Silver Nanopaste Viscosity Control for Screen Printing
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Solution Overview
Problem
Existing bonding materials with silver nanoparticles face challenges in achieving optimal viscosity and thixotropy, leading to issues like texture generation on printed surfaces and reduced bonding strength, especially when high-temperature treatments are required for binders or leveling agents, which can compromise weather resistance and bonding stability.
Innovation Solution
A bonding material comprising silver nanoparticles with an average primary particle diameter of 1 nm to 200 nm, coated with an organic substance having 8 or less carbon atoms, and a dispersion medium, along with a viscosity modifier like 2-methoxyethoxyacetic acid or 2-butoxyethoxyacetic acid, which maintains low viscosity and thixotropy, ensuring a smooth coating film and stable bonding strength even at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a bonding material containing silver nanoparticles is used to reduce the amount of metal component, then the metal usage is decreased, but the viscosity and thixotropy control becomes difficult leading to texture generation on printed surfaces
Solution Approach 1:
The patent applies parameter changes by carefully controlling the particle size distribution of silver nanoparticles (D10: 10-50 nm, D50: 80-150 nm, D90: 200-400 nm) and adjusting the viscosity ratio between applied and fired states to 0.1-0.5. This precise parameter optimization enables proper paste flow during printing while preventing screen gauze texture formation, thus achieving smooth surfaces with reduced metal content.
Solution Approach 2:
The patent utilizes the dynamic viscosity change of the paste through thixotropy control. The viscosity ratio (applied/fired) of 0.1-0.5 indicates the paste becomes less viscous during application and returns to higher viscosity during firing. This dynamic behavior allows the paste to flow smoothly through the screen during printing then maintain shape and prevent texture formation on the printed surface.
2Stability of the object's composition
If a binder is added to improve viscosity and thixotropy, then the paste stability is improved, but high-temperature heat treatment is required which compromises weather resistance
Solution Approach 1:
The patent replaces traditional organic binders with short-lived, high-temperature-resistant materials. Specifically, it uses water as the primary vehicle and adds sacrificial organic substances like polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC) that decompose at relatively low temperatures (200-400°C). These sacrificial materials provide temporary viscosity and thixotropy control during application, then decompose during firing to leave no harmful residues, thereby maintaining weather resistance.
Solution Approach 2:
The patent utilizes phase transitions of water and sacrificial organic materials during the firing process. Water evaporates at 100°C, and the sacrificial organics decompose at 200-400°C, creating a multi-stage phase transition process. This allows the paste to maintain stability during application (liquid state) and then progressively transform during firing, eliminating the need for high-temperature binder treatments while preserving weather resistance.
3Shape
If a leveling agent is added to uniformize surface tension, then the coating film uniformity is improved, but the bonding strength and weather resistance on the bonding interface are reduced
Solution Approach 1:
The patent achieves coating film uniformity by controlling the viscosity ratio parameter (applied/fired viscosity) to 0.1-0.5 and optimizing nanoparticle concentration (30-80 wt%). This parameter optimization provides natural leveling during printing without requiring additional leveling agents, thereby maintaining bonding strength and weather resistance at the interface.
Solution Approach 2:
The patent extracts the leveling function from the composition by relying on the inherent thixotropic properties of the nanopaste formulation. The controlled viscosity ratio (0.1-0.5) enables the paste to self-level during the printing process through its own rheological behavior, eliminating the need to add separate leveling agents that would compromise bonding strength and weather resistance.
4Ease of operation
If the viscosity of the paste is reduced to improve printability, then the coating can be applied more easily, but the dimensional stability of the coating film deteriorates
Solution Approach 1:
The patent utilizes dynamic viscosity control through thixotropy, where the viscosity ratio (applied/fired) is optimized to 0.1-0.5. During printing, the paste exhibits lower viscosity for easy application and screen passage, then returns to higher viscosity during firing to maintain dimensional stability. This dynamic rheological behavior enables both excellent printability and coating stability without contradiction.
Solution Approach 2:
The patent optimizes the viscosity ratio parameter to 0.1-0.5, creating a significant difference between applied and fired viscosities. This parameter change enables the paste to be easily applied at low viscosity during printing, then stabilize at higher viscosity during firing, achieving both good printability and dimensional stability through controlled rheological transformation.
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 provides a smooth coating film without texture generation, enabling high-reliability bonding at low temperatures with enhanced bonding strength and improved weather resistance, suitable for mass printing and maintaining dimensional stability.
Implementation Method 1
silver nanoparticles which have an average primary particle diameter of 1 nm to 200 nm and have been coated with an organic substance having 8 or less carbon atoms
Implementation Method 2
a thixotropic ratio (a viscosity measured at a shear rate of 3.1 [1/s] / a viscosity measured at a shear rate of 15.7 [1/s]) of 4 or lower
Data Source
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AI summary
A bonding material using silver nanoparticles considerably changes in coating-material property in response to a slight change in composition, and the stability thereof has been insufficient for large-amount application. A bonding material which uses silver nanoparticles, meets the requirements for mass printing, attains dimensional stability, and gives a smooth printed surface is provided. The bonding material includes silver nanoparticles which have at least an average primary particle diameter of 1 nm to 200 nm and have been coated with an organic substance having 8 or less carbon atoms, a dispersion medium, and a viscosity modifier composed of an organic substance, and has a viscosity (measured at a shear rate of 15.7 [1/s]) of 100 Pa·s or lower and a thixotropic ratio (measured at a shear rate of 3.1 [1/s]/measured at a shear rate of 15.7 [1/s]) of 4 or lower.