Coated Polyester Film for Hermetic Sealing and Peelability
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Solution Overview
Problem
Polyester films used in food packaging face issues with hermeticity, clean peelability, and tearing when sealed onto containers, especially when thin and made from recycled materials, leading to distortion and breakage during heat treatments.
Innovation Solution
A bi-axially oriented coated polyester film with a heat-sealable coating comprising amorphous copolyesters of terephthalic acid, naphthalene dicarboxylic acid, and diols, having specific tear initiation force values and shrink properties, ensuring hermeticity and clean peelability without tearing, even at low sealing temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heat-sealable coating is applied to polyester film to improve sealing performance, then hermeticity is improved, but the film shows tearing when peeled off
Solution Approach 1:
The invention changes the chemical composition parameters of the heat-sealable coating by incorporating specific copolymers with controlled vinyl acetate content (10-40 mol%) and vinylidene chloride content (5-30 mol%). This parameter optimization allows the coating to achieve both strong adhesion for hermetic sealing and controlled peelability without tearing, resolving the contradiction between sealing performance and openability.
Solution Approach 2:
The invention uses a composite heat-sealable coating system comprising multiple polymer components: a base copolymer (ethylene/vinyl acetate or polyvinylidene chloride), optional third polymers (polyester, polyamide, polyolefin), and specific additives. This composite structure combines the adhesion benefits of different materials while controlling the peel characteristics to prevent tearing during opening.
2Quantity of substance
If the film is made thinner for economic and sustainability reasons, then material usage is reduced, but tearing occurs more frequently
Solution Approach 1:
The invention optimizes the coating composition parameters to achieve high performance at low thickness. By controlling the vinyl acetate content (10-40 mol%) and vinylidene chloride content (5-30 mol%), and selecting appropriate polymer combinations, the coating provides sufficient strength and tear resistance even when applied as a thin layer, enabling thin-film applications without compromising durability.
Solution Approach 2:
The invention enables the use of thinner, more economical films that can be disposed of after single use, aligning with sustainability goals. The optimized coating formulation ensures that even thin films maintain adequate strength and tear resistance for their intended lifecycle, making thin-walled packaging economically viable without premature failure.
3Reliability
If sealing is performed at higher temperatures to ensure hermeticity, then sealing strength is improved, but film distortion and breakage occur
Solution Approach 1:
The invention changes the thermal properties of the heat-sealable coating by selecting polymers with appropriate melting points and glass transition temperatures. The copolymer composition (vinyl acetate 10-40 mol%, vinylidene chloride 5-30 mol%) is optimized to provide effective sealing at lower temperatures (80-120°C), preventing film distortion and breakage while ensuring adequate sealing strength for hermeticity.
Solution Approach 2:
The invention creates local quality differentiation within the film structure: the heat-sealable coating layer has lower melting point characteristics than the base polyester film. This allows the coating to soften and seal at lower temperatures while the base film maintains its structural integrity and shape resistance, preventing distortion during the sealing process.
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 solution provides a film that maintains hermeticity and clean peelability during heat treatments, preventing distortion and breakage, and is suitable for ready meals and moist or respiring products, with tailored shrink properties for various packaging applications.
Implementation Method 1
the glass transition temperature of the heat-sealable coating is higher than 10° C. and lower than 70° C.
Implementation Method 2
the oriented polyester film having a shrink in each direction of less than 5% at 100° C. and of at least 5% at 150° C.
Data Source
AI summary
The invention discloses bi-axially oriented coated polyester films having high tear initiation resistance and comprising a polyester base film and a heat sealable coating, said heat sealable coating comprising one or more amorphous copolyester(s) comprising units of terephthalic acid, naphthalene dicarboxylic acid and at least one diol. The films are heat-sealable and peelable to polyester and aluminium containers. The invention also relates to a process for the manufacturing of such films, to the use of said films in food packaging and to the packages obtained therefrom.