Partially Coated Polyolefin Films for Controlled Tear Strength
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Solution Overview
Problem
Polyolefin films, such as polyethylene, used in packages often have high tear strength which can make it difficult to open packages designed to be torn, as high tear strength is undesirable for such designs.
Innovation Solution
A partially coated film with a polyurethane coating on less than 25% of the surface area, reducing tear resistance in the coated region to facilitate easy tearing and puncturing, while maintaining desirable mechanical properties in the uncoated areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyolefin films are used to provide high tear strength, then mechanical strength is improved, but ease of opening by tearing deteriorates
Solution Approach 1:
The patent applies a polyurethane coating to only a portion of the polyolefin film surface (less than 25% coverage), creating localized regions with different tear properties. The coated regions have reduced tear strength to facilitate easy opening, while the uncoated regions maintain high tear strength for structural integrity.
Solution Approach 2:
The film is divided into functionally distinct zones: coated areas that serve as easy-tear opening regions and uncoated areas that provide structural strength. This segmentation allows different portions of the same film to fulfill contradictory requirements simultaneously.
2Ease of operation
If polyurethane coating is applied to reduce tear resistance, then ease of opening is improved, but mechanical strength deteriorates
Solution Approach 1:
The polyurethane coating is applied selectively to create localized easy-tear zones rather than coating the entire film. This ensures that tear resistance is reduced only where needed for opening, while the majority of the film retains its original mechanical strength.
Solution Approach 2:
Instead of coating the entire film surface, the patent applies coating to less than 25% of the surface area. This partial application is sufficient to create easy-opening functionality without compromising the overall mechanical strength of the package.
3Ease of operation
If coating coverage is increased to enhance easy-tear regions, then ease of opening is improved, but loss of substance increases
Solution Approach 1:
The patent applies polyurethane coating to less than 25% of the film surface area, which is the minimum coverage needed to create effective easy-tear zones. This partial coverage minimizes coating material consumption while achieving the desired easy-opening functionality.
Solution Approach 2:
By optimizing the coating coverage parameter to less than 25%, the patent achieves the optimal balance between ease of opening and material efficiency. This parameter optimization ensures sufficient easy-tear performance without excessive coating material usage.
Data Source
AI summary
The present invention provides coated films and packages formed from such films. In one aspect, a partially coated film comprises (a) a film having two outer surfaces, wherein a first outer surface is provided by a film layer that comprises from 70 to 100 percent by weight of a polyolefin having a density of 0.860 to 0.965 g/cm3; and (b) a coating on the first outer surface of the film comprising polyurethane, wherein the coating covers less than 25% of the surface area of the first outer surface of the film and wherein the coated portion of the film exhibits an Elmendorf tear in at least one of the machine direction or cross direction that is at least 20% less than the Elmendorf tear of the uncoated portion in the same direction, with the Elmendorf tear being measured in accordance with ASTM D1922.