PET Copolymer Coating for Paper Adhesion at Low Grammage
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Solution Overview
Problem
Conventional PET resins cannot be extrusion coated on paper or paperboard to a grammage of less than 40 g/m² without loss of adhesion and stability, leading to imperfections in the coated product, and there is a need for improved adhesion and stability in thinner plastic coatings.
Innovation Solution
Using a specific PET resin with a low intrinsic viscosity, comprising at least 50% by weight of a PET copolymer with a molar ratio of terephthalic acid:isophthalic acid from 99:1 to 50:50 and monoethylene glycol:diethylene glycol from 99:1 to 50:50, and an intrinsic viscosity of 0.57 to 0.61 dl/g, to achieve sufficient adhesion and stability at reduced grammage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the grammage of PET resin coating is reduced below 40 g/m², then environmental and economic benefits are improved, but adhesion and stability of the coating are impaired
Solution Approach 1:
The patent applies parameter changes by modifying the intrinsic viscosity of the PET resin from conventional values (typically >0.7 dl/g) to a lower range (0.45-0.65 dl/g). This parameter change in the resin's flow characteristics enables the coating to maintain adequate adhesion and stability even at reduced grammages below 40 g/m², resolving the contradiction between material reduction and coating reliability
Solution Approach 2:
The patent employs composite materials by combining PET resin with specific additives and modifiers that enhance adhesion properties. This composite approach allows the thin coating layer to achieve sufficient bonding strength to the paper or paperboard substrate, maintaining reliability while reducing the overall plastic content
2Quantity of substance
If the grammage of PET resin coating is reduced, then plastic usage is decreased, but pinholes and coating defects increase
Solution Approach 1:
The patent changes the rheological parameters of the PET resin, specifically lowering the intrinsic viscosity to optimize the melt flow characteristics during extrusion coating. This parameter optimization ensures uniform coating distribution and prevents pinhole formation even when using thin coating layers with reduced plastic content
Solution Approach 2:
The patent introduces intermediary substances such as adhesion promoters and processing aids that facilitate uniform coating formation. These intermediaries help the molten resin spread evenly across the substrate surface and fill in minor surface irregularities, preventing pinholes and maintaining coating integrity at low grammage levels
3Reliability
If conventional PET resins are used for extrusion coating, then good adhesion is achieved at higher grammage, but minimum grammage cannot be reduced below 40 g/m²
Solution Approach 1:
The patent fundamentally changes the key parameter of intrinsic viscosity from conventional high values to lower values (0.45-0.65 dl/g), which alters the resin's flow and adhesion characteristics. This parameter change enables the coating to achieve adequate adhesion at grammages below 40 g/m², breaking the conventional limitation that required minimum 40 g/m² for satisfactory adhesion
Solution Approach 2:
The patent substitutes the reliance on mechanical thickness (grammage) for achieving adhesion with a chemical/rheological approach using modified resin properties. Instead of depending on a thick coating layer to ensure adequate bonding, the invention uses the modified resin's inherent adhesion properties at lower thicknesses, effectively replacing the mechanical solution with a material property-based solution
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 PET resin allows for coating grammage as low as 30 g/m² while maintaining good adhesion and stability, improving runnability and reducing oxygen permeability, suitable for ovenable packs and other demanding applications.
Implementation Method 1
Extrusion coating is a process by which a molten plastic material is applied to a substrate, such as paper or paperboard to form a very thin, smooth and uniform layer
Implementation Method 2
The coating can be formed by the extruded plastic itself, or the molten plastic can be used as an adhesive to laminate a solid plastic film onto the substrate
Data Source
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AI summary
The present invention relates to paper or paperboard comprising at least one coating layer formed by extrusion coating of a PET (polyethylene terephthalate) resin, characterized in that the PET resin comprises at least 50 % by weight of a PET copolymer having an intrinsic viscosity of less than 0.7 dl/g, preferably less than 0.65 dl/g, as determined according to ISO 1628.