Dual-Solvent Printing Ink Formulation Suppresses Coffee Ring Effect
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Solution Overview
Problem
Current printing ink formulations for OLED and QLED technologies face challenges such as low material utilization rates, high costs, and non-uniform film thickness due to the 'coffee ring effect' during inkjet printing, which affects the performance and uniformity of optoelectronic devices.
Innovation Solution
A dual-solvent printing ink formulation is developed, comprising a first solvent with a high boiling point and a second solvent with lower surface tension and higher viscosity, which are miscible and evaporable, to prevent nozzle clogging and reduce the 'coffee ring effect, resulting in a uniform functional material film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single solvent is used in printing ink formulation, then the formulation is simple, but the film uniformity is poor due to coffee ring effect
Solution Approach 1:
The patent uses a composite solvent system comprising multiple solvents with different properties (e.g., high boiling point solvent like o-dichlorobenzene combined with low surface tension solvent like 1-octanol). This composite approach allows the ink formulation to achieve both good dissolving power and suppressed coffee ring effect, resulting in uniform film deposition while maintaining reasonable formulation complexity
Solution Approach 2:
The patent systematically adjusts key parameters of the solvent system including boiling point (≥160°C), surface tension (20-50 dyne/cm), and viscosity (1-100 cP) to optimize printing performance. By changing these physical parameters within specific ranges, the formulation achieves uniform film thickness without requiring overly complex compositions
2Manufacturing precision
If solvent with low surface tension is used, then the coffee ring effect is reduced, but the viscosity increases
Solution Approach 1:
The patent carefully selects solvents and adjusts their ratios to achieve surface tension within 20-50 dyne/cm while keeping viscosity between 1-100 cP. For example, using 1-octanol (surface tension 27.6 dyne/cm, viscosity 7.9 cP) or 2-ethyl-1-hexanol (surface tension 27.0 dyne/cm, viscosity 6.5 cP) provides low surface tension without excessive viscosity increase
Solution Approach 2:
The patent combines solvents with complementary properties to balance surface tension and viscosity. By mixing high boiling point solvents with low surface tension additives in optimized ratios, the formulation achieves both low surface tension for uniform deposition and acceptable viscosity for proper inkjet printing flow characteristics
3Reliability
If high boiling point solvent is used, then nozzle clogging is prevented, but the evaporation time increases
Solution Approach 1:
The patent specifies boiling point ≥160°C for the main solvent to prevent nozzle clogging during printing operations. This parameter ensures the solvent remains liquid at printing temperatures and does not crystallize or solidify in the nozzle, maintaining reliable printing operation without excessive evaporation time
4Manufacturing precision
If polymer additives are used to regulate physical parameters, then the ink properties are improved, but the charge transport capability is reduced
Solution Approach 1:
The patent extracts and eliminates polymer additives from the ink formulation, relying instead on carefully selected small molecule solvents with appropriate physical properties. This removal of insulating polymer components prevents degradation of charge transport capability while maintaining ink stability and printability through proper solvent selection
Solution Approach 2:
The patent achieves ink property control by adjusting solvent parameters (boiling point, surface tension, viscosity) rather than adding polymer additives. This parameter-based approach regulates ink flow and deposition characteristics without introducing insulating materials that would harm charge transport in the resulting film
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 dual-solvent system enhances the uniformity and stability of the printed film, improving the performance and yield of optoelectronic devices by suppressing edge flow and ensuring a flat, uniform thickness, thus addressing the limitations of existing formulations.
Implementation Method 1
the solvent could be evaporable from the printing ink formulation to form a functional material film
Implementation Method 2
the second solvent has a surface tension less than that of the first solvent... the difference in surface tension between the second solvent and the first solvent is at least 2 dyne/cm... suppressing edge flow and ensuring a flat, uniform thickness
Implementation Method 3
the first solvent and the second solvent are miscible
Data Source
AI summary
A printing ink formulation includes a functional material and a solvent being evaporable from the printing ink formulation to form a functional material thin film. The solvent is formed by mixing at least two organic solvents including a first solvent and a second solvent. The solvent system containing at least two solvents can effectively dissolve the functional material without the need of adding an additive, and can also effectively prevent the occurrence of a “coffee-ring effect”, and accordingly, the thin film containing a uniform thickness and a strong electron transmission capability can be obtained.