PVDF/HFP Copolymer Thick Film for EL Lamp Silver Migration
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Solution Overview
Problem
Current electroluminescent (EL) lamp technologies face issues with degradation over time, particularly exacerbated by high voltage/frequency, temperature, and humidity, leading to reduced lamp lifetime and solubility limitations in common solvents like glycol ethers, as well as challenges with silver electrode migration and increased incidence of short circuits.
Innovation Solution
The development of screen-printable pastes using PVDF/HFP copolymers with specific melt viscosity and DSC melt temperature ranges, allowing for stable solution viscosities and improved solubility in glycol ether solvents, which enables the use of silver electrodes without significant migration and extends the lifetime of EL lamps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fluoropolymer resins are used in EL lamp paste compositions, then the paste can be screen-printed and applied to substrates, but the resins exhibit poor solubility in common solvents like glycol ethers
Solution Approach 1:
The patent modifies the chemical structure of fluoropolymer resins by adjusting composition parameters (copolymer ratios of VF2 and HFP, molecular weight, viscosity ranges) to achieve both screen-printability and solubility in glycol ether solvents. Specifically, using PVDF/HFP copolymers with controlled melt viscosity (0.5-5.0 Pa·s) and melt temperature (90-110°C) enables dissolution in glycol ethers while maintaining paste applicability
Solution Approach 2:
The patent creates composite resin systems by combining fluoropolymer resins with specific plasticizers and solvents. The medium comprises glycol ether solvents (30-70 wt%), plasticizers (10-40 wt%), and resin (10-40 wt%), forming a composite composition that achieves both solubility and screen-printability requirements
2Illumination intensity
If silver electrodes are used in EL lamps, then the lamp achieves uniform lighting and desired performance, but silver migration occurs in the presence of water leading to short circuits
Solution Approach 1:
The patent introduces a protective dielectric layer composition that acts as an intermediary barrier between the silver electrode and the environment. This layer, containing barium titanate powder (40-70 wt%) in a fluoropolymer-based medium with glycol ether solvents, prevents water contact with silver while maintaining electrical insulation and structural integrity
Solution Approach 2:
The patent optimizes the dielectric layer composition parameters, specifically using barium titanate with controlled particle size and distribution, and adjusting the resin-to-solvent ratio to create a dense, impermeable barrier that prevents silver migration while maintaining good adhesion to the electrode
3Illumination intensity
If EL lamps operate at high voltage and frequency, then the lamp produces desired brightness, but degradation occurs exponentially leading to reduced lifetime
Solution Approach 1:
The patent modifies the resin binder parameters (using PVDF/HFP copolymers with specific melt viscosity and temperature characteristics) and dielectric layer composition (barium titanate content, plasticizer ratios) to reduce degradation rates. These parameter changes enable the lamp to maintain brightness at high voltage/frequency operation while extending operational lifetime by reducing exponential degradation
4Ease of manufacture
If carbon electrodes are used instead of silver, then the cost is reduced and silver migration is avoided, but the resistivity is higher leading to less uniform lighting in large lamps
Solution Approach 1:
The patent optimizes the dielectric layer and paste composition parameters to enable better utilization of carbon electrode conductivity. By adjusting the resin composition, plasticizer content, and firing conditions, the patent maximizes the conductive network formation in carbon electrodes, achieving improved uniformity in large lamps while maintaining cost advantages
Data Source
AI summary
The present invention relates to a thick film composition comprising: a) functional component; b) PVDF/HFP polymer resin, a copolymer of PVDF/HFP polymer resin, or mixtures thereof; dissolved in c) organic solvent, with the provisos that the PVDF/HFP resin has i) a melt viscosity of 0.2-0.7 kPoise and ii) a DSC melt temperature in the range of 85-98° C.