Multilayer Polycarbonate Polyester Film Flexibility
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Solution Overview
Problem
Multilayer polymer films often become hazy or cracked when bent or impacted, lacking sufficient impact resistance and flexibility, especially when their thickness exceeds 100 micrometers.
Innovation Solution
A multilayer film comprising alternating layers of a polycarbonate copolymer and a semi-crystalline polyester, with an interdiffusion region formed between the layers, achieving a thickness of 40 μm to 80 μm and exhibiting high dynamic flexibility, impact resistance, and optical transparency through specific solubility parameter matching and processing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If multilayer polymer films are made thicker to improve impact resistance, then impact resistance is improved, but the films become less flexible and more prone to cracking when bent
Solution Approach 1:
The film is divided into multiple thin layers (at least 16 layers of each polymer A and polymer B) with alternating composition. This segmentation allows the film to maintain flexibility while achieving impact resistance through the collective behavior of many thin layers, avoiding the cracking issues associated with thick single-layer films.
Solution Approach 2:
The invention uses a composite structure with alternating layers of amorphous polymer A and semi-crystalline polymer B. This composite material approach combines the advantages of both polymers: the amorphous polymer provides flexibility and transparency, while the semi-crystalline polymer provides strength and impact resistance, resolving the contradiction between flexibility and impact resistance.
2Ease of operation
If multilayer films are made with many alternating layers to improve flexibility and impact resistance, then dynamic flexibility is improved, but the films become hazy when bent or impacted
Solution Approach 1:
The invention creates local quality differences by forming an interdiffusion region at the interfaces between polymer A and polymer B layers. This interdiffusion region has a differential solubility parameter (ΔδAB) within a specific range (1.5-3.0 MPa^1/2), which ensures optimal adhesion and prevents haze formation at the interfaces, while the bulk layers maintain their individual properties for flexibility and transparency.
Solution Approach 2:
The invention controls the differential solubility parameter (ΔδAB) between the two polymers within a specific range (1.5-3.0 MPa^1/2) to optimize the interdiffusion and adhesion at layer interfaces. This parameter control prevents excessive interdiffusion that would cause haze while ensuring sufficient adhesion to maintain film integrity during bending and impact, thus preventing haziness.
3Reliability
If multilayer films use high layer counts (e.g., 16+ layers of each polymer) to achieve desired properties, then impact resistance and flexibility are improved, but manufacturing complexity increases
Solution Approach 1:
The invention uses a dynamic coextrusion process where the multilayer structure is formed continuously during extrusion rather than through sequential lamination of pre-formed layers. This dynamic approach allows the complex multilayer structure to be manufactured in a single continuous process, reducing manufacturing complexity despite the high number of layers, by integrating the layer formation into the extrusion process itself.
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 demonstrates greater than 200,000 cycles of dynamic flexibility, transmission of over 89%, haze less than 1%, and impact dent depth of less than 15 μm, making it suitable for flexible and foldable applications like electronic device covers.
Implementation Method 1
an interdiffusion region between each polymer A and polymer B; wherein a differential solubility parameter (ΔδAB) of polymer A towards polymer B (ΔδAB) is 2.6 MPa1/2≤ΔδAB≤3.0 MPa1/2; and wherein the polycarbonate copolymer and the semi-crystalline polyester commingle at an interface of polymer A layer and polymer B layer
Data Source
AI summary
A multilayer film can comprise: a plurality of layers, preferably 4 layers to 128 layers, comprising: a polymer A layer comprising a polycarbonate copolymer and a polymer B layer comprising a semi-crystalline polyester; wherein a differential solubility parameter (ΔδAB) of polymer A towards polymer B (ΔδAB) is greater than or equal to 2.6 MPa1/2; and an interdiffusion region between each polymer A and polymer B. The multilayer film has a dynamic flexure of greater than or equal to 200,000 cycles, as determine by bending 180° on a 10 mm radius cylinder at a rate of 1 hertz. The multilayer film has a total thickness of 40 μm to 70 μm, a transmission at 360 nm to 750 nm of greater than or equal to 89% and a haze of less than or equal to 1%.