Solar Cell Backsheet Aqueous Adhesive Pinhole Reduction
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Solution Overview
Problem
Photovoltaic module backsheets with aqueous adhesive and weather-resistant layers face issues of pinholes, poor adhesion, and yellowing under hot and humid conditions due to the use of polyisocyanate crosslinking agents.
Innovation Solution
A backsheet for photovoltaic modules is developed with an aqueous adhesive layer containing a water-soluble or dispersible binder and a water-dispersible core/shell polyisocyanate, optimized to minimize pinholes and yellowing by controlling the ratio of isocyanate groups to hydroxyl groups and combining with other crosslinking agents like oxazolines or carbodiimides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If polyisocyanate crosslinking agents are used in aqueous adhesive layers, then curing speed is improved, but pinholes and poor adhesion occur under hot and humid conditions
Solution Approach 1:
The patent changes the chemical parameters of the crosslinking agent by using core/shell structured polyisocyanates with controlled isocyanate content (1-10% by weight) and specific shell thickness. This parameter optimization allows the adhesive to cure at appropriate speeds while preventing pinhole formation and maintaining adhesion under hot and humid storage conditions.
Solution Approach 2:
The patent employs a composite crosslinking system combining polyisocyanate crosslinkers with alternative crosslinking agents such as oxazolines or carbodiimides. This composite approach balances curing speed with long-term adhesion reliability, as the polyisocyanate provides initial crosslinking while the alternative agents ensure stable performance under environmental stress.
2Speed
If polyisocyanate crosslinking agents are used in aqueous adhesive layers, then curing speed is improved, but yellowing increases upon storage under hot and humid conditions
Solution Approach 1:
The patent optimizes the isocyanate group content parameter within a specific range (1-10% by weight of the adhesive layer) and controls the shell-to-core ratio of the polyisocyanate particles. This parameter control enables sufficient curing speed while minimizing yellowing by preventing excessive isocyanate reactions that produce colored byproducts under hot and humid storage conditions.
Solution Approach 2:
The patent converts the potential harm of polyisocyanate yellowing into a benefit by using alternative crosslinking agents (oxazolines or carbodiimides) that provide crosslinking functionality without the yellowing side effect. These alternative agents compensate for any yellowing tendency while maintaining the curing speed advantage of polyisocyanates.
3Object-affected harmful factors
If aqueous coating solutions are used for adhesive and outer layers, then environmental friendliness is improved, but pinholes and poor adhesion occur
Solution Approach 1:
The patent optimizes the water content and composition parameters of the aqueous coating solution, using deionized water and controlling the pH and ionic strength. This parameter optimization ensures proper wetting and adhesion while maintaining the environmental benefits of aqueous formulations. The controlled water quality prevents pinhole formation during drying.
Solution Approach 2:
The patent uses a composite binder system in the aqueous adhesive layer, combining polyurethane dispersions with acrylic or vinyl acrylic copolymers. This composite polymer system maintains excellent adhesion and film formation in aqueous environments, overcoming the typical defects of aqueous coatings while preserving their environmental advantages.
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 results in a backsheet with reduced pinholes, improved adhesion, and minimal yellowing, enhancing the durability and performance of photovoltaic modules under challenging environmental conditions.
Implementation Method 1
An adhesive layer is provided on one side of the support, wherein the adhesive layer is coated from an aqueous composition, the aqueous composition comprising a water soluble or dispersible binder and a water dispersible core/shell polyisocyanate
Implementation Method 2
the adhesive layer is coated from an aqueous composition
Data Source
Figure 1
Figure 2
AI summary
A backsheet (1) for a photovoltaic module (5) comprising: - a support, - an adhesive layer provided on one side of the support, and characterized in that the adhesive layer is coated from an aqueous composition, the aqueous composition comprising a water soluble or dispersible binder and a water dispersible core/shell polyisocyanate.