Polyester Film Adhesion via Crystallinity Control
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Solution Overview
Problem
Polyester films used as back sheets for solar cells experience deterioration in adhesion over time, especially when exposed to wind and rain, leading to separation issues due to reduced adhesion strength, particularly in moist environments.
Innovation Solution
A method of manufacturing a polyester film with a specific crystallinity distribution on its surface, achieved by controlling the terminal carboxylic acid group content, pre-melting peak temperature, and using a biaxial extruder, which involves solid phase polymerization with varying ethylene glycol and water vapor concentrations, and applying a coating layer followed by stretching, to enhance adhesion between the film substrate and the coating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyester film is used as a back sheet for solar cells, then it provides electrical insulation and protection, but the adhesion between the film substrate and coating layer deteriorates over time especially in moist environments
Solution Approach 1:
The invention changes the chemical parameter of the polyester film substrate by controlling the terminal carboxylic acid group content to 3-20 eq/ton and the pre-melting peak temperature distribution to 1-10°C. These parameter changes create optimal surface properties that maintain high adhesion strength between the coating layer and substrate even after long-term exposure to moist environments, resolving the contradiction between adhesion durability and service life.
Solution Approach 2:
The invention creates local quality differences by establishing a specific crystallinity distribution within the polyester film substrate. The crystallinity is controlled to be 30-70% in the central portion and 10-50% in the surface portion, creating distinct local regions with different properties. This local quality differentiation enhances both the overall structural integrity and the surface adhesion properties, allowing the film to maintain reliability throughout its extended service life.
2Strength
If the adhesion strength is increased to prevent separation, then the film maintains integrity, but the manufacturing complexity increases due to multiple process parameters
Solution Approach 1:
The invention applies preliminary action by controlling the terminal carboxylic acid group content and pre-melting peak temperature distribution during the resin preparation stage, before film formation. This preliminary control of chemical and thermal parameters ensures that the polyester film substrate inherently possesses the necessary adhesion properties, eliminating the need for complex post-processing or additional manufacturing steps to achieve high adhesion strength.
Solution Approach 2:
The invention achieves universality by using a biaxial extruder that simultaneously performs multiple functions: it controls the crystallinity distribution, regulates the terminal carboxylic acid group content, and manages the pre-melting peak temperature distribution all in a single device. This multi-functional approach simplifies the manufacturing process while maintaining high adhesion strength, reducing the need for separate processing equipment or steps.
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 method results in a polyester film with improved adhesion properties that maintains high adhesion strength even after accelerated testing, effectively preventing separation and ensuring durability in outdoor conditions.
Implementation Method 1
obtaining the polyester resin by subjecting a polyester raw resin to a solid phase polymerization
Implementation Method 2
providing a coating layer on at least one surface of the polyester film substrate
Implementation Method 3
stretching the polyester film substrate provided with the coating layer at least once
Data Source
AI summary
A method of manufacturing a polyester film, including: preparing a polyester film substrate having an amount of a terminal carboxylic acid group (AV) of from 3 eq/ton to 20 eq/ton, by using a polyester resin having a temperature distribution of a pre-melting peak (Tm′) of from 1° C. to 10° C.; providing a coating layer on at least one surface of the polyester film substrate; and stretching the polyester film substrate provided with the coating layer at least once.