottles. This parameter change ensures that the crystalline component melts first during recycling, creating a lubricating effect that prevents blocking, while the PETG matrix maintains separation readiness.
2Object-generated harmful factors
If the melting point of the heat-shrinkable film is increased to suppress blocking, then the blocking phenomenon is reduced, but the fittability of the film on PET bottles deteriorates
Solution Approach 1:
The patent precisely controls the melting point parameter of the crystalline polyester component within 80-120°C, which is the optimal range that simultaneously achieves blocking suppression and fittability maintenance. This specific parameter range allows the film to shrink properly on PET bottles while preventing flake adhesion during recycling.
Solution Approach 2:
The patent introduces local quality differentiation by having the crystalline polyester component melt at a specific temperature range (80-120°C) that is lower than the PET bottle melting temperature but sufficient to prevent blocking. This localized melting behavior occurs only in the crystalline domains, while the amorphous PETG matrix maintains the overall film integrity and fittability.
3Shape
If conventional heat-shrinkable films are used, then the film provides adequate shrinkage properties, but the film adheres to itself during recycling causing clogging in pipes and difficulty in pellet production
Solution Approach 1:
The patent applies preliminary anti-action by incorporating the low-melting-point crystalline polyester component that proactively prevents blocking before it occurs. During recycling, this component melts first at 80-120°C, creating a lubricating effect that prevents flake adhesion and subsequent clogging, thereby maintaining high recycling efficiency throughout the process.
Solution Approach 2:
The crystalline polyester component acts as an intermediary substance that facilitates the recycling process. It melts at a specific temperature range to create a lubricating layer between PET flakes, preventing direct adhesion and clogging, while the amorphous PETG matrix maintains the film's structural integrity and shrinkage properties.
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 film effectively prevents the blocking phenomenon during recycling, allowing for the production of well-shaped recycled pellets while ensuring good fittability on PET bottles, reducing the need for manual removal and lowering production costs.
Implementation Method 1
it has become clear that the blocking phenomenon can be suppressed by using a heat-shrinkable polyester film including a crystalline polyester resin (low-melting-point crystalline polyester resin) having a melting point of 80° C. to 120° C.
Implementation Method 2
when a heat treatment of immersing the heat-shrinkable polyester film in hot water at 80° C. for 10 seconds is performed, the thermal shrinkage ratio in the main shrinkage direction is 30% or more
Data Source
AI summary
The blocking phenomenon at the time of recycling can be effectively suppressed. Provided is a heat-shrinkable polyester film derived from a first polyester resin and a second polyester resin as a plurality of polyester resins having different crystallinity, the heat-shrinkable polyester film satisfying the following characteristics (A) to (E).(A) and (B): The first polyester resin includes terephthalic acid, in which a reaction amount of ethylene glycol is in the range of 50 mol % or more and below 90 mol %, and the second polyester resin includes terephthalic acid, in which a reaction amount of ethylene glycol is 90 mol % or more.(C) and (D): When predetermined isothermal crystallization measurement is performed, an exothermic peak appears within 12 minutes from the start, including a cooling process time, and the heat quantity of the exothermic peak is 5 to 35 J/g.(E): The thermal shrinkage ratio in the main shrinkage direction as measured under predetermined conditions is 20% to 60%.